Flow-assembled Janus catalyst arrays for low-energy-barrier cascade dechlorination and mineralization of chlorinated...

Dechlorination and mineralization of chlorinated organic compounds (COCs) in water treatment hold critical environmental significance; however, they face fundamental kinetic limitations in conventional approaches that exhibit inadequate control over on-demand redox reactions. A critical need exists to harness spatiotemporally decoupled redox reactions to reduce overall energy barriers of dechlorination and mineralization. Herein, we pioneer a water flow-guided location-selective loading (HF-LSL) strategy that enables precise spatial organization of Pd (for H* production) and PdAu (for •OH production) catalysts on two opposing surfaces of microwire arrays. By utilizing the H₂ and O₂ produced from water electrolysis, the engineered Janus architecture in the flow-through system enables alternating production of H* and •OH along the flow-directed path, creating spatiotemporally decoupled radical processes that prevent cross-quenching while maximizing radical utilization and synergy. This leads to enhanced dechlorination and mineralization of 2,4-dichlorophenol, compared with the flow-through systems without Janus analogues. Theoretical calculations unveil that the enhancement originates from sequential dechlorination by H* and then by •OH, a cascade reaction pathway with the lowest energy barriers. Furthermore, the presence of H* facilitates the mineralization of intermediates such as maleic acid and fumaric acid by •OH. The flow-through system maintains excellent treatment performance across typical realistic water matrices and COCs (e.g., 4-chlorophenol, 2,3,6-trichlorophenol, and trichloroacetic acid). The HF-LSL strategy establishes a universal platform for spatially programming multifunctional catalysts, opening transformative opportunities in tandem catalysis for advanced water treatment.