HNO3-involved one-step low temperature solvothermal synthesis of N-doped TiO2 nanocrystals for efficient photocatalytic reduction of Cr(VI) in water

Abstract

A one-step low temperature (180°C) solvothermal route, which utilized HNO3 as the nitrogen source, was proposed for the synthesis of nanocrystalline N-doped TiO2 (denoted as TiO2-HNO3). The structure, composition, BET specific surface area and optical properties of TiO2-HNO3 were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, high resolution transmission electron microscopy, N2 adsorption–desorption isotherms and UV–vis diffuse reflectance spectroscopy. The photocatalytic properties of TiO2-HNO3 were tested for the reduction of Cr(VI) in water under both UV and visible light (λ>420nm) irradiation, and compared with those of TiO2-NH3·H2O (which was solvothermally synthesized using NH3·H2O as the nitrogen source) and TiO2 P25. The photocatalytic results demonstrated that TiO2-HNO3 possessed much higher photocatalytic activity than TiO2-NH3·H2O and TiO2 P25 in the reduction of aqueous Cr(VI) under both UV and visible light (λ>420nm) irradiation, and the dosage of TiO2-HNO3 and the initial concentration of Cr(VI) aqueous solution had significant effects on the efficiency of Cr(VI) reduction. Besides, Cr(VI) was reduced to Cr(III) after the TiO2-HNO3-mediated photocatalytic reactions. The present work suggests that HNO3 is a promising nitrogen source for low temperature solvothermal synthesis of nanocrystalline N-doped TiO2, which can be applied as a visible light-activated photocatalyst in efficient utilization of solar energy for treating Cr(VI) wastewater.