Role of oxygen, nitrogen and sulfur functionalities on the surface of nanoporous carbons in CO2 adsorption: A critical review

In todays' perspective, separation of CO2 from different gas streams is extremely important. Besides the key separation need of CO2 that lies with its isolation from N-2 in flue gas, different other separation needs of CO2 includes natural gas separation, biogas upgrading, direct CO2 capture from air and purification other gas streams from the mixtures of CO2. The technical challenges of CO2 separation varies with the type of gas mixtures and CO2 concentration. Within different CO2 separation techniques, adsorptive separation of CO2 has gained attention owing to its low cost, regenerability and zero hazard. Among different types of adsorbents, nanoporous carbons are highly attractive because of their lowest cost, versatile synthesis protocol and efficient separation. In past several years, both computation and experimental results established that few selected heteroatoms, including oxygen, nitrogen and sulfur on the surface of porous carbon influences CO2 adsorption to a great extent compared to pristine carbons. This critical review summed up the synthesis procedure, characterization protocol and surface characteristics of oxygen, nitrogen and sulfur functionalized porous carbons, specific type of functionalities in each type of heteroatom that particularly influences CO2 adsorption and computational results as well as experimental findings that corroborated the positive role of heteroatoms in CO2 separation. At the end, few sets of critical comments and recommendations have been provided on the need of accurate analysis, exact interpretation of the role of heteroatoms in CO2 separation and future direction of research that might benefit the CO2 separation by heteroatom doped carbons in real-world.