Synergetic activation of peroxymonosulfate by Co3O4 modified g-C3N4 for enhanced degradation of diclofenac sodium under visible light irradiation

•Co3O4-g-C3N4 composite was prepared through the thermal polycondensation method.•Co3O4-g-C3N4 presents a synergetic effect for PMS activation under visible light.•PMS can be activated by photogenerated electrons and Co3O4 itself.•Sulfate and hydroxyl radicals were mainly responsible for diclofenac sodium degradation.•A high stability of the Co3O4-g-C3N4 particles for PMS activation was exhibited.

Co3O4 nanoparticles modified g‐C3N4 composites (Co3O4-g-C3N4) were prepared and used as a visible light responsive photocatalyst for the removal of diclofenac sodium (DCF). The Co3O4-g-C3N4 with 0.20% Co3O4 loading exhibited the highest photocatalytic activity towards DCF degradation among the various Co3O4 loading. In the presence of peroxymonosulfate (PMS), the removal efficiency of DCF with an initial concentration of 10 mg/L was greatly increased from 20% to 100% within 30 min and the first order-kinetic constant was increased from 0.00469 to 0.08403 min−1. Influencing factors including DCF concentrations, PMS concentrations, and initial pH values were investigated in details. Low pH value was favorable to DCF degradation. Reactive oxygen species generated in the photocatalytic process were identified by radical quenching tests and electron spin response. It was proposed that both sulfate and hydroxyl radicals contributed to the degradation of DCF. PMS could be activated by photogenerated electrons from the Co3O4-g‐C3N4 hybrids under visible light, as well as the Co3O4 itself to generate sulfate radicals jointly. Hydroxyl radicals were generated from the reaction between sulfate radicals and H2O/OH−. As a result, DCF was efficiently degraded.

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