Zeolitic Imidazolate Framework Structures Research Articles

Integrated drug delivery system loading ROS-generating antitumor drugs for signal-amplified photoacoustic imaging and multimodal tumor therapy

The usefulness of antitumor drugs that produce reactive oxygen species (ROS) in accurate tumor diagnosis and treatment has been underestimated. Here, β-Lapachone (Lapa, antitumor drugs), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS, precursor photoacoustic agents) and 2, 2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH, free radical initiators) were successfully loaded into zeolitic imidazolate framework (ZIF) in situ by a one-pot method and named Lapa/ABTS/AIPH@ZIF-67 nanoparticles (LBIZ NPs). After entering the tumor cell, the ZIF structure of LBIZ NPs is disrupted in the acidic tumor microenvironment, which results in the release of Co2+ and drugs. In one hand, Lapa and Co2+ together increased hydroxyl radicals (•OH) levels to achieve Enhanced-Chemodynamic therapy (ECDT). As the amount of •OH went up, the amount of ABTS•+, the oxidation product of ABTS, would also increase, thus increasing the sensitivity and contrast of photoacoustic imaging. In the other hand, the photothermal effect produced by ABTS•+ induces AIPH to crack and release alkyl radicals (•R) to achieve thermodynamic therapy. The LBIZ NPs achieved more effective tumor treatments by fully utilizing light and heat energy. Hence, this integrated drug delivery system is able to achieve signal-amplified photoacoustic imaging and Enhanced-Chemodynamic/Photothermal/Thermodynamic trimodal combination therapy. This work provides a new insight into the application of ROS-generating antitumor drugs to precise imaging of tumors.

Highly selective methane sensing based on enhanced dual sieving effects by ZnO/Pd@Co node-replaced ZIF-8 nanorods

Highly selective methane sensing remains a formidable challenge in the field of metal oxide semiconductor (MOS)-based gas sensors. To address this issue, zeolitic imidazolate framework (ZIF) modulation is considered as an effective approach because of its pore size sieving and polarity sieving effects. In this work, core-shell ZnO/Pd@Co node-replaced ZIF-8 (ZIF-8/67) nanorods were synthesized by self-sacrificial template method, followed by post-synthetic modification of ZIF-8. When the replacement ratio of Co nodes reached 12.4%, ZnO/Pd@ZIF-8/67 exhibited a response of 12.2% to 500 ppm CH4 at 210°C but no response to 50 ppm CO, 50 ppm NH3 and 5 ppm NO2, showing excellent selectivity. By limiting rotational freedom of 2-methylimidazole, Co node replacement decreased the effective pore size from 4.0 to 4.2 Å to 3.8–4.0 Å and hindered the diffusion of NO2 with the dynamic diameter of 4.5 Å, thus enhancing the pore size sieving effect. Moreover, polarity sieving effect is also enhanced due to the favourable adsorption of polar CO (3.76 Å) and NH3 (2.6 Å) by ZIF. Therefore, the selectivity of nonpolar CH4 (3.8 Å) was improved. This work provides a new strategy for reasonably controlling and modulating the ZIF structure to achieve high selectivity in MOS-based sensors.

Structural Chemistry of Zeolitic Imidazolate Frameworks.

Zeolitic imidazolate frameworks (ZIFs) are a subclass of reticular structures based on tetrahedral four-connected networks of zeolites and minerals. They are composed of transition-metal ions and imidazolate-type linkers, and their pore size and shape, surface area, and functionality can be precisely controlled. Despite their potential, two questions remain unanswered: how to synthesize more diverse ZIF structures and how ZIFs differentiate from other crystalline solids. In other words, how can we use our understanding of their unique structures to better design and synthesize ZIFs? In this Review, we first summarize the methods for synthesizing a wide range of ZIFs. We then review the crystal structure of ZIFs and describe the relationship between their structure and properties using an in-depth analysis. We also discuss several important and intrinsic features that make ZIFs stand out from MOFs and discrete molecular cages. Finally, we outline the future direction for this class of porous crystals.

Zeolitic imidazolate frameworks: From bactericidal properties to tissue regeneration.

