Review on Metal-Organic Framework Classification, Synthetic Approaches, and Influencing Factors: Applications in Energy, Drug Delivery, and Wastewater Treatment

Synthesis and characterisation of antimicrobial metal-organic frameworks as multi-drug carriers

Antibiotic resistance is a significant global concern, necessitating the development of either new antibiotics or advanced delivery methods. With this in mind, we report on the synthesis and characterisation of a new family of Metal-Organic Frameworks (MOFs), OnG6 MOFs, designed to act as multi-drug carriers for bacterial infection treatment. OnG6 is based on the pro-drug 4,4'-azodisalicylic acid (AZDH4), which in vivo produces two equivalents of para-aminosalicylic acid (ASA), a crucial drug for M. tuberculosis treatment. X-ray and computational studies revealed that OnG6 MOFs are mesoporous MOFs with etb topology and an [M2(AZD)] formula (M = Zn, OnG6-Zn; Mg, OnG6-Mg; Cu, OnG6-Cu; and Co, OnG6-Co), featuring 1-dimensional channel type pores of 25 Å diameter. OnG6 MOFs are the first reported MOFs bearing the ligand AZDH4, joining the family of mesoporous MOFs arranged in a honeycomb pattern. They absorb isoniazid (INH) and ciprofloxacin (CIPRO) with the former being a specific antibiotic for M. tuberculosis, and the latter being a broader-spectrum antibiotic. The stability of the MOFs and their capacity for antibiotic uptake depend on the nature of the metal ion, with OnG6-Mg demonstrating the highest drug absorption. The antimicrobial activity of these species was assessed against S. aureus and E. coli, revealing that the carriers containing CIPRO displayed optimal efficacy.

Confinement-Induced Biocatalytic Activity Enhancement of Light- and Thermoresponsive Polymer@Enzyme@MOF Composites

Metal-organic frameworks (MOFs) are favorable hosting materials for fixing enzymes to construct enzyme@MOF composites and to expand the applications of biocatalysts. However, the rigid structure of MOFs without tunable hollow voids and a confinement effect often limits their catalytic activities. Taking advantage of the smart soft polymers to overcome the limitation, herein, a protection protocol to encapsulate the enzyme in zeolitic imidazolate framework-8 (ZIF-8) was developed using a glutathione-sensitive liposome (L) as a soft template. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were first anchored on a light- and thermoresponsive porous poly(styrene-maleic anhydride-N,N-dimethylaminoethyl methacrylate-spiropyran) membrane (PSMDSP) to produce PSMDSP@GOx-HRP, which could provide a confinement effect by switching the UV irradiation or varying the temperature. Afterward, embedding PSMDSP@GOx-HRP in L and encapsulating PSMDSP@GOx-HRP@L into hollow ZIF-8 (HZIF-8) to form PSMDSP@GOx-HRP@HZIF-8 composites were performed, which proceeded during the crystallization of the framework following the removal of L by adding glutathione. Impressively, the biocatalytic activity of the composites was 4.45-fold higher than that of the free enzyme under UV irradiation at 47 °C, which could benefit from the confinement effect of PSMDSP and the conformational freedom of the enzyme in HZIF-8. The proposed composites contributed to the protection of the enzyme against harsh conditions and exhibited superior stability. Furthermore, a colorimetric assay based on the composites for the detection of serum glucose was established with a linearity range of 0.05-5.0 mM, and the calculated LOD value was 0.001 mM in a cascade reaction system. This work provides a universal design idea and a versatile technique to immobilize enzymes on soft polymer membranes that can be encapsulated in porous rigid MOF-hosts. It also holds potential for the development of smart polymer@enzyme@HMOFs biocatalysts with a tunable confinement effect and high catalytic performance.

The influence of HKUST-1 and MOF-76 hand grinding/mechanical activation on stability, particle size, textural properties and carbon dioxide sorption

In this study, we explore the mechanical treatment of two metal-organic frameworks (MOFs), HKUST-1 and MOF-76, applying various milling methods to assess their impact on stability, porosity, and CO2 adsorption capacity. The effects of different mechanical grinding techniques, such as high-energy ball milling and hand grinding, on these MOFs were compared. The impact of milling time, milling speed and ball size during high-energy ball milling was assessed via the Design of Experiments methodology, namely using a 33 Taguchi orthogonal array. The results highlight a marked improvement in CO2 adsorption capacity for HKUST-1 through hand milling, increasing from an initial 25.70 wt.% (5.84 mmol g-1) to 41.37 wt.% (9.40 mmol g-1), marking a significant 38% increase. In contrast, high-energy ball milling seems to worsen this property, diminishing the CO2 adsorption abilities of the materials. Notably, MOF-76 shows resistance to hand grinding, closely resembling the original sample's performance. Hand grinding also proved to be well reproducible. These findings clarify the complex effects of mechanical milling on MOF materials, emphasising the necessity of choosing the proper processing techniques to enhance their stability, texture, and performance in CO2 capture and storage applications.

