Enhanced gaseous benzene degradation by bimetallic MIL-101(Fe, Cu) activated persulfate system: Efficiency and mechanism

Abstract

Persulfate oxidation is a promising technology for air pollution control but still suffers from degrading refractory volatile organic compounds (VOCs) under mild conditions. Metal-doped metal-organic frameworks (MOFs) offer a novel strategy to enhance persulfate activation and VOCs degradation. Herein, a novel bimetallic MIL-101 (Fe, Cu) is prepared for more effective degradation of gaseous benzene via persulfate activation. Under optimal conditions (Fe/Cu ratio of 1:4, persulfate concentration of 7 mM/L, pH of 5, and reaction temperature of 70 °C), the MIL-101(Fe1, Cu4) activated persulfate system achieves a benzene degradation efficiency of 79.1 %, a value significantly higher than that of MIL-101(Fe) (20.1 %). The enhanced performance can be attributed to the synergistic effect of Fe²⁺/Fe³⁺ and Cu²⁺/Cu⁺ redox interactions facilitating the activation of persulfate and generation of radical species. Density functional theory (DFT) calculations indicate an increase in the adsorption energy of MIL-101(Fe) in the presence of Cu doping from −3.46 eV to −5.92 eV along with a rise in the Fermi energy level from 0.5 eV to 1.33 eV, enhancing the electron density and mobility. A reaction energy diagram is provided to illustrate the reaction pathways and transition states involved in the degradation of benzene. Overall, the incorporation of Cu in MOFs significantly enhances the efficiency of persulfate-based oxidation systems toward VOCs degradation.