Surface Fe^IV═O Induced Highly Selective Phenol Polymerization via Proton-Coupled Electron Transfer

Organic polymerization offers a sustainable alternative for water decontamination and resource recovery; however, its popularization is bottlenecked by the unsatisfactory selectivity of traditional electron transfer processes. In this study, we demonstrate that surface high-valent iron-oxo species (≡Fe^IV═O) on nanoscale zerovalent iron (nZVI), characterized by an unoccupied d_z² orbital and a terminal-oxo moiety, can realize highly efficient phenol recovery via a proton-coupled electron transfer (PCET) pathway for phenol transformation into phenoxyl radicals with final polymers of 3231 g mol^-1 in average molecular weight and an impressive polymeric selectivity of 92.6%, surpassing those reported in free radical-/catalyst-oxidant complex-based systems driven by electron transfer (below 77.0%). This PCET-induced polymerization was facilitated by the hydrogen bond formed between ≡Fe^IV═O and phenol, and kinetically obeyed a dual descriptor model comprising pK_a and vertical ionization potential, as unveiled by using representative para-substituted phenolic compounds. Furthermore, the high-performance treatment of real phenol wastewater in continuous-flow operations underscores the significant potential of ≡Fe^IV═O for sustainable water decontamination. This study proposes a prospective strategy for pollutant removal and highlights the significance of ≡Fe^IV═O in resource utilization through selective organic polymerization.