Diffusion coefficients in nanoporous solids derived from membrane permeation measurements

Based on the molecular understanding of the interplay of diffusion and adsorption, new membrane materials can be developed and the operational conditions of gas separation membranes can be optimized. Therefore, numerous diffusion and adsorption studies are conducted to optimize membrane materials. However, in an opposite way, transport or Fickian diffusion coefficients DT can be derived from membrane permeation studies with surprising accuracy. From measuring the gas transport through nanoporous supported thin-layer membranes or through mixed matrix membranes with nanoporous fillers in a polymer matrix, the transport diffusion coefficients DT of gases in novel nanoporous materials such as zeolites, MOFs, COFs… can be estimated

Microwave-assisted synthesis, characterization and modeling of cpo-27-mg metal-organic framework for drug delivery

The coordination polymer CPO-27-Mg was rapidly synthesized under microwave irra-diation. This material exhibits a sufficiently high drug loading towards aspirin (~8% wt.) and paracetamol (~14% wt.). The binding of these two molecules with the inner surface of the metal-organic framework was studied employing the Gaussian and Plane Wave approach of the Density Functional Theory. The structure of CPO-27-Mg persists after the adsorption of aspirin or paracetamol and their desorption energies, being quite high, decrease under solvent conditions. © 2021 by the authors. Li-censee MDPI, Basel, Switzerland

Improvement of hydrothermal stability of zeolitic imidazolate frameworks

The metal-organic framework ZIF-8, which undergoes hydrolysis under hydrothermal conditions, is endowed with high water-resistance after a shell-ligand-exchange-reaction. The stabilized ZIF-8 retains its structural characteristics with improved application performances in adsorption and membrane separation. © 2013 The Royal Society of Chemistry

Microwave-assisted synthesis of well-shaped UiO-66-NH2 with high CO2 adsorption capacity

In a detailed study, the influence of microwave irradiation, synthesis time and temperature, addition of acetic acid (HAc) as a modulator on the morphology, crystallinity and stability of UiO-66-NH2 is investigated to develop a reliable and reproducible strategy for the preparation of well-shaped UiO-66-NH2. The UiO-66-NH2 were characterized by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and gas adsorption. It is found that well-shaped UiO-66-NH2 with a high CO2 adsorption capacity can be synthesized in a short time by microwave heating. The UiO-66-NH2 crystals synthesized by microwave heating are of high quality and show a superior CO2 adsorption capacity (5.8 mmol/g at 273k and 1 bar) due to the strong interactions between the -NH2 group and CO2. The CO2/N-2 selectivity of the obtained UiO-66-NH2 at 298 K and 1 bar is 66, which is much higher than that of the pristine UiO-66 of 17.8

Organosilica functionalized zeolitic imidazolate framework ZIF-90 membrane for CO2/CH4 separation

The separation of CO2/CH4 is reported by using 3-aminopropyltriethoxysilane (APTES) modified zeolitic imidazolate framework ZIF-90 membrane. The as-prepared ZIF-90 membrane was modified by APTES based on an imine condensation reaction between the free aldehyde groups of the ZIF-90 frameworks and the amino groups of APTES. After APTES modification, the morphology, purity and crystallinity of the ZIF-90 membrane keep unchanged. Attributing to both pore mouth narrowing and sealing of invisible intercrystalline defects of the polycrystalline ZIF-90 layer, the separation performances of the APTESmodified ZIF-90 membrane are remarkably enhanced. For the separation of equimolar CO2/CH4 mixture at 225 C and 1 bar, a CO2 permeance of 1.26 x 10(-8) mol m(-2) s(-1) Pa-1 and a CO2/CH4 selectivity of 4.7 are obtained, which is of promising in the potential application of CO2 separation and removal. (c) 2013 Elsevier Inc. All rights reserved

Ethene/ethane separation by the MOF membrane ZIF-8: molecular correlation of permeation, adsorption, diffusion

