Hyper-crosslinked tetraphenylborate as a regenerable sorbent for Cs sequestration in aqueous media through cation-π interactions.

Practical adsorbents that could efficiently collect radioactive Cesium (Cs) are critically important in achieving proper management and treatment measures for nuclear wastes. Herein, a hyper-crosslinked tetraphenylborate-based adsorbent (TPB-X) was prepared by reacting TPB anions as Cs binding sites with dimethoxymethane (DMM) as crosslinker. The most efficient TPB-X synthesis was attained at 1:4 TPB/DMM mole ratio with sorbent yield of 81.75%. Various techniques such as FTIR, TGA-DTG, N adsorption/desorption and SEM-EDS reveal that TPB-X is a water-insoluble, thermally stable and highly porous granular sorbent. Its hierarchical pore structure explains its very high BET surface area (1030 m g). Sequestration of Cs by TPB-X involves its exchange with H followed by its binding with the phenyl rings of TPB through cation-π interactions. The Cs adsorption in TPB-X is endothermic and spontaneous, which adheres to the Hill isotherm model (q = 140.58 mg g) and follows pseudo-second order kinetics (k = 0.063 g mg h). Calculations from the density functional theory reveal that the binding of TPB anion is strongest for Cs. Thus, TPB-X was able to selectively capture Cs in simulated surface water containing Na, K, Mg, and Ca and in HLLW containing Na, Rb, Sr, and Ba. Hyper-crosslinking was found beneficial in rendering TPB-X reusable as the sorbent was easily retrieved from the feed after Cs capture and was able to withstand the acid treatment for its regeneration. TPB-X exhibited consistent performance with no sign of chemical or physical deterioration. TPB-X offers a practical approach in handling Cs contaminated streams as it can be repeatedly used to enrich Cs in smaller volume of media, which can then be purified for Cs reuse or stored for long-term natural Cs decay process.