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.

A novel Ag-loaded 4 Å zeolite as an efficient catalyst for epoxidation of styrene

In this study, a novel Ag-loaded 4 Å zeolite was synthesized through the combined action of strong ultrasound and a high-voltage electrostatic field (the Z-Ag-UE) and its catalytic activity was evaluated in the epoxidation of styrene. The prepared catalysts were characterized using XRD, SEM, XPS, BET, TG, ICP-OES. The results showed that the silver evenly dispersed inside the octahedral 4 Å zeolite structure rather than being attached to the surface of the material like in the impregnation method, and this Ag-loaded 4 Å zeolite had a high surface area, uniform particle size distribution, and excellent high temperature thermal stability. The catalytic performance of the Ag-loaded 4 Å zeolite was investigated by varying the reaction conditions such as the amount of catalyst, temperature, and reaction time. Under optimized conditions, the Ag-loaded 4 Å zeolite showed high selectivity and conversion for the epoxidation of styrene, achieving a conversion rate of up to 98% and a selectivity of 94%. In particular, the catalyst had excellent recyclability and was reused more than fifteen times with the catalytic performance remaining unchanged. This method of loading metal prepared under external field conditions provides a new method and idea for future research in related fields.

MOFs for next-generation cancer therapeutics through a biophysical approach-a review

Metal-organic frameworks (MOFs) have emerged as promising nanocarriers for cancer treatment due to their unique properties. Featuring high porosity, extensive surface area, chemical stability, and good biocompatibility, MOFs are ideal for efficient drug delivery, targeted therapy, and controlled release. They can be designed to target specific cellular organelles to disrupt metabolic processes in cancer cells. Additionally, functionalization with enzymes mimics their catalytic activity, enhancing photodynamic therapy and overcoming apoptosis resistance in cancer cells. The controllable and regular structure of MOFs, along with their tumor microenvironment responsiveness, make them promising nanocarriers for anticancer drugs. These carriers can effectively deliver a wide range of drugs with improved bioavailability, controlled release rate, and targeted delivery efficiency compared to alternatives. In this article, we review both experimental and computational studies focusing on the interaction between MOFs and drug, explicating the release mechanisms and stability in physiological conditions. Notably, we explore the relationship between MOF structure and its ability to damage cancer cells, elucidating why MOFs are excellent candidates for bio-applicability. By understanding the problem and exploring potential solutions, this review provides insights into the future directions for harnessing the full potential of MOFs, ultimately leading to improved therapeutic outcomes in cancer treatment.

Metal organic framework-based polymeric hydrogel: A promising drug delivery vehicle for the treatment of breast cancer

The constraints associated with current cancer therapies have inspired scientists to develop advanced, precise, and safe drug delivery methods. These delivery systems boost treatment effectiveness, minimize harm to healthy cells, and combat cancer recurrence. To design advanced drug delivery vehicle with these character, in the present manuscript, we have designed a self-healing and injectable hybrid hydrogel through synergistically interacting metal organic framework, CuBTC with the poly(vinyl alcohol) (PVA). This hybrid hydrogel acts as a localized drug delivery system and was used to encapsulate and release the anticancer drug 5-Fluorouracil selectively at the targeted site in response to the physiological pH. The hydrogel was formed through transforming the gaussian coil like matrix of PVA-CuBTC into a three-dimensional network of hydrogel upon the addition of crosslinker; borax. The biocompatible character of the hydrogel was confirmed through cell viability test. The biocompatible hybrid hydrogel then was used to encapsulate and studied for the pH responsive release behavior of the anti-cancer drug, 5-FU. The in vitro cytotoxicity of the drug-loaded hydrogel was evaluated against MCF-7 and HeLa cells. The study confirms that the hybrid hydrogel is effective for targeted and sustained release of anticancer drugs at cancer sites.

