Synergy of adsorption and visible light photocatalysis to decolor methyl orange by activated car
饮用水中有机污染物光催化降解研究进展
![饮用水中有机污染物光催化降解研究进展](https://img.taocdn.com/s3/m/5ef49d9b9b6648d7c0c74621.png)
饮用水中有机污染物光催化降解研究进展本文综述了TiO2光催化技术在饮用水有机物污染物降解处理中的应用研究进展,分析了存在的问题,展望了饮用水中有机污染物光催化降解材料研究的发展方向。
标签:光催化;饮用水;有机污染物1、引言饮用水污染对人类健康带来了严峻的挑战,据世界卫生组织(WHO)调查表明,全球有80%的疾病和50%的儿童死亡都与饮用水水质不良有关。
饮用水中的有机污染物主要来源于水源中天然存在的有机物(NOM)、人工合成有机物(SOC)、消毒副产物(DBPs)等,具有致癌、致畸和致突变等作用,威胁着饮用水安全,危害人类健康,因而有必要大力开展饮用水深度处理技术研发,有效去除饮用水中难降解有机污染物[1-4]。
光催化氧化技术作为一种新型环境保护技术,具有无二次污染,能耗低、反应快、操作简单、效率高等优点,逐渐成为饮用水深度处理中的研究热点。
TiO2因其无毒、廉价、稳定、来源丰富、氧化能力强及可以重复利用等特点[5-7],使其成为最具潜力的绿色环保型光催化材料。
TiO2在光催化反应过程中,产生具有强氧化性的羟基自由基(·OH)及活性氧类(HO2·和O2·-),能有效降解饮用水中的天然有机物、人工合成有机物、消毒有机副产物等,并将其矿化为H2O、CO2和相应的无机离子(Cl-、Br-、SO42-、NO3-等),使饮用水达到深度净化效果[8-10]。
2、饮用水中天然有机物光催化降解研究天然存在的有机物主要为腐殖质(腐殖酸、富里酸和胡敏酸)。
它是饮用水消毒副产物的主要前体,其含量高低决定了饮用水中消毒副产物水平的高低。
He等[11]采用TiO2催化剂在光反應器中进行实验,在自然阳光照射下,探讨了催化剂负载量、PH值、初始浓度和光照时间等条件对腐殖酸(HA)去除效果的影响,结果表明,TiO2在自然阳光照射下可有效去除水中腐殖酸(HA)。
刘文等[12]以P-25型纳米TiO2作为催化剂,对富里酸(FA)进行了光催化氧化的实验研究,测得当FA初始浓度为9.42mg/L,TiO2投加量为0.3g/L,PH=7.00,光照40min时,FA的去除率达到98%。
SCI写作句型汇总
![SCI写作句型汇总](https://img.taocdn.com/s3/m/fdcd6994970590c69ec3d5bbfd0a79563d1ed45b.png)
SCI写作句型汇总S C I论文写作中一些常用的句型总结(一)很多文献已经讨论过了一、在Introduction里面经常会使用到的一个句子:很多文献已经讨论过了。
它的可能的说法有很多很多,这里列举几种我很久以前搜集的:A.??Solar energy conversion by photoelectrochemical cells?has been intensively investigated.?(Nature 1991, 353, 737 - 740?)B.?This was demonstrated in a number of studies that?showed that composite plasmonic-metal/semiconductor photocatalysts achieved significantly higher rates in various photocatalytic reactions compared with their pure semiconductor counterparts.C.?Several excellent reviews describing?these applications are available, and we do not discuss these topicsD.?Much work so far has focused on?wide band gap semiconductors for water splitting for the sake of chemical stability.(DOI:10.1038/NMAT3151)E.?Recent developments of?Lewis acids and water-soluble organometalliccatalysts?have attracted much attention.(Chem. Rev. 2002, 102, 3641?3666)F.?An interesting approach?in the use of zeolite as a water-tolerant solid acid?was described by?Ogawa et al(Chem.Rev. 2002, 102, 3641?3666)G.?Considerable research efforts have been devoted to?the direct transition metal-catalyzed conversion of aryl halides toaryl nitriles. (J. Org. Chem. 2000, 65, 7984-7989) H.?There are manyexcellent reviews in the literature dealing with the basic concepts of?the photocatalytic processand the reader is referred in particular to those by Hoffmann and coworkers,Mills and coworkers, and Kamat.(Metal oxide catalysis,19,P755)I. Nishimiya and Tsutsumi?have reported on(proposed)the influence of the Si/Al ratio of various zeolites on the acid strength, which were estimated by calorimetry using ammonia. (Chem.Rev. 2002, 102, 3641?3666)二、在results and discussion中经常会用到的:如图所示A. GIXRD patterns in?Figure 1A show?the bulk structural information on as-deposited films.?B.?As shown in Figure 7B,?the steady-state current density decreases after cycling between 0.35 and 0.7 V, which is probably due to the dissolution of FeOx.?C.?As can be seen from?parts a and b of Figure 7, the reaction cycles start with the thermodynamically most favorable VOx structures(J. Phys. Chem. C 2014, 118, 24950?24958)这与XX能够相互印证:A.?This is supported by?the appearance in the Ni-doped compounds of an ultraviolet–visible absorption band at 420–520nm (see Fig. 3 inset), corresponding to an energy range of about 2.9 to 2.3 eV.B. ?This?is consistent with the observation from?SEM–EDS. (Z.Zou et al. / Chemical Physics Letters 332 (2000) 271–277)C.?This indicates a good agreement between?the observed and calculated intensities in monoclinic with space groupP2/c when the O atoms are included in the model.D. The results?are in good consistent with?the observed photocatalytic activity...E. Identical conclusions were obtained in studies?where the SPR intensity and wavelength were modulated by manipulating the composition, shape,or size of plasmonic nanostructures.?F.??It was also found that areas of persistent divergent surfaceflow?coincide?with?regions where convection appears to be consistently suppressed even when SSTs are above 27.5°C.(二)1. 值得注意的是...A.?It must also be mentioned that?the recycling of aqueous organic solvent is less desirable than that of pure organic liquid.B.?Another interesting finding is that?zeolites with 10-membered ring pores showed high selectivities (>99%) to cyclohexanol, whereas those with 12-membered ring pores, such as mordenite, produced large amounts of dicyclohexyl ether. (Chem. Rev. 2002, 102,3641?3666)C.?It should be pointed out that?the nanometer-scale distribution of electrocatalyst centers on the electrode surface is also a predominant factor for high ORR electrocatalytic activity.D.?Notably,?the Ru II and Rh I complexes possessing the same BINAP chirality form antipodal amino acids as the predominant products.?(Angew. Chem. Int. Ed., 2002, 41: 2008–2022)E. Given the multitude of various transformations published,?it is noteworthy that?only very few distinct?activation?methods have been identified.?(Chem. Soc. Rev., 2009,?38, 2178-2189)F.?It is important to highlight that?these two directing effects will lead to different enantiomers of the products even if both the“H-bond-catalyst” and the?cata lyst?acting by steric shielding have the same absolute stereochemistry. (Chem. Soc. Rev.,?2009,?38, 2178-2189)G.?It is worthwhile mentioning that?these PPNDs can be very stable for several months without the observations of any floating or precipitated dots, which is attributed to the electrostatic repulsions between the positively charge PPNDs resulting in electrosteric stabilization.(Adv. Mater., 2012, 24: 2037–2041)2.?...仍然是个挑战A.?There is thereby an urgent need but it is still a significant challenge to?rationally design and delicately tail or the electroactive MTMOs for advanced LIBs, ECs, MOBs, and FCs.?(Angew. Chem. Int. Ed.2 014, 53, 1488 – 1504)B.?However, systems that are?sufficiently stable and efficient for practical use?have not yet been realized.C.??It?remains?challenging?to?develop highly active HER catalysts based on materials that are more abundant at lower costs. (J. Am. Chem.Soc.,?2011,?133, ?7296–7299)D.?One of the?great?challenges?in the twenty-first century?is?unquestionably energy storage. (Nature Materials?2005, 4, 366 - 377?)众所周知A.?It is well established (accepted) / It is known to all / It is commonlyknown?that?many characteristics of functional materials, such as composition, crystalline phase, structural and morphological features, and the sur-/interface properties between the electrode and electrolyte, would greatly influencethe performance of these unique MTMOs in electrochemical energy storage/conversion applications.(Angew. Chem. Int. Ed.2014,53, 1488 – 1504)B.?It is generally accepted (believed) that?for a-Fe2O3-based sensors the change in resistance is mainly caused by the adsorption and desorption of gases on the surface of the sensor structure. (Adv. Mater. 2005, 17, 582)C.?As we all know,?soybean abounds with carbon,?nitrogen?and oxygen elements owing to the existence of sugar,?proteins?and?lipids. (Chem. Commun., 2012,?48, 9367-9369)D.?There is no denying that?their presence may mediate spin moments to align parallel without acting alone to show d0-FM. (Nanoscale, 2013,?5, 3918-3930)(三)1. 正如下文将提到的...A.?As will be described below(也可以是As we shall see below),?as the Si/Al ratio increases, the surface of the zeolite becomes more hydrophobic and possesses stronger affinity for ethyl acetate and the number of acid sites decreases.(Chem. Rev. 2002, 102, 3641?3666)B. This behavior is to be expected and?will?be?further?discussed?below. (J. Am. Chem. Soc.,?1955,?77, 3701–3707)C.?There are also some small deviations with respect to the flow direction,?whichwe?will?discuss?below.(Science, 2001, 291, 630-633)D.?Below,?we?will?see?what this implies.E.?Complete details of this case?will?be provided at a?later?time.E.?很多论文中,也经常直接用see below来表示,比如:The observation of nanocluster spheres at the ends of the nanowires is suggestive of a VLS growth process (see?below). (Science, 1998, ?279, 208-211)2. 这与XX能够相互印证...A.?This is supported by?the appearance in the Ni-doped compounds of an ultraviolet–visible absorption band at 420–520 nm (see Fig. 3 inset), corresponding to an energy range of about2.9 to 2.3 eVB.This is consistent with the observation from?SEM–EDS. (Chem. Phys. Lett. 2000, 332, 271–277)C.?Identical conclusions were obtained?in studies where the SPR intensity and wavelength were modulated by manipulating the composition, shape, or size of plasmonic nanostructures.?(Nat. Mater. 2011, DOI: 10.1038/NMAT3151)D. In addition, the shape of the titration curve versus the PPi/1 ratio,?coinciding withthat?obtained by fluorescent titration studies, suggested that both 2:1 and 1:1 host-to-guest complexes are formed. (J. Am. Chem. Soc. 1999, 121, 9463-9464)E.?This unusual luminescence behavior is?in accord with?a recent theoretical prediction; MoS2, an indirect bandgap material in its bulk form, becomes a direct bandgapsemiconductor when thinned to a monolayer.?(Nano Lett.,?2010,?10, 1271–1275)3.?我们的研究可能在哪些方面得到应用A.?Our ?ndings suggest that?the use of solar energy for photocatalytic watersplitting?might provide a viable source for?‘clean’ hydrogen fuel, once the catalyticef?ciency of the semiconductor system has been improved by increasing its surface area and suitable modi?cations of the surface sites.B. Along with this green and cost-effective protocol of synthesis,?we expect that?these novel carbon nanodots?have potential applications in?bioimaging andelectrocatalysis.(Chem. Commun., 2012,?48, 9367-9369)C.?This system could potentially be applied as?the gain medium of solid-state organic-based lasers or as a component of high value photovoltaic (PV) materials, where destructive high energy UV radiation would be converted to useful low energy NIR radiation. (Chem. Soc. Rev., 2013,?42, 29-43)D.?Since the use of?graphene?may enhance the photocatalytic properties of TiO2?under UV and visible-light irradiation,?graphene–TiO2?composites?may potentially be used to?enhance the bactericidal activity.?(Chem. Soc. Rev., 2012,?41, 782-796)E.??It is the first report that CQDs are both amino-functionalized and highly fluorescent,?which suggests their promising applications in?chemical sensing.(Carbon, 2012,?50,?2810–2815)(四)1. 什么东西还尚未发现/系统研究A. However,systems that are sufficiently stable and efficient for practical use?have not yet been realized.B. Nevertheless,for conventional nanostructured MTMOs as mentioned above,?some problematic disadvantages cannot be overlooked.(Angew. Chem. Int. Ed.2014,53, 1488 – 1504)C.?There are relatively few studies devoted to?determination of cmc values for block copolymer micelles. (Macromolecules1991, 24, 1033-1040)D. This might be the reason why, despite of the great influence of the preparation on the catalytic activity of gold catalysts,?no systematic study concerning?the synthesis conditions?has been published yet.?(Applied Catalysis A: General 2002, 226, ?1–13)E.?These possibilities remain to be?explored.F.??Further effort is required to?understand and better control the parameters dominating the particle surface passivation and resulting properties for carbon dots of brighter photoluminescence. (J. Am. Chem. Soc.,?2006,?128?, 7756–7757)2.?由于/因为...A.?Liquid ammonia?is particularly attractive as?an alternative to water?due to?its stability in the presence of strong reducing agents such as alkali metals that are used to access lower oxidation states.B.?The unique nature of?the cyanide ligand?results from?its ability to act both as a σdonor and a π acceptor combined with its negativecharge and ambidentate nature.C.?Qdots are also excellent probes for two-photon confocalmicroscopy?because?they are characterized by a very large absorption cross section?(Science ?2005,?307, 538-544).D.?As a result of?the reductive strategy we used and of the strong bonding between the surface and the aryl groups, low residual currents (similar to those observed at a bare electrode) were obtained over a large window of potentials, the same as for the unmodified parent GC electrode. (J. Am. Chem. Soc. 1992, 114, 5883-5884)E.?The small Tafel slope of the defect-rich MoS2 ultrathin nanosheets is advantageous for practical?applications,?since?itwill lead to a faster increment of HER rate with increasing overpotential.(Adv. Mater., 2013, 25: 5807–5813)F. Fluorescent carbon-based materials have drawn increasing attention in recent years?owing to?exceptional advantages such as high optical absorptivity, chemical stability, biocompatibility, and low toxicity.(Angew. Chem. Int. Ed., 2013, 52: 3953–3957)G.??On the basis of?measurements of the heat of immersion of water on zeolites, Tsutsumi etal. claimed that the surface consists of siloxane bondings and is hydrophobicin the region of low Al content. (Chem. Rev. 2002, 102, 3641?3666)H.?Nanoparticle spatial distributions might have a large significance for catalyst stability,?given that?metal particle growth is a relevant deactivation mechanism for commercial catalysts.?3. ...很重要A.?The inhibition of additional nucleation during growth, in other words, the complete separation?of nucleation and growth,?is?critical(essential, important)?for?the successful synthesis of monodisperse nanocrystals. (Nature Materials?3, 891 - 895 (2004))B.??In the current study,?Cys,?homocysteine?(Hcy) and?glutathione?(GSH) were chosen as model?thiol?compounds since they?play important (significant, vital, critical) roles?in many biological processes and monitoring of these?thiol?compounds?is of great importance for?diagnosis of diseases.(Chem. Commun., 2012,?48, 1147-1149)C.?This is because according to nucleation theory,?what really matters?in addition to the change in temperature ΔT?(or supersaturation) is the cooling rate.(Chem. Soc. Rev., 2014,?43, 2013-2026)(五)1. 相反/不同于A.?On the contrary,?mononuclear complexes, called single-ion magnets (SIM), have shown hysteresis loops of butterfly/phonon bottleneck type, with negligiblecoercivity, and therefore with much shorter relaxation times of magnetization. (Angew. Chem. Int. Ed., 2014, 53: 4413–4417)B.?In contrast,?the Dy compound has significantly larger value of the transversal magnetic moment already in the ground state (ca. 10?1?μB), therefore allowing a fast Q TM. (Angew. Chem. Int. Ed., 2014, 53: 4413–4417)C.?In contrast to?the structural similarity of these complexes, their magnetic behavior exhibits strong divergence.?(Angew. Chem. Int. Ed., 2014, 53: 4413–4417)D.?Contrary to?other conducting polymer semiconductors, carbon nitride ischemically and thermally stable and does not rely on complicated device manufacturing. (Nature materials, 2009, 8(1): 76-80.)E.?Unlike?the spherical particles they are derived from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape. (Science 2001,? 294, 1901-1903)2. 发现,阐明,报道,证实可供选择的词包括:verify, confirm, elucidate, identify, define, characterize, clarify, establish, ascertain, explain, observe, illuminate, illustrate,demonstrate, show, indicate, exhibit, presented, reveal, display, manifest,suggest, propose, estimate, prove, imply, disclose,report, describe,facilitate theidentification of?举例:A. These stacks appear as nanorods in the two-dimensional TEM images, but tilting experiments?confirm that they are nanoprisms.?(Science 2001,? 294, 1901-1903)B. Note that TEM?shows?that about 20% of the nanoprisms are truncated.?(Science 2001,? 294, 1901-1903)C. Therefore, these calculations not only allow us to?identify?the important features in the spectrum of the nanoprisms but also the subtle relation between particle shape and the frequency of the bands that make up their spectra.?(Science 2001,? 294, 1901-1903)D. We?observed?a decrease in intensity of the characteristic surface plasmon band in the ultraviolet-visible (UV-Vis) spectroscopy for the spherical particles at λmax?= 400 nm with a concomitant grow th of three new bands of λmax?= 335 (weak), 470 (medium), and 670 nm (strong), respectively. (Science 2001,? 294, 1901-1903)E. In this article, we present data?demonstrating?that opiate and nonopiate analgesia systems can be selectively activated by different environmental manipulationsand?describe?the neural circuitry involved. (Science 1982, 216, 1185-1192)F. This?suggests?that the cobalt in CoP has a partial positive charge (δ+), while the phosphorus has a partial negative charge (δ?),?implying?a tran sfer of electron density from Co to P.?(Angew. Chem., 2014, 126: 6828–6832)3. 如何指出当前研究的不足A. Although these inorganic substructures can exhibit a high density of functional groups, such as bridging OH groups, andthe substructures contribute significantly to the adsorption properties of the material,surprisingly little attention has been devoted to?the post-synthetic functionalization of the inorganic units within MOFs. (Chem. Eur. J., 2013, 19: 5533–5536.)B.?Little is known,?however, about the microstructure of this material. (Nature Materials 2013,12, 554–561)C.?So far, very little information is available, and only in?the absorber film, not in the whole operational devices. (Nano Lett.,?2014,?14?(2), pp 888–893)D.?In fact it should be noted that very little optimisation work has been carried out on?these devices. (Chem. Commun., 2013,?49, 7893-7895)E. By far the most architectures have been prepared using a solution processed perovskite material,?yet a few examples have been reported that?have used an evaporated perovskite layer. (Adv. Mater., 2014, 27: 1837–1841.)F. Water balance issues have been effectively addressed in PEMFC technology through a large body of work encompassing imaging, detailed water content and water balance measurements, materials optimization and modeling,?but very few of these activities have been undertaken for?anion exchange membrane fuel cells,? primarily due to limited materials availability and device lifetime. (J. Polym. Sci. Part B: Polym. Phys., 2013, 51: 1727–1735)G. However,?none of these studies?tested for Th17 memory, a recently identified T cell that specializes in controlling extracellular bacterial infections at mucosal surfaces. (PNAS, 2013,?111, 787–792)H. However,?uncertainty still remains as to?the mechanism by which Li salt addition results in an extension of the cathodicreduction limit. (Energy Environ. Sci., 2014,?7, 232-250)I.?There have been a number of high profile cases where failure to?identify the most stable crystal form of a drug has led to severe formulation problems in manufacture. (Chem. Soc. Rev., 2014,?43, 2080-2088)J. However,?these measurements systematically underestimate?the amount of ordered material. ( Nature Materials 2013, 12, 1038–1044)(六)1.?取决于a.?This is an important distinction, as the overall activity of a catalyst will?depend on?the material properties, synthesis method, and other possible species that can be formed during activation.?(Nat. Mater.?2017,16,225–229)b.?This quantitative partitioning?was determined by?growing crystals of the 1:1 host–guest complex between?ExBox4+?and corannulene. (Nat. Chem.?2014,?6177–178)c.?They suggested that the Au particle size may?be the decisive factor for?achieving highly active Au catalysts.(Acc. Chem. Res.,?2014,?47, 740–749)d.?Low-valent late transition-metal catalysis has?become indispensable to?chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of high-valent transition-metal complexes and the challenges associated with synthesizing them.?(Nature2015,?517,449–454)e.?The polar effect?is a remarkable property that enables?considerably endergonic C–H abstractions?that would not be possible otherwise.?(Nature?2015, 525, 87–90)f.?Advances in heterogeneous catalysis?must rely on?the rational design of new catalysts. (Nat. Nanotechnol.?2017, 12, 100–101)g.?Likely, the origin of the chemoselectivity may?be also closely related to?the H?bonding with the N or O?atom of the nitroso moiety, a similar H-bonding effect is known in enamine-based nitroso chemistry. (Angew. Chem. Int. Ed.?2014, 53: 4149–4153)2.?有很大潜力a.?The quest for new methodologies to assemble complex organic molecules?continues to be a great impetus to?research efforts to discover or to optimize new catalytic transformations. (Nat. Chem.?2015,?7, 477–482)b.?Nanosized faujasite (FAU) crystals?have great potential as?catalysts or adsorbents to more efficiently process present and forthcoming synthetic and renewablefeedstocks in oil refining, petrochemistry and fine chemistry. (Nat. Mater.?2015, 14, 447–451)c.?For this purpose, vibrational spectroscopy?has proved promising?and very useful.?(Acc Chem Res. 2015, 48, 407–413.)d.?While a detailed mechanism remains to be elucidated and?there is room for improvement?in the yields and selectivities, it should be remarked that chirality transfer upon trifluoromethylation of enantioenriched allylsilanes was shown. (Top Catal.?2014,?57: 967.?)e.?The future looks bright for?the use of PGMs as catalysts, both on laboratory and industrial scales, because the preparation of most kinds of single-atom metal catalyst is likely to be straightforward, and because characterization of such catalysts has become easier with the advent of techniques that readilydiscriminate single atoms from small clusters and nanoparticles. (Nature?2015, 525, 325–326)f.?The unique mesostructure of the 3D-dendritic MSNSs with mesopore channels of short length and large diameter?is supposed to be the key role in?immobilization of active and robust heterogeneous catalysts, and?it would have more hopeful prospects in?catalytic applications. (ACS Appl. Mater. Interfaces,?2015,?7, 17450–17459)g.?Visible-light photoredox catalysis?offers exciting opportunities to?achieve challenging carbon–carbon bond formations under mild and ecologically benign conditions. (Acc. Chem. Res.,?2016, 49, 1990–1996)3. 因此同义词:Therefore, thus, consequently, hence, accordingly, so, as a result这一条比较简单,这里主要讲一下这些词的副词词性和灵活运用。
