Metal-Free Amine-Anchored Triazine-Based Covalent Organic Polymers for Selective CO2 Adsorption and Conversion to Cyclic Carbonates Under Mild Conditions

Abstract

Attaining both large uptake and high conversion of CO2 under mild reaction conditions within a metal-free covalent organic polymer (COP) is an attractive and challenging strategy for CO2 utilization because CO2 is an abundant and renewable C1 source and a main greenhouse gas. In this study, novel amine-anchored covalent triazine aromatic polymers (CTP-1-NH2 and CTP-2-NH2) were synthesized from 2-amino-4,6-dichloro-1,3,5-triazine, biphenyl, and 1,3,5-triphenylbenzene via facile Friedel–Crafts arylation for CO2 adsorption and conversion reaction. At 273 K and 1 bar, CTP-1-NH2 and CTP-2-NH2 exhibited CO2 uptakes of 187.4 and 224.41 mg/g and CO2/N2 selectivity of 69.45 and 61.38, respectively, outperforming many previously reported COP materials. Moreover, metal-free CTP-1-NH2 with tetrabutylammonium bromide (n-Bu4NBr) exhibited high epoxide conversion and product selectivity under mild (40 °C and 1 bar) and solvent-free conditions within 36 h of reaction time, which were very much comparable to the performances of many metal-coordinated COP catalysts. The spent catalyst was also highly reusable with no active species leaching. A plausible mechanism for CO2 cycloaddition over the CTP-1-NH2 catalyst is proposed. Incorporating amine functionalities into a nitrogen-rich structure could be a promising strategy for developing materials with simultaneous CO2 capture and conversion.