Surface studies of nano-sized TiO2 powders prepared by different methods showed that the preparation method had great impact on the surface properties. XPS measurements showed that the oxygen composition was related to the preparation method. The chloride method yielded the lowest amount of surface oxygen (29%) and sol-gel prepared powder showed the greatest amount of surface oxygen (66%) in the form of surface hydroxyl groups. The remaining oxygen was identified as lattice oxygen. The powder prepared by the sol-gel method contained carbon impurities originating from residual alkoxy groups. Supercritical sol-gel prepared powder and powder prepared by the sulphate method revealed same trends regarding oxygen composition with 44-47% being surface oxygen; neither contained carbon impurities. The results obtained from XPS were confirmed by FTIR measurements. (c) 2004 Elsevier B.V. All rights reserved.