ZIF-8 Loading Research Articles

Fabrication of novel particle electrode γ-Al2O3@ZIF-8 and its application for degradation of Rhodamine B.

Due to the high Brunauer-Emmett-Teller (BET) surface area of zeolitic imidazolate framework (ZIF)-8, a secondary crystallization method was used to prepare a particle electrode of γ-Al2O3@ZIF-8. According to the results from a field emission scanning electron microscope (SEM) and X-ray diffractometer (XRD), the particle electrode of γ-Al2O3 was successfully loaded with ZIF-8, and the BET surface area (1,433 m2/g) of ZIF-8 was over ten times that of γ-Al2O3. The key operation parameters of cell voltage, pH, initial RhB concentration and electrolyte concentration were all optimized. The observed rate constant (kobs) of the pseudo-first-order kinetic model for the electrocatalytic oxidation (ECO) system with the particle electrode of γ-Al2O3@ZIF-8 (15.2 × 10-2 min-1) was over five times higher than that of the system with the traditional particle electrode of γ-Al2O3 (2.6 × 10-2 min-1). The loading of ZIF-8 on the surface of γ-Al2O3 played an important role in improving electrocatalytic activity for the degradation of Rhodamine B (RhB), and the RhB removal efficiency of the three-dimensional (3D) electrocatalytic system with the particle electrode of γ-Al2O3@ZIF-8 was 93.5% in 15 min, compared with 27.5% in 15 min for the particle electrode of γ-Al2O3. The RhB removal efficiency was kept over 85% after five cycles of reuse for the 3D electrocatalytic system with the particle electrode of γ-Al2O3@ZIF-8.

Efficient Separation of Ethanol-Methanol and Ethanol-Water Mixtures Using ZIF-8 Supported on a Hierarchical Porous Mixed-Oxide Substrate.

This work reports a new approach for the synthesis of a zeolitic imidazolate framework (ZIF-8) composite. It employs the direct growth of the crystalline ZIF-8 on a mixed-metal oxide support TiO2–SiO2 (TSO), which mimics the porous structure of Populus nigra. Using the natural leaf as a template, the TSO support was prepared using a sol–gel method. The growth of the ZIF-8 layer on the TSO support was carried out by the seeds and second growth method. This method facilitates the homogeneous dispersion of ZIF-8 crystals at the surface of the TSO composite. The ZIF-8@TSO composite adsorbs methanol selectively, mainly due to the hierarchical porous structure of the mixed oxide support. As compared with the as-synthesized ZIF-8, a 50% methanol uptake is achieved in the ZIF-8@TSO composite, with only 25 wt % ZIF-8 loading. IAST simulations show that the ZIF-8@TSO composite has a preferential adsorption toward methanol when using an equimolar methanol–ethanol mixture. An opposite behavior is observed for the as-synthesized ZIF-8. The results show that combining MOFs and mixed-oxide supports with bioinspired structures opens opportunities for synthesizing new materials with unique and enhanced adsorption and separation properties.

Rational matching between MOFs and polymers in mixed matrix membranes for propylene/propane separation

Mixed matrix membranes (MMMs) have attracted tremendous attention in the field of gas separation, which adopts the synergistic advantages of the polymer and inorganic phase. However, the MMMs rarely generate sufficient selectivity for energy-efficient gas separation, even if the dispersed molecular sieve is highly selective. Here, an unprecedented improvement (∼4.5-fold) of both C3H6/C3H8 permeability and selectivity on the crosslinked poly(ethylene oxide) (XLPEO) membranes containing ZIF-8 nanocrystals. When the ratio of polymer-to-sieve permeability (Rc/d) is in the range of 0.004–0.36, both C3H6/C3H8 permeability and selectivity increases with the ZIF-8 loading, and the separation performance on MMMs can approach and surpass the-state-of-the-art polymer upper bound. Besides C3H6/C3H8 separation, the universality of this proposed polymer-sieve matching law is suitable for other gas-pairs on MOF-based MMMs.

