Template-Free Synthesis of Core-Shell TiO2 Microspheres Covered with High-Energy {116}-Facet-Exposed N-Doped Nanosheets and Enhanced Photocatalytic Activity under Visible Light

Core-shell TiO2 microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high-energy facets of TiO2 also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core-shell structure is difficult to achieve and requires multiple-steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high-energy facet production. Therefore, it is still a significant challenge to develop low-temperature, template-free, shapecontrolled, and relative green self-assembly routes for the formation of core-shell-structured TiO2 microspheres with high-energy facets. Here, we report a template-and hydrofluoric acid free solvothermal self-assembly approach to syn-thesize core-shell TiO2 microspheres covered with highenergy {116}-facet-exposed nanosheets, an approach in which 1,4-butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high-energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6-tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core-shell structure, {116}plane- oriented nanosheets, in situ N doping, and large surface areas has been found.