Photocatalytic decomposition of acetic acid into biogas and hydrogen was performed over Cu/TiO2 photocatalysts synthesized by the sol-gel method. Samples with different Cu loadings (0, 0.5, 1 and 10 wt.%) were prepared by two different methods (in situ and impregnation), and then they were heat treated at 500 degrees C either in air or in argon. Structural and surface characterization of the photocatalysts was carried out. The influence of the synthesis variables on their efficiency in the photocatalytic decomposition of acetic acid in aqueous solution was analyzed. The photodegradation results show that all the prepared materials are more active than commercial TiO2, used as a reference, and reveal that the presence of copper improves the activity of pure TiO2. Cu/TiO2 photocatalysts prepared by the in situ method and heat treated in argon show the best results. This can be explained considering that these synthesis conditions lead to more efficient interaction between Cu species and TiO2, to a more developed porosity and to a more suitable distribution of copper oxidation states (large contribution of Cu-(I) and Cu-(0) seem to give better activity). Catalysts with 0.5 wt.% copper are the most active, likely because copper species are highly dispersed and interact efficiently with TiO2. Thus, the activity of a Cu/TiO2 catalyst produced in situ, heat treated in Ar atmosphere and with a 0.5 wt.% Cu content is double than that of the TiO2 commercial catalyst. (C) 2016 Elsevier B.V. All rights reserved.