CO2 adsorption using functionalized metal-organic frameworks under low pressure: Contribution of functional groups, excluding amines, to adsorption

Selective and effective capture of CO2 from off-gases or even from the atmosphere is very important to prevent global warming. Recently, CO2 adsorption using porous materials has attracted much attention because of its high efficiency and the low corrosiveness of porous adsorbents. Especially, metal-organic frameworks (MOFs, typical porous materials) have been deeply studied for CO2 adsorption because MOFs have strong points like very high porosity, designable structure, and ready modification. Functionalized MOFs have been very useful in CO2 adsorption in increasing the adsorption capacity, selectivity, and heat of adsorption although the porosity could be reduced by loading functional groups (FGs) onto the MOFs. In this review, we analyzed comprehensively the contribution of FGs (excluding the well-known amino group) of MOFs to CO2 adsorption under low pressure. Although there have been a few reports to compare the contribution of some FGs to CO2 adsorption, there are various contradictory results; moreover, to the best of our knowledge, there has been no comprehensive review that analyses the relative contribution of FGs to the adsorption so far. It can be concluded that FGs, especially the ones (such as -OLi, -SO3Li, -NO2, and -SO3H) that can increase the dipole moment of linkers of MOFs, are highly effective in CO2 adsorption mainly because of effective electrostatic interactions. Finally, prospects were given, based on the summary of this review, for future research.