Growth Of Zeolitic Imidazolate Framework-8 Research Articles

Facile synthesis of multifunctional zeolitic imidazolate framework-8 coatings on diverse bare substrates using a one-step strategy

Rational growth of metal–organic frameworks (MOFs) with controllable morphology and surface properties has been challenging. In this study, facile synthesis of zeolitic imidazolate framework-8 (ZIF-8) in solutions as well as direct in-situ growth of ZIF-8 on various untreated substrates was studied systematically. ZIF crystals with controllable morphology and size were prepared by simply adjusting the ethanol content in the co-solvent system, achieving a rational synthesis of ZIFs in controlled environments. More importantly, co-solvent content was proved to be crucial in the inter-dimensional topotactic phase transformation from a 2-dimensional ZIF-L to a three-dimensional ZIF-8. Then, the facile in-situ crystallization of ZIF-8 on a variety of untreated substrates was studied. With the use of co-solvents, ZIF-8 crystals were formed uniformly and continuously on all substrates regardless of the nature of the support material, including organic supports such as nylon membranes, 3D printed meshes, melamine sponges, mask filter layers, fabric, metallic support stainless-steel meshes, and ceramic pellet. This facile coating strategy provided controllable crystal coating morphology, size, and coating density, without surface modification/pre-treatment steps which are commonly used in the synthesis of high-quality ZIF coatings/membranes. The ZIF-8 coated substrates prepared in a co-solvent system displayed superior performance in some environmental remediation and biomedical applications. For example, the ZIF-8-coated nylon membrane achieved an impressive 96 ∼ 98 % small oil droplet removal from emulsions while maintaining a high water flux of ∼ 1200 L m−2h−1 bar−1. The superhydrophobic ZIF-8-coated melamine sponges were effective for fast oil adsorption. Last but not least, the ZIF-8-coated masks demonstrated greatly improved antibacterial activities. Overall, the co-solvent synthesis method reported in this work has enabled a one-step universal strategy for the direct growth of zeolitic imidazolate framework coating on diverse bare substrates with controlled surface properties and thus showed significant commercial potential in environmental and biological applications.

Synchronously Repairing Core/Surface Defects of Carbon Fibers by In Situ Growth of ZIF-8 and Uniquely Matched High-Energy Irradiation.

Currently, the actual mechanical properties of carbon fibers (CF) differ significantly from the theoretical values. This is primarily attributed to significant limitations imposed by structural defects, greatly hindering the widespread application of CF. To solve this problem, we used in situ growth of zeolitic imidazolate framework-8 (ZIF-8) and γ rays to modulate the core-shell of CF in this study. For the surface structure of CF during the process of γ irradiation, the organic structure within ZIF-8 gradually degrades and forms a cross-linking structure with the surface defects of the CF. This process significantly enhances the binding strength between inorganic material from the postdecomposition of ZIF-8 and the carbon layer on the surface of CF, repairing the surface defects. For the internal structure of CF, γ irradiation can improve the orientation of the internal micropores of CF and increase the degree of internal graphitization of CF. In this paper, an in-depth analysis of CF before and after repair was conducted by using characterization techniques such as nanoindentation and ultrasmall angle X-ray scattering (USAXS). Compared to unmodified CF, its mechanical properties improved by approximately 19.99%, which exceeds that in approximately 95% of similar works in the field.

Designing a MOF-functionalized Nanofibrous Aerogel via Vapor-Phase Synthesis.

