Activated Carbon-Supported Nanoscale Zero-Valent Iron for CO2 Biomethanation: Stability, Transport in Porous Media, and Potential Reaction Pathways.

Nanoscale zero-valent iron (nZVI) is an effective electron donor for the microbial reduction of CO2 to methane as an energy carrier. Nevertheless, the natural aggregation of nanostructures in aqueous porous media such as oil reservoirs is still a challenge in practical applications. To address this gap, iron-carbon nanocomposites (nZVI/AC) were synthesized using activated carbon (AC) as a support, and their dispersibility, transport behavior, and effects on the bioconversion of CO2 to methane were systematically investigated to explore their feasibility of serving as electron donors for the bioconversion of CO2 to methane in practical applications. Scanning electron microscopy (SEM) showed that AC effectively mitigated nZVI aggregation in aqueous solutions. Sedimentation and column experiments demonstrated that nZVI/AC exhibited improved colloidal stability and enhanced transport in porous media. In methanogenic microbial culture experiments, nZVI/AC was found to facilitate CO2 biomethanation compared with the no-addition control. Electrochemical, structural, and compositional analyses revealed that nZVI/AC possessed enhanced electron transfer capability and a higher dissolution rate, with siderite (FeCO3) identified as the primary reaction product. This study opens a new window for the design of iron-based composites with synergistic properties for CO2 biotransformation and the advancement of CO2 fixation and resource utilization in oil reservoirs.