Hydrated titania was prepared by a sol-gel method, taking tetraisopropyl orthotitanate as starting material, and then promoted with different weight percentages of sulfate by an incipient wetness impregnation method. The materials were characterized by various advanced techniques such as PXRD, BET surface area, N-2 adsorption-desorption measurements, FTIR, and SEM. Analytical results demonstrated that TiO2 is mesoporous in nature, and sulfate modification could inhibit the phase transformation and enhance the thermal stability of TiO2. It was also found that sulfate modification could reduce the crystallite size and increase the specific surface area of the catalysts. The degradation of methyl orange under solar radiation was investigated to evaluate the photocatalytic activity of these materials. Effects of different parameters such as pH of the solution, amount of catalyst, additives, and kinetics were investigated. At 2.5 wt% sulfate loading, the average percentage of degradation of methyl orange was nearly two times than that of neat TiO2. The photocatalytic degradation followed first-order kinetics. (c) 2007 Elsevier Inc. All rights reserved.