Designing 3D mechanically robust and high-surface-area substrates for uniform and high-density deposition of metal-organic frameworks (MOFs) provide a promising strategy to enhance surface accessibility and application of these highly functional materials. Nanofibrous aerogel (NFA) with its highly porous self-supported structure composed of interconnected nanofibrous network offers an ideal platform in this regard. Herein, a facile one-pot strategy is introduced, which utilizes direct deposition of MOF on the nanofibrous surface of the NFAs. NFAs are synthesized using electrospun polyacrylonitrile/polyvinylpyrrolidone (PAN/PVP) polymer nanofibers containing zinc acetate (Zn(Ac)2), which are subjected to freeze drying and thermal treatment. The latter converts Zn(Ac)2 to zinc oxide (ZnO), providing the sites for MOF growth while also adding mechanical integrity to the NFAs through cyclization of the PAN. Exposure of the NFA to the vapor-phase of organic ligand, 2-methylimidazole (2-MeIm) enables in situ growth of zeolitic imidazolate framework-8 (ZIF-8) MOF on the NFA. ZIF-8 loading on the NFAs is further improved by more than tenfold by synthesizing ZnO nanorods/protrusions on the nanofibers, which enables more sites for MOF growth. These findings underscore a significant advancement in designing MOF-based hybrid aerogels, offering a streamlined approach for their use in diverse applications, from catalysis to sensing and water purification.

Unified Roadmap for ZIF-8 Nucleation and Growth: Machine Learning Analysis of Synthetic Variables and Their Impact on Particle Size and Morphology.

Metal-organic frameworks (MOFs) have settled in the scientific community over the last decades as versatile materials with several applications. Among those, zeolitic imidazolate framework 8 (ZIF-8) is a well-known MOF that has been applied in various and diverse fields, from drug-delivery platforms to microelectronics. However, the complex role played by the reaction parameters in controlling the size and morphology of ZIF-8 particles is still not fully understood. Even further, many individual reports propose different nucleation and growth mechanisms for ZIF-8, thus creating a fragmented view for the behavior of the system. To provide a unified view, we have generated a comprehensive data set of synthetic conditions and their final outputs and applied machine learning techniques to analyze the data. Our approach has enabled us to identify the nucleation and growth mechanisms operating for ZIF-8 in a given sub-space of synthetic variables space (chemical space) and to reveal their impact on important features such as final particle size and morphology. By doing so, we draw connections and establish a hierarchy for the role of each synthetic variable and provide with rule of thumb for attaining control on the final particle size. Our results provide a unified roadmap for the nucleation and growth mechanisms of ZIF-8 in agreement with mainstream reported trends, which can guide the rational design of ZIF-8 particles which ultimately determine their suitability for any given targeted application. Altogether, our work represents a step forward in seeking control of the properties of MOFs through a deeper understanding of the rationale behind the synthesis procedures employed for their synthesis.

ZIF-8/balsa wood derived N-doped porous carbon as self-supporting electro-Fenton cathode for efficient antibiotics degradation

Efficient electrochemical advanced oxidation processes (EAOPs) based on carbon catalysts are highly promising candidates for green environmental remediation technologies. Wood derived N-doped porous carbon (WNPC) was prepared the balsa wood with in-situ growth of zeolitic imidazolate framework-8 (ZIF-8) was used as precursor. WNPC acted as self-supporting electric Fenton cathode with high yield and selectivity (96 %) of in-situ H2O2 generation, which effectively avoided the use binder for powder material. Owing to abundant N-doping and oxygen functional groups, the H2O2 yield of WNPC was three times that of balsa wood derived carbon (WC) in electro-Fenton system. The graphite-N promoted the electron transfer, while the pyridinic-N could enhance the selectivity of the 2e-ORR for H2O2 generation. Furthermore, the specific surface area of WNPC was 10 times of WC, with improved hydrophilicity and accelerated electron transfer. The removal efficiency of tetracycline hydrochloride (TC) achieved 91 % within 120 min in electro-Fenton system with WNPC and Fe2+, which was much higher than that with WC (63 %). Free radical scavenging and electron paramagnetic resonance experiments confirmed that ·OH and O2–· were the main active substances for TC degradation in electro-Fenton system. In addition, WNPC has good stability, reusability, and comparable degradation performance of various organic pollutants, and also had efficient degradation performance with actual water. This research proposed a novel strategy to construct efficient electro-Fenton catalyst with wood as precursor, which provides an advancing electrocatalytic methods to achieve efficient and environmentally conscious water purification.

