Improved CO2 capture performances of ZIF-90 through sequential reduction and lithiation reactions to form a hard/hard structure

Post-synthetic functionalization or modification has been regarded as a promising strategy to treat surfaces of adsorbents for their applications in targeted adsorption and separation processes.In this work,a novel microporous adsorbent for carbon capturing was developed via functionalization of zeolitic imidazolate framework-91(ZIF-91)to generate a hard/hard(metal-oxygen)structure named as lithium-modified ZIF-91(ZIF-91-OLi compound).To this purpose,the ZIF-91 compound as an intermediate product was achieved by reduction of ZIF-90 in the presence of NaBH4 as a good reducing agent.Afterwards,acidic hydrogen atoms in the hydroxyl groups of ZIF-91 were exchanged with lithium cations via reaction of n-BuLi compound as an organo lithium agent through an appropriate procedure.In particular,the as-synthesized ZIF-91-OLi operated as an excellent electron-rich center for CO2 adsorption through trapping the positive carbon centers in the CO2 molecule.DFT calculations revealed that the presence of lithium over the surface of ZIF-91-OLi adsorbent plays an effective role in double enhancement of CO2 storage via creating a strong negative charge center at the oxygen atoms of the imidazolate linker as a result of the lithium/hydrogen exchange system.Finally,the selectivity of CO2/N2 was investigated at different temperatures,revealing the ZIF-91-OLi as a selective adsorbent for industrial application.