Effect of urea on the photoactivity of titania powder prepared by sol–gel method

The synthesis of nanocrystalline titania powders from the hydrolysis of Ti(OBun)4 in the presence of urea was investigated. DRS results showed that a redshift occurred in the absorption edge of titania with increasing the content of urea. XRD results indicated that urea showed a retarding effect on the transformation of titania from anatase to rutile. Moreover, the addition of urea resulted in a higher Brunauer–Emmett–Teller (BET) surface area as well as a larger average pore size of TiO2 nanoparticles. The average pore size of urea/TiO2 gels calcined at 500 °C increased with the increase of urea content, while the specific surface area increased with the amount of urea to reach a maximum at 10% and then decreased with further increase of the amount of urea. The maximal specific surface area of 64.4 m2 g−1 was obtained for 10% urea/TiO2 gels calcined at 500 °C, which showed an average particle size of 15 nm and pore size distribution in the range of mesopores centered at 5.8 nm. The photocatalytic experiments exhibited that titania nanoparticles prepared in the presence of urea could effectively photodegrade methyl orange under visible light irradiation due to the redshift of the absorption edge. The maximum photoactivity was achieved when the content of urea was 10%, which was attributed to the higher specific surface area.