Zeolitic Imidazolate Framework-8 Layer Research Articles

Organic-inorganic hybrid ZIF-8/MXene/cellulose-based textiles with improved antibacterial and electromagnetic interference shielding performance

Despite the tremendous efforts on developing antibacterial wearable textile materials containing Ti3C2Tx MXene, the singular antimicrobial mechanism, poor antibacterial durability, and oxidation susceptibility of MXene limits their applications. In this context, flexible multifunctional cellulosic textiles were prepared via layer-by-layer assembly of MXene and the in-situ synthesis of zeolitic imidazolate framework-8 (ZIF-8). Specifically, the introduction of highly conductive MXene enhanced the interface interactions between the ZIF-8 layer and cellulose fibers, endowing the green-based materials with outstanding synergistic photothermal/photodynamic therapy (PTT/PDT) activity and adjustable electromagnetic interference (EMI) shielding performance. In-situ polymerization formed a MXene/ZIF-8 bilayer structure, promoting the generation of reactive oxygen species (ROS) while protecting MXene from oxidation. The as-prepared smart textile exhibited excellent bactericidal efficacy of >99.99 % against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) after 5 min of NIR (300 mW cm−2) irradiation which is below the maximum permissible exposure (MPE) limit. The sustained released Zn2+ from the ZIF-8 layer achieved a bactericidal efficiency of over 99.99 % within 48 h without NIR light. Furthermore, this smart textile also demonstrated remarkable EMI shielding efficiency (47.7 dB). Clearly, this study provides an elaborate strategy for designing and constructing multifunctional cellulose-based materials for a variety of applications.

In vivo evaluation of bone regeneration using ZIF8-modified polypropylene membrane in rat calvarium defects.

The profound potential of zeolitic imidazolate framework 8 (ZIF8) thin film for inducing osteogenesis has been previously established under in vitro conditions. As the next step towards the clinical application of ZIF8-modified substrates in periodontology, this in vivo study aimed to evaluate the ability of the ZIF8 crystalline layer to induce bone regeneration in an animal model defect. Following the mechanical characterization of the membranes and analysing the in vitro degradation of the ZIF8 layer, in vivo bone regeneration was evaluated in a critical-sized (5-mm) rat calvarial bone defect model. For each animal, one defect was randomly covered with either a polypropylene (PP) or a ZIF8-modified membrane (n = 7 per group), while the other defect was left untreated as a control. Eight weeks post surgery, bone formation was assessed by microcomputed tomography scanning, haematoxylin and eosin staining and immunohistochemical analysis. The ZIF8-modified membrane outperformed the PP membrane in terms of mechanical properties and revealed a trace Zn+2 release. Results of in vivo evaluation verified the superior barrier function of the ZIF8-coated membrane compared with pristine PP membrane. Compared with the limited marginal bone formation in the control and PP groups, the defect area was almost filled with mature bone in the ZIF8-coated membrane group. Our results support the effectiveness of the ZIF8-coated membrane as a promising material for improving clinical outcomes of guided bone regeneration procedures, without using biological components.

Construction of a thermally stable ZIF-8 membrane embedded inside a porous support for H2/CO2 separation: Close interlocking between membrane grains and porous support grains

Zeolitic imidazolate framework-8 (ZIF-8) membranes have emerged as promising wall candidates for use in membrane reactors. These membranes can improve the water gas shift (WGS) reaction performance because of their exceptional thermal stability and marked H2/CO2 sieving ability. Here, we propose a modified counter diffusion scheme to form an unprecedented, thermally stable ZIF-8 membrane: Pre-deposition of a zinc precursor (zinc acetate dihydrate) and subsequent solvothermal reaction with a methanolic solution of the ligand (2-methylimidazole). It appears that the pre-deposition and drying of the Zn precursor on and inside a porous support were key to retarding the diffusion of the Zn source, thus leading to the primary contact between the Zn source and ligand molecules within the porous support. As a result, it is likely that a continuous ZIF-8 layer was formed on the top surface and, more preferentially, at the interface with the grains of the porous support, reaching an infiltration depth of approximately 80 μm. Accordingly, this allowed for the effective blocking of the support pores by ZIF-8 grains, as well as their high dispersion. Notably, the resulting ZIF-8 membrane exhibited a maximum H2/CO2 separation factor of ca. 8.7 at a WGS reaction temperature of 300 °C. Unlike the conventional membrane architecture, ZIF-8 grains were densely embedded inside the porous support, thus reducing the risk of mechanical damage. Furthermore, the unique membrane structure was desirable for securing superior thermal stability for reliable and sustainable H2/CO2 separation at 300 °C for up to 72 h.