In Situ-Derived N-Doped ZnO from ZIF-8 for Enhanced Ethanol Sensing in ZnO/MEMS Devices.

Microelectromechanical systems (MEMS) gas sensors have numerous advantages such as compact size, low power consumption, ease of integration, etc., while encountering challenges in sensitivity and high resistance because of their low sintering temperature. This work utilizes the in situ growth of Zeolitic Imidazolate Framework-8 (ZIF-8) followed by its conversion to N-doped ZnO. The results obtained from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that the in situ derivation of ZIF-8 facilitates the adhesion of ZnO particles, forming an island-like structure and significantly reducing the interfaces between these particles. Furthermore, powder X-ray diffraction (XRD) analysis, elemental mapping, and X-ray photoelectron spectroscopy (XPS) analysis confirm the conversion of ZIF-8 to ZnO, the successful incorporation of N atoms into the ZnO lattice, and the creation of more oxygen vacancies. The ZIF-8-derived N-doped ZnO/MEMS sensor (ZIF (3)-ZnO/MEMS) exhibits remarkable gas sensitivity for ethanol detection. At an operating temperature of 290 °C, it delivers a substantial response value of 80 towards 25 ppm ethanol, a 13-fold enhancement compared with pristine ZnO/MEMS sensors. The sensor also exhibits an ultra-low theoretical detection limit of 11.5 ppb to ethanol, showcasing its excellent selectivity. The enhanced performance is attributed to the incorporation of N-doped ZnO, which generates abundant oxygen vacancies on the sensor's surface, leading to enhanced interaction with ethanol molecules. Additionally, a substantial two-order-of-magnitude decrease in the resistance of the gas-sensitive film is observed. Overall, this study provides valuable insights into the design and fabrication strategies applicable to high-performance MEMS gas sensors in a broader range of gas sensing.

In situ growth of ZIF-8 on nanofibrous membrane for long-term ultra-high flux coalescence separation of oil-in-water emulsion

The presence of oil-in-water (O/W) emulsions poses a serious threat to the equilibrium of aquatic ecosystems, contaminates potable water resources, and disrupts the structure of soil layers. Consequently, there is an urgent need for effective and economically viable methods for removing emulsified oil droplets from water. The coalescence method has been proposed as an effective means of separating O/W emulsions. In this study, we developed an in situ growth strategy to decorate zeolitic imidazolate framework-8 (ZIF-8) on electrospun polyacrylonitrile (PAN) nanofibers for coalescence separation. The in situ growth process commenced with pretreatment to activate the PAN membrane, creating anchor sites for zinc ions, which was followed by immersion in precursors of ZIF-8 particles. The incorporation of ZIF-8 enhanced amphiphilicity, and roughness, and imparted a positive charge to the membrane, which was anticipated to effectively demulsify and coalesce oil droplets with a negative charge. The ZIF-8/PAN nanofiber membrane obtained a separation ratio exceeding 99.9 % for surfactant-free emulsions and 97.1 % for surfactant-stabilized emulsions. It also demonstrated an ultra-high permeation flux of 21,177 L m−2 h−1 and 14,118 L m−2 h−1, respectively, in a long-term continuous separation process.

Creation of Wood-Based Hierarchical Superstructures via In Situ Growth of ZIF-8 for Enhancing Mechanical Strength and Electromagnetic Shielding Performance.