Understanding the origins of reversible and hysteretic pathways of adsorption phase transitions in metal-organic frameworks

Phase behavior of nanoconfined fluids adsorbed in metal-organic frameworks is of paramount importance for the design of advanced materials for energy and gas storage, separations, electrochemical devices, sensors, and drug delivery, as well as for the pore structure characterization. Phase transformations in adsorbed fluids often involve long-lasting metastable states and hysteresis that has been well-documented in gas adsorption-desorption and nonwetting fluid intrusion-extrusion experiments. However, theoretical prediction of the observed nanophase behavior remains a challenging problem. The mesoscopic canonical, or mesocanonical, ensemble (MCE) is devised to study the nanophase behavior under conditions of controlled fluctuations to stabilize metastable and labile states. Here, we implement and apply the MCE Monte Carlo (MCEMC) simulation scheme to predict the origins of reversible and hysteric adsorption phase transitions in a series of practical MOF materials, including IRMOF-1, ZIF-412, UiO-66, Cu-BTC, IRMOF-74-V, VII, and IX. The MCEMC method, called the gauge cell method, allows to produce Van der Waals type isotherms with distinctive swings around the phase transition regions. The constructed isotherms determine the positions of phase equilibrium and spinodals, as well as the nucleation barriers separating metastable states. We demonstrate the unique capabilities of the MCEMC method in quantitative predictions of experimental observations compared with the conventional grand canonical and canonical ensemble simulations. The MCEMC method is implemented in the open-source RASPA and LAMMPS software packages and recommended for studies of adsorption behavior and pore structure characterization of MOFs and other nanoporous materials.

Metal-organic frameworks for biomedical applications: A review

Metal-organic frameworks (MOFs) are emergent materials in diverse prospective biomedical uses, owing to their inherent features such as adjustable pore dimension and volume, well-defined active sites, high surface area, and hybrid structures. The multifunctionality and unique chemical and biological characteristics of MOFs allow them as ideal platforms for sensing numerous emergent biomolecules with real-time monitoring towards the point-of-care applications. This review objects to deliver key insights on the topical developments of MOFs for biomedical applications. The rational design, preparation of stable MOF architectures, chemical and biological properties, biocompatibility, enzyme-mimicking materials, fabrication of biosensor platforms, and the exploration in diagnostic and therapeutic systems are compiled. The state-of-the-art, major challenges, and the imminent perspectives to improve the progressions convoluted outside the proof-of-concept, especially for biosensor platforms, imaging, and photodynamic therapy in biomedical research are also described. The present review may excite the interdisciplinary studies at the juncture of MOFs and biomedicine.

The good, the bad, and the ugly of metals as antimicrobials

We are now moving into the antimicrobial resistance (AMR) era where more antibiotic resistant bacteria are now the majority, a problem brought on by both misuse and over use of antibiotics. Unfortunately, the antibiotic development pipeline dwindled away over the past decades as they are not very profitable compounds for companies to develop. Regardless researchers over the past decade have made strides to explore alternative options and out of this we see revisiting historical infection control agents such as toxic metals. From this we now see a field of research exploring the efficacy of metal ions and metal complexes as antimicrobials. Such antimicrobials are delivered in a variety of forms from metal salts, alloys, metal complexes, organometallic compounds, and metal based nanomaterials and gives us the broad term metalloantimicrobials. We now see many effective formulations applied for various applications using metals as antimicrobials that are effective against drug resistant strains. The purpose of the document here is to step aside and begin a conversation on the issues of use of such toxic metal compounds against microbes. This critical opinion mini-review in no way aims to be comprehensive. The goal here is to understand the benefits of metalloantimicrobials, but also to consider strongly the disadvantages of using metals, and what are the potential consequences of misuse and overuse. We need to be conscious of the issues, to see the entire system and affect through a OneHealth vision.

Morphology Control of Mixed Metallic Organic Framework for High-Performance Hybrid Supercapacitors

The study presents the binder-free synthesis of mixed metallic organic frameworks (MMOFs) supported on a ternary metal oxide (TMO) core as an innovative three-dimensional (3D) approach to enhance electron transport and mass transfer during the electrochemical charge-discharge process, resulting in high-performance hybrid supercapacitors. The research demonstrates that the choice of organic linkers can be used to tailor the morphology of these MMOFs, thus optimizing their electrochemical efficiency. Specifically, a NiCo-MOF@NiCoO2@Ni electrode, based on terephthalic linkers, exhibits highly ordered porosity and a vast internal surface area, achieving a maximum specific capacity of 2320 mC cm-2, while maintaining excellent rate capability and cycle stability. With these performances, the hybrid supercapacitor (HSC) achieves a maximum specific capacitance of 424.6 mF cm-2 (specific capacity 653.8 mC cm-2) and 30.7 F cm-3 with energy density values of 10.1 mWh cm-3 at 167.4 mW cm-3 (139.8 µWh cm-2 at 2310 µW cm-2), which are higher than those of previously reported MMOFs based electrodes. This research introduces a novel approach for metal organic framework based HSC electrodes, diverging from the traditional emphasis on metal ions, in order to achieve the desired electrochemical performance.

