MIL-100@ZIF-67 Enhanced Microbial Electroreduction of CO2 to Produce CH4 by Promoting Electron Transfer

Abstract

To improve the conversion rate of carbon dioxide (CO₂) to methane (CH₄) in a microbial electrochemical system (MES), the zeolitic imidazolate framework ZIF-67(Co) with electron storage properties was first grown in situ on MIL-100(Fe) with excellent CO₂ adsorption properties by a hydrothermal method. The obtained binary core–shell MIL@ZIF material was then adsorbed by carbon felt on a cathode to grow biofilms composed of electroactive microorganisms for characterization and testing in an MES. This system exhibited a CH₄ production rate of 0.42 mmol L_R^–1 d^–1, along with an impressive faradaic efficiency of 96.4%. Three-dimensional excitation–emission matrix spectra of extracellular polymeric substances indicated that those containing higher contents of humic acid shifted electron pairs and converted redox states to facilitate electron transfer. MIL@ZIF enriched hydrogenotrophic methanogens and electrogenic bacteria in microbial communities with enhanced gene expression of electrically conductive pili and cytochrome C to strengthen interspecies electron transfer. MIL@ZIF enhanced CO₂ adsorption and electron storage, reinforcing electron transfer chains and boosting CH₄ yield by a factor of 10.7.