Reduced thermal rearrangement temperature via formation of zeolitic imidazolate framework (ZIF)-8-based nanocomposites for hydrogen purification

Thermally rearranged polymers are a class of heterocyclic microporous polymers generated by in situ thermal rearrangement (TR) of ortho-hydroxy polyamides or polyimides at elevated temperatures to produce polybenzoxazole (PBO). Poly(hydroxyamide) (PHA) was selected as a model polymer to generate amide-derived PBO (APBO) owing to its lower TR temperature. A nano-size zeolitic imidazolate framework of ZIF-8 was synthesized and incorporated into the PHA matrix to form PHA-ZIF8 nanocomposites. Due to the presence of ZIF-8 inside the PHA matrix, interchain interactions in the PHA matrix may be inhibited that results in a reduced TR temperature for PHA conversion into APBO. Differential scanning calorimetry (DSC) confirmed that the TR temperature of PHA-ZIF8 nanocomposites decreases as a function of ZIF-8 loading. In addition, the conversion of PHA into APBO and the structural integrity of ZIF-8 before and after TR were visualized by Fourier-transform infra-red (FTIR) spectroscopy and X-ray diffractometer (XRD), respectively. Subsequent measurements of gas transport properties of both PHA-ZIF8 and APBO-ZIF8 nanocomposites revealed that the synergistic amalgamation of TR and formation of nanocomposites can boost hydrogen separation performance, particularly H2/CH4, of APBO-ZIF8-35% close to the 2008 upper-bound.

Creation of tiny defects in ZIF-8 by thermal annealing to improve the CO2/N2 separation of mixed matrix membranes

Thermal-annealed ZIF-8 nanoparticles were added into poly(styrene-co-butadiene) (SBC) to improve the permselectivity of mixed matrix membranes (MMMs). After thermal annealing process, polar atoms were produced by the broken Zn–N bond in the ZIF-8 framework. These polar atoms were beneficial in promoting the affinity toward CO2 and improved the permselectivity of the MMMs. Thermal annealing post-treatment also affected the crystallinity, functional group, and framework structure of ZIF-8. When annealing at mild temperature (300 °C), the tiny defect of ZIF-8 framework developed by removing impurity from ZIF-8 framework and broken Zn-N bond, which is benefit for creating surface area, window pore size, and un-paired –N bond, and thus improving the crystallinity. Compared with the raw-ZIF-8 MMMs, the CO2 permeability and CO2/N2 selectivity of annealed ZIF-8 MMMs enhanced because of the polar atoms produced after annealing process. The MMMs exhibited the best gas permeation performance when the annealed ZIF-8 loading weight was 20 wt%. Compared with the pure SBC membrane, CO2 permeability increased from 13.48 barrer to 39.74 barrer, and CO2/N2 selectivity almost doubled from 11.91 to 22.00.

Zeolitic imidazolate framework-8 derived zinc oxide/ carbon nanofiber as freestanding electrodes for lithium storage in lithium-ion batteries

Zeolitic imidazolate framework-derived carbon and metal oxide composites are promising for applications in lithium-ion batteries due to their morphology and porous structure. Herein, we report freestanding carbon nanofibers grafted with amorphous ZnO where the rhombic dodecahedral morphology of the parent (ZIF8) is maintained. The impacts of ZIF8 loading temperature on particle size after pyrolysis and on the electrochemical properties of these hybrid structures for LIBs are investigated. Polyacrylonitrile nanofiber loaded with ZIF8 at 45 °C exhibits a perfect sodalite topology and optimized particle size. The carbonized freestanding composite fibers have a high specific capacity of 818 mAh·g−1 at a current density of 100 mA·g−1 after 100 cycles. This remarkable performance of ZIF8-derived ZnO is due to its loading and coordination chemistry, which facilitates flexible volume changes and continuity in electrical conductivity through a continuous carbon nanofiber.

