Stability Of ZIF-8 Research Articles

Chemical spray pyrolysis deposited ZnO/ZIF-8 and cobalt doped ZnO/ZIF-8 composite thin films for highly sensitive and selective ammonia sensing at room temperature

ZnO is a widely studied metal oxide for gas sensor applications concerning its biocompatibility and physio-chemical properties. However, the high operating temperature and low response are drawbacks. ZIF-8, the metal-organic framework of Zinc and imidazolate, is renowned for its gas adsorption property. The poor stability of ZIF-8 also limits its application as an effective gas sensor. Thus, a composite thin film of ZnO and ZIF-8 is deposited on a glass substrate using the chemical spray pyrolysis technique to detect ammonia at room temperature (300 K). The composite thin film is stable, has a good response, and is repeatable. Further, to enhance the sensor response at room temperature, Co is doped to the ZnO/ZIF-8 composite thin films. The sensor response for 1 ppm of ammonia for the Co doped ZnO/ZIF-8 is 301 at room temperature. Along with the gas adsorption capability of ZIF-8 providing more active sites, the change in morphology from flakes to spherical grains on doping with Co provided higher active surface area and free electrons and all together instigated fast redox reaction and conduction mechanism in ZnO. Hence, the Co doped ZnO/ZIF-8 composite thin films have an enhanced response of 117,285 to 50 ppm of ammonia.

Enhancing permeability and stability of ZIF-8/PEBA pervaporation membrane through interface-induced directional nanoparticle distribution

Mixed matrix membranes exhibit enhanced selectivity and permeability, but stability still needs to be improved. In this study, we prepared ZIF-8/PEBA mixed matrix membranes with different loadings and used interface induction to control the directional distribution of nanoparticles. The controlled directional distribution of ZIF-8 in PEBA was studied by optical microscopy and scanning electron microscopy. The effects of different ZIF-8 loading amounts on the formation and pervaporation performance of mixed matrix membranes were thoroughly studied. The prepared membrane was applied to 1 wt% n-butanol aqueous solution, achieving a high flux of 4.9 kg m−2 h−1 and a separation factor of 18.8. The directional distribution of nanoparticles in PEBA prevents direct contact with the feed liquid and effectively protects the structural stability of ZIF-8. The resulting ZIF-8/PEBA membrane showed excellent stability after more than 100 h of operation.

Engineering the activity and stability of ZIF-8(Zn/Co)@g-C3N4 nanocomposites and their synergistic action in converting atmospheric CO2 into cyclic carbonates

The development of novel catalytic materials that integrate multifunctional sites has significant implications for expanding the utilization of CO2 resources. However, simultaneously achieving high activity and stability remains a formidable challenge. In this study, a series of ZIF-8(Zn/Co)@g-C3N4 nanocomposites were prepared by employing a thermo-physical compounding strategy that involved the combination of nitrogen-rich graphitic carbon nitride (g-C3N4) nanosheets with ZIF-8(ZnCo). The influences of different compositions of g-C3N4 and ZIF-8(Zn/Co) on the catalyst structure were systematically investigated. Subsequently, the catalytic activities of these nanocomposites towards the cycloaddition reaction between CO2 and epoxide were examined under different conditions. The presence of abundant Lewis base sites in g-C3N4 facilitates CO2 activation, while multiple Lewis acid sites in ZIF-8(Zn/Co) enable efficient epoxide activation. By working synergistically with a co-catalyst, tetrabutylammonium bromide (TBAB), CO2 and epoxides can be efficiently reacted to synthesize the corresponding cyclic carbonates under mild or even atmospheric pressure conditions. The catalytic reaction conditions were optimized, and both the catalyst's recycling performance and the scope of epoxides with various substituents were investigated. The integration of g-C3N4 and ZIF-8(Zn/Co) endows the catalytic material with exceptional structural stability and remarkable catalytic activity, thereby providing a new platform for highly efficient CO2 conversion.

