Carbon dioxide capture in MOFs: The effect of ligand functionalization

The carbon dioxide challenge is one of the most pressing problems facing our planet. Physisorption between certain adsorbents and CO2 molecules could allow conveniently reversible processes to capture CO2 gas. Metal–organic frameworks (MOFs) have recently attracted intense research interest because of their permanent porous structures, large surface areas, and potential applications as novel adsorbents. Tuning the interior pores of MOFs to improve their adsorption characteristics is considered an effective approach to enhance gas adsorption/separation performance. Recently, there is a growing interest to explore the impact of grafting functional groups with variable polarities (NH2, OH, CO2H, CF3, SO3H, NO2,…) onto the surfaces of MOFs through their organic ligands or directly coordinated to open metal centers on the CO2 capture/separation performance. Ligand functionalization in MOFs has been demonstrated to enhance gas adsorption and while ligand functionalization does not change the overall structure of the frameworks, it can influence the gas uptake behavior. In this review, we show how ligand functionalization influences the CO2 affinity and adsorption capacity of MOFs. The comparisons drawn in this review have sought to provide a roadmap for the future development of functionalized MOFs.