Metal-Organic Framework for Aluminum based Energy Storage Devices: Utilizing Redox Additives for Significant Performance Enhancement

There are various methods being tried to address the sluggish kinetics observed in Al-ion batteries (AIBs). They mostly deal with morphology tuning, but have led to limited improvement. A new approach is proposed to overcome this limitation. It focuses on the use of a redox additive modified electrolyte in combination with framework like materials, which have wider channels. The ordered microporous and interconnected framework of ZIF 67, with large surface area, effectively facilitates the diffusion of aluminum ions. Therefore, AIBs are able to exhibit a superior discharge capacity of 288 mAh g-1 at 0.2 A g-1 current density with robust cycling stability. The addition of potassium ferricyanide as a redox-active species in an aqueous solution of aluminum chloride (supporting electrolyte) leads to significant enhancement in the specific capacity with much higher cycling stability. Al-ion based BatCap devices can be assembled by using ZIF 67 as the cathode, ZIF 67 derived porous carbon as the anode, and a redox additive modified electrolyte. The BatCap device exhibits excellent energy density of 86 Wh kg-1 at a power density of 2 KW kg-1, which is higher than reported aqueous AIBs. The ex situ characterization clearly explains the unexplored mechanism of redox additives in AIBs.

Morphological and Structural Characterization of (Pt, Au, and Ag) Nanoparticle/Zn-MOF-74 Composites

Metallic nanoparticles (NPs) were decorated onto Zn-MOF-74 crystals by photoreducing different metal precursors (Pt, Au, and Ag) using ultraviolet (UV) light in an aqueous solution with different metal concentrations without using additional stabilizers. X-ray diffraction revealed the three-dimensional structural integrity and crystallinity conservation of Zn-MOF-74 crystals during the UV decoration process. Raman spectroscopy showed a minor rearrangement in the structure of the Zn-MOF-74 crystal surface after NP decoration. X-ray photoelectron spectroscopy confirmed the metal oxidation states of Zn and NPs. High-resolution transmission electron microscopy images proved the surface decoration of Zn-MOF-74 crystals with spherical metallic NPs with diameters between 2.4 and 9.8 nm.

Spin crossover in {Fe(pyrazine)[M(CN)4]} (M = Ni, Pt) thin films assembled on fused silica substrates

Thin films with thicknesses in the range between ca. 10-50 nm of the spin crossover (SCO) compound {Fe(pyrazine)[μ4-M(CN)4]} (M = Ni, Pt) have been deposited on fused silica substrates using a sequential assembly method and 4-pyridinecarboxylic acid as anchoring layer. Film morphology and crystallinity were assessed by means of atomic force microscopy and grazing incidence X-ray diffraction, respectively. The intensity of the π-π* transition of the pyrazine ligand at 270 nm, being rather insensitive to the spin state of the complex, was used to follow the film growth as a function of different deposition parameters. On the other hand, the spin state changes were inferred from the temperature dependence of absorption bands appearing at 540, 490 and 310 nm in the low spin state. In line with their amorphous nature, each film displays a very gradual thermal spin crossover between ca. 100-300 K, independently of its thickness and deposition conditions. These results are not only interesting to better understand the effects of size reduction and organization on the SCO phenomenon, but the deposition of these SCO compounds on electrically insulating and/or optically transparent oxide surfaces opens also the door for various photonic or electronic applications.

Connecting chemical worlds for a sustainable future

Chemistry plays a central role in science and is the basis of one of the major, more impactful, and diverse industries. However, to address the most pressing global challenges, we must learn to create connections in an effective and meaningful way, with other disciplines, industries, and society at large. Here, we present the IUPAC Top Ten Emerging Technologies in Chemistry as an example of an initiative that highlights the value of the most promising advances in chemistry and contributes to creating connections to accelerate sustainable solutions for our society and our planet.

