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

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.