Bimetallic Zeolitic Imidazole Frameworks for Improved Stability and Performance of Intrusion-Extrusion Energy Applications.

Hydrophobic flexible zeolitic imidazole frameworks (ZIFs) represent reference microporous materials in the area of mechanical energy storage, conversion, and dissipation via non-wetting liquid intrusion-extrusion cycle. However, some of them exhibit drawbacks such as lack of stability, high intrusion pressure, or low intrusion volume that make them non-ideal materials to consider as candidates for real applications. In this work, we face these limitations by exploiting the hybrid ZIF concept. Concretely, a bimetallic SOD-like ZIF consisting of Co and Zn ions was synthesized and compared with Co-ZIF (ZIF-67) and Zn-ZIF (ZIF-8) showing for the first time that the hybrid ZIF combines the good stability of ZIF-8 with the higher water intrusion volume of ZIF-67. Moreover, it is shown that the hybrid-ZIF approach can be used to tune the intrusion/extrusion pressure, which is crucial for technological applications.

ZIF-8 based porous liquids with high hydrothermal stability for carbon capture

Porous liquids (PLs), a novel material that combines both permanent porosity and fluidity, show enormous potential in gas capture and separation applications. However, MOF nanoparticles, as permanent porosity providers in PLs, have poor hydrothermal stability limiting their use in industries with the presence of water. In this study, the shell-ligand exchange reaction (SLER) was employed to replace the 2-methylimidazole on the surface of ZIF-8 crystals with 5,6-dimethylbenzimidazole, which improved the hydrothermal stability of ZIF-8 efficiently. The adsorption kinetic results showed that first-order kinetics could better predict the behavior of ZIF-8-based PLs in CO2 capture. Compared with ZIF-8-PLs, the CO2 capture capacity of ZIF-8-SLER-PLs was increased 30 % at 40 °C. When exposed to water at 80 °C for 20 days, ZIF-8-SLER retains its intact crystal morphology, high surface area and hydrothermal stability. Meanwhile, the 83 % CO2 adsorption capacity of ZIF-8-SLER (20 days) was retained. However, the pore structure of pristine ZIF-8 was collapsed seriously after hydrothermal experiment, and the CO2 adsorption capacity of ZIF-8 (20 days) was decreased by 40.6 % due to the lack of protection by hydrophobic ligands. This study opens a new pathway to use MOFs-based porous liquids for CO2 capture in industrial applications with the presence of water.

Synthesize and characterization of ZIF-8/NaP zeolite composites as a stable acid-base catalyst for organic reactions

Two ZIF-8/NaP zeolite nanocomposites were synthesized through two different methods by adding ZIF-8 or its precursors on the zeolite mother gel and subsequently characterized. The preparation of a micro-meso structure catalyst with strong acid sites was confirmed. The obtained composites were used for esterification reaction of acetic acid by four different alcohols and aldol condensation of benzaldehyde derivatives 2-X and 4-X to evaluate catalytic activities and compare synthesis methods on the applications. The results show that ZIF-8/NaP composite catalyst brings 94.7% and 91.4% efficiency for esterification and aldol condensation reactions, respectively. This catalyst leads to stabilize the structure of ZIF-8 and increase the stability of ZIF-8 in acidic media.

Reversible Growth of Halide Perovskites via Lead Oxide Hydroxide Nitrates Anchored Zeolitic Imidazolate Frameworks for Information Encryption and Decryption.

