Adsorption of gases on small–pore aluminum bisphosphonate MOF MIL–91(Al)

In this work, the adsorption isotherms of small pore bisphosphonate MOF MIL–91(Al) was evaluated for permanent gases viz., CO2, CO, N2, CH4, C2H6 and C3H8. Gravimetric adsorption measurements were performed at three different temperatures 294, 318, 358 K and a wide range of pressures. For all measured gases type–1 adsorption isotherm was observed. Isotherms were modeled using the Virial equation and calculated fit parameters were used to calculate the enthalpy of adsorption. CO2 exhibits moderate enthalpy of adsorption along with excellent selectivity on MIL–91 (Al), thereby making it an attractive adsorbent for gas separation applications. A small pore bisphosphonate MIL–91(Al) is one of the few porous phosphonate MOFs studied so far on adsorption. Ideal Adsorbed Solution Theory predictions show that CO2 exhibits excellent selectivity over CO, CH4 and N2, making it an attractive adsorbent for gas separation applications.