Zeolitic imidazolate frameworks (ZIFs), as a very well-known subset of metal-organic frameworks (MOFs), have attracted considerable attention in biomedicine due to their unique structural features such as tunable pore size, high surface area, high thermal stability, biodegradability, and biocompatibility. Moreover, it is possible to load a wide variety of therapeutic agents, drugs, and biomolecules into ZIF structures during the fabrication process owing to the ZIFs' porous structure and concise synthesis methods under mild conditions. This review focuses on the most recent advances in the bioinspiration of ZIFs and ZIF-integrated nanocomposites in boosting antibacterial efficiencies and regenerative medicine capabilities. The first part summarizes the various synthesis routes and physicochemical properties of ZIFs, including size, morphology, surface, and pore size. The recent advancements in the antibacterial aspects of using ZIFs and ZIF-integrated nanocomposites as carriers for antibacterial agents and drug cargo are elaborated. Moreover, the antibacterial mechanisms based on the factors affecting the antibacterial properties of ZIFs such as oxidative stress, internal and external triggers, the effect of metal ions, and their associated combined therapies, are discussed. The recent trends of ZIFs and their composites in tissue regeneration, especially bone regeneration and wound healing, are also reviewed with in-depth perspectives. Finally, the biological safety aspects of ZIFs, the latest reports about their toxicity, and the future prospects of these materials in regenerative medicine have been discussed.

Efficient, Stable, and Solvent‐Free Synthesized Single‐Atom Catalysts: Carbonized Transition Metal‐Doped ZIF‐8 for the Hydrogen Evolution Reaction**

AbstractHerein we present non‐noble metal single‐atom catalysts (SACs) based on carbonized transition metal‐doped zeolitic imidazolate frameworks (ZIFs) as stable and efficient electrocatalysts for the hydrogen evolution reaction in acidic media. In this work, earth‐abundant metals are embedded in a porous N‐rich carbon matrix by pyrolyzing metal‐doped ZIF structures and characterized by spectroscopic, microscopic, and electrochemical methods. The complete synthesis of these high surface area SACs was carried out without any solvents and hence offers a promising route for a more sustainable catalyst production and industrial upscaling. As the best‐performing catalyst, cobalt SAC illustrated already with a low cobalt loading of <0.3 at.% a substantial increase in activity with an overpotential of −322 mV for −10 mA cm−2, and high stability during electrolysis at −10 mA cm−2 for 12 h in acidic media, with only a small decrease of 33 mV to more negative potentials after the initiation period.

XRD and Spectroscopic Investigations of ZIF-Microchannel Glass Plates Composites.

In this study, new composite materials comprising zeolitic imidazolate framework (ZIF) structures and microchannel glass (MCG) plates were fabricated using the hydrothermal method and their morphological and spectral properties were investigated using XRD, SEM, FTIR, and Raman spectroscopy. XRD studies of powder samples revealed the presence of an additional phase for a ZIF-8 sample, whereas ZIF-67 samples, which were prepared through two different chemical routes, showed no additional phases. A detailed analysis of the FTIR and micro-Raman spectra of the composite samples revealed the formation of stable ZIF structures inside the macropores of the MCG substrate. The hydrophilic nature of the MCG substrate and its interaction with the ZIF structure resulted in the formation of stable ZIF-MCG composites. We believe that these composite materials may find a wide range of important applications in the field of sensors, molecular sieving.

Biomimetic Mineralization of Iron-Fumarate Nanoparticles for Protective Encapsulation and Intracellular Delivery of Proteins.

Biomimetic mineralization of proteins and nucleic acids into hybrid metal−organic nanoparticles allows for protection and cellular delivery of these sensitive and generally membrane-impermeable biomolecules. Although the concept is not necessarily restricted to zeolitic imidazolate frameworks (ZIFs), so far reports about intracellular delivery of functional proteins have focused on ZIF structures. Here, we present a green room-temperature synthesis of amorphous iron-fumarate nanoparticles under mildly acidic conditions in water to encapsulate bovine serum albumin (BSA), horseradish peroxidase (HRP), green fluorescent protein (GFP), and Cas9/sgRNA ribonucleoproteins (RNPs). The synthesis conditions preserve the activity of enzymatic model proteins and the resulting nanoparticles deliver functional HRP and Cas9 RNPs into cells. Incorporation into the iron-fumarate nanoparticles preserves and protects the activity of RNPs composed of the acid-sensitive Cas9 protein and hydrolytically labile RNA even during exposure to pH 3.5 and storage for 2 months at 4 °C, which are conditions that strongly impair the functionality of unprotected RNPs. Thus, the biomimetic mineralization into iron-fumarate nanoparticles presents a versatile platform for the delivery of biomolecules and protects them from degradation during storage under challenging conditions.