A label-free aptasensor based on electrodeposition of gold nanoparticles on silver-based metal-organic frameworks for measuring ochratoxin A in black and red pepper

Since ochratoxin A (OTA) is immunotoxic, teratogenic and carcinogenic, it is very important to monitor this compound in food samples. In the present work, the development and fabrication of a label-free electrochemical aptasensor based on the gold nanoparticles/silver-based metal-organic framework (AuNPs/Ag-MOF) for the determination of ochratoxin A (OTA) is introduced. The aptasensor was fabricated by electrodeposition of AuNPs on a glassy carbon electrode modified with Ag-MOF. The characteristics of the synthesized Ag-MOF were determined by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and UV-Visible spectroscopy. The aptamer was immobilized on the modified electrode and then OTA was incubated on it. The process of different stages of the aptasensor construction has been confirmed by two methods of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) and using [Fe(CN)6]3-/4- as a redox probe. The EIS method has also been used for the OTA quantitative determination. The difference in charge transfer resistance (Rct) before and after the interaction of OTA with the immobilized aptamer was considered as the analytical response of the aptasensor. Using the developed aptasensor, it is possible to measure OTA in the concentration range of 1.0 × 10-3 to 200.0 ng mL-1 with a detection limit of 2.2 × 10-4 ng mL-1. Finally, the ability of the aptasensor to measure OTA in red and black pepper was investigated and completely satisfactory results were obtained.

Polymorphism and Structural Variety in Sn(II) Carboxylate Coordination Polymers Revealed from Structure Solution of Microcrystals

The crystal structures of four coordination polymers constructed from Sn(II) and polydentate carboxylate ligands are reported. All are prepared under hydrothermal conditions in KOH or LiOH solutions (either water or methanol-water) at 130-180 °C and crystallize as small crystals, microns or less in size. Single-crystal structure solution and refinement are performed using synchrotron X-ray diffraction for two materials and using 3D electron diffraction (3DED) for the others. Sn2 (1,3,5-BTC)(OH), where 1,3,5-BTC is benzene-1,3,5-tricarboxylate, is a new polymorph of this composition and has a three-dimensionally connected structure with potential for porosity. Sn(H-1,3,5-BTC) retains a partially protonated ligand and has a 1D chain structure bound by hydrogen bonding via ─COOH groups. Sn(H-1,2,4-BTC) contains an isomeric ligand, benzene-1,2,4-tricarboxylate, and contains inorganic chains in a layered structure held by hydrogen bonding. Sn2 (DOBDC), where DOBDC is 2,5-dioxido-benzene-1,4-dicarboxylate, is a new polymorph for this composition and has a three-dimensionally connected structure where both carboxylate and oxido groups bind to the tin centers to create a dense network with dimers of tin. In all materials, the Sn centers are found in highly asymmetric coordination, as expected for Sn(II). For all materials phase purity of the bulk is confirmed using powder X-ray diffraction, thermogravimetric analysis, and infrared spectroscopy.

MOFs and MOF-Based Composites as Next-Generation Materials for Wound Healing and Dressings

In recent years, there has been growing interest in developing innovative materials and therapeutic strategies to enhance wound healing outcomes, especially for chronic wounds and antimicrobial resistance. Metal-organic frameworks (MOFs) represent a promising class of materials for next-generation wound healing and dressings. Their high surface area, pore structures, stimuli-responsiveness, antibacterial properties, biocompatibility, and potential for combination therapies make them suitable for complex wound care challenges. MOF-based composites promote cell proliferation, angiogenesis, and matrix synthesis, acting as carriers for bioactive molecules and promoting tissue regeneration. They also have stimuli-responsivity, enabling photothermal therapies for skin cancer and infections. Herein, a critical analysis of the current state of research on MOFs and MOF-based composites for wound healing and dressings is provided, offering valuable insights into the potential applications, challenges, and future directions in this field. This literature review has targeted the multifunctionality nature of MOFs in wound-disease therapy and healing from different aspects and discussed the most recent advancements made in the field. In this context, the potential reader will find how the MOFs contributed to this field to yield more effective, functional, and innovative dressings and how they lead to the next generation of biomaterials for skin therapy and regeneration.

Unveiling the MIL-53(Al) MOF: Tuning Photoluminescence and Structural Properties via Volatile Organic Compounds Interactions

MIL-53(Al) is a metal-organic framework (MOF) with unique properties, including structural flexibility, thermal stability, and luminescence. Its ability to adsorb volatile organic compounds (VOCs) and water vapor makes it a promising platform for sensing applications. This study investigated the adsorption mechanism of MIL-53(Al) with different VOCs, including ketones, alcohols, aromatics, and water molecules, focusing on structural transformations due to pore size variation and photoluminescence properties. The reported results assess MIL-53(Al) selectivity towards different VOCs and provide insights into their fundamental properties and potential applications in sensing.

