Synergetic effects of defects and acid sites of 2D-ZnO photocatalysts on the photocatalytic performance.

Regulation of defects and surface acidic sites of photocatalysts is an efficient approach to improve the photocatalytic activity. Ultrathin 2D-ZnO photocatalysts were prepared to uncover the synergetic effects of defects and surface acidic sites on the photocatalytic activity. The reaction constant for photocatalytic degradation of MB upon ZnO-S is 2.26, 2.82, 12.2 times higher than that of SH-500, SO-500, and ZnO-R, respectively. The results revealed that the surface defects, hydroxyl group and chemisorbed water played pivotal roles in the generation of reactive oxygen species (ROS). Although the limited improvement of visible absorption was achieved after introduction of oxygen vacancy (VO), the overall photocatalytic activity decreased due to the reduced ROS production capacity shown by density functional theory (DFT) calculations. Hydroxyl radical is the key ROS in degradation of organics, and electron contributes a little bigger than hole in the generation of hydroxyl radical. Importantly, the decrease in surface acidic sites resulted in the decreased photocatalytic activity, proven by the dynamics of photoinduced carriers. This study reveals that the improved photocatalytic activity of 2D-ZnO photocatalysts can be attributed to the synergetic effects of surface defects and acidic sites rather than the enhanced visible absorption resulted from the VO introduction.

Photocatalytic Properties Dependent on the Interfacial Defects of Intergrains within TiO2 Mesocrystals.

The regulation of interfacial defects of nanocrystals aligned orderly in a superstructured photocatalyst is an effective approach to improve the photocatalytic performance. However, the synthesis of ordered self-assemblies with abundant interfacial defects and reactive sites is hard to achieve, and applications are limited due to the unclear physicochemical properties, which result from the unique mesocrystalline microstructures. It is reported herein that the photocatalytic properties depend on the interfacial defects of intergrains in anatase TiO2 mesocrystals (TMCs). Research reveals that the photocatalytic activity largely depends on defects, such as lattice distortion and oxygen vacancies, which are located at highly aligned interfaces of intergrains within TMCs. Moreover, the mesocrystalline TiO2 photocatalysts exhibit higher photocatalytic performance in organic degradation and hydrogen evolution, compared with single crystals and polycrystals; this can be ascribed to an appropriate amount of interfacial defects at the intergrains and improved carrier separation efficiency through the highly oriented interfaces. In addition, the photocatalytic performance of the TMCs could be further improved through regulation of defects by undergoing an annealing process under a redox atmosphere. This work can provide an avenue to defect engineering for improved photocatalytic performance.