Large Cages of Zeolitic Imidazolate Frameworks.

The design and synthesis of permanently porous materials with extended cage structures is a long-standing challenge in chemistry. In this Account, we highlight the unique role of zeolitic imidazolate frameworks (ZIFs), a class of framework materials built from tetrahedral nodes connected through imidazolate linkers, in meeting this challenge and illustrate specific features that set ZIFs apart from other porous materials. The structures of ZIFs are characteristic of a variety of large, zeolite-like cages that are covalently connected with neighboring cages and fused in three-dimensional space. In contrast to molecular cages, the fusion of cages results in extraordinary architectural and chemical stability for the passage of gases and molecules through cages and for carrying out chemical reactions within these cages while keeping the cages intact. The combination of the advantages from both cage chemistry and extended structures allows uniquely interconnected yet compartmentalized void spaces inside ZIF solids, rendering their wide range of applications in catalysis, gas storage, and gas separation.While the field of ZIFs has seen rapid development over the past decade, with hundreds of ZIF structures built from dozens of different cages of varying composition, size, and shapes reported, rational approaches to their design are largely unknown. In this Account, we summarize a vast number of cages formed in reported ZIFs and then review how the thermodynamic factors and traditional guest-templating strategies from zeolites influence the formation of cages. We highlight how the link-link interactions perform in the ZIF formation mechanism and serve as a means to target the formation of frameworks containing cages of specific sizes with structures exhibiting a level of complexity as yet unachieved in discrete coordination cages. For example, the giant ucb cage features a dimension of 46 Å and the complex moz cage is constructed from as many as 660 components.With the finding of these large and complex cages in ZIFs, we envision that the collection of cage structures will further be diversified by a mixed-linker approach utilizing a more complex combination of link-link interactions or by creating multivariant (MTV) systems that have been realized in other framework materials yet not widely employed in ZIFs. The more complicated cage structures can provide extra variations in chemical environments, and in addition to that, MTV systems can generate inhomogeneity inside each type of cage structure. The fused cages at such complexity that are difficult to be realized in solution environments will potentially enable more complex materials for smart applications.

Temperature-dependent photonic properties of porous-shaped metal-organic frameworks on porous silicon substrates

A novel technique is introduced in this research to increase the surface roughness of metal-organic frameworks (MOF) to enhance the light absorption effect. To this end, porous silicon (PS) was selected as a template and zeolitic imidazolate frameworks (ZIF), a subset of MOFs, were deposited on the porous skeleton using the solvothermal method. It was found that the synthesized ZIF layers followed the physical pattern of porous silicon and developed a porous-shaped MOF thin film. The X-ray diffraction analysis proved the formation of polycrystalline ZIF-67 structures on the PS substrate with a dominant crystal orientation of (011). The SEM results showed the homogeneous formation of ZIF-67 on the top of the PS walls. The porous substrate provided sufficient nuclei for facilitating the formation of a compact and continuous ZIF top layer. Moreover, the morphology and crystalline properties of the PS substrate remained intact after the deposition of ZIF structures. The porous-shaped ZIF-67/PS sample exhibited an intense and sharp photoluminescence peak, reflecting its capability to capture the incident photon and generate electron-hole pairs. Thus, it can be regarded as a suitable candidate for light detection applications. The optoelectrical properties of the synthesized samples were further explored by the metallization of the ZIF/PS structures to fabricate metal–semiconductor–metal photodetectors whose current–voltage curves were measured upon exposure to different wavelengths. The photocurrent was found to be temperature-dependent with outstanding photosensitivity to ultraviolet radiation at lower temperatures. Therefore, porous-shaped ZIF-67 nanostructures on PS substrates can be a promising candidate for ultra-fast and highly sensitive UV detectors at low temperatures.

