MOF stability and gas adsorption as a function of exposure to water, humid air, SO2, and NO2

Abstract

Gas adsorption and stability to liquid water, humid air, and acid gasses on metal organic frameworks have been studied using a high-throughput adsorption measurement system. Among the seven MOFs studied, Cu-HF, Zn-NDC, and Ni-NIC showed higher CO2/N2 sorption selectivities, (8–12), than the other MOFs (∼4), mainly due to high CO2 adsorption. Long term (5days) NO2 exposure, as well as exposure to liquid water, resulted in partial decomposition of the original structure of Zn-NDC with a corresponding 26–30% decrease in CO2 adsorption capacity. No noticeable changes in X-ray diffraction (XRD) patterns were observed for the other MOFs with small variations in adsorption capacities, indicating structural robustness to acid gas and liquid water. Short-term exposure to humid air (3d) and acid gasses (2d) caused a decrease in CO2 and N2 adsorption capacity for Cu-HF and an increase in adsorption capacity for Ni-NIC. Measurements indicate that pore flexibility in Cu-HF, Zn-NDC, Ni-NIC and Cu-NH2 is modulated by temperature: large SF6 molecules are rejected from the pores at room temperature (as expected based on kinetic diameter), but N2, which does adsorb internally at room temperature, is rejected from the pores at 77K.