The low formation energies of metal halide perovskites endow them with potential luminescent materials for applications in information encryption and decryption. However, reversible encryption and decryption are greatly hindered by the difficulty in robustly integrating perovskite ingredients into carrier materials. Here, we report an effective strategy to realize information encryption and decryption by reversible synthesis of halide perovskites, on the lead oxide hydroxide nitrates (Pb13O8(OH)6(NO3)4) anchored zeolitic imidazolate framework composites. Benefiting from the superior stability of ZIF-8 in combination with the strong bond between Pb and N evidenced by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, the as-prepared Pb13O8(OH)6(NO3)4-ZIF-8 nanocomposites (Pb-ZIF-8) can withstand common polar solvent attack. Taking advantage of blade-coating and laser etching, the Pb-ZIF-8 confidential films can be readily encrypted and subsequently decrypted through reaction with halide ammonium salt. Consequently, multiple cycles of encryption and decryption are realized by quenching and recovery of the luminescent MAPbBr3-ZIF-8 films with polar solvents vapor and MABr reaction, respectively. These results provide a viable approach to integrate the state-of-the-art materials perovskites and ZIF for applications in information encryption and decryption films with large scale (up to 6 × 6 cm2), flexibility, and high resolution (approximate 5 μm line width).

The chemical stability of ZIF-8 in aldehyde under air conditions

ZIF-8 evolved from the rhombic dodecahedra into a new octahedron in crotonaldehyde under air conditions.

In Situ Synthetic ZIF-8/Carbon Aerogel Composites as Solid-Phase Microextraction Coating for the Detection of Phthalic Acid Esters in Water Samples.

In this study, a hybrid composite featuring zeolitic imidazolate framework-8/carbon aerogel (ZIF-8/CA) was synthesized via in situ nucleation and growth of ZIF-8 nanoparticles inside carbon aerogels. The novel material was used as the solid-phase microextraction (SPME) coating for the five phthalic acid esters (PAEs) detection by coupling with a gas chromatography–flame ionization detector (GC-FID). Compared with bare carbon aerogel, the ZIF-8/CA presented the best performance, which is attributed to the unique advantages between the high surface area of CA and high hydrophobic properties, the thermal stability of ZIF-8, and their synergistic adsorption effects, such as molecular penetration, hydrogen bond, and π–π stacking interactions. Under the optimized conditions, the as-proposed ZIF-8/CA fiber provided a wide linearity range from 0.2 to 1000 μg L−1 and a low detection limit of 0.17–0.48 μg L−1 for PAEs analysis. The intra-day and inter-day of signal fiber and the fiber–fiber relative standard deviations were observed in the ranges of 3.50–8.16%, 5.02–10.57%, and 5.66–12.11%, respectively. The method was applied to the determination of five PAEs in plastic bottled and river water samples.

Mesoporous carbon promoting the efficiency and stability of single atomic electrocatalysts for oxygen reduction reaction

Single-atom Fe–N–C electrocatalysts are attracting more attentions as one most promising transition metal based single-atom catalyst towards the oxygen reduction reaction (ORR). However, the inaccessibility of internal Fe-Nx active sites and insufficient stability hinder their large-scale application. Herein, a facile benzoate-assisted self-template strategy which could dramatically enhance the oxygen reduction reaction catalytic performance and stability of ZIF-8 derived atomically dispersed Fe–N–C catalysts (Fe-SA/Meso-C) is developed. The sodium benzoate used in the present work is effective for promoting the formation of Fe–N–C catalysts with denser accessible active sites as well as mesopores with diameters ranging from 2.5 to 5 nm. These structural advantages make the synthesized Fe-SA/Meso-C catalysts afford excellent electrocatalytic performance for the ORR in 0.1 M KOH with a positive half-wave potential (E1/2) of 0.926 V vs. RHE and exceptionally high kinetic current density (Jk) of 92.5 mA cm−2 at 0.85 V. Beyond that, Fe-SA/Meso-C shows outstanding long-term stability with over 90% activity retain after 90 h chronoamperometry i-t test as well as superior tolerance to methanol crossover. More importantly, the assembled zinc-air battery with Fe-SA/Meso-C as the cathode material achieves a high peak power density of 166.2 mW cm−2 and a high specific capacity of 776.1 mA h g−1. Our results reveal that small mesopores in atomically dispersed Fe–N–C electrocatalysts could facilitate mass transport, increase the accessibility of active sites and optimize the interface between electrolyte and carbon matrix, thus optimizing their electrocatalytic performance for the ORR. This work paves a way to the design and synthesis of stable single-atom electrocatalysts with optimized structure, electrochemical performance and promising applications.

