铋系氧化物薄膜制备及光电性能研究

发布时间：2018-02-26 16:53

本文关键词： BiVO_4 薄膜静电诱导自组装光电性能光催化　出处：《陕西科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：铋系氧化物由于其具有无毒,可见光响应,储量丰富等优势而被认为是一种在光催化领域有研究前景的光催化材料。目前对其的研究主要集中在粉体光催化剂上,而其在降解过程中存在着在水中易凝聚、失去活性、使光的穿透力受阻,难于分离和回收和不适用于连续流体体系等问题限制了其在光催化领域的广泛应用。而采用适当的方法将铋系氧化物制备成薄膜便有望突破上述限制。为此本工作采用静电诱导层层自组装和旋涂法的方法合成铋系氧化物薄膜,研究了其工艺对其形貌结构,光电性能,催化效果等的影响,探讨BiVO_4薄膜的生成机理,研究薄膜的光电性能与光催化性能之间的联系;揭示其内部电荷运动规律以及催化机理。主要研究内容如下:(1)用静电诱导层层自组装的方法制备单斜相BiVO_4薄膜。前驱液浓度为0.01 mol/L,晶化温度为500 oC时制备的单斜相BiVO_4薄膜具有较高的光生电子-空穴分离率和电荷转移效率,可见光下照射180 min后对罗丹明B降解率为26%。反应初期,功能化的基板诱导吸附[Bi(NO_3)_3VO_2]~+胶粒,形成[Bi(NO_3)_3VO_2]-O-FTO前驱薄膜层,前驱液中酸性的逐渐减弱,溶液中形成电中性的BiOVO_3胶核,被基板上[Bi(NO_3)_3VO_2]层诱导吸附,形成(BiOVO_3)[Bi(NO_3)_3VO_2]层,随着时间的增加溶液的zeta电位逐渐增加,形成[(BiOVO_3)NO_3]~-胶粒,被基板上(BiOVO_3)[Bi(NO_3)_3VO_2]层诱导吸附,形成[(BiOVO_3)NO_3](BiOVO_3)[Bi(NO_3)_3VO_2]层,随着时间的增加,前驱液中NH~(3+),被进一步吸附,形成NH_3[(BiOVO_3)NO_3](BiOVO_3)[Bi(NO_3)_3VO_2]层,晶化处理后形成BiVO_4薄膜。(2)用静电诱导层层自组装的方法制备出BiVO_4/Ti O_2复合薄膜。复合薄膜中BiVO_4与TiO_2之间形成了类p-n结的界面结构,电子从BiVO_4向TiO_2方向传递、空穴从TiO_2向BiVO_4方向传递。光照瞬间复合薄膜没有出现明显的阳极尖峰表面电子复合率降低。复合薄膜与单一薄膜相比拥有高的氧化能力和载流子浓度。(3)用旋涂法制备CeO_2/Ce_xBi_(2-x)WO_6电极薄膜,发现CeO_2/Ce_xBi_(2-x)WO_6异质结形成的负光电流现象与光催化过程中空穴和超氧自由基为活性物种有关,异质结结构的存在增加了光生电子-空穴分离率以及减少了电荷转移时间。CeO_2/Ce_xBi_(2-x)WO_6光催化效果改善的因素主要是由于异质结结构光生促进电荷和Ce~(3+)的取代导致光生电子-空穴的复合过程的延缓。(4)微波溶剂热中乙醇和Er~(3+)能抑制Bi_2WO_6的形成。煅烧后形成高结晶性的Er~(3+)掺杂Bi_(2-x)Er_xWO_6晶体,用旋涂法制备将Bi_(2-x)Er_xWO_6光电极。Er~(3+)掺杂使Bi_(2-x)Er_xWO_6电极表面光电子复合率增加为70.93%和表面光电流增加,具有较高的氧化能力和可移动电子。电极的电荷转移电阻从1415 kΩ减到826.1 kΩ,表明电子-空穴分离率较强。电极在波长为542 nm和654 nm处出现光电转换特征峰。其光电流较大的原因主要是由于Er~(3+)掺杂引入了大量缺陷和Er~(3+)所带来的上转化效应引起的。
[Abstract]:Bismuth oxide is considered to be a promising photocatalyst in the field of photocatalysis due to its advantages of nontoxic, visible light response and abundant reserves. At present, the research on bismuth oxides is mainly focused on powder photocatalysts. In the process of degradation, it is easy to agglomerate in water and lose its activity, which hinders the penetration of light. It is difficult to separate and recover and is not suitable for continuous fluid systems, which limits its wide application in photocatalysis. However, it is expected to break the above limit by using appropriate methods to prepare bismuth oxide thin films. Bismuth oxide thin films were synthesized by electrostatic induced layer-by-layer self-assembly and spin-coating. The effects of the process on the morphology, photoelectricity and catalytic performance of BiVO_4 films were studied. The formation mechanism of BiVO_4 films and the relationship between the photocatalytic properties and the optoelectronic properties of the films were studied. The main research contents are as follows: (1) monoclinic BiVO_4 thin films were prepared by electrostatic induction layer by layer self-assembly. The monoclinic BiVO_4 films were prepared at the precursor concentration of 0.01 mol / L and the crystallization temperature of 500oC. Phase BiVO_4 thin films have