Given the escalating prevalence of electromagnetic pollution, there is an urgent need for the development of high-performance electromagnetic interference (EMI) shielding materials. Herein, wood-based electromagnetic shielding materials have gained significant popularity due to their exceptional performance as building materials. In this study, a novel wood-based composite with electromagnetic shielding properties is developed. Through the in situ growth of zeolitic imidazolate framework-8 (ZIF-8) crystals on wood fibers, coupled with uniform integration of carbon nanotubes (CNTs), a multifunctional composite named ZIF-8/Poplar-CNT composite is synthesized via a one-step thermoforming process. The incorporation of CNTs endows the composites with excellent EMI shielding effectiveness (EMI SE). Among these elements, despite ZIF-8 crystals not possessing intrinsic electromagnetic shielding functionality, their distinctive dodecahedral structure proves adept at scattering and reflecting electromagnetic waves within the composites, further improving the electromagnetic shielding effect. Hence, the ZIF-8/Poplar-CNT composite (56.95dB) has ≈10dB higher EMI SE compared to that of the composites without ZIF-8 crystals. Meanwhile, ZIF-8 crystals endow the materials with excellent tensile strength (54.84MPa, enhanced by 4 times). Moreover, the introduction of Zn2+ provides superior antibacterial properties. The potential applications of ZIF-8/Poplar-CNT composites extend to diverse areas such as building decoration, electronic products, and medical equipment.

ZIF-8-decorated wood sponge derived from biomimetic mineralization of polydopamine

Zeolitic imidazolate framework-8 (ZIF-8) is extensively researched and used because of its exclusive structural and excellent physicochemical properties; however, significant challenges of alleviating the adverse effects of its particle form in many aspects are still faced by the scientific community. In this study, in situ growth of ZIF-8 within the pore channels and surfaces of green cellulose-based wood sponge was attempted through polydopamine-mediated incubation. The wood sponge was prepared by eliminating lignin and hemicellulose from natural balsa wood. Then, the sponge was impregnated with dopamine aqueous solution to yield polydopamine-covered wood sponge (PWS). ZIF-8 crystals were ultimately in situ grown in the substrate after sequential impregnation with zinc nitrate hexahydrate and 2-methylimidazole aqueous solutions at room temperature. Additionally, the effects of the deposition concentration of the dopamine aqueous solution and ZIF-8 incubation time were investigated. The obtained ZIF-8@PWS was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis and thermogravimetric analysis. Finally, the toluene adsorption performance of porous ZIF-8@PWS in aqueous solution was also briefly evaluated, and it was demonstrated that the maximum adsorption capacity was 106.4 mg/g and the removal rate was as high as 94.2%. This work validates the envisioned universal protocol of preparing ZIF-8-decorated porous substrates through the integrated mediating role of polydopamine.

Encapsulation of lipase in zeolitic imidazolate framework-8 induced by polyethyleneimine to form a honeycomb structure with enhanced activity

Embedding an enzyme in the metal-organic frameworks (MOFs) gives good protection to the fragile enzyme. However, this may also restrain the enzyme activity because of the decreased substrate accessibility. Encapsulation of lipase AK from Pseudomonas fluorescens for preparing the enzyme-MOF composite (AK@ZIF-8-PEI) was performed through a new strategy based on polyethyleneimine and enzyme induced in-situ growth of zeolitic imidazolate framework-8 (ZIF-8). Characterizations indicate that AK@ZIF-8-PEI has a honeycomb structure and the hierarchical porosity formed during the preparation, which provides adequate mass transfer channels for catalytic applications. Activity evaluation shows that specific activity of AK@ZIF-8-PEI is 8-fold than the commercial lipase powder. AK@ZIF-8-PEI is demonstrated as an efficient catalyst in kinetic resolution of α-naphthol enantiomers through enantioselective transesterification. Within 12 h, the conversion and substrate enantiomeric excess (ees) reaches 49.8 % and 96.4 %, achieving an improved resolution than previous researches.

