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Dutch Resolution of Racemates and the Roles of Solid Solution Formation and Nucleation Inhibition

Top Curr Chem(2007)269:159–197DOI10.1007/128_2006_095©Springer-Verlag Berlin Heidelberg2007Published online:13January2007Dutch Resolution of Racematesand the Roles of Solid Solution Formationand Nucleation InhibitionRichard M.Kellogg1(u)·Bernard Kaptein2·Ton R.Vries11Syncom BV,Kadijk3,9747Groningen AT,The Netherlandsr.m.kellogg@syncom.nl2DSM Research,Life Sciences—Advanced Synthesis&Catalysis,P.O.Box18,6160Geleen MD,The Netherlands1Introduction (160)1.1Basic Aspects of Resolutions (162)2Aggregation in Supersaturated Solutions (163)2.1Nucleation,Crystal Growth and Tailor-Made Additives (168)2.2Theory of Nucleation (173)3Dutch Resolution (175)3.1Basic Principles (175)3.2Reverse(Reciprocal)Dutch Resolution (178)3.3Solid Solution Behavior in Dutch Resolution (182)3.4Nucleation Inhibition in Dutch Resolution (184)4Conclusions (192)References (194)Abstract An overview is given of the principles of Pasteur resolutions via separation of diastereomeric salts.Thereafter,primary nucleation processes of(chiral)organic com-pounds in supersaturated solution are considered followed by crystal growth in the presence of tailor-made additives.A representative example of a Dutch Resolution is pre-sented,the concept of families of resolving agents is deﬁned and examples are given.The phenomenon of reversed Dutch Resolution,resolution of mixtures of families of race-mates,is illustrated.The roles of both solid solution formation and nucleation inhibition in Dutch Resolution are discussed.The work is concluded with the results of a broadly based search for nucleation inhibitors for phenylethyl amine as resolving agent.This search can serve as a model for the discovery of nucleation inhibitors for other resolving agents.The speciﬁc role of bifunctional family members of resolving agents as possible nucleation inhibitors is also discussed.Keywords Nucleation inhibition·Resolving agents·Supersaturation·Families·Aggregation·Chirality·Enantiomeric enrichmentAbbreviationsAbu2-aminobutyric acidAsn asparagine160R.M.Kellogg et al. Asp aspartic acidβdegree of supersaturation C initial/C equilibriumCys cysteinede diastereomeric excessDSC differential scanning calorimetryee enantiomeric excessglc gas liquid chromatographyGlu glutamic acidIle isoleucineHis histidineHpg4-hydroxyphenylglycinehplc high performance liquid chromatographyLeu leucineLys lysineNMR nuclear magnetic resonanceNva norvalineOrn ornithinePhe phenylalaninePhg phenylglycineSEM scanning electron microscopySTM scanning tunneling microscopySer serineTEM tunneling electron microscopyThr threonineTrp tryptophaneTyr tyrosineVal valineXRPD X-ray powder diffractogramS factor Fogassi value:2·yield·de in diastereomeric salt resolution1IntroductionDutch Resolution is a modiﬁcation of the Pasteur technique to resolve race-mates into their enantiomers by formation of diastereomeric salts,which can be separated by crystallization[1–10].Selective formation of the de-sired enantiomer by enantioselective synthesis,stoichiometric or catalytic,is the complementary/competitive technology that bypasses racemate separa-tion[11].W e note also the recent interest in the special but relatively rare occurrence of spontaneous asymmetric synthesis[12–14].The classical approach devised by Pasteur for the separation of enan-tiomers in a racemate was published in1854and has not changed through the years[1–3].Pasteur’s original resolution of tartaric acid1with the aid of a stoichiometric quantity of quinotoxin,a degradation product of quinine,is shown in Scheme1.Dutch Resolution of Racemates161Scheme1Original Pasteur experiment for the resolution of racemic tartaric acid The concept,interaction of an enantiomerically pure base(acid)with a racemic acid(base)by means of proton transfer to form two diastereomeric salts separable by solubility differences,is deceptively simple.Many organic compounds are,of course,neither especially acidic nor ba-sic and do not lend themselves to this methodology.A rough division on the basis of properties is given in Scheme2.Scheme2Classiﬁcation of various methods to separate racematesTo circumvent this complication it may be possible in a multistep syn-thesis to resolve an acidic or basic intermediate.Neutral compounds may in some cases be converted reversibly to acidic or basic derivatives.Neutral com-pounds as well as acids and bases may also sometimes be resolved by covalent bonding with an enantiomerically pure material followed by separation of the diastereomers by,for example,crystallization or chromatography followed by release of the chiral auxiliary.Resolution of neutral compounds via inclu-sion compounds is on occasion possible and practical[15].On an analytical scale in the majority of cases separation of racemates is possible with chiral162R.M.Kellogg et al. hplc and/or glc.Racemates can also often be separated on preparative scale by chiral chromatography and simulated moving bed chromatography can be applied on bulk scale[16,17].Each of these techniques is a separate technol-ogy,none of which will be discussed here.The applicability of each of these methods as compared to(catalytic)asymmetric synthesis is determined by the nature of the compounds,scale and costs.Modern drug development is dependent on a rapid and dependable supply of pure enantiomers the structural diversity of which can be enormous.Reso-lution of racemates obtained as intermediates is a much-used technology to accomplish this.In the early stages of drug development this is often carried out at the gram scale and time is of the essence.A resolution procedure for commercial application may be far different from that used in the laboratory for rapid resolution of material that has never been resolved before.Dutch Resolution will,as is discussed in this overview,turn out to be more suited for rapid,small-scale resolutions.1.1Basic Aspects of ResolutionsFor early phase pharma applications both enantiomers of the racemate are often required.In a resolution via diastereomeric salts an obvious rapid way to obtain both enantiomers of the racemate is to carry out separate reso-lutions with each enantiomer of the resolving agent.For resolving agents like mandelic acid and tartaric acid this is feasible because both enantiomers are available in quantity and not excessively expensive.However,for resolving agents like brucine,(+)-camphor sulfonic acid,quinine,quinidine,etc only a single enantiomer is readily available.Sometimes a structurally different resolving agent will lead to salts the least soluble of which will contain the de-sired other enantiomer of the racemate.Development of new resolving agents (see further)has done much to widen the scope of diastereomeric resolutions. Recently,it has been shown that in some cases by variation of the dielectric constant of the solvent a single resolving agent can be used to derive either enantiomer of the racemate[18,19].It is not clear,however,how general this methodology is.As noted by Jacques,Collet and Wilen[4]“Indeed,what is wrong with the traditional way of carrying out resolutions is a lack of real understand-ing...Such understanding is equally necessary...for the study of systems enriched in one enantiomer produced by other methods”[21].This lack of understanding applies particularly dramatically to the nucleation processes in solution that lead to subsequent mon practical prob-lems are that the resolving agent used must readily form crystalline salts with the racemates,that the solubilities of these salts differ appreciably,i.e.that the eutectic composition should be well removed from50:50,that the chi-ral centers in the racemate not be too far removed from the acidic or basicDutch Resolution of Racemates163 centers and that crystallization of the less soluble diastereomer in reason-able diastereomeric excess occurs within an experimentally acceptable time. It has been estimated that around75%of attempted classical diastereomeric resolutions fail[4]!These are intrinsic points of the resolution itself.In addition one has to be able to determine fairly quickly how successful a resolution has been.In gen-eral this entails access to chiral hplc or glc facilities.Successful performance of resolutions on a regular basis requires experience in the choice of resolving agents and conditions(solvents and temperature,for example),excellent ex-perimental skill in the form of people with experience and suitable analytical capacities readily at hand.Considerable effort is necessary to set up working conditions where all these criteria are met simultaneously.There are more matters of concern.The salts often do not precipitate in an enantiomerically pure form but rather are only enriched and have to be puriﬁed further usually by additional crystallization.Precipitation of a di-astereomeric salt can only start once supersaturation has been achieved,that is to say that the concentration considerably exceeds the solubility.The con-centrations and solvent or solvent combination can have a profound effect as noted by Sakai[18].The reader is again referred to Jacques,Collet and Wilen[4]for a detailed and quantitative analysis of many of these factors as well as modiﬁed methods of diastereomeric resolutions such as the use of sub-stoichiometric quantities of resolving agents or the Pope and Peachy ap-proach in which part of the resolving agent is replaced by an achiral(mineral) acid or base.2Aggregation in Supersaturated SolutionsCrystallization starts with nucleation.This process must be discussed brieﬂy as a preliminary to Dutch Resolution.Nucleation occurs in the area of super-saturation.Many factors affect nucleation:the degree of supersaturation,the rate of cooling and possible presence of“seeds”just to mention a few possibil-ities.As nuclei transform into crystals a complicated dynamic situation arises in which crystal growth competes with nucleation.The kinetics and mech-anisms of primary nucleation probably often differ from those of secondary nucleation that occurs as nuclei split off from growing crystals[22,23].Resolutions take place from“impure”solutions in which two diastere-omeric salts are present.Rationalization and control of the process require understanding of what happens at the molecular scale in both phases.The mechanisms of crystal growth are reasonably well understood,but the na-ture of the supramolecular structures in supersaturated solution that lead to nucleation and then to crystallization are usually unknown.Models for pre-diction of the effects of stereochemistry on these structures are essentially164R.M.Kellogg et al. unavailable.Aggregation in solution is obviously highly dependent on the solution itself:for example,aggregation principles in aqueous solution are fundamentally different from those in nonaqueous solvents.Nucleation and crystallization are not the same processes.An incomplete list of possibilities,in addition to or prior to desired crys-tallization,of the many things that can happen in the area of supersaturation includes phase separation,liquid crystal formation,micelle formation,vesicle formation,gel formation and chemical reaction of the components.Supersat-uration(metastable)zones are the temperature zones between the dissolution temperature and the(lower)temperature at which precipitation(the exper-imentally observable consequence of nucleation)takes place.The width of such zones depends,among other things,on the concentration and rate of cooling.The classical approach to explanation of nucleation is to consider that molecules on the surface of a small nucleus will have a positive free energy relative to those in the interior,which will be stabilized through aggregation and which will have a negative free energy relative to those in solution.For a spherical nucleus the surface effect is dependent on the square of the ra-dius of the growing nucleus whereas the bulk effect is dependent on the third power of the radius.In classical theory based on formation of spherical nuclei the critical nucleation radius r c is that at which overall stabilization is real-ized.Somewhere on the path from critical nucleation radius to crystal growth an ordered packing will begin after which growth will proceed on crystal sur-faces(Fig.1)[24].Basic mathematical aspects of the theory of nucleation will be discussed in Sect.2.2.Unfortunately,the assumption of formation of ideal spherical nuclei is probably in most cases not applicable and can be badly misleading especially when the individual molecules are chiral.Free energy minimization during nucleation can be(and is)achieved via other shapes.W eissbuch,Lahav and Leiserowitz[25]cogently argue on the basis of various experimental obser-vations that there is much evidence that nuclei are not spherical and that the shape and internal structure of the critical nucleus should be treated as a variable in theoretical approaches.Chirality,particularly in the reso-Fig.1Simpliﬁed model of aggregation in supersaturated solutionDutch Resolution of Racemates165 lution of diastereomeric salts,will also be expressed in some fashion during nucleation.Molecular chirality should be recognized at the early stage of supramolecular aggregates that lead to nucleation and not only at the stage of crystallization.There are no spectroscopic methods to observe directly in solution the structure and composition of nanometer-sized aggregates/nuclei.However, clues(in addition to those given in[25])as to how aggregation can work are available via other sources.W e know much about the ordered arrangements of liquid crystals[26].The aggregation involved in micelle formation has been studied in great depth[27].V esicle formation has been the subject of ex-tensive study[28].These noncrystalline structures are illustrative of what can happen in solution.The techniques of tunneling electron microscopy(TEM) and scanning electron microscopy(SEM)provide surprisingly detailed infor-mation at the level of individual molecules for cases where the aggregates can be trapped and immobilized on a surface.Consider the aggregation behavior of some organic salts,which might be reasonable models for the salts formed in diastereomeric salt resolutions. Ionic interactions are in general much stronger than noncovalent interactions that bind neutral compounds together.An instructive example is provided by salt2as shown in Fig.2[29,30].This pure enantiomer of tartaric acid provided with a gemini ammonium cation does not crystallize but rather gelates solvent CHCl3quite effectively. Neither the racemate nor the meso compound acts as a gelator nor do they crystallize.Examination of dried and frozen pure enantiomer by transmis-sion electron microscopy(TEM)revealed long,twisted ribbonﬁbers,left handed for(R,R)and right handed for(S,S)tartrates.On use of a gemini ammonium salt with a C16chain it was observed that an enantiomerically enriched composition did not undergo phase separation(e.g.a preliminaryFig.2Cyro-TEM images of the twisted ribbons formed at A0%(racemate);B50%and C100%enantiomeric excess of tartrate salt1.Permission to use thisﬁgure has been kindly given by Nature Publishing Group166R.M.Kellogg et al. to conglomerate formation)but rather formed helical ribbons with a longer pitch.The lower the enantiomeric purity the greater the pitch indicating that there is a continuous composition change of the enantiomers(resembles solid solution behavior in crystalline compounds).The corresponding D-glucarate and L-malate salts do not form ribbons but rather amphiphilic bilayers.If the aliphatic chains of the ammonium head groups are shorter micelle formation takes place.It is reasonable to suggest that the crystallization of the tartrates has been derailed by gel formation.The detailed information at the molecular level provided by TEM is indicative of the potential formation of a racemic com-pound on crystallization rather than a conglomerate.In other words molecu-lar chirality is being expressed at the level of formation of chiral supramo-lecular aggregates.The aggregation behavior in aqueous solution exhibited by a chiral non-racemic glycerol derived phosphate4is strikingly similar(Fig.3)[31–33].The TEM photographs of frozen,immobilized material show for struc-turally related3(Scheme3)only plate-like aggregates wherein the molecular chirality is not clearly expressed whereas for4a long,right-hand coiled he-lix is formed.These helixes subsequently assemble into superhelixes in which molecular chirality is again clearly expressed at the supramolecular level.Compound5is liquid crystalline and uncharged[34].With the aid of scan-ning tunneling microscopy(STM)imaging on a conducting graphite surface the immobilized individual molecules of5can be recognized(Fig.4).The(S)enantiomer in the unit cell stacks tilted to the right whereas the (R)enantiomer stacks with a tilt to the left.The racemate shows areas withFig.3Illustration of the formation of right-handed helicalﬁbers upon self-assembly of phospholipid4.Permission to use thisﬁgure has been kindly given by the American Chemical SocietyScheme3Phospholipid2forms only plate-like aggregates rather than helicesDutch Resolution of Racemates167Fig.4Enantiomorphous STM images obtained from(S)and(R)enantiomorphs of5in which two dimensional chiral monolayer systems can be seen.Permission to use this ﬁgure has been kindly given by Wileya right-hand tilt and other areas with a left-hand tilt.Clearly racemic5 exhibits conglomerate behavior and has undergone spontaneous symmetry breaking on deposition.Molecular chirality is expressed immediately in the supramolecular structures observed.Why5exhibits conglomerate behavior is unknown.Regardless of the great contrasts in structures of the molecules as well as conditions(two rather than three-dimensional pictures are obtained)it is a common phenomenon that aggregation observed by STM,TEM and re-lated techniques occurs not by the formation of spherical nuclei but rather by association into rope-like structures,which continue to grow in size.These aggregates might be rough models for the structures of the nuclei that lead to crystallization.Helix formation is a common manner to express molecular chirality at the supramolecular level[35–37].Low molecular weight(<500)organic gelators have been studied exten-sively and their behavior well illustrates some of the above points.Such molecules have a pronounced tendency to gel organic solvents rather than to crystallize.Low molecular weight hydrogelators are also common.The aggre-gation processes are known to proceed along the lines given in Fig.5.Long ﬁbers form and these,if entangled,lead to gels rather than crystals[38–40].Fig.5Model of aggregation of anisotropic molecules into chains leading eitherﬁnally to crystals or gels168R.M.Kellogg et al. The coils formed lead to gelation of organic solvents.The arrangement is not a thermodynamic minimum;in due course(weeks in general)crystallization can set in.2.1Nucleation,Crystal Growth and Tailor-Made AdditivesFor a successful resolution nucleation must lead to crystallization.Classical resolutions can be very time consuming owing to difﬁculties in obtaining a crystalline diastereomeric salt.Often this difﬁculty is explained by the low (50%diastereomeric)purity of the least soluble salt in solution.The interplay of crystallization,together with primary and secondary(occurs as crystal-lization takes place)nucleation,is profoundly complex[22].Nucleation and crystal growth inhibition by the more soluble diastereomer could play an im-portant role.“Family”behavior in the inhibition of crystal growth in the special case of conglomerates was recognized early by Lahav and colleagues,who refer to the effects of“tailor-made”additives[25].This work will be surveyed brieﬂy as a preliminary to further discussion of Dutch Resolution.Not much is known about the inhibition of crystal growth of diastere-omeric salts.To our knowledge in the literature only one example of addition of a tailor-made additive in a classical resolution has been described[41–43]. Sakai et al.investigated the effect of the various“dimeric”stereoisomers 8a–c of the racemate to be resolved as habit modiﬁers in the resolution of (±)-1-phenylethylamine6a with(R)-(–)-mandelic acid7as illustrated in Scheme4.Scheme4The effect of habit modiﬁers in the resolution of phenethylamine6a by man-delic acid7It was shown that the(R,R)-dimer8a at concentrations as low as 0.007mol%had a signiﬁcant impact on the morphology,and changed the crystal shape of the least soluble(R)-6a·(R)-7diastereomeric salt from needle-like to hexagonal plates and thereby improved the isolation of this salt on centrifugation.Meso8b was reported to be a much poorer habit modiﬁer, and addition of(S,S)-8c had no effect.The efﬁcient habit modiﬁcation caused by(R,R)-8a is explained by a strong double chiral recognition at the surface of the{011}plane of the growing(R,R)-salt,thus preventing the incorporation of(R)-6a ammonium ions.On the other hand,enantioselective nucleation/growth inhibition has fre-quently been described for the direct resolution of racemates by preferential crystallization.A prerequisite for the direct resolution of racemates is con-glomerate behavior,i.e.the spontaneous crystallization of the enantiomers as mirror image crystals(enantiomorphs).This requirement resembles eutec-tic behavior as a precondition for an efﬁcient resolution via diastereomeric salt formation.Principles derived from enantioselective nucleation and crys-tal growth inhibition of conglomerates can,with care,be extrapolated to resolution via diastereomeric salt formation.A compilation of organic com-pounds known to show conglomerate behavior is given in the standard book of Jacques,Collet and Wilen[4].It is estimated that approximately5–10%of all racemates fulﬁl this requirement.The role of“tailor-made”additives that act as enantioselective nucle-ation/growth inhibitors in the direct resolution of conglomerates has been ex-tensively studied especially for amino acids,which exhibit the required con-glomerate behavior.In1982Lahav et al.described the inhibitor-induced reso-lution of threonine(Thr),glutamic acid(Glu·HCl),asparagine(Asn·H2O), p-hydroxyphenylglycine(Hpg·pTsOH)and histidine(as the metastable con-glomerate His·HCl·H2O)amongst other conglomerates.Direct resolution could be achieved by addition of small amounts of a different but structurally related enantiomerically pure amino acid[44].For example,the crystalliza-tion of(RS)-Thr in the presence of1–2mol%of the(S)-enantiomer of Asn, Glu,Asp,His,Lys,Phe or(R)-Cys resulted in the preferential crystalliza-tion of the(R)-enantiomer of threonine in40–95%enantiomeric excess.An overview of the results for the direct resolution of other amino acids and derivatives by tailor-made additives is given in Table1.On the basis of these and other examples Lahav deﬁned the“rule of rever-sal”:stereoselective adsorption of an enantiopure“tailor-made”additive S at the surface of the growing crystals of the enantiomer with the same absolute conﬁguration(S)results in a drastic decrease in their rate of growth and thus allows preferential(faster)crystallization of the opposite(R)-enantiomer as illustrated in Scheme5.Preferential adsorption of the additive(0.5–3mol%)on the crystal of the analogous absolute conﬁguration is sufﬁcient to inhibit the further growth of this enantiomorph.In the adsorption mechanism the additive preferablyTable1Resolution of amino acid conglomerates using tailor-made additives Conglomerate Chiral additive Crystalline Refs.enantiomerGlu(S)-Asp,(S)-Leu(R)-Glu[45]Asp(S)-Glu(R)-Asp[45]Glu(S)-Glu(γ-Me)(R)-Glu[46]Cu(Asp)2(S)-Glu,(S)-Ala,(S)-Ile(R)-Cu(Asp)2[47–49](R)-Glu,(R)-Ala(S)-Cu(Asp)2Thr(S)-Glu,(S)-Gln,(S)-Asn,(R)-Thr[44,49,51–53] (S)-Phe,(S)-His,(S)-Lys,(S)-Asp,(R)-Cys,(S)-Pro,(S)-Ala,(S)-PAL a(S)-PMAL b(S)-Thr(R)-Glu,(R)-Asn,(R)-PAL,(R)-PMALAsn·H2O(S)-Glu,(S)-Gln,(S)-Asp,(R)-Asn[44,49,51] (S)-Ser,(S)-Lys,(S)-Orn,(S)-His,(S)-PAL,(S)-PMAL(S)-Asn(R)-Glu,(R)-Asp,(R)-PAL,(R)-PMALGlu·HCl(S)-Lys,(S)-Orn,(S)-His,(R)-Glu[44,51](S)-Thr,(S)-Tyr,(S)-Leu,(R)-Cys,(S)-PAL,(S)-PMAL(S)-Glu(R)-PAL,(R)-PMALp-Hpg·pTSA(S)-Phg,(S)-Tyr,(S)-Phg(p-Me),(R)-p-Hpg[44](S)-Phe,(S)-DOPA,(S)-(αMe)DOPAHis·HCl·H2O(S)-Trp,(S)-Phe,(S)-PAP c(R)-His[44,51,54] (R)-PAP(S)-HisMet·HCl·H2O(R)-PAL,(R)-PMAL(S)-Met[50] Cys·HCl(R)-PAL,(R)-PMAL(R)-Cys[51] Ile·HCl(S)-PAL,(S)-PMAL,(S)-Phe(R)-Ile[51,55] Val·HCl(R)-PAL,(R)-PMAL(S)-Val[51,55](S)-Phe(R)-ValLeu·HCl(S)-PAL,(S)-PMAL,(S)-Phe(R)-Leu[51,55](R)-PAL,(R)-PMAL(S)-LeuAc-Nva·NH4d(S)-Ac-Ala·NH4salt(S)-Ac-Nva·NH4[56]Ac-Abu·NH4e(S)-Ac-Ala·NH4salt(S)-Ac-Abu·NH4[56] polymeric additives:a(S)-PAL:poly-(Nε-acryloyl-(S)-lysine)b(S)-PMAL:poly-(Nε-methacryloyl-(S)-lysine)c(S)-PAP:poly-(p-(acrylamido)-(S)-phenylalanine)d Nva=norvaline[CH3CH2CH2CH(NH2)CO2H]e Abu=2-aminobutyric acid[CH3CH2CH(NH2)CO2H]Scheme5The effect of tailor-made additives S’in the resolution of a conglomerate binds to a crystal with the same absolute conﬁguration,but only at those sur-faces where the(structurally different)side chain of the adsorbate emerges from the crystal.The growing face of the crystal is thereby changed and growth is slowed[57,58].The adsorption to speciﬁc crystal faces may re-sult in inhibition of the crystal growth but can also result in a change of the morphology of the crystals as is represented in Fig.6.In this manner the change of the crystal habit of one of the enantiomorphs of asparagine on addition of small amounts of(R)-cysteine could be used as the basis for separation by sieving the(R)-and(S)-crystals of asparagine based on their crystal size[59].Polymers grafted with amino acids as tailor-made additives seem in gen-eral to be more efﬁcient than monomeric additives.This is likely due to adsorption to multiple binding sites(polydentate)in addition to the shield-ing of the crystal surface by the polymer backbone[58].Polymeric additives also have been successfully applied to prevent lamellar twinning in the cases of methionine,cysteine and valine[60].In addition to crystal growth inhibition,the addition of polymeric tailor-made additives also can retard the dissolution of the enantiomorphous crys-tal,as was shown for the dissolution of(R)-methionine·HCl monohydrateFig.6Speciﬁc absorption on fast growing faces of a needle-like crystal and the corres-ponding morphology changescrystals in the presence of the polymeric additive poly-(Nε-methacryloyl-(R)-lysine)[50].The use of polymeric tailor-made additives is not limited to the similarity principle of the conglomerate and the additive as described above for amino acids.For example,block polymers of polyethyleneglycol and polyethylen-imine grafted with various chiral groups R∗have been applied in the direct resolution of calcium tartrate and sodium ammonium tartrate(Pasteur’s salt) as shown in Scheme6[61].Scheme6Examples of polymeric tailor-made additives applied in the resolution of cal-cium tartrate and sodium ammonium tartrateThere is clearly a delicate balance between adsorption resulting in growth inhibition and incorporation of the inhibitor in the growing crystal,as La-hav et al.observed for the crystallization on Asn·H2O with Asp as the additive[49].In this case a true solid solution was formed with incor-poration of10–12%of Asp.Others have found similar co-crystallization results[62,63].In contrast to nucleation or crystal growth inhibition,Shiraiwa et al. have described the direct resolution of three different conglomerate forming N-acetyl amino acid ammonium salts on addition of(S)-N-acetyl-alanine am-monium salt as the result of an increased solubility of one of the enantiomers of the conglomerate.In this case large amounts of additives are used,up to 100mol%based on the racemate[56].Remarkably enough,this resulted in crystallization of the enantiomer of the conglomerate having the same abso-lute stereochemistry as the additive.For a detailed and excellent discussion of(enantioselective)crystal nu-cleation the reader is referred to a review by W eissbuch,Lahav and Leis-erowitz[25].。

