BiVO4/石墨烯异质界面的电子态与光催化性能研究

The shortage of renewable energy and deterioration of environmental pollution become two crucial issues restricting the sustainable development of society in the long-term future. Semiconductor photocatalysis which has potential applications in degradation of pollutants and water splitting is believed to be one of the main approaches to solve these two problems simultaneously. How to effectively separate the photo-induced electrons and holes is crucial to improve the quantum yield and catalytic activity. Previous investigations have illustrated that both the difference in band edge energy and the built-in electric field cross the semiconductor heterojuction can be used for that purpose, moreover, the band offset near the interface is dominant in the charge separation. However, the dependence of the band offset on the interface structure as well as the doping state is unclear. In this proposal, taking BiVO4/graphene heterojuction as an example, first-principle will be exploited to calculate and analyze the energy and bonding state of interface, according to the crystal symmetry, atoms at some typical lattice points will be substituted for interface doping, and stable interface configurations will be determined referencing to the energetics and bonding states. Based on this, the changes in the energy band structure, partial density of states and absorption spectrum are studied, and the effect of doping elements on the band offset will be discussed. Typical doped samples with given crystal orientation will be prepared in experiment. PL spectrum will be measured to disclose the suppressive effect of heterojunction on the recombination of electrons and holes. As for typical heterojunction samples, photocatalysis tests will be carried out experimentally, and try to clarify the physical mechanism for the enhanced photocatalysis of BiVO4/graphene. The results will be helpful to the design of new-type semiconductor photocatalysis.

可再生能源的短缺和环境污染的恶化成为制约社会长远发展的重大问题，半导体光催化降解污染物或分解水制氢成为解决此类问题的重要途径之一。如何有效分离光生电子和空穴是提高半导体光催化剂量子产率和活性的关键。研究表明，利用半导体异质结的内建电场或能级差可达到这一目的，且已明确界面处带边偏移量的制约作用。然而，关于带边偏移量与界面结构及掺杂状态的关联关系仍不明朗。本项目拟以BiVO4/石墨烯异质结为例，计算分析界面能和界面键合状态，根据晶体对称性进行替位式掺杂，确定掺杂界面的稳定构型；考察其电子结构、态密度及吸收光谱的变化，探讨界面掺杂元素对带边偏移量的调控作用；制备典型界面取向及掺杂的异质结样品，基于PL光谱测量揭示异质结对电子-空穴对复合的抑制作用；进行光催化降解实验，结合理论分析，阐明BiVO4/石墨烯异质结对光催化特性增强的物理机制，为新型半导体光催化剂的设计提供参考。

环境污染和能源危机是制约当前社会经济发展的两个重要问题。光催化材料既可以有效利用太阳能，又可以降解污染物，成为材料学领域的重要研究方向。本项目结合理论计算模拟和实验表征分析，系统研究了BiVO4基纳米复合材料的基本物理特性及其光催化性质，已顺利完成了各项研究内容，达到预期目标。部分研究结果已在Journal of Materials Science, Computational Materials Science, RSC Adv, The European Physical Journal B, Physica E, Materials Science and Engineering B等国际期刊发表学术论文24篇，其中SCI检索22篇。培养硕士研究生2名。课题负责人和研究生等参加相关学术研讨班4人次。取得的重要进展有：(1) 基于第一性原理计算揭示了压力对BiVO4的力、电、光及催化性能的影响规律，发现T-1相和M相表现几乎相同的光学特性；(2) 发现BiVO4在任何情况下都是间接带隙半导体，带隙随压力的增加而减小，O 2p、V 3d和Bi 6s电子态的杂化增强，使带边向较低的能量转移，介电函数、光学折射率、吸收系数和反射率在低能区发生红移；(3) 基于第一性原理计算发现 O空位导致BiVO4由间接带隙变为直接带隙，且增强了O 2p、V 3d和Bi 6s轨道的杂化，带隙减小，静态介电常数和折射率均大于理想的BiVO4；(4) 发现O空位导致介电函数、折射率、吸收系数、反射率、损失函数和电导率在低能量范围发生红移；（5）研究了不同浓度的N、Fe掺杂单斜相BiVO4的能带结构和态密度。相比于理想BiVO4，N掺杂使材料的禁带宽度变窄，其中1×1×1和2×1×1结构为间接带隙半导体，表现为金属导电，2×2×1超晶胞结构变为直接带隙，其禁带宽度值最小，表现为半导体特性。说明N掺杂浓度不同导致材料具有不同的导电性；Fe掺杂未改变1×1×1晶胞的导电性，仍保持半导体特性，Fe掺杂BiVO42×1×1、2×2×1晶胞时材料展现金属性；(6) 发现利用乙二醇和乙二胺辅助的水热法合成BiVO4时，当PH值从1到7变化时，BiVO4的形貌从花生状、捆状、花状到星状变化，选择合适的V源及Bi源制备了不同形貌的BiVO4和Ag纳米颗粒复合的结构，复合界面对光催化性能有增强效应。