A simple, cheap and reproducible method to produce a C-doped TiO2 photocatalyst is presented, which can harvest visible light. This doped catalyst is able to degrade a stable organic dye molecule, Remazol Brilliant Blue (R) (RBB), under sunlight and visible light alone and its activity is compared to P25. XPS analysis clearly showed that carbon was introduced into the TiO2 lattice but at much lower doping levels than initially added during the synthesis. BET and diffuse reflectance spectroscopy indicated that the doped catalysts had larger surface area and improved light absorption in the visible region than P25. However, under full sunlight this did not translate into improved photocatalytic activity when compared to P25. Even though the UV cut-off sunlight spectrum permitted P25 to discolor RBB, no actual dye mineralization was observed by total organic carbon (TOC) analysis. In contrast, the doped catalyst did not only achieve discoloration of RBB but also removed 70% of organic carbon. This gives the doped catalyst a clear advantage to operate with visible light alone, which can be produced in a much more economical way, and may therefore reduce treatment costs of wastewater from textile and other industries using dyes. Among several reactive dyes, RBB was particularly found to be the most recalcitrant to discoloration with TiO2 and this study opens a way to address this issue. The photocatalytic mechanism is discussed. (C) 2013 Elsevier B.V. All rights reserved.