Flexible phosphonium and sulfonate pair-to-pair self-assembled ionic organic single crystals for iodine capture

In this work, four flexible chain phosphonium-based ionic organic single crystals (IOCs) are first facilely prepared by pair-to-pair ionic self-assembly of phosphonium salts and sulfonic acids (salts) under mild conditions. Their structures, morphology, stability, and surface areas are characterized in detail. Featuring a wealth of sulfonate and phenyl groups as powerful active sites for iodine adsorption, these materials exhibit considerable capture capacities. An in-depth investigation of the adsorption mechanism reveals that iodine adsorption on these materials occurs in three distinct states (I₂, I₃ ^-, and I₅ ^-) and follows a mixed-mode adsorption process, involving both physical and chemical interactions. Consequently, this study not only presents a new kind of single crystalline material based on flexible phosphonium and sulfonic anionic pairs, but also significantly hints at the application possibility of this kind of IOC in some other fields.