Carbon-Doped Titanium Dioxide: Visible Light Photocatalysis and EPR Investigation

X-band EPR studies of a series of undoped and carbon-doped titania powders reveal the presence of a carbon-centered radical species. The concentration of spins is five to six orders of magnitude smaller than the total carbon content. Photoexcitation of the carbon-doped samples increases the corresponding EPR signal intensities both under ultraviolet and visible light irradiation. After illumination, the original intensity is restored within a few hours. Samples with higher carbon radical concentration reveal higher photocatalytic activity in degradation of 4-chlorophenol under visible light irradiation.