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

Herein, "knitted" tetrabenzo-24-crown-8 ether sulfonate (X-S-TB24CE8) was prepared to afford a practical hy-drophilic Cs+ adsorbent. Cyclic TB24CE8 ligands were hyper-crosslinked with dimethoxymethane in the pres-ence 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+center dot center dot center dot 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 x 10-3 g mg-1 min-1). In seawater containing Cs+, X-S-TB24CE8 exhibits a strong preference for Cs+ over Na+ (alpha Cs+Na+ = 483), K+ (alpha Cs+ K+ = 76), Mg2+ (alpha Cs+ Mg2+ = 66), and Ca2+ (alpha Cs+ Ca2+ = 35). X-S-TB24CE8 demonstrated consistent adsorption/desorption performance without under-going any physical or chemical decomposition. These findings indicate that X-S-TB24CE8 holds significant po-tential as a competitive and practical adsorbent for Cs+ sequestration.