Titanium dioxide nanoparticles with high visible-light photocatalytic activity were prepared by the solvothermal method with titanium tetra-n-butoxide as starting material in acetone. The products were characterized by XRD, TEM, TG-DTA, DRS and FT-IR. DRS results showed that the products, irrespective of their anatase or amorphous forms, had significant absorption in the visible-light region. The photocatalytic degradation of methyl orange solutions revealed that the anatase products had a higher visible-light photocatalytic activity than the amorphous ones. It is suggested that two surface complexes, formed between titanium dioxide and methyl orange molecules, and formed between titanium dioxide and the new organic moieties from the autoclaving, contribute synergistically to the high visible-light photocatalytic efficiency. (c) 2007 Elsevier Ltd. All rights reserved.