“Knitted” tetrabenzo-24-crown-8 ether sulfonate as reusable and practical hydrophilic adsorbent for aqueous Cs+ sequestration

Abstract

Herein, “knitted” tetrabenzo-24-crown-8 ether sulfonate (X-S-TB24CE8) was prepared to afford a practical hydrophilic Cs+ adsorbent. Cyclic TB24CE8 ligands were hyper-crosslinked with dimethoxymethane in the presence of Cs+ template followed by sulfonation to introduce -SO3- groups. Thorough characterization of X-S-TB24CE8 using FTIR, TGA, EA, N2 adsorption/desorption, DLS, XPS, and SEM-EDX confirms its hydrophilic nature and thermal stability. It possesses a granulated porous structure that can be easily recovered by filtration. Removal of Cs+ by X-S-TB24CE8 involves a 1:1:2 TB24CE8:Cs+:SO3- coordination with additional Cs+···SO3- interaction from free sulfonate groups. The Cs+ adsorption follows the Sips isotherm model (Qmax = 233.07 mg g−1) and pseudo-second order kinetics (k2 = 2.63 × 10−3 g mg−1 min−1). In seawater containing Cs+, X-S-TB24CE8 exhibits a strong preference for Cs+ over Na+ (αNa+Cs+= 483), K+ (αK+Cs+= 76), Mg2+ (αMg2+Cs+= 66), and Ca2+ (αCa2+Cs+= 35). X-S-TB24CE8 demonstrated consistent adsorption/desorption performance without undergoing any physical or chemical decomposition. These findings indicate that X-S-TB24CE8 holds significant potential as a competitive and practical adsorbent for Cs+ sequestration.