High-efficiency iodine capture in waste biomass-based activated carbon: Effects of biomass types on iodine adsorption and its mechanism

The generation of radioactive iodine during nuclear energy utilization threatens ecological and public safety. While porous activated carbon shows promise for iodine capture, balancing performance with production costs remains challenging. In this study, porous activated carbons (ACs) were synthesized from agricultural residues including rice straw, corn stover, soybean straw, rapeseed straw, and rapeseed cake through hydrothermal carbonization and KOH activation. Results revealed that the rapeseed cake-derived carbon possessed the highest specific surface area of 2025 m2/g, delivering exceptional iodine capacities of 5078 mg/g in the vapor phase, 1128 mg/g in cyclohexane solution, and 2187 mg/g in aqueous solution. Notably, the highly developed mesoporous network in this sample was fundamentally dictated by its distinctively low cellulose content of 13.27% during activation. Vapor and aqueous iodine captures were dominated by micro- and mesopores, whereas cyclohexane uptake was governed by micropores. Adsorption behavior followed pseudo-second-order kinetics and Langmuir isotherm models, indicating a monolayer process dominated by physisorption with a minor chemisorption contribution. These findings provide a theoretical foundation cost-effective iodine adsorbents and promoting the high-value utilization of agricultural waste.