Effect of Zeolitic Imidazole Framework-8 nanocrystals on hydrocarbon permselective Poly(dimethylsiloxane) membrane as probed by small-angle neutron scattering

Hydrocarbon permselective membranes comprising of Poly (dimethylsiloxane) (PDMS) with Zeolitic Imidazole Framework (ZIF)-8 nanocrystals have been explored. ZIF-8—PDMS membranes of different ZIF-8 loadings were prepared in different solvents. The polymer chain conformations were observed by Ornstein-Zernike model fit to their small-angle neutron scattering profiles. The chain conformations were found to be varied for the membranes with different ZIF-8 loadings. The Debye-Anderson-Brumberger model showed larger scattering domains for the ZIF-8—PDMS membranes prepared in toluene than the membranes prepared in n-heptane. The membrane (toluene) of optimal ZIF-8 loading exhibited ∼60% increment of hydrocarbon permeability but ∼2% increment of N2 permeability as against ∼300% increment of hydrocarbon permeability and >30% of N2 permeability for the membrane (n-heptane) of the similar ZIF-8 loading. This different phenomenon of hydrocarbon permeability enhancement for the membranes with the ZIF-8 loading can be attributed to their different membrane nanostructures.

Enhancing the CO2 plasticization resistance of PS mixed-matrix membrane by blunt zeolitic imidazolate framework

A novel design to synthesize a defect-free mixed-matrix membrane (MMM) exhibiting superior gas separation performance via fully dispersed blunt zeolitic imidazolate framework (ZIF-8) in polymer matrix has been proposed for the first time. The sphericity and interconnected six-membered-ring (6-MR) pore porosity of ZIF-8 was controlled through an aqueous synthetic process by using a non-ionic surfactant (Pluronics, P123) and deionized water as solvent. The use of surfactant in ZIF-8 synthesis resulted in blunt nanocrystals with increased sphericity and 6-MR pore volume as confirmed by scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherm measurements. Subsequent pure gas permeation tests showed that blunt ZIF-8 increased CO2/N2 separation performance through “ideal morphology” in MMMs as a result of the excellent dispersion of ZIF-8 and good ZIF-8-polymer interfacial adhesion within the polymer matrix. A significant increase in CO2/N2 separation results were obtained with the MMM containing 10wt% loading of blunt ZIF-8 (P51), CO2 permeability of 21.5 Barrer (172.6%), and mixed-gas CO2/N2 selectivity of 43.9 (205.6%). The MMMs further displayed good aging-resistance properties for over 40 days, with considerable potential for long-term operation.

Effect of hydrophobic and hydrophilic nanoparticles loaded in D2EHPA/M2EHPA - PTFE supported liquid membrane for simultaneous cationic dyes pertraction

Cationic dyes mixture pertraction experiments of Rhodamine B (RhB) and Methylene Blue (MB) using a flat sheet supported liquid membrane (SLM) were performed. Mono-(2-etylhexyl) ester of phosphoric acid (M2EHPA) and bis-(2-etylhexyl) ester of phosphoric acid (D2EHPA) mixture was used as carrier and Sesame oil to dilute the carrier due to its very high viscosity. Acetic acid (AA) was also used as stripper phase. Influences of hydrophobic and hydrophilic nanoparticles were loaded in a carrier at different loadings (from 0 to 6 mg mL−1) on dyes pertraction at constant operating conditions were investigated. It was found that hydrophilic nanoparticles, including ZnO and TiO2 decrease dyes pertraction, while hydrophobic nanoparticles, including ZIF-8 and Fe3O4 favorably increase this parameter. ZIF-8 was found as the most effective nanoparticles on increasing dyes pertraction and the optimum loading was 2 mg mL−1. Also, the important process parameters that influence on the dyes mixture pertraction efficiency such as feed concentration, carrier concentration, feed pH and strip concentration were studied. In order to investigate the effects of operating parameters, all experiments were performed at a constant 2 mg mL−1 ZIF-8 loading. Optimum pertraction efficiency of RhB and MB were 90.6 and 79.4%, respectively. They were obtained after 10 h pertraction at optimum experimental conditions with feed concentration of 100 mg L−1, carrier concentration of 35% (vol), strip concentration of 0.5 mol L−1, and feed pH of 6. Effect of time on pertraction efficiencies at the optimum conditions were also studied.

Hierarchically Porous Graphene/ZIF-8 Hybrid Aerogel: Preparation, CO2 Uptake Capacity, and Mechanical Property.

