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

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 degrees 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.