Photocatalytic behaviors of silica-loaded mesoporous titania

Silica-loaded mesoporous titania composites with Si/(Ti+Si) molar ratios, alpha, of 0.045, 0.091, 0.167 and 0.27 were prepared by the sol-gel method. The photocatalytic activity and the adsorptive ability of the composites were evaluated based on the photodegradation of methylene blue (MB) under UV irradiation with a wavelength of 365 nm. The rates of MB adsorption onto the composites were measured in darkness. There was no adsorption of MB on pure mesoporous titania. However, because of the high adsorptive ability of silica, silica-loaded mesoporous titania indicated a significant adsorption rate at an early stage and attained a state of equilibrium after a lapse of 1 h. As a result of the photodegradation test of MB, a silica-mesoporous titania composite (alpha = 0.091) showed the highest rate of MB removal among the synthesized composites. We proposed a kinetic model for simultaneous adsorption and photodegradation for the composites. The photodegradation behaviors were analyzed separately, and divided into adsorbed and unadsorbed MB. The photodegradation of unadsorbed MB occurred on pure mesoporous titania. Meanwhile, photodegradation of adsorbed MB on silica-loaded mesoporous titania proceeded simultaneously with that of unadsorbed MB. The catalytic activity of the silica-mesoporous titania composite (alpha = 0.091) was also highest among the synthesized composites. These results indicated that the high catalytic activity of the low silica content composite (alpha = 0.091) was caused by the suitable dispersion of silica on the titania support to the improvement of catalytic activity. (C) 2011 Elsevier B.V. All rights reserved.