Development of positively charged porous organic polymers for $CO_2$ conversion

Abstract

With rise in greenhouse gas and $CO_2$ level in atmosphere, various consequences are affecting global climatic issues, economies and concern for general populations health. In order to contend with potential harms to global impact, Carbon Capture Storage (CCS) and Carbon Capture Utilization (CCU) strategies have been widely developed by scientific communities. While CCS focuses on carbon dioxide storage at high temperature, CCU further approaches the global issues by applying its stored carbon dioxide and utilize into making something useful. However, as carbon dioxide is known to be at the most stable form, large amount of energy is required to convert it back into something useful. For CCU strategy to be feasible as a probable strategy, one must consider the carbon footprint, thus conversion must take absolute minimal amount of energy. Previous studies have indicated conversion of carbon dioxide into cyclic carbonates may be a feasible strategy as it requires comparably low energy and does not require a redox reagent to change states in a suitable catalytic system. However, from sustainable perspective, the challenge associated with most of previously reported systems requires high pressure condition with use of co-catalyst to enhance the reaction activity. Our approach uses nano-porous materials having inherent features such as high specific surface area and high porosity with tenability of chemical functionalities. Thus, we expect its intrinsic nature of nano-porous materials will furnish the availability of active sites per amount of substrate, hence accelerating the overall rate of reaction. Hereby, we report comprehensive synthesis of quaternary ammonium salts grafted nano-porous covalent organic polymers (COPs). Furthermore, we report exceptional carbon dioxide utilization in ambient pressure without using co-catalyst and solvent. We observed that our positive charged COP catalyst showed excellent conversion and selectivity for substrates like epichlorohydrin under ambient pressure and co-catalyst/additive free conditions. Also, the catalyst shows high conversion (>99%), high selectivity (>99%), and thermal stability up to $400^\circ C$.