化学化工英语试题及答案

化学化工英语试题及答案一、选择题（每题2分，共20分）1. Which of the following is a chemical element?A. WaterB. OxygenC. HydrogenD. Carbon答案：B, C, D2. The chemical formula for table salt is:A. NaOHB. NaClC. HClD. NaHCO3答案：B3. What is the process called when a substance changes from a solid to a liquid?A. SublimationB. VaporizationC. MeltingD. Condensation答案：C4. In the periodic table, which group contains alkali metals?A. Group 1B. Group 2C. Group 17D. Group 18答案：A5. What is the name of the process where a substance decomposes into two or more substances due to heat?A. CombustionB. OxidationC. ReductionD. Decomposition答案：D6. Which of the following is a physical property of a substance?A. ColorB. TasteC. SolubilityD. Reactivity答案：A7. What is the term for a compound that releases hydrogen ions (H+) when dissolved in water?A. BaseB. AcidC. SaltD. Neutral答案：B8. The law of conservation of mass states that in a chemical reaction:A. Mass is lostB. Mass is gainedC. Mass remains constantD. Mass can be converted into energy答案：C9. Which of the following is a type of chemical bond?A. Ionic bondB. Covalent bondC. Hydrogen bondD. All of the above答案：D10. What is the name of the process where a substance absorbs energy and changes from a liquid to a gas?A. MeltingB. VaporizationC. SublimationD. Condensation答案：B二、填空题（每题2分，共20分）1. The symbol for the element iron is ________.答案：Fe2. The pH scale ranges from ________ to ________.答案：0 to 143. A compound that produces a basic solution when dissolvedin water is called a ________.答案：base4. The smallest particle of an element that retains its chemical properties is called a ________.答案：atom5. The process of separating a mixture into its individual components is known as ________.答案：separation6. The study of the composition, structure, and properties of matter is called ________.答案：chemistry7. The process of a substance changing from a gas to a liquid is called ________.答案：condensation8. A(n) ________ reaction is a type of chemical reactionwhere two or more substances combine to form a single product. 答案：synthesis9. The volume of a gas at constant temperature and pressureis directly proportional to the number of ________.答案：moles10. The process of converting a solid directly into a gas without passing through the liquid phase is known as ________. 答案：sublimation三、简答题（每题10分，共30分）1. Explain what is meant by the term "stoichiometry" in chemistry.答案：Stoichiometry is the calculation of the relative quantities of reactants and products in a chemical reaction.It is based on the law of conservation of mass and involvesthe use of balanced chemical equations and the molar massesof substances to determine the amounts of reactants needed to produce a certain amount of product or the amounts ofproducts formed from a given amount of reactant.2. Describe the difference between a physical change and a chemical change.答案：A physical change is a change in the state or form of a substance without altering its chemical composition. Examples include melting, freezing, and boiling. A chemical change, on the other hand, involves a change in the chemical composition of a substance, resulting in the formation of new substances. Examples include combustion and rusting.3. What are the three main types of chemical bonds, and givean example of each.答案：The three main types of chemical bonds are ionic bonds, covalent bonds, and metallic bonds. An ionic bond is formed when electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions. An example is the bond between sodium (Na) and chloride (Cl) in table salt (NaCl). A covalent bond is formed when two atoms share electrons, as seen in water (H2O) where hydrogen atoms share electrons with oxygen. Metallic bonds occur in metals, where a "sea" of delocalized electrons is shared among positively charged metal ions, as in sodium metal。