Bio-Inspired Self-Adaptive Nanocomposite Array: From Non-antibiotic Antibacterial Actions to Cell Proliferation.

Pathogenic bacterial infection and poor native tissue integration are two major issues encountered by biomaterial implants and devices, which are extremely hard to overcome within a single surface, especially for those without involvement of antibiotics. Herein, a self-adaptive surface that can transform from non-antibiotic antibacterial actions to promotion of cell proliferation is developed by in situ assembly of bacteriostatic 3,3'-diaminodipropylamine (DADP)-doped zeolitic imidazolate framework-8 (ZIF-8) on bio-inspired nanopillars. Initially, the nanocomposite surface shows impressive antibacterial effects, even under severe bacterial infection, due to the combination of mechano-bactericidal activity from a nanopillar structure and bacteriostatic activity contributed by pH-responsive release of DADP. After the complete degradation of the ZIF-8 layer, the refurbished nanopillars not only can still physically rupture bacterial membrane but also facilitate mammalian cell proliferation, due to the obvious difference in cell size. More strikingly, the nanocomposite surface totally avoids the usage of antibiotics, eradicating the potential risk of antimicrobial resistance, and the surface exhibited excellent histocompatibility and lower inflammatory response properties as revealed by in vivo tests. This type of self-adaptive surface may provide a promising alternative for addressing the intractable implant-associated requirements, where antibiotic-free antibacterial activity and native tissue integration are both highly needed.

Zeolitic Imidazolate Framework‑8 (ZIF-8) modified titanium alloy for controlled release of drugs for osteoporosis

The aim of this work was to prepare a biocompatible implant material that enables the release of drug for osteoporosis—risedronate. To achieve this goal, a titanium implant coated with a biocompatible Zeolitic Imidazolate Framework 8 (ZIF-8) layer was prepared that promotes osseointegration at the bone-implant interface. The modifications of the titanium alloy as well as sorption and desorption processes were confirmed using a variety of methods: SEM, EDS XPS, and FT-IR imaging (to determine surface modification, drug distribution, and risedronate sorption), and UV–Vis spectroscopy (to determine drug sorption and release profile). Both the ZIF-8 layer and the drug are evenly distributed on the surface of the titanium alloy. The obtained ZIF-8 layer did not contain impurities and zinc ions were strongly bounded by ZIF-8 layer. The ZIF-8 layer was stable during drug sorption. The drug was released in small doses for 16 h, which may help patients recover immediately after surgery. This is the first case of using ZIF-8 on the surface of the titanium alloy as carrier that releases the drug under the influence of body fluids directly at the site of the disease. It is an ideal material for implants designed for people suffering from osteoporosis.

In-situ regulation of zinc metal surface for Dendrite-Free Zinc-ion hybrid supercapacitors

Aqueous Zn-ion hybrid supercapacitors (ZHSCs) combine the high power density of supercapacitors with the high energy density of batteries. However, the growth of dendrite and spontaneous Zn corrosion damage the service life of ZHSCs and further seriously restrict their large-scale application in energy storage fields. Herein, we study the corrosion mechanism of Zn metal in ZnSO4 solution and report a method for the modification of Zn anode with zeolitic imidazolate framework-8 (ZIF-8) layer grown in-situ. The obtained ZIF-8 layer with hydrophobicity can not only inhibit Zn corrosion and induce Zn electroplating/peeling on the Zn surface, but also promote uniform deposition of Zn during charge/discharge processes. As a result, the prepared dendrite-free Zn electrode shows low polarization (89.0 mV at 10 mA cm−2) and high cycling stability (over 800 h at 10 mA cm−2), and the developed ZHSC maintains a high capacity retention of 96% after 13,000 cycles at 5 A g−1. Furthermore, a solar power supply system is assembled by the ZHSC and monocrystalline silicon plates to certify the utility of the device, and it can light a LED successfully. This study provides a simple and inexpensive strategy to manipulate the Zn electrodeposition behavior from dendrites to non-dendritic structures, which builds a way for the development of practical ZHSCs with mild electrolytes.

