Two step pore expansion assisted by KOH activation of nitrogen-doped biochar for enhanced gaseous iodine adsorption

Abstract

In this study, a highly efficient and cost-effective adsorbent for gaseous iodine, nitrogen-doped KOH-activated coconut shell biochar (NKBC), is presented. A two-step pore expansion assisted by KOH activation process, enhanced by nitrogen doping, created a hierarchical porous structure with ultra-high specific surface area of 2977.90 m 2 /g, large total pore volume of 2.19 cm 3 /g and available micropore volume of 1.17 cm 3 /g, resulting in an iodine adsorption capacity of 6635 mg/g at 75℃ within 3 hours. The low desorption rate (12.93 % at room temperature) highlights the material's stability. Grey relational analysis identified specific surface area and pore structure as key determinants of adsorption capacity, while pore size distribution and nitrogen content significantly influenced desorption. DFT calculations confirmed the enhanced iodine adsorption by nitrogen functionalities and the effectiveness of micro- and narrow mesopores in iodine capture. This sustainable approach offers a significant advancement in developing high-capacity adsorbents for the effective remediation of radioactive iodine. • NKBC possesses an ultra-high specific surface area of 2977.90 m 2 /g. • NKBC showcases a unique hierarchically porous structure. • NKBC achieves ultra-high gaseous iodine adsorption capacity of 6635 mg/g. • The mechanism of two step pore expansion is revealed.