疏肝利胆颗粒提取工艺优选及药效学实验研究

基金项目：甘肃省重点研发计划-社会发展类项目（20YF3FA030）；兰州大学第一医院院内基金项目（ldyyyn2018-31）；甘肃省教育厅创新能力提升项目（2019C-22）；甘肃省医院中药制剂产业技术创新联盟通信作者：魏玉辉，E-mail：*****************引用本文：张玉春，靳永文，王利军，等.疏肝利胆颗粒提取工艺优选及药效学实验研究[J].西南医科大学学报.2023，46（6）：489-494.DOI：10.3969/j.issn.2096-3351.2023.06.006胆汁淤积性肝损伤是一种常见的肝病，发病率较高，全球约10%~20%的人受胆汁淤积症的困扰[1-2]。

胆汁淤积（cholestasis ）是由胆汁合成缺陷和/或排泌异常造成胆酸盐在肝脏中蓄积，长期蓄积可对肝细胞造成损伤，导致肝炎、肝纤维化、肝硬化甚至肝癌[3]。

目前，美国食品药品监督管理局（Food and Drug Adminis‑tration ，FDA ）批准用于治疗胆汁淤积的药物仅有熊去氧胆酸（ursodeoxycholic acid ，UDCA ）和奥贝胆酸（obeticholic acid ，OCA ）[4-6]，但其疗效不尽如人意[7-8]。

因此，面对胆汁淤积症治疗药物疗效欠佳的问题，仍需寻找更加安全有效的治疗药物。

中医药在胆汁淤积性肝损伤的治疗中疗效显著[9]，其主要方法为清热燥湿、保肝利胆[10]。

消炎利胆丸方是兰州大学第一医院院内中药制剂，经40年临床验证，在治疗胆石症、胆囊炎和胆汁淤积方面疗效明确、毒副作用小且患者认可度高。

该方由柴胡、木香、炒枳实、青皮等8味中药组成。

然而，消炎利胆丸为大蜜丸剂，吞咽困难者或儿童服用不便，且限制了糖尿病患者的使用。

为了促进消炎利胆丸由院内制剂走向市场，让更多胆石症、胆囊炎和胆汁淤积患者受益，有必要将其进一步开发为不含糖、便于服用、携带方便的医院制剂。

安庆2024年小学六年级第3次英语第1单元真题

安庆2024年小学六年级英语第1单元真题考试时间：90分钟（总分:120）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：The chemical symbol for technetium is ______.2、What do you call a fear of spiders?A. AgoraphobiaB. ArachnophobiaC. ClaustrophobiaD. Nyctophobia答案:B3、听力题：The __________ is a famous area known for its training grounds.4、填空题：Certain plants can ______ (增强) the local economy.5、听力题：The chemical formula for sodium oxalate is ______.6、What do we call a person who designs buildings?A. ArchitectB. EngineerC. ContractorD. Builder答案:A7、What is the name of the famous scientist who discovered the laws of motion?A. Albert EinsteinB. Isaac NewtonC. Galileo GalileiD. Charles Darwin答案: BThis ________ (玩具) teaches me about science.9、填空题：I like to eat _____ (水果) in summer.10、听力题：The ancient Egyptians used ________ to document their history.11、听力题：I need to ________ my lunch.12、填空题：My pet ___ (小鸟) sings every morning.13、填空题：A ______ (小径) can lead through a garden.14、听力题：We will _______ (hike) in the mountains.15、What is the term for a baby pig?A. CalfB. PigletC. LambD. Kid答案: B16、填空题：The __________ (历史的启迪) can motivate change.17、Which day comes after Monday?A. SundayB. TuesdayC. WednesdayD. Thursday18、填空题：The owl is wise and can turn its _________ (头) 180 degrees.19、听力题：The soup is ___ (hot/cold) today.20、听力题：The __________ is a region known for its historical significance.The _____ (植物生长周期) includes various stages.22、听力题：We need to ___ (clean) our room.23、听力题：Many galaxies are moving away from us, suggesting the universe is ______.24、填空题：The _______ (The Great Depression) led to significant changes in government policy.25、填空题：She has a beautiful _______ (声音).26、Which of these is a type of transportation?A. BicycleB. TreeC. HouseD. Mountain答案:A27、填空题：My ________ (祖父) loves to tell stories about his adventures.28、填空题：I saw a _______ (小刺猬) in the garden.29、填空题：I enjoy playing ________ (棋类游戏) with my family.30、What is the name of the first spacecraft to successfully land on Mars?A. Viking 1B. SpiritC. OpportunityD. Curiosity31、听力题：The chemical formula for strontium carbonate is _____.32、填空题：A ____(community safety initiative) promotes public well-being.33、Which one is a cold drink?A. CoffeeB. TeaC. LemonadeD. Soup34、填空题：I like to dance with my ________ (玩具名称).35、What is the process of water turning into vapor called?A. EvaporationB. CondensationC. PrecipitationD. Filtration答案:A36、What is the fastest land animal?A. CheetahB. LionC. HorseD. Gazelle答案:A37、What do we call the science of studying space?A. BiologyB. ChemistryC. AstronomyD. Geology38、填空题：The goldfish is one of the most popular ______ (宠物) in homes.39、Which animal has a long trunk?A. GiraffeB. ElephantC. RhinoD. Hippopotamus答案:B40、 (3) is known for its deserts and wildlife. 填空题：The ____41、What is the capital of Bangladesh?A. DhakaB. ChittagongC. KhulnaD. RajshahiI want to create a video game about my toy ____. (玩具名称)43、What do you call a place where animals are kept for public viewing?A. FarmB. ZooC. AquariumD. Park答案:B44、听力题：I have a ___ (cool) skateboard.45、填空题：I went to the zoo and saw a ______.46、听力填空题：I love reading mystery books. My favorite author is __________.47、What is the capital of Sweden?A. OsloB. CopenhagenC. StockholmD. Helsinki答案: C48、听力题：A horse gallops across the _____.49、What is the name of the famous bear who loves honey?a. Paddington Bearb. Winnie the Poohc. Balood. Smokey Bear答案:b50、填空题：The butterfly flutters from flower to ______ (花).51、填空题：The _______ (猫) likes to hide in boxes.52、听力题：A __________ is a substance made up of only one type of atom.I enjoy cooking with my _______ (家庭成员). It’s a fun way to spend time together.54、填空题：I _______ (想要) a new toy for my birthday.55、填空题：My favorite place is the ______ (海边).56、How many continents are there?A. FiveB. SixC. SevenD. Eight57、听力题：I love to ______ in the summer. (swim)58、What do we call the liquid part of blood?A. PlasmaB. SerumC. PlateletsD. Hemoglobin答案:A59、What is the name of the fairy tale character who had a red hood?A. CinderellaB. Sleeping BeautyC. Little Red Riding HoodD. Snow White答案: C60、填空题：A _____ (章鱼) can fit through small openings.61、填空题：The ferret is very _________. (好动)62、填空题：I have a kind . (我有一个善良的。

材料科学与工程基础(英文)_南京航空航天大学中国大学mooc课后章节答案期末考试题库2023年

材料科学与工程基础（英文）_南京航空航天大学中国大学mooc课后章节答案期末考试题库2023年1.The driving force for steady-state diffusion is the __________.答案:concentration gradient2.Diffusion coefficient is with the increasing diffusion temperature.答案:exponentially increased;3.Due to , alloys are usually than pure metals of the solvent.答案:solid solution strengthening, stronger;4.The finer the grains, the larger the , and .答案:strength, hardness, toughness;5.With plastic deformation,the increase of dislocationdensity will result in .答案:higher strength;6.In general, Brinell Hardness test is to measure thematerial’s hardness.答案:relatively softer7.Yield strength is corresponding to the occurrenceof deformation.答案:noticeable plastic8.Strain Hardening is also named as .答案:work hardening9.Vacancy diffusion is usually interstitial one.答案:slower than10.Edge and screw dislocations differ in what way?答案:angle between Burgers vector and line direction.11. A ____ may form when impurity atoms are added to a solid, in which case theoriginal crystal structure is retained and no new phases are formed.答案:solid solution12.One explanation for why graphite powder acts so well as a “solid lubricant”is .答案:carbon atoms in graphite are covalently bonded within planar layers but have weaker secondary bonds between layers13.Substitutional atom (impurity) is an example of ______.答案:point defect14.Interstitial solid solution belongs to .答案:finite solid solution;15.The atomic packing factor for FCC is .答案:0.7416.The coordination number of BCC crystal structure is .答案:817.The crystal structure of Cu is ?答案:FCC18.How many atoms does the face centered cubic unit cell contain?答案:Four19.If the electron configuration of Fe is 1s2 2s2 2p6 3s2 3p6 3d6 4s2, then theelectron configurations for the Fe3+ is 1s2 2s2 2p6 3s2 _____.答案:3p6 3d520.Bonds in most metals are referred to as ______.答案:Non-directional21.Covalent bonding occurs as a result of _________ sharing.答案:electron22.Which of the following is NOT an example of primary bonding?答案:Van der Waals23.Atomic weight (A) of an element corresponds to the weighted average of theatomic masses of the atom’s naturally occurring ___________.答案:isotopes24.The point on a phase diagram where the maximum number of allowablephases are in equilibrium is .答案:eutectic point25.Sterling silver (92.5%Ag/7.5%Cu) is an example of ___________.答案:Solid solution26.Engineering stress-strain curve and true stress-strain curve are equal up to .答案:Yeild point27.Among thefollowingtypical transformations of austenite in steels,____________transformation is diffusionless.答案:martensitic28.The heat-treatable aluminum alloy can be strengthened by .答案:Both of above29.In the as-quenched state, martensite is very hard and so brittle that a heattreatment known as must be accomplished sequently.答案:tempering30.During heat treatment of steel, austenite transforms into martensite by .答案:quenching31.Which of the following plane has the highest planar density for fcc.答案:(111)32.Which of the following describes recrystallization?答案:Diffusion dependent with no change in phase composition33.Heating the cold-worked metal progresses in three stages: .答案:recovery, recrystallization, grain growth;34.Strength is increased by making dislocation motion .答案:difficult35.The boundary above which only liquid phase exist is called _________.答案:liquidus36.We have an annealed carbon steel which has hardness of 150HBS. Supposewe know the hardness of Pearlite is 200HBS and the hardness of Ferrite is 80HBS, determine the carbon amount of this steel.答案:0.45%37.The maximum solubility of C in γ-austenite - solid solution is .答案:2.1438.In a plain steel that contains 0.2 percentage carbon, we should expect: .答案:a 25% pearlite and 75% pro-eutectoid ferrite39. A copper-nickel alloy is high-temperature heat treated; the diffusion of Cuinto Ni and Ni into Cu regions is referred to as _____________________.答案:Inter-diffusion40.The phase diagram of Sn-Pb alloy is called .答案:Eutectic phase diagram。