Designing bimetallic zeolitic imidazolate frameworks (ZIFs) for aqueous catalysis: Co/Zn-ZIF-8 as a cyclic-durable catalyst for hydrogen peroxide oxidative decomposition of organic dyes in water.

ZIF-8 is well known hybrid material that is self-assembled from inorganic and organic moieties. It has several potential applications due to its unique structure. One of these potential applications is in advanced oxidation processes (AOP) via a heterogeneous catalysis system. The use of modified ZIF-8/H2O2 for the destruction of the azo dye methyl orange (MO) is presented in this work to explore its efficacy. This work presents the bimetallic Co/Zn-ZIF-8 as an efficient catalyst to promote H2O2 oxidation of the MO dye. Co/Zn-ZIF-8 was synthesized through a hydrothermal process, and the pristine structure was confirmed using XRD, FTIR, and XPS. The Co/Zn-ZIF-8/H2O2 system successfully decolorized MO at the selected pH 6.5. It was found that more than 90% of MO (10 ppm) was degraded within only about 50 minutes. Proposed radical and redox mechanisms are presented for H2O2 decomposition where the redox mechanism is suggested to predominate via a Co(ii)/Co(iii) redox consecutive cyclic process.

Evaluation of ZIF-8 and ZIF-90 as Heat Storage Materials by Using Water, Methanol and Ethanol as Working Fluids

The increasing demand for heating/cooling is of grave concern due to the ever-increasing population. One method that addresses this issue and uses renewable energy is Thermochemical Energy Storage (TCES), which is based on the reversible chemical reactions and/or sorption processes of gases in solids or liquids. Zeolitic imidazolate frameworks (ZIFs), composed of transition metal ions (Zn, Co, etc.) and imidazolate linkers, have gained significant interest recently as porous adsorbents in low temperature sorption-based TES (sun/waste heat). In this study, we examined two different sodalite-type ZIF structures (ZIF-8 and ZIF-90) for their potential heat storage applications, based on the adsorption of water, methanol and ethanol as adsorbates. Both ZIF structures were analysed using PXRD, TGA, SEM and N2 physisorption while the % adsorbate uptake and desorption enthalpy was evaluated using TGA and DSC analysis, respectively. Among the studied adsorbent–adsorbate pairs, ZIF-90-water showed the highest desorption enthalpy, the fastest sorption kinetics and, therefore, the best potential for use in heat storage/reallocation applications. This was due to its significantly smaller particle size and higher specific surface area, and the presence of mesoporosity as well as polar groups in ZIF-90 when compared to ZIF-8.

Melting Point Depression and Phase Identification of Sugar Alcohols Encapsulated in ZIF Nanopores

Author(s): Dames, C; Urban, JJ; Kang, H | Abstract: Sugar alcohols (SAs) have attractive characteristics as phase-change materials, but their relatively high melting temperature limits their application in the real world. Nanoconfinement can be a useful parameter to reduce the melting temperature to pragmatic ranges. Using molecular dynamics simulations, we investigate the phases and behaviors of encapsulated SA in ZIF-8 and ZIF-11, which cannot be experimentally observed. Based on reliable partial charges for the zeolitic imidazolate framework (ZIF) structures calculated by a density functional theory, structural analysis shows that the SA's attractive interaction with the ZIF structure frustrates the SA crystallization and also elucidates the second-order phase transition between amorphous phases. A methodology is suggested to determine the phase transition temperature of confined materials and used to quantify the melting temperature depression of the ZIF-confined SAs. We also explored the thermal conductivity of SA-in-ZIF composites. Phonon frequency analysis verifies that the presence of SA molecules enhances the heat transfer by adding heat pathways between the nanoporous structure of ZIFs.