发光调控 英语
![发光调控 英语](https://img.taocdn.com/s3/m/ea3bbbf4f424ccbff121dd36a32d7375a417c627.png)
发光调控英语Title: The Complexity and Intricacies of Luminescence RegulationLuminescence regulation, a field at the intersection of physics, chemistry, and biology, holds immense potential in various applications ranging from displays and lighting to biomedical imaging and sensing. It involves the precise control of the emission of light from a material, either spontaneously or in response to an external stimulus. This article delves into the complexities and intricacies of luminescence regulation, exploring its principles, techniques, and evolving applications.Firstly, it's crucial to understand the fundamental mechanisms of luminescence. Luminescence occurs when a material absorbs energy, either in the form of light, electricity, or heat, and subsequently emits light. This process is typically characterized by the excitation of electrons within the material, followed by their relaxation and emission of photons. The color and intensity of the emitted light depend on the material's chemical composition, structure, and the nature of the excitation.Luminescence regulation involves manipulating these mechanisms to achieve desired emission properties. One approach is through the use of dopants or activators, which introduce additional energy states within the material. These dopants can enhance or modify the emission spectrum, enabling the tuning of color and intensity. Another method involves manipulating the material's physical structure, such as through nanostructuring or the use of porous materials, to alter the path and efficiency of light emission.Moreover, the field of luminescence regulation has benefited significantly from the advancement of synthetic techniques and material science. The ability to synthesize materials with precise compositional and structural control has opened new avenues for precise luminescence tuning. For instance, the development of colloidal quantum dots and perovskite nanocrystals has enabled the creation of luminescent materials with tunable emission wavelengths and high brightness.In terms of applications, luminescence regulation finds widespread use in various fields. In displays and lighting,luminescent materials are used to generate vibrant colors and efficient light emission. The precise control of emission properties enables the creation of displays with high color accuracy and contrast, as well as lighting systems with optimized energy efficiency.In the biomedical field, luminescent materials have revolutionized imaging and sensing techniques. Fluorescence microscopy, for instance, relies on the ability to label specific molecules or cells with luminescent probes, enabling their visualization with high spatial and temporal resolution. Luminescent probes are also used in biosensing applications, where they can detect and quantify biological analytes with high sensitivity and specificity.Furthermore, the emergence of photoluminescence-based solar cells has highlighted the potential of luminescence regulation in renewable energy applications. By engineering the luminescent properties of photovoltaic materials, researchers aim to improve the efficiency and stability of solar cells, addressing key challenges in solar energy conversion.However, the field of luminescence regulation remains challenging and evolving. The complexity of luminescent mechanisms, coupled with the diverse range of materials and applications, poses significant challenges in achieving precise and reliable luminescence control. Ongoing research efforts are focused on developing novel materials and techniques that can further enhance the performance and versatility of luminescent systems.In conclusion, luminescence regulation represents a vibrant and dynamic field with vast potential for innovation and applications. As the understanding of luminescent mechanisms deepens and synthetic techniques improve, the capabilities of luminescent materials will continue to expand, opening new doors in various fields from displays and lighting to biomedicine and renewable energy.。
光与物质相互作用英文
![光与物质相互作用英文](https://img.taocdn.com/s3/m/2457e848974bcf84b9d528ea81c758f5f61f293b.png)
光与物质相互作用英文Light-Matter Interaction.Light and matter interact in a variety of ways,including absorption, emission, scattering, and reflection. These interactions are essential for many natural phenomena, such as photosynthesis, vision, and the colors of objects. They are also used in a wide range of technologies, such as lasers, solar cells, and optical fibers.Absorption.When light is absorbed by matter, the energy of thelight is transferred to the matter. This can cause the matter to become excited, which can lead to a change in its chemical or physical properties. For example, absorption of light can cause a molecule to dissociate, or it can causean electron to be promoted to a higher energy level.Emission.When matter emits light, the energy of the light comes from the matter itself. This can happen when an excited atom or molecule returns to its ground state, or it can happen when an electron recombines with a hole. Emission of light is the basis for many light sources, such as lasers and LEDs.Scattering.When light is scattered by matter, the direction of the light is changed. This can happen when light interacts with particles that are smaller than the wavelength of light, or it can happen when light interacts with rough surfaces. Scattering of light is responsible for the blue color of the sky and the white color of clouds.Reflection.When light is reflected by matter, the direction of the light is changed, but the wavelength of the light remains the same. This can happen when light interacts with asmooth surface, such as a mirror, or it can happen when light interacts with a transparent material, such as glass. Reflection of light is used in a variety of applications, such as mirrors, lenses, and optical fibers.The interaction of light with matter is a complex and fascinating topic. It is essential for understanding a wide range of natural phenomena and technologies.Here are some additional details about each of the four types of light-matter interactions:Absorption.When light is absorbed by matter, the energy of the light is transferred to the matter. This can cause the matter to become excited, which can lead to a change in its chemical or physical properties. For example, absorption of light can cause a molecule to dissociate, or it can cause an electron to be promoted to a higher energy level.The amount of light that is absorbed by matter dependson the wavelength of the light and the properties of the matter. Some materials, such as metals, are very good at absorbing light, while other materials, such as glass, are very poor at absorbing light.Emission.When matter emits light, the energy of the light comes from the matter itself. This can happen when an excited atom or molecule returns to its ground state, or it can happen when an electron recombines with a hole.The wavelength of the light that is emitted by matter depends on the energy difference between the two states involved in the transition. For example, when an electron recombines with a hole in a semiconductor, the energy difference between the two states is typically in the visible range, so the emitted light is visible light.Scattering.When light is scattered by matter, the direction of thelight is changed. This can happen when light interacts with particles that are smaller than the wavelength of light, or it can happen when light interacts with rough surfaces.The amount of light that is scattered by matter depends on the size and shape of the scattering particles and the wavelength of the light. For example, small particles scatter light more effectively than large particles, and short-wavelength light is scattered more effectively than long-wavelength light.Reflection.When light is reflected by matter, the direction of the light is changed, but the wavelength of the light remains the same. This can happen when light interacts with a smooth surface, such as a mirror, or it can happen when light interacts with a transparent material, such as glass.The amount of light that is reflected by matter depends on the refractive index of the material. The refractive index is a measure of how much light is bent when it passesfrom one material to another. Materials with a high refractive index, such as glass, reflect more light than materials with a low refractive index, such as air.。
法布里珀罗基模共振英文
![法布里珀罗基模共振英文](https://img.taocdn.com/s3/m/81b951db6429647d27284b73f242336c1fb93055.png)
法布里珀罗基模共振英文The Fabryperot ResonanceOptics, the study of light and its properties, has been a subject of fascination for scientists and researchers for centuries. One of the fundamental phenomena in optics is the Fabry-Perot resonance, named after the French physicists Charles Fabry and Alfred Perot, who first described it in the late 19th century. This resonance effect has numerous applications in various fields, ranging from telecommunications to quantum physics, and its understanding is crucial in the development of advanced optical technologies.The Fabry-Perot resonance occurs when light is reflected multiple times between two parallel, partially reflective surfaces, known as mirrors. This creates a standing wave pattern within the cavity formed by the mirrors, where the light waves interfere constructively and destructively to produce a series of sharp peaks and valleys in the transmitted and reflected light intensity. The specific wavelengths at which the constructive interference occurs are known as the resonant wavelengths of the Fabry-Perot cavity.The resonant wavelengths of a Fabry-Perot cavity are determined bythe distance between the mirrors, the refractive index of the material within the cavity, and the wavelength of the incident light. When the optical path length, which is the product of the refractive index and the physical distance between the mirrors, is an integer multiple of the wavelength of the incident light, the light waves interfere constructively, resulting in a high-intensity transmission through the cavity. Conversely, when the optical path length is not an integer multiple of the wavelength, the light waves interfere destructively, leading to a low-intensity transmission.The sharpness of the resonant peaks in a Fabry-Perot cavity is determined by the reflectivity of the mirrors. Highly reflective mirrors result in a higher finesse, which is a measure of the ratio of the spacing between the resonant peaks to their width. This high finesse allows for the creation of narrow-linewidth, high-resolution optical filters and laser cavities, which are essential components in various optical systems.One of the key applications of the Fabry-Perot resonance is in the field of optical telecommunications. Fiber-optic communication systems often utilize Fabry-Perot filters to select specific wavelength channels for data transmission, enabling the efficient use of the available bandwidth in fiber-optic networks. These filters can be tuned by adjusting the mirror separation or the refractive index of the cavity, allowing for dynamic wavelength selection andreconfiguration of the communication system.Another important application of the Fabry-Perot resonance is in the field of laser technology. Fabry-Perot cavities are commonly used as the optical resonator in various types of lasers, providing the necessary feedback to sustain the lasing process. The high finesse of the Fabry-Perot cavity allows for the generation of highly monochromatic and coherent light, which is crucial for applications such as spectroscopy, interferometry, and precision metrology.In the realm of quantum physics, the Fabry-Perot resonance plays a crucial role in the study of cavity quantum electrodynamics (cQED). In cQED, atoms or other quantum systems are placed inside a Fabry-Perot cavity, where the strong interaction between the atoms and the confined electromagnetic field can lead to the observation of fascinating quantum phenomena, such as the Purcell effect, vacuum Rabi oscillations, and the generation of nonclassical states of light.Furthermore, the Fabry-Perot resonance has found applications in the field of optical sensing, where it is used to detect small changes in physical parameters, such as displacement, pressure, or temperature. The high sensitivity and stability of Fabry-Perot interferometers make them valuable tools in various sensing and measurement applications, ranging from seismic monitoring to the detection of gravitational waves.The Fabry-Perot resonance is a fundamental concept in optics that has enabled the development of numerous advanced optical technologies. Its versatility and importance in various fields of science and engineering have made it a subject of continuous research and innovation. As the field of optics continues to advance, the Fabry-Perot resonance will undoubtedly play an increasingly crucial role in shaping the future of optical systems and applications.。
HP20
![HP20](https://img.taocdn.com/s3/m/97d5576dddccda38366baf01.png)
Typical propertiesDIAION™ & SEPABEADS™ Synthetic AdsorbentsGENERAL FEATURESynthetic adsorbents are a series of products based on ion-exchange resin manufacturing technology, and are designed for the uses as solid extractant. Synthetic adsorbents have large surface area and fine pore structures inside the particle like activated carbon. For this porous characteristic, they can effectively adsorb organic compounds from aqueous solutions. Extraction processes with synthetic adsorbents enables reducing solvent amount and safer operations compared with conventional solvent extraction techniques.PROPERTIESA synthetic adsorbent is spherical particle, and inside it, there exist effective fine pore structures suitable for the diffusion of solutesSmaller solutes can penetrate into the particle by diffusing through the pores, when a solution is allowed to contact with adsorbent particles.On the contrary, molecules that are larger than pore size cannot penetrate into the inside of particle. Consequently, such molecules are not adsorbedon synthetic adsorbents (this phenomenon is so-called molecular sieving effect).APPLICATION FIELDSSynthetic adsorbents are used for the separation of valuable compounds from plant extracts and fermentation products for pharmaceutical intermediates and food additives.STABILITYSynthetic adsorbents are stable in acidic, alkaline solutions and in organic solvents, and they can be easily regenerated under mild conditions for repeated uses.Types of Synthetic adsorbents and Selection GuideCHEMICAL STRUCTUREThere are three types of chemical structures for synthetic adsorbents; aromatic, modified aromatic and methacrylic series.The chemical structure dominates the degree of hydrophobicity of synthetic adsorbents. Hydrophobicity of adsorbent is important in selecting a suitable type of adsorbent according to the chemical nature of target compounds.Mitsubishi Chemical supplies wide variety of synthetic adsorbents with different pore structures. The most appropriate type of adsorbent can be selected according to the pore size of adsorbent and the molecular size of the target compound (or sometimes unfavorable compounds to be removed).Another important parameter is surface area of resins. Adsorbent with large surface area shows high uptake capacity, especially for small molecules.Pore size distribution of Synthetic AdsorbentsPARTICLE SIZEStandard synthetic adsorbents have ca 0.5 mm mean particle diameter. This size is designed for most industrial scale processes.Smaller particle size adsorbents are used for fine separation/purification applications as reversed-phase chromatographic packing materials.Characteristics of synthetic adsorbentsProductChemicalstructureProperties Usage OthersDIAION™HP20Aromatic surface areaca. 600 m2/gpore radius200-300 Awidely used for adsorptionof organic compounds andnatural productsmolecular weight less thanseveral tens of thousandoperated in mildadsorption/desorption conditionssuitable for separation of non-porous,moderately porous substancesDIAION™ HP21surface area-600 m2/gpore radius100-120 Amolecules less than severalthousandsSEPABEADS™SP825 surface areaca 900 m2/gpore radius50-60 Amolecules less thanthousand, high uptakecapacity,similar polarity to HP20 and HP21especially for molecules less thanseveral hundred, eliminate largermoleculesSEPABEADS™SP850 surface areaca 900 m2/gpore radius30-50 Amolecules less than severalhundred, high uptakecapacityDI AION™HP2MG Methacrylicsurface areaca 600 m2/gpore radius200-300 Ahydrophilic, suitable foradsorption of moderateporous and slightly poroussubstanceseffective for polyphenols and acertain surfactants, which are nottreated with aromatic adsorbentsDIAION™ & SEPABEADS™ Synthetic AdsorbentsAromatic Type DIAION™ HP20, HP21Widely used in refining of pharmaceuticals and natural extracts, since these are suitable for adsorbing large molecules because of their relatively large pore sizes and have superior adsorption/ desorption.HP20 and HP21 are widely used in a variety of industrial applications, especially adsorption, desalting and decolorization of natural products and small proteins.Aromatic Type SEPABEADS™ SP825L, SP850SP825L and SP850 are also high porous, styrenic adsorbents. They have much larger surface area and a narrower, more uniform pore-size distribution than HP20 grades. They offer nearly two times the surface area of HP20, or twice the capacity for small molecules ( < 1500mw). These grades are recommended for adsorption, desalting, and decolorizaion.Aromatic type SEPABEADS™ SP700SEPABEADS™ SP700 is synthetic adsorbent with larger surface area and high adsorption capacity. Its pore structure is designed for absorption/desorption for substances.SEPABEADS™ SP700 shows high uptake capacity and efficient desorption performance of target molecule.。