Mechanobiology of Dental Pulp Stem Cells at the Interface of Aqueous-Based Fabricated ZIF8 Thin Film.

The limited knowledge on how biological systems sense and respond to the mechanical properties of metal-organic framework (MOF) thin films is a critical restriction factor for their extensive usage. To bridge this gap, we performed an in vitro study for defining and linking surface characteristics at the interface of the zeolitic imidazolate framework-8 (ZIF8) thin layer to stem cell behavior. First, the physio-mechanical properties of the ZIF8 layer grown on polydopamine (PDA) and tannic acid (TA) layers have been studied. The response of dental pulp stem cells (DPSCs) to different surface states was examined. The results showed that the uniform crystalline microstructure of the ZIF8 on PDA and TA effectively led to the 61- and 388-fold increased surface roughness, 3- and 2.5-fold moderated elastic modulus, almost 3-fold elevated surface free energy, and highly charged surfaces (ζ = -60 mV for TA/ZIF8), respectively. Beyond the inherent bioactivity of the ZIF8 layer, these substrate cues promoted advanced cell adhesion (∼two times) and high proliferation rate. Furthermore, we found a substantial increment in the differentiation efficiency of DPSCs on the ZIF8 layer, in a way that the expression of functional adipocyte (PPARG) and osteoblast (SPP1) markers was, respectively, elevated around 30 000- and 10 000-fold on the TA/ZIF8-coated silicon wafer (SW). Our findings support the impact of fabrication strategy on the biointerface properties of the ZIF8 layer and bring SW/TA/ZIF8 as a robust platform for managing stem cells for biomedical applications.

ZIF-8 membranes supported on silicalite-seeded substrates for propylene/propane separation

Zeolitic Imidazolate Framework-8 (ZIF-8) membranes have shown great potential for effective separation of industrially important propylene/propane gas mixtures. In this work, we coated the silicalite seed nanoparticles on the anodic alumina oxide (AAO) substrate in order to increase membrane-substrate bonding. ZIF-8 membrane was synthesized on a silicalite-seeded AAO substrate by secondary growth method. It was found that high quality ZIF-8 membrane was fabricated due to strong attachment of silicalite seed crystals to AAO substrates through hydrogen bonding. Moreover, when ZnCl2 was used as the Zn source, the ZIF-8 layer was formed with larger ZIF-8 crystal size and a more intergrown surface than the layer in which ZnNO3 was used. An excellent propylene/propane separation factor of 170 was obtained in a silicalite-seeded ZIF-8 membrane with ZnCl2, which is twice that of a ZIF-8 membrane synthesized without the seeding process, and which is 3.6 times higher than a silicalite-seeded ZIF-8 membrane with ZnNO3.

Enhanced water permeance of a polyamide thin-film composite nanofiltration membrane with a metal-organic framework interlayer

Constructing an interlayer between porous substrate and polyamide (PA) film is an effective strategy to overcome the ubiquitous trade-off between permeability and selectivity, which are both important properties for nanofiltration performance. In this study, a poly(sodium 4-styrenesulfonate) (PSS) assisted interfacial synthesis method was proposed to fabricate a zeolitic imidazolate framework-8 (ZIF-8) interlayer between the PA film and microporous poly(ether sulfone) (PES) membrane. The addition of PSS to Zn2+ containing aqueous solution was able to stabilize the ZIF-8 layer formed at the water/n-hexane interface and benefited the homogeneous loading of ZIF-8 on the substrate with effective coverage of the macrovoids. The surface of ZIF-8 loaded PES membrane became smoother and more negatively charged, providing improved conditions for interfacial polymerization to form a thin, loose, and defect-free PA film. The pure water permeance of the TFC membrane containing modified ZIF-8 interlayer was 9.6 L m-2 h-1·bar-1, twice that of the pristine TFC membrane. Meanwhile, its rejection of sodium sulfate, rhodamine B, and acid fuchsin was well maintained. The introduction of ZIF-8 interlayer via the PSS assisted interfacial synthesis method was a promising technique to fabricate high-performance NF membrane for water treatment.

