Asymmetric Active Center Triggers Side-On Photo-Fenton-Like Reaction Through Polar Charge Transfer and Self-Adapting Sulfur Vacancies

The Fenton-like process driven by visible-light (photo-Fenton-like) holds immense promise for abating emerging contaminants through offering efficient charge transfer in peroxymonosulfate (PMS) activation. However, the catalytic interface charge transfer limitations, weak adsorption interactions, and high dissociation energy of the short O─O bond hinders efficient PMS activation in these systems. Herein, asymmetric active centers were constructed in a Cu-doped Zn₃In₂S₆ photocatalyst (Cu–ZIS_V) to accelerate PMS activation kinetics via modulating the polar charge transfer and activation pathway of PMS. The resulting asymmetric Cu–S_V–Zn sites resulted in an increase in the first-order kinetic constant of Cu–ZIS_V by 4.87 times (0.1674 min⁻¹) through polar charge transfer, outperforming the previously reported sulfur vacancy-based photocatalysts. Self-adapting S vacancies triggered by Cu-doping regulated the traditional activation of PMS from end-on-type to side-on-type. The synergistic effect of polar charge transfer and the side-on surface-bound PMS complex (side-on PMS*) facilitated the stretching of O─O bonds (1.362–1.493 Å) in PMS and lowered the free energy barrier by 85% (1.176–0.175 eV), significantly promoting the generation of reactive oxygen species (ROS). This study offers new insights for improving the efficiency of side-on photo-Fenton-like reactions via self-adapting modulation, providing a promising strategy for efficient photo-Fenton-like processes in practical water treatment.