N/O-Codoped Ultrathin Porous Biochar Derived from Casein for Fast Adsorption of Iodine

The release of radioactive iodine into the environment poses a significant threat, as it can contaminate soil, water, and food chains, leading to detrimental effects on ecosystems and biodiversity. Hence, employing the adsorption method proves to be a simple yet effective approach for treating radioactive waste. N/O-codoped ultrathin porous biochar, synthesized from casein using NaHCO₃ activation, emerges as a potential candidate for adsorption materials. The saturation level of I₂ adsorption in 100 mg L^-1 iodine-cyclohexane solution is 73 mg·g^-1 at 20 min. The density functional theory (DFT) calculations and experiments attribute this phenomenon to the presence of graphite nitrogen (N_G) and C-OH groups on the biochar surface. Furthermore, the pseudo-first-order model fits better with the experimental values, suggesting that the adsorption of iodine by the adsorbent is primarily physisorption-based. The Freundlich isotherm is suitable for iodine adsorption of biochar, owing to the abundance of adsorption sites within the porous structure, particularly at the edges, which enhance the adsorption activity. Significantly, the study highlights that N_G adsorptive sites exhibit 1.5 times higher adsorption activity compared to C-OH adsorptive sites, underscoring the essential role of N_G in iodine adsorption for electron transfer. Overall, these findings underscore the potential of N/O-codoped ultrathin porous biochar in effectively mitigating the presence of radioactive I₂, showcasing its promise in addressing environmental challenges associated with radioactive contamination.