In situ iodine generation enables solution-phase polymerization of organic pollutants for continuous resource...

Oxidation-driven polymerization of organic pollutants offers a route to convert contaminants into value-added products and enable continuous resource recovery from water, but conventional heterogeneous processes are plagued by polymeric overlayers that foul catalyst surfaces and hinder long-term operation. Here, we realize solution-phase polymerization of 4-chlorophenol (4-CP) by relocating key bond-forming steps from catalyst interfaces into the bulk aqueous phase. In a facet-engineered bismuth oxyiodide/hydrogen peroxide (BiOI/H₂O₂) system, BiOI directs H₂O₂ activation toward in situ generation of freely diffusing, moderately oxidizing iodine (I₂) as the dominant reactive species. Accordingly, I₂ drives 4-CP polymerization predominantly in solution rather than on the solid surface, delivering a record 73% retention of polymeric products in the aqueous phase. In situ scanning electrochemical cell microscopy (SECCM) directly visualizes the spatial generation of I₂ and its subsequent reaction with 4-CP. Complementary spectroscopy and density functional theory reveal that the (110) facet of BiOI stabilizes H₂O₂ adsorption via a hydrogen-bond bridging configuration that promote O-O bond cleavage and I₂ formation, whereas other favors radical pathway. This "facet-species-phase" strategy, in which catalyst facets govern the dominant reactive species and thus direct solution-phase polymerization, enables fouling-resistant advanced oxidation that couples water purification with continuous resource recovery.