Preparation Of Nitrogen-Modified Titania And Its Photocatalytic Performance In Cr(Ⅵ) Reduction

The application of titania photocatalysts as promising environment protective material is attracting considerable attention in wastewater treatment and air purification because of its nontoxicity, low cost, chemical stability and high catalytic activity. However, TiO2can be activated only under UV light of wavelengths≤387nm irradiation due to its wide band gap (3.2eV for crystalline anatase phase). The solar spectrum usually contains only3%-5%UV light which makes the possibility of employing solar light in TiO2photocatalysis limited. Therefore, development of an efficient process that can shift the optical response of TiO2from UV to visible spectral range seems to be the most appropriate strategy.In this paper, a series of nitrogen-modified TiO2(N-TiO2) catalysts with different nitrogen content were prepared by an acid-sol method, in which tetrabutyl titanate was used as the precursor and urea as the nitrogen source. The samples were then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible diffuse reflectance spectroscopy (UV-Vis/DRS). The photocatalytic activities were evaluated by reduction rate of Cr(VI) aqueous solution under visible light, the influence of different hole scavengers and initial pHs on the reduction activity were also discussed. Results indicated that acid pH condition was beneficial to Cr(VI) photo-reduction and the reaction rate was greatly improved by formic acid with an optimal additional amount. The N-TiO2sample had higher photocatalytic activity than bare TiO2and N-TiO2sample with10%(molar ratio) nitrogen calcined at400℃held the highest photocatalytic efficiency. The optimal reduction rate was63%after2h reaction time when the initial pH was3and formic acid as a hole scavenger. The high visible light photocatalytic activity of the N-TiO2sample calcined at400℃was mostly attributed to the melon condensation products which acted as visible-light sensitizers. The analysis based on atomic absorption indicated that the total chrome in water was dropped gradually during the photoreduction process, which may be due to the complexation actions between the reduction-generated Cr(III) and surface hydroxylated TiO2.