Tailoring d-p orbital hybridization of single-atom Cu-N2S sites for enhanced photo-Fenton reaction.

Although single-atom catalysts (SACs) are emerging as advanced heterogeneous catalysts for Fenton-like reactions, enhancing their performance by precisely tailoring d-p orbital hybridization remains challenging. Herein, single Cu atoms with a unique Cu-N2S asymmetric coordination structure are designed and fabricated to catalyze photo-Fenton reactions. Density functional theory (DFT) calculation reveals that strong d-p orbital hybridization elevates the HOMO energy level and promotes splitting of d-orbital energy levels, thereby regulating the adsorption affinity of single-atom Cu sites toward H2O2 via a unique anti-d-band-center principle. Consequently, the Cu-N2S single sites exhibit unique photo-switching behavior, transforming the inactive sites into Fenton-active ones under light irradiation, thereby enabling sustained and enhanced generation of hydroxyl radicals for efficient degradation of various organic micropollutants. The developed photo-Fenton system achieves 98.9% removal of sulfamethoxazole, along with broad pH applicability (pH 3-11), high tolerance for complex water matrices, and exceptional durability for long-term operation. This work highlights the critical role of single-atom coordination symmetry in modulating electronic orbital structures, providing an avenue for the rational design of advanced Fenton-like catalysts.