Highly Selective Singlet Oxygen Generation via an Asymmetric Co–O–Fe Dual-site for Enhanced Water Treatment: Importance of Switching the Ozone Activation Pathway

The singlet oxygen ( 1 O 2 )-driven nonradical oxidation pathway has shown great promise for the degradation of organic pollutants with high ionization potentials (IPs) in complex water matrices because of its longer half-life and stronger resistance to environmental interference. However, the symmetric configuration of the active sites (e.g., Fe–O–Fe) in heterogeneous catalysts largely restricts the efficacy of 1 O 2 generation during ozone activation. In this study, we constructed an asymmetric Co–O–Fe dual-site in bimetallic metal‒organic frameworks (MOFs) with enhanced electron delocalization to switch the ozone activation pathway from radical-dominant to nonradical-dominant. By combining experimental and theoretical analyses, we revealed that breaking the symmetry of iron sites with Co incorporation optimizes the local electronic structure, thereby facilitating ozone adsorption and reducing the O‒O bond scission energy barrier to produce 1 O 2 . As a result, the constructed asymmetric Co–O–Fe dual-site demonstrates impressive 6.6 and 2.0 fold increases in 1 O 2 selectivity and phenol degradation efficiency, surpassing the performance of the state-of-the-art ozonation catalysts. Furthermore, the Co–O–Fe dual-site/O 3 system could efficiently and stably remove diverse high-IP organic pollutants in complex water matrices, following a positive linear correlation ( R 2 > 0.97) between the kinetic rate constants and theoretical IP values, which further highlights the unique and critical role of 1 O 2 . This work advances the understanding and design of efficient dual-site catalysts for selective 1 O 2 generation and sustainable high-IP pollutant degradation.