石墨相氮化碳的制备及其光催化性能的研究

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学校代码:10255

学号:2131347

DONGHUA UNIVERSITY

硕士学位论文

石墨相氮化碳的制备及其光催化性能的研究Preparation and Photocatalytic Properties of Graphite phase

Carbon Nitride

专业:环境工程

作者:史振涛

导师:许士洪(副教授)

完成日期:2015年5月

东华大学

硕士学位论文答辩委员会成员名单

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石墨相氮化碳的制备及其光催化性能的研究

摘要

近年来,半导体光催化技术得到了快速的发展。聚合物半导体石墨相氮化碳(g-C3N4)因其无毒、催化活性高、氧化能力强、且具有优异的化学稳定性和独特的电子能带结构、不含金属组分等优点而得到广泛研究。但是由于聚合物的材料特性,将g-C3N4作为光催化剂还存在如比表面积小、光生电子-空穴复合严重、量子效率低和禁带宽度较大而不能有效利用太阳光等严重制约其在能源、环境光催化领域的大规模推广应用的问题。因此,为了更好的利用太阳光,对g-C3N4进行制备优化及改性以得到较高可见光响应的光催化剂是非常必要的。

在本论文中,作者通过2种简单温和的方法制备出了在可见光下有较好光催化活性的石墨相氮化碳(g-C3N4)光催化剂。同时,结合XRD、UV-Vis、SEM、TEM、BET、TGA等实验手段,研究了不同制备条件对g-C3N4光催化剂的结构及催化性能的影响。结果如下:

1、以双氰胺为原料,通过改变煅烧时间及煅烧温度制备g-C3N4光催化剂。XRD结果表明在一定温度区间内随着煅烧温度的升高g-C3N4的结晶度先变好后变差。UV-Vis的结果表明制备的g-C3N4光催化剂吸收边在460 nm左右。实验还研究了不同煅烧温度、时间对g-C3N4光催化性能的影响,并初步探究了其催化机理。可见光下降解

甲基橙的结果表明,550℃煅烧240 min时,g-C3N4光催化剂具有最佳催化活性。在2.5 h内,对甲基橙的降解率可达86.2%。

2、以三聚氰氯和三聚氰胺为原料乙腈为溶剂,制备了g-C3N4纳米棒光催化剂。XRD结果表明所制备的光催化剂为石墨相结构且随着温度的升高样品的结晶度先变好后变差。SEM结果表明所制备的纳米棒直径约25nm,长1μm。UV-Vis的结果表明样品的吸收边随着温度、时间的增加而红移。可见光下降解甲基橙的实验结果表明,200℃保温48h时,g-C3N4光催化剂具在2.5 h内对甲基橙的降解率可达99.7%。

3、以双氰胺代替三聚氰胺,制备了g-C3N4纳米球光催化剂。UV-Vis结果表明制备的光催化剂样品具有优异的可见光活性。SEM 和TEM结果表明所制备的光催化剂多数为纳米球且直径约200nm。可见光下降解甲基橙的实验结果表明,200℃保温36h时,g-C3N4光催化剂2.5 h内对甲基橙的降解率可达99.8%。

关键词:g-C3N4;光催化剂;双氰胺,三聚氰氯,三聚氰胺,可见光

PREPARATION AND PHOTOCATALYTIC PROPERTIES OF GRAPHITE PHASE CARBON NITRID

ABSTRACT

The semiconductor photocatalytic technology has been developed rapidy in recent years. Graphite phase carbon nitride (g-C3N4), a metal-free photocatalyst has been drawn much attention because of its non-toxic、high catalytic activity、excellent chemical stability, and the unique advantages of electronic band structure. But due to the material properties of the polymer, the g-C3N4photocatalyst has some problems, such as small specific surface area, recombination of generated electron-hole serious, low quantum efficiency and larger band gap, inefficiency use of solar etc, which restrict its application in energy and environmental photocatalysis. Therefore, in order to make a better use of sunlight, preparing g-C3N4 optimized and modified to obtain a higher visible light responsive is necessary.

In this paper, graphite phase carbon nitride (g-C3N4) was prepared by two kinds of simple methods. Meanwhile, XRD、UV-Vis、SEM、TEM、BET、TGA and other experimental methods were used to study the effects of different preparation conditions on the structure and catalytic properties of g-C3N4. Some conclusions have been made as follows:

(1) A metal-free photocatalyst g-C3N4with layer structure was prepared by calcining dicyandiamide, showing high visible-light photocatalytic activity for the degradation of methyl orange in water. X-ray diffractometer (XRD)、scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize the structure of photocatalyst g-C3N4. The results indicate that the photocatalyst is graphite-like carbon nitride and the size of the particles is about 5-7 nm. The spectrum of UV-vis absorption indicates that the absorption edge of the g-C3N4 was 460 nm,corresponding to the band gap energy of 2.7 eV. The degradation experiments of methyl orange in water show that its degradation efficiency can reach 86.2% in 2.5 h. The photocatalytic mechanism experiments indicate that h+and • O2- play a major role in the degradation of methyl orange in water.

(2) A photocatalyst g-C3N4 with nanorod morphology was prepared by hydrothermal in acetonitrile with cyanuric chloride and melamine. X-ray diffractometer (XRD), scanning electron

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