小学下册T卷英语第二单元综合卷

小学下册英语第二单元综合卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.What color is an orange?A. BlueB. YellowC. OrangeD. Green2.What is the name of the famous artist known for his work with color?A. Claude MonetB. Vincent van GoghC. Pablo PicassoD. Salvador Dalí3.What do we call the process of breathing in?A. InhaleB. ExhaleC. BreatheD. Respire4.What is the common name for the edible part of a plant?A. FruitB. RootC. LeafD. StemA5.The symbol for silicon is _____.6.My favorite _____ is a cuddly lion.7._____ (asparagus) is a spring delicacy.8.My friend is very __________ (友好).9.In spring, flowers start to __________ as the weather gets warmer. (盛开)10.The first female Prime Minister of the UK was _______ Thatcher.11.What is the name of the famous detective created by Sir Arthur Conan Doyle?A. Hercule PoirotB. Sherlock HolmesC. Sam SpadeD. Philip MarloweB12.What shape has three sides?A. SquareB. CircleC. TriangleD. Rectangle13.She has a _____ (happy/sad) face.14.The frog's croak is loud and ______ (引人注意).15.Which season comes after summer?A. WinterB. SpringC. AutumnD. FallC16.The _____ (树木) provide shade on hot days.17.The ________ (植物繁殖技术) evolves constantly.18.The country with the most volcanoes is ________ (火山最多的国家是________).19. A reaction that produces energy is called an ______ reaction.20.What is the main ingredient in mayonnaise?A. EggB. OilC. VinegarD. All of the above21.The __________ (植物的生理) is fascinating to study.22.The __________ (历史的旅程) is ongoing.23.My cat watches ______ (小鸟) from the window.24.What is the name of the famous character created by J.K. Rowling?A. Frodo BagginsB. Harry PotterC. Katniss EverdeenD. Percy JacksonB Harry Potter25.Saturn has ______ moons.26.The baby is _____ (睡觉).27. A _______ can provide a backdrop for photos.28.The macaw is known for its bright ________________ (羽毛).29.The _____ of a planet can affect its climate.30.What is the main ingredient in sushi?A. NoodlesB. RiceC. BreadD. Chicken31.We can learn about ______ (植物的用途) in daily life.32. A __________ is a large area of water surrounded by land.33.What do we call the place where books are kept?A. LibraryB. StoreC. SchoolD. Office34.Electric fields can exert ______ (forces) on charged particles.35.What is the name of the fairy tale character who had a magic wand?A. CinderellaB. Fairy GodmotherC. Snow WhiteD. Rapunzel36.Metamorphism occurs when rocks are subjected to high ______ and temperature.37.I have a toy ________ that I built.38.What do we call the famous American holiday celebrated on July 4th?A. ThanksgivingB. Independence DayC. Memorial DayD. Labor DayB39.What do you call the study of weather?A. BiologyB. MeteorologyC. AstronomyD. GeologyB40.The children are ___ (laughing) and having fun.41.What is the opposite of 'rough'?A. SmoothB. CoarseC. HarshD. UnevenA42.My brother’s birthday is in __________. (月份)43.I have a special ______ (相册) where I keep all my favorite ______ (照片).44.What do we call a person who specializes in plants?A. BotanistB. ZoologistC. EcologistD. Agronomist45. A __________ is a geological feature formed by the action of waves.46.What color is the sky on a clear day?A. GreenB. BlueC. YellowD. GrayB47.I enjoy doing magic tricks with my ________ (玩具名称).48.The __________ (历史的回声) resonates deeply.49.An acid has a sour taste and can turn __________ paper red.50.What do we call a person who runs a business?A. EmployeeB. EmployerC. ManagerD. Boss51.The hawk has excellent ______ (视力) for spotting prey.52.Elements in the same column of the periodic table have similar __________.53.The goldfish swims in a _________. (圆形池)54.The ______ is known for its elaborate courtship dance.55.I believe that dreams can come true if __________.56.What is the name of the sweet treat made with cream and sugar?A. PuddingB. FlanC. CustardD. Whipped CreamC57.Metals can be found on the ______ side of the periodic table.58.What is the opposite of wet?A. DryB. DampC. MoistD. Humid59.Kittens are baby _______ (猫).60.Certain plants can ______ (提供) shelter for animals.61. A __________ is a geological formation that has been shaped by erosion.62.What do we call the process of change in the seasons?A. TransformationB. TransitionC. VariationD. EvolutionB63.What do you call the time period when dinosaurs lived?A. CretaceousB. JurassicC. TriassicD. All of the above64.The chemical formula for tridecylic acid is ______.65.The symbol for potassium is _____.66.What is the capital city of Kosovo?A. PristinaB. GjakovaC. MitrovicaD. Ferizaj67.How many legs does an insect have?A. 4B. 6C. 8D. 10答案:B68.The sun is _______ (setting) in the evening.69.Where does the President of the United States live?A. The White HouseB. The CapitolC. The PentagonD. The CourthouseA70.How many hours are in a day?A. 12B. 24C. 36D. 4871.The hawk's keen eyesight helps it spot prey from high ________________ (位置).72.The dog is _____ (sleeping/eating).73.What is the largest mammal in the world?A. ElephantB. Blue WhaleC. GiraffeD. HippoB74.What do you call the part of the plant that grows underground?A. StemB. LeafC. RootD. Flower75.Friction can slow down a ______.76.The smallest unit of an element is called an _____.77. A hedgehog rolls up into a ______ (球) when scared.78.I want to learn ________ (游泳).79.Respiration is a chemical process that occurs in ________.80. A saturated solution contains the maximum amount of dissolved ______.81.What do we call the act of planting seeds in the ground?A. HarvestingB. SowingC. WateringD. WeedingB82.I often tell my little sister to call me . (我常常告诉我的妹妹叫我)83.The sun is _______ in the sky.84.I like to play ________ (排球) with my classmates.85.Do you like ________ or tea?86.What is the name of the president of the USA?A. KingB. Prime MinisterC. MayorD. PresidentD87.What is the hardest natural substance on Earth?A. GoldB. IronC. DiamondD. SilverC Diamond88.I like to help my dad ________ (洗车).89.The river is _______ (很大)。

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小学上册英语第6单元暑期作业(含答案)英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The pizza is ________ and hot.2.The ________ (海洋研究) unveils mysteries of the deep.3.She is a _____ (心理学家) who helps people manage stress.4.The Earth's core is extremely ______ and dense.5.The _______ (The Roman Republic) preceded the Roman Empire.6.Plants can _____ (adapt) to their environment.7.Rock layers are often studied to understand the history of the ______.8.I can ________ (swim) in the pool.9.What do you call an animal that eats both plants and meat?A. HerbivoreB. CarnivoreC. OmnivoreD. Insectivore答案:C10.The process of making biodiesel involves _______ oils.11.The amount of matter in an object is its ______.12.Which fruit is known for its spiky skin and sweet insides?A. PineappleB. KiwiC. MangoD. Papaya答案:A13.The chemical symbol for ytterbium is ______.14.What do you call a sweet, baked treat filled with cream?A. ÉclairB. Cream puffC. PâtéD. All of the above答案:D15.The __________ was a significant movement for women's rights. (女性选举权运动)16.The simplest type of sugar is called a ______.17.The ______ is known for his scientific discoveries.18.What do we use to write on a chalkboard?A. PenB. PencilC. ChalkD. Marker答案:C19. A porcupine has _______ (刺) for protection.20.I need to ______ my room today. (clean)21.My sister's favorite _____ is a unicorn.22.What do we call the process of taking care of plants?A. GardeningB. CookingC. DrawingD. Writing答案:A23.What do we call the study of plants?A. BiologyB. BotanyC. ZoologyD. Ecology答案:B Botany24.I want to _______ a special event this year.25.What do you call a place where you can borrow books?A. LibraryB. BookstoreC. SchoolD. Office答案:A26.Chemical safety involves understanding how to handle _____ and hazardous materials properly.27.What is the opposite of 'old'?A. YoungB. MatureC. AgedD. Elderly答案:A28.The monkey swings from ______ to ______.29.The ______ thrives in tropical climates.30.My friend has a nice .31.The capital of Thailand is __________.32.I can use my __________ (玩具名) to __________ (动词).33.The boy has a cool ________.34.The process of saponification produces __________ from fats and oils.35.What is the capital of Brunei?A. Bandar Seri BegawanB. Kuala BelaitC. TutongD. Seria答案:A36.The cake is ______ (decorated) with frosting.37.My grandmother knits __________. (毛衣)38.The capital of Mexico is ________ (墨西哥城).39.What do you call a person who speaks two languages?A. MonolingualB. BilingualC. TrilingualD. Polyglot答案:B40.What is the process of changing from a liquid to a gas called?A. FreezingB. MeltingC. EvaporationD. Condensation答案:C41.What is the name of the famous American actress known for "The Hunger Games"?A. Jennifer LawrenceB. Kristen StewartC. Emma WatsonD. Shailene Woodley答案:A42.What is the capital city of Greece?A. AthensB. RomeC. IstanbulD. Cairo答案:A43.The capital of Switzerland is __________.44.h Revolution began in ________ (1789). The Fren45.What is the term for the effect of rotation on weather patterns on Earth?A. Coriolis EffectB. Weather SystemC. Atmospheric CirculationD. Wind Patterns46.The _____ (海滩) is sunny.47.What do you call a person who fixes pipes?A. ElectricianB. PlumberC. CarpenterD. Mason答案:B48. A chemical reaction that occurs when a fuel burns is called a ______ reaction.49.What do you call the season when leaves fall from trees?A. SpringB. SummerC. FallD. Winter答案:C50.The __________ is a famous mountain in Japan. (富士山)51.What is the opposite of ‘easy’?A. SimpleB. DifficultC. HardD. Challenging52.I find inspiration in __________. He/She has achieved so much and teaches me that anything is possible if I believe in myself. I hope to follow in his/her footsteps.53.I have a _____ for my birthday. (party)54.The __________ is where most plant and animal life exists.55.My sister is passionate about __________ (科学).56.What is a group of lions called?A. PackB. PrideC. FlockD. Herd答案:B57.The __________ of an element is determined by the number of protons it has.58.I listen to _______ (音乐) while studying.59. A compound is a substance made of two or more different _____.60.The dog is _______ (在追逐)小球.61.Which fruit is known for being very sour?A. BananaB. LemonC. PeachD. Melon答案:B62.I have a new ______ (toy) car.63.My dad tells me __________. (冒险故事)64.The element with the symbol I is __________.65.The main gas in the atmosphere is _______.66.How many vowels are in the English alphabet?A. FiveB. SixC. SevenD. Four67.The city of Istanbul is located in ________ (伊斯坦布尔位于________).68.The ancient Greeks held games every four years in ________.69.My dad enjoys going to the ____ (gym).70.In a __________ (化学方程式), reactants are written on the left side.71.What is the main ingredient of pizza?A. DoughB. RiceC. BreadD. Noodles答案:A72. A chemical reaction can be observed through changes in ______.73.What is the capital of Myanmar?A. YangonB. MandalayC. NaypyidawD. Bagan答案:C Naypyidaw74.The _______ (The War on Terror) began after the September 11 attacks.75. Wall was built using forced ________ (劳动力). The Grea76.The _______ can help reduce stress.77.What is the capital of Angola?A. LuandaB. CabindaC. BenguelaD. Lobito答案:A78.The _____ (根系) of a plant can spread wide under the soil.79.I saw a _______ (bird/fish) in the tree.80.My dad cooks ______ on weekends. (breakfast)81.What is the largest ocean on Earth?A. Atlantic OceanB. Indian OceanC. Arctic OceanD. Pacific Ocean答案:D82. A ____ is a small animal that loves to scamper around.83. A simple machine like a lever helps us to ______ (lift) heavy things.84.They are _____ (playing) frisbee.85.I enjoy playing with my toy ________ (玩具名称) during weekends.86.I like to ______ at the library. (read)87.What do you call a young duck?A. DucklingB. ChickC. CalfD. Foal88.My brother is a ______. He plays video games.89. A cow gives us _________ (牛奶).90.We have a ______ (学校) trip next week.91.I have a new _______ to play with (我有一个新的_______可以玩).92. A __________ is a chemical change that produces gas.93.She has many ________.94.The __________ is known for its rich history.95.What is the name of the planet we live on?A. MarsB. EarthC. JupiterD. Venus96. A saturated solution contains the maximum amount of ______ dissolved.97.The chemical formula for lead(II) oxide is ______.98. A sound wave is a type of ______ wave.99.The chemical symbol for selenium is ______.100.Chemical reactions can release or absorb ________.。

