Comparative investigation of mesoporous- and non-mesoporous-assembled TiO 2 nanocrystals for photocatalytic H 2 production over N-doped TiO 2 under visible light irradiation

Abstract

In this paper, N-doped mesoporous-assembled TiO 2 and N-doped non-mesoporous-assembled commercial TiO 2 (Degussa P-25) nanocrystals were comparatively investigated for photocatalytic H 2 production from water splitting under visible light irradiation. The mesoporous-assembled TiO 2 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 TiO 2 photocatalysts and urea, as a N source, at different N contents and calcination temperatures. All prepared photocatalysts were systematically characterized by N 2 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 TiO 2 prepared at a urea:TiO 2 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 TiO 2, 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 TiO 2 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.