Study of visible light photocatalytic activity achieved by NMP solvent treatment of polymorphic titania

Visible light active polymorphic titania samples were prepared by post-treatment of a water-based ambient condition sol (WACS) sample using a solvent-based ambient condition sol (SACS) process with N-methylpyrrolidone (NMP) as the solvent. SACS samples were calcined in either air or nitrogen atmosphere under various conditions. Nitrogen incorporation of SACS titania was investigated by CHN analysis and X-ray photoelectron spectroscopy (XPS). All samples were also characterized by X-ray diffraction, N2 physisorption, UV/Vis absorption spectroscopy, and TEM and compared to a commercial titania powder, Degussa P25. The calcination conditions, especially the temperature and calcination atmosphere, have an influence on the BET surface area, crystallite size, titania phase content, and photocatalytic activity, evaluated by the degradation of methyl orange dye under visible light irradiation. SACS calcined in air at 200 °C for 2 h showed the best visible light activated photocatalytic performance in this study.