不对称自由基反应英文
![不对称自由基反应英文](https://img.taocdn.com/s3/m/063286d7bdeb19e8b8f67c1cfad6195f302be867.png)
不对称自由基反应英文Asymmetric Radical Reactions: An Insight into Their Mechanism and Applications.Introduction.Asymmetric radical reactions have emerged as a powerful tool in organic synthesis, enabling the synthesis of chiral compounds with high enantiomeric purity. These reactions differ significantly from their symmetric counterparts, as they involve the generation and utilization of chiral radicals. These chiral radicals can undergo a range of reactions, including substitution, addition, and cyclization, leading to the formation of enantiomerically enriched products.Mechanism of Asymmetric Radical Reactions.The mechanism of asymmetric radical reactions typically involves three key steps: radical generation, chiralitytransfer, and radical termination.Radical Generation.The first step involves the generation of a radical species. This can be achieved through various methods, such as photolysis, thermal decomposition, or redox reactions. The generated radical can be chiral or achiral, depending on the starting materials and the conditions used.Chirality Transfer.The second step involves the transfer of chirality from a chiral auxiliary or catalyst to the radical species. This chirality transfer can occur through covalent or non-covalent interactions between the catalyst/auxiliary and the radical. The nature of these interactions determines the stereoselectivity of the reaction.Radical Termination.The final step involves the termination of the radicalspecies, leading to the formation of the desired product. This termination can occur through various mechanisms, such as coupling with another radical species, hydrogen atom abstraction, or disproportionation.Applications of Asymmetric Radical Reactions.Asymmetric radical reactions have found widespread applications in various fields of organic synthesis, including the synthesis of natural products, pharmaceuticals, and functional materials.Synthesis of Natural Products.Natural products often possess complex chiral structures, making their synthesis challenging. Asymmetric radical reactions have proven to be effective tools for the synthesis of such chiral natural products. For example, the use of chiral radicals generated from appropriate precursors has enabled the enantioselective synthesis of alkaloids, terpenes, and amino acids.Pharmaceutical Applications.The enantiomers of chiral drugs often differ significantly in their biological activities, making it crucial to control their enantiomeric purity. Asymmetric radical reactions can be used to synthesize enantiomerically enriched chiral drugs with high selectivity. This approach has been successfully applied to the synthesis of various drugs, including anti-inflammatory agents, anticancer agents, and antiviral agents.Functional Materials.Chiral materials possess unique physical and chemical properties that make them useful in various applications, such as displays, sensors, and catalysts. Asymmetricradical reactions can be used to synthesize chiral building blocks for the preparation of such materials. For instance, chiral polymers can be synthesized by utilizing asymmetric radical polymerization reactions, leading to the formation of materials with controlled chirality and tailored properties.Conclusion.Asymmetric radical reactions have emerged as powerful tools for the synthesis of enantiomerically enriched chiral compounds. Their unique mechanism, involving chirality transfer from a chiral catalyst/auxiliary to the radical species, enables high selectivity and enantiopurity in the product. The widespread applications of asymmetric radical reactions in organic synthesis, particularly in the synthesis of natural products, pharmaceuticals, and functional materials, highlight their importance in modern chemistry.Future Perspectives.Despite the significant progress made in the field of asymmetric radical reactions, there are still numerous challenges and opportunities for further exploration.Improving Selectivity and Efficiency.One of the key challenges in asymmetric radical reactions is achieving high selectivity and efficiency. While significant progress has been made in this area, there is still room for improvement. Future research could focus on developing new chiral catalysts/auxiliaries that can promote asymmetric radical reactions with higher selectivity and efficiency.Expanding the Scope of Reactions.Currently, the scope of asymmetric radical reactions is limited by the availability of suitable precursors and the reactivity of the generated radicals. Future research could aim to expand the scope of these reactions by developing new methods for generating radicals with desired functionalities and reactivities.Applications in Sustainable Chemistry.In the context of sustainable chemistry, asymmetric radical reactions offer an attractive alternative to traditional synthetic methods. By utilizing renewableresources and mild reaction conditions, asymmetric radical reactions could contribute to the development of more sustainable synthetic routes for the preparation of chiral compounds.Integration with Other Techniques.The integration of asymmetric radical reactions with other techniques, such as photocatalysis, electrochemistry, and microfluidics, could lead to the development of new and innovative synthetic methods. By combining the advantages of these techniques, it may be possible to achieve even higher selectivity, efficiency, and scalability in asymmetric radical reactions.In conclusion, asymmetric radical reactions have emerged as powerful tools for the synthesis of enantiomerically enriched chiral compounds. While significant progress has been made in this area, there are still numerous opportunities for further exploration and development. Future research in this field could lead tothe discovery of new and innovative synthetic methods with improved selectivity, efficiency, and sustainability.。
生物质材料对水体中染料和其他有机污染物的吸附
![生物质材料对水体中染料和其他有机污染物的吸附](https://img.taocdn.com/s3/m/b6c7ecdc76a20029bd642d50.png)
文章编号:1672-2019(2009)01-0019-05·综述·生物质材料对水体中染料和其他有机污染物的吸附顾迎春1,郑静2,石碧1(1.四川大学制革清洁技术国家工程实验室,四川成都610065;2.成都信息工程学院图书馆,四川成都610225)摘要:大量研究表明:纤维素基生物质、甲壳素和微生物对水体中染料的吸附容量低于商品活性碳对染料的吸附容量;虽然壳聚糖对一些阴离子型染料有相当大的吸附容量,但由于其性能不稳定,因此难以获得大规模工业应用。
关于生物质对其他有机污染物吸附性能的研究报道相对较少,说明这方面的研究有待于进一步深入和拓展。
废弃皮胶原是一类来源极其丰富的生物质,近年来的研究发现:基于皮胶原研制的新型吸附剂对水体中的阴离子型染料和有机酸能有效去除,有可能在染料和有机废水处理方面得到应用。
关键词:生物质,吸附,染料,有机污染物,皮胶原中图分类号:TQ028文献标识码:Adsorption of dyes and other organic pollutants on biomassmaterials from aqueous solutionsGU Ying-chun 1,ZHENG Jing 2,SHI Bi 1(1.National Engineering Laboratory for Clean Technology of Leather Manufacture,Sichuan University,Chengdu 610065,China;2.Library of Chengdu University of Information andTechnology,Chengdu,610225,China)Abstract :A large number of researches have indicated that the adsorption capacities of dyes on cellulose-based biomass,chitin and microbe were lower than those on commercial activated carbons from aqueous solutions.Al -though the adsorption capacities of some anionic dyes on chitosan were great considerably,the properties of chitosan were not stable enough to acquire the industrial application on large scale.The relatively fewer reports illustrate that there should be more profound and extended research concerned with the adsorption characteristics of other organic pollutants on biomass.Waste hide collagen is a type of very abundant biomass.The recent investigation has found that a novel adsorbent based on hide collagen had the effective removal of anionic dyes and organic acids from aqueous solutions and might have the potential usefulness on the treatment of dye and organic wastewater.Key words :biomass,adsorption,dyes,organic pollutions,hide collagen收稿日期:2008-12-07*基金项目:国家科技支撑计划课题(No.2006BAC02A09);四川省重点科学与技术研究项目(04SG012-009);四川大学青年科学基金(200452)[通讯作者]石碧,E-mail:shibi@ or sibitannin@ ,Tel:(028)85405508第17卷第1期中国医学工程Vol.17No.12009年3月China Medical EngineeringMar.2009对水体中染料和其他有机污染物吸附性能的研究的主要目的是对染料和有机废水进行脱色和净化处理。
电化学吸附英文
![电化学吸附英文](https://img.taocdn.com/s3/m/d2c3f74e58eef8c75fbfc77da26925c52cc591a2.png)
电化学吸附英文Electrochemical AdsorptionElectrochemical adsorption is a fundamental process in many important applications, such as energy storage, catalysis, and environmental remediation. This process involves the interaction between a solid surface and dissolved species, leading to the accumulation of the latter on the former. The driving force behind this phenomenon is the interplay between electrical and chemical forces, which can be harnessed to achieve desirable outcomes.At the heart of electrochemical adsorption is the concept of the electrical double layer, which describes the distribution of ions and charged species at the interface between a solid surface and a liquid electrolyte. This double layer, which can be several nanometers thick, is composed of an inner layer of specifically adsorbed ions and an outer layer of more diffusely distributed ions. The potential difference across this double layer, known as the surface potential, plays a crucial role in determining the extent and nature of the adsorption process.One of the key factors that influence electrochemical adsorption isthe surface charge of the solid material. Depending on the pH of the solution and the point of zero charge (PZC) of the solid, the surface can be positively or negatively charged. This surface charge, in turn, affects the adsorption of ions and molecules from the solution. For example, if the surface is positively charged, it will preferentially adsorb anions from the solution, while a negatively charged surface will attract cations.The strength of the adsorption interaction is also influenced by the chemical nature of the adsorbate and the adsorbent. Specific interactions, such as hydrogen bonding, ion-dipole interactions, and van der Waals forces, can all contribute to the overall adsorption energy. Additionally, the morphology and surface area of the adsorbent material can play a significant role in the adsorption capacity and kinetics.One of the key applications of electrochemical adsorption is in the field of energy storage. In electrochemical capacitors, also known as supercapacitors, the storage of energy is achieved through the reversible adsorption and desorption of ions at the electrode-electrolyte interface. The high surface area of the electrode materials, combined with the rapid kinetics of the adsorption process, allows for the development of high-power energy storage devices with long cycle life.Another important application of electrochemical adsorption is in the area of catalysis. Many catalytic processes, such as fuel cell reactions and electrochemical water splitting, involve the adsorption of reactants and intermediates on the catalyst surface. The controlled adsorption of these species can enhance the catalytic activity and selectivity, leading to improved efficiency and performance.Environmental remediation is yet another field where electrochemical adsorption plays a crucial role. The removal of heavy metals, organic pollutants, and other contaminants from water and wastewater can be achieved through the adsorption of these species onto electrode materials. The ability to tune the surface properties of the adsorbent, as well as the application of an external electric field, can enhance the selectivity and efficiency of the adsorption process.In addition to these well-established applications, electrochemical adsorption is also being explored in emerging fields, such as electrochemical sensors, energy harvesting, and biomedical applications. The versatility and tunability of this process make it a valuable tool in the development of innovative technologies.To further advance the understanding and application of electrochemical adsorption, ongoing research is focused on several key areas. These include the development of novel adsorbent materials with tailored surface properties, the investigation of thefundamental mechanisms governing the adsorption process, and the optimization of the operating conditions and system design for various applications.In conclusion, electrochemical adsorption is a complex and multifaceted phenomenon that underpins a wide range of important technologies. By harnessing the interplay between electrical and chemical forces, researchers and engineers can harness the power of this process to address pressing challenges in energy, environment, and beyond. As our understanding of electrochemical adsorption continues to deepen, we can expect to see even more innovative applications emerge in the years to come.。
氧化锌可见光催化
![氧化锌可见光催化](https://img.taocdn.com/s3/m/62c647a669dc5022aaea0057.png)
Green chemistry approach for the synthesis of ZnO–carbon dotsnanocomposites with good photocatalytic properties under visiblelightHakima Bozetine a ,b ,Qi Wang c ,Alexandre Barras d ,Musen Li c ,Toufik Hadjersi b ,Sabine Szunerits d ,Rabah Boukherroub d ,⇑aFacultédes Sciences,a r t i c l e i n f o Article history:Received 17September 2015Revised 25November 2015Accepted 1December 2015Available online 2December 2015Keywords:ZnOCarbon quantum dots NanocompositePhotocatalytic activity Visible lighta b s t r a c tWe report on a simple and one-pot synthetic method to produce ZnO/carbon quantum dots (ZnO/CQDs)nanocomposites.The morphological features and chemical composition of the nanocomposites were characterized using X-ray photoelectron spectroscopy (XPS),Fourier transform infrared (FTIR)spec-troscopy,thermogravimetric analyses (TGA),X-ray diffraction (XRD),scanning electron microscopy (SEM)and transmission electron microscopy (TEM).The optical properties of the nanocomposites were examined using UV–visible (UV–vis)spectrophotometry.The photocatalytic activity of the ZnO/CQDs was evaluated for the degradation of a model organic pollutant,rhodamine B,under visible light irradi-ation at room temperature.The highly efficient photodegradation capability of the nanocomposite was demonstrated by comparison with ZnO particles,prepared using identicalexperimental conditions.Overall,the present approach adheres to green chemistry principles and the nanocomposite holds pro-mise for the development ofremarkably efficient catalytic systems.Ó2015Elsevier Inc.All rights reserved.1.IntroductionThe last decade has witnessed a huge interest in the synthesis of carbon quantum dots (CQDs)and their applications in various/10.1016/j.jcis.2015.12.0010021-9797/Ó2015Elsevier Inc.All rights reserved.⇑Corresponding author.E-mail address:rabah.boukherroub@iemn.univ-lille1.fr (R.Boukherroub).fields due to their ease of synthesis and functionalization,their outstanding properties such as size-and wavelength-dependent luminescence emission,resistance to photobleaching and good biocompatibility[1–4].CQDs can be synthesized using different methods that can be roughly classified into‘‘top-down”and ‘‘bottom-up”approaches.Top-down methods consist on‘‘break-ing”of larger carbon structures into smaller objects,while the bottom-up techniques rely on CQDs formation from molecular pre-cursors.The bottom-up approach has the benefits of sustainability and compliance with green chemistry principles.Among these methods,chemical or thermal oxidation of molecular precursors represents an interesting route to synthesize CQDs in high quanti-ties[1–4].Integration/hybridization of carbon materials with inorganic functional components represents a robust strategy for developing new functionalities and improving their properties.Therefore, methodologies for constructing inorganic hybrid materials with organic materials integrated in well-defined architectures are of significant importance and may pave a way for screening new effi-cient photocatalytic materials.Hybridization of CQDs with differ-ent materials such as TiO2[5–11],SiO2[5],Fe2O3[12,13],Ag3PO4 [14],Cu2O[15],and CdS[16]has been reported.Zinc oxide(ZnO),an important group II–VI semiconductor with a wide band gap(3.37eV),is an interesting material due to its good photocatalytic activity,low cost,abundance of its components and ease of preparation in bulk or nanostructured forms[17,18].ZnO is thus largely investigated for removing environmental pollutants related to wastewater,polluted air,and spilled water[17,18].How-ever,the large band gap of ZnO limits its use as UV light photocat-alyst,which represents a major limitation as only5%of sunlight is usable or captured by undoped ZnO.Thus enhancing the photocat-alytic activity of ZnO under visible light to meet the demands of practical application is still a challenge both fundamentally and technologically.Shifting the optical response of ZnO to the visible range will have a positive effect on its photocatalytic efficiency in this part of the spectrum.Therefore,a great deal of research has focused on lowering the threshold energy for excitation in order to utilize a larger fraction of visible light for conversion to photo-chemical energy.To extend ZnO absorption to the visible range,several strategies are adopted such as doping with metal and non metal elements and formation of heterostructures[19,20].Despite the numerous reports on the synthesis and the simulta-neous efforts made to exploit CQDs for various applications,the synthesis of ZnO/CQDs nanocomposites was investigated only in a few reports with the aim to promote ZnO photocatalytic activity under visible light irradiation[21–24].Herein,we developed a simple route to prepare ZnO/CQDs nanocomposites using a solution phase technique.The method involves CQDs formation by the chemical reaction of D-fructose and NaOH,followed by addition of zinc salt at pH10.The photocat-alytic activity of the nanocomposite was evaluated by the photo-catalytic degradation of rhodamine B under visible light irradiation.The results showed that the nanocomposite was active under visible light irradiation and its efficiency was much higher than that of ZnO prepared under otherwise similar experimental conditions.2.Experimental section2.1.MaterialsD-Fructose,sodium hydroxide(NaOH),zinc acetate dihydrate [Zn(CH3COO)2Â2H2O],terephthalic acid and rhodamine B(RhB) were obtained from Sigma–Aldrich and used without further purification.2.2.Preparation of ZnO/CQDs nanocompositesInitially,carbon quantum dots(CQDs)aqueous solution was prepared by mixing5mL of D-fructose(500mM)and5mL of NaOH(500mM).Then,the solution was heated at50°C for30min.ZnO/CQDs hybrid nanostructures were synthesized by a hydrothermal method at low temperature.Typically,0.274g (125mM)of Zn(CH3COO)2Â2H2O were dissolved in the previously prepared CQDs solution at room temperature.The pH of the solu-tion was adjusted to10through dropwise addition of8M NaOH aqueous solution and stirring vigorously for15min at room tem-perature.Then,the solution was transferred into a20mL Teflon-beaker and heated at80°C for3h.Thefinal product was collected by centrifugation,washed with deionized water several times to remove the impurities andfinally dried in air for12h at80°C (ZnO–CQDs80°C)or200°C(ZnO–CQDs200°C).Pure ZnO was prepared by similar method.Typically0.274g (125mM)of Zn(CH3COO)2Â2H2O were dissolved in10mL of 250mM aqueous NaOH solution and then transferred into a 20mL Teflon beaker and heated at80°C for3h.Thefinal powder was dried at200°C for12h(ZnO).2.3.Photocatalytic degradation of rhodamine BThe photocatalytic performance of the ZnO/CQDs nanocompos-ite was evaluated using a pollutant