Highly efficient removal of triiodide from contaminated water using urea-impregnated activated carbon from biomass

A sustainable strategy has been developed for the efficient removal of triiodide (I3–), a stable analogue of radioactive iodide, from aqueous solutions using activated carbons (ACs). The ACs were derived from agricultural biomass – specifically rice husk, buckwheat husk, and walnut shell. Carbonized biomass was impregnated with urea and subsequently activated with potassium hydroxide (KOH) to enrich the carbon surface with nitrogen-containing groups and achieve high surface area. The removal of I3– spiked in water was very effective with activated carbons with urea and KOH from rice husk and buckwheat husk, with uptakes up to 1212 ± 9 mg/g and 1099 ± 5 mg/g, respectively. These values almost tripled the uptake of I3– by a commercial granular activated carbon used in the water industry and also outperformed their respective physically and chemically (with KOH) AC carbons. The Langmuir and the Freundlich isotherm models provided insights into the adsorption mechanisms, confirming the beneficial effect of urea functionalization, particularly at equilibrium concentrations < 100 mg I3– /L. These findings highlight the advantages of using urea-impregnated biomass-derived ACs as cost-effective, scalable materials for the remediation of triiodide and, subsequently, the equivalent species from radioactive iodine in water treatment applications. Future work should address the scalability of the process to produce the best-performing ACs, as well as their performance in effluents from the nuclear industry.