Effects of doping Mg2+ on the pore structure of MIL-101 and its adsorption selectivity for CH4/N2 gas mixtures

Abstract

In this paper, one kind of porous materials had been prepared by doping Mg2+ on MIL-101 materials using hydrothermal method. Based on the low-pressure nitrogen adsorption (LPNA), X-Ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and High-pressure methane adsorption (HPMA) analyzer, the characteristics of new materials and its adsorption selectivity had been measured and analyzed systematically. Results show that doped Mg2+ would greatly increase the specific surface areas of MIL-101 by 58.2% at the most. Moreover, the pore structure of MIL-101 @ Mg2+ materials tend to be uniform. Compared with MIL-101 parental material, the single crystal size would be decreased by 100–200 nm. From XRD and TEM results, it can be concluded that the chemical skeleton structure of MIL-101 @ Mg2+ series materials are greatly similar with that of parental MIL-101 and not be destroyed by doping Mg2+. Doping Mg2+ increases the adsorption capacity of CH4 and N2 at different level because doping proper amount of Mg2+ restrains the generation of H bond, which has a positive effect on methane gas adsorption. Based on the maximum adsorption capacity and the hysteresis of adsorption and desorption curves, it can be concluded that the optimal Mg2+ doping amount is determined of 12.8%. And, according to the theory of Ideal Adsorbed Solution Theory (IAST), the separation coefficient of CH4/N2 selective adsorption also indicates that MIL-101@12.8% Mg2+ presents the largest adsorption separation coefficient and highest separation potentials.