model,rhodamine B(RhB), under visible light irradiation.The photodegradation reaction was carried out in a1cm spectrometric quartz cuvette under vis-ible light illumination using a xenon arc lamp(k>420nm).Typi-cally,1.5mg of the photocatalyst was dispersed in2mL of RhB aqueous solution with an initial concentration of(5Â10À6M). Prior to visible irradiation,the suspension was continuously stirred for about30min to reach an adsorption–desorption equilibrium between RhB dye and photocatalyst under dark conditions.Then, the stable aqueous dye solution was exposed to visible light illumi-nation at room temperature in air through with a cut offfilter (k=420nm,to suppress the light with wavelength shorter than 420nm)using a visiblefiber lamp(Spot Light Source400–700nm,L9566-03,Hamamatsu,Japan)under constant stirring. The intensity of the light was measured using a PM600TM Laser Fiber Power Meter(Coherent Inc.,USA)and was determined as being0.5W cmÀ2.The whole quartz cuvette was directly trans-ferred at different irradiation time intervals in a UV–vis spec-trophotometer.The concentration of RhB was determined by monitoring the changes in the absorbance maximum at554nm [25–27].2.4.Analysis of hydroxyl radicalsThe formation of hydroxyl radicals at the photoilluminated photocatalyst/water interface was detected byfluorescence measurements using terephthalic acid as a probe molecule[27]. A2mL solution of5Â10À4M terephthalic acid and2Â10À3M aqueous NaOH in the presence of1.5mg of ZnO/CQDs or ZnO was irradiated under visible light and thefluorescence was recorded. Fluorescence spectra of the generated2-hydroxyterephthalic acid were measured on a Cary Eclipse spectrophotometer from Agilent Technologies.Thefluorescence spectra were recorded after15min irradiation using k ex=315nm.2.5.Characterizations2.5.1.X-ray diffraction(XRD)The X-ray diffraction(XRD)patterns were recorded in the range of10–90°on a Rigaku D/Max-kA X-ray diffractometer using Cu K a radiation(k=1.54Å)at40kV and30mA.H.Bozetine et al./Journal of Colloid and Interface Science465(2016)286–2942872.5.2.Scanning electron microscopy(SEM)and energy dispersiveX-ray(EDX)SEM images and EDX spectra of thefilms were obtained using an FEI Nova NanoSEM450scanning electron microscope with FEG(field emission gun,Schottky type)system equipped with an energy dispersive X-ray analyzer at an accelerating voltage of 20kV.The samples were prepared by casting ethanol suspension of ZnO/CQDs nanocomposite on clean silicon wafers followed by dry-ing in an oven at60°C to remove completely the solvent.2.5.3.Transmission electron microscopy(TEM)The HRTEM images were acquired using a JEOL JEM-2100(JEOL, Japan)transmission electron microscope operating at an accelera-tion voltage of200kV.The samples were drop-coated from ethanolic dispersion of ZnO/CQDs samples onto carbon-coated copper TEM grids and the solvent was evaporated under gentle heating.2.5.4.X-Ray photoelectron spectroscopy(XPS)X-ray photoelectron spectroscopy(XPS)measurements were performed with an ESCALAB220XL spectrometer from Vacuum Generators featuring a monochromatic Al K a X-ray source (1486.6eV)and a spherical energy analyzer operated in the CAE (constant analyzer energy)mode(CAE=100eV for survey spectra and CAE=40eV for high-resolution spectra),using the electromag-netic lens mode.The detection angle of the photoelectrons is30°, as referenced to the sample surface.After subtraction of the Shirley-type background,the core-level spectra were decomposed into their components with mixed Gaussian–Lorentzian(30:70) shape lines using the CasaXPS software.Quantification calculations were performed using sensitivity factors supplied by PHI.2.5.5.UV–Vis spectrophotometryThe absorption spectra of solutions in quartz cuvette with an optical path of10mm were recorded using a Perkin Elmer Lambda UV/Vis950spectrophotometer in the wavelength range400–800nm.The samples were dispersed in water at a concentration of10À5M.2.5.6.FTIR spectroscopyFourier transform infrared(FTIR)spectra were recorded using a ThermoScientific FTIR instrument(Nicolet8700)with a resolution of4cmÀ1.Dried ZnO/CQDs sample(1mg)was mixed with KBr powder(100mg)in an agate mortar.The mixture was pressed into a pellet under10tons load for2–4min,and the spectrum was recorded immediately.Sixteen accumulative scans were collected. The signal from a pure KBr pellet was subtracted as the background.2.5.7.Thermogravimetric analysis(TGA)Thermogravimetric analysis(TGA)measurements were carried out in Al2O3crucibles in static under nitrogen atmosphere at a heating rate of10°C/min using a TA Instruments Q50thermogravi-metric analyzer.3.Results and discussionThe last decade has witnessed an ever increasing interest in the synthesis of CQDs and their nanocomposites because of the inter-est of these materials in various areas ranging from labeling,catal-ysis and optoelectronics[1–4].ZnO/CQDs hybrid structures have been prepared using hydrothermal[21,23,28],sol gel[29],and solution dispersion[22,30–33]techniques.In the present work, we have adopted a slightly modified green chemistry approach,first developed by Li et al.,for the preparation of CQDs[34].The direct reaction of an equimolar D-fructose aqueous solution with NaOH at50°C afforded the CQDs.The fructose solution itself is a colorless and transparent liquid.Upon addition of NaOH,the solu-tion started to exhibit a visible yellow coloration(after10min), which indicated that an appreciable amount of CQDs begun to form.The CQDs were freely dispersed in water without ultrasonic stirring.The pH value of the fresh CQDs solution was in the range of6–7.Fig.1a displays the UV–vis absorption spectrum of CQDs solution.It shows a broad absorbance in the region250–380nm; the peak at296nm was ascribed to the n–p⁄transition of the C@O band and the p–p⁄transition of the conjugated C@C band, indicating the formation of carbon nanodots[35].Fig.1b exhibits thefluorescence spectra of the CQDs dispersion recorded at various excitation wavelengths from340to420nm with a20nm incre-ment.It could be seen that the emission peak of the CQDs solution shifted from450to470nm when the excitation wavelength increased from340to420nm,respectively and then blue-shifted to460nm upon excitation at380and400nm.The emission spec-trum intensity increased in the excitation wavelength range340–400nm and decreased beyond400nm.The dependence of the emission wavelength and intensity on the excitation wavelength is a common phenomenon observed in carbon-based quantum dots[36].288H.Bozetine et al./Journal of Colloid and Interface Science465(2016)286–294ZnO/CQDs investigated in this work were produced using the green chemistry approach described above in a one pot process. After CQDs formation at50°C,zinc salt was introduced in the solu-tion after adjusting the pH to10using concentrated NaOH and then heated at80°C for3h.The resulting nanocomposite was fur-ther annealed at80or200°C for12h.The X-ray diffraction(XRD) pattern of the resulting ZnO/CQDs nanocomposite annealed at 80°C for12h is depicted in Fig.2a.The diffraction peaks at 2h=31.68°,34.35°,36.09°,47.36°,56.48°,62.70°,66.23°,67.87°, 68.99°and76.77°were respectively assigned to(100),(002), (101),(102),(110),(103),(200),(112),(201)and(202)crys-talline planes of hexagonal ZnO wurtzite structure(JCPD36-1451).Moreover,the ZnO/QCDs nanocomposite had a preferred orien-tation along the(101)crystalline plane.The peaks of the CQDs were not obviously observed in the XRD patterns of the nanocom-posite due to their little content and/or non-crystalline structure. The result indicated that addition of CQDs had no obvious influ-ence on the crystallinity and phase purity of the nanocomposite. No obvious change was noticed in the XRD pattern of the ZnO/ CQDs sample annealed at200°C for12h,suggesting that ZnO crys-tallization occurred already at80°C(Fig.2b).The data is in accor-dance with that reported on ZnO/CQDs prepared using different approaches[22,23,29].The structure and substructures of ZnO/CQDs nanocomposite were further characterized by scanning electron microscopy (SEM),transmission electron microscopy(TEM)and high-resolution TEM(HR-TEM).Fig.3depicts SEM images of the ZnO/ CQDs nanohybrids annealed at80or200°C for12h.It shows both samples are in cluster-based frameworks;the ZnO/CQDs(80°C) nanocomposite displayed clusters with an average diameter of 124±6nm(determined from a statistical study of30particles, Fig.3a),while the cluster size increased to425±11nm after annealing at200°C(Fig.3b).Fig.4exhibits TEM images of ZnO/CQDs nanohybrids.It indi-cates that each ZnO/CQDs cluster is made of ZnO/CQDs particles (Fig.4a and d).And under high resolution TEM observation,we can identify the CQDs(light spots with irregular lattice)uniformly dispersed among ZnO nanoparticles(Fig.4b and e);the lattice fringes of the nanoparticles with2.82Åspacing,correspond to the(100)crystal plane of hexagonal ZnO.The selected area elec-tron diffraction(SAED)pattern indicates that the ZnO nanocrystals possess a hexagonal wurtzite polycrystalline structure,in which thefive diffraction rings are indexed to the same positions as those from bulk ZnO(JCPDS card no.36-1451)(Fig.4c and f).The chemical composition of the ZnO/CQDs nanocomposites was examined using energy dispersive X-ray analysis(Fig.5).The results showed that the nanocomposites were composed of only Zn,O,and C,suggesting that the structures were mixed C materials and ZnO nanocrystals.Interestingly,annealing the nanocomposite at200°C for12h induced some carbon and oxygen loss,due most likely to removal of some labile functional groups(Table1).To further investigate the presence of CQDs in the ZnO/CQDs heterostructures and the interaction between ZnO and CQDs,we performed FT-IR analysis(Fig.6).Fig.6a depicts the FTIR spectrum in transmission mode of the ZnO prepared by zinc acetate precip-itation in NaOH.It shows peaks at865cmÀ1characteristic of Zn A O vibrations and a broad band at3377cmÀ1attributed to A OH stretching of the surface adsorbed water molecules[22,28].The presence of bands at1400and1574cmÀ1are most likely due to residual acetate groups in the material.The FTIR spectrum of the CQDs comprises a main and broad peak of O A H stretching vibra-tion mode at3392cmÀ1.The band at1587cmÀ1is assigned to C@C stretching of polycyclic aromatic hydrocarbons,while the peaks at1062and1416cmÀ1correspond to C A O vibrations of oxy-gen containing groups(Fig.6b).Compared to CQDs,the FTIR spec-trum of ZnO/CQDs nanocomposite shows peaks at3392,1574, 1408and1046cmÀ1(Fig.6c).The slight blue shift of the peaks can be explained by interaction between ZnO and CQDs[29].XPS was further used to evaluate the chemical composition of the ZnO/CQDs nanocomposites.The full survey spectrum of ZnO/ CQDs indicates the presence of zinc(Zn),carbon(C1s)and oxygen (O1s),in accordance with the chemical composition of the nanocomposite(Fig.7A).The C1s high resolution XPS spectrum of the ZnO/CQDs annealed at80°C can befitted with four peaks at 284.1,285.0,286.1and288.3eV attributed to sp2(C A C),sp3 (C A C,and C A H),C A O and C@O bonds,respectively with Zn/C=0.08(Fig.7B).After annealing the sample at200°C for 12h,the Zn/C ratio increased to0.16most likely due to removal of carbon containing oxygen groups.The result is corroborated by the C1s high resolution spectrum of the sample.Fig.7C shows that the C1s can be decomposed into three peaks at284.0,285.0 and288.1eV,corresponding to sp2(C A C),sp3(C A C,and C A H) and C@O bonds,respectively.The peak assigned to C A O in the sample annealed at80°C completely disappeared after annealing at200°C.No peak of Zn A C bond is found in both Zn2p and C1s spectra,suggesting that CQDs do not exist as dopant in the nanocomposite[22].Fig.S2depicts the O1s high resolution spectra of the ZnO/CQDs samples annealed at80and200°C.The O1s spectrum of the ZnO/CQDs(80°C)can be deconvoluted in three peaks at binding energies of528.3,530.2and532.0eV ascribed to C@O,oxygen-containing groups(C A OH,C A O A C)and Zn A O, respectively(Fig.S2A).After annealing at200°C for12h,the O1s XPS spectrum comprises similar bands with a slight increase of the components related to C@O and Zn A O.Thermogravimetric analysis(TGA)is widely used method to characterize thermal stability of materials.Fig.S3reveals the TGA curve of ZnO/CQDs annealed at200°C.The sample showed a small(1.4%)weight loss in the temperature range below110°C due most likely to adsorbed water.A sharp loss of$10%was observed between250and400°C ascribed to loss of oxygen-containing groups.The optical properties of ZnO and ZnO/CQDs nanocomposites were studied by measuring their UV–Vis absorption spectra (Fig.8).The UV–Vis absorption spectrum of ZnO nanoparticles, prepared by precipitation in NaOH,exhibits the characteristic spectrum with its fundamental absorption edge rising at381nm (Fig.8a).The ZnO/CQDs(80°C)displays characteristic absorption bands at259nm due to pÀp⁄electron transition of the CQDsH.Bozetine et al./Journal of Colloid and Interface Science465(2016)286–294289and a weak absorption edge at368nm of ZnO.The absorption above400nm is quite weak with respect to that of ZnO(Fig.8b). After annealing at200°C for12h,the spectrum comprises similar features with a clear increase of absorption in the visible region (Fig.8c).To demonstrate the potential of the ZnO/CQDs,we have inves-tigated the photodegradation of rhodamine B(RhB),as a pollutant model,under visible light irradiation.Fig.9shows the changes in the UV–vis absorption of a RhB aqueous solution(5Â10À6M)con-taining1.5mg of ZnO/CQDs photocatalyst as a function of the irra-diation time.The characteristic absorption peak of RhB at(554nm) gradually decreases as the visible light irradiation time increases. Also,the decrease of the absorption peak at554nm is accompa-nied with a concomitant blue shift due to a stepwise deethylation of RhB;the ethyl groups of tetraethylated RhB are deethylated one by one(corresponding peak of N,N,N0-triethylated rhodamine at 539nm,N,N0-diethylated rhodamine at522nm,and N-ethylated rhodamine at510nm).The fully deethylated molecule(completely N-deethylated product of RhB)displays a characteristic absorption band at498nm[25].Fig.10A shows the kinetics of RhB photodegradation in the absence and presence of different photocatalysts.The direct irradi-ation of RhB led to about23%degradation after105min irradiation under visible ing ZnO nanoparticles,prepared by precipita-tion in NaOH,caused70%degradation under otherwise identical experimental conditions.The photodegradation efficiency of RhB using ZnO/CQDs(80°C)was more than83%within105min under visible light irradiation.The ZnO–CQDs nanocomposite annealed atFig.3.SEM images of ZnO/CQDs nanocomposites annealed at80°C(a)and200°C(b).4.TEM images of ZnO–CQDs nanocomposites annealed at80°C(a,b)and200°C(d,e),selected-area electron diffraction(SAED)patterns of ZnO–CQDs annealed at and200°C(f).200°C exhibited much higher photocatalytic activity than all tested photocatalysts with 94%degradation of RhB after 105min irradiation.The photodegradation rate is calculated by the following equation:Photodegradation rate ¼ððC 0ÀC Þ=C 0ÞÃ100ð1Þwhere C 0is the initial concentration and C the concentration at time t .Moreover,the photocatalytic degradation of RhB dye followed pseudo-first order kinetics and the rate constant was determined by the following relation:lnC 0C¼kt ð2ÞFig.5.Energy-dispersive X-ray spectra of ZnO/CQDs nanocomposites annealed 80°C (a)and 200°C (b).Table 1EDX analyses of ZnO/CQDs nanocomposites annealed at 80and 200°C.SampleElement C (at.%)O (at.%)Zn (at.%)Zn/O Zn/C ZnO/Cdots (80°C)26.7648.5524.680.510.92ZnO/Cdots (200°C)21.6443.5634.790.801.61100015002000250030003500T r a n s m i t a n c e (a .u .)Wavenumbers (cm -1)(a)(b)(c)15741408157415871046106214001416337733923392865Fig. 6.Transmission FTIR spectra of (a)ZnO,(b)CQDs and (c)ZnO/CQDs nanocomposite annealed at 80°C.Interface Science 465(2016)286–294291The pseudo-first order rate constant k was calculated by plotting ln C 0ÀÁversus time,where C 0and C denote the RhB concentration at time t =0and t ,respectively (Fig.10B).Table 2summarizes the calculated apparent reaction rate con-stants k and the corresponding correlation coefficient values.The results indicate that the photocatalytic reaction rate of ZnO/CQDs (200°C)is 1.25and 1.82times larger than that of ZnO/CQDs (80°C)and ZnO,respectively.In heterogeneous catalyst,the main advantage is the reusability of the catalyst.The catalyst reusability is an important perfor-mance of the photocatalytic process,because a significant cost reduction on the treatment of dye effluent is indispensable.To assess the stability of the photocatalyst,ZnO/CQDs (200°C)nanocomposite was used for several photocatalytic runs.The results in Fig.11indicate that the activity of ZnO/CQDs only slightly decreased and 88%RhB degradation was achieved after four runs.The photocatalytic degradation of organic dyes by semiconduc-tor catalyst under visible-light irradiation typically includes twomechanisms.The first one is based on the excitation of the semi-conductors by light irradiation to form photogenerated electron/hole pairs.The other one is based on the excitation of dyes,in which the dye acts as a sensitizer of visible light and excited elec-trons will be transferred from the dye to the conduction band to become a cationic dye radical followed by self-degradation or degradation by reactiveoxidation.Table 2Degradation rate constants of rhodamine B using ZnO and ZnO/CQDs catalysts.Photocatalysts k (min À1)RhB without catalyst 0.003Pure ZnO0.011ZnO/CQDs 80°C 0.016ZnO/CQDs 200°C0.020292H.Bozetine et al./Journal of Colloid and Interface Science 465(2016)286–294The positive effects of carbon materials on the photocatalytic performance of ZnO have been demonstrated in several reports[24].In these hybrid structures,carbon materials can either act as a photoelectron reservoir to store and shuttle the photogener-ated electrons from the semiconductor,or serve as an organic dye-like‘‘photosensitizer”.Moreover,the high adsorption capacity of carbon materials is also expected to improve the photocatalytic process[24].ZnO is a wide band gap(3.37eV)material and as such it is only active under UV light irradiation.However,the UV–Vis curves show that ZnO absorbs in the visible range(Fig.8),which is the first requirement for an enhanced visible light-activated process. This is induced by the presence of a large density of defect levels in the bandgap[20].Therefore,electron transfer between these levels or between the acceptor level and the CB can occur under sub-band gap illumination during the photocatalysis process. Indeed,our results clearly showed that ZnO was active under vis-ible light irradiation(k>420nm).It became also clear that intro-ducing CQDs to ZnO improved significantly the photocatalytic activity of ZnO under visible light irradiation.From the UV–Vis measurements(Fig.8),the ZnO/CQDs displayed higher absorption in the visible region,which is favorable for enhanced photocat-alytic activity.Besides the increase of visible light absorption through hybridization with CQDs,one should also consider a better electron–hole separation and a reduced interfacial transfer time, which may account for higher performance of ZnO/CQDs nanocom-posite[29].Finally,the high adsorption capacity of CQDs for organic dyes is another beneficial effect,because semiconductor-based heterogeneous photocatalysis is a surface-confined process.To gain a better knowledge on the active species involved in the photocatalytic process,we have carried outfluorescence measure-ments using terephthalic acid as a probe molecule[27,37,38]. Indeed,terephthalic acid reacts with hydroxyl groups(ÅOH)to pro-duce a stronglyfluorescent molecule,2-hydroxyterephthalic acid, with a maximum intensity ually,thefluorescence intensity of2-hydroxyterephthalic acid is proportional to the amount of hydroxyl radicals produced during the photocatalytic process.Fig.12depicts thefluorescence spectra(k ex=315nm)of a5Â10À4M solution of terephthalic acid in2Â10À3M aqueous NaOH in the presence of1.5mg of ZnO or ZnO/CQDs irradiated for30min under visible light.In absence of photocatalyst,thefluorescence spectrum of the terephthalic acid in NaOH aqueous solution displayed a small peak with k max at$425nm.The intensity of this peak remained unchanged upon visible light irradiation,suggesting that visible light alone was not sufficient to generateÅOH radicals.Upon addi-tion of1.5mg of ZnO,a significant increase of the intensity at 425nm was observed,supportingÅOH radicals’generation at the ZnO/CQDs water interface.More importantly,the amount ofÅOH radicals is much higher than that generated using ZnO photocata-lyst within the same period.From these results,it was evident that the amount of hydroxyl radicals generated upon visible light irra-diation using ZnO/CQDs was higher than that produced using ZnO under otherwise identical experimental conditions,independent of the photochemical pathway followed.The results are in accor-dance with the higher performance of the ZnO/CQDs photocatalyst for the degradation of RhB.It has to be noticed that under our experimental conditions, only a fraction ofÅOH radicals was detected and the concentration ofÅOH was underestimated due to the short lifetime and relatively low diffusion rate ofÅOH[37].4.ConclusionIn summary,we have developed a simple,one-pot method for the synthesis of ZnO/CQDs nanocomposites.This cost effective technique obeys to the‘‘green chemistry”principles as it takes place in aqueous solution.The method is easy to carry out and takes place at low temperature,as compared to previously reported techniques.The potential of the ZnO/CQDs was demon-strated for the photocatalytic decomposition of an organic pollu-tant,rhodamine B,under visible light irradiation.The results of photocatalytic experiments indicated that ZnO/CQDs nanocompos-ites exhibited a superior photocatalytic performance than pure ZnO.The presence of the carbon material improved the photocat-alytic performance of the nanocomposites through various schemes such as enhanced dye adsorption and/or better charge separation.Moreover,the detection of hydroxyl radicals byfluores-cence measurements suggests that these species play an important role in the photocatalytic process.The results provided in this work are very promising in view of various photocatalytic applications of the ZnO/CQDs nanocomposites for the degradation of emerging contaminants such pharmaceuticals,pesticides and personal careH.Bozetine et al./Journal of Colloid and Interface Science465(2016)286–294293。
