Comparative investigation of mesoporous- and non-mesoporous-assembled TiO2 nanocrystals for photocatalytic H2 production over N-doped TiO2 under visible light irradiation

In this paper, N-doped mesoporous-assembled TiO2 and N-doped non-mesoporous-assembled commercial TiO2 (Degussa P-25) nanocrystals were comparatively investigated for photocatalytic H2 production from water splitting under visible light irradiation. The mesoporous-assembled TiO2 photocatalyst with nanocrystalline and narrow monomodal pore size distribution characteristics was synthesized by a sol–gel process with the aid of structure-directing surfactant under mild conditions. The N-doping technique was directly performed by calcining the mixture of the TiO2 photocatalysts and urea, as a N source, at different N contents and calcination temperatures. All prepared photocatalysts were systematically characterized by N2 adsorption–desorption, Brunauer–Emmett–Teller (BET) surface area analysis, Barrett–Joyner–Halenda (BJH) pore size distribution analysis, UV–visible spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). From the experimental results, it was found that N-doped mesoporous-assembled TiO2 prepared at a urea:TiO2 molar ratio of 1:1 and a calcination temperature of 250 °C exhibited relatively high photocatalytic activity toward hydrogen production. For the N-doped commercial TiO2, the preparation conditions of a molar ratio of 0.5:1 and a temperature of 250 °C showed the best photocatalytic activity, but was still less photocatalytically active than N-doped mesoporous-assembled TiO2 prepared at the optimum conditions. The results indicated the importance of the mesoporous characteristic of the photocatalyst in enhancing the photocatalytic activity by increasing the specific surface area and N-doping capability.