聚合物支撑的金属有机骨架膜的制备及其气体分离性能

由于MOF(金属有机骨架)膜与基底之间的作用力较薄弱,所以制备具有高的H_2渗透性和H_2/CO_2选择性的致密连续的大面积金属有机骨架膜仍具有巨大挑战。本文选取多孔Al_2O_3作为基底,在表面涂覆一层PIM-1(一种固有微孔聚合物),并对其进行羧基化处理,使得表面具有大量的羧基基团,随后利用羧基与金属之间的相互作用,原位生长得到了两种致密连续的聚合物支撑的MOF膜(PIM-1-COOH/ZIF-8和PIM-1-COOH/HKUST-1)。通过XRD的表征可以看出MOF膜是纯相的并且具有较高的结晶性;SEM的测试结果表明MOF膜是致密连续的并且MOF膜与基底之间紧密结合。气体分离测试结果表明,这两种MOF膜对H_2具有较高的渗透性以及H_2/CO_2选择性。在常温常压下,对于PIM-1-COOH/ZIF-8和PIM-1-COOH/HKUST-1膜,H_2/CO_2双组分气体的分离系数分别为7.32、9.69,并且它们H_2的渗透通量分别高于3.16×10~(-6)、1.14×10~(-6) mol·m~(-2)·s~(-1)·Pa~(-1)。在单组份测试中,这两种MOF膜的H_2/CO_2的理想分离系数分别为7.70、12.04;H_2的渗透通量分别高达3.73×10~(-6)、3.86×10~(-6) mol·m~(-2)·s~(-1)·Pa~(-1),这就表明这两种MOF膜有望在H_2的纯化和分离方面广泛应用。

Fabrication of Polymer-Supported Metal Organic Framework Membrane and Its Gas Separation Performance

The fabrication of compact, continuous, and large-scale metal organic framework (MOF) membranes with high permeability and H₂/CO₂ selectivity remains challenging because of the wake interaction between the MOF membrane and the substrate. In addition, substrates with smooth and plain surfaces and suitable pore size are required to prepare high-quality MOF membranes because it is difficult to obtain dense and continuous MOF membranes on a substrate with large pores and rough surfaces. To overcome these challenges, numerous MOF membrane growth methods have emerged, including in situ (direct) growth, secondary (seeded) growth, and layer-by-layer growth methods as well as electrostatic spinning and the chemical modification of the substrate. Among these methods, usage of substrates suitable for surface-functionalization is a promising technique. Herein, Al₂O₃ was selected as the substrate and was coated with PIM-1 (one polymer of intrinsic microporosity), followed by carboxylation of PIM-1 to furnish a large number of carboxyl groups on the surface. In situ growth of the MOF membrane using the interactions between the carboxyl group and the metal yielded two types of compact, continuous, and large-scale polymer-supported MOF membranes (PIM-1-COOH/ZIF-8 and PIM-1-COOH/HKUST-1). Furthermore, the fabricated polymer-supported MOF membrane structures were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Gas separation experiments were performed to explore the gas permeability and selectivity of the prepared MOF membranes. The XRD characterization confirmed the pure phase and high crystallinity of the MOF membranes. The SEM images showed that the MOF membranes were compact and continuous with a tight combination between the MOF crystal membrane and the substrate. Gas separation measurements showed that both MOF membranes exhibited high H₂ permeability and selectivity for H₂/CO₂. For the PIM-1-COOH/ZIF-8 and PIM-1-COOH/HKUST-1 membranes, the 1 : 1 binary mixtures gas separation factors of H₂/CO₂ calculated as the gas molar ratios in the permeate and retentate side 7.32 and 9.69, respectively, at room temperature and atmospheric pressure. The H₂/CO₂ mixture separation factors of the two MOF membranes exceeded the corresponding Knudsen constants (4.7), with H₂ permeances higher than 3.16 × 10^-6 and 1.14 × 10^-6 mol·m^-2·s^-1·Pa^-1, respectively. The ideal separation factors of H₂/CO₂ of both MOF membranes calculated as the ratio of single gas permeances were 7.70 and 12.04, respectively, with the respective H₂ permeances of up to 3.73 × 10^-6 and 3.86 × 10^-6 mol·m^-2·s^-1·Pa^-1. Because of their outstanding characteristics, these novel MOF membranes can be widely used in the fields of H₂ purification and separation.