Synergistic KOH-thiourea activation of corncob biochar for ultrahigh-capacity and stable gaseous iodine capture

A synergistic KOH-thiourea strategy constructs N, S co-doped hierarchical porous biochar. • The biochar achieves an ultrahigh iodine uptake of 6700 mg/g with low desorption. • DFT reveals enhanced iodine adsorption from defect and N/S-induced interactions. Radioactive gaseous iodine generated during nuclear fuel reprocessing poses a serious challenge to off-gas treatment due to its high mobility and radiotoxicity. Herein, a two-step synergistic activation strategy using thiourea and KOH was developed to fabricate N, S co-doped hierarchical porous biochar (NSKBC) from corncob waste. Benefiting from the combined regulation of pore structure and surface chemistry, NSKBC exhibits a surface area of 2923.30 m 2 ·g −1 and delivers an iodine adsorption capacity of 6700 mg/g at 75℃, with only 13% desorption after 24 h at room temperature and ∼80% capacity retention after five adsorption–desorption cycles. Mechanistic investigations based on grey relational analysis, FTIR characterization, and density functional theory (DFT) calculations reveal that abundant micropores provide effective physical confinement, while carbon defects and N/S doped sites enhance iodine binding stability through synergistic physical and chemical interactions. This work offers an efficient and sustainable strategy for designing high-performance biochar adsorbents for radioactive gaseous iodine capture. Download: Download high-res image (132KB) Download: Download full-size image