Enhancing bone scaffold interfacial reinforcement through in situ growth of metal–organic frameworks (MOFs) on strontium carbonate: Achieving high strength and osteoimmunomodulation

Bioceramics have been extensively used to improve osteogenesis of polymers because of their excellent bone-forming capabilities. However, the inadequate interfacial bonding between ceramics and polymers compromises their mechanical properties. In this study, zeolitic imidazolate framework-8 (ZIF-8) was grown in situ on strontium carbonate (SrCO3) to construct a core–shell SrCO3@ZIF-8, which was then added to poly-l-lactic acid (PLLA) to print a SrCO3@ZIF-8/PLLA composite scaffold using selective sintering technology. First, ZIF-8 characterized by its multiple organic ligands, forms a robust interface with PLLA. Second, SrCO3 characterized by its negative zeta potential in solution, exhibits the ability to adsorb positively charged zinc ions. This, in turn, promotes the in situ growth of ZIF-8 on SrCO3, eventually achieving perfect bonding between the second phase and the PLLA matrix. Our findings indicated that the composite scaffold exhibited the highest compressive strength (21.93 MPa) and significantly promoted the osteogenic differentiation of mouse mesenchymal stem cells. Moreover, the in vivo results established that the SrCO3@ZIF-8/PLLA scaffold significantly accelerated bone regeneration efficiency in rat femur defects. The prepared scaffold, with its favorable mechanical properties and osteogenic activity, shows considerable promise for applications in bone repair.

High-efficiency air filter aerogel resembling blood cell with heterogeneous epitaxial growth of zeolitic imidazolate framework-8 anchored on tunicate cellulose nanofibers for integrated air cleaning

Metal-organic frameworks (MOFs) possess highly ordered porous structures and photocatalytic capabilities, making them ideal for air cleaning and antibacterial applications. However, the crystallization kinetics of MOFs constrain their crystal structure, which limits their practical usage for air cleaning and other applications. Herein, we present a non-MOF template strategy to achieve heterogeneous epitaxial growth of zeolitic imidazolate framework-8 (ZIF-8) on cellulose extracted from tunicate. TEMPO-oxidation tunicate cellulose nanofibers (TOCNFs) have a high length-diameter ratio (>1000) and negatively charged carboxyl and hydroxyl groups that serve as suitable templates to promote heterogeneous nucleation of the ZIF-8 crystal, thereby resulting in the fabrication of a unique porous structure resembling blood cell. The ZIF-8@TOCNFs aerogel shows good porosity performance, achieving a maximum particulate matter (PM) removal efficiency of 95.80 % with a low pressure drop of 14 Pa at an air-flow velocity of 0.34 m/s. Compared to other works and commercial filters, ZIF-8@TOCNFs aerogel exhibits a higher quality factor (QF) of up to 0.197 Pa−1. Furthermore, ZIF-8@TOCNFs aerogel also demonstrates remarkable antibacterial and antiviral performance without UV photocatalysis. This unique design of ZIF-8@TOCNFs aerogel opens a new avenue for non-MOF template growth of MOF-on-MOF heterostructures and provides a novel strategy for preparing high-performance air filters with an integrated performance of low pressure drop, high removal efficiency and QF, great antibacterial and antiviral properties.

Aromatic polymer dual-confined magnetic metal-organic framework microspheres enable highly efficient removal of dyes, heavy metals, and antibiotics

Considering the diversified threats to freshwater, it is challenging to achieve highly efficient treatment of wastewater containing organic dyes, antibiotics, and heavy metal ions. Herein, we put forward a series of magnetic adsorbents based on an aromatic polymer-mediated dual-confinement strategy. The aromatic polymer plays double roles in both encapsulating magnetic Fe3O4 nanoparticles and providing nucleation sites for the metallic and organic precursors of zeolitic imidazolate framework-8 (ZIF-8). The internal and external confinement enables stable magnetic response and subsequent epitaxial growth of ZIF-8, resulting in recyclable metal–organic framework (MOF) microspheres as adsorbents. The BET specific surface area of the MOF microspheres is up to 1002.0 m2·g−1, and the maximum adsorption capacities of malachite green (MG), tetracycline (TC), and Cu(II) predicted by the Langmuir isotherm at 303.15 K are 1823.60, 909.09 and 2305.44 mg‧g−1, respectively. The MOF microspheres exhibit excellent broad-spectrum adsorption capacities for the three pollutants in neutral and strongly alkaline environments. In addition, the overall adsorption performances remain positive after 5 cycles of adsorption–desorption experiments accompanied by nearly invariable saturation magnetization. This study develops a competitive magnetic adsorbent for the multi-targeted removal of dyes, heavy metals, and antibiotics, which can balance the cost-effective preparation, impressive adsorption capacities, and high cycling stabilities toward the remediation of complex wastewater.

