离子液体中钒酸铁基材料的设计及其增强光催化性能研究

发布时间：2018-09-07 16:17

【摘要】：自上世纪以来,环境污染和能源短缺问题日渐突出,研发绿色能源是趋大势之举。在现有众多可再生资源中,太阳能作为绿色环保、安全无害以及储量最大的资源,利用前景极为广阔。光催化技术作为一项可直接将太阳能转化为化学能的新兴技术,可有效利用太阳光进行能源转化和环境净化,是同时实现环保和节能的有效途径。在光催化技术中,光催化材料的设计至关重要。如今,研发高效实用的新型光催化剂已成为光催化领域的研究热点,通过构建异质结体系以开发新型高效半导体光催化剂是常用的有效策略。本文旨在以铁基离子液体为铁源,探索新型钒酸铁(FeVO_4)催化剂的合成及其复合光催化材料在环境净化方面的应用。文中通过简单可控的方法制备了FeVO_4、gC_3N_4/FeVO_4和Ag_3VO_4/FeVO_4三种新型光催化材料,采用多种表征手段确定上述光催化材料的微观结构、形貌及光学性能。同时在可见光辐照条件下考察上述材料降解有机污染物的光催化活性及稳定性。最后对光催化材料的结构及其活性之间的关系展开了深入研究,并提出了相应的光催化机理。具体研究内容如下:(1)以1-辛基-3-甲基咪唑四氯合铁([Omim]FeCl4)为铁源,通过离子液体辅助水热和煅烧两步法制得介孔FeVO_4纳米棒光催化剂。通过对该材料进行X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、紫外-可见漫反射光谱(DRS)和比表面积分析(BET)等一系列基础表征方法确定其表观结构、形貌及内在光电性能。结果表明离子液体中所制备的介孔FeVO_4纳米棒光催化材料形貌均一,孔径(3-7 nm)分布均匀,且具有较大的比表面积(255.83 m2/g)。所制备的催化剂禁带宽度为2.35 eV,有较宽的紫外可见光谱吸收范围。同时,在可见光辐照条件下,光催化活性实验显示介孔FeVO_4纳米棒类芬顿光催化剂不仅可应用于有色染料(罗丹明B)的快速有效降解,还对四环素无色有机污染物也具有较高的光催化降解性能。此外,通过与常规的无机盐为铁源制备的FeVO_4纳米材料对比可知,离子液体中合成的FeVO_4具有更为优良的表面性能、光电化学性能和光催化活性。由此可确定离子液体[Omim]FeCl4在材料制备过程中不但可作为反应源,还可作为模板剂对纳米棒的形成以及结构性能的调控起到了重要作用。最后提出了FeVO_4作为一种三效异相光芬顿催化剂降解污染物的可能机理。(2)通过水热合成法成功制备了g-C_3N_4/FeVO_4光催化剂。采用XPS、FT-IR、SEM、TEM和DRS等基础表征方法确定材料的表观结构、形貌及光学性能。表征结果表明,FeVO_4纳米棒均匀分布并附着在薄层g-C_3N_4表面,并在两者接触界面处形成异质结结构;薄层g-C_3N_4的引入拓宽了FeVO_4的光吸收阈值,提高了其光生载流子的迁移传输效率;可见光催化降解实验结果表明,在光催化反应6 h后,20 wt%g-C_3N_4/FeVO_4对RhB降解效率(99.4%)最高,而薄层g-C_3N_4和FeVO_4的RhB降解效率分别为74.5%和14.7%。光催化机理分析表明,g-C_3N_4和FeVO_4之间的能带位置匹配良好,有利于光生载流子的传输和分离,从而导致g-C_3N_4/FeVO_4光催化性能相比于单体有极大提升。(3)通过原位合成法成功制备了Ag_3VO_4/FeVO_4光催化剂。采用XRD、XPS、SEM、TEM、DRS和PL等基础表征确定材料的表观结构、形貌及光学性能。表征结果表明,Ag_3VO_4颗粒均匀分布并附着在FeVO_4纳米棒表面,并在两者接触界面处形成异质结结构;Ag_3VO_4的引入拓宽了FeVO_4的光吸收阈值,提高了材料光生载流子的迁移传输效率;可见光催化降解实验结果表明,在光催化反应3 h后,40 wt%Ag_3VO_4/FeVO_4对RhB降解效率(99.7%)最高,而Ag_3VO_4单体的RhB降解效率仅为59.4%。光催化机理分析表明,Ag_3VO_4和FeVO_4的能带位置匹配良好,有利于光生载流子的传输和分离,从而致使Ag_3VO_4/FeVO_4光催化性能相比于单体有极大提升。
[Abstract]:Since the last century, the problem of environmental pollution and energy shortage has become increasingly prominent, and the development of green energy is a trend. Among the many existing renewable resources, solar energy, as a green, safe and harmless resource with the largest reserves, has a very broad prospect of utilization. Nowadays, the research and development of new photocatalysts with high efficiency and practicability has become a hot spot in the field of photocatalysis. Heterojunction system can be constructed to develop new photocatalysts. New efficient semiconductor photocatalysts are commonly used as effective strategies. The purpose of this paper is to explore the synthesis of novel ferric vanadate (FeVO_4) catalysts and the application of their composite photocatalytic materials in environmental purification using iron-based ionic liquids as iron sources. Three novel photocatalytic materials, FeVO_4, gC_3N_4/FeVO_4 and Ag_3VO_4/FeVO_4, have been prepared by simple and controllable methods. The microstructure, morphology and optical properties of the photocatalytic materials were determined by various characterization methods. The photocatalytic activity and stability of the materials for degradation of organic pollutants were investigated under visible light irradiation. The specific research contents are as follows: (1) Mesoporous FeVO_4 nanorod photocatalyst was prepared by ionic liquid assisted hydrothermal method and calcination using 1-octyl-3-methylimidazolium ferric tetrachloride ([Omim] FeCl_4) as