Recent Progress on Nickel- and Iron-Based Metallic Organic Frameworks for Oxygen Evolution Reaction: A Review

Developing sustainable energy solutions to safeguard the environment is a critical ongoing demand. Electrochemical water splitting (EWS) is a green approach to create effective and long-lasting electrocatalysts for the water oxidation process. Metal organic frameworks (MOFs) have become commonly utilized materials in recent years because of their distinguishing pore architectures, metal nodes easy accessibility, large specific surface areas, shape, and adaptable function. This review outlines the most significant developments in current work on developing improved MOFs for enhancing EWS. The benefits and drawbacks of MOFs are first discussed in this review. Then, some cutting-edge methods for successfully modifying MOFs are also highlighted. Recent progress on nickel (Ni) and iron (Fe) based MOFs have been critically discussed. Finally, a comprehensive analysis of the existing challenges and prospects for Ni- and Fe-based MOFs are summarized.

Advances and Applications of Metal-Organic Frameworks (MOFs) in Emerging Technologies: A Comprehensive Review

Metal-organic frameworks (MOFs) that are the wonder material of the 21st century consist of metal ions/clusters coordinated to organic ligands to form one- or more-dimensional porous structures with unprecedented chemical and structural tunability, exceptional thermal stability, ultrahigh porosity, and a large surface area, making them an ideal candidate for numerous potential applications. In this work, the recent progress in the design and synthetic approaches of MOFs and explore their potential applications in the fields of gas storage and separation, catalysis, magnetism, drug delivery, chemical/biosensing, supercapacitors, rechargeable batteries and self-powered wearable sensors based on piezoelectric and triboelectric nanogenerators are summarized. Lastly, this work identifies present challenges and outlines future opportunities in this field, which can provide valuable references.

An in-depth physicochemical investigation of drug-loaded core-shell UiO66 nanoMOFs

Nanosized UiO66 are among the most studied MOF materials. They have been extensively applied in various areas, such as catalysis, gas absorption, electrochemistry, chemical sensing, and biomedical applications. However, the preparation of stable nano-sized UiO66 for drug delivery applications is challenging because of the high tendency of UiO66 to aggregate during storage. To address this issue, we coated UiO66 with oligomers made of crosslinked cyclodextrins. The coated UiO66 exhibited a good stability upon storage for more than three weeks, even for low quantities of coating materials. The resulting core-shell UiO66 were characterized using a set of complementary methods including microscopies, spectroscopies, X-ray diffraction, and thermogravimetric investigations. Size distribution was assessed by orthogonal methods. Cisplatin was loaded in the core-shell nanoparticles, followed by an in-depth analysis by asymmetric flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS). This method combines the extremely high elemental selectivity and ultratrace detection limits of mass spectrometry with the capacity of AF4 to differentiate the diverse populations present in the sample. Free cisplatin and UiO66-associated cisplatin could be well separated by AF4. AF4-ICP-MS/MS analysis provided the exact drug loading, without the need of separating the nanoparticles from their suspension media. These data suggest the potential of AF4-ICP-MS/MS in the optimization of drug delivery systems.

Crystalline Porous Material-Based Nanogenerators: Recent Progress, Applications, Challenges, and Opportunities

Nanogenerator (NG) is a potential technology that allows to build self-powered systems, sensors, flexible and portable electronics in the current Internet of Things (IoT) generation. Nanogenerators include piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), convert different forms of mechanical motion into useful electrical signals. They have evolved and expanded their applications in various fields since their discovery in 2006 and 2012. Material selection is crucial for designing efficient NGs, with high conversion efficiencies. In the recent past, crystalline porous mat erials (metal-organic frameworks (MOFs) and covalent organic frameworks (COFs)) have been widely reported as potential candidates for nanogenerators, owing to their special properties of large surface area, porosity tailoring, ease of surface, post-synthesis modification, and chemical stability. The present organized review provides a complete overview of all the crystalline porous materials (CPMs)-based nanogenerator devices reported in the literature, including synthesis, characterization, device fabrication, and potential applications. Additionally, this review article discusses current challenges, future directions, and perspectives in the field of CPMs-NGs.