A hierarchical zeolitic imidazole framework (ZIF) combining a micropore with a mesoporous structure is desirable to enhance mass transport and gives rise to novel applications. Here, hierarchically porous graphene/ZIF-8 hybrid aerogel (GZAn) materials were successfully prepared by a two-step reduction strategy and a layer-by-layer assembly method. To avoid a tedious dry step and the use of an energy-consuming freeze-drying technology, a reduced graphene oxide hydrogel with different reduction degrees was chosen as a template to grow ZIF-8 crystals in situ. The parameter of density and elemental analysis was adopted to calculate the amount of ZIF-8 in GZAn materials for different assembly cycles. The distribution of micropores and mesopores of GZAn materials was controlled by changing the loading of ZIFs in GZAn materials. Furthermore, GZA8 materials showed enhanced CO2 uptake capacity (0.99 mmol g-1, 298 K, 1 bar) than pure ZIF-s crystals and pure graphene aerogels, showing an excellent synergistic effect of hierarchical pore structures. Meanwhile, with the increase of ZIF-8 loading, the mechanical robustness of GZAn was uplifted obviously. This work provides an efficient method to prepare hierarchically porous ZIFs-based materials with good CO2 uptake capacity and tunable mechanical robustness.

In situ growth of microporous ZIF-8 nanocrystals on a macroporous phyllosilicate mineral

Microporous zeolitic imidazolate frameworks (ZIFs) have shown great potential in many application fields. However, the small dimensions of ZIF nanoparticles make them difficult to employ in practical systems. To overcome this problem, a novel and efficient strategy has been developed to immobilize ZIF crystals on a macroporous phyllosilicate mineral. As an example, water-stable ZIF-8 nanocrystals were synthesized and assembled on the dopamine-modified surface of expanded vermiculite using the sequential addition of methanol solutions of Zn(NO3)2·6H2O and 2-methylimidazole. The ZIF-8 nanoparticle-decorated mineral exhibited a dense growth of microporous ZIF-8 nanocrystals of 80±10nm, resulting in 9.8wt% of ZIF-8 loading and a BET surface area of 120m2/g.

Partial pore blockage and polymer chain rigidification phenomena in PEO/ZIF-8 mixed matrix membranes synthesized by in situ polymerization

Abstract Nanostructured zeolitic imidazolate frameworks (ZIF-8) was incorporated into the mixture of poly (ethylene glycol) methyl ether acrylate (PEGMEA) and pentaerythritol triacrylate (PETA) to synthesize mixed matrix membranes (MMMs) by in situ polymerization for CO 2 /CH 4 separation. The solvent-free polymerization between PEGMEA and PETA was induced by UV light with 1-hydroxylcyclohexyl phenyl ketone as initiator. The chemical structural characterization was performed by Fourier transform infrared spectroscopy. The morphology was characterized by scanning electron microscope. The average chain-to-chain distance of the polymer chains in MMMs was investigated by X-ray diffraction. The thermal property was evaluated by differential scanning calorimetry. The CH 4 and CO 2 gas transport properties of MMMs are reported. The relationship between gas permeation–separation performances or physical properties and ZIF-8 loading is also discussed. However, the permeation–separation performance was not improved in Robeson upper bound plot compared with original polymer membrane as predicted. The significant partial pore blockage and polymer rigidification effect around the ZIFs confirmed by the increase in glass temperature and the decrease in the d -spacing, were mainly responsible for the failure in performance improvement, which offset the high diffusion induced by porous ZIF-8.

Matrimid®/polysulfone blend mixed matrix membranes containing ZIF-8 nanoparticles for high pressure stability in natural gas separation

