Ferrate(VI) Activation with Nanoconfined Cu–Mg Sites for Water Treatment: Selective Cu(III) Production via Support-Dependent Redox Catalysis

This study demonstrated that catalyst support played a crucial role in tailoring the redox reactions of ferrate (Fe(VI)) with nanoconfined Cu, promoting the production of Cu(III) as a highly reactive nonradical oxidant. The reactivity of the heterogeneous Fe(VI) activator (confined Cu–Mg; present primarily in the oxidation state of +2), prepared by calcining mixtures of Cu/Mg nitrates in the presence of inorganic/organic supports, was substantially higher with g-C3N4 as the metal nanoconfinement host than with SiO2 and montmorillonite k10 (k10). The structure of the Cu–Mg sites was sensitive to the support type. Mg as the adhesive agent bridged Cu atoms with a graphitized carbon phase to cause CuMg cluster formation unique to g-C3N4, which enhanced the metal–support interactions and thus facilitated interfacial electron transfer from Cu sites to Fe(VI) for selective Cu(III) formation. The superiority of Cu–Mg–C3N4/Fe(VI) in organic oxidation at pH = 8 arose from preferential Cu(III) production based on UV–visible absorption and in situ Raman spectra, reactivity toward multiple organics, and density functional theory-calculated energetics of electron transfer from CuMg clusters and Cu(II)-to-Cu(III) conversion. This contrasts with the behaviors of Cu–Mg–SiO2 and Cu–Mg–k10 (accommodating Cu and Mg as separate phases) in Fe(VI) activation, which initiated Fe(V)/Fe(IV)-induced oxidation as the main degradation route.