With the rapid development of electronic technology, the electroless copper–nickel plating process produces a significant amount of copper–nickel complex wastewater. The traditional methods face difficulties in achieving wastewater treatment and recovering valuable metal resources. In this study, we propose a new environmentally friendly and efficient treatment process for the separation and recovery of Cu(II) and Ni(II). The photocatalyst TiO2-500, calcined at 500 °C, exhibits excellent photo-reduction performance, selectively reducing Cu(II) in the hybrid wastewater to copper. Even after 5 cycles, TiO2-500 photocatalyst maintains good catalytic performance. Following Cu removal, the remaining Ni(II) in the residual wastewater is effectively adsorbed by a chitosan (CS) membrane with an adsorption capacity of 76.7 mg/g. The separation ratio of Cu–Ni reaches 6290.37 in the photocatalytic process. We conducted a comprehensive investigation of the factors that influence the selective recovery of Cu and Ni ions. Our findings reveal that the disparity in reduction potentials between Cu2+ and Ni2+ plays a crucial role in achieving effective separation of Cu and Ni in chemical plating wastewater through photocatalysis. Specifically, under the experimental conditions described in this paper, the reduction potential of Ni2+ (E(Ni2+/Ni) = − 0.33 V) presents a significant challenge for its photoreduction on TiO2-500, which has a conduction potential of − 0.31 V. Moreover, the catalyst surface carries a positive charge and exhibits weak adsorption of Ni2+, resulting in the majority of Ni2+ ions remaining in solution. This characteristic facilitates subsequent adsorption and separation of Ni2+ ions.Additionally, we further elucidated the mechanisms underlying these two processes. The establishment of this process holds immense significance for treating Cu–Ni mixed wastewater and recovering valuable heavy metal resources.