Amine-Functionalized Metal Organic Framework as a Highly Selective Adsorbent for CO2 over CO

An amine-functionalized metal organic framework, TEPA-MIL-101, was prepared by grafting tetraethylenepentamine (TEPA) on the coordinatively unsaturated Cr(III) sites of MIL-101 for the selective adsorption of CO2 over CO. The adsorbents were characterized using various techniques. The results indicate that the TEPA molecule was successfully grafted on Cr(III) without destroying the intrinsic structure of MIL-101. Isotherms for CO2 and CO adsorption on MIL-101 and TEPA-MIL-101 were obtained to determine the effects of the grafted TEPA on the CO2 adsorption capacity and selectivity. The results show that the CO2 capacity on TEPA-MIL-101 was higher than that on MIL-101 at lower pressures, whereas the CO capacity sharply decreased. The selectivity for CO2 over CO was clearly improved from 1.77 to 70.2 at 298 K and total pressure 40 kPa. The density functional theory calculation for the adsorption of CO2 and CO on TEPA indicates that the bonding energy of CO2 is obviously higher than that of CO. Analysis of the cyclic adsorption performance reveals the high stability of the adsorbent. On the basis of the experimental and simulation results, the grafting of amines on coordinatively unsaturated sites of metal organic frameworks is an effective method of achieving selective adsorption of CO2 over CO.