Towards efficient photocatalytic degradation of organic pollutants in hierarchical TiO₂/SnO p-n heterojunction under visible-light irradiation

Preparation of a p-n heterojunction with hierarchical structure is of great significance for photocatalysis due to its large specific surface area, abundant active sites and increased charge separation rate. Herein, we designed the novel p-n heterojunction photocatalyst TiO₂/SnO microflower (TiO₂/F-SnO) with hierarchical architecture by decorating TiO₂ nanoparticles on the surface of the SnO microflower via a simple hydrothermal route. Compared to pure TiO₂ and TiO₂/SnO with a microplate structure (TiO₂/P-SnO), TiO₂/F-SnO heterojunctions exhibited significantly enhanced photocatalytic performances for organics removal such as toluidine blue O (TBO) and methylene blue (MB) under daylight fluorescent lamp irradiation (350-800 nm). The improved performance was not only ascribed to the promoted charge transfer and separation efficiency induced by the formation of p-n junction, but also attributed to the larger specific surface area, sufficient active sites and stronger redox ability provided by the hierarchical microflowers. Moreover, after three photocatalytic cycles (24 h), the TiO₂/SnO heterojunction still exhibited a stable photocatalytic activity. Finally, the photocatalytic enhancement mechanism for the TiO₂/SnO heterojunction was proposed based on band alignments calculation and the active species trapping experiments.