Nanocrystalline cuprous oxide (Cu2O) thin films were prepared via a one-step chemical bath deposition (CBD) method. The effects of a chelating agent on the orientation, morphology, crystallite size, and photocatalytic activity of the thin films were carefully examined using X-ray diffractometry, scanning electron microscopy, and UV-vis spectrophotometry. The results confirmed that the crystallite size as well as the orientation of the films was dependent on the volume of trisodium citrate (TSC), demonstrating that the band gap ranged from 2.71 eV to 2.49 eV. The morphology and number density of the thin films also depended on the volume of TSC. In addition, the obtained Cu2O thin films could degrade methyl orange (MO) efficiently in the presence of H2O2 under visible-light irradiation, and the mechanism for the enhanced photocatalytic activity of the Cu2O thin films with the assistance of H2O2 was also explored in detail. (C) 2013 Elsevier B.V. All rights reserved.