Iodine adsorption by thiophene-based covalent organic polymer: a study of structural influence on performance

Abstract

A novel covalent organic polymer (COP) derived from tris(4-aminophenyl)amine (TPA) and 4,4′-(thiophene-2,5-diyl) dibenzaldehyde (T) moieties was constructed and synthesized (TPAT-COP). The synthesized polymer has been successfully characterized by FT-IR, ¹³C CP-MAS NMR and surface studies (e.g., BET and SEM), revealing a surface area of 1199 m² g⁻¹ and a microporous nature with a mean pore diameter of 1.54 A^°. Further, TGA analysis shows extraordinary stability of the material even at high temperature. Accompanying this, TPAT-COP exhibits an exceptionally high iodine (I₂) adsorption capacity (467 wt%) in the vapour phase as well as in the liquid phase (3.89 g g⁻¹), which is on par with or even surpasses that of the most advanced thiophene based COPs. These results are the outcome of the meticulous design of the polymer embedded with sulphur sites and covalent bridges, which can counterbalance the low surface area and pore volume. Comprehensive analysis using FT-IR, XPS, and morphological data corroborated by computational studies like DFT calculation and Non-Covalent Interaction (NCI) using multiwfn software demonstrates the higher affinity of the sulphur atom in thiophene ring and the nitrogen atom in imine linkage towards iodine. Further, the outcomes were compared with organometallic based COP (DAPA-COP) to validate the introduction of thiophene units has significantly improved the adsorption capacity of iodine. As a result, a remarkably high retention rate and reversibility were achieved. Thus, a simple, cost-effective design and strategy defined the synthesized COP as a viable tool for rapid I₂ adsorption.