Abstract Plasticization is of important concern in high pressure natural gas separation. Majority of the pure polymers and MOF-MMM systems suffer from plasticization at low pressures. Combination of polymer blending and MMM approach could lead to plasticization resistant membranes with improved membrane performance. In this work, the gas separation performance of Matrimid® and PSF blend membranes containing ZIF-8 nanoparticles, were studied. The effect of ZIF-8 loading on the gas transport and plasticization behavior of the blend-MOF MMMs was investigated. Gas permeability measurements of PI/PSF-ZIF-8 MMMs showed significant improvements in permeability of both CO2 and CH4, compared to pure reference polymer membrane. At a high loading of 30 wt% ZIF-8, MMM showed an enhancement of 136% in CO2 permeability compared to the pure PI/PSF membrane, while the selectivity stayed constant. This increase in the permeability could be related to the moderate increase in sorption capacity and faster diffusion of gases through the ZIF-8 nanoparticles. More detailed analysis of the gas transport performance of the MMMs showed that the CO2 permeability and the CO2/CH4 selectivity were mainly governed by the increase in CO2 diffusion coefficient. Blend MMMs were considerably more resistant to plasticization phenomenon compared to the pure PI membrane. For pure gases, native PI/PSF blend membrane showed a plasticization pressure of ∼18 bar, which increased to ∼25 bar up to 30 wt% ZIF-8 loading. Short and long CO2 exposure time experiments, with different upstream pressures, showed that the permeability stayed constant in time at pressures below the plasticization pressure while a noticeable increase in permeability was recorded in time at higher pressures. Additionally, these experiments showed that the extent of dilation in the pure PI/PSF membrane was much higher compared to the PI/PSF-ZIF-8 MMMs. In mixed gas (50/50 mol% CO2/CH4) experiments, the pure PI/PSF membrane and the MMMs did not show plasticization over the pressure range investigated, as confirmed by a constant mixed gas CH4 permeability and nearly constant selectivity with pressure. While the pure PI and PI-ZIF-8 MMMs showed the plasticization behavior. Comparing the mixed gas performance of PI/PSF-ZIF-8 membranes with that of pure PI/PSF membranes at high pressures an increase of 197% in CO2 permeability and 30% in CO2/CH4 selectivity was obtained. These results showed that the combination of polymer blending and the mixed matrix membrane approach offers a simple and economically versatile tool to approach higher CO2 permeabilities and CO2/CH4 selectivities while maintaining a stable separation performance in processes involving higher CO2 partial pressures.

Highly efficient polymer–MOF nanocomposite membrane for pervaporation separation of water/methanol/MTBE ternary mixture

Novel polymer–MOF nanocomposite membranes are prepared via the incorporation of ZIF-8 nanocrystals into cardo polyetherketone (PEK-c) for pervaporation separation of water/methanol/MTBE ternary mixtures. The ZIF-8 nanocrystals with 20–40nm size are synthesized for preparing membranes. The resulting membranes have ZIF-8 nanocrystals dispersed homogeneously and embedded in the membrane matrix with adjustable ZIF-8 loading of up to 20wt%. Moreover, the membranes have homogeneous microstructure, good thermal and mechanical stabilities. They show favorable pervaporation performances for separation of the water/methanol/MTBE mixtures. The incorporation of ZIF-8 greatly enhances the permeation flux. At the low ZIF-8 loading, the water selectivity increases and the total separation factor is very high and greater than 1.97×104. Typically, the membrane with 4wt% ZIF-8 has the total flux of 1.48kgμmm−2h−1, water and total separation factor of 181 and 1.97×104 respectively. The newly developed nanocomposite membranes have a great potential in high-efficient purification of MTBE.

Application of poly (amide-b-ethylene oxide)/zeolitic imidazolate framework nanocomposite membrane in gas separation

Mixed matrix membranes (MMMs) are gaining increasing interest in academic and industrial research due to their combined, desirable properties of both polymers and organic/inorganic filler as important materials. In this work, synthesized zeolitic imidazolate framework (ZIF-8) suspension (10–50 wt%) was directly incorporated into a [poly (amide-b-ethylene oxide) Pebax® 1657] matrix in order to improve the gas separation performance of the membrane. Dynamic light scattering (DLS) analysis showed an average diameter of 77.4 nm for the prepared nanoparticles. The transparent membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffractometry (XRD). These indicated excellent dispersion of nanoparticles, which was achieved by ultrasonication before casting the solution. Incorporation of ZIF-8 as filler in the polymer matrix led to improved thermal and mechanical stability of the membranes. This was confirmed by TGA and tensile analyses, indicating good contacts provided at the polymer/filler interfaces. The effect of ZIF-8 loading (up to 50 wt%) on membrane performance was investigated and it showed an optimum loading of 30 %. Single gas (CO2, N2 and CH4) permeation tests revealed rapid, enhanced permeability of the nanocomposite membranes without significant changes in selectivity (compared to those of the pristine polymeric membrane). The permeability increases for CO2, CH4 and N2 in the optimum Pebax® 1657/ZIF-8 (30 wt%) membrane were found in the stated order as 111, 88 and 99 %. The study revealed that Pebax® 1657/ZIF-8 membranes displayed better gas permeation properties compared to those of Pebax® 1657.