high photoelectron hole separation rate and charge transfer efficiency. The degradation rate of rhodamine B under visible light irradiation for 180 min was 26.5%. At the beginning of the reaction, the functional substrate induced adsorption of [Bi(NO_3)_3VO_2] ~ colloid particles to form [Bi(NO_3)_3VO_2] -O-FTO precursor film layer. The acidity of the precursor solution gradually weakened, and an electrically neutral BiOVO_3 gel nucleus was formed in the solution. The [Bi(NO_3)_3VO_2] layer was induced to adsorb on the substrate to form a [Bi(NO_3)_3VO_2] layer. With the increase of time, the zeta potential of the solution gradually increased, resulting in the formation of [BiOVO3HNO3]-Bi(NO_3)_3VO_2 particles, which were induced to be adsorbed by the BiOVO3] [Bi(NO_3)_3VO_2] layer on the substrate, forming a [BiOVO3No3] BiOVO3] [Bi(NO_3)_3VO_2] layer. With the increase of time, NH~(3 in the precursor solution was further adsorbed. The formation of NH_3 [BiOVO3No3] BiOV _ 3] [Bi(NO_3)_3VO_2] layer, after crystallization, the formation of BiVO_4 thin films. (2) BiVO_4/Ti O _ 2 composite films were prepared by layer by layer self-assembly method induced by static electricity. The interface structure between BiVO_4 and TiO_2 was formed, and electrons were transferred from BiVO_4 to TiO_2. Hole transfer from TiO_2 to BiVO_4. There is no obvious decrease of electron recombination rate on anodic peak surface of the composite film. The composite film has higher oxidation ability and carrier concentration than single film. Preparation of CeO_2/Ce_xBi_(2-x)WO_6 electrode films, It was found that the negative photocurrent in the formation of CeO_2/Ce_xBi_(2-x)WO_6 heterostructures was related to the existence of holes and superoxide radicals as active species during photocatalysis. The existence of heterojunction structure increases the photoelectron hole separation rate and reduces the charge transfer time. Ceo\%\%\%\% Cex\\%\%\%\%\%\%\%\%\%\%\%\%\\%\\%\\\%\\\. The delay in the process of electron-hole recombination. (4) ethanol and Er~(3 in microwave solvothermal can inhibit the formation of Bi_2WO_6. After calcination, a highly crystallized Er~(3) doped Bi_(2-x)Er_xWO_6 crystal is formed. The photoelectron recombination rate on the surface of Bi_(2-x)Er_xWO_6 electrode was increased to 70.93% and the photocurrent on the surface was increased by doping Bi_(2-x)Er_xWO_6 photoelectrode. The charge transfer resistance of the electrode was reduced from 1415 k 惟 to 826.1 k 惟, indicating that the electron-hole separation rate was strong. The photoelectricity conversion peak appeared at the wavelength of 542 nm and 654 nm. The reason for the large flow is mainly due to the introduction of a large number of defects in Er~(3 doping and the upconversion effect brought about by Er~(3).
【学位授予单位】：陕西科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2

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