Polydopamine-stabilized ZIF-8: Improved water stability and lubrication performance

ZIF-8, a novel lubricant additive, is considered to have great potential in reducing friction and wear due to large specific surface area, thermal stability and mechanical flexibility. However, ZIF-8 nanoparticles readily hydrolyze in aqueous solutions, transforming into large-sized lamellar and rod-like materials, which is a major bottleneck as a water-based lubricant additive. Herein, a strategy is proposed to functionalize ZIF-8 via mussel-inspired polydopamine (PDA) polymerization process to improve its lubrication stability in the water phase. The modified ZIF-8 (PDA@ZIF-8) can firmly “locked” water molecules on the surface of PDA to protect internal structure of ZIF-8, and improve its dispersion and stability of ZIF-8 in water. Moreover, ZIF-8@PDA tribofilm and iron oxide chemical protection film are formed during the friction process, and the low shear strength water layer between the contact surfaces contribute to achieving powerful synergistic lubricating effects, resulting in friction coefficient and wear track width reduce by 65% and 66%, respectively. Therefore, this work provides a promising alternative for expanding the practical application of ZIF-8 in aqueous environment and tribology.

Zeolitic Imidazolate Frameworks as Latent Thermal Initiators in the Curing of Epoxy Resin.

The curing of a mixture of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA) with zeolitic imidazolate frameworks (ZIFs)—ZIF-7, ZIF-8, ZIF-11, and ZIF-14—as latent thermal initiators has been critically evaluated. For ZIF-8 and ZIF-14, the % conversion values for GPE were 92 and 93%, respectively, for curing at 100 °C and for 1 h. With regard to the stability of ZIF-8 and ZIF-14 in the GPE-MHHPA mixture, the % conversion values for GPE were 11 and 12% for storage over 8 days at 25 °C. The ZIF-8 and ZIF-14 initiators exhibited excellent thermal latency for heating at 100 °C and showed good stability for storage at 25 °C. To evaluate the practicality of the resin curing system, the reactions of 2,2-bis(4-glycidyloxyphenyl)propane (DGEBA) and MHHPA with ZIFs were studied by differential scanning calorimetry. Prominent exothermic peaks for ZIF-8 and ZIF-14 were observed at 157 and 162 °C, respectively; by comparison, for the commercially available microencapsulated latent thermal initiators HX-3088 and HX-3722, the respective peak maxima were 177 and 181 °C, respectively. The exothermic peak maxima for ZIF-8 and ZIF-14 were lower than those for HX-3088 and HX-3722. The ZIF-8 and ZIF-14 initiators can be stored in precured epoxy resin at 25 °C and cured by lower temperatures compared with commercially-available initiators HX-3088 and HX-3722.

ZnCDs/ZnO@ZIF-8 Zeolite Composites for the Photocatalytic Degradation of Tetracycline

Considering the photocatalytic performance of CDs, ZnO, and the unique porous nanostructure and stability of ZIF-8, we prepared ZnCDs/ZnO@ZIF-8 zeolite composites. The resultant material represented an enhanced ability for the photodegradation of TC compared with that of ZnCDs and ZnO. The photocatalytic degradation efficiency reached over 85%. The catalytic activity of the composites was maintained after four cycles. The experimental result indicated that ⋅O2 radical was the active species in the reaction.