食品工艺学课件
![食品工艺学课件](https://img.taocdn.com/s3/m/8838d5ed760bf78a6529647d27284b73f2423663.png)
⾷品⼯艺学课件Processing of fruitsInstructor: mingfeng zheng(郑明锋) phd.Email:vanheng@/doc/bca037d13186bceb19e8bb68.htmlCell: 138********注意:课件全部根据⽼师提供的ppt整理,在编号上可能会有些问题,所以⼤家将就着看,祝⼤家考试顺利。
Chapter one:introductionFruit quality and preprocessingObjectsThrough the introduction, the students knowThe relationship between quality of fruit and the processed product,The relationship between composition of fruit and the processed product,Quality attributes of fresh fruits, and quality measurementspreprocessing methods and technologies1.1 classification of fruitsFruits are commonly classified by growing region as follows. Temperate zone, subtropical, and tropical. Growing region and environmental conditions specific to each regionsignificantly affect fruit quality. Examples of fruit grown in each region are listed below:1) temperate zone fruits2) subtropical fruits3) tropical fruits(1) temperate zone fruitsPome fruits(仁果类): apple, asian pear (nashi), european pear, quince榅桲果Stone fruits: apricot杏, cherry, nectarine, peach, plumSmall fruits and berries: grape (european and american types), strawberry, raspberry, blueberry, blackberry, cranberry (2) subtropical fruitsCitrus fruits: grapefruit, lemon, lime, orange, pummelo, tangerine, and mandarinNoncitrus fruits: avocado, cherimaya, fig, kiwifruit, olive, pomegranate(3) tropical fruitsMajor tropical fruits: banana, mango, papaya, pineappleMinor tropical fruits: carambola, cashew apple, durian, guava,longan, lychee, mangosteen, passion fruit, rambutan1.2 quality of raw materialsThe quality of processed fruit products depends on their quality at the start of processing; How maturity at harvest, Harvesting methods,Post harvest handling proceduresMaintenance in fresh fruits between harvest and process initiation.Quality attributes of fresh fruitsAppearance、exture factors、flavor components、nutritional quality、safety factorsAppearance factorsSize、shape、color、freedom from defects and decay.Texture factorsFirmness, crispness, juiciness.Flavor componentsSweetness, sourness (acidity), astringency, (收敛),bitterness, aroma, off-flavors,Nutritional qualityFruit's content of vitamins (a and c are the most important in fruits), minerals, dietary fiber, carbohydrates, proteins. Safety factorsResidues of pesticides, presence of heavy metals, mycotoxins produced by certain species of fungi, microbial contamination.1.3 losses in fresh fruits after harvastWater loss,Physical injuries,physiological breakdown, decayLoss of acidity, flavor, color, and nutritive valueFactors influence fruit qualityIn the orchard,During transportation,Throughout the handling system (sorting, sizing, ripening, and storage).The total time between harvesting and processingMinimizing the delays throughout the post harvest handling system greatly reduces finality loss, especially in highly perishable fruits such as strawberries, blackberries, apricots, and cherries.1.4 contribution of fruits to human nutritionEnergy (calories)VitaminsMineralsDietary fiberThe us. Department of agriculture and other organizations currently encourage consumers to participate in the "five a day" program which focuses on consumption of five servings of either fruit or vegetables each day.Energy (calories)(1) carbohydrates: banana, breadfruit, raisin葡萄⼲(2) proteins & amino acids: nuts, dried apricot and fig(3) fats. Avocado, olive, nutsFruits typically contain between 10% and 25% carbohydrates, a small amount (less than1.0%) of proteins, and a very small amount (less than 0.5 %) of fat. Carbohydrates, sugars,and starches are broken down to co2, water, and energy during metabolism. Carbohydrates and fats provide most of the calories the body requires for heat and energy.Vitamins(1) fresh fruits and vegetables contribute about 91% of vitamin c, 48% of vitamin a, 27% of vitamin b6, 17% of thiamin硫胺(维⽣素b1) to diet.(2) the following fruits are important contributors (based on their vitamin content and the amount consumed) to the supply of indicated vitamins in the u.s. Diet:*vitamin a: apricot, peach, cherry, orange, watermelon, cantaloupe*vitamin c: strawberry, orange, grapefruit, banana, apple, cantaloupe* niacin烟酸: peach, banana, orange, apricot"*riboflavin核黄素: banana, peach, orange, apple* thiamin: orange, banana, grapefruit, appleMinerals(1) fresh fruits and vegetables contribute about 26% of the magnesium镁and 19% of the iron to the u.s. Diet.(2) the following fruits are important contributors to the supply of indicated minerals in the us. Diet:* potassium钾: banana, peach, orange, apple* phosphorus磷: banana, orange, peach, raisin, fig*calcium: tangerine, grapefruit, orange* iron: strawberry, banana, apple, orangeDietary fiber(1) all fruits and nuts contribute to the dietary fiber in the diet. Dietary fiber consists of cellulose, hemicellulose, lignin⽊质素, and pectic substances, which are derived primarily from fruit cell walls and skin.(2) the dietary fiber content of fruits ranges from 0.5-1.5% (fresh weight basis).(3) dietary fiber plays an important role in relieving constipation by increasing water-holding capacity of feces. Its consumption is also linked to decreased incidence of cardiovascular disease, diverticulosis, and colon cancer.factors influefncing composition and quality of fruitsPreharvest factors(1) genetic: selection of cultivars, differences in raw fruit composition, durability, and response to processing. Fruit cultivars grown for fresh market sale will not be the optimal cultivars for processing.(2) climatic: temperature, light, wind--climatic factors may have a strong influence on nutritional quality of fruits. Light intensity significantly affects vitamin concentration, and temperature influences transpiration rate, which will affect mineral uptake and metabolism. ?(3) cultural practices: soil type, soil nutrient and water supply, pruning修剪, thinning, pest control-fertilizer addition may significantly affect the mineral content of fruit.1. 5 maturity at harvest and harvesting methodMaturity at harvest is one of the primary factors affecting fruit composition, quality, and storage life. Although most fruits reach peak eating quality when harvested fully ripe, they are usually picked mature, but not ripe, to decrease mechanical damage during postharvest handling. Harvesting may also mechanically damage fruit; therefore, choice of harvest methodshould allow for maintenance of quality.Postharvest factors1) environmental,2) handling methods,3) time period between harvesting and consumption(1) environmentalTemperature, relative humidity, atmospheric composition,(2) handling methodsPostharvest handling systems involve the channels through which harvested fruit reaches the processing facility or consumer. Handling methods should be chosen such that they maintain fruit quality and avoid delays.(3) time period between harvesting and consumptionDelays between harvesting and cooling or processing may result in direct losses (due to water loss and decay) and indirect losses (decrease in flavor and nutritional quality).Fruit maturity, ripening, and quality relationshipsMaturity at harvest is the most important factor that determines storage life and final fruit quality. Immature fruits are of inferior quality when ripened. Overripe fruits are likely to become soft and with insipid flavor soon after harvest. Fruits picked either too early or too late in the season are more susceptible to physiological disorders and have a shorter storage life than those picked at mid-season.Maturity and ripeningIn general, fruits become sweeter, more colorful, and softer as they mature.Some fruits are usually picked mature but unripe so that they can withstand the postharvest handling system when shipped long distances. Most currently used maturity indices are based on a compromise between those indices that would ensure the best eating quality to the consumer and those that provide the needed flexibility in transportation and marketing.Carbohydrates(碳⽔化合物)Carbohydrates : fresh fruits vary greatly in their carbohydrate content, with a general range being between 10% and 25%;. The texture, taste, and food value of a fresh fruit is related to its carbohydrate content. Sucrose, glucose, and fructose are the primary sugars found in fruits.Fructose is sweeter than sucrose, and sucrose is sweeter than glucose.Starch is converted to sugar as the fruits mature and ripen.Proteins(蛋⽩质)Fruits contain less than 1% protein (as opposed to 9-20% protein in nuts such as almond, and walnut). Changes in the level and activity of proteins resulting from permeability changes in cell membranes may be involved in chilling injury. Enzymes, which catalyze metabolic processes in fruits, are proteins that are important in the reactions involved in fruit ripening and senescence.Enzymes in fruits:(Organic acids(有机酸)Organic acids are important intermediate products of metabolism. The krebs (tca) cycle is the main channel for the oxidation of organic acids in living cells, and it provides the energy required for maintenance of cell integrity. Organic acids aremetabolized into manyconstituents, including amino acids, which are the building blocks of proteins.Citric acid、malic acid、tartaric acid、oxalic acidPigments(⾊素)Pigments undergo many changes during the maturation and ripening of fruits.(1) loss of chlorophyll (green color), which is influenced by ph changes, oxidative conditions, and chlorophyllase action(2) synthesis and/or revelation of carotenoids (yellow and orange colors)(3) development of anthocyanins (red, blue, and purple colors.Beta-carotene is a precursor to vitamin a. Carotenoids are very stable and remain intact in fruit tissues, even when extensive senescence has occurred.Phenolic compounds(酚类化合物)Total phenolic content is higher in immature fruits than in mature fruits and is the main substrate involved in enzymatic browning of cut, or otherwise damaged, fruit tissues when exposed to air.Enzymatic browning(酶促褐变)Enzymatic browning occurs due to the oxidation of phenolic compounds and is mediated, in the presence of o2, by the enzyme polyphenoloxidase (ppo). The initial product of oxidation is usually o-quinone, which is highly unstable and undergoes polymerization to yield brown pigments of higher molecular weight. Polyphenoloxidase catalyzes the following tworeactions:Volatiles(挥发性)Volatiles are responsible for the characteristic aroma of fruits. They are present in extremely small quantities (c <100µg/g fresh wt.).Volatile compounds are largely esters(酯), alcohols, acids, aldehydes(醛), an d ketones (low-molecular weight compounds).VitaminsThe water-soluble vitamins includeVitamin c,Thiamin硫胺(维⽣素b1),Riboflavin核黄素,Niacin烟酸, vitamin b6,Folacin叶酸, vitamin b12, biotin维⽣素h. Fat soluble vitamins include vitamins a, d, e, and k.Fat-soluble vitamins are less susceptible to postharvest losses.Vitamin cAscorbic acid is most sensitive to destruction when the commodity is subjected to adverse handling and storage conditions. Losses are enhanced by extended storage, highertemperatures, low relative humidity, physical damage, and chilling injury. Postharvest losses in vitamins a and b are usually much smaller than losses in vitamin c.1.7 biological factors involved in postharvest deterioration (变坏) of fruits ?Respiration (呼吸作⽤)Ethylene productionTranspiration (蒸腾作⽤)Physiological disordersPhysical damagePathological breakdownRespirationStored organic materials (carbohydrates, proteins, fats) are broken down into simple end products with a release of energy. Oxygen (o2) is used in this process, and carbon dioxide (co2) is produced.The loss of stored food reserves in the commodity during respiration hastens senescence as the reserves that provide energy to maintain the commodity's living status are exhausted. ?Food value (energy value) for the consumer is lost; it has reduced flavor quality, with sweetness especially being lost; and salable dry weight is lost (especially important for commodities destined for dehydration). The energy released as heat.Ethylene productionEthylene, the simplest of the organic compounds affecting the physiological processes of plants, is produced by all tissues of higher plants. As a plant hormone, ethylene regulates many aspects of growth development, and senescence and is physiologically active in traceamounts (less than 0.1 ppm).Transpiration or water lossWater loss is the main cause of deterioration because it results not only direct quantitative.Losses (loss of salable weight) hut also in loss of its appearance, loss of cripsness, andjuiciness), and nutritional quality.The dermal system (outer protective coverings) governs the regulation of water loss by the commodity.Physiological disorders(1) freezing injury :usually results in immediate collapse of the tissues and total loss.(2) chilling injury when fruits (mainly those of tropical and subtropical origin) are held at temperatures above their freezing point and below 5-15℃, depending on the commodity. ?(3) heat injury results from exposure to direct sunlight or to excessively high temperatures.Symptoms include surface scalding, uneven ripening, excessive softening, and desiccation. ?(4) very low (<1%) oxygen and/or elevated (>20%) carbon dioxide concentration can result in physiological breakdown of all fruits.Physical damageVarious types of physical damage (surface injuries, impact bruising, vibration bruising, etc.) Are major contributors to deterioration. Mechanical injuries are not only unsightly, but also accelerate water loss, stimulate higher respiration and ethylene production rates, and favor decay incidence.Pathological breakdownDecay is one of the most common or apparent causes of deterioration; however, attack by many microorganisms usually follows mechanical injury or physiological breakdown, which allows entry to the microorganism. Pathogens can infect healthy tissues and become the primary cause of deterioration.Environmental factors influencing deterioration of fruits(影响⽔果变坏的环境因素)Temperature,Relative humidity,Air movement,Atmospheric composition,Ethylene,Harvesting procedures Postharvest handling proceduresDumping、Sorting、Sizing、Cooling、Storage、RipeningDumping:Fresh fruits should be handled with care throughout the postharvest handling system in order to minimize mechanical injuries. Dumping in water or in flotation tanks should be used for fruits. If dry dumping systems are used, they should be well padded bruising. Sorting:Manual sorting is usually carried out to eliminate fruit exhibiting defects or decay. For some fruits, it may also be necessary to sort the fruit into two or more classes of maturity or ripeness.Mechanical sorters, which operate on the basis of color, soluble solids, moisture, or fat content, are being implemented and may greatly reduce time and labor requirements. Sizing:In some cases, sizing the fruits into two or more size categories may be required before processing. Sizing can be done mechanically on the basis of fruit dimension or by weight.Mechanical sizing can be a major source of physical damage to the fruit if the machines are not adequately padded and adjusted to the minimum possible fruit drop heights Ripening:Ripening before processing may be required for certain fruits (banana, kiwifruit, mango, papaya, peach, pear, plum, melon) that are picked mature but unripe. Ethylene treatment can be used to obtain faster and more uniform ripening. The optimum temperature range for ripening is 15-25℃and, within this range, the higher the temperature, the faster the ripening. Relative humidity should be maintained between 90% and 95 % during ripening. Cooling:Cooling is utilized to remove field heat and lower the fresh fruit's temperature to near its optimum storage temperature. Cooling can be done using cold water (hydrocooling) or cold air (forced-air cooling or "pressure cooling"). Highly perishable fruits, such as strawberries, bush berries, and apricots, should be cooled to near 4℃within six hours of harvest. Other fruits should be cooled to their optimum temperature within twelve hours of harvest. Storage:Short-term or long-term storage of fresh fruits may be needed before processing to regulate the product flow and extend the processing season. The relative humidity in the storage facility should be kept between 90% and 95%.To reduce decay, elevated c02 (15-20%) may be added to the atmosphere within pallet covers for strawberries, bush berries, and cherries, and sulfur dioxide (200 ppm) fumigation may be used on grapes.1.8 quality measurementsMany quality measurements can be made before a fruit crop is picked in order to determine if proper maturity or degree of ripeness has developed.ColourColour may be measured with instruments or by comparing the colour of fruit on the tree with standard picture charts. TextureTexture may be measured by compression by hand or by simple type of plungers.Soluble solidsAs fruit mature on the tree