Photocatalysts based on nanostructured TiO2 and carbon blacks (CB) particles were obtained by chemical (sol-gel) and physical (mechanical grinding) preparation techniques. Characterization of these samples by XRD, FT-IR and dye adsorption studies was combined with optical and scanning photoelectrochemical analysis in an attempt to explain the photodegradation efficiency of these materials. The superior adsorption of sol-gel materials in the aqueous dye solutions did not account for the differences observed in photocatalytic activity, where the sol-gel composite outperforms the physical mixture or TiO2 alone by one digit. Data on the photoelectrochemical activity of these composites showed the abundance of inactive sites in the mixtures, while the sol-gel composite showed a uniform active surface. Rectification properties brought up by carbon in sol-gel composites and plus the abundance of hydroxyl groups on the oxide surface are proposed to be responsible for the long-term activity of these photocatalysts. (c) 2006 Elsevier B.V. All rights reserved.