Insights into high pressure gas adsorption properties of ZIF-67: Experimental and theoretical studies

Abstract

Cobalt 2-methylimidazolate framework (ZIF-67) of SOD topology has been synthesized by solvothermal method in a 2 L schott duran bottle using methanol or dimethylformamide (DMF) as solvents which yielded ~ 2.5 g of material. The effect of solvent in defining the morphology and surface properties has been studied for methanol and DMF. The Powder X-ray diffraction pattern has been refined by Rietveld method (space group = I-43 m, a = 17.0545(4) Å). Diffuse reflectance UV–Vis and X-ray photoelectron spectroscopic methods, probed the presence of Co(II). Cobalt is tetrahedrally coordinated to N atoms of 2-methylimidazole linker, making metal sites saturated, which do not play a major role in gas adsorption. Gas adsorption properties of ZIF-67 have been studied for H2 and CO2 guest molecules at high pressures. ZIF-67 has revealed H2 adsorption properties at 40 bar owing to storage capacity of 0.28 wt% at 300 K and 2.84 wt% at 77 K. At 300 K and 1 bar the material adsorbs 3.9 wt% of CO2 gas but at high pressure of 50 bar, ZIF-67 shows extraordinary CO2 adsorption capacity of 51.4 wt%, proving itself as potential candidate for CO2 capture. Theoretical calculations to obtain absolute adsorption isotherm curves adopting Unilan model reveals CO2 adsorption capacity of 49.2 wt% and heat of adsorption of −9.9 kJ/mol.