Hierarchical Pore Structures and High ZIF-8 Loading on Matrimid Electrospun Fibers by Additive Removal from a Blended Polymer Precursor

A novel method for increasing the effective nanoparticle loading in electrospun fibers is presented involving the electrospinning of polymer blends with suspended ZIF-8 crystals. Initially, varying ratios of Matrimid 5218 and poly(ethylene oxide) (PEO) are electrospun, followed by methanol washes to remove PEO to form porous Matrimid nanofibers. After an optimum surface area is found from the ratio of 1:1 Matrimid:PEO by weight, the metal-organic-framework ZIF-8 is suspended in the polymer blend and electrospun to form ZIF-8 impregnated fibers. After PEO removal from ZIF-8 impregnated fibers, it is found that the ZIF-8 remains in the porous fibers, resulting in drastic increases in ZIF-8:nanofiber loadings, increased gas uptake, and increased accessible ZIF-8 within the fibers. This method is anticipated to work for many different nanoparticle–polymer systems, having implications in the fields of filtration, sensing, catalysis, and adsorption.

Interactive Thermal Effects on Metal-Organic Framework Polymer Composite Membranes.

Polymeric membranes are important tools for intensifying separation processes in chemical industries, concerning strategic tasks such as CO2 sequestration, H2 production, and water supply and disposal. Mixed-matrix and supported membranes have been widely developed; recently many of them have been based on metal-organic frameworks (MOFs). However, most of the impacts MOFs have within the polymer matrix have yet to be determined. The effects related to thermal behavior arising from the combination of MOF ZIF-8 and polysulfone have now been quantified. The catalyzed oxidation of the polymer is strongly affected by the MOF crystal size and distribution inside the membrane. A 16 wt % 140 nm-sized ZIF-8 loading causes a 40 % decrease in the observed activation energy of the polysulfone oxidation that takes place at a temperature (545 °C) 80 °C lower than in the raw polymer (625 °C).

Utilizing low ZIF-8 loading for an asymmetric PSf/ZIF-8 mixed matrix membrane for CO2/CH4 separation

Illustration of gas permeation across different zif-8 loading in asymmetric membrane.

Simultaneous Spray Self‐Assembly of Highly Loaded ZIF‐8–PDMS Nanohybrid Membranes Exhibiting Exceptionally High Biobutanol‐Permselective Pervaporation

The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed-matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self-assembly of a zeolitic imidazolate framework (ZIF)-polymer suspension and a cross-linker/catalyst solution as a method for the fabrication of a well-dispersed ZIF-8-PDMS nanohybrid membrane with an extremely high loading. The ZIF-8-PDMS membrane showed excellent biobutanol-permselective pervaporation performance. When the ZIF-8 loading was increased to 40 wt%, the total flux and separation factor could reach 4846.2 g m(-2) h(-1) and 81.6, respectively, in the recovery of n-butanol from 1.0 wt% aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect-free mixed-matrix membranes for many applications.

Development of dual layer of ZIF-8/PEBAX-2533 mixed matrix membrane for CO2 capture

A new kind of self-supported dual layer mixed matrix membrane was developed in this work using ZIF-8 as inorganic filler in PEBAX-2533 polymer matrix. The developed dual layer flat sheet mixed matrix membrane was characterized to investigate the morphology of organic-based and inorganic-based layer. The gas separation properties of the mixed matrix membranes were tested using single gases CO2, CH4, N2, and O2 and a mixture of CO2 and N2 in dry and humidified conditions. The permeability of all examined gases increased as the inorganic filler content increased in the matrix membranes, and specifically it increased dramatically for CO2 in all cases, single feed gas and dry and humidified mixed gas. The CO2/N2 selectivity decreased slightly from 33.8 for the pure PEBAX membrane to 32.3 for the mixed matrix membrane with 35% ZIF-8 loading, while more significant drop in CO2/N2 selectivity was observed in experiments using mixed gases.