Hybrid Benzimidazole–Dichloroimidazole Zeolitic Imidazolate Frameworks Based on ZIF-7 and Their Application in Mixed Matrix Membranes for CO₂/N₂ Separation

Abstract

Mixed-linker zeolitic imidazolate frameworks (ZIFs) with the sodalite (sod) topology type and based on ZIF-7 have been prepared by direct synthesis from the mixtures of benzimidazole (BzIm) and 4,5-dichloroimidazole (dcIm). Incorporation of dcIm into the ZIF-7 structure gives ZIF-7/COK-17 hybrids with rhombohedral symmetry that do not show the “open-to-closed form” structural transition upon solvent removal exhibited by ZIF-7. They show Type I isotherms for low molecular weight gases and high affinity for CO2 even at low partial pressures. Synthesis under mild conditions gives ZIF nanoparticles (250–400 nm) suitable for incorporation into mixed matrix membranes (MMMs): these were prepared with both glassy (Matrimid) and rubbery (PEBAX 1657) polymers. Permeation tests at 298 K and 1.2 bar reveal that the incorporation of Zn­(BzIm0.55dcIm0.45)2 nanoparticles at up to ca. 12 wt % gives defect-free membranes with enhanced CO2 permeability in both polymer matrices, with retention of selectivity (Matrimid) or with an enhancement in selectivity that is most pronounced for the smaller nanoparticles (PEBAX). The membrane with the best performance exhibits a selectivity of ca. 200 for CO2/N2 (a 4-fold increase compared to the pure polymer) and a CO2 permeability of 64 Barrer. At the relatively low loadings investigated, the MMMs’ performance obeys the Maxwell model, and the intrinsic property of diffusivity of the ZIFs can be extracted as a result.

Effect of Boron-Doping on Gate-Opening CO2 Adsorption in Zinc-Benzimidazolate Coordination Networks

“…ZIF-7 and bim showed no peaks in the 800–850 cm –1 region (Figure S5c). The previously reported ZIF-7 shows no IR peak in the 800–840 cm –1 region . The reason why the peak of B-ZIF-7­(NO 3 ) in the 800–840 cm –1 region does not coincide perfectly with that of the starting material H­[B­(bim) 4 ] is probably due to the formation of a coordination network by Zn 2+ and B­(bim) 4 – .…”

Hyper-Cross-Linked Polymers with Sulfur-Based Functionalities for the Prevention of Aging Effects in PIM-1 Mixed Matrix Membranes

“…The permeation properties of the MMMs were tested using the constant volume-variable pressure method in an in-house built time-lag apparatus, which has been detailed in previous works. ,, Permeability coefficients for pure N 2 and CO 2 have been measured at ambient temperature and 1.2 bar. From these measurements, CO 2 /N 2 selectivity has been determined, by dividing the CO 2 coefficient permeability by the N 2 coefficient permeability.…”

Unravelling the structure of CO2 in silica adsorbents: an NMR and computational perspective

“…In the last years, many studies have emerged focusing on the selective CO 2 adsorption from real mixtures with different origins using distinct solid sorbents. 46,64,65,[81][82][83][84][85][86][87][88][89][90][91] However, few studies have been published investigating the adsorption mechanisms in AMPS by ssNMR. The studies published in this respect will be briefly discussed below, emphasizing the utility of NMR techniques to address the subject.…”