BTCA-functionalized chitosan aerogel for efficient Th(iv) recovery: adsorption performance and mechanistic insights

Abstract

Acid-stable and selective adsorbents are essential for efficient Th(IV) recovery from acidic aqueous systems. In this work, a BTCA-functionalized carboxyl-rich chitosan aerogel (CCS-BTCA) was prepared to improve the stability and Th(IV) binding ability of chitosan-based adsorbents. The optimized CCS-BTCA exhibited a high Th(IV) adsorption capacity of 229.0 mg g⁻¹ at pH 3.0, and the Langmuir maximum adsorption capacity reached 279.4 mg g⁻¹. Kinetic fitting showed that the adsorption process followed the pseudo-second-order model, with a calculated equilibrium adsorption capacity of 225.7 mg g⁻¹ and R² = 0.993, indicating a chemisorption-dominated process. The equilibrium adsorption data were better fitted by the Langmuir model with R² = 0.991, suggesting monolayer adsorption on relatively homogeneous active sites. CCS-BTCA also showed strong selectivity toward Th(IV) in a multi-ion system, with a distribution coefficient higher than 4000 mL g⁻¹, and retained 80.9% of its initial adsorption capacity after five adsorption–desorption cycles. XPS analysis and DFT calculations indicated that BTCA-derived oxygen-containing groups, especially carboxyl/carboxylate and carbonyl groups, participated in Th(IV) binding through ligand exchange and inner-sphere Th–O coordination. These results demonstrate that BTCA functionalization is an effective strategy for constructing acid-stable, carboxyl-rich chitosan aerogels for selective Th(IV) recovery.