Superhydrophobic ZIF-8-Based Dual-Layer Coating for Enhanced Corrosion Protection of Mg Alloy.

Magnesium (Mg) and its alloys are regarded as the most promising engineering materials because of their unique property. However, the Mg alloys were easily corroded in humid environments, which restricted their wider applications. Herein, the superhydrophobic ZIF-8/PVDF/LDH (SZPL) double-layered coating was fabricated on Mg alloys via electrodeposition and dip-coating methods, which consisted of the underlying layered double hydroxide (LDH) transition structure and top superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer. Besides, the LDH transition structure not only worked as a protection shield but also strengthened the binding force between the substrate and the top superhydrophobic ZIF-8 layer. The top superhydrophobic ZIF-8 layer could serve as an armor on the LDH layer to further prevent the corrosive ions from infiltrating the microporous defects. In addition, the as-prepared SZPL double-layered coating showed robust superhydrophobic and self-cleaning properties, which could block the electrolyte invasion. Furthermore, the electrochemical tests demonstrated that the SZPL coating highly enhanced the corrosion protection ability of Mg alloys. Moreover, the superhydrophobic ZIF-8-based coating could still retain excellent anticorrosion property after immersion in 3.5 wt % NaCl solution for 7 days. The enhanced anticorrosion ability was ascribed to the fact that a synergistic effect of the underlying LDH transition layer hindered the transmission of aggressive ions and the top superhydrophobic ZIF-8-based coating decreased the contact area of the substrate with corrosive solution. Therefore, such coatings offer a new strategy for fabricating excellent anticorrosive coatings with robust superhydrophobicity and self-cleaning performance on metal substrates.

Surface modification of polyvinylidene fluoride membranes with ZIF-8 nanoparticles layer using interfacial method for BSA separation and dye removal

In this research, porous polyvinylidene fluoride (PVDF) membranes were prepared by the phase inversion method and coated with ultra-thin zeolitic imidazolate framework-8 (ZIF-8) layer using interfacial synthesis to fabricate an inorganic-organic nanofiltration membrane with good antifouling properties. The ZIF-8 layer was created by interfacial reaction of Zn2+ aqueous solution and 2-methylimidazole/n-hexane solution by two steps immersion of the PVDF support in these solutions with different contact times (1, 2, 3, 5 and 8 h). The coated ZIF-8 layer on the surface of membranes was characterized with SEM, EDX, ATR-FTIR and XRD analyses. Effect of the ZIF-8 on membrane hydrophilicity was studied by the water contact angle analysis. Also, water flux, BSA protein solution flux and dye rejection were investigated using a dead-end membrane cell test. The results showed that the membranes flux was significantly increased by modifying the membrane surface by ZIF-8 due to hydrophilicity improvement and formation of special water-pass channels in ZIF-8 layer. With increasing reaction time of interfacial synthesis, the flux decreased due to the increased thickness of the deposited layer. Three types of dyes (Rhodamine B, Reactive Green 19 and Direct Black 38) were applied for rejection test and the fabricated membranes indicated high capability in the dyes solution removal (74%, 82% and 98%, respectively). The ZIF-8 coated membranes presented appropriate antifouling properties.