光伏发电英文文献Ultra-High Efficiency Photovoltaic

Ultra-High Efﬁciency Photovoltaic Cells for Large Scale Solar Power GenerationYoshiaki NakanoAbstract The primary targets of our project are to dras-tically improve the photovoltaic conversion efﬁciency and to develop new energy storage and delivery technologies. Our approach to obtain an efﬁciency over40%starts from the improvement of III–V multi-junction solar cells by introducing a novel material for each cell realizing an ideal combination of bandgaps and lattice-matching.Further improvement incorporates quantum structures such as stacked quantum wells and quantum dots,which allow higher degree of freedom in the design of the bandgap and the lattice strain.Highly controlled arrangement of either quantum dots or quantum wells permits the coupling of the wavefunctions,and thus forms intermediate bands in the bandgap of a host material,which allows multiple photon absorption theoretically leading to a conversion efﬁciency exceeding50%.In addition to such improvements, microfabrication technology for the integrated high-efﬁ-ciency cells and the development of novel material systems that realizes high efﬁciency and low cost at the same time are investigated.Keywords Multi-junctionÁQuantum wellÁConcentratorÁPhotovoltaicINTRODUCTIONLarge-scale photovoltaic(PV)power generation systems, that achieve an ultra-high efﬁciency of40%or higher under high concentration,are in the spotlight as a new technology to ease drastically the energy problems.Mul-tiple junction(or tandem)solar cells that use epitaxial crystals of III–V compound semiconductors take on the active role for photoelectric energy conversion in such PV power generation systems.Because these solar cells operate under a sunlight concentration of5009to10009, the cost of cells that use the epitaxial crystal does not pose much of a problem.In concentrator PV,the increased cost for a cell is compensated by less costly focusing optics. The photons shining down on earth from the sun have a wide range of energy distribution,from the visible region to the infrared region,as shown in Fig.1.Multi-junction solar cells,which are laminated with multilayers of p–n junctions conﬁgured by using materials with different band gaps,show promise in absorbing as much of these photons as possible,and converting the photon energy into elec-tricity with minimum loss to obtain high voltage.Among the various types of multi-junction solar cells,indium gallium phosphide(InGaP)/gallium arsenide(GaAs)/ger-manium(Ge)triple-junction cells that make full use of the relationship between band gaps and diverse lattice con-stants offered by compound semiconductors have the advantage of high conversion efﬁciency because of their high-quality single crystal with a uniform-size crystal lat-tice.So far,a conversion efﬁciency exceeding41%under conditions where sunlight is concentrated to an intensity of approximately5009has been reported.The tunnel junction with a function equivalent to elec-trodes is inserted between different materials.The positive holes accumulated in the p layer and the electrons in the adjacent n layer will be recombined and eliminated in the tunnel junction.Therefore,three p–n junctions consisting of InGaP,GaAs,and Ge will become connected in series. The upper limit of the electric current is set by the mini-mum value of photonﬂux absorbed by a single cell.On the other hand,the sum of voltages of three cells make up the voltage.As shown in Fig.1,photons that can be captured in the GaAs middle cell have a smallﬂux because of the band gap of each material.As a result,the electric currentoutputAMBIO2012,41(Supplement2):125–131 DOI10.1007/s13280-012-0267-4from the GaAs cell theoretically becomes smaller than that of the others and determines the electric current output of the entire tandem cell.To develop a higher efﬁciency tandem cell,it is necessary to use a material with a band gap narrower than that of GaAs for the middle cell.In order to obtain maximum conversion efﬁciency for triple-junction solar cells,it is essential to narrow down the middle cell band gap to 1.2eV and increase the short-circuit current density by 2mA/cm 2compared with that of the GaAs middle cell.When the material is replaced with a narrower band gap,the output voltage will drop.However,the effect of improving the electric current balance out-performs this drop in output voltage and boosts the efﬁ-ciency of the entire multi-junction cell.When a crystal with such a narrow band gap is grown on a Ge base material,lattice relaxation will occur in the middle of epitaxial crystal growth because the lattice constants of narrower band-gap materials are larger than that of Ge (as shown in Fig.2).As a result,the carrier transport properties will degrade due to dislocation.Researchers from the international research center Solar Quest,the University of Tokyo,aim to move beyond such material-related restrictions,and obtain materials and structures that have effective narrow band gaps while maintaining lattice matching with Ge or GaAs.To achieve this goal,we have taken three approaches as indicated in Fig.3.These approaches are explained in detail below.DILUTE NITROGEN-ADDED BULK CRYSTAL Indium gallium nitride arsenide (InGaNAs)is a bulk material consists of InGaAs,which contains several percent of nitrogen.InGaNAs has a high potential for achieving a narrow band gap while maintaining lattice matching with Ge or GaAs.However,InGaNAs has a fatal problem,that is,a drop in carrier mobility due to inhomogeneousdistribution of nitrogen (N).To achieve homogeneous solid solution of N in crystal,we have applied atomic hydrogen irradiation in the ﬁlm formation process and addition of a very small amount of antimony (Sb)(Fig.3).The atomic hydrogen irradiation technology and the nitrogen radical irradiation technology for incorporating N efﬁciently into the crystal can be achieved only through molecular beam epitaxy (MBE),which is used to fabricate ﬁlms under high vacuum conditions.(Nitrogen radical irradiation is a technology that irradiates the surface of a growing crystal with nitrogen atoms that are resolved by passing nitrogen through a plasma device attached to the MBE system.)Therefore,high-quality InGaNAs has been obtained only by MBE until now.Furthermore,as a small amount of Sb is also incorporated in a crystal,it is nec-essary to control the composition of ﬁve elements in the crystal with a high degree of accuracy to achieve lattice matching with Ge or GaAs.We have overcome this difﬁculty by optimizing the crystal growth conditions with high precision and devel-oped a cell that has an InGaNAs absorption layer formed on a GaAs substrate.The short-circuit current has increased by 9.6mA/cm 2for this cell,compared with a GaAs single-junction cell,by narrowing the band gap down to 1.0eV.This technology can be implemented not only for triple-junction cells,but also for higher efﬁciency lattice-matched quadruple-junction cells on a Ge substrate.In order to avoid the difﬁculty of adjusting the compo-sition of ﬁve elements in a crystal,we are also taking an approach of using GaNAs with a lattice smaller than that of Ge or GaAs for the absorption layer and inserting InAs with a large lattice in dot form to compensate for the crystal’s tensile strain.To make a solid solution of N uniformly in GaNAs,we use the MBE method for crystal growth and the atomic hydrogen irradiation as in the case of InGaNAs.We also believe that using 3D-shaped InAs dots can effectively compensate for the tensile strainthatFig.1Solar spectrum radiated on earth and photon ﬂux collected by the top cell (InGaP),middle cell (GaAs),and bottom cell (Ge)(equivalent to the area of the ﬁlled portions in the ﬁgure)occurs in GaNAs.We have measured the characteristics of a single-junction cell formed on a GaAs substrate by using a GaNAs absorption layer with InAs dots inserted.Figure 4shows that we were able to succeed in enhancing the external quantum efﬁciency in the long-wavelength region (corresponding to the GaNAs absorp-tion)to a level equal to GaAs.This was done by extending the absorption edge to a longer wavelength of 1200nm,and increasing the thickness of the GaNAs layer by increasing the number of laminated InAs quantum dot layers.This high quantum efﬁciency clearly indicates that GaNAs with InAs dots inserted has the satisfactory quality for middle cell material (Oshima et al.2010).STRAIN-COMPENSATED QUANTUM WELL STRUCTUREIt is extremely difﬁcult to develop a narrow band-gap material that can maintain lattice matching with Ge orGaAs unless dilute nitrogen-based materials mentioned earlier are used.As shown in Fig.2,the conventionally used material InGaAs has a narrower band gap and a larger lattice constant than GaAs.Therefore,it is difﬁcult to grow InGaAs with a thickness larger than the critical ﬁlm thickness on GaAs without causing lattice relaxation.However,the total ﬁlm thickness of InGaAs can be increased as an InGaAs/GaAsP strain-compensated multi-layer structure by laminating InGaAs with a thickness less than the critical ﬁlm thickness in combination with GaAsP that is based on GaAs as well,but has a small lattice constant,and bringing the average strain close to zero (Fig.3.).This InGaAs/GaAsP strain-compensated multilayer structure will form a quantum well-type potential as shown in Fig.5.The narrow band-gap InGaAs layer absorbs the long-wavelength photons to generate electron–hole pairs.When these electron–hole pairs go over the potential bar-rier of the GaAsP layer due to thermal excitation,the electrons and holes are separated by a built-in electricﬁeldFig.2Relationship between band gaps and lattice constants of III–V-based and IV-based crystalsto generate photocurrent.There is a high probability of recombination of electron–hole pairs that remain in the well.To avoid this recombination,it is necessary to take out the electron–hole pairs efﬁciently from the well and transfer them to n-type and p-type regions without allowing them to be recaptured into the well.Designing thequantumFig.3Materials and structures of narrow band-gap middle cells being researched by thisteamFig.4Spectral quantum efﬁciency of GaAs single-junction cell using GaNAs bulk crystal layer (inserted with InAs dots)as the absorption layer:Since the InAs dot layer and the GaNAs bulk layer are stacked alternately,the total thickness of GaNAs layers increases as the number of stacked InAs dot layers is increased.The solid line in the graph indicates the data of a reference cell that uses GaAs for its absorption layer (Oshima et al.2010)well structure suited for this purpose is essential for improving conversion efﬁciency.The high-quality crystal growth by means of the metal-organic vapor phase epitaxy (MOVPE)method with excellent ability for mass production has already been applied for InGaAs and GaAsP layers in semiconductor optical device applications.Therefore,it is technologically quite possible to incorporate the InGaAs/GaAsP quantum well structure into multi-junction solar cells that are man-ufactured at present,only if highly accurate strain com-pensation can be achieved.As the most basic approach related to quantum well structure design,we are working on fabrication of super-lattice cells with the aim of achieving higher efﬁciency by making the GaAsP barrier layer as thin as possible,and enabling carriers to move among wells by means of the tunnel effect.Figure 6shows the spectral quantum efﬁ-ciency of a superlattice cell.In this example,the thickness of the GaAsP barrier layer is 5nm,which is not thin enough for proper demonstration of the tunnel effect.When the quantum efﬁciency in the wavelength range (860–960nm)that corresponds to absorption of the quan-tum well is compared between a cell,which has a con-ventionally used barrier layer and a thickness of 10nm or more,and a superlattice cell,which has the same total layer thickness of InGaAs,the superlattice cell demonstrates double or higher quantum efﬁciency.This result indicates that carrier mobility across quantum wells is promoted by even the partial use of the tunnel effect.By increasing the P composition in the GaAsP layer,the thickness of well (or the In composition)can be increased,and the barrier layer thickness can be reduced while strain compensation is maintained.A cell with higher quantum efﬁciency can befabricated while extending the absorption edge to the long-wavelength side (Wang et al.2010,2012).GROWTH TECHNIQUE FOR STRAIN-COMPENSATED QUANTUM WELLTo reduce the strain accumulated in the InGaAs/GaAsP multilayer structure as close to zero as possible,it is nec-essary to control the thickness and atomic content of each layer with high accuracy.The In composition and thickness of the InGaAs layer has a direct effect on the absorption edge wavelength and the GaAsP layer must be thinned to a satisfactory extent to demonstrate fully the tunnel effect of the barrier layer.Therefore,it is desirable that the average strain of the entire structure is adjusted mainly by the P composition of the GaAsP layer.Meanwhile,for MOVPE,there exists a nonlinear rela-tionship between the P composition of the crystal layer and the P ratio [P/(P ?As)]in the vapor phase precursors,which arises from different absorption and desorption phenomena on the surface.As a result,it is not easy to control the P composition of the crystal layer.To break through such a difﬁculty and promote efﬁcient optimiza-tion of crystal growth conditions,we have applied a mechanism to evaluate the strain of the crystal layer during growth in real time by sequentially measuring the curvature of wafers during growth with an incident laser beam from the observation window of the reactor.As shown in Fig.7,the wafer curvature during the growth of an InGaAs/GaAsP multilayer structure indicates a periodic behavior.Based on a simple mechanical model,it has become clear that the time changes ofwaferFig.5Distribution of potential formed by the InGaAs/GaAsP strain-compensated multilayer structure:the narrow band-gap InGaAs layer is sandwiched between wide band-gap GaAsP layers and,as a result,it as quantum well-type potential distribution.In the well,electron–hole pairs are formed by absorption of long-wavelength photons and at the same time,recombination of electrons and holes takes place.The team from Solar Quest is focusing on developing a superlattice structure with the thinnest GaAsP barrier layercurvature are proportionate to the strain of the crystal layer relative to a substrate during the growing process.One vibration cycle of the curvature is same as the growth time of an InGaAs and GaAsP pair (Sugiyama et al.2011).Therefore,the observed vibration of the wafer curvature reﬂects the accumulation of the compression strain that occurs during InGaAs growth and the release of the strain that occurs during GaAsP growth.When the strain is completely compensated,the growth of the InGaAs/GaAsP pair will cause this strain to return to the initial value and the wafer curvature will vibrate with the horizontal line as the center.As shown in Fig.7,strain can be compensated almost completely by adjusting the layer structure.Only by conducting a limited number of test runs,the use of such real-time observation technology of the growth layer enables setting the growth conditions for fabricating the layer structure for which strain has been compensated with highaccuracy.Fig.6Spectral quantum efﬁciency of GaAs single-junction cell using InGaAs/GaAsP superlattice as theabsorption layer:This structure consists of 60layers of InGaAs quantum wells.The graph also shows data of a reference cell that uses GaAs for its absorption layer (Wang et al.2010,2012)Fig.7Changes in wafer curvature over time during growth of the InGaAs/GaAsP multilayer structure.This graph indicates the measurement result and the simulation result of the curvature based on the layer structure(composition ?thickness)obtained by X-ray diffraction.Since compressive strain is applied during InGaAs growth,the curvature decreases as time passes.On the other hand,since tensile strain is applied during GaAsP growth,the curvature changes in the oppositedirection (Sugiyama et al.2011)FUTURE DIRECTIONSIn order to improve the conversion efﬁciency by enhancing the current matching of multi-junction solar cells using III–V compound semiconductors,there is an urgent need to create semiconductor materials or structures that can maintain lattice matching with Ge or GaAs,and have a band gap of1.2eV.As for InGaNAs,which consists of InGaAs with several percent of nitrogen added,we have the prospect of extending the band edge to1.0eV while retaining sufﬁcient carrier mobility for solar cells by means of atomic hydrogen irradiation and application of a small quantity of Sb during the growth process.In addition,as for GaNAs bulk crystal containing InAs dots,we were able to extend the band edge to1.2eV and produce a high-quality crystal with enoughﬁlm thickness to achieve the quantum efﬁciency equivalent to that of GaAs.These crystals are grown by means of MBE. Therefore,measures that can be used to apply these crys-tals for mass production,such as migration to MOVPE, will be investigated after demonstrating their high efﬁ-ciency by embedding these crystals into multi-junction cells.As for the InGaAs/GaAsP strain-compensated quantum well that can be grown using MOVPE,we are working on the development of a thinner barrier layer while compen-sating for the strain with high accuracy by real-time observation of the wafer curvature.We have had the prospect of achieving a quantum efﬁciency that will sur-pass existing quantum well solar cells by promoting the carrier transfer within the multilayer quantum well struc-ture using the tunnel effect.As this technology can be transferred quite easily to the existing multi-junction solar cell fabrication process,we strongly believe that this technology can signiﬁcantly contribute to the efﬁciency improvement of the latest multi-junction solar cells. REFERENCESOshima,R.,A.Takata,Y.Shoji,K.Akahane,and Y.Okada.2010.InAs/GaNAs strain-compensated quantum dots stacked up to50 layers for use in high-efﬁciency solar cell.Physica E42: 2757–2760.Sugiyama,M.,K.Sugita,Y.Wang,and Y.Nakano.2011.In situ curvature monitoring for metalorganic vapor phase epitaxy of strain-balanced stacks of InGaAs/GaAsP multiple quantum wells.Journal of Crystal Growth315:1–4.Wang,Y.,Y.Wen,K.Watanabe,M.Sugiyama,and Y.Nakano.2010.InGaAs/GaAsP strain-compensated superlattice solar cell for enhanced spectral response.In Proceedings35th IEEE photovoltaic specialists conference,3383–3385.Wang,Y.P.,S.Ma,M.Sugiyama,and Y.Nakano.2012.Management of highly-strained heterointerface in InGaAs/GaAsP strain-balanced superlattice for photovoltaic application.Journal of Crystal Growth.doi:10.1016/j.jcrysgro.2011.12.049. AUTHOR BIOGRAPHYYoshiaki Nakano(&)is Professor and Director General of Research Center for Advanced Science and Technology,the University of Tokyo.His research interests include physics and fabrication tech-nologies of semiconductor distributed feedback lasers,semiconductor optical modulators/switches,monolithically integrated photonic cir-cuits,and high-efﬁciency heterostructure solar cells.Address:Research Center for Advanced Science and Technology, The University of Tokyo,4-6-1Komaba,Meguro-ku,Tokyo153-8904,Japan.e-mail:nakano@rcast.u-tokyo.ac.jp。

solution annealed and precipitation hardened -回复

solution annealed and precipitation hardened-回复解决方案——退火固溶和沉淀硬化引言：金属材料在工程层面的应用越来越广泛，但这些材料的力学性能和耐久性常常需要得到进一步增强。

