Spatial engineering of adjacent pair single-atom catalyst for reaction-pathway decoupling in advanced oxidation

The limitation of single active sites in advanced oxidation processes (AOPs) involving biomolecules (pollutant and oxidant) is inevitable, which necessitates a rational design of catalysts for reaction-pathway decoupling. Herein, the adjacent pair single-atom catalyst (Co₂/CN) was designed to achieve the bifunctional catalysis for efficient PMS-AOP. The Co₂/CN-PMS system achieved degradation rate of levofloxacin (LF) to 0.1 min^-1, significantly outperforming single-atom analogues (Co₁/CN: 0.014 min^-1), and superior to previously reported PMS-AOPs heterogeneous catalytic systems for LF degradation. Experiments and density functional theory (DFT) calculations reveal that adjacent pair Co₁ sites with high d-band center enhance the affinity of pollutant adsorption, leading to the co-adsorption geometric configuration for pollutant and PMS (pollutant-Co-Co-PMS). This configuration with dual reaction sites decouples the PMS activation and pollutant degradation, thus avoids the competitive adsorption of pollutant and PMS. In the meantime, the spatial configuration of Co₂ dual reaction sites greatly reduce the migration distance of the active singlet oxygen (¹O₂) produced from PMS activation for pollutant decomposition. This work pioneers the bifunctionality of adjacent pair single-atom catalysts in AOPs. For the first time, the design paradigm of paired single-atom catalysts has been shifted from "seeking electronic modulation between sites" to a new dimension of "establishing functional division between sites".