Halloysite@polydopamine/ZIF-8 Nanocomposites for Efficient Removal of Heavy Metal Ions

In this study, polymeric nanocomposites of zeolitic imidazolate frameworks (ZIFs) were synthesized by assembly of a biomimetic polymer-polydopamine (PDA)onto halloysite nanotubes (HNTs@PDA), followed by the in situ growth of zeolitic imidazolate framework-8 (ZIF-8) on the surface of HNTs@PDA. The obtained nanocomposites (HNTs@PDA/ZIF-8) prevented agglomeration of ZIFs and increased the number of active sites derived from PDA. The factors influencing heavy metal ions (Pb2+, Cd2+, Cu2+, and Ni2+) adsorption by HNTs@PDA/ZIF-8 were discussed. The Langmuir model was able to well describe the adsorption, and the maximum adsorption capacity of HNTs@PDA/ZIF-8 was calculated to be 285.00 mg/g for Cu2+, 515.00 mg/g for Pb2+, 185 mg/g for Cd2+ and 112.5 mg/g for Ni2+. Thermodynamic parameters confirmed that the adsorption was exothermic and spontaneous. Moreover, HNTs@PDA/ZIF-8 has good regenerability, which is very important in practical applications. The adsorption mechanism study showed that electrostatic attraction, coordination reactions and ion-exchange were the main mechanisms between the adsorbents and heavy metal ions. Hence, HNTs@PDA/ZIF-8 is a promising candidate for removing heavy metal ions from wastewater.

Biodegradable MOFilters for Effective Air Filtration and Sterilization by Coupling MOF Functionalization and Mechanical Polarization of Fibrous Poly(lactic acid).

High-performance air filtration materials are important for addressing the airborne pollutants. Herein, we propose an unprecedented access to biodegradable poly(lactic acid) (PLA)-based MOFilters with excellent filtering performance and antibacterial activity. The fabrication involved a stepwise in situ growth of zeolitic imidazolate framework-8 (ZIF-8) crystals at the surface of microfibrous PLA membranes, followed by mechanical polarization under high pressure and low temperature (5 MPa, 40 °C) to trigger the ordered alignment of dipoles in PLA chains and ZIF-8. The unique structural features allowed these PLA-based MOFilters to achieve an exceptional combination of excellent tensile properties, high dielectric constant (up to 2.4 F/m), and enhanced surface potential as high as 4 kV. Arising from the remarkable surface activity and electrostatic adsorption effect, a significant increase (from over 12% to nearly 20%) in PM0.3 filtration efficiency was observed for the PLA-based MOFilters compared to that of pure PLA counterparts, with weak relation to the airflow velocities (10-85 L/min). Moreover, the air resistance was controlled at a considerably low level for all the MOFilters, that is, below 183 Pa even at 85 L/min. It is worth noting that distinct antibacterial properties were achieved for the MOFilters, as illustrated by the inhibitive rates of 87 and 100% against Escherichia coli and Staphylococcus aureus, respectively. The proposed concept of PLA-based MOFilters offers unprecedented multifunction integration, which may fuel the development of biodegradable versatile filters with high capturing and antibacterial performances yet desirable manufacturing feasibility.

