(339c) Hyper-Crosslinked Tetraphenylboron (TPBx) As a Versatile Platform Material for the Development of Sorbents for Various Metal Ions

Hyper-crosslinked tetraphenylboron (TPBx) is a water insoluble, thermally stable and chemically resilient material. It is characterized by a highly porous network with hierarchical pore structure comprised mainly of micropores and mesopores, which explains its very high BET surface area (1030 m² g^-1). Its chemical architecture consists mainly of benzene moieties which permit further functionalization of different moieties. Such modifications can alter its properties in liquid media and its interaction with substrates, opening TPBx to a myriad of potential applications which include cation adsorption, and establishing TPBx as a versatile platform material for sorbent development similar to carbon nanotubes and mesoporous silica. Herein, a demonstration of this versatility is presented.

Two adsorbents were prepared from TPBx through a series of simple functionalization reactions, first with sulfonation affording SO₃H-TPBx, followed by its reduction to the thia-functionalized form SH-TPBx. It is worth noting that TPBx withstands prolonged exposure to harsh reaction conditions during these functionalization steps which underscore its chemical stability --- to a strong oxidizing acid in the first step, and to reflux conditions in benzene in the second.

SO₃H-TPBx and SH-TPBx possess high BET surface areas (> 600 m² g^-1) and were found to retain the morphology and hierarchical porous structure of TPBx. Both TPBx analogs exhibit remarkably enhanced wettability and dispersibility in aqueous media and effectively adsorb their target metal ions (Cs⁺ and Sr²⁺ for SO₃H-TPBx, Pt⁴⁺ and Pd²⁺ for SH-TPBx) over a wide pH range, suggesting possible applications in metal ion decontamination and retrieval strategies in acidic and alkaline water wastes and in various types of water resources (surface and ground water). The inherent porosity and enhanced hydrophilicity of these TPBx analogs, along with their rich collection of spatially organized negative charges contributed by sulfur groups and tetraphenylboron moieties, seem to converge to create highly favorable conditions for cation adsorption resulting in very fast kinetics (equilibrium achieved in ~ 1 min), essentially complete contaminant removal even with very dilute contaminant concentrations in the feed (~ 2 mg L^-1), and high sorption capacities (e.g. 360 mg g^-1 and 115 mg g^-1 for Cs⁺ and Sr²⁺, respectively, when using SO₃H-TPBx). Moreover, the physical and chemical resilience of these TPBx analogs allows for their regeneration and repeated use. Overall, these results suggest that TPBx can serve as platform material for the development of highly efficient and practical cation sorbents.

This work 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).