its concentration of juice solids, which are mostly sugars, changes. The concentration of soluble solids in the juice can be estimated with arefractometer or a hydrometer液体⽐重计.Acid contentThe acid content of fruit changes with maturity and affects flavour. Acid concentration can be measured by a simple chemical titration on the fruit juice. But for many fruits the tartness and flavour are really affected by the ratio of sugar to acid. Sugar to acid ratioIn describing the taste of tartness of several fruits and fruit juices, the term "sugar to acid ratio" or "brix to acid ratio" are commonly used. The higher the brix the greater the sugar concentration in the juice; the higher the "brix to acid ratio" the sweeter and lees tart is the juice.1.9 preprocessing1.9.1 harvestingThe above and other measurements, plus experience, indicate when fruit is ready for harvesting and subsequent processing.1.9.2 reception - quality and quantity1.9.3 temporary storage before processing1.9.4 washingHarvested fruit is washed to remove soil, micro-organisms and pesticide residues.Fruit washing is a mandatory processing step; it would be wise to eliminate spoiled fruit before washing in order to avoid the pollution of washing tools and/or equipment and the contamination of fruit during washing.1.9.5 sortingFruit sorting covers two main separate processing operations:Removal of damaged fruit and any foreign bodies (which might have been left behind after washing);Qualitative sorting based on organoleptic criteria and maturity stage.Mechanical sorting for size is usually not done at the preliminary stage. The most important initial sorting is for variety and maturity.1.9.6 trimming and peeling (skin removal)This processing step aims at removing the parts of the fruit which are either not edible or difficult to digest especially the skin.Up to now the industrial peeling of fruit and vegetables was performed by three procedures: Mechanically;By using water steam;Chemically; this method consists in treating fruit and vegetables by dipping them in a caustic soda solution at a temperature of 90 to 100°c; the concentration of this solution as well asthe dipping or immersion time varying according to each specific case.1.9.7 cuttingThis step is performed according to the specific requirements of the fruit processing technology.1.9.8 blanchingA brief heat treatment to vegetables some fruits to inactivate oxidative enzyme systems such as catalase, peroxidase, polyphenoloxidase, ascorbic acid oxidase, and lipoxygenase. ?When the unblanched tissue is disrupted or bruised and exposed to air, these enzymes come in contact with substrates causing softening, discoloration, and the production of off flavors. ?It is most often standard practice to blanch fruits in order to prevent quality deterioration. ?Although the primary purpose of blanching is enzyme inactivation.There are several other benefits blanching initially cleanses the product;Decreases the microbial load,Preheats the product before processing.Softens the fruit, facilitates compact packing in the can.Expell intercellular gases in the raw fruitImproved heat transfer during heat processing.Water blanching is generally of the immersion type or spray type as the product moves on a conveyor.Steam blanching often involves belt or chain conveyors upon which the product moves through a tunnel containing live steam.adequacy of blanching is usually based on inactivation of one of the heat resistant enzymes (peroxidase or polyphenol oxidase).During the blanching process, it is imperative that certain enzymes that have the potential to cause flavour and textural changes be inactiviated. The process involves a brief heattreatment applied to most vegetables and also to some fruits in order to inactivate oxidative enzyme system such as catalase, peroxidase, polyphenoloxidase,ascorbic acid oxidase, and lipoxygenase.When unblanched tissue is disrupted or bruised and exposed to air,these enzymes come in contact with substrate causing softening,discoloration, and the production of off-flavours.Since this action can potentially occur during the period prior to heat processing, it is most often standard practice to blanch fruits in order to prevent quality deterioration.1.9.9 ascorbic/citric acid dipAscorbic acid or vitamin c minimises fruit oxidation primarily by acting as an antioxidant and itself becoming oxidised in preference to catechol⼉茶酚-tannin compounds.It has been found that increased acidity also helps retard oxidative colour changes and so ascorbic acid plus citric acid may be used together. Citric acid further reacts with (chelates) metal ions thus removing these catalysts of oxidation from the system.1.9.10 sulphur dioxide treatmentSulphur dioxide may function in several ways:Sulphur dioxide is an enzyme poison against common oxidising enzymes;It also has antioxidant properties; i.e., it is an oxygen acceptor (as is ascorbic acid);Further so2 minimises non enzymatic maillard type browning by reacting with aldehyde醛groups of sugars so that they are no longer free to combine with amino acids;Sulphur dioxide also interferes with microbial growth.In many fruit processing pre-treatments two factors must be considered:Sulphur dioxide must be given time to penetrate the fruit tissues;So2 must not be used in excess because it has a characteristic unpleasant taste and odour, and international food laws limit the so2 content of fruit products, especially of those which are consumer oriented (e.g. Except semi-processed products oriented to further industrial utilisation).5.2.11 sugar syrupSugar syrup addition is one of the oldest methods of minimising oxidation.Sugar syrup minimises oxidation by coating the fruit and thereby preventing contact withatmospheric oxygen.Sugar syrup also offers some protection against loss of volatile 挥发性的fruit esters 酯and itcontributes sweet taste to otherwise tart fruits.It is common today to dissolve ascorbic acid and citric acid in the sugar syrup for addedeffect or to include sugar syrup after an so 2 treatment.QuestionsWhat factors influence the quality of fruits after harvest?How to maintain the fruit in good quality before the processing begin?第⼀节果蔬原料特性新鲜果蔬原料的特点 ? 果蔬原料的化学成分原料的化学成分与加⼯的关系1.新鲜果蔬原料的特点易腐性、季节性、区域性2.果蔬中的化学成分(chemical composition in fruits and vegetables )3.化学成分与加⼯的关系(relation between chemical composition and processing )3.1 ⽔分(water)果蔬中⽔的含量:⼤多数在80%以上,含⽔量⾼的如冬⽠(wax gourd)可达96%以上。
化学发光共振能量转移英文
![化学发光共振能量转移英文](https://img.taocdn.com/s3/m/73fcf43449d7c1c708a1284ac850ad02de8007bb.png)
化学发光共振能量转移英文Chemiluminescence Resonance Energy Transfer, or CRET,is a fascinating phenomenon in the chemistry world. It's kind of like when two dancers get into a perfect rhythmwith each other on the dance floor. One dancer, let's callit the "donor," emits energy in the form of light, and the other, the "acceptor," catches that energy and releases it as its own unique light.Imagine it like a game of "pass the ball" in basketball, but with energy instead. The donor molecule passes its excited state energy to the acceptor molecule, and that's when the magic happens. It's a really cool way to study how molecules interact with each other and how they transfer energy.In the lab, we often use CRET to study proteins andother biomolecules. It's like having a superpower to see what's happening on the molecular level. We can design special molecules that glow when they come into contactwith each other, and that tells us when and where certain interactions are occurring.One day, I was just sitting there, watching my experiment under the microscope, and suddenly, there was this beautiful glow. It was like a little light show happening right.。
210978233_基于磺酸基共价有机框架快速测定牛奶中氟喹诺酮类抗生素残留
![210978233_基于磺酸基共价有机框架快速测定牛奶中氟喹诺酮类抗生素残留](https://img.taocdn.com/s3/m/417b21ce690203d8ce2f0066f5335a8102d266b2.png)
张璐,姜伟. 基于磺酸基共价有机框架快速测定牛奶中氟喹诺酮类抗生素残留[J]. 食品工业科技,2023,44(7):269−277. doi:10.13386/j.issn1002-0306.2022050089ZHANG Lu, JIANG Wei. Sulfonic Acid-based Covalent Organic Framework for the Rapid Determination Towards Fluoroquinolone Antibiotic Residues in Milk[J]. Science and Technology of Food Industry, 2023, 44(7): 269−277. (in Chinese with English abstract).doi: 10.13386/j.issn1002-0306.2022050089· 分析检测 ·基于磺酸基共价有机框架快速测定牛奶中氟喹诺酮类抗生素残留张 璐,姜 伟*(南昌市检验检测中心,江西南昌 330000)摘 要:为了拓展基于新型纳米材料的固相萃取技术在复杂食品基质中的应用,本文制备了磺酸基共价有机框架材料(TpPa-SO 3H ),将其作为固相萃取吸附剂,结合高效液相色谱(high performance liquid chromatography ,HPLC )用于牛奶中3种氟喹诺酮类(fluoroquinolones ,FQs )抗生素的快速分析。
通过机械研磨法快速制备磺酸基共价有机框架TpPa-SO 3H ,探究其作为新型高效固相萃取吸附剂在FQs 抗生素检测方面的优势。
通过系统研究吸附剂用量、样品溶液pH 、吸附时间和解吸条件等因素,探究材料结构性能对固相萃取效率的影响以及方法重现性和定量分析能力。
结果表明:TpPa-SO 3H 具有超大的比表面积和丰富的磺酸基功能位点,能够与FQs 抗生素实现高效且选择性结合,通过优化,吸附时间为4.0 min 时,萃取回收率为94.23%~98.68%,结果显著优于国家标准方法。
高级氧化和可见光照射协同作用下Bi2WO6对有机污染物降解的催化活性增强
![高级氧化和可见光照射协同作用下Bi2WO6对有机污染物降解的催化活性增强](https://img.taocdn.com/s3/m/7394aa92ab00b52acfc789eb172ded630b1c98e1.png)
物 理 化 学 学 报Acta Phys. -Chim. Sin. 2024, 40 (4), 2304050 (1 of 12)Received: April 27, 2023; Revised: August 4, 2023; Accepted: August 4, 2023; Published online: August 10, 2023. *Correspondingauthors.Emails:*****************(Y.P.); **************.cn(C.P.);Tel:+86-158********(Y.P.);+86-177********(C.P.).The project was supported by the Anhui Provincial Natural Science Foundation, China (2108085MB44) and the Anhui University of Science and Technology 2022 Graduate Student Innovation Fund, China (2022CX2101).安徽省自然科学基金(2108085MB44), 安徽理工大学2022年研究生创新基金(2022CX2101)资助项目© Editorial office of Acta Physico-Chimica Sinica[Article] doi: 10.3866/PKU.WHXB202304050 Enhanced Catalytic Activity of Bi 2WO 6 for Organic Pollutants Degradationunder the Synergism between Advanced Oxidative Processes and Visible Light IrradiationYuanqing Wang, Yusong Pan *, Hongwu Zhu, Yanlei Xiang, Rong Han, Run Huang, Chao Du, Chengling Pan *School of Materials Science and Engineering, Anhui University of Science and Technology, Huainan 232001, Anhui Province, China. Abstract: Environmental problems have become more and more serious with the continuous development of industrialized society. Especially, the problem of industrial wastewater has been a hot research issue in the field of catalytic degradation. Coupling photocatalysis and advanced oxidation processes (AOPs) is considered to be an efficient organic pollutant degradation technology due to its high efficiency, non-selectivity, and mild treatment conditions. In this article, the authors focused on the synthesis andcharacterization of Bismuth tungstate (Bi 2WO 6) nanoflowers, which were prepared using a straightforward hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) surfactant. To investigate the micro-morphology, crystal phase, surface chemical element states, and optical characteristics of the Bi 2WO 6 nanoflowers, various methods such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflection spectroscopy (DRS) were used. The catalytic performance of the Bi 2WO 6 nanoflowers was then investigated for degrading organic pollutants under different catalytic systems. The removal efficiency of Rhodamine B (RhB) was up to 96.39% within 40 min under vis/potassium monopersulfate triple salt (PMS)/ Bi 2WO 6 system, which is obviously superior to that in both PMS/ Bi 2WO 6 (38.77% in 40 min) and vis/Bi 2WO 6 (31.82% in 40 min) systems, indicating that synergistic effects between visible-light irradiation and PMS accelerated the catalytic activity of Bi 2WO 6 on the RhB degradation. The researchers also investigated the effect of ambient conditions on the catalytic performance of the systems, such as catalyst dosage, PMS concentration, pH value, and ion concentration. Interestingly, the vis/PMS/Bi 2WO 6 system demonstrated high removal efficiency (up to 90%) despite changes in these parameters. However, the catalytic degradation rate (k ) was influenced by these parameters in this system. Conversely, the environmental parameters have obvious influence on the catalytic degradation rate (k ) under vis/PMS/ Bi 2WO 6 system. The results showed that when the catalyst dosage and PMS concentration increased, so did the K value. On the other hand, the K value increased firstly and then decreased with the rise of pH value in the catalytic system. And the catalytic degradation rate reached its maximum value (0.1502 min −1) at pH = 7 in the catalytic system. Interestingly, the presence of Cl − in the system would be beneficial for promoting the catalytic degradation efficiency.Conversely, the existence of CO 32−in the system would obviously inhibit the catalytic degradation efficiency. The result of the cycling experiments also verified that the catalyst possessed excellent stability for the degradation of organic dyes. Furthermore, the researchers conducted quenching experiments and EPR (electron paramagnetic resonance) tests, whichrevealed the crucial roles of superoxide radicals (•O − 2) and singlet oxygen (1O 2) in the degradation of organic pollutants. Overall, the excellent catalytic activity of Bi 2WO 6 in the vis/PMS synergistic catalytic system was attributed to its outstandingvisible-light-response photocatalysis activity and the superior ability of bismuth ions in activating PMS.Key Words: Photocatalysis; Advanced oxidation processes; Bi2WO6; Peroxymonosulfate; Rhodamine B高级氧化和可见光照射协同作用下Bi2WO6对有机污染物降解的催化活性增强汪园青,潘育松*,朱红梧,向妍蕾,韩蓉,黄润,杜超,潘成岭*安徽理工大学材料科学与工程学院,安徽淮南 232001摘要:随着工业化社会的不断发展,环境问题日益严重。
吸附束缚(cvd法)硅烷气中的硅
![吸附束缚(cvd法)硅烷气中的硅](https://img.taocdn.com/s3/m/805922d86aec0975f46527d3240c844769eaa038.png)
吸附束缚(cvd法)硅烷气中的硅英文回答:CVD (Chemical Vapor Deposition) is a widely used technique for the synthesis of silicon films. In CVD,silicon is deposited from a gas phase onto a substrate, forming a thin film. One of the commonly used precursorsfor silicon deposition is silane gas (SiH4). Silane gas is introduced into a reaction chamber, where it undergoes thermal decomposition to produce silicon atoms. Thesesilicon atoms then adsorb onto the surface of the substrate, leading to the formation of a silicon film.The adsorption of silicon atoms from silane gas ontothe substrate surface is a crucial step in the CVD process. It involves the interaction between the silicon atoms and the substrate surface, which can be influenced by various factors such as temperature, pressure, and the nature ofthe substrate. The adsorption process can be described by the Langmuir adsorption isotherm, which relates the surfacecoverage of adsorbates to the gas pressure.The adsorption of silicon atoms onto the substrate surface is a reversible process. Once the silicon atoms are adsorbed, they can also desorb back into the gas phase. The balance between adsorption and desorption determines the coverage of silicon atoms on the substrate surface. By controlling the process parameters, such as temperature and pressure, it is possible to optimize the adsorption and achieve the desired coverage of silicon atoms.中文回答:化学气相沉积(CVD)是一种广泛应用的合成硅薄膜的技术。
Nitrogen-Doped Titanium Dioxide as Visible-Light-Sensitive
![Nitrogen-Doped Titanium Dioxide as Visible-Light-Sensitive](https://img.taocdn.com/s3/m/27ee04e3102de2bd960588ef.png)
© XXXX American Chemical Society
A
/10.1021/cr5000738 | Chem. Rev. XXXX, XXX, XXX−XXX
Review /CR
Nitrogen-Doped Titanium Dioxide as Visible-Light-Sensitive Photocatalyst: Designs, Developments, and Prospects
Ryoji Asahi,*,† Takeshi Morikawa,† Hiroshi Irie,‡ and Takeshi Ohwaki†
† ‡
Toyota Central Research and Development Laboratories, Inc., Nagakute, Aichi 480-1192, Japan Clean Energy Research Center, University of Yamanashi, Kofu, Yamanashi 400-8511, Japan
Chemical Reviews TiO2 has not been widely applied to indoor use. Thus, for the more efficient utilization of incoming solar and room light energy, expanding the range of indoor applications of TiO2 has been investigated for many years through attempts to increase the sensitivity of TiO2 to visible light. Since the early 1980s, there have been numerous studies on the introduction of various transition-metal ions (iron (Fe), chromium (Cr), cobalt (Co), manganese (Mn), vanadium(V), molybdenum (Mo), etc.) as a dopant into the TiO2 lattice36−57 and on the introduction of oxygen (O) defects.58−60 However, the metal-doped TiO2 and O-defective TiO2 photocatalysts proposed in these studies have not been developed for practical applications because some of them exhibited poor photocatalytic activity and others exhibited poor reproducibility in improvement of activity. Thus, studies on the development of visible-light-sensitive TiO2 photocatalysts in the last two decades of the 20th century were generally unsuccessful. The other approach to the visible-light sensitization of TiO2 is so-called dye sensitization, which was studied in the late 1990s. For example, it is well-known that TiO2 containing a covalently attached Ru complex exhibits visible-light absorption. In this system, upon the excitation of the Ru complex, electrons in the conduction band (CB) of TiO2 injected from the excited Ru complex can produce hydrogen peroxide (H2O2) with which organic substances are degraded. Another example of dye sensitization is the platinum−chloride (H2[PtCl6] (or PtCl4))-modified TiO2 system reported by Kisch et al.61−66 and Ishibai et al.67 In this system, Pt(IV) chloride absorbs visible light to generate two new redox centers (2Pt4+(Cl−)4 + hν → Pt3+(Cl−)4 + Pt4+Cl0(Cl−)3). The oxidative center can be described as a type of Cl0/Cl− pair weakly coordinated to a metal center, while the reductive center can be described as Pt4+/Pt3+. Pt3+ reverts to Pt4+ when electrons are injected into the CB in TiO2 followed by the reduction of O2, while Cl reverts to Cl− upon the oxidation of organic compounds (upon extracting electrons from organic compounds). While these dye/complex catalysis systems show a large visible-light response and unique selectivity in photocatalysis, they have low stability under light irradiation.68−70 Also, using expensive metal complex makes it difficult to apply to practical use. The visible-light absorption of TiO2 by nitrification processing was first reported by Noda et al.71 and Sato72 in 1986. Sato showed photocatalytic reactions of CO and ethane under visible light, and concluded that visible-light sensitization was attributed to NOx-doping in TiO2. In 2001, Asahi et al. predicted by the first-principles calculations that doping of nitrogen (N) among possible anions should be effective for visible-light sensitization in TiO2, and demonstrated that Ndoped TiO2 has significant photocatalytic activities under visible light in experiment.73,74 Since then, N-doped TiO2 has attracted considerable attention, and its visible-light sensitivity has been independently confirmed by many researchers. Since the realization of N-doped TiO2, various types of TiO2 doped with nonmetal elements, such as sulfur (S),75−79 carbon (C),80,81 and iodine (I),82,83 have been widely studied as visible-light-sensitive photocatalysts. Numerous papers have been published on nonmetal-doped TiO2, including monoanion- and di-anion-doped TiO2 and even tri-anion-doped TiO2, as well as anion-and-cation-codoped TiO2.84−91 Among them, N-doped TiO2 is still leading visible-light-sensitive photocatalysts; it is now widely used in practice for environmental applications even under indoor irradiation. The material
Literature review on solar adsorption
![Literature review on solar adsorption](https://img.taocdn.com/s3/m/4b7e8723aaea998fcc220ea6.png)
Institute of refrigeration and cryogenics, Shanghai Jiao Tong University, Shanghai 200030, People’s Republic of China Received 16 January 2001; accepted 15 February 2001
3. Solar adsorption cooling alternatives . . . . . . . . . . . . 3.1. Solar t . . . . . . . . . . 3.2. Solar adsorption refrigeration systems for ice-making 3.3. Solar desiccant cooling and air-conditioning systems . 4. 5. 6. 7. 8. 9.
