Drug carrier wonders: Synthetic strategies of zeolitic imidazolates frameworks (ZIFs) and their applications in drug delivery and anti-cancer activity

With the rapid advancement of nanotechnology, stimuli-responsive nanomaterials have emerged as a feasible choice for the designing of controlled drug delivery systems. Zeolitic imidazolates frameworks are a subclass of Metal-organic frameworks (MOFs) that are recognized by their excellent porosity, structural tunability and chemical modifications make them promising materials for loading targeted molecules and therapeutics agents. The biomedical industry uses these porous materials extensively as nano-carriers in drug delivery systems. These MOFs not only possess excellent targeted imaging ability but also cause the death of tumor cells drawing considerable attention in the current framework of anticancer drug delivery systems. In this review, the outline of stability, porosity, mechanism of encapsulation and release of anticancer drug have been reported extensively. In the end, we also discuss a brief outline of current challenges and future perspectives of ZIFs in the biomedical world.

2D MOF derived cobalt and nitrogen-doped ultrathin oxygen-rich carbon nanosheets for efficient Fenton-like catalysis: Tuning effect of oxygen functional groups in close vicinity to Co-N sites

Developing highly efficient catalysts for peroxymonosulfate (PMS) activation is an important issue in advanced oxidation processes (AOPs) technology. In this work, cobalt and nitrogen-doped ultrathin oxygen-rich carbon nanosheets derived from 2D metal-organic framework (MOF) were successfully fabricated. The as-prepared catalyst can effectively degrade tetracycline (TC) with a high reaction constant (0.088 min^-1). Quenching test, electron paramagnetic resonance (EPR) technology, and the electrochemical test indicate that the radical pathway plays a minor role in the degradation process, the ¹O₂ based nonradical pathway dominates the reaction. Experimental and density functional theory (DFT) studies revealed that the Co-N sites on the carbon structure serve as the dominant active sites, and the oxygen functional groups in close vicinity to Co-N sites can dramatically influence local electronic structure and its interaction with PMS molecule, a high correlation between the reaction constant and hydroxy groups content could be due to the Co-N sites close to hydroxyl groups has a moderate PMS adsorption energy. This work provides new insight into the design of highly efficient Fenton-like catalysts.

Two-Dimensional Zeolitic Imidazolate Framework ZIF-L: A Promising Catalyst for Polymerization

Here, for the first time, a 2D and leaf-like zeolitic imidazolate framework (ZIF-L) is reported for the synthesis of ultrahigh molecular weight (UHMW) poly(methyl methacrylate) (PMMA) with Mn up to 1390 kg mol−1. This synthesis method is a one-step process without any co-catalyst in a solvent-free medium. SEM, PXRD, FT-IR, TGA, and nitrogen sorption measurements confirmed the 2D and leaf-like structure of ZIF-L. The results of PXRD, SEM, TGA demonstrate that the catalyst ZIF-L is remarkably stable even after a long-time polymerization reaction. Zwitterionic Lewis pair polymerization (LPP) has been proposed for the catalytic performance of ZIF-L on methyl methacrylate (MMA) polymerization. This MMA polymerization is consistent with a living system, where ZIF-L could reinitiate the polymerization and propagates the process by gradually growing the polymer chains.

Simultaneous transformation of 2D to 3D and doped metal transitions of zeolitic imidazole frameworks under solid phase and free-solvent conditions

The post-thermal treatment (PTT) method was applied for crystal transformation on the structure of zeolitic imidazolate frameworks (ZIFs) from 2D to 3D under solvent-free conditions. The investigation was performed based on bridging of the cobalt ions by the 2-methylimidazole linker to form the ZIF structure. Extensive characterization revealed that the reaction mechanism was a transformation in the solid crystal phase and resulted from the de-coordination of the framework and reformation of the crystalline structure. In addition, the PTT method opens the opportunity to simultaneously dope transition metals (Zn, Co, Fe, Ni, and Mn) in the framework during the transformation of ZIFs. The materials with doped metals showed enhanced properties and excellent performance for applications including gas adsorption, dye degradation, and the catalytic activity of CO₂ fixation.

The Progress and Prospect of Zeolitic Imidazolate Frameworks in Cancer Therapy, Antibacterial Activity, and Biomineralization

The progressive development of zeolitic imidazolate frameworks (ZIFs), as a subfamily of metal-organic frameworks (MOFs), and their unique features, including tunable pore size, large surface area, high thermal stability, and biodegradability/biocompatibility, have made them attractive in the field of biomedicine, especially for drug delivery and biomineralization applications. The high porosity of ZIFs gives them the opportunity for encapsulating a high amount of therapeutic drugs, proteins, imaging cargos, or a combination of them to construct advanced multifunctional drug delivery systems (DDSs) with combined therapeutic and imaging capabilities. This review summarizes recent strategies on the design and fabrication of ZIF-based nansystems and their exploration in the biomedical field. First, recent developments for the adjustment of particle size, functionality, and morphology of ZIFs are discussed, which are important for achieving optimized therapeutic/theranostic nanosystems. Second, recent trends on the application of ZIF nanocarriers for the loading of diverse cargos, including anticancer medicines, antibiotic drugs, enzymes, proteins, photosensitizers, as well as imaging and photothermal agents, are investigated in order to understand how multifunctional DDSs can be designed based on the ZIF nanoparticles to treat different diseases, such as cancer and infection. Finally, prospects on the future research direction and applications of ZIF-based nanomedicines are discussed.

