Preparation and characterization of mesoporous N-doped and sulfuric acid treated anatase TiO2 catalysts and their photocatalytic activity under UV and Vis illumination

Nitrogen-doped TiO₂ catalysts were prepared by a precipitation method. The samples were calcined at 400 °C for 4 h in air. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature N₂-adsorption was used for structural characterization and UV-diffuse reflectance (UV-DR) was applied to investigate the optical properties of the as-prepared samples. It was found that microporous N-doped catalysts have solely anatase crystalline structure. Acidic treatment of the calcined samples was performed using sulfuric acid agitation. The crystalline structure remained unchanged due to surface treatment, while the porosity and the surface areas were decreased dramatically. Optical characterization of the doped catalysts showed that they could be excited by visible light photons in the 400–500 nm wavelength range (λ_g,1=390 nm, λ_g,2=510 nm). It was also established that surface treatment enhances the Vis-light absorption of the N-TiO₂ powders. Finally the catalysts were tested in the photocatalytic degradation of phenol in aqueous suspensions. Two different light sources were used; one of them was a UV-rich high pressure Hg-lamp, while the other was a tubular visible light source. We found that using visible light illumination N-doped, acid treated TiO₂ samples were more catalytically active than non-doped TiO₂ catalysts.