Efficient synthesis of covalent organic frameworks in supercritical carbon dioxide and their application in iodine capture

Abstract

Covalent organic frameworks (COFs) are commonly synthesized via solvothermal methods at high temperatures for more than 72 hours, utilizing hazardous organic solvents as reaction media. Here, we propose a methodology for the rapid (2-hour) synthesis of imine-linked and hydrazone-linked COFs in supercritical carbon dioxide (scCO₂), thereby preventing most of the drawbacks of traditional solvothermal methods. The crystallinity and porosity of COFs synthesized in scCO₂ (designated as scCO₂-COFs) are comparable to or better than those obtained by traditional solvothermal approaches. Furthermore, the iodine adsorption capacity of these scCO₂-COFs is analyzed. The results suggest that the synthesized scCO₂-COFs have a remarkable iodine adsorption capacity in the range of 1.01 to 6.38 g g⁻¹ at 75 °C under ambient pressure conditions. The adsorbed iodine in the scCO₂-COFs can be rapidly released into methanol, and their exceptional iodine adsorption capacity can be maintained after five runs. The outcomes of this research could unlock new opportunities for designing and synthesizing scCO₂-COFs, aimed at a broad range of environmental applications.