为了满足这些要求，金属材料被应用于多种加工工艺，其中退火固溶和沉淀硬化是最常见的两种方法。

本文将详细介绍这两种方法的原理、过程和应用。

1. 退火固溶退火固溶是将金属材料加热至其固溶温度，然后缓慢冷却，以消除材料内部的晶格缺陷，提高材料的塑性和韧性。

1.1 原理当金属材料的晶格结构发生缺陷时，如晶格孔洞或晶点缺陷，材料的机械性能会受到不利影响。

加热材料至固溶温度时，金属晶格开始扩散，缺陷逐渐消失。

此时，晶粒内部的几何和电子结构也会重新排列，增加了塑性和韧性。

冷却过程中，新的晶粒形成，晶界消除了部分位错，从而提高材料的力学性能。

1.2 过程退火固溶通常包含三个主要步骤：加热、保温和冷却。

首先，将金属材料加热至其固溶温度，确保晶格扩散发生。

然后，保持材料在固溶温度下一段时间，使晶粒内部的几何和电子结构重新排列。

最后，缓慢冷却材料，形成新的晶粒。

1.3 应用退火固溶常用于加工硬度高、脆性低的金属材料，如铝合金和不锈钢。

这种方法可以使材料更易于加工和塑性变形，提高其韧性。

例如，铝合金在退火固溶后可以更好地用于汽车和航空航天领域。

2. 沉淀硬化沉淀硬化是通过向金属材料中加入可溶性合金元素，然后热处理使其形成沉淀相，从而提高材料的硬度和强度。

2.1 原理合金元素的添加可以改变原始金属材料的晶格结构，从而影响其力学性能。

在热处理过程中，合金元素在固溶度或过饱和度下溶解，当材料迅速冷却时，合金元素无法在短时间内扩散并形成溶解相。

溶解相会沉淀在晶界或晶粒内，形成固溶体和沉淀相的共存结构，从而提高材料的硬度和强度。

2.2 过程沉淀硬化的过程包含两个关键步骤：固溶化和时效处理。

首先，将合金元素加入金属材料中，推动合金元素在固溶温度下溶解，形成固溶体。

《ZnO@ZnS复合材料多声子共振拉曼散射和光致发光性质研究》

《ZnO@ZnS复合材料多声子共振拉曼散射和光致发光性质研究》一、引言近年来，随着纳米材料科学的发展，ZnO@ZnS复合材料因其独特的物理和化学性质引起了广泛关注。

这种复合材料由氧化锌（ZnO）和硫化锌（ZnS）组成，具有优异的电子、光学和光电性能。

其中，多声子共振拉曼散射和光致发光性质是该材料的重要物理特性之一。

本文旨在研究ZnO@ZnS复合材料的这些性质，并探讨其潜在的应用价值。

二、材料制备与表征ZnO@ZnS复合材料的制备过程主要采用化学气相沉积法。

首先，制备出高质量的ZnO纳米结构作为基底，然后在其表面生长ZnS层，形成复合材料。

通过控制生长条件，可以获得不同比例的ZnO和ZnS组成的复合材料。

为了验证所制备的ZnO@ZnS复合材料的结构和性质，我们采用了多种表征手段。

包括X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）等。

这些表征结果表明，我们成功制备了高质量的ZnO@ZnS复合材料，且具有较好的均匀性和结晶性。

三、多声子共振拉曼散射研究拉曼散射是研究物质分子结构的一种重要方法。

在ZnO@ZnS复合材料中，由于多声子共振效应的存在，拉曼散射现象表现出独特的特点。

我们利用高分辨率拉曼光谱仪对样品进行了拉曼散射研究。

在研究中发现，当激光能量与材料的能级相匹配时，多声子共振拉曼散射现象尤为明显。

此外，我们还观察到随着ZnS含量的增加，拉曼散射强度也发生变化。

这表明复合材料的结构和组成对其拉曼散射性质具有重要影响。

四、光致发光性质研究光致发光是研究半导体材料光学性质的重要手段之一。

在ZnO@ZnS复合材料中，由于ZnO和ZnS的能级差异，光致发光现象表现出丰富的光谱特征。

我们利用光谱仪对样品的光致发光性质进行了研究。

研究发现，在紫外光激发下，ZnO@ZnS复合材料表现出明显的光致发光现象。

随着ZnS含量的增加，发光强度和光谱特征也发生变化。

这表明复合材料的能级结构和电子态对其光致发光性质具有重要影响。

厦门“PEP”2024年小学5年级下册第五次英语第二单元真题试卷(含答案)

厦门“PEP”2024年小学5年级下册英语第二单元真题试卷(含答案)考试时间：90分钟（总分:140）B卷一、综合题(共计100题共100分)1. 选择题：What is the name of the sport played with a round ball and two nets?A. BasketballB. SoccerC. VolleyballD. Tennis答案: B2. 选择题：Which fruit is yellow and curved?a. Appleb. Bananac. Oranged. Pear答案:B3. 选择题：What type of star is our Sun?A. Red giantB. White dwarfC. Yellow dwarfD. Blue supergiant4. 填空题：My favorite _____ is a puzzle toy.5. 听力题：A chicken is a common ______ raised for eggs and meat.6. 填空题：I love to grow _____ (香草) at home.7. 选择题：What is the term for removing the outer layer of something?A. PeelingB. CuttingC. ChoppingD. Slicing答案：A8. 填空题：The ________ gives us shade.9. 选择题：What is the color of a typical sunflower?A. RedB. YellowC. BlueD. Green10. 选择题：What is the capital of Nigeria?A. AbujaB. LagosC. KanoD. Port Harcourt11. 填空题：The __________ (历史的身份认同) shapes group dynamics.12. 听力题：I want to go to the ________.13. 选择题：What is the name of the famous American singer known for her role in "The Wizard of Oz"?A. Judy GarlandB. Marilyn MonroeC. Audrey HepburnD. Grace Kelly答案: A. Judy Garland14. 选择题：Which insect makes a web?A. AntB. ButterflyC. Spider答案: C15. 选择题：What does a light-year measure?A. TimeB. DistanceC. SpeedD. Mass16. 选择题：What is the term for a large, flat area of land?A. PlateauB. ValleyC. BasinD. Plain答案:D17. 填空题：I enjoy making ______ (陶艺) pieces during art class.18. 听力题：The larger the mass, the greater the ______.19. 填空题：The capital of Portugal is ________ (里斯本).20. 听力填空题：I am fascinated by science. Experiments show how things work in our world. One experiment I enjoyed was __________ because it taught me __________.21. 选择题：What is the largest planet in our solar system?A. EarthB. MarsC. JupiterD. Saturn22. 听力题：The chemical symbol for fluorine is ______.23. 选择题：What is the term for a baby pig?A. CalfB. PigletC. Lamb答案: B24. 填空题：A _____ (果汁) can be made from fresh fruits.25. 选择题：What do we call a large area of flat land with few trees?a. Hillb. Mountainc. Plaind. Valley答案:c26. 听力题：The clouds are ___. (fluffy)27. 听力题：The chemical formula for propanol is _____.28. 选择题：What do we call the person who creates software?A. EngineerB. ProgrammerC. ScientistD. Designer29. 选择题：What do we call the area where a river meets the ocean?A. DeltaB. EstuaryC. BayD. Coast30. 选择题：What is the name of the famous dog in the movie "The Wizard of Oz"?A. TotoB. SpikeC. RexD. Max答案: A31. 听力题：I like to ______ my homework before dinner. (finish)What do you call the science of studying the Earth?A. BiologyB. GeologyC. ChemistryD. Physics33. 填空题：I planted a _____ (树) in my yard.34. 选择题：What is the capital of Iraq?A. BaghdadB. MosulC. BasraD. Erbil35. 选择题：What is the main ingredient in ice cream?A. MilkB. WaterC. JuiceD. Soda36. 听力题：The weather is _______ (perfect) for a picnic.37. 选择题：What is the common name for the "common cold"?A. InfluenzaB. FluC. VirusD. Cold答案: D38. 填空题：The _____ (乌龟) basks in the sun on a rock.39. 选择题：What do we call a group of fish swimming together?A. SchoolB. FlockC. PodD. GaggleI read a ___ (book) before bed.41. 选择题：What do we call a baby cat?A. PuppyB. KittenC. CalfD. Chick答案:B42. 填空题：The __________ (历史的探索) invites insight.43. 选择题：Which animal is known for living in a hive?A. AntB. BeeC. SpiderD. Fly答案:B44. 听力题：The fish is swimming in the ___ (lake/ocean).45. 听力题：A chemical reaction can occur at different _____.46. 填空题：I can find inspiration in my ________ (玩具名称).47. 填空题：The ________ was a significant period of artistic achievement.48. 选择题：What is the main ingredient in bread?A. SugarB. FlourC. RiceD. Meat49. 听力题：The chemical properties of a substance can be observed during a ______.50. 听力题：__________ are used in laboratories to measure the volume of liquids.An example of a chemical change is _______ cooking.52. 选择题：What is the name of the bear that loves honey?A. Polar BearB. Grizzly BearC. Winnie the PoohD. Brown Bear53. 选择题：What is the opposite of far?A. NearB. CloseC. DistantD. Both A and B答案:D54. 填空题：The frog croaks loudly near the _______ (水).55. 选择题：What is the term for a baby horse?A. CalfB. FoalC. KidD. Pup答案:B56. 听力题：The _____ (leaf/tree) is green.57. 听力题：We will go to the _____ (zoo/museum) this weekend.58. 听力题：I want to be a ______ (doctor) when I grow up.59. 听力题：The teacher is _____ a story. (reading)60. 填空题：The dolphin plays in the ______ (波浪).61. 填空题：The __________ (人文研究) enhances our understanding of society.What is the opposite of "day"?A. NightB. NoonC. AfternoonD. Morning63. 填空题：The _____ (生命) of a plant begins as a seed.64. 填空题：A ______ (自然保护区) can protect vulnerable species.65. 听力题：We can ___ a picnic in the garden. (have)66. 填空题：The ______ (植物分类) helps identify species.67. 听力题：I have a _____ (新) bike.68. 填空题：A _____ (植物发展) can lead to sustainable practices.69. 选择题：What do we call a group of bees?A. SwarmB. ColonyC. FlockD. Hive答案:B. Colony70. 填空题：We visit the ______ (天文馆) to learn about space.71. 填空题：The _____ (气候变化) poses risks to many plant species.72. 填空题：The __________ is a major city located on the coast. (迈阿密)73. 听力题：A ______ has unique patterns on its skin.The ancient Romans spoke _____.75. 选择题：Which planet is known as the Blue Planet?A. MarsB. EarthC. NeptuneD. Uranus答案:B76. 选择题：What do you call a place where you can borrow books?A. LibraryB. BookstoreC. SchoolD. Office77. 填空题：A pharaoh ant is a common ______ (蚂蚁).78. 听力题：The chemical symbol for cesium is _____.79. 听力题：A chemical reaction can release ______.80. 选择题：What do you call a round fruit that is red or green?A. BananaB. AppleC. OrangeD. Grape81. 填空题：The chocolate is ________ (融化).82. 填空题：The _____ (植物生长) is influenced by many factors.83. 听力题：The state of matter that has a definite volume but no definite shape is ______.84. 听力题：The _______ of a spring can be measured in Newtons.The __________ is a natural system that supports life.86. 填空题：I want to learn to ________ (制作手工艺).87. 填空题：The __________ (历史的丰厚底蕴) inform practices.88. 填空题：The bat uses _______ (回声定位) to navigate.89. 选择题：What is the term for the changing of seasons?A. ClimateB. WeatherC. PhenomenonD. Cycle答案：D90. 选择题：Which of these numbers is even?A. 3B. 5C. 8D. 1191. 听力题：The girl is very ________.92. 听力题：The ____ has a long body and is often mistaken for a snake.93. 填空题：My favorite game is ________ (棋).94. 听力题：A nova is a sudden increase in the brightness of a ______.95. 选择题：What do we use to cut paper?A. TapeB. GlueC. ScissorsD. Ruler答案: C. Scissors96. 选择题：What do you call a person who studies plants and animals?A. ScientistB. DoctorC. ArtistD. Teacher答案: A. Scientist97. 填空题：The dog barks loudly at the ______.98. 填空题：The ________ (小溪) flows through the forest and is very peaceful.99. 填空题：A _____ (海星) has five arms and lives in the sea.100. 填空题：The cat loves to chase a _________. (激光点)。

红外光谱研究znalla氧化物上甘油碳酸酯生成机理

红外光谱研究znalla氧化物上甘油碳酸酯生成机理甘油碳酸酯是一种重要的化工原料，可以广泛应用于化妆品、塑料、涂料、树脂、医药等领域。

本研究通过红外光谱技术，研究了在znalla氧化物的催化下甘油碳酸酯的生成机理。

实验结果表明，在催化剂znalla的存在下，甘油碳酸酯可通过甘油与二氧化碳反应形成。

反应开始时，观察到znalla表面的氧化物被还原为金属氧化物，同时甘油的羟基与znalla表面金属离子发生配位作用，促使碳酸酯的形成。

通过对反应过程中不同物质的红外光谱分析，发现CO2的吸收峰在碳酸酯的形成过程中明显增强，甘油羟基O-H伸缩振动峰的强度也有所减弱。

综合以上实验结果，可以得出znalla催化剂对甘油碳酸酯生成的主要作用机理为：催化剂表面的金属离子与甘油分子的羟基形成配位作用，帮助二氧化碳的吸附和还原，促进碳酸酯的形成。

这一研究结果为促进甘油碳酸酯的合成工艺、催化剂的设计和改进提供了重要的理论参考。

《ZnO-ZnMgO多量子阱中电子子带跃迁光吸收》范文

《ZnO-ZnMgO多量子阱中电子子带跃迁光吸收》篇一ZnO-ZnMgO多量子阱中电子子带跃迁光吸收一、引言在光电子材料领域中，氧化锌（ZnO）和其合金材料因其独特的物理和化学性质，如高光学透明度、高电子迁移率等，被广泛用于光电器件和光电子功能材料。