Current Perspectives and Mini Review on Zeolitic Imidazolate Framework-8 (ZIF-8) Membranes on Organic Substrates

Zeolitic Imidazolate Framework (ZIF) membranes have been considered as promising membrane for gas separation processes due to their robustness and good separation capabilities. The separation of hydrogen (H2) from larger gases is one of their potential applications. Among the different types of ZIF, ZIF-8 is considered as potential candidates for H2 separation owing to its small aperture size and excellent chemical stability. In recent years, ZIF-8 membranes have been fabricated on both inorganic and polymeric substrates. The fabrication of the ZIF-8 layer on polymeric substrates is more challenging than its inorganic counterpart because of the incompatibility issue between organic substrates and ZIF-8. However, the flexible nature of polymeric substrates offers better mechanical stability at high pressure than inorganic substrates. The purpose of this mini-review is to present the state of the art and challenges of research on ZIF-8 membrane synthesis on different polymeric substrates. These challenges include the formation of cracks and defects due to compatibility issues and membrane stability at different operating conditions. Current research results showed excellent gas separation properties of ZIF-8 membranes on polymeric substrates that can surpass the trade-offline of gas permeability and selectivity.

Uniform zeolitic imidazolate framework coating via in situ recoordination for efficient polysulfide trapping

The “shuttle effect” in lithium sulfur battery system is the most prominent challenge hampering its further development and application in the energy storage industry. Metal-organic framework (MOF) derived carbon materials are considered to be efficient sulfur hosts to confine the polysulfides because of the unique porous structure and the heteroatom doping. However, a strong acid wash step is usually needed to remove the metal or metal oxide residual after pyrolysis, which will produce a large amount of acidic waste solution and increase the complexity of the synthetic process. Herein, instead of being removed, the uniformly dispersed ZnO nanoparticles in the pyrolytic polyhedra from zeolitic imidazolate framework-8 (ZIF-8) is directly used as the metal source to prepare a new ZIF-8 coating layer. This novel structure possesses not only the unique inner porous structure and high conductivity of pyrolytic carbon, but also the extra protection from ZIF-8 layer with both physical confinement and chemisorption to polysulfides. The resulting cathode displays an initial capacity of 1410 mAh g−1 at 0.2 C, and desirable cycling stability and rate capability are also obtained.

Development of a Wireless Surface Acoustic Wave Methane Sensor Using a Metal-Organic Framework As a Sensing Layer for Natural Gas Pipelines

Methane emission from the processing and transportation of fossil fuels can create serious environmental and safety issues as well as a financial burden. The need to monitor the energy infrastructure creates an opportunity for developing low-cost and robust sensors with wireless options. Wireless surface acoustic wave (SAW) devices, which are highly sensitive, cost-efficient, and passive, are a potential candidate for these applications. Nanoporous metal-organic frameworks (MOFs), which can selectively adsorb large amounts of gases in engineered pores at ambient conditions, are potential sensing layers. Here, we present on the development of a wireless and passive SAW sensor using the MOF zeolitic imidazolate framework-8 (ZIF-8) as the sensing layer for methane detection at ambient conditions. The SAW delay lines (nominal operating frequency = 436 MHz) were custom fabricated on Y-Z LiNbO3 piezoelectric substrates and coated with a 500 nm thick ZIF-8 layer using a dip coating method. The devices were excited by 428 MHz RF pulses to test for various concentrations of CO2 and CH4 in N2 background at a constant gas flow rate. Wireless measurements were performed via dipole antennas of nominal resonant frequency 433 MHz. When the sensor was exposed to the gases, surface acoustic wave phase shifted in a negative direction relative to the N2 baseline. This shift was attributed to the decrease in SAW velocity due to the increased mass of the MOF film upon gas adsorption. The CO2 and CH4 sensitivities extracted as the slopes of the respective calibration curves were 1.26 deg/vol-% and 0.03 deg/vol-%, respectively. It is important to note that currently tested minimum concentrations of CO2 and CH4 were 1% and 20%, respectively. Also, the wireless measurements were highly affected by the housing and metal reflectors around it. The demonstration on wireless methane sensing is of great importance for remote monitoring of methane emission sites and transmission pipelines. Our current investigations are focused in advancing the detection limit for leak detection and addressing the electromagnetic interferences in wireless measurement caused by the housing.