Enhanced enzymatic performance of immobilized lipase on metal organic frameworks with superhydrophobic coating for biodiesel production

Inspired by the interfacial catalysis of lipase, Herein, the hydrophobic ZIF-L coated with polydimethylsiloxane (PDMS) were prepared by chemical vapor deposition (CVD) and used to immobilize lipase from Aspergillus oryzae (AOL) for biodiesel production. The results showed that the PDMS coating enhanced the stability of ZIF-8 and ZIF-L in PBS. Immobilization efficiency of AOL on PDMS-modified ZIF-L was 96% under optimized conditions. The resultant immobilized lipase (AOL@PDMS-ZIF-L) exhibited higher activity recovery (430%) than AOL@ZIF-L. Meanwhile, compared with free lipase, the AOL@PDMS-ZIF-L exhibited better storage stability and thermal stability. After 150 days of storage, the free lipase retained only 20% of its original activity of hydrolyzing p-NPP, while the AOL@PDMS-ZIF-L still retained 90% of its original activity. The biodiesel yield catalyzed from soybean oil by free lipase was only 69%, However, the biodiesel yield by AOL@PDMS-ZIF-L reached 94%, and could still be maintained at 85% even after 5 consecutive cycles. It is believed that this convenient and versatile strategy has great promise in the important fields of immobilized lipase on MOF for biodiesel production.

Topological evolution of correlated band structures and heavy-fermion-like behavior in a molybdenum-based metal organic framework C48S36Mo6

Owing to the fascinating properties of two dimensional transition metal dichalcogenides and the stability of ZIF-8 as the subclass of metal organic frameworks (MOFs), we propose a Mo-based MOFs material C48S36Mo6 containing organic ligands connecting to each other by Mo4+ metal ions. We reveal heavy-fermion-like electronic behaviour that results from highly localized impurity-like Mo-d electrons and tiny energy difference (<0.4 meV/atom) between antiferromagnetic and ferromagnetic state, using the generalized gradient approximation and its combination with Coulomb correlation U. Considering thermal fluctuation and weak magnetic exchange energy, C48S36Mo6 is a nonmagnetic metal at room temperature, and magnetic insulator at low temperature with a correlation-driven metal–insulator transition. Our Wannier functions analysis indicates that topological properties of energy bands around the Fermi level can be perturbed by correlation U, leading to moving of close nodal lines in three dimensional momentum space. Further introducing of spin–orbit coupling opens a small inverted energy gap of 3 meV at original nodal line due to bulk inversion symmetry. If a gate voltage of 48 meV is applied, the Fermi level will fall into the small energy gap of band inversion, and the system will realize a phase transition from Kondo metal to topological Kondo insulator.

Three-Dimensionally Ordered Macroporous Mixed Metal Oxide as an Indicator for Monitoring the Stability of ZIF-8

Three-dimensionally ordered macroporous (3DOM) ZnO-CeO2-Al2O3 (MMO)@ZIF-8 was synthesized via a vapor-phase pseudomorphic transformation from 3DOM MMO and 2-methylimidazole that maintained the peri...

Intrinsic and Extrinsic Responses of ZIF-8 under High Pressure: A Combined Raman and X-ray Diffraction Investigation

ZIF-8 is a prototypical porous material in the family of zeolitic imidazolate frameworks, and its structural stability is of great significance for a wide range of practical applications. Here, the intrinsic and extrinsic structural and mechanical responses of nanosized ZIF-8 perturbed by high external pressure have been comparatively investigated based on our in situ Raman measurements in different pressure environments, accompanied by synchrotron X-ray diffraction measurements and results from previous reports. An improvement of both the chemical and crystallographic stability of ZIF-8, rather than an intrinsic quick deterioration, can be observed when penetrating guest molecules get into the pores. Spectral evidence demonstrates that the C═C section of the imidazolate ring is an optimal interaction site for the penetrating methanol, water, and nitrogen molecules. We further find that water molecules can cleave Zn–N bonds to bring linker-associated defects to ZIF-8. When compressed in the nonpenetrating silicone oil as a pressure transmitting medium (PTM) or when no PTM is used, irreversibility is observed, while samples show a highly reversible transformation both in the short-range and long-range regions upon decompression from a partially or entirely amorphous state in penetrating PTM. Furthermore, the released samples transform to a dense bulk state in the absence of penetrating PTM instead of preserving the original nanosized particles when penetrating pressure transmitting fluids is present. Moreover, the compressible behavior of ZIF-8 varies and is found to be strongly influenced by the size and polarity of molecules in the pores. The present results indicate that the stability, compressibility, and reversibility of ZIF-8 under pressure are closely related to the pressure environments and the characteristics of the guest molecules in the PTM. Thus, this study sheds light on the available mechanical modifications and selectable applications of ZIF-8 as gas absorbents for the future.