Empowering the Water Oxidation Activity of the Bimetallic Metal-Organic Framework by Annexing Gold Nanoparticles over the Catalytic Surface

Electrocatalytic water splitting to an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER) is believed to be the most important application for sustainable hydrogen generation. Being a four-electron, four-proton transfer process, the OER plays the main obstacle for the same. Therefore, designing an effective electrocatalyst to minimize the activation energy barrier for the OER is a research topic of prime importance. The metal-organic framework (MOF) with a highly porous network is considered an appropriate candidate for the OER in alkaline conditions. Apart from several MOFs, the bimetallic one has an advantageous electrocatalytic performance due to the synergistic electronic interaction between two metal ions. However, most bimetallic MOFs have an obstacle to electrocatalytic application due to their low conductive nature, and therefore, they possess a barrier for charge transfer kinetics at the interface. Surface functionalization via various nanoparticles (NPs) is believed to be the most effective strategy for nullifying the conductive issue. In this work, we have designed a CoNi-based bimetallic MOF that was surface-functionalized by Au NPs (Au@CoNi-Bpy-BTC) for the OER under alkaline conditions. Au@CoNi-Bpy-BTC required an overpotential of just 330 mV, which is 56 mV lower as compared to the pristine MOF. Impedance analysis confirms an improved conductivity and charge transfer at the interface, where Au@CoNi-Bpy-BTC possesses a lower Rct value than CoNi-Bpy-BTC materials. Moreover, the Au-decorated MOF shows an 8.5 times increase in the TOF value compared to the pristine MOF. Therefore, this noble strategy toward the surface functionalization of MOFs via noble metal NPs is believed to be the most effective strategy for developing effective electrocatalysts for electrocatalytic application in energy-related fields. Overall, this report displays an exceptional correlation between the decorated NPs over the MOF surface, which can regulate the OER activity, as confirmed by experimental analysis.

Enzyme Cascade Electrode Reactions with Nanomaterials and Their Applicability towards Biosensor and Biofuel Cells

Nanomaterials, including carbon nanotubes, graphene oxide, metal-organic frameworks, metal nanoparticles, and porous carbon, play a crucial role as efficient carriers to enhance enzyme activity through substrate channeling while improving enzyme stability and reusability. However, there are significant debates surrounding aspects such as enzyme orientation, enzyme loading, retention of enzyme activity, and immobilization techniques. Consequently, these subjects have become the focus of intensive research in the realm of multi-enzyme cascade reactions. Researchers have undertaken the challenge of creating functional in vitro multi-enzyme systems, drawing inspiration from natural multi-enzyme processes within living organisms. Substantial progress has been achieved in designing multi-step reactions that harness the synthetic capabilities of various enzymes, particularly in applications such as biomarker detection (e.g., biosensors) and the development of biofuel cells. This review provides an overview of recent developments in concurrent and sequential approaches involving two or more enzymes in sequence. It delves into the intricacies of multi-enzyme cascade reactions conducted on nanostructured electrodes, addressing both the challenges encountered and the innovative solutions devised in this field.

Metal-organic frameworks: Drug delivery applications and future prospects

Background and purpose

Metal-organic frameworks (MOFs) have gained incredible consideration in the biomedical field due to their flexible structural configuration, tunable pore size and tailorable surface modification. These inherent characteristics of MOFs portray numerous merits as potential drug carriers, depicting improved drug loading, site-specific drug delivery, biocompatibility, biodegradability, etc.

Review approach

The current review article sheds light on the synthesis and use of MOFs in drug delivery applications. In the beginning, a brief overview of the key components and efficient fabrication techniques for MOF synthesis, along with its characterization methods, have been presented. The MOFs-based formulations have been critically discussed. The application of the design of experiments (DoE) approach to optimize MOFs has been elucidated. The MOFs-based formulations, especially the application of stimuli-responsive MOFs for site-specific drug delivery, have been deciphered. Along with drug release kinetic models, several administration methods for MOFs have also been enunciated. Subsequently, MOFs as future potential drug carriers have been elaborated.

Key results and conclusion

Recently, MOFs have emerged as versatile drug delivery carriers possessing customization potential and meeting the needs of spatio-temporal drug delivery. Researchers have devised several environment-friendly approaches for MOF construction and surface modification. Owing to stimuli-responsive potential, MOFs have demonstrated their prominent therapeutic efficacy via several routes of administration. The numerous benefits of MOFs would certainly open up a new vista for its novel drug delivery applications.

Environmental Potential of Carbonized MOF-5/PANI Composites for Pesticide, Dye, and Metal Cations-Can They Actually Retain Them All?