其中，ZnO/ZnMgO多量子阱（MQW）作为一种具有显著能级结构和光子效应的异质结构，近年来引起了广泛的关注。

本篇论文将重点研究ZnO/ZnMgO多量子阱中电子子带跃迁的光吸收现象。

二、ZnO/ZnMgO多量子阱的结构与性质ZnO/ZnMgO多量子阱是由交替生长的ZnO和ZnMgO层组成，其结构具有周期性。

由于两种材料之间的能级差异，形成了势阱和势垒，使得电子在量子阱中形成子带结构。

这种结构使得电子在受到光激发时，能够在不同子带之间发生跃迁。

三、电子子带跃迁的原理当光照射到ZnO/ZnMgO多量子阱上时，光子的能量将激发电子从低能级子带跃迁到高能级子带。

这种跃迁过程中，电子会吸收光子的能量并发生能级跃迁。

跃迁过程中产生的光吸收系数与光子的能量有关，可以通过测量光吸收系数来研究电子子带跃迁的能级结构和跃迁过程。

四、实验方法与结果本实验采用光谱技术，测量了不同波长的光照射下ZnO/ZnMgO多量子阱的光吸收系数。

通过分析实验数据，我们得到了电子在不同子带之间的跃迁过程和相应的能级结构。

实验结果表明，随着光子能量的增加，电子在子带之间的跃迁逐渐发生，且跃迁过程中存在明显的光吸收峰。

这些光吸收峰的位置和强度与量子阱的结构和材料性质密切相关。

五、讨论与分析根据实验结果，我们可以分析ZnO/ZnMgO多量子阱中电子子带跃迁的机制和影响因素。

首先，量子阱的结构对电子的跃迁过程具有重要影响。

不同层厚、不同材料比例的量子阱将产生不同的能级结构和光吸收特性。

其次，温度也会影响电子的跃迁过程。

随着温度的升高，热激发将使得电子更容易从低能级子带跃迁到高能级子带。

此外，光子的能量、波长等因素也会对电子的跃迁过程产生影响。

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612Chem.Mater.2010,22,612–623DOI:10.1021/cm901917aSolid Solution of GaN and ZnO as a Stable Photocatalyst for OverallWater Splitting under Visible Light†Kazuhiko Maeda and Kazunari Domen*Department of Chemical System Engineering,The University of Tokyo,7-3-1Hongo,Bunkyo-ku,Tokyo113-8656,JapanReceived June30,2009.Revised Manuscript Received August18,2009Large-scale hydrogen production from water using only solar energy is an ultimate goal for the supply of clean,recyclable energy,and several reactions and schemes have been proposed.Overall water splitting using a particulate photocatalyst is one attractive solution with a wide range of applications.A number of photocatalysts have been proposed,and some have achieved high quantum efficiencies.Unfortunately,most of these photocatalysts consist of metal oxides and work only in the ultraviolet(UV)region.To effectively utilize solar energy,it is necessary to develop a material that will function under visible light.This paper reviews the recent development of such a photocatalyst,specifically focusing on efforts by the authors’group to prepare a solid solution of GaN and ZnO.This new material is capable of splitting water into hydrogen and oxygen under visible light(λ>400nm)with good reproducibility.1.IntroductionCatalytic splitting of pure water into hydrogen and oxygen in the presence of semiconductor powders using visible light is a promising approach for storing solar energy as chemical energy.1,2The reaction(eq1)is a typical“uphill reaction”,having a large positive change in the Gibbs free energy(ΔG0=238kJ/mol).2H2O f2H2þO2ð1ÞThe half-reactions are described as follows:2Hþþ2e-f H2ð2Þ2H2Oþ4hþf O2þ4Hþð3ÞResearch in this field was initially triggered by the demon-stration of photoelectrochemical water splitting using a single-crystal titanium dioxide(rutile)photoanode and a platinum cathode with an external bias.1Over the past decades,while many semiconducting materials have been reported to be active for the reaction,none have demon-strated stable,reproducible overall water splitting cap-ability under visible light irradiation.The major obstacle to progress in this field has been the lack of a suitable compound that meets the following three requirements: (1)a band gap narrower than3eV,(2)band-edge potentials suitable for overall water splitting,and(3)stability in the photocatalytic reaction.Specifically,the band gap must be sufficiently small to allow the absorption of visible light(<3eV),and the band edges must be located in a position that allows for the reduction and oxidation of water by photoexcited electrons and holes.In general, efficient photocatalytic materials contain either transi-tion-metal cations with a d0electronic configuration (e.g.,Ti4+and Ta5+)3-5or typical metal cations with a d10electronic configuration(e.g.,In3+and Sn4+)6,7as principal cation components.8The empty d or sp orbitals form the bottom of the conduction band.The top of the valence band of a metal-oxide photocatalyst with d0-or d10-metal cations usually consists of O2p orbitals,which are located at about+3eV or higher vs a normal hydro-gen electrode(NHE),thus producing a band gap too wide to absorb visible light.9As some nonoxide compounds such as CdS and CdSe have band edge potentials suitable for water splitting under visible light,these compounds were carefully examined for visible light utilization.How-ever,no successful photocatalytic systems have been established because of a lack of oxygen production due to the instability of the materials.10Because N2p orbitals have higher potential energy than O2p orbitals,it would be interesting to use a metal nitride or metal oxynitride as a photocatalyst.The authors’group has developed(oxy)nitrides,such as TaON,11-14 Ta3N5,15,16and LaTiO2N,17,18as potential candidates for overall water splitting under visible light.Unfortunately, overall water splitting using these oxynitrides has not been achieved,at least partly due to the relatively high defect densities in the bulk and at the surfaces of these materials.However,some of them do function as a build-ing block for H2evolution in a two-step water splitting system(Z-scheme)under visible light.19,20These(oxy)nitrides are composed of transition metal cations of Ti4+,Nb5+, or Ta5+,which have an empty d orbital.Because of their†Accepted as part of the2010“Materials Chemistry of Energy ConversionSpecial Issue”.*Corresponding author.Tel.:+81-3-5841-1148.Fax:+81-3-5841-8838,E-mail:domen@chemsys.t.u-tokyo.ac.jp./cm Published on Web09/14/2009r2009American Chemical SocietyReview Chem.Mater.,Vol.22,No.3,2010613 electronic band structure,d10-semiconductors containingtypical metal cations have an advantage as a photocata-lyst,compared to materials with d0electronic configura-tion.6,7The top of the valence band in transition-metaloxides with a d0electronic configuration consists of O2porbitals,whereas the bottom of the conduction band iscomposed of empty d orbitals of the transition metals.Intypical metal oxides with a d10electronic configuration,however,the bottom of the conduction band consists ofhybridized s,p orbitals of the metals,although the valenceband is essentially formed by O2p orbitals.The hybri-dized s,p orbitals have large dispersion,increasing themobility of photogenerated electrons in the conductionband and promoting photocatalytic activity.6,7(Oxy)nitrides with a d10electronic configuration aretherefore of interest as potentially efficient photocatalystsfor overall water splitting.In evaluating such d10-com-pounds according to this hypothesis,it was found that β-Ge3N4loaded with RuO2nanoparticles functions as a photocatalyst for overall water splitting.21-24This wasthe first case involving a nonoxide photocatalyst for thecleavage of pure water.Since this discovery,the photo-catalytic properties and effects of post-treatment toenhance the activity of Ge3N4have been examined indetail.22,23The relationship between the structuralcharacteristics and the photocatalytic performanceof Ge3N4has also been investigated.24Unfortunately,the band gap ofβ-Ge3N4is about3.8eV,which isresponsive only to ultraviolet light.21,23This forced usto search for a new d10compound that can function undervisible light.In this article,the development of such a material isdescribed,focusing on a solid solution of gallium nitride(GaN)and zinc oxide(ZnO).As schematically illustratedin Figure1,photocatalytic overall water splitting on asemiconductor powder involves several steps.Amongthese,suppressing recombination between photogener-ated electrons and holes in a photocatalyst is the mostimportant to achieving the reaction.The effects of phys-icochemical properties on water splitting activity havebeen investigated for many metal-oxide photocatalysts,2d,7whereas little information is available for nonoxidephotocatalysts.As the solid solution is the first successfulexample of achieving overall water splitting under visiblelight(λ>400nm)with good reproducibility,25-40it is agood example for studying such physicochemical effectson activity.From the viewpoint of solid-state materialschemistry,we would like to pay attention to the refine-ment of the base photocatalyst,although our recent studyhas revealed that the photocatalytic activity is signifi-cantly enhanced upon modification of nanostructuredcocatalysts based on rhodium and chromium as H2evolution sites.29-36It is also noted that a similar wurt-zite-type solid solution consisting of ZnGeN2and ZnOwas recently reported as an active photocatalyst forvisible-light-driven overall water splitting.41-44Physico-chemical effects on photocatalytic activity of GaN-ZnOsolid solutions,which will be mentioned below,can there-fore be applicable to ZnGeN2-ZnO solid solutions.2.Initial Concept for Designing GaN-ZnO SolidSolutionsTo devise a new d10-(oxy)nitride with a visible light response,our initial focus was on gallium nitride(GaN), which has been studied extensively for application in light-emitting diodes and laser diodes.45,46Although GaN was confirmed to have potential for overall water splitting,its large band gap(ca.3.4eV)restricts its use of visible photons.47-49Nevertheless,we believed that this situation could be overcome by the following strategy. For II-VI semiconductors containing Zn2þions as a principal component(e.g.,ZnAl2O4),it has been re-ported that p-d repulsion(e.g.,O2p-Zn3d)shifts the valence-band maximum upward without affecting the conduction-band minimum.50Similarly,it was hypothe-sized that p-d repulsion may occur when a zinc(II) compound is incorporated into the GaN lattice,causing the top of the valence band formed by N2p atomic orbitals to rise to a higher potential energy(i.e.,N2p-Zn3d repulsion),narrowing the band gap for GaN. Because both GaN and ZnO have wurtzite structures with similar lattice parameters,51,52a solid solution can be formed between the two(Figure2).In this context, ZnO was chosen as a partner for GaN to form a solid solution with visible light response.The expected band structure of GaN-ZnO solid solution is illustrated in Figure3.Preparation of the solid solution was first attempted by nitriding a mixture ofβ-Ga2O3and ZnO under a flow of ammonia at∼1223K.As shown in Figure4,the as-obtained products were yellow powders,depending on the preparation condition.The yellow color clearly in-dicates visible-light-absorption by this material,consis-tent with the initial hypothesis.Elemental analysis by inductive coupled plasma optical emission spectroscopy (ICP-OES)revealed that the ratios of Ga to N and Zn to O were close to1,and that the nitrogen and oxygen con-centrations increased with increasing gallium and zinc concentrations.25X-ray diffraction(XRD)analysis showed that the prepared material had a wurtzite structure similar to GaN and ZnO,and that the diffraction peaks were between those of GaN and ZnO(as will be discussed below in more detail).Based on these results,it was con-cluded that the obtained material was indeed a solid solution Figure1.Schematic illustration of overall water splitting on a hetero-geneousphotocatalyst.614Chem.Mater.,Vol.22,No.3,2010Maeda and Domen of GaN and ZnO(represented as(Ga1-x Zn x)(N1-x O x)hereafter),and more systematic study was begun.3.Effect of Nitridation ConditionsThermal ammonolysis is a convenient technique for synthesizing particulate metal(oxy)nitrides from the corre-sponding precursors,and the physicochemical properties of the products can be controlled through appropriate adjust-ment of the preparation conditions.15,18,24,53-57In general, the functionality(e.g.,photocatalytic activity)of a given material is strongly dependent on its physicochemical characteristics.15,18,24,57Therefore,investigating the rela-tionship between the functionality and physicochemical characteristics of a material should provide useful infor-mation for further refinement of such systems.The physicochemical properties of(Ga1-x Zn x)(N1-x O x)and the optimal preparation conditions were investigated in an attempt to improve the activity of the material for overall water splitting.26Figure5shows XRD patterns from samples obtained by nitriding a mixture ofβ-Ga2O3and ZnO(Zn/Ga=1by mole)at1123K for several periods.GaN and ZnO data are shown for comparison.A single hexagonal wurtzite phase similar to the GaN and ZnO was obtained for allFigure2.Crystal structure and lattice constants of GaN and ZnO. Figure3.Schematic illustration of band structures of GaN,ZnO,and their solid solution.Figure4.Photographs of GaN,ZnO,and(Ga1-x Zn x)(N1-x O x)solid solutions.Figure5.Powder XRD patterns of samples obtained by nitriding a mixture ofβ-Ga2O3and ZnO(molar ratio Zn/Ga=1)under a flow of NH3at1123K for several time periods.ZnO and GaN references were purchased from Kanto Chemicals and Mitsubishi Chemicals Co.,respec-tively.Review Chem.Mater.,Vol.22,No.3,2010615prepared samples,but nitridation for less than 5h did not lead to the formation of the single wurtzite phase.In addition to the peaks assigned to the solid solution,some small peaks assigned to ZnO and ZnGa 2O 4were observed in the nitridation products.The positions of the diffrac-tion peaks shifted to higher angles (2θ)with increasing nitridation time,indicating that the obtained samples were not physical mixtures of GaN and ZnO phases,but rather solid solutions of GaN and ZnO.The zinc and oxygen concentration in the solid solution thus decreased with reduction of the ZnO content and subsequent vola-tilization of zinc in the solid solution due to exposure to a reductive atmosphere during nitridation.This peak shiftis reasonable,as the ionic radius of Zn 2þ(0.74A)is larger than that of Ga 3þ(0.61A).58Thus,there was a linear relationship between the lattice constants (a and c )and the composition (x )of (Ga 1-x Zn x )(N 1-x O x ).26Figure 6shows scanning electron microscope (SEM)images of the same samples.Particles prepared by nitri-dation for less than 15h were irregularly shaped,whereas those nitrided for longer periods became more regular and larger with increasing nitridation time.This change in particle shape agrees well with the XRD measurements,in which the peaks became stronger and narrower with increasing nitridation time (Figure 5).These measure-ments reveal that the crystallization of the nitridation products proceeds gradually from 5to 30h during nitri-dation at 1123K.Transmission electron microscope (TEM)images and an electron diffraction pattern of (Ga 1-x Zn x )(N 1-x O x )prepared by nitridation for 15h are shown in Figure 7.The figure clearly reveals that the sample consisted primarily of well-crystallized submicro-meter particles with a wurtzite structure,as indicated by the lattice fringe and electron diffraction patterns.Energy dispersive X-ray spectroscopy (EDS)analysis for each spot area (ca.20nm)revealed that the atomic composi-tion of the material deviates from spot to spot,even in the same primary particle.Such nonuniformity in atomic composition is indicative of simultaneous diffusion of constituent ions of the starting mixtures (i.e.,Ga 3þ,Zn 2þ,and O 2-)and nitridation at the solid -solid boundary between β-Ga 2O 3and ZnO.UV -visible diffuse reflectance spectra for the same set of