铋系层状半导体同质结的构筑、能带调控及光催化特性研究

Separation efficiency of photogenerated charge carriers is an important factor determining performance of photocatalysts. Fabrication of homojunction, capable of effectively increasing the separation of charge carriers without introduction of other elements, is hopeful to become one of the most effective way to increase photocatalytic performance, but current fabrication methods of homojunctions are few and their mechanism research must be deepened. Especially, homojunction research on bismuth-based layered semiconductors has been little reported. Thus, this project intends to focus on bismuth-based layered semiconductors, tune their energy band structures by several methods, such as changing micromorphologies (e.g. shape and exposed crystal facets), adjusting surficial structure (e.g. defect amount) and self-doping of elements, and clarify related mechanisms. Afterwards, homojunctions will be fabricated by methods of in-situ growth and mixture calcination after choosing energy band-matching samples from as-prepared materials with different band gap levels, after which the component ratios in the homojunctions will be optimized. We will systematically investigate the relationship among energy band structures of homojunctions, separation efficiency of photoinduced charge carriers and photocatalytic activity, and, associating experimental and theoretical results, learn and illustrate the mechanisms for homojunction formation and homojunction-induced photoactivity enhancement from the level of energy bands. This project will not only provide effective accommodation methods of bismuth-based semiconductor energy band structures and a series of high efficient homojunctions, but also enrich basic theory of semiconductor homojunctions and pave the way for other homojunction construction.

光生载流子分离效率是决定光催化剂活性的重要因素。构筑同质结可有效提高载流子分离效率而又无需引入其它元素，有望成为提高光催化剂活性最有效的手段之一，但当前同质结构筑方法较少，机理研究需进一步深化。特别是对于铋系层状半导体，同质结研究还鲜见报道。因此，本项目拟以铋系层状半导体为研究对象，通过改变微观形貌（形状、暴露晶面等）、调节表面结构（如缺陷数量）及元素自掺杂等方法调控半导体能带结构，阐明调控机制，并从所制备能带结构各异的材料中选取能带匹配的样品，采用原位生长、混合煅烧等方法构筑同质结，优化同质结组成，系统研究同质结能带结构、光生载流子分离效率及光催化活性间的内在关系，结合实验及理论计算结果，从能带水平上认识和揭示同质结形成及增进光催化活性的机理。本课题不仅可凝练出铋系半导体能带结构的有效调控方法，合成出系列高活性同质结，而且能够极大丰富半导体同质结基础理论，为其它同质结构筑提供借鉴和指导。

二维层状半导体光催化剂（如铋系材料和聚合氮化碳）具有较大应用前景，但由于光生电荷分离效率低、可见光吸收弱、比表面积小等原因，其光催化活性还无法满足实际应用需求。在本项目资助下，我们主要采用三个策略增强铋系半导体和聚合氮化碳（CN）的光催化性能。首先，构建同质结和异质结：分别采用无溶剂法和氰尿酸阻聚法成功合成了BiOCl同质结和CN同质结，重点揭示了形貌对材料能带结构的影响，阐明了同质结形成及增进光生电荷分离机理，从而诠释了材料光催化活性显著提高的原因，为后续同质结研究提供了理论支撑；通过表面原位生长或沉积法制备了In(OH)3/Bi2MoO6、ReS2/CN、共轭聚烯/CN、CuInS2/WO3等异质结，确认了材料的结构、组成，详细表征了材料的物理化学性质（比表面积、光吸收、光电化学性质等）和光催化性能，探究了其能带匹配和光生电荷迁移机制，阐释了构效关系。其次，通过元素掺杂调控材料能带结构：首次采用“高价金属盐氧化法”制备了高稳定性的Mn、Sn和Sb掺杂的CN，考察了掺杂离子对材料结构、性质、能带结构和光催化活性的影响，并与采用传统方法制备的In掺杂CN的稳定性和光催化活性进行对比，表明了新方法的有效性；首次合成了Si掺杂CN，发现Si替换C可显著增进材料的光生电荷分离和光催化性能；通过详细考察Fe掺杂对Bi2WO6能带结构的影响，进一步阐明了金属掺杂对层状半导体能带结构的有效调控作用。最后，采用酸/乙醇处理成功合成了介孔三聚氰胺，并以此为前驱体制备了多级介孔CN，探究了介孔形成机理，可为基于介孔CN光催化剂的制备提供技术指导。本项目的顺利完成，极大丰富了同质结、金属掺杂CN和多级介孔CN的制备技术及相关基础理论，具有巨大的潜在应用价值和重要的理论指导意义。