Hierarchical porous and hydrophilic metal-organic frameworks with enhanced enzyme activity

Metal-organic frameworks (MOFs) for enzyme encapsulation-induced biomimetic mineralization under mild reaction conditions are commonly microporous and hydrophobic, which result in a rather high mass transfer resistance of the reactants and restrain the enzyme catalytic activity. Herein, we prepared a type of hierarchical porous and hydrophilic MOF through the biomimetic mineralization of enzymes, zinc ions, 2-methylimidazole, and lithocholic acid. The hierarchical porous structure accelerated the diffusion process of the reactants and the increased hydrophilicity conferred interfacial activity and increased the enzyme catalytic activity. The immobilized enzyme retained higher catalytic activity than the free enzyme and exhibited enhanced resistance to alkaline, organic, and high-temperature conditions. The nanobiocatalyst was reusable and showed long-term storage stability.

Constructing ZIF-8 derived C-ZnS/ZnMoO4@MoS2 and C-ZnS/MoS2 nanocomposites using a simple one-pot strategy to enhance photocatalytic degradation activity

Efficient C-ZnS/ZnMoO4@MoS2 and C-ZnS/MoS2 nanocomposite photocatalysts, using ZIF-8 derived C-ZnO as a precursor were successfully synthesized using a simple one-pot procedure. This is the first application that involves transforming ZIF-8 into C-ZnMoO4 for photocatalysis. The C-ZnS/ZnMoO4@MoS2 and C-ZnS/MoS2 heterostructures were characterized by X-ray diffraction, UV-vis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, photocurrent measurements, scanning electron microscopy and transmission electron microscopy. The ZM2 sample of C-ZnS/ZnMoO4@MoS2 exhibited enhanced photocatalytic activity of about 2.9 times as high as that of ZIF-8 derived C-ZnO in the reduction of tetracycline hydrochloride, and also showed obvious photocatalytic activity 1.81 and 3.33 times as high as that of a ZM3 sample of C-ZnS/MoS2 and ZIF-8 derived C-ZnO in the degradation of RhB, respectively. The improved photodegradation activity is a result of the heterogenous structure and the tighter contact between C-ZnS and C-ZnMoO4 compared with the physical contact of general heterogenous photocatalysts. The C-ZnS/ZnMoO4@MoS2 heterostructure photocatalyst is expected to be a new type of nanomaterial for the degradation of pollutants from wastewater.

ZIF-8 derived ZnO/Zn6Al2O9/Al2O3 nanocomposite with excellent photocatalytic performance under simulated sunlight irradiation

The ZIF-8 derived ZnO/Zn₆Al₂O₉/Al₂O₃ nanocomposite exhibits an unprecedented photocatalytic degradation activity toward MO of high concentration.

Formation mechanism of rod-like ZIF-L and fast phase transformation from ZIF-L to ZIF-8 with morphology changes controlled by polyvinylpyrrolidone and ethanol

Rod-like ZIF-L was formed through a self-assembly mechanism, and phase transformation from ZIF-L to ZIF-8 occurred once ethanol was used as the washing solvent.

Shape control in ZIF-8 nanocrystals and metal nanoparticles@ZIF-8 heterostructures

Shape control in metal-organic frameworks still remains a challenge. We propose a strategy based on the capping agent modulator method to control the shape of ZIF-8 nanocrystals. This approach requires the use of a surfactant, cetyltrimethylammonium bromide (CTAB), and a second capping agent, tris(hydroxymethyl)aminomethane (TRIS), to obtain ZIF-8 nanocrystals with morphology control in aqueous media. Semiempirical computational simulations suggest that both shape-inducing agents adsorb onto different surface facets of ZIF-8, thereby slowing down their crystal growth rates. While CTAB molecules preferentially adsorb onto the {100} facets, leading to ZIF-8 particles with cubic morphology, TRIS preferentially stabilizes the {111} facets, inducing the formation of octahedral crystals. Interestingly, the presence of both capping agents leads to nanocrystals with irregular shapes and higher index facets, such as hexapods and burr puzzles. Additionally, the combination of ZIF-8 nanocrystals with other materials is expected to impart additional properties due to the hybrid nature of the resulting nanocomposites. In the present case, the presence of CTAB and TRIS molecules as capping agents facilitates the synthesis of metal nanoparticle@ZIF-8 nanocomposites, due to synergistic effects which could be of use in a number of applications such as catalysis, gas sensing and storage.