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
1. Introduction In the early years of this century, sorption refrigeration was frequently used, later with the development of cheap reliable compressors and electrical motors, the improvement in power station efficiency and the introduction of CFCs in the 1930s, sorption refrigeration became a niche technology [1]. Heat-driven sorption refrigeration cycles have existed in patent literature since at least 1909, and refrigerators were commercially available in the 1920s. In 1929, Miller described several systems which utilized silica gel and sulfur dioxide as an adsorbent/adsorbate pair [2]. However, recent years have witnessed increasing interest in this technology for many different reasons. The main arguments in favor are that sorption systems are quiet, long lasting, cheap to maintain and environmentally benign. Refrigeration technology is required to evolve due to the new environmental regulation. The first regulation concerning the depletion of the ozone layer (Montreal protocol, 1988) decided to phase-out chlorofluorocarbons (CFCs) and then hydrochlorofluorocarbons (HCFCs). More recently adsorptive processes have been proposed for heat pump and refrigeration as consistent alternative to vapor compression systems. Ecological problems concerning the emission of CFCs from refrigerating units
高考英语一轮复习 完形填空阅读理解基础训练12
![高考英语一轮复习 完形填空阅读理解基础训练12](https://img.taocdn.com/s3/m/bffbc1cf9fc3d5bbfd0a79563c1ec5da51e2d656.png)
入舵市安恙阳光实验学校云南省楚雄市2015高考英语完形填空、阅读理解一轮基础训练(12)及答案【考点剖析】[2013·安徽卷]阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项。
If you want to learn a new language, the very first thing to think about is why. Do you need it for a __36__ reason, such as your job or your studies? __37__ perhaps you're interested in the __38__,films or music of a different country and you know how much it will help to have a __39__ of the language.Most people learn best using a variety of __40__, but traditional classes are an ideal(理想的)start for many people. They __41__ an environment where you can practice under the __42__ of someone who's good at the language. We all lead __43__ lives and learning a language takes __44__. You will have more success if you study regularly, so try to develop a __45__. It doesn't matter if you haven't got long. Becoming fluent in a language will take years, but learning to get by takes __46__.Many people start learning a language and soon give up. “I'm too__47__,” they say. Yes, children do learn language s more __48__ than adults, but research has shown that you can learn a language at any __49__. And learning is good for the health of your brain, too. I've also heard people __50__ about the mistakes they make when __51__. Well, relax and laugh about your mistakes __52__ you're much less likely to make them again.Learning a new language is never __53__. But with some work and devotion, you'll make progress. And you'll be __54__ by the positive reaction of some people when you say just a few words in __55__ own language. Good luck!36.A.technical B.political C.practical D.physical 37.A.After B.So C.Though D.Or38.A.literature B.transport C.agriculture D.medicine 39.A.view B.knowledge C.form D.database40.A.paintings B.regulations C.methods D.computers 41.A.protect B.change C.respect D.provide42.A.control B.command C.guidance D.pressure43.A.busy B.happy C.simple D.normal44.A.courage B.time C.energy D.place45.A.theory B.business C.routine D.project 46.A.some risks B.a lot less C.some notes D.a lot more 47.A.old B.nervous C.weak D.tired48.A.closely B.quickly C.privately D.quietly 49.A.age B.speed C.distance D.school50.A.worry B.hesitate C.think D.quarrel51.A.singing B.working C.bargaining D.learning 52.A.if B.and C.but D.before53.A.tiresome B.hard C.interesting D.easy54.A.blamed B.amazed C.interrupted D.informed 55.A.their B.his C.our D.your【要点综述】本文属于议论文,主要讲述了学习一门外语的意义,以及在学习过程中会遇到的一些困知,后一分句说的是“任何年龄的人都能学好外语”,故选A。
Isomerization and Aggregation of the Solar Cell Dye D149
![Isomerization and Aggregation of the Solar Cell Dye D149](https://img.taocdn.com/s3/m/660afd0552ea551810a68725.png)
Isomerization and Aggregation of the Solar Cell Dye D149
Ahmed El-Zohry, Andreas Orthaber, and Burkhard Zietz*
Department of Chemistry - Ångström Laboratories, Box 523, SE-751 20 Uppsala, Sweden ABSTRACT: D149, a metal-free indoline dye, is one of the most promising sensitizers for dye-sensitized solar cells (DSSCs) and has shown very high solar energy conversion efficiencies of 9%. Effective electron injection from the excited state is a prerequisite for high efficiencies and is lowered by competing deactivation pathways. Previous investigations have shown surprisingly short-lived excited states for this dye, with maximum lifetime components of 100−720 ps in different solvents and less than 120 ps for surface-adsorbed D149. Using steady-state and time-resolved fluorescence, we have investigated the photochemical properties of D149 in nonpolar and polar solvents, polymer matrices, and adsorbed on ZrO2, partially including a coadsorbent. In solution, excitation to the S2 state yields a product that is identified as a photoisomer. The reaction is reversible, and the involved double-bond is identified by NMR spectroscopy. Our results further show that lifetimes of 100−330 ps in the solvents used are increased to more than 2 ns for D149 in polymer matrices and on ZrO2. This is in part attributed to blocked internal motion due to steric constraint. Conversely, concentration-dependent aggregation leads to a dramatic reduction in lifetimes that can affect solar cell performance. Our results explain the unexpectedly short lifetimes observed previously. We also show that photochemical properties such as lifetimes determined in solution are different from the ones determined on semiconductor surfaces used in solar cells. The obtained mechanistic understanding should help develop design strategies for further improvement of solar cell dyes.
The extended atmosphere and evolution of the RV Tau star R Scuti
![The extended atmosphere and evolution of the RV Tau star R Scuti](https://img.taocdn.com/s3/m/304d870c52ea551810a68753.png)
a r X i v :a s t r o -p h /0203234v 1 14 M a r 2002Astronomy &Astrophysics manuscript no.February 1,2008(DOI:will be inserted by hand later)The extended atmosphere and evolution of the RV Tau star,R Scuti ⋆M.Matsuura 1,I.Yamamura 2,A.A.Zijlstra 1,and T.R.Bedding 31Department of Physics,UMIST,P.O.Box 88,Manchester M601QD,UK2Institute of Space and Astronautical Science (ISAS),Yoshino-dai 3-1-1,Sagamihara,Kanagawa,229-8510,Japan 3School of Physics,University of Sydney 2006,AustraliaReceived:03December 2001;Accepted:11March 2002Abstract.We analyze ISO/SWS spectra of the RV Tau star R Scuti.The infrared spectra are dominated by H 2O emission bands.The near-and mid-infrared excess is attributed to H 2O;the dust contribution is less important.We also identify CO,SiO and CO 2bands.The various molecular emission bands originate from an extended atmosphere,an atmosphere above the photosphere.The extended atmosphere of R Sct is formed from matter which gradually have lifted up from the photosphere through the pulsations of the star.In contrast to the abundant molecules around the star,the silicate dust feature is weak and the dust mass-loss rate is only ˙Md =10−11M ⊙yr −1.This implies that there might be a process to inhibit dust formation from molecules.RV Tau stars are commonly considered as post-AGB stars.While a detached dust envelope around R Sct is consistent with such an interpretation,we show that its period evolution is slower than expected.We argue that R Sct may be a thermal-pulsing AGB star,observed in a helium-burning phase.Key words.stars:AGB and post-AGB –stars:atmospheres –stars:circumstellar matter –infrared:stars –stars:variables:general –stars:individual:R Sct1.IntroductionRV Tau stars are pulsating variables characterized by al-ternating deep and shallow minima in their light curves.They are generally considered to be post-AGB stars with low initial masses (∼1M ⊙;Jura 1986).The abundance ratios show that they have experienced first dredge-up at the bottom of the red giant branch (Giridhar et al.2000).Based on their infrared dust excesses,RV Tau stars are classified into two groups:those with extensive warm dust and those without evidence of dust in the near-infrared region (Goldsmith et al.1987).R Sct is the brightest star in the visible in the latter group.R Sct (HR 7066;HIP 92202)has a reported period of 147days (Kholopov et al.1988).The effective temperature varies from 4750to 5250K (Shenton et al.1994);the spectral type may vary as late as M3at minimum phase (Kholopov et al.1988).An atmosphere beyond the photosphere,which we call an extended atmosphere later on in this paper,hasbeen2M.Matsuura et al.:The atmosphere and evolution of R SctV [m a g ]JD-2450000Fig.1.The visual light curve of R Sct (Mattei 1995,private communication).The magnitudes are averaged in 5-day bins.The date at which the ISO/SWS observed this star is shown by the vertical line.estimated as φ=0.60from the AAVSO light curve (Fig.1;Mattei 1995,private communication),where φ=0.0cor-responds to the nearest previous deep minimum.The spectra were obtained using the full-grating scan mode (AOT 01,scan speed 1).The wavelength range covers 2.35–45.2µm,but the signal-to-noise ratio is poor above 20µm and these data are not used.The spectral reso-lution is λ/∆λ=300–500,depending on the wavelength.The data were reduced using the SWS Interactive Analysis package.The calibration parameters of October 1999were used for the wavelength,detector responsivity,and abso-lute flux calibrations.The spectra were re-gridded to a constant wavelength resolution of λ/∆λ=300.To identify the molecular features,we calculate molec-ular spectra using a circular slab model,which was used previously for analysing spectra of Mira variables (e.g.,Yamamura et al.1999).We adopt a multiple layer model.This is an approximation for a shell that shows a temperature and density gradient;the model layers do not necessarily represent discrete shells.Line lists for H 2O,CO 2,SiO and CO were taken from Partridge &Schwenke (1997),HITRAN (Rothman et al.2001a),Langhoff&Bauschlicher (1993),and HITEMP (Rothman et al.2001b),respectively.The solar isotopic abundance ratio is adopted for H 2O and SiO.Bujarrabal et al.(1990)derive 12C/13C <∼10and we assume 10%of carbon atomsare 13C.For the energy level populations of the molecules,local thermodynamic equilibrium (LTE)is assumed.A line width of 5km s −1is assumed for all the molecules.We use a black body as the background source illuminat-ing the molecular layers.We assume that the background is a black-body with a temperature of 5000K.The near-and mid-infrared spectrum,which is in the Rayleigh Jeans region of the black body,is insensitive to the black-body temperature.The synthesized spectrum is not significantly affected by the black-body temperature with in the range 5000–7000K.Table 1.The parameters of synthesized molecular spec-tra.We adopt two H 2O components:one is needed to re-produce the absorption at 2.7µm and the other causes the strong emission features over the whole wavelength region.The size of the water layer,R ,is given relative to the stellar radius (R ∗).The features are indicated as either emission (em)or absorption (ab).CO 40003.0×1021 1.6em H 2O-122001.2×1021 2.8em SiO =T H 2O −18.0×1020=R H 2O −1emH 2O-212005.0×1019 5.5ab (2.7µm)em (6.2µm)CO 28003×101810.5ab (4.2µm)em (13µm)M.Matsuura et al.:The atmosphere and evolution of R Sct 3F [J y ]Wavelength [µm]Fig.2.The ISO/SWS spectra of R Sct (black line).The locations of the major molecular features on R Sct are indicated.The spectra of R Sct is compared with that of an oxygen-rich AGB star,o Cet (grey line;flux is scaled).These two stars show similar spectra below 4.5µm.Note that the spectral resolution of o Cet is twice as high as that of R Sct.density distribution as would be expected for a constant mass-loss rate.The temperature of the dust grains was cal-culated by solving the energy equilibrium,assuming the optically thin condition.For the calculation of the dust temperature distribution,the central star was assumed to be a black body of 5000K.The star was then replaced by the molecular model spectra,and the radiation trans-fer was re-calculated.We used the dust opacity of ‘warm oxygen-deficient circumstellar dust’(set 1)in Ossenkopf et al.(1992).The parameters required to reproduce the 10µm sil-icate emission are a dust mass-loss rate of ˙Md =1.5×10−11M ⊙yr −1,and an inner radius of 50R ∗,assuming the outflow velocity is 10km s −1(Bujarrabal et al.1988).The stellar radius (R ∗)was taken as 6×1012cm,and the luminosity as 4000L ⊙.The outer radius of the dust shell in Fig.3is R o =5×104R ∗.However,the spectra can be well reproduced within the range of R o =103–105R ∗,and we do not well constrain R o .Note that the radii of the molecular layers are measured relative to the stellar radius;the assumed value of R ∗=6×1012cm is only used for the dust model.4.Discussion4.1.Evidence for molecules in the extendedatmosphereSeveral molecules are detected in the ISO/SWS spectra of R Sct.The range of excitation temperatures (800–4000K)is lower than that of the underlying star,confirming that these molecules are not photospheric.Several kinds of molecules,with different transition energies,are detectedin emission.The implication is that these molecules ex-tend beyond the background continuum source (the star).In thermal equilibrium,theoretical model atmospheres predict that H 2O and CO 2are stable in atmospheres cooler than 2000–2500K (i.e.,late M)and that SiO is stable below 3000K (Tsuji 1964).The effective tempera-ture of R Sct is 4750–5250K (Shenton et al.1994).Thus,these three molecules must be located in ‘an extended at-mosphere’,a region cooler than the photosphere of R Sct,i.e.located above the photosphere.For infrared CO emission,non-LTE effects have been proposed (summarized in Oudmaijer et al.1995).However,these non-LTE effects have difficulty explain-ing all the emission features,since several molecules with various transition energy are seen in emission at the same time.It is most likely that the extension of the atmosphere around the star is responsible for the emission bands.R Sct occasionally shows TiO absorption in the visible spectra at minimum.TiO is present in the photospheres of cool stars,and is used for the spectral classification of M-type stars.Its presence has been used to assign R Sct a spectral class as late as M4occasionally at minimum phase (e.g.Preston et al.1963;Cardelli 1989).The phase of the ISO/SWS observation is 0.60(i.e.intermediate be-tween deep minima).It is unlikely that the spectral type was early M at the moment of the ISO/SWS observation,and there is no evidence that the star ever shows a spec-tral type of late M required for stable presence of water-vapour.This supports the conclusion that these molecules are not photospheric.It seems unlikely that stellar pulsa-tion on its own can reduce the stellar temperature from ∼5000K to the 3500K required for the formation of TiO.4M.Matsuura et al.:The atmosphere and evolution of R Sct345678910Wavelength [µm]162O onlyFig.3.(A)The ISO/SWS spectra of R Sct(top)are compared with synthesized spectra,which are offset.One synthesized spectra includes molecules only;the other also includes a dust excess.Most part of the ISO/SWS spectra are well reproduced by the synthesized spectra containing only the molecular bands.A weak dust excess is observed at10µm.(B)Synthesized spectra containing only H2O.The black line shows the2200K H2O layer only,and the grey line shows both H2O layers(2200K and1200K).For comparison,the background source,a5000K black body is also presented.H2O bands are seen in emission;the global shape of the spectra are dominated by H2O bands with an excitation temperature of2200K.The1200K component contributes to the absorption at2.7µm and the emission at6.2µm.Even this molecule may be located in the extended atmo-sphere.The spectral type of R Sct,which is later than that of other RV Tau stars,may reflect in part its extended atmosphere.The spectral energy distribution is enhanced in the infrared region,due to the presence of the non-photospheric molecular emission bands in infrared.The resultant effective temperature would underestimate the actual temperature of the photosphere.Without the ex-tended atmosphere,the effective temperature of R Sct could be more similar to that of other RV Tau stars. 4.2.The envelope structure of R SctAlthough the molecules are not photospheric,the excita-tion temperatures(800–4000K)and radii(1–10R∗)show that these molecules are still located near the star.This suggests that they formed recently.In our SWS data,the absorption features of H2O are seen superimposed on the H2O emission features. The cooler layer causing the absorption features and the warmer layer causing the emission are therefore seen along the same line on sight,with the cooler component mask-ing the spectra from the warmer layer.This is possible for a disk structure if it is seen approximately edge-on, but in general such a configuration is easier to explain if the atmosphere consists of an extended shell with a more spherical shape.The extended atmosphere proposed here describes the region above but still close to the photosphere,located inside the dust formation radius,at a temperature of T∼1000K.The region outside the dust formation ra-dius is referred to as the circumstellar envelope.Extended molecular atmospheres are seen in pulsating Mira vari-ables,where they are caused by the pulsations(e.g.,Scholz 2001).The extended atmosphere bridges the region be-tween the photosphere and the dust forming region,and supplies gas from the photosphere to the dust forming re-gion.The extended atmosphere and the circumstellar en-velope can be distinguished by the temperatures and the velocity profiles of the molecules.The molecules in the extended atmosphere show complicated velocity profiles, often varying with a time scale of one period,and some-times moving inward.The circumstellar envelope tracesM.Matsuura et al.:The atmosphere and evolution of R Sct 5NormalizedF [J y ]NormalizedF [J y ]NormalizedF [J y ]NormalizedFig.4.The ISO/SWS spectra of R Sct compared with the synthesized spectra (the left scale).Each molecular component is normalized to the background source and is indicated on the right scale.The quality of the ISO/SWS data is lower above 13µm and the line intensity of each CO 2line is not reliable.the dust-driven wind,where the velocity can be approxi-mated with a near-constant expansion velocity.There have been previous indications of this extended atmosphere in R Sct.Mozurkewich et al.