Synergistic effects among metal cations on the catalytic activity for the Fenton reaction are drawing much attention. Effects of pH of the solution on these synergistic effects have not been reported as far as we know. In the present study, 3D CuCo2S4 assembled by nanosheets was synthesized as a catalyst for the Fenton reaction. Compared with the most catalysts displayed high levels of the activity at an acidic condition, the CuCo2S4 showed excellent catalytic activity at pH =11, which is significant higher than that reported in a reference. The e(-) and center dot OH played a key role in the Fenton reaction. The most center dot OH may be formed through the reaction between Cu+ and H2O2 at pH = 11, and Co2- and H2O2 at pH = 5. The center dot O-2(-) formation was improved with the pH increased. The enhanced electrical conductivity of CuCo2S4 at pH = 11 induced the excellent activity. (C) 2020 Elsevier B.V. All rights reserved.