Boosting Cr(VI) Reduction via Microwave Catalysis Using Oxygen-Vacancy-Rich MnFe₂O₄@ZnFe₂O₄ Heterojunctions

Abstract

The rapid and selective removal of carcinogenic hexavalent chromium (Cr(VI)) from water remains a critical challenge for sustainable environmental remediation. This work reports the elaborate design of oxygen-vacancy-rich MnFe₂O₄@ZnFe₂O₄ (MZFO-V_O) heterojunction microspheres for highly efficient microwave-assisted Cr(VI) reduction under mild conditions. At an initial pH of ~7, with a catalyst dosage of 2 g L^-1 and a temperature of 100°C, the MZFO-V_O heterojunction composite achieved complete removal of Cr(VI) from a 50 mg L^-1 solution within 35 min under microwave irradiation. Density-functional theory calculations revealed that the introduced vacancies reduced the work function to 4.66 eV, suggesting a lowered energy barrier for bulk-to-surface electron migration. Moreover, Fe–O anchoring sites were identified as the active centers that enable efficient adsorption and reduction of dichromate ions, which is accompanied by significant charge transfer from Fe to the adsorbate. The synergistic coupling of defect-induced polarization and conduction losses, and efficient microwave absorption collectively underpins the high activity and operational stability of MZFO-V_O. These findings establish a clear design route for next-generation microwave catalysts and highlight the practical potential of vacancy-modulated ferrite heterostructures for rapid, energy-efficient treatment of Cr(VI)-contaminated water.

Keywords

Cr(VI) reduction / DFT calculation / microwave catalysis / MnFe₂O₄@ZnFe₂O4 / oxygen vacancies

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2026 The Author(s). Carbon Neutralization published by Wenzhou University and John Wiley & Sons Australia, Ltd.