基于Aurivillius-Sillenite结构光催化材料的性能调控研究

Photocatalysis is one of the major technologies for the energy and environmental fields, involving the production of fuels/chemicals and in the clean-up of hazardous or polluting wastes. However, the performance of photocatalyst is weakened by bulk recombination at large applied potentials. Therefore, attempts were made to increase electron-hole separation in these semiconductors. The 2-D nanosheet structured semiconductors with the Aurivillius-Sillen phases, would be found to be suitable for photocatalytic applications due to their unique layered structure and the existence of a strong electric field between the halide and [Bi2O2]2+ layer in favour of effective separation and diffusion of the electron-hole pair. It draws interest to reveal the relationship between the electron structures, crystal structures and photocatalytic properties as so to direct the research on photocatalysts to achieve high photocatalytic activities. This proposal focuses on (1)tailoring the composition and thereby the band gap of the semiconductors with Aurivillius-Sillen phases by the theoretical calculation.(2) We will tune the microstructures and band structure of the photocatalysts by inducing different ionic coordination polyhedron. The interaction between the ns2np0 electron lone-pair of Bi3+ and different ionic coordination will induce the deformation and polarization, which couples with the internal electric field will affect the band structure and diffusion of the charge carriers. (3)Photocatalytic activities of the as-synthesized samples will be evaluated by photoreduction of CO2 and water splitting. The relationship between the electronic configuration, crystal structure and photocatalytic properties would be set up and revealed.(4) The theoretical calculation and the experimental results will be used to interpret the influence of the ionic coordination polyhedron on the photocatalytic activities of the photocatalysts and to enhance the photocatalytic efficiencies. On the base of investigation of mechanism, novel and highly efficient visible light photocatalysts will be synthesized and applied.

针对光催化材料中光生电子-空穴对容易复合、迁移效率低等容易导致光电转换效率低下的问题，本项目拟以二维超薄Aurivillius-Sillenite结构的光催化材料为研究对象，研究其晶体结构-材料维度-光催化性能三者之间的关系，探索影响光生载流子分离/迁移的内在机制等基础科学问题。具体包括：理论分析计算引入离子配位多面体对材料能带结构和成键机制的影响；制备出具有二维超薄结构的Aurivillius-Sillenite结构的光催化材料，研究离子配位多面体偶极矩极化效应与层间内电场相互协同作用对载流子分离/迁移的影响；对含有不同配位多面体及不同尺度的样品进行光催化性能表征，进而指导合成高效的光催化材料；将实验与理论预测结果相结合，揭示光生载流子在二维超薄Aurivillius-Sillenite结构材料中的分离/迁移规律，深刻认识光电材料中载流子输运的物理机制,实现对高效光催化材料的制备与应用。

提高光催化反应的效率在于解决催化材料中光生电子-空穴对容易复合、迁移效率低等问题，本项目以Aurivillius–Sillenite结构的光催化材料为研究对象，研究其晶体结构-材料维度-光催化性能三者之间的关系，探索影响光生载流子分离/迁移的内在机制等基础科学问题。具体包括以下两个部分：(1)光催化材料的尺度、微观结构调控与光催化性能之间的规律性研究。通过调控合成条件，获得了量子尺寸到亚微米尺寸厚度可调的BiOCl、BiOIO3等具有典型Aurivillius–Sillenite结构的光催化材料。进一步的光解水反应及依赖于牺牲剂的光催化析氢反应结果表明， 通过调控光催化材料的二维厚度，可以调控材料的能带结构和表面性能，为开发新型高效的光催化材料提供了新的思路和实验基础。特别是将具有较大的偶极距的IO3-离子引入到[Bi2O2]2+夹层结构中，使得晶体内部由于正负电荷不对称而产生极性，这种极性结构延<001>方向周期性排列，在材料内部产生了延该方向的极化电场。这种内建电场的强度随着极性结构的增加而增强，即在极化方向上厚度增加，内建电场的强度增强，更加有利于光生载流子的分离，减少了电子和空穴的复合几率，从而提高光催化反应效率。此外，通过对介孔WO3材料的表面氟化处理，基于氟离子较强的电负性，在材料表面形成局部极化场，促进了空穴与电子的分离。空穴氧化OH-产生的活性自由基•OH对苯甲醇进行氧化，使得空穴对苯甲醇的氧化过程转化为间接氧化过程，实现了在水体系中苯甲醇到苯甲醛选择性氧化过程中超高的选择性(~99%)和较高的转化率(~57%)。（2）基于内建电场性质的压电催化性能探究。基于（1）部分的研究工作，发现了卤氧化铋、二硫化钼等材料具有一定的压电响应性，进而分别开展了超声激发MoS2分解水生成氢气，以及超声激发BiOCl压电催化水和氧反应生成H2O2的反应。这种压电效应与催化作用耦合的思想，为半导体催化以及纳米能量转换器件提供了新的解决思路，有望拓宽压电材料在催化领域的应用。