Iron Oxide Anchored on Porous Carbon Derived from Metal–Organic Frameworks as an Efficient Catalyst toward In Situ Generation of H2O2 and a Hydroxyl Radical for Methylene Blue Degradation in Microbial Fuel Cells

In spite of the huge challenge of treating organic dye wastewater, bioelectrochemical systems are gaining attention due to their ability to treat dye wastewater in an ecofriendly and low-consumption manner. In this study, a porous CZIF-8/Fe3O4 composite was prepared using a metal–organic framework material as a precursor and used as a bioelectro-Fenton catalyst in a microbial fuel cell-combined electron-Fenton (MFC-EF) system for in situ H2O2 generation and •OH production. The abundant pyrrole-N (62.37%) in CZIF-8 was the main active site for the reduction of oxygen to H2O2, and the in situ-generated H2O2 was immediately heterogeneously catalyzed by Fe3O4 to •OH for methylene blue (MB) degradation. The maximum hydrogen peroxide yield in the MFC-EF system with CZIF-8/Fe3O4 was 45.1 μmol/L and the maximum power density was 146.0 mW/m2. The degradation efficiency of MB was 92.64% with a kinetic rate constant of 0.176 h–1 at 23 h in the MFC-EF system with CZIF-8/Fe3O4. After five cycles of long-term operation, the MB removal efficiency decreased by only 19.7%, indicating that CZIF-8/Fe3O4 was stable in the MFC-EF system. This research provides a novel strategy to construct an electrocatalyst for recovering energy and degrading pollutants simultaneously in a microbial fuel cell-combined electron-Fenton system.