samples are shown in Figure 8A,along with GaN and ZnO data for comparison.As suggested from the photo-graphs (Figure 4),the absorption edges of (Ga 1-x Zn x )-(N 1-x O x )were at longer wavelengths than those of GaN or ZnO,but shifted to shorter wavelengths with increas-ing nitridation time.The band gap of the present samples was roughly estimated to be 2.6-2.8eV,based on the onsets of the diffuse reflectance spectra,which were substan-tially smaller than those of GaN (3.4eV)or ZnO (3.2eV).Figure 8B shows the relationship between the estimated band gap energy and the ZnO concentration of (Ga 1-x Zn x )-(N 1-x O x ).Here,the band gap energy decreased with increa-sing ZnO concentration,indicating that the visible-light-response of (Ga 1-x Zn x )(N 1-x O x )comes from the presence of ZnO in the crystal.The photoluminescence and photo-luminescence excitation spectra of (Ga 1-x Zn x )(N 1-x O x )Figure 6.SEM images of samples obtained by nitriding a mixture of β-Ga 2O 3and ZnO (molar ratio Zn/Ga =1)under a flow of NH 3at 1123K for several time periods.Figure 7.TEM images and an electron diffraction pattern of a sample obtained by nitriding a mixture of β-Ga 2O 3and ZnO (molar ratio Zn/Ga=1)under a flow of NH 3at 1123K for 15h.Results of EDS analysis are alsoshown.616Chem.Mater.,Vol.22,No.3,2010Maeda and Domenwith compositions of x=0.05-0.20(i.e.,GaN-rich)mea-sured at10K suggested that the visible light absorption of this material occurs via Zn-related acceptor levels.59This idea,however,contradicts our previous density func-tional theory(DFT)calculations,which indicate that the bottom of the conduction band for(Ga1-x Zn x)-(N1-x O x)is mainly composed of4s and4p orbitals of Ga,while the top of the valence band consists of N2p orbitals followed by Zn3d and O2p orbitals.2b This idea remains valid for the solid solution with stoichiometric unit cells.For a dilute solid solution,however,it is natural to consider the local inhomogeneity of the Zn and O atom densities.In such circumstances,empty impurity levels appear just above the valence band,and/or filled impurity levels appear just below the conduction band.These impurity levels may explain the photoluminescence ex-perimental results,and were characterized by our DFT calculations with nonstoichiometric unit cells.Very re-cently,Muckerman et al.and Huang et al.have studied the same material using theoretical calculations.60Their results are essentially identical to those obtained in our previous study.The photocatalytic activity of as-prepared(Ga1-x Zn x)-(N1-x O x)for overall water splitting was negligible,re-gardless of the preparation conditions.However,the modification of(Ga1-x Zn x)(N1-x O x)with nanoparticulate transition-metal oxides(e.g.,NiO,RuO2,or Rh2-y Cr y O3) resulted in clearly observable H2and O2evolution.This modification involved the deposition of metal-oxide nanoparticles on the surface of the(Ga1-x Zn x)(N1-x O x) as H2evolution sites.Table1lists the photocatalytic activity for overall water splitting using samples prepared under various nitridation conditions.Data including the chemical composition and specific surface area are also included in the table.A trade-off relationship between activity and nitridation conditions was observed;specifi-cally,the activity increased,up to a certain point,as nitri-dation progressed,but further nitridation resulted in decreased activity.It also appeared that the activity was nearly independent of the specific surface area,unlike the behavior generally observed in metal-oxide photocata-lysts.7Taking a series of samples prepared at1123K for different durations as an example,the largest increase in activity was obtained in the range between5and15h of nitridation(entries1-3,Table1),where the XRD peak became stronger and narrower(Figure5)and the particle shape became more regular(Figure6).The increase in activity with nitridation time was therefore considered to be associated with the crystallization of(Ga1-x Zn x)-(N1-x O x),which reduced the number of defects acting as recombination centers between photogenerated electrons and holes.Nitridation for longer than15h had reduced the activity of the catalyst from its maximum value,which seemed to be attributable to a decrease in zinc concentra-tion at the surface of the catalysts.X-ray photoelectron spectroscopy(XPS)and EDX analysis revealed that the zinc concentration in the(Ga1-x Zn x)(N1-x O x)decreased with increasing nitridation time,and the degree of the decrease was more prominent at the surface than in the bulk.26Under the present nitridation conditions,ZnO species in(Ga1-x Zn x)(N1-x O x)were reduced to zincFigure8.(A)Diffuse reflectance spectra of samples obtained by nitriding a mixture ofβ-Ga2O3and ZnO(molar ratio Zn/Ga=1)under a flow of NH3at1123K for several time periods.ZnO and GaN references were purchased from Kanto Chemicals and Mitsubishi Chemicals Co.,respec-tively.(B)Relationship between band gap energies and ZnO concentra-tion(x)of the(Ga1-x Zn x)(N1-x O x).Table1.Effect of Nitridation Conditions on the Chemical Composition, Specific Surface Area,and Photocatalytic Activity for Overall Water Splitting under UV and Visible Light Irradiation(λ>300nm)nitridation conditions aactivity c(μmol h-1) entry T(K)time(h)Zn/Gaatomic ratio bspecific surfacearea/m23g-1H2O2 1112350.287.9 2.5 1.5 2100.177.48.7 4.1 3150.137.42914 4200.10 6.7209.2 5300.05 5.814 6.9 6117330.358.1 1.4 1.2 750.08 5.011 5.2 8100.05 5.1157.0 9150.06 4.910 4.9 10200.05 4.77.7 3.2 11122310.298.3 3.9 1.8 1230.07 5.314 6.9 1350.06 5.0157.4 14100.04 3.511 5.0 15150.04 3.7 4.5 2.0a A mixture ofβ-Ga2O3and ZnO(Zn/Ga=1by mole)was employed as a starting material.In all cases,a single wurtzite phase was observed in XRD measurements.b Estimated from EDX measurements.c Reaction conditions:catalyst,0.3g(1.5wt%NiO loaded by impregnation with Ni(NO3)2followed by calcination in air at573K for1h);reactant solution,pure water(420mL);reaction vessel,Pyrex inner-irradiation-type;light source,high-pressure mercury lamp(450W).Listed are average rates of H2and O2evolution after5h ofreaction.Review Chem.Mater.,Vol.22,No.3,2010617metal,which volatized to zinc vapor.The remnant oxygen was removed as H2O,but not completely.This situation resulted in vacancies at zinc sites at the catalyst surface, which acted as recombination centers between photogen-erated electrons and holes.This idea is supported by the difficulty of preparing a high-activity catalyst at tempera-tures above1173K(Table1).This was attributed to the formation of zinc-and/or oxygen-related defects at the (Ga1-x Zn x)(N1-x O x)surface at such high temperatures. Conversely,it was difficult to obtain a single phase of (Ga1-x Zn x)(N1-x O x)at temperature below1073K,even with extended nitridation periods,probably because of the poor reactivity of the starting materials with NH3gas at lower temperatures.Thus,the optimal temperature for preparation of(Ga1-x Zn x)(N1-x O x)is considered to be1123K.A typical time course of overall water splitting on (Ga1-x Zn x)(N1-x O x),prepared at the above-optimized condition under irradiation by UV and visible light(λ> 300nm)is shown in Figure9.In this case,RuO2nano-particles were employed as a promoter.The gas phase was evacuated every5h,and the reaction was allowed to proceed for a total of25h to evaluate stability.At the initial stage of the reaction,the evolution ratio of H2to O2 was slightly larger than that expected from the stoichi-ometry,and the activity decreased with increasing reac-tion time.Nevertheless,the activity stabilized in the fourth run,at an H2/O2ratio of2.The total evolution of H2and O2after25h was7.48mmol,substantially exceeding the total amount of catalyst(3.56mmol) employed for the reaction.It has also been confirmed by XRD,XPS,and X-ray absorption fine-structure spectroscopy(XAFS)that the crystal structure of the catalyst and the valence state of both the surface and bulk did not change,even after reaction for3days at the optimal reaction conditions.32Figure10shows the de-pendence of the rate of H2and O2evolution on the wavelength of incident light.The H2and O2evolution rates both decreased as the cutoff wavelength increased. The longest wavelength available for the water splitting reaction was460nm,corresponding to the absorption edge of the catalyst.This result clearly indicates that the reaction proceeded photocatalytically through light ab-sorption by(Ga1-x Zn x)(N1-x O x).It has been reported that O2evolution occurs on a ZnO electrode as a result of degradation when employed as a photoanode for water oxidation in a photoelectrochemical cell.61Interestingly, it was confirmed through18O-isotopic H2O cleavage experiments that the O2evolution on(Ga1-x Zn x)-(N1-x O x)was due to water oxidation,with the XRD pattern of the sample remaining unchanged after the reaction.25Control experiments showed no gas evolution in the absence of either a photocatalyst or a light source. These results lead us to conclude that(Ga1-x Zn x)-(N1-x O x)functions as a stable photocatalyst for overall water splitting under visible light.For nonoxide photocatalysts,it is important to note the effect of self-decomposition by photogenerated holes in the valence band of the material,since this process competes with the water photooxidation reaction(eq3). In overall water splitting using(Ga1-x Zn x)(N1-x O x) modified with cocatalysts,a negligible amount of N2 evolution(∼10μmol)was detected in the initial stage of the reaction(first1-2h).This was attributed to the oxidation of N3-species near the(Ga1-x Zn x)(N1-x O x) surface to N2,as has been observed for other(oxy)nitride photocatalysts.11,15,17,18,19a,20-24,57,622N3-þ6hþf N2ð4ÞHowever,the production of N2was completely sup-pressed as the reaction proceeded,indicative of good stability of the material.This behavior is very different from conventional nonoxide photocatalysts such as cad-mium sulfide(CdS),where photogenerated holes oxidize the material itself under overall water splitting conditions without participating in water oxidation due to the inherent instability of the material.104.Effect of Starting MaterialsIn a typical synthesis,(Ga1-x Zn x)(N1-x O x)can be obtained by nitriding a mixture ofβ-Ga2O3and ZnO at temperatures higher than1123K under a flow of NH3,asFigure9.Typical time course of overall water splitting under UV and visible irradiation(λ>300nm)on3.5wt%RuO2-loaded(Ga1-x Zn x)-(N1-x O x)(entry3,see Table1).Catalyst(0.3g);reactant solution,pure water(390mL);light source,high-pressure mercury lamp(450W);inner-irradiation-type Pyrex reaction vessel.Figure10.Dependence of the rates of H2and O2evolution by5wt% RuO2-loaded(Ga1-x Zn x)(N1-x O x)(entry3,see Table1)on the cutoff wavelength of the incident light.Catalyst(0.3g);an aqueous solution adjusted to pH3by H2SO4(200mL);light source,xenon lamp(300W) attached with a cutoff filter;top-irradiation-type Pyrex reactionvessel.618Chem.Mater.,Vol.22,No.3,2010Maeda and Domendescribed above.It is essential to understand the detailed effects of the starting materials on nitridation in order to develop a highly active photocatalyst.It is generally known that the starting material affects the physicochem-ical properties (e.g.,crystallinity,surface structure,and composition)of the final product that play a crucial role in determining the activity.5-7The effects of the starting materials on physicochemical and photocatalytic properties of the resulting (Ga 1-x Zn x )-(N 1-x O x )have thus been systematically investigated.39,40Table 2summarizes the results of preparation and the photocatalytic activity of the final products using various Ga and Zn compounds.First of all,R -,β-,and γ-Ga 2O 3and GaN were tested as Ga-sources for synthesizing (Ga 1-x Zn x )(N 1-x O x ).The use of R -and γ-Ga 2O 3as the starting material resulted in successful production of (Ga 1-x Zn x )(N 1-x O x )(entries 2and 3),as in the case of β-Ga 2O 3(entry 1).Despite the similarity in XRD pat-terns,specific surface area,and chemical composition,the activity of the sample prepared using γ-Ga 2O 3was 1order of magnitude lower than that of those derived from R -and β-Ga 2O 3.40One possible explanation for this low activity is that the γ-derived sample had a rough surface structure.Figure 11shows SEM images of (Ga 1-x Zn x )-(N 1-x O x )prepared using various Ga 2O 3polymorphs,whose SEM data are also displayed.(Ga 1-x Zn x )-(N 1-x O x )prepared using R -and β-Ga 2O 3exhibited simi-lar morphology with a relatively smooth surface struc-ture.On the other hand,the sample prepared using γ-Ga 2O 3contained fine particles and structural imperfec-tions,although some well-crystallized particles were also observed.Such surface-roughness can function as traps for photogenerated electrons and holes,reducing the efficiency of photocatalysis.γ-Ga 2O 3consists of agglom-erates several micrometers in size,composed of aggre-gated primary particles smaller than 50nm.Therefore,it appears that the contact of γ-Ga 2O 3with ZnO in the mixture of starting materials becomes inevitably less intimate than when using R -or β-Ga 2O 3.This situation would result in morphological roughness of the resulting (Ga 1-x Zn x )(N 1-x O x ).This idea was further supported by another experiment,in which the effect of the Zn/Ga molar ratio in the starting material was investigated,as will be discussed below.On the other hand,nitridation of GaN and ZnO in the same manner did not lead to the production of (Ga 1-x Zn x )(N 1-x O x )(entry 4).The XRD pattern of the obtained product was identical to that of the starting GaN.This indicates that the ZnO in the starting material volatized by exposure to a reductive atmosphere derived from NH 3at high temperatures,Table 2.Effect of Starting Materials on the Preparation of (Ga 1-x Zn x )(N 1-x O x )and Photocatalytic Activity for Overall Water Splitting underVisible Light Irradiation (λ>400nm )Zn/Ga atomic ratioactivity c (μmol h -1)entry starting material crystal phase in product a in starting materialin product b H 2O 21β-Ga 2O 3þZnO solid solution 1.00.132701342R -Ga 2O 3þZnO solid solution 1.00.143161623γ-Ga 2O 3þZnO solid solution 1.00.1332164GaN þZnO GaN1.0no data no data no data 5ZnGa 2O 4solid solution 0.50.25<0.506ZnGa 2O 4þZnO solid solution1.00.292131117β-Ga 2O 3þZnsolid solution þZnGa 2O 4þetc.1.0no datano datano dataaDetermined by XRD measurements.b Estimated from EDX measurements.c Reaction conditions:catalyst,0.3g (1wt %Rh and 1.5wt %Cr loaded by impregnation with Na 3RhCl 632H 2O and Cr(NO 3)339H 2O followed by calcination in air at 623K for 1h);reactant solution,aqueous solution adjusted to pH 4.5by H 2SO 4(370mL);reaction vessel,Pyrex inner-irradiation-type;light source,high-pressure mercury lamp (450W).Listed are steady rates of H 2and O 2evolution in 5h of reaction.Figure 11.SEM images of (Ga 1-x Zn x )(N 1-x O x )obtained by nitriding a mixture of ZnO and either (a)R -Ga 2O 3,(b)β-Ga 2O 3,or (c)γ-Ga 2O 3.Data for the Ga polymorphs are alsoshown.。