Highly efficient and reversible iodine capture utilizing amorphous conjugated covalent triazine-based porous polymers: Experimental and computational studies

Abstract

A robust conjugated covalent triazine framework, CTF-DPA, has been synthesized through a facile Friedel-Crafts alkylation reaction using cyanuric chloride as the cross-linking agent and diphenylacetylene (DPA) as the backbone building block. Benefiting from its unique textural and structural features such as high specific surface area (943 m2 g−1), accessible pores, and abundant π-electrons, CTF-DPA exhibits outstanding iodine-capturing performance. It features an ultrahigh iodine vapor capture capacity of 5.12 g g−1 at 75 °C and 1 bar and a remarkable iodine adsorption capacity of 667 mg g−1 in n-hexane solution. To the best of our knowledge, these are among the highest iodine adsorption capacities reported for porous organic polymers. In contrast, an analog CTF synthesized with trans-stilbene (TS) replacing DPA instead features a slight decrease in specific surface area (919 m2 g−1) but a noticeable reduction in iodine adsorption capacities. The iodine uptake mechanism was investigated by Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy as well as computationally. Density-functional theory (DFT) calculations reveal that charge transfer from conjugated C≡C, phenyl, and triazine moieties to iodine molecules facilitates the generation of charged (poly)iodide species (e.g.,I3−), enhancing the adsorption affinity/capacity. Moreover, CTF-DPA could be recycled five times while preserving above 87.6% of its initial iodine uptake capacity.