Interfacial Coupling of Perfluorooctanoic Acid Defluorination with Chromium(VI) Reduction in Aqueous Microdroplets

Per- and polyfluoroalkyl substances (PFAS) and hexavalent chromium (Cr(VI)) frequently coexist in industrial waters, but their contrasting redox requirements complicate simultaneous remediation. Here we show that aqueous microdroplets transform this apparent incompatibility into cooperative interfacial reactivity. At the air–water interface, perfluorooctanoic acid (PFOA) and Cr(VI) undergo mutually promoted transformation under ambient conditions. Cr(VI) increases PFOA defluorination by approximately 63%, whereas PFOA enhances Cr(VI) reduction by approximately 41%. Mechanistic analyses identify an oxygen-coupled interfacial redox network in which O2-derived peroxides, H2O2 turnover and Cr-mediated radical generation maintain the flux of reactive intermediates. Molecular dynamics simulations and density functional theory calculations indicate that PFOA spontaneously enriches at the interface and reorganizes the ionic environment to promote K+-mediated co-localization of Cr(VI). This association electronically activates the headgroup-proximal C–F bond and, together with interfacial confinement, reduces the α-C–F cleavage barrier from 2.80 to 1.39 eV. Together, these findings reveal how microdroplet interfaces spatially and electronically coordinate organofluorine bond cleavage with metal reduction, providing a framework for cooperative remediation of complex contaminant mixtures.