CO2 sorption behavior of imidazole, benzimidazole and benzoic acid based coordination polymers

Non corrosive gas, such as CO2, is an environment greenhouse pollutant, but at the same time it is a reusable material with a highly attractive application profile and potential as a building block to create added value for the chemical industry. Current technologies for carbon capture are cumbersome, energy intensive and expensive. However, amongst new developments, porous coordination polymers (PCPs) are being viewed as materials with great potential for CO2 capture. The ability to flexibly design and tune properties of such materials results in different levels of affinity for CO2 sorption/desorption. Imidazole/benzimidazole and benzoic acid based coordination polymers are of interest from the view point that various architectures such as rigid, flexible, interpenetrating, etc., can be designed to influence cavity pore size and different types of supramolecular interactions existing within the pores. CO2 sorption, in these structures, not only depends on surface area and void volume but is also influenced by the electronic environment, i.e., functionalization of the pores with either coordinatively unsaturated metal ions or Lewis base groups. In this review, other important influencing factors including strong non-covalent interactions (π-π bonding, anion-π bonding, CH-π bonding, and H-bonding) present on the pore walls, facilitating selective adsorption of CO2 molecules in substantial quantities (even if Langmuir surface area is very low) are discussed. These interaction potentials in the pores decide quantitatively the sorption of CO2 as function of temperature and pressure.