(167z) Cs+ Sequestration from Aqueous Media Using Hyper-Crosslinked Tetraphenylborate

One attractive material for Cs⁺ sequestration is tetraphenylborate or TPB anion (BPh₄^-), which is known to form insoluble complexes with large metal ions like Cs⁺. As such, the earliest works on TPB for Cs⁺ sequestration were via precipitation, where Cs⁺ exchanges with Na⁺ and forms a complex between four phenyl rings of two TPB anions via cation-Ï€ interactions. In lieu of precipitation, some studies have fabricated TPB as composite sorbents for Cs⁺, which involved its immobilization in calcium alginate (as KBPh₄) and in polyacrylonitrile (PAN) as NaBPh₄.

In this study, a different approach is reported for the development of TPB-based sorbent for Cs⁺ sequestration. Instead of immobilization, a TPB-based polymer was prepared by crosslinking TPB monomers with dimethoxymethane (DMM). Unlike its water-soluble salt (i.e. NaBPh₄), crosslinked TPB (TPB-X) is insoluble in water and its granular configuration makes it easy to separate from the feed after Cs⁺ sequestration. The covalent nature of the linkages also provides resilience to acid-induced decomposition, making regeneration and reuse of TPB-X possible. TPB-X exhibits a highly porous structure composed of micropores and mesopores, and registers a very high BET surface area (1030 m² g^-1) and pore volume (1.039 cm³ g^-1). The preference of TPB-X for Cs⁺ is attributed to the combined effect of low desolvation penalty and low ligand strain when the Cs⁺-TPB complex is formed.

The fabricated TPB-X was thoroughly characterized and its Cs⁺ adsorption performance was evaluated in terms of isotherm, kinetics and thermodynamic properties. Its potential application in water treatment was determined using different types of contaminated feed sources. The reusability of TPB-X was examined through cycled Cs⁺ sequestration-regeneration and its stability in acidic media was observed via physico-chemical characterization after multiple acid regenerations.

This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (2020R1A2C1003560, 2021R1A2C2093746, and 2021R1H1A2008284), Basic Science Research Program through the Ministry of Education (2020R1A6A1A03038817).