The newly developed MOF membrane ZIF-8 separates an equimolar ethene/ethane mixture at room temperature for 1 and 6 bar feed pressure, respectively, with a selectivity of 2.8 and 2.4. Independent sorption uptake studies of an ethene/ethane mixture on a big ZIF-8 single crystal by IR microscopy detection show in combination with grand canonical Monte Carlo simulations that this moderate ethene selectivity of the ZIF-8 membrane can be explained by the interplay of a preferential ethane adsorption selectivity competing with a preferential ethene diffusion selectivity. This means, that ethane adsorbs stronger than ethene, but ethene diffuses faster and overcompensates the adsorption preference of ethane, resulting in a membrane permeation selectivity for ethene

Highly hydrogen-permselective zeolitic imidazolate framework ZIF-8 membranes prepared on coarse and macroporous tubes through repeated synthesis

Highly hydrogen-permselective zeolitic imidazolate framework ZIF-8 membranes are prepared on coarse and macroporous Al2O3 tubes through a repeated synthesis strategy for the separation of H-2/CO2, H-2/CH4, and H-2/C3H8 mixtures. Since the amino-groups of 3-aminopropyltriethoxysilane (APTES) can coordinate to the free Zn2+ centers and thus bind the growing nano-crystals directly, the nucleation and growth of well intergrown. ZIF-8 membranes could be promoted through a repeated synthesis of the ZIF-8 layer on APTES-modified macroporous Al2O3 tubes. The SEM and XRD characterizations indicate that a dense and phase-pure ZIF-8 membrane with a thickness of about 25.0 mu m can be formed on the alumina tubes by microwave synthesis at 105 degrees C for 3 h, and no cracks, pinholes or other defects were observed in the membrane layer. The ZIF-8 membranes were evaluated in single gas permeation and mixed gas separation. Attributed to the preferential adsorption affinity and capacity as well as a highly porous structure with nano-sized channels, the ZIF-8 membrane displays a high hydrogen permselectivity. For the separation of equimolar H-2/CO2, H-2/CH4, H-2/C3H8 mixtures at 100 degrees C and 2 bar, the mixture separation factors of H-2/CO2, H-2/CH4, and H-2/C3H8 are 5.6, 44.0, 328.6, with a H-2 permeance of about 1.1 x 10(-7) mol m(-2) s(-1) Pa-1, which is promising for potential applications in hydrogen purification and separation. (C) 2015 Elsevier B.V. All rights reserved

Silver-exchanged zeolite LTA molecular sieving membranes with enhanced hydrogen selectivity

In the present work, we report a new road to enhance the gas separation performances of the zeolite Na-LTA membrane by tuning the pore size of zeolite LTA through silver cation exchange. Through the functionalization of the alumina support by using 3-aminopropyltriethoxysilane (APTES), a thin, phase pure and well intergrown zeolite Na-LTA membrane with a thickness of about 5.0 mu m can be facilely prepared on the APTES-modified macroporous alpha-Al2O3 tube. After a following silver exchange treatment of the as-synthesized zeolite Na-LTA membranes, the sodium ions in zeolite Na-LTA framework are replaced by silver ions, thus forming zeolite Ag-LTA membranes with a narrower pore diameter. The zeolite Ag-LTA membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that both the morphology and structure of the zeolite Na-LTA membrane keep unchanged after silver-exchange, and no cracks, pinholes or other defects are observed in the membrane layer. The zeolite Ag-LTA membrane shows high hydrogen selectivity due to the reduction of pore size of the zeolite Ag-LTA. For the separation of the binary mixture at 50 degrees C and 2.0 bar, the separation factor of H-2/C3H8 is alpha approximate to 120.8, which by far exceeds alpha approximate to 19.4 of the starting Na-LTA membrane, and are also much higher than the separation factors previously reported for the H2/C3H8 mixture on zeolite membranes. (C) 2016 Elsevier B.V. All rights reserved