In Situ Synchrotron X-ray Scattering Investigation of Cathodic ZIF-8 Deposition on Graphite Using 3D-Printed Cells

Electrochemical approaches provide unique means to fabricate thin films of metal-organic frameworks (MOFs). However, the kinetics of electrochemical MOF deposition has not been quantitatively investigated so far. In this study, we report the first in situ measurements of electrochemical MOF growth using transmission synchrotron X-ray scattering. Electrochemical cells based on poly(lactic acid) with two windows were fabricated using fused-deposition modeling. The resulting three-dimensional (3D)-printed cells, the surface of which was coated with paraffin wax to prevent solvent percolation through the polymer material, were used to monitor the cathodic growth of zeolitic imidazolate framework-8 (ZIF-8) on graphite in a methanol solution containing ZnCl2 and 2-methylimidazole (Hmim) at different cathodic potentials. The resulting time-resolved X-ray diffraction data showed a gradual increase in crystal size with negligible changes in crystal orientation during the cathodic ZIF-8 deposition. More importantly, the time-resolved data provided a means to quantitatively assess the kinetics of the cathodic ZIF-8 growth using the Gualtieri model, revealing that the cathodic potential and Hmim concentration affected crystal growth kinetics but not nucleation kinetics. These ZIF-8 samples exhibited changes in X-ray diffraction patterns after being washed with methanol and dried in air, indicating that in situ measurements are essential to investigate mechanisms behind MOF electrodeposition.

Synthesis of nanofiltration membranes with enhanced monovalent and divalent selectivity using β-cyclodextrin, tannic acid and ZIF-8

β-cyclodextrin (β-CD) and tannic acid (TA) together as an organic phase and zeolitic imidazolate framework-8 (ZIF-8) as an additive can be used along with trimesoyl chloride (TMC) as a monomer to synthesize nanofiltration (NF) membranes. Those membranes have better separation performance and provide higher flux. In this study, a new NF membrane was synthesized using them to investigate the effects of monomer concentration, substrate morphology, and reaction temperature on membrane performance. The results showed that when the concentrations of both β-CD and TA were 1 wt%, the membranes had the highest selectivity (2.99) for monovalent and divalent salts. A 10-fold increase in TMC concentration (0.05 to 0.5 wt%) optimized membrane selectivity and flux. When both spongy and cavernous structures were present in the substrate, the membranes could achieve >85 % removal of monovalent and divalent salts. After the introduction of ZIF-8, the roughness of the membrane increased, and the removal rate of monovalent salts decreased significantly, resulting in a salt selectivity of 7.97 and a flux up to 27.81 ± 1.17 L/(m2 h). The growth of ZIF-8 on the membrane surface was assisted by an increase in the reaction temperature.

Controllable surfactant-directed zeolitic-imidazolate-8 growth on swollen 2D zeolites

To meet society’s need for more and more specialized materials, this work focuses on the preparation of porous metal–organic framework (MOF)–zeolite hybrid materials based on two 2D zeolites, namely, IPC-1P (Institute of Physical Chemistry - 1 Precursor) and the metal–organic framework ZIF-8 (Zeolitic Imidazolate Framework-8). Using the previously well-established assembly–disassembly–organization–reassembly method, the zeolite was (i) synthesized, (ii) hydrolyzed to a layered zeolite, (iii) the interlayer distance was increased using the swelling agent cetyltrimethylammonium chloride, and (iv) nanocrystals of ZIF-8 were grown stepwise on the zeolite surface but predominantly at the edges of the crystallites where the openings to the interlayer region are located. This selective MOF growth and attachment was facilitated by a combination of intercalation of the metal ions and the swelling agent between the zeolite layers. The influence of the solvent and the number of additional steps on the ZIF-8 growth on the zeolite was systematically investigated, and the synthesis protocol was successfully adapted to a further two-dimensional silicate RUB-18 (Ruhr-Universität Bochum - 18). This paves the way toward the controlled preparation of more MOF–zeolite hybrid materials, which might provide interesting properties for future applications.