Acoustic Sensors Coated with a Metal-Organic Framework for Room Temperature Monitoring of Carbon Dioxide and Methane

Greenhouse gases emissions such as carbon dioxide and methane which are generated from the processing and use of fossil fuels have created serious environmental concerns. The need to monitor the emissions of these gases in mobile and stationary point sources present novel challenges in sensor design. Surface acoustic SAW devices, which offer high sensitivity, low cost, wireless and passive options as well as tunable selectivity when coated with proper sensing materials, can be a potential platform for monitoring these gases. However, many coating materials including metal oxides and polymers are not suitable for developing room temperature gas sensors due to their poor interaction capacity (physisorption or chemisorption) with the gases. Recently, metal-organic frameworks (MOFs) have drawn a considerable attention in sensing applications for their high sorption capacity at ambient condition and functional tenability. Here, we present on the development of surface acoustic wave (SAW) carbon dioxide and methane sensors by applying the zeolitic imidazolate framework-8 (ZIF-8) MOF as the sensing layer. The SAW delay lines with the nominal operating frequency of 436 MHz were custom fabricated on Y-Z LiNbO3 piezoelectric substrates and 9 MHz quartz crystal microbalance (QCM) resonators made of At-cut quartz and gold electrodes were purchased from INFICON. The transducers were coated with 200 nm thick ZIF-8 layer by simple solution-based dip coating method and exposed to various gases at room temperature in a N2 environment. Relative to pure N2, the sensors showed a good response to CO2 and CH4 while remaining neutral to CO and air. The resonance frequency of the QCM sensor decreased by 217 and 9.2 Hz and the phase of the SAW in the delay line changed by 0.72 and 0.04 radian for pure CO2 and CH4, respectively. The responses of the sensors varied linearly with the concentrations of either gas. From a linear fit, the sensitivities of the QCM sensor to CO2 and CH4 were evaluated to be 2.18 Hz/vol-% and 0.1 Hz/vol-%, respectively. Similarly, the SAW sensor showed a sensitivity of 0.39 deg/vol-% to CO2 while its response to various concentrations of CH4 is under study. Since ZIF-8 is a non-conducting material and its stiffness changes negligibly upon gas adsorption for thin film cases, the mass loading effect can be considered the dominant sensing mechanism for both sensors. When the coated films adsorbed the gas molecules, their mass density increased thereby inducing a decrease in acoustic velocity which was recorded in terms of frequency or phase change. Given that the SAW sensors can be operated in wireless and passive mode, the current study is of great importance in developing passive sensors for distant monitoring of greenhouse gases in the environment and at other emission sites.

Polyamide thin film composite membranes containing ZIF-8 for the separation of pharmaceutical compounds from aqueous streams

Abstract Pharmaceutical compounds which are hydrophilic and biologically persistent are being recognized as new unregulated contaminants in water. The hydrophilic characteristic deters their removal through biological processes and adsorption. However, electrostatic repulsion and size sieving in nanofiltration (NF) can be used for the removal of these compounds. Although both NF and reverse osmosis (RO) are options for removal of pharmaceutical compounds from aqueous feeds, the high pressure (and therefore high energy consumption) and membrane fouling remain serious concerns. Therefore development of improved membranes continues to be a key research area. Metal organic frameworks (MOF) are a class of porous crystalline compounds which offer advantages of large surface area and controlled porosity. MOFs have been used as adsorbents. More recently, MOF membranes and MOF incorporated polymeric membranes have gained importance. In this work, MOF incorporated polymeric membrane was prepared and tested for removal of the common analgesic acetaminophen (or paracetamol, MW 151 g/mol). Thin film polyamide composite membranes were synthesized by interfacial polymerization with zeolitic imidazolate framework-8 (ZIF-8). Two different structures were prepared and characterized (i) polysulfone (PSF) support membranes with ZIF-8 and polyamide (PA) separation layer, and (ii) layer-by layer (LBL) polyamide/ZIF-8 nanocomposite membrane on top of PSF support. The latter synthesis protocol produced defect free TFC membrane with 55% acetaminophen retention and permeance equivalent to conventional PSF/PA membrane.