Synthesis and Characterization of Hybrid Metal Zeolitic Imidazolate Framework Membrane for Efficient H2/CO2 Gas Separation

In this paper, we propose mixed metal ions in the node of the zeolitic imidazolate framework (ZIF) structure. The hybrid metal ZIF is formed for the gas separation of hydrogen and carbon dioxide. In the first stage, the nanoparticles were prepared as a coating on a substrate, and acting as secondary growing nuclei. The hybrid metal ZIF structures were characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). N2 adsorption–desorption isotherms determined surface area, and scanning electron microscopy (SEM) was used to observe the microstructure and surface morphology. The hybrid metal ZIF-8-67 powder had the largest surface area (1260.40 m2 g−1), and the nanoparticles (100 nm) could be fully dense-coated on the substrate to benefit the subsequent membrane growth. In the second stage, we prepared the hybrid metal ZIF-8-67 membrane on the pre-seeding substrate with mixed metal nanoparticles of cobalt and zinc, by the microwave hydrothermal method. Cobalt ions were identified in the tetrahedral coordination through UV–Vis, and the membrane structure and morphology were determined by XRD and SEM. Finally, a gas permeation analyzer (GPA) was used to determine the gas separation performance of the hybrid metal ZIF-8-67 membrane. We successfully introduced zinc ions and cobalt ions into the ZIF structure, where cobalt had a strong interaction with CO2. Therefore, GPA analysis showed an excellent H2/CO2 separation factor due to lower CO2 permeability. The CO2 permeance was ~0.65 × 10−8 mol m−2 s−1 Pa−1, and the separation factors for H2/CO2 and H2/N2 were 9.2 and 2.9, respectively. Our results demonstrate that the hybrid metal ZIF-8-67 membrane has a superior H2/CO2 separation factor, which can be attributed to its very high specific surface area and structure. Based on the above, hybrid metal ZIF-8-67 membranes are expected to be applied in hydrogen or carbon dioxide gas separation and purification.

Enhancing selectivity of ZIF-8 membranes by short-duration postsynthetic ligand-exchange modification

Post-synthesis modification of zeolitic imidazolate framework (ZIF) membranes offers new opportunities to tailor ZIF structures and improve their separation performance. This work utilizes membrane surface ligand exchange (MSLE) to replace methylimidazole (MeIM) with 5,6-dimethylbenzimidazole (DBIM) and investigates its effect on the gas separation properties of ZIF-8 membranes containing varying amounts of intercrystalline defects (perfect and imperfect membranes). Upon short time (0.5 h) MSLE modification, the pristine ZIF-8 membrane shows a significant enhancement in H2/C2H6 selectivity (12–22) and C3H6/C3H8 selectivity (150–188) with small declines in gas permeance (29.5% for H2, 6.5% for C3H6). MSLE modification also improves the separation performance of imperfect ZIF-8 membranes, but to a lesser extent (C3H6/C3H8 selectivity increasing from 37.5 to 63.3). Some of the MeIM in the ZIF-8 membrane crystals are replaced by bulkier DBIM, facilitated by the presence of the intercrystalline pores resulting in more exchange on the imperfect membrane. The short-duration ligand exchange reduces intracrystalline pore diffusivity, to a greater extent for larger molecules as compared to smaller molecules, leading to a reduction in gas permeance and an increase in separation factor. However, long-duration (5 h) MSLE modification on a perfect ZIF-8 membrane lowers the C3H6/C3H8 selectivity due to an increase in the intercrystalline transport for bulkier C3H8 with an increase in C3H6 permeance due to enhanced solubility within the modified ZIF-8 structure.

Capacitive deionization using carbon derived from an array of zeolitic-imidazolate frameworks

Abstract Capacitive deionization (CDI) represents one of the most thermodynamically efficient technologies for brackish water desalination. Its performance is highly reliant on the surface properties of carbon-based electrodes. Zeolitic-imidazolate framework (ZIF)-derived carbon materials have emerged among the most promising candidates owing to their high structural and compositional tuneability. However, the impacts of the precursory ZIF structure on the properties of the final carbon, and therefore, CDI capacity and efficiency remain to be further explored. In this work, four Zn-based ZIFs with different side-chain substitutions on the imidazolates were synthesized on a gram scale with high yields to produce N-doped carbons by pyrolysis. The resulting carbons along with four commercial carbon blacks were characterized physically and electrochemically to explore the structure-performance relationship. We demonstrated that the imidazole side-chain substitution alters the ZIF's decomposition during pyrolysis, influencing the elemental compositions, surface properties, wettability and graphitization levels. The diverse carbon properties result in variable double layer capacitance and charge-transfer resistance, ultimately impacting the CDI performance. Among these carbons, Zn (4abIm)2-C afforded the greatest salt adsorption capacity of 14.19 mgNaCl·gC−1, while Zn (mIm)2-C showed the highest overall salt adsorption capacity and rate; both exceeded the performance of the commercial carbon blacks.

