TiO₂ nanosheet/NiO nanorod hierarchical nanostructures: p-n heterojunctions towards efficient photocatalysis

TiO₂ nanosheet/NiO nanorod heterojunction hybrids have been developed through a hydrothermal route, where NiO nanorods (size: 5 nm in diameter and 20-40 nm in length) are deposited at the {0 0 1} facet of anatase TiO₂ nanosheets. The photocatalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption-desorption analysis, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy and time-resolved fluorescence. The TiO₂/NiO photocatalysts exhibited good photocatalytic activities towards the degradation of methyl blue (MB) and phenol, and hydrogen generation efficiency under visible light irradiation. The maximum rate constant can be reached 0.0279 min^-1 and 0.0135 min^-1 respectively, which are about 12 and 10 times higher than that of TiO₂ nanosheets. And the hydrogen generation efficiency is 10 times higher than physical mixing of TiO₂ and NiO. Photocatalytic degradation efficiency remains more than 90% after 6 times cycle dye degradation, and the H₂ production efficiency is almost the same after four cycles, suggesting good stability and reusability. The enhanced photocatalytic activities are associated with the rational design of TiO₂/NiO hierarchical heterojunctions which ensues high photogenerated charge separation efficiency. With the improved photocatalytic performance, the TiO₂/NiO heterojunction hybrids are expected to be potential photocatalysts in environmental and energy related areas.