In-situ growth of zeolitic imidazolate framework-8 on polypyrrole nanotubes for highly efficient and reversible capture of radioiodine

Effective capture of radioiodine derived from nuclear reactor accidents and spent fuel reprocessing is of critical significance for the sustainable development of nuclear energy. Herein, we reported the successful synthesis of core-shell PPyNT@ZIF-8 (PZ) nanocomposites with ZIF-8 nanocrystals decorating polypyrrole nanotubes (PPyNT) through a facile, self-assembly procedure. Taking advantage of abundant electron-rich nitrogen atoms of polypyrrole skeleton as well as the high specific surface areas and porosities, these PZ nanocomposites had potential application in radioiodine capture. The maximum uptake capacity of as-synthesized PZ nanocomposites for vapor iodine reached up to 603.8 wt% within 5 h. Additionally, PZ nanocomposites exhibited excellent recycle abilities, as the uptake capacity of PZ-3 still remained 381.7 wt% (63.2% of the initial capacity) after five capture-release cycles. In iodine/cyclohexane solution, the maximum iodine adsorption capacity was 837.9 mg g-1 and all of the loaded iodine could be effectively released in ethanol solution. The excellent iodine capture performance was primarily attributed to the strong affinity between the Lewis acidic iodine molecules and the Lewis basic nitrogen atoms to form polyiodide ions. Considering their excellent iodine adsorption capacity and superior stability, PZ nanocomposites could be employed to effectively eliminate radioactive iodine.

ZiF-8 induced carbon electrodes for selective lithium recovery from aqueous feed water by employing capacitive deionization system

The demand for lithium (Li) will grow from about 500,000 metric tons of lithium carbonate equivalent in 2021 to 3–4 million metric tons in 2030. To meet the Li demand, the separation of Li-mixed monovalent and divalent cations is critical for Li extraction from an aqueous medium. Capacitive deionization (CDI) and membrane capacitive deionization (MCDI) have recently emerged as viable water treatment technologies, yet ion-specific selective recovery using CDI systems is still under-investigated. In this study, the electrode surface of each system was modified to improve Li+ selectivity. Metal-organic frameworks (MOF), particularly zeolitic imidazolate framework-8 (ZiF-8), have shown substantial promise due to their tunable pore size and pore channel chemistry. Through an aqueous medium-based surface modification, we offer a simple technique of synthesizing ZiF-8 on carbon electrodes and underneath the cation exchange membrane (CEM). The bare CDI and MCDI systems initially showed poor selectivity towards Li+ in the mono and divalent ion incorporated simulated solutions. The relative selectivity (ρMLi; (M = metal ions)) in the CDI system was estimated as 0.73, 0.43, 0.67, and 0.58 for Na+, K+, Mg2+, and Ca2+, respectively, which was 0.93, 0.97, 0.39, and 0.30 in the MCDI system. In the case of bare activated carbon (AC) electrodes, the difference of hydration enthalpy played a critical role in Li+ selectivity towards other monovalent ions. However, despite having high hydration enthalpy, the Mg2+ and Ca2+ showed low Li+ selectivity due to the superior charge density of divalent ions. On the other hand, after the modification of AC electrodes with in-situ growth of ZiF-8 on the surface, the Li+ selectivity for monovalent Na+ and K+ was estimated at 3.08 and 1.12, respectively, which is 4.2 and 2.6 times higher than the bare AC electrode, respectively. Besides, compared to Na+, the trade-off between the low dehydration energy of K+ and the rapid ion transit of dehydrated Li+ made separating challenging. Consequently, for divalent Mg2+ and Ca2+, coulombic attraction dominated both in the bare CDI and MCDI systems. This research sheds light on using the newly developed ZiF-8 coating for selective Li recovery.