Adsorption of hydrogen and carbon dioxide in zeolitic imidazolate framework structure with SOD topology: experimental and modelling studies

The aim of this work is to develop insights into adsorption of hydrogen and carbon dioxide in a zeolitic imidazolate framework, ZIF-8, using high-pressure adsorption studies, adsorption isotherm model fitting, and DFT investigation of preferential adsorption sites and binding energies. The robustness of ZIF series metal–organic frameworks has drawn interest towards its utility in large scale applications in gas storage and separation. We use room temperature synthesis of ZIF-8 using DMF as a solvent, and benchmarked it against typical solvothermal synthesis. The resulting material is characterized using XRD, SEM, TG–DSC and N2 adsorption isotherm. High-pressure volumetric adsorption of the activated materials is conducted to analyze the hydrogen and carbon dioxide storage capacities up to 50 and 40 bar, respectively. ZIF-8 shows maximum H2 storage capacity of 3.13 wt% at 50 bar and 77 K, and CO2 storage capacity of 46 wt% at 40 bar and 300 K. The parameters of Unilan adsorption isotherm are estimated from the equilibrium adsorption data and isosteric heats of adsorption for H2 and CO2 on ZIF-8 are computed. DFT calculations are used to obtain preferential adsorption sites of H2 and CO2. Adsorption enthalpy values were calculated from DFT as − 7.08 and − 25.98 kJ/mol, respectively for H2 and CO2 at the most preferred sites. We found a close agreement between isosteric heat of adsorption of hydrogen (− 4.68 kJ/mol) and the enthalpy of hydrogen adsorption from DFT (− 6.04 kJ/mol) at 77 K.

Alkali metals-promoted capacity of ZIF-8 and ZIF-90 for carbon capturing: A molecular simulation study

Huge emission of greenhouse gases to the atmosphere owing to extensive industrial activities of human societies causes irreparable damage to the environment. In this paper, to enhance the adsorption capacity of the most important greenhouse gas, carbon dioxide (CO2), in two types of the most significant and stable of zeolitic imidazolate framework (ZIF) materials, named as ZIF-8 and ZIF-90, a subset of MOF materials, ligand functionalization using various alkali metals is performed through Density functional theory (DFT) and Grand Canonical Monte Carlo (GCMC) simulations. This strategy (ligand functionalization) was employed for enhancing the host-guest interactions and subsequently higher CO2 adsorption. Therefore, at first step, ZIF-8 and ZIF-90 were synthesized via a convenient and environmentally-friendly method and characterized with different techniques including XRD, FT-IR and N2 adsorption-desorption. Afterwards, CO2 adsoprtion isotherms over the as-prepared samples were experimentally measured and compared to the results from GCMC simulation to confirm the usability of the selected force field in our simulations. The obtained results revealed a good agreement between simulation and experimental data over both pristine ZIF-8 and ZIF-90. At the second step, the alkali-functionalized ZIF structures are designed using lithium (Li), potassium (K) and sodium (Na) cations by DFT calculations. Thereafter, CO2 adsorption capacity in the all alkali-functionalized ZIF structures is evaluated by GCMC simulation. Li indicated the highest impact on the adsorption uptake in both structures through enhancing electrostatic and dispersion interactions between adsorbate molecules and adsorbent atoms leading to higher binding energies. Our simulation results also revealed that at 1 bar and 298 K, the CO2 uptakes over the Li-functionalized-ZIF-8 and -90 are increased to 7 and 9 times and reach to surprising values of 6 and 9 mmol/g, respectively. Heat of adsorption was eventually calculated for CO2 over the Li-functionalized-ZIF structures and chemisorption was observed which is very important for regeneration of the adsorbents in practical situations.

