Asymmetric Triple Catalytic Sites on Ternary‐Metal Sulfides Enable Superior Radical‐Nonradical Synergy in Water Purification

Abstract The synergistic interplay between radical and nonradical reactive oxygen species (ROS) can enhance organic pollutant degradation. However, spatial orientation between different active sites is usually uncontrolled, leading to limited synergy due to disparities in ROS lifetimes. To overcome this problem, asymmetric triple catalytic sites (ATCSs) are constructed on ternary‐metal sulfides. Each node of ATCSs contains a transition metal atom that is spatially close yet electronically distinct from another. FeCoNiS 4 is selected through computational screening, where metal atoms with different ROS selectivity are only 4.5 Å apart. In situ X‐ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations confirm the existence of ATCSs: Ni site selectively generates radicals ( • OH/SO 4 •− ), while Fe and Co sites selectively mediate nonradical ( 1 O 2 ) pathways. Compared with FeCoNi, which contains randomly distributed active sites, higher specific rate constants (2.3 and 3.3 folds for degradation and TOC removal rates) are observed for FeCoNiS 4 . Analysis of degradation intermediates reveals simultaneous attacks by radicals and nonradicals on the same organic molecule. DFT shows a lower energy barrier for bond cleavage under synergistic effects. These results highlight the importance of the spatial orientation of different active sites in maximizing synergy between different ROS, which is overlooked in existing studies.