A Simple Step toward Enhancing Hydrothermal Stability of ZIF-8.

ZIF-8 is a flexible zeolitic imidazole-based metal–organic framework and has been extensively studied because of its high structural stability. However, ZIF-8 is hydrolyzed in water at higher temperature, resulting in degradation of its crystalline and porous structure. In order to prevent ZIF-8 from structural collapse due to the hydrolysis reaction of the metal–ligand bond and/or ligand substitution reaction, it is effective to shield the metal–ligand bond from the attack of water molecules. This work reports on the thermal and hydrothermal stability of mechanochemically synthesized ZIF-8 and presents an incredibly simple step to modify the outermost surface of ZIF-8, improving the hydrothermal stability. The partial carbonization resulting in the formation of a carbon-rich outermost layer endowed ZIF-8 with not only high hydrothermal stability but also a high adsorption rate on liquid phase adsorption.

A hydrogen evolution reaction induced unprecedentedly rapid electrocatalytic reduction of 4-nitrophenol over ZIF-67 compare to ZIF-8

ZIF-8 is built with Zn2+ tetrahedrally bridging with imidazole units, whereas ZIF-67 has the similar structure with Co2+ replacing the Zn ions. ZIF-8 and ZIF-67 were synthesized by a single step at room temperature, and the detailed characterization through XRD and FE-SEM study revealed similar surface morphology of the two isostructural ZIFs. Again, the chemical and thermal stability studies exhibited the better stability of ZIF-8 over ZIF-67. The through characterizations also revealed the better surface area and porosity and adsorption of 4-nitrophenol over ZIF-8 compare to ZIF-67. Interesting, in spite of inferior physical properties, ZIF-67 revealed better electrocatalytic properties between the isostructural ZIFs. ZIF-67 showed unprecedentedly fast reduction of 4-nitrophenol to 4-aminophenol, whereas the reduction of 4-nitrophenol over ZIF-8 took almost 180 min, in-spite of better adsorption. The detailed mechanistic studies revealed that the electrocatalytic reduction of 4-nitrophenol over ZIF-8 electrode underwent through an orthodox 6e− system pathway to produce 4-aminophenol through hydroxyl amine and nitroso containing intermediates. Whereas, ZIF-67 produced hydrogen through water splitting that directly reduced 4-nitrophenol to 4-aminophenol with complete product selectivity.

Polyphenylene Sulfide Ultrafine Fibrous Membrane Modified by Nanoscale ZIF-8 for Highly Effective Adsorption, Interception, and Recycling of Iodine Vapor.

In this study, two novel composite membranes containing nanoscale ZIF-8 and polyphenylene sulfide (PPS) nonwoven fabric were prepared via hydrothermal (PPS-ZIF-8) and biomimetic mineralization (PPS-ZIF-8-BSA; BSA, bovine serum albumin) approaches. The biomimetic mineralization approach in particular was extremely rapid and mild, and crystalline ZIF-8 was coated on the PPS substrate in only a few seconds at room temperature. The maximum iodine adsorption capacities of the PPS-ZIF-8 and PPS-ZIF-8-BSA membranes were 2.51 and 2.07 g/g, respectively. The composite fibrous membranes were able to capture trace iodine vapor under differential pressures ranging from 0 to 1000 Pa without almost any iodine vapor leakage. The composite membranes can be applied in harsh environments because of the excellent stability of ZIF-8 and the PPS high-performance fibers. This study provides a promising strategy to fabricate novel adsorption materials for the collection of radioactive iodine during nuclear waste disposal.