We report the characterization of vanadium-modified N/Si co-doped TiO2 (VNSiT) in an aqueous solution and its capacity for the photocatalytic decomposition of dimethyl sulfoxide (DMSO) and methylene blue (MB) under visible light irradiation. The two synthesized VNSiTs were V(0.005)-NSiT and V(0.02)-NSiT, which contained different amounts of V2O5 mounted on N-doped Si(0.2)-TiO2 (NSiT) by annealing at 600 degrees C. The VNSiTs exhibited absorbance in the range of 420-520 nm. The isoelectric points of both were three, which is much lower than that of bare TiO2 due to the presence of the negatively charged vanadium species (e.g., vanadate) in the VNSiTs. This resulted in particles with a small average hydrodynamic diameter and high dispersibility formed at pH 7-10 in an aqueous solution. The decomposition rate of DMSO, which is an OH radical scavenger, in the presence of V(0.005)-NSiT and V(0.02)-NSiT under visible light irradiation for 10 h was 40% and 29%, respectively. It was found that an excess of vanadium species caused a decrease in the decomposition efficiency of DMSO. In addition, the VNSiTs strongly adsorbed MB, a basic dye, under dark conditions, but could not decompose it under visible light irradiation possibly because of the strong electrostatic attraction of the VNSiTs to the ionic MB species in water. (c) 2013 Elsevier B.V. All rights reserved.