The environmental application of the carbonized composites of the Zn-containing metal-organic framework MOF-5 and polyaniline (PANI) in its emeraldine salt and base forms (C-(MOF-5/PANI)) was investigated for the first time. Textural properties and particle size distributions revealed that composites are dominantly mesoporous and nanoscale in nature, while Raman spectroscopy revealed the ZnO phase beneath the carbon matrix. Adsorption of pesticide, dye, and metal cation on C-(MOF-5/PANI) composites in aqueous solutions was evaluated and compared with the behavior of the precursor components, carbonized MOF-5 (cMOF), and carbonized PANIs. A lower MOF-5 content in the precursor, a higher specific surface area, and the pore volume of the composites led to improved adsorption performance for acetamiprid (124 mg/g) and Methylene Blue (135 mg/g). The presence of O/N functional groups in composites is essential for the adsorption of nitrogen-rich pollutants through hydrogen bonding with an estimated monolayer capacity twice as high as that of cMOF. The proton exchange accompanying Cd2+ retention was associated with the Zn/Cd ion exchange, and the highest capacity (9.8 mg/g) was observed for the composite synthesized from the precursor with a high MOF-5 content. The multifunctionality of composites was evidenced in mixtures of pollutants where noticeably better performance for Cd2+ removal was found for the composite compared to cMOF. Competitive binding between three pollutants favored the adsorption of pesticide and dye, thereby hindering to some extent the ion exchange necessary for the removal of metal cations. The results emphasize the importance of the PANI form and MOF-5/PANI weight ratio in precursors for the development of surface, porosity, and active sites in C-(MOF-5/PANI) composites, thus guiding their environmental efficiency. The study also demonstrated that C-(MOF-5/PANI) composites retained studied pollutants much better than carbonized precursor PANIs and showed comparable or better adsorption ability than cMOF.

A Smartphone-Integrated Molecularly Imprinted Fluorescence Sensor for Visual Detection of Chlortetracycline Based on N,P-Codoped Carbon Dots Decorated Iron-Based Metal-Organic Frameworks

The residue of chlortetracycline is potentially hazardous to human health; it is meaningful to exploit a portable, rapid, sensitive, and selective method for detection of chlortetracycline (CTC). In this study, a novel fluorescence bionic sensing probe (NH2-MIL-53&N,P-CDs@MIP) was successfully prepared based on the nitrogen and phosphorus codoped carbon dots decorated iron-based metal-organic frameworks combining with molecular imprinted polymer for the detection of CTC. A fluorescence intensity-responsive "on-off" detection of CTC on account of the inner-filter effect (IFE) was achieved by NH2-MIL-53&N,P-CDs@MIP. Under the optimal conditions, the fluorescence quenching degree of NH2-MIL-53&N,P-CDs@MIP presented a good linear relationship with the CTC concentration in the range 0.06-30 μg mL-1 and the limit of detection (LOD) was 0.019 μg mL-1. The fluorescent probe was applied to detect CTC in milk samples, and experimental results showed a good recovery rate (88.73%-96.28%). Additionally, a smartphone-integrated fluorescence sensing device based on NH2-MIL-53&N,P-CDs@MIP was exploited to replace the expensive and bulky fluorescence spectrophotometer for quantitative determination of CTC with the LOD of 0.033 μg mL-1. The sensing system showed high selectivity, strong stability, high specificity, and portability, which provide a great strategy for the quantitative detection of antibiotic residue.

Current Status and Challenges for Metal-Organic-Framework-Assisted Conversion of Biomass into Value-Added Chemicals

Owing to the abundance of availability, low cost, and environmental-friendliness, biomass waste could serve as a prospective renewable source for value-added chemicals. Nevertheless, biomass conversion into chemicals is quite challenging due to the heterogeneous nature of biomass waste. Biomass-derived chemicals are appealing sustainable solutions that can reduce the dependency on existing petroleum-based production. Metal-organic frameworks (MOFs)-based catalysts and their composite materials have attracted considerable amounts of interest in biomass conversion applications recently because of their interesting physical and chemical characteristics. Due to their tunability, the catalytic activity and selectivity of MOF-based catalyst/composite materials can be tailored by functionalizing them with a variety of functional groups to enhance biomass conversion efficiency. This review focuses on the catalytic transformation of lignocellulosic biomass into value-added chemicals by employing MOF-based catalyst/composite materials. The main focus is given to the production of the platform chemicals HMF and Furfural from the corresponding (hemi)cellulosic biomass, due to their versatility as intermediates for the production of various biobased chemicals and fuels. The effects of different experimental parameters on the conversion of biomass by MOF-based catalysts are also included. Finally, current challenges and perspectives of biomass conversion into chemicals by MOF-based catalysts are highlighted.

Metal-organic frameworks as photocatalysts in energetic and environmental applications

Metal-organic frameworks (MOFs) are an exciting new class of porous materials with great potential for photocatalytic applications in the environmental and energy sectors. MOFs provide significant advantages over more traditional materials