In Situ Expanding Pores of Dodecahedron-like Carbon Frameworks Derived from MOFs for Enhanced Capacitive Deionization

The pores of dodecahedron-like carbon frameworks derived from metal-organic frameworks (MOFs) were in situ expanded via a surfactant-template strategy, which were originally demonstrated to enhance capacitive deionization (CDI). The dodecahedron-like carbon frameworks were obtained through carbonization of zeolitic imidazolate framework-8 (ZIF-8) using the cetyltrimethylammonium bromide as a supramolecular template. It is found that the dodecahedron-like carbon frameworks derived from ZIF-8 possess efficiently expanded pores while retaining the original morphology and high nitrogen contents. Compared to those of the normal ZIF-8-derived carbon, the obtained materials exhibit a hierarchically porous structure with a higher specific surface area and an improved pore volume. Electrochemical studies of the obtained electrode demonstrate that this material has a high specific capacitance and lower inner resistance. More importantly, the obtained material shows a higher salt adsorption capacity (20.05 mg/g) than the normal ZIF-8-derived carbon (13.01 mg/g). Furthermore, the obtained electrode presents a rapid salt removal rate and excellent cycling stability. The significantly enhanced deionization behavior of the obtained materials is due to the combination effect of its large accessible surface area, large pore volume, and rich nitrogen doping. The results reveal that in situ expanding pores of carbon frameworks derived from MOFs is an ideal way for constructing electrode materials with enhanced CDI performance. The present work may pave a path for the design and development of highly efficient MOF-derived electrode materials.

Acid-promoted synthesis of UiO-66 for highly selective adsorption of anionic dyes: Adsorption performance and mechanisms

UiO-66 was modulated by addition of acetic acid or HCl in the precursor solution. The resulting acetic acid-promoted UiO-66has more regular octahedral structures and high surface areas of 892-1090m²/g. Anionic dyes (methyl orange (MO) and Congo red (CR)) and cationic dyes (methylene blue (MB) and rhodamine B (RhB)) were examined for the selective dye adsorption on various UiO-66. The acid-promoted UiO-66 exhibits an excellent selective adsorption to anionic dyes, where the adsorption capacities of MO and MB are 84.8 and 13.2mg/g, respectively. However, UiO-66 prepared without acid shows similar adsorption to both anionic dye MO (70.4mg/g) and cationic dye MB (67.5mg/g). Mixed dyes (MO/MB and MO/RhB) adsorption on acid-promoted UiO-66 further proves the selective adsorption to anionic dyes. The adsorption mechanism was studied by testing the Zeta potential of acid-promoted UiO-66, and more positive Zeta potential (hydrogen ions) of UiO-66 is beneficial to the anionic dye adsorption.

Comparative Study of MIL-96(Al) as Continuous Metal-Organic Frameworks Layer and Mixed-Matrix Membrane

MIL-96(Al) layers were prepared as supported metal-organic frameworks membrane via reactive seeding using the α-alumina support as the Al source for the formation of the MIL-96(Al) seeds. Depending on the solvent mixture employed during seed formation, two different crystal morphologies, with different orientation of the transport-active channels, have been formed. This crystal orientation and habit is predefined by the seed crystals and is kept in the subsequent growth of the seeds to continuous layers. In the gas separation of an equimolar H2/CO2 mixture, the hydrogen permeability of the two supported MIL-96(Al) layers was found to be highly dependent on the crystal morphology and the accompanied channel orientation in the layer. In addition to the neat supported MIL-96(Al) membrane layers, mixed-matrix membranes (MMMs, 10 wt % filler loading) as a composite of MIL-96(Al) particles as filler in a continuous Matrimid polymer phase have been prepared. Five particle sizes of MIL-96(Al) between 3.2 μm and 55 nm were synthesized. In the preparation of the MIL-96(Al)/Matrimid MMM (10 wt % filler loading), the following preparation problems have been identified: The bigger micrometer-sized MIL-96(Al) crystals show a trend toward sedimentation during casting of the MMM, whereas for nanoparticles aggregation and recrystallization to micrometer-sized MIL-96(Al) crystals has been observed. Because of these preparation problems for MMM, the neat supported MIL-96(Al) layers show a relatively high H2/CO2 selectivity (≈9) and a hydrogen permeance approximately 2 magnitudes higher than that of the best MMM.

Controllable synthesis of Pd@ZIF-L catalysts by an assembly method

Pd@ZIF-L catalysts with uniform morphology and better catalytic performance were fabricated by controlling the 2-MeIM/Zn²⁺ and PVP/Zn²⁺ molar ratios.

Fast adsorption of methyl blue on zeolitic imidazolate framework-8 and its adsorption mechanism

Zeolitic imidazolate framework-8 (ZIF-8) is synthesized and the adsorption behavior and mechanism of methyl blue (MB) are studied in detail.