The preparation and adsorption performance of Co-doped MIL-101(Cr) for low-concentration C3F8

Abstract

Octafluoropropane (C3F8) is a kind of super greenhouse gas, and the low concentration of octafluoropropane makes it difficult to be adsorbed and removed. In this study, a series of Co-doped MOFs (CoxCr-MIL-101) have been successfully synthesized using a hydrothermal method without the addition of strong acids such as HF. The structural properties of the prepared CoxCr-MIL-101 are characterized using SEM, XRD, nitrogen adsorption desorption test, etc. The adsorption properties of C3F8 are measured by single-component isothermal adsorption experiments and fixed bed adsorption breakthrough experiments. The adsorption mechanism was investigated via the adsorption theory models. The results show that the introduction of cobalt ions can effectively improve the adsorption capacity of MIL-101, among which the Co0.2Cr-MIL-101 exhibits the best adsorption performance. The C3F8 equilibrium adsorption capacity reaches 0.077 mmol/g at 298 K and 180 Pa, which is 3.03 times that of the pristine MIL-101 and the dynamic adsorption capacity is 20.710 mmol/g (298 K, 1.2 L/min), which is 9.37 times that of the pristine MIL-101. Inspiringly, the IAST separation selectivity of C3F8/N2 at 100 kPa is up to 146.7, which is 14.3 times that of the pristine MIL-101. More importantly, the co-modified adsorbent showed better thermal stability and cyclic stability. In addition, Co0.2Cr-MIL-101 fits the Freundlich isothermal adsorption model, and the adsorption mechanism analysis shows that the high adsorption capacity of Co0.2Cr-MIL-101 benefits from the unique pore structure and abundant active sites of the modified MOFs.