Growth and characterization of zeolitic imidazolate framework-8 nanocrystalline layers on microstructured surfaces for liquid crystal alignment

The coverage of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals deposited on patterned sol–gel films is significantly affected by the surface morphology. The ZIF-8 layer can induce vertical alignment of a typical nematic liquid crystal (LC) E7.

Thickness Reduction of the Zeolitic Imidazolate Framework-8 Membrane by Controlling the Reaction Rate during the Membrane Preparation

The layer thickness of a zeolitic imidazolate framework-8 (ZIF-8) membrane was successfully reduced in order to obtain high permeance of propylene. The ZIF-8 membranes for propylene/propane separation were prepared using a counter-diffusion method by changing the solution concentration and the molar ratio of 2-methylimidazole to zinc ion (Hmim/Zn2+). ZIF-8 layers with different thicknesses were formed in the outermost regions of porous α-alumina capillary substrates, and the minimum thickness of the ZIF-8 layer was 5 µm. Single-component gas permeation properties were measured using propylene and propane at a temperature of 298 K, and the permeability, diffusivity, and solubility were analyzed. The maximum propylene/propane permselectivity of 135, diffusivity selectivity of 125, and solubility selectivity of 1.1 were obtained at a Hmim/Zn2+ ratio of 1 with a propylene permeance of 1.1×10−9 mol·m−2·s−1·Pa−1. By contrast, a propylene/propane permselectivity of 113 with a propylene permeance of 3.3×10−9 mol·m−2·s−1·Pa−1 was obtained at a Hmim/Zn2+ ratio of 0.33. The thickness of the ZIF-8 layer, the permselectivity of propylene/propane, and the permeance of propylene were controlled by regulating the concentration and the Hmim/Zn2+ ratio for the synthesis of the ZIF-8 membrane by the counter-diffusion method.

Diffusive separation of propylene/propane with ZIF-8 membranes

The contribution of diffusive separation of propylene/propane was determined from the permeation properties of zeolitic-imidazolate framework-8 (ZIF-8)11ZIF, zeolitic-imidazolate framework. membranes. These membranes were prepared using a counter diffusion method, resulting in the formation of an 80μm-thick ZIF-8 layer on the outermost section of a porous α-alumina capillary substrate. Single-component gas permeation properties were investigated using helium, hydrogen, carbon dioxide, oxygen, nitrogen, methane, propylene, and propane at temperatures ranging from 298 to 363K. The molecular sieve gas permeation properties of the ZIF-8 membranes increased with reaction time, which is consistent with the evolution of ZIF-8 crystal formation. The ZIF-8 membrane permeances of hydrogen and propylene reached 9.1×10−8 and 2.5×10−9molm−2s−1Pa−1, respectively. The ideal separation factors for hydrogen/propane and propylene/propane at 298K were found to be 2000 and 59, respectively. The diffusion separation factor increased with decreasing temperature, reaching 23, while the solution separation factor remained 2.7. Therefore, the separation of propylene/propane was attributed to be mainly governed by diffusive separation.

Oriented Zeolitic Imidazolate Framework-8 Membrane with Sharp H2/C3H8 Molecular Sieve Separation

A highly oriented zeolitic imidazolate framework 8 (ZIF-8) composite membrane was prepared by seeding and secondary growth. By dip-coating, preformed ZIF-8 nanocrystals were attached to the surface of a porous α-alumina support using polyethyleneimine as the coupling agent. After solvothermal treatment, a continuous and well-intergrown ZIF-8 layer was obtained. X-ray diffraction analysis of the membrane showed preferred orientation of the {100} plane parallel to the support. Further time-dependent investigations by scanning and transmission electron microscopy as well as X-ray diffraction indicated that the preferred orientation develops during an evolutionary growth process. In gas mixture permeation experiments, the membrane showed good performance in H2/hydrocarbon separation. A sharp molecular sieve separation is observed for an equimolar H2/C3H8 mixture with a separation factor above 300.