Highly efficient capture of thorium ion by citric acid-modified chitosan gels from aqueous solution

A novel citric acid-modified chitosan gel (CSCA) was synthesized through a simple one-step process and was used to extract thorium ions from wastewater. The CSCA samples with varying chemical compositions were analyzed using SEM with mapping EDS, FT-IR, and static water contact angle measurements, and their adsorption behaviors were studied in detail. The results showed that the adsorption performance of CSCA improves with the increase of CA content in the sample. CSCA possesses an impressive capacity for thorium adsorption of 279.8 mg/g. Furthermore, it showed an ultra-fast adsorption rate and reached equilibrium within 30 min. In terms of recyclability, the CSCA still retained more than 86% of its initial adsorption capacity after 6 cycles of reuse. Density functional theory (DFT) analysis reveals that the good selectivity of this material towards thorium ions should be attributed to the high density of adsorption sites and strong interaction between carboxyl groups and thorium ions. This work could be beneficial in the design and synthesis of new polymer materials for extracting thorium.