Organic pollutants in electroplating wastewater can be removed by photodegradation, however the effect mechanism of heavy metal ions on photocatalytic activity still remains unknown. Herein, we firstly reported the self-assembly synthesis of titanium dioxide/reduced graphene oxide (TiO2/rGO) composites for phenol-4-sulfonic acid (PSA) removal, and investigated the effects of Cu2+ ions on photocatalytic efficiency. During the self-assemble process, rGO nanosheets were connected together to form network macropores, and simultaneously induced the deposition of hierarchically nanostructured TiO2 microspheres. The synergetic effects of TiO2 microspheres and rGO nanosheets improved the photocatalytic activity by enhancing light adsorption ability, stabilizing electron-hole separation and decreasing band gap energy. The Cu2+ ions in wastewater showed positive and negative effects on PSA photodegradation. In the photocatalytic reaction, the electron-induced reduction reaction of Cu(II) into Cu(0) or Cu(I) took place, which inhibited electron-hole recombination and thus enhanced photocatalytic activity. However, the high chemical stability of PSA-Cu(II) complex compounds held back PSA photodegradation. The appropriate concentrations of Cu2+ ions at around 25 mg/L accelerated PSA photodegradation over TiO2/rGO composites. The PSA degradation into CO2 and H2O was performed by using hydroquinone, benzoquinone and maleic acid as degradation intermediates. Hence, TiO2/rGO composites are novel multifunctional photocatalysts to purify electroplating wastewater. (C) 2020 Elsevier Inc. All rights reserved.