单斜相钒酸铋的光催化及光电化学性能研究

发布时间：2018-02-14 00:52

本文关键词： 钒酸铋光催化光电化学氮化碳多孔结构　出处：《兰州理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：太阳光照射下,光催化及光电催化分解水能够从水中产生绿色的氢气已经受到了广泛的关注。然而,在提高能量转换效率方面仍然存在诸多挑战,例如,利用宽波长的光子来制备氢气,促进特定波长下的反应效率,以及提高半导体材料的寿命。由于光催化和光电催化材料的半导体特性决定着光照时材料是否能被激发,以及有多少光生载流子能够迁移到分解水的反应表面。因此,调控这些特性是发展光分解水的最主要方面。首先,对于一个特定的半导体材料,表面修饰不仅能够活化半导体来分解水,而且可以促进电荷分离、提升半导体材料在光激发时的稳定性。其次,形成p-n结对光电化学分解水的效率有显著影响。本文利用单斜相钒酸铋半导体材料具有可见光响应的优点,分别构建了钒酸铋基的三元复合的纳米片光催化剂以及多孔结构的光电阳极并对其表面进行了助催化剂修饰。通过各种表征手段对催化剂的结构、组成、形貌等物理化学性质进行表征分析,在可见光下降解有机染料作为模型反应研究所制备光催化剂的活性,以及光电流密度和光电化学产氢能力来考察光电阳极的光电化学性能。主要的研究内容与结果如下:(1)利用乙醇胺作为形貌控制剂,通过水热法一步合成BiOCl/BiVO4复合纳米片,后又将金属Bi用原位还原法沉积在该纳米片表面。最终得到的Bi/BiOCl/BiVO4三元复合纳米片同时具有p-n异质结和金属表面等离子共振结构。光催化和光电化学性能测试结果表明,该新型的具有混合结构的光催化剂具有可见光下优异的对RhB的降解能力和瞬态光电流响应。(2)通过简单的滴涂-焙烧法,一步合成孔径可调的BiVO4纳米多孔薄膜。表征和测试结果表明,孔径分布在300-400 nm的BiVO4纳米多孔薄膜表现出优异的光吸收、电荷分离能力以及光电化学性能。更重要的是,我们探索并解释了导致多孔BiVO4光电阳极如此高效的光电转换效率的原因。具体来说,利用一种新型的检测手段,同步光照射光电子能谱(SIXPS)直接观测到了BiVO4纳米多孔薄膜内部光生电子-空穴的有效分离。另外,光学测试证明,多孔结构中存在光的衍射和限域效应,从而促进了对可见光的吸收。(3)利用简单的浸渍法将超薄的g-C3N4纳米片均匀地覆盖在纳米多孔的BiVO4光电极表面。并且通过新型的同步光照射光电子能谱(SIXPS)技术揭示了半导体材料体相内光生电荷的迁移过程,结果表明,超薄的g-C3N4纳米片能够有效抑制BiVO4中光生电荷的复合,而且光生空穴能快速迁移到纳米片表面进行氧化水的反应。另一方面,莫特-肖特基和电化学阻抗谱进一步表明超薄的g-C3N4层状结构能够显著提高载流子密度,促进光电极/电解液反应界面光生电荷的迁移。正如预期的一样,超薄的g-C3N4纳米片负载后的BiVO4多孔光电极呈现出比Co-Pi和FeOOH修饰的更加优异的光电化学氧化水性能。
[Abstract]:Photocatalysis and photocatalytic decomposition of water from water to produce green hydrogen from water has attracted widespread attention under sunlight. However, there are still many challenges in improving energy conversion efficiency, such as, Hydrogen is prepared by using photons of wide wavelength to promote the reaction efficiency at specific wavelengths and to increase the lifetime of semiconductor materials. Because the semiconductor properties of photocatalytic and photocatalytic materials determine whether the materials can be excited under light, And how many photo-generated carriers can migrate to the surface of the reaction to decompose water. Therefore, the regulation of these properties is the most important aspect of the development of photodissociated water. First, for a particular semiconductor material, Surface modification can not only activate semiconductors to decompose water, but also promote charge separation and enhance the stability of semiconductor materials under photoexcitation. The formation of p-n junction has a significant effect on the efficiency of photochemical decomposition of water. In this paper, the monoclinic bismuth vanadate semiconductor material has the advantage of visible light response. The composite nanocrystalline photocatalyst of bismuthyl vanadate and the porous photoanode were constructed, and the surface of the catalyst was modified with cocatalyst. The structure and composition of the catalyst were studied by various characterization methods. The physical and chemical properties, such as morphology, were characterized and analyzed. The photocatalyst was prepared by degradation of organic dyes under visible light as a model reaction institute. The photochemical properties of photoanode were investigated by photocurrent density and photochemical hydrogen production ability. The main contents and results are as follows: 1) using ethanolamine as morphology control agent, BiOCl/BiVO4 composite nanocrystals were synthesized by hydrothermal method. Then the metal Bi was deposited on the surface of the film by in-situ reduction method. The resulting Bi/BiOCl/BiVO4 ternary composite nanocrystals have both p-n heterojunction and metal surface plasmon resonance structure. The photocatalytic and photoelectrochemical properties of the composite nanocrystals are measured. The novel photocatalyst with mixed structure has excellent degradation ability and transient photocurrent response of RhB under visible light. One-step BiVO4 nano-porous films with adjustable pore size. Characterization and measurement results show that BiVO4 nano-porous films with pore size distribution between 300 and 400 nm exhibit excellent photoabsorption, charge separation and photochemical properties. We have explored and explained why the photovoltaic conversion efficiency of porous BiVO4 photoanode is so high. Simultaneous photoelectron spectroscopy (SIX PS) has directly observed the effective separation of photogenerated electrons and holes in BiVO4 nanoporous films. In addition, optical measurements show that there are diffraction and limiting effects of light in porous structures. Thus, the absorption of visible light is promoted. The ultra-thin g-C _ 3N _ 4 nanoparticles are uniformly covered on the surface of BiVO4 photoelectrode by a simple impregnation method, and the results are revealed by a new type of simultaneous photoelectron irradiation photoelectron spectroscopy (SIX) technique. The transfer process of photogenerated charges in the bulk phase of semiconductor materials, The results show that the ultrathin g-C _ 3N _ 4 nanoparticles can effectively inhibit the recombination of photogenerated charges in BiVO4, and the photogenerated holes can migrate rapidly to the surface of the nanoparticles for the oxidation of water, on the other hand, Mott-Schottky and electrochemical impedance spectroscopy further show that the ultra-thin g-C _ 3N _ 4 layered structure can significantly increase the carrier density and promote photoinduced charge transfer at the interface of photoelectrode / electrolyte reaction. The BiVO4 porous photoelectrodes supported on ultrathin g-C _ 3N _ 4 nanoparticles exhibit better photoelectrochemical oxidation performance than those modified by Co-Pi and FeOOH.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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