iron source. The results show that the mesoporous FeVO_4 nanorods prepared in ionic liquids have uniform morphology, uniform pore size (3-7 nm) distribution and large specific surface area (255.83 m2/g). The band gap of the catalyst is 2.35 eV and the absorption range of UV-Vis spectrum is wider. At the same time, the photocatalytic activity experiment shows that the mesoporous FeVO_4 nanorod-like Fenton photocatalyst can be used not only for the fast and effective degradation of colored dye (Rhodamine B), but also for the colorless organic pollutants of tetracycline. In addition, compared with the conventional inorganic salts as iron source, the synthesized FeVO_4 nano-materials have better surface properties, photoelectrochemical properties and photocatalytic activity. As a template, FeVO_4 plays an important role in the formation of nanorods and the regulation of their structure and properties. Finally, the possible mechanism of FeVO_4 as a three-way heterogeneous photocatalyst for the degradation of pollutants is proposed. (2) The g-C_3N_4/FeVO_4 photocatalyst was successfully prepared by hydrothermal synthesis. The basic characterization methods such as XPS, FT-IR, SEM, TEM and DRS were used to confirm the results. The characterization results show that the FeVO_4 nanorods are uniformly distributed and adhere to the thin layer of g-C_3N_4 and form a heterojunction structure at the contact interface between the two materials; the introduction of thin layer of g-C_3N_4 broadens the optical absorption threshold of FeVO_4 and improves the transport efficiency of the photogenerated carriers; and the visible-light catalysis decreases. The results showed that 20 wt% g-C_3N_4/FeVO_4 had the highest degradation efficiency (99.4%) for RhB after 6 h of photocatalytic reaction, while the degradation efficiency of thin layer g-C_3N_4 and FeVO_4 was 74.5% and 14.7% respectively. The photocatalytic mechanism analysis showed that the energy band position between g-C_3N_4 and FeVO_4 matched well, which was beneficial to the transmission and separation of photogenerated carriers, and thus conducting. (3) Ag_3VO_4/FeVO_4 photocatalyst was successfully prepared by in-situ synthesis. The material was characterized by XRD, XPS, SEM, TEM, DRS and PL to determine the apparent structure, morphology and optical properties. The characterization results showed that Ag_3VO_4 particles were uniformly distributed and adhered to FeVO_4 nanorods. The introduction of Ag_3VO_4 broadened the optical absorption threshold of FeVO_4 and improved the transport efficiency of photogenerated carriers. The results of visible-light photocatalytic degradation showed that 40 wt% Ag_3VO_4/FeVO_4 had the highest degradation efficiency (99.7%) for RhB after 3 h of photocatalytic reaction, while Ag_3VO_4 had the highest degradation efficiency (99.7%) for RhB. The photocatalytic degradation efficiency of Ag_3VO_4 and FeVO_4 was only 59.4%. The analysis of photocatalytic mechanism showed that the band positions of Ag_3VO_4 and FeVO_4 matched well, which was beneficial to the transmission and separation of photogenerated carriers, and the photocatalytic performance of Ag_3VO_4/FeVO_4 was greatly improved compared with that of monomer.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;X505

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