Sulfate ions bonded to titanium ions on the surface of internally sulfated TiO2 greatly improved its photocatalytic activity for the degradation of organic pollutants in reverse osmosis concentrate (ROC). The catalysts were characterized with XRD, BET, SEM, FTIR, EDS, UV-vis DRS, ICP/MS, XPS and Mott-Schottky plots etc. For the activity difference of sulfated TiO2 (S-TO) catalysts, reasons on crystal phase, primary particle size, surface area (SA), pores, band gap (E-g), microscopy morphology and Br6nster acid sites were ruled out. The activity difference of S-TO catalysts was attributed to the spatial distribution of sulfate species. Sulfate species on the S-TO catalysts functioned as electron traps. Surface sulfate species improved activity while bulk core sulfate species hindered it. Based on XPS Ti 2p binding energy (BE) and measured Eg from UV-vis DRS, band positions of catalysts were calculated illustrating electron trapping and transferring. Sulfate ions lowered the energies of both CB and VB of S-TO catalysts compared with the pure anatase TiO2. (C) 2015 Elsevier B.V. All rights reserved.