(1987)found ev-idence for velocity variations with a period of 142days in the molecular absorption lines.The variation is at-tributed to the pulsation shocks in the extended atmo-sphere.This variation is also found in sodium line (L`e bre &Gillet 1991).Hinkle et al.(1996)reported that CO showed complicated velocity profiles,while OH and H 2O,which have lower dissociation energies,showed single ve-locity profiles.All molecular lines showed time variability.They concluded that CO is located near the photosphere and is strongly affected by the stellar pulsation,while H 2O is present in a more extended atmosphere.The pulsation shocks propagating into the inner re-gion of the molecular atmosphere should not be so strong that the molecules are completely destroyed.However,the shocks can initially aid the formation of some molecules(Duari et al.1999).The molecules may subsequently ac-cumulate in a region above the sodium layer.We used multiple shells as an approximation to the structure of the atmosphere.In reality,a single shell with a temperature and density gradient is more likely,where the inner,warmer region contributes to the emission and the outer,cooler region causes the absorption on the emis-sion bands.The temperature and the density will show discontinuities at the pulsation shocks,which could still lead to multiple discrete shells.However,the shocks do not reach 10R ∗,and the outer shell is expected to be more continuous.Recently,H 2O molecules have been found in K-and M-giants and supergiants whose effective temperatures are too high for the presence of water (Tsuji 1997,2001;Jennings &Sada 1998).These H 2O molecules are located above atmospheres,as we have found for R Sct.The extra atmosphere with molecules is commonly seen in cool red (super-)giants.Many RV Tau stars show an under-abundance of re-fractory elements in the photospheric spectra,similar to depletion patterns seen in the interstellar medium.To ex-plain this effect,re-accretion of gas from a long-lived bi-nary disk has been proposed where gas and dust have become separated (Waters et al.1992).Such a disk has been reported for the RV Tau star AC Her (Van Winckel et al.1998;Jura et al.2000).These disks are located in the circumstellar envelope.R Sct shows a relatively small depletion (Giridhar et al.2000).Giridhar et al.argued that RV Tau stars with late spectral type,such as R Sct,have enlarged atmospheres:the accreted,depleted gas mixes with stellar,non-depleted gas in the extended at-mosphere and reduces the depletion.For R Sct,there is strong evidence that the enlarged atmosphere exists from the ISO/SWS observations.4.3.VariabilityIn Table A.1,we summarize published infrared photomet-ric data of R Sct.One set of observations,taken near visible minimum (φ=0.07,JD=24433051),shows fainter magnitudes at all infrared bands.Except for this event,the magnitudes are comparable at all phases.The magni-tudes estimated from the ISO/SWS spectra are also con-sistent with other observations at other phases.At the N -band,H 2O emission increases the flux by a factor of two compared to the brightness of the central star (Fig.5).The constancy of the infrared magnitudes suggests that the molecules were continuously present around the star over the 30years of observation,and did not form shortly before the time of the ISO/SWS observations.The visual light curve of R Sct shows a number of episodes of deep minima over this time,one coinciding with the ISO observations and another with the IRAS observations (Fig.6).Before this time,the activity was generally less.The extended molecular layers may be re-lated to this increased activity,but no spectroscopic or6M.Matsuura et al.:The atmosphere and evolution of R Sctinfrared photometric data is available covering the earlier, less active period.With an expansion velocity of5km s−1, the hot water layer lags behind the pulsation of the star from the photosphere by less than a year.It is therefore of interest that R Sct has been relatively quiescent over the past3years:the effect of this on the water layer could be investigated.4.4.Mass-loss historyR Sct shows an excess in the IRAS60µm band(Fig.5). There is also a weak12µm excess in the IRAS band, but our results show that this is mostly due to the H2O emission in the10µm region,with only a minor con-tribution from dust(Fig.3).The dust mass-loss rate which we estimate from the10µm silicate emission is ˙Md=1.5×10−11M⊙yr−1.This mass-loss rate cannot produce the observed60µm excess,and an additional cold dust component is needed.Alcolea&Bujarrabal(1991)adopt a two-component dust shell model based on the0.4–100µm spectra.For the inner shell they derive a dust mass-loss rate of˙M d= 4.2×10−11M⊙yr−1,which is comparable to our result from the10µm excess.For the outer shell they derive ˙Md=2.4×10−9M⊙yr−1.The CO-derived gas mass-loss rate from12CO J=1–0and2–1lines is˙M=2×10−7M⊙yr−1(Bujarrabal et al.1988).If a gas-to-dust ratio of100is assumed,the gas mass-loss rate derived from CO is comparable to the mass-loss rate of the outer shell estimated from the dust shell model.Also,the low excitation temperature of the millimeter CO rotation line suggests that the CO traces the past mass-loss rate.The implication is that the mass-loss rate of R Sct has reduced by about a factor of100(Alcolea&Bujarrabal1991). Using the inner radius of the outer(cold)dust shell of 3.7×1016cm and the CO expansion velocity of5km s−1, Alcolea&Bujarrabal estimated the elapsed time after the large mass loss ceased as∼2000yr.This issue will be discussed in the next section.The low current dust mass-loss rate raises a peculiar point.The SiO column density derived here is compara-ble to that of Mira variables(Yamamura et al.1999). R Sct should therefore have a sufficiently large amount of SiO for silicate dust formation.However,the current dust mass-loss rate is two orders of magnitudes lower than that of Mira variables(typically˙M d=10−9M⊙yr−1–10−8M⊙yr−1).This suggest a process to inhibit the dust formation from the molecules.The hotter radiationfield from the star,compared to Miras,may affect the dust formation sequence.For AGB stars,the extended atmosphere is thought to be built up by pulsations,while radiation pressure on dust is the main mechanism driving the mass loss(e.g., Fleischer et al.1992;H¨o fner&Dorfi1997).It is there-fore conceivable that both low metallicity and less dust grains operate at small mass-loss in R Sct,even if the in-Fig.5.The ISO/SWS spectra are shown with the IRAS fluxes(the100µm band is an upper limit)and UV and IR photometric data(Goldsmith et al.1987).A4200K black body,fitting the UV and IR photometric data(Goldsmith et al.1987)is also plotted.Zero points and effective wave-length for thefilters from Evans(1994)are adopted for the data in Goldsmith et al.(1987)termediate reservoir of SiO has the same size as in Mira variables.4.5.Evolutionary statusRV Tau stars are commonly assumed to be post-AGB stars with low initial mass.For the RV Tau stars with IRAS60µm excess,the cessation of the mass loss oc-curred aboutfive hundreds years ago(Jura1986).R Sct also shows evidence for a larger mass-loss rate in the past, and is also suggested to be in the post-AGB phase(Alcolea &Bujarrabal1991).The mass loss ceased at the time the star would have left the AGB.The effective temperature(T eff)at AGB is in the range of2000–3000K,and the current effec-tive temperature of R Sct is in the range4000–6000K. Using the time since the mass-loss reduction of2000yr, we obtain a rate of increase of the stellar temperature d T eff/d t=1–1.5K yr−1.This rate can be compared to calculations by Bl¨o cker(1995)of the temperature gradient as function of the post-AGB evolutionary time scale(in terms of log d t/d T effyr K−1,Fig.6in his paper).The post-AGB time is calculated from the end of the high mass-loss rate.The rate wefind for R Sct is reproduced for the early post-AGB evolution by the model tracks of stellar(core) mass range of0.61,0.57and0.55M⊙.These masses are at the lower end of post-AGB mass ranges,and may indicate a progenitor star with low initial mass.Together with the evolution towards higher T eff,the period of the star will also reduce as the stellar radius becomes smaller.R Sct is one of the oldest variable stars known,discovered in1785by Edward Pigott,observing from York.He observed the star regularly ter it was observed extensively by Argelander from Bonn,be-M.Matsuura et al.:The atmosphere and evolution of R Sct7 tween1843and1862,and very good coverage is availablefrom this time.This long-term light curve allows us tosearch for evidence of period evolution.If all RV Tau stars are post-AGB,they are expectedto evolve at constant luminosity towards higher effectivetemperatures.We use the period equation for AGB starslog P=1.949log R−0.9log M−2.07(1)from Wood(1990),where P is the period in days,R andM are the stellar radius and mass in solar units.TakingL=4πR2T4eff=const,where L is the luminosity,we canrewrite the equation aslog P=−3.898log T eff+0.975log L−0.9log M−2.62.(2)This implies that the rate of period change is closelyrelated to the temperature evolution:˙P(3)T effThe right-hand side corresponds to the calculated tem-perature increase of∼1K yr−ing the present periodof140days,a change of−11days per century is expected.This should be easily detectable in the amateur archivesand historical observations.Zsoldos(1995)has noted thelack of observed secular period changes in other RV Taustars and stressed that the low-mass post-AGB interpre-tation must be considered uncertain.We have analyzed published observations of R Sctto search for evidence of period decrease.Individual vi-sual observations were taken from the databases of theAFOEV1,the BAAVSS2and the VSOLJ3,which extendback over more than a century.The top panel of Fig.6shows the light curve after averaging into5-day bins.Thedeep minima occur with a period of about140days,andthey alternate with the much shallower secondary min-ima.We used wavelet analysis(Bedding et al.1998)tomeasure period evolution in both the140-day period andits70-day harmonic.These are shown in the middle andbottom panels of Fig.6,respectively.While R Sct showssubstantial period jitter,there is no evidence for a seculartrend in the mean period during the past century.The evolution of the primary and harmonic periods isplotted in Fig.7as open symbols.We also show closedsymbols which are derived from wavelet analysis of earlierpublished dates of minima.Those data are sparse,withsome measurements around1800and then a large gapuntil1860.Period determinations during the1800s were also madeby the observers themselves.The values are somewhatscattered,but fall into two groups:around60days andaround70days.A summary of these determinations canbe found in M¨u ller&Hartwig(1918).As they discuss,8M.Matsuura et al.:The atmosphere and evolution of RSctFig.6.The visual light curve over the 100years (top)and its wavelet analysis (the second panel is for the primary period and the third panel is for the secondary period).The horizontal scale is JD −2400000.al.1992,Vassiliadis &Wood 1993,Bl¨o cker1995).The pe-riod evolution slows down and reverses during the helium-burning phase.The phase lasts for ∼5000yr.This phase may fit the period evolution,and time scale for the de-tached dust shell,quite well.We therefore suggest the possibility that R Sct is not a post-AGB star,but is an AGB star in the helium-burning phase of the thermal-pulse cycle.5.ConclusionsWe find H 2O,SiO,CO 2,and CO in the ISO/SWS spec-tra of R Sct.H 2O emission dominates the near-and mid-infrared spectra.The molecules are probably located in a spherical extended atmosphere.Pulsations may gradually lift up the gas from the photosphere to the extended at-mosphere.Molecular formation appears to take place in the extended atmosphere.The column density estimated from the infrared SiO bands is comparable to that in Mira variables,however,the current dust mass-loss rate of R Sct is lower than Miravariables by two orders of magnitudes.The high effective temperature may prevent dust formation around this star.While a high mass-loss rate in the past is indicated by an excess at 60µm,and by the CO millimeter wavelength emission,the current mass-loss rate is two orders of magni-tude lower:the dust mass-loss rate ˙Md =10−11M ⊙yr −1.The reduction in the mass-loss rate,and the time scale,can be explained if R Sct is a low-mass post-AGB star.However,the period evolution is too slow for post-AGB evolution.We therefore suggest that R Sct may be an AGB star in the helium-burning phase of the thermal-pulse cy-cle.As future work,monitoring of the infrared photomet-ric bands could help in understanding the structure of the extended atmosphere in this star,as well as in Mira vari-ables.The infrared light curve of Mira variables shows a phase delay of maximum phase by about φ=0.1.For the infrared variability of Mira variables,dust might be im-portant (e.g.Winters et al.1994),but molecules in the pulsating atmosphere contribute as well (Matsuura et al.M.Matsuura et al.:The atmosphere and evolution of R Sct9Fig.7.The period variation of R Sct over200years. The upperfigure is for the primary period and the lower figure for the harmonic period.The upper horizontal scale shows the years.The predicted period variation from the post-AGB evolutionary track is shown by the dotted lines (Sec.4.5).The observed variation is shown by the dashed line,where the harmonic period isfitted with the linear function of P=[70.71±0.33]−[0.03±0.10]×10−4×(JD−240000):i.e.,the period is constant over200years (long dash line).2002).If the same infrared phase delay is found for R Sct the contribution of molecules on the infrared light-curve will be strengthened.In Table A.1,the infrared photom-etry shows slightly fainter magnitudes at phaseφ=0.07 (JD=244,3051.31).More frequent observations of the in-frared light curve couldfind a phase delay. Acknowledgements.We acknowledge Dr.Mattei and the American Association of Variable Star Observers(AAVSO) for light curve of R Sct.Ten-micron data for R Sct,listed in the appendix,was taken with TIMMI-2on ESO3.6m telescope.We gratefully thank the instrumental team and support astronomers for their assistance.The advice by Dr. Kester for IRAS was useful.This research was supported by PPARC grant.I.Y.acknowledges support by Grant-in-Aid for Encouragement of Young Scientists(No.13740131)from Japan Society for the Promotion of Science.Appendix A:Infrared photometryInfrared photometric data taken from the literature are listed in Table A.1.The data are taken from Gehrz(1972), Lloyd Evans(1985),Goldsmith et al.(1987),and Shenton et al.(1994).The zero points for the IRAS bands are taken from Wainscoat et al.(1992).Theflux density of the ISO/SWS spectra is converted to magnitude,using filter transmission in van der Bliek et al.(1996)and zero points in Evans(1994)the for L-and M-bands.For N-and Q-bands,effective centre wavelengths and widths in Evans (1994)are used.We measured an N-band magnitude with TIMMI-2on3.6m Telescope of ESO on4August,2001, using a narrow bandfilter at10.4µm.HD133774was used as a calibration source adopting the template in Cohen (1999).The zero point for the10.4µmfilter is calculated from the spectrum of Vega(Cohen et al.1995). ReferencesAlcolea,J.,&Bujarrabal,V.,1991,A&A245,499 Argelander F.W. A.,1869,Astron.Beobachtungen zur Sternwarte Bonn,7,315Bowen,G.H.,&Willson,L.A.,1991,ApJ375,L53 Bedding,T.R.,Zijlstra,A.A.,Jones,A.,&Foster,G.,1998, MNRAS301,1073Bujarrabal,V.,Bachiller,R.,Alcolea,J.,&Martin-Pintado, J.,1988,A&A206,L17Bujarrabal,V.,Alcolea,J.,&Bachiller,R.,1990,A&A234, 355Bl¨o cker,T.,1995,A&A299,755Cardelli,J.A.,&Howell,S.B.,1989,AJ98,311Cohen,M.,Witteborn,F.C.,Walker,R.G.,Bregman,J.D.,& Wooden,D.H.,1995,AJ110,275Cohen,M.,Walker,R.G.,Carter,B.,Hammersley,P.,Kidger, M.,&Noguchi,K.,1999,AJ.117,1864de Graauw,Th.,Haser,L.N.,Beintema,D.A.,et al.,1996, A&A315,L49Duari,D.,Cherchneff,I.,&Willacy,K.,1999,A&A341,L47 Evans,A.,‘The Dusty Universe’,1993,Ellis Horwood Fleischer,A.J.,Gauger,A.,&Sedlmayr,E.,1992,A&A266, 321Gehrz,R.D.,1972,ApJ178,715Giridhar,S.,Lambert,D.L.,&Gonzalez,G.,2000,ApJ531, 521Goldsmith,M.J.,Evans,A.,Albinson,J.S.,&Bode,M.F., 1987,MNRAS227,143Hinkle,K.H.,Pollard,K.R.,&Wahlgren,G.M.,1996ASP Conf.Vol.92,1996,H.Morrison and A.Sarajedini,eds., 204.H¨o fner,S.,&Dorfi,E.A.,1997,A&A319,648IRAS Catalogs and Atlases:Explanatory Supplement,1988, ed.Beichman,C.A.,Neugebauer,G.,Habing,H.J.,Clegg, P.E.,Chester,T.J.,Washington DC.Jennings,D.E.,&Sada,P.V.,1998,Sci.279,844Jura,M.,1986,ApJ309,732Jura,M.,Chen,C.,&Werner,M.W.,2000,ApJ541,264 Kessler,M.,Steinz,J.A.,Anderegg,M.E.,et al.,1996, A&A315,L27Kholopov,P.N.,Samus,N.N.,Frolov,M.S.,et al.,1988, General Catalogue of Variable Stars.4th Ed.,Nauka Publishing HouseLanghoff,S.R.,&Bauschlicher,Jr.C.W.,1993,Chem.Phys.Lett.211,305L`e bre,A.,&Gillet,D.,1991,A&A251,549Lloyd Evans,T.,1985,MNRAS217,493Matsuura,M.,Yamamura,I.,Cami,J.,Onaka,T.,& Murakami,H.,2002,A&A383,972Mattei,J.A.,1963–1985,AAVSO Monograph3:R Sct Mattei,J.A.,1986–1990,AAVSO Monograph3:R Sct, Supplement1Mattei,J.A.,1991–1995,AAVSO Monograph3:R Sct, Supplement2Mozurkewich, D.,Gehrz,R.D.,Hinkle,K.H.,&Lambert,D.L.,1987,ApJ314,242M¨u ller,G.,&Hartwig,E.,1918,Geschichte und Literatur des Lichtwechsels(Poeschel&Trepte,Leipzig)。