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.