缺陷对TiO2光催化性能的影响：PAT和HRTEM研究

TiO2-based materials have attracted intense research attention in a broad range of applications, such as organic pollutants degradation, hydrogen production via water splitting, solar conversion, catalysis, and sensor. However, The photocatalytic reactivity is highly influenced by the kind and quantityof vacancy and defect of the crystal. Do the vacancy and defects promote or inhibit the photocatalytic activy? This problem is under controversy up to date. It is difficult to find suitable photocatalysts possessing accurate surface and bulk defects and vacancies to characterize their photocatalytic reactivity, which is the greatest challenge. We plan to prepare three kinds of TiO2 crystals: single crystal, mesocrystal and polycrystal, that possess the almost identical morphology, crystal phase and proportion of crystal facets. Especially, the TiO2 mesocrystal, that possesses the controlled subcrystals and the ordered architecture at some extent, can be regarded as an intermediate between single crystal and polycrystal.We are going to perform a systematic research on the life-time of positrons in the three crystals via PAT combined with other advanced techniques,such as HRTEM and TRDRS, so as to exactly confirm the quantification of the surface defect, disfigurement in crystal lattice and defect unit in the ordered architecture. Then the photocatalytic reactivity can be obtained via characterizing the quantum efficiency of oxidation reaction of nitrobenzene with oxygen and reduction of nitrosobenzene. Thus the issue that cannot be resolved for a long time can be settled via the model reaction. It can provide a valuable theorematical foundation for the practical industry application of TiO2 crystals.

空位和缺陷严重影响TiO2的光催化效率，但促进还是抑制的争论一直存在。解决这个难题的最大挑战是难以制备准确控制表面和晶格缺陷种类和数目的材料，建立模型考察其对应的光催化效率。本研究课题首先制备相同形貌的三类TiO2光催化材料：单晶、介晶和多晶，特别是介晶（mesocrystals）TiO2,它是由可控的微晶单元在一定程度上的有序组装体，正好介于单晶和多晶之间，利用正电子湮灭技术(PAT)结合高分辨电镜(HRTEM)和时间分辨漫反射光谱(TRDRS)等技术对三类二氧化钛晶体中正电子的寿命的进行系统研究和比较，准确定量表面空位缺陷、晶格缺陷和长程有序的单元缺陷，然后模型光催化半反应，如氧化（亚硝基苯/O2）-还原(亚硝基苯/甲醇),测定其量子效率，由此构效关系解决长期以来悬而未决的是表面缺陷、晶格序排列还是晶格缺陷决定光生电子-空穴的复合速率的问题，从而确定缺陷与光催化活性的关系。

空位和缺陷严重影响TiO2的光催化效率，但促进还是抑制的争论一直存在。解决这个难题的最大挑战是难以制备准确控制表面和晶格缺陷种类和数目的材料，建立模型考察其对应的光催化效率。本研究课题首先制备相同形貌的TiO2单晶、介晶和多晶，利用正电子湮灭技术、高分辨电镜、和瞬态荧光对缺陷的类型、浓度、分布和寿命进行系统的分析；利用吸附/脱附和原位红外等技术对缺陷种类及分布进行系统研究；结合催化剂降解有机污染物和光催化分解水产氢的性能构建催化剂缺陷微结构与性能的内在联系。由此构效关系解决长期以来悬而未决的是表面缺陷、晶格序排列还是晶格缺陷决定光生电子-空穴的复合速率的问题，从而确定缺陷与光催化活性的关系。研究表明，有序的介晶微结构有利于光生电子和空穴的分离和传输，从而提高了光催化性能；缺陷调控的同时，对金属氧化物半导体催化剂表面的活性物种有一定影响，增加表面氧缺陷导致表面酸性降低，特别是Bronsted酸，从而降低了催化剂的光催化活性；此外，表面氧缺陷的增多产生可见光吸收，但降低了紫外吸收，因此不能全面提高光催化性能。本研究为金属氧化物半导体缺陷工程和表面物种的调控来改善催化剂的光催化性能提供了有力的参考。