Self-Sustaining Ce(IV)/Ce(III) Cycle for Spontaneous Surface Hydroxyl Radical Generation.

Advanced oxidation processes are indispensable for water remediation yet face a fundamental activity-selectivity trade-off, where reactive species are competitively quenched by complex aqueous matrices. While surface-confined chemistry, specifically utilizing surface-adsorbed hydroxyl radicals (•OHads), provides an appealing kinetic strategy to shield reactions from bulk-phase scavengers, its generation typically requires substantial energy inputs. Here, we report the spontaneous evolution of •OHads via a lattice-engineered 2D CeO2/βC3N4, comprising bilayer CeO2 and monolayer β carbon nitride (βC3N4). Unlike conventional CeO2, where surface Ce4+ sites are blocked by stable oxygen terminations (i.e., Ce4+═O), the unique architecture of CeO2/βC3N4 stabilizes reactive Ce4+ sites via a surface superoxide layer (i.e., Ce4+-•O2-). Upon dispersion into an aqueous system, this superoxide layer undergoes rapid protonation, exposing accessible Ce4+ sites for water oxidation to generate •OHads. Complementary in situ characterizations, isotope-labeled mass spectrometry, and theoretical calculations reveal thermodynamically favorable and stoichiometrically balanced one-electron oxygen reduction and water oxidation pathways, enabling self-sustaining Ce4+/Ce3+ redox cycling and continuous •OHads generation. This work establishes a pollutant-triggered paradigm for matrix-resilient water remediation by leveraging •OHads, eliminating the need for chemical additives or external energy inputs.