Electrochemical actuators based on nitrogen-doped carbons derived from zeolitic imidazolate frameworks

In this study, an electrochemical actuator was prepared by porous nitrogen-doped carbon (NDC) electrode derived from a zeolitic imidazolate framework (ZIF). The microstructure, morphology, and composition of NDC were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The NDC exhibited ZIF structures and the specific capacitance of NDC was 224.1 F∙g−1 in KOH aqueous solution (25 mV∙s−1). Furthermore, the electrochemical actuator based on NDC electrode displayed reliable and large bending deformations under low input voltages. The influence of NDC content on electromechanical performance of actuator was investigated. With the increase of NDC content, the actuating displacement of actuator first increased and then decreased, and the 20%NDC electrode based actuator showed the best actuating performance. The tip peak-to-peak displacement and bending strain of the 20%NDC based actuator were 17.5 mm and 0.20% under the applied voltage of ±3 V at a frequency of 0.1 Hz. Therefore, zeolitic imidazolate frameworks can be applied to provide significant improvements in electrochemical actuators, which can play key roles as technological advances toward bioinspired actuating devices for next-generation soft and wearable electronics.

A review on zeolitic imidazolate frameworks use for crude oil spills cleanup

Oil spills are a global concern by virtue of their distractive effects on the ecosystem. Many studies have examined the use of porous materials as sorbents for contaminants from different polluted waters. For example, hydrophobic metal organic frameworks, especially zeolitic imidazolate frameworks (ZIFs) with high porosity, have attracted lots of attention. ZIFs are a subclass of metal organic frameworks and display an excellent performance toward oil/water separation compared with other porous materials. Nevertheless, the performance of ZIFs toward oil spills cleanup has not been reviewed. Accordingly, this article overviews the different methods for ZIF preparation, their corresponding structure, and their various applications as sorbents and in particular, recent developments in cleaning up oil spills with meso and micro-porous ZIFs. The investigation of the literatures revealed that the effective parameters on the performance of porous ZIFs are specific surface area, pore diameters of ZIF, and the size of cavities due to interconnecting of ZIF particles. The ZIF-8 with a high surface area of 1408 m2/g and 1384.2 m2/g and adsorption capacity up to 3000 mg/g was studied more than the other ZIF structures. Models predications revealed the maximum adsorption capacity of 6633 mg/g for ZIF-8. Recently, investigations focused on carbonitride foam and melamine sponge as templates of ZIF powder. In comparison with synthesis methods, dip coating as a facial synthesis method was introduced for production and anchoring ZIF particles on the substrate. The recyclability of crude oil and the reusability of the ZIF sorbents are highlighted. Moreover, this article reviews recent developments of ZIFs synthesis, current challenges, and prospects for the use of ZIFs in oil/water separation. The findings of this study can help to better understand widespread applications of ZIFs, effective features of a sorbent, and methods to improve adsorption capacity. As cleaning up oil spills is known as an important issue, this is the first study on ZIFs in particular oil/water separation which provides a summary of researches in a simple form along with recent developments compared to published reviews. Cited as : Shahmirzaee, M., Hemmati-Sarapardeh, A., Husein, M.M., Schaffie, M., Ranjbar, M. A review on zeolitic imidazolate frameworks use for crude oil spills cleanup. Advances in Geo-Energy Research, 2019, 3(3): 320-342, doi: 10.26804/ager.2019.03.10

Tuning n-Alkane Adsorption on Mixed-Linker Zeolitic Imidazolate Framework-8-90 via Controllable Ligand Hybridization: Insight into the Confinement from an Energetics Perspective

Linker hybridization provides enormous tunability of structures and properties of zeolitic imidazolate frameworks (ZIFs). We synthesized hybrid ZIF-8-90 structures by using binary organic ligands and examined their compositional and structural evolution using multiple techniques including field emission scanning electron microscopy (FESEM), Raman, X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), N2 adsorption, and 1H NMR analyses. Well-designed ligand compositions of ZIF structures contribute to the continuously switchable pore structures. The average micropore diameter shrinks from 0.72 to 0.65 nm, while the mesopore width monotonically increases from 2.18 to 3.29 nm as the carboxaldehyde-2-imidazole (OHC-IM) proportion rises from 0.31 for ZIF-8-90-S1 to 0.88 for ZIF-8-90-S5. An increase in framework polarity can lead to the strengthened guest–host interaction and therefore energetically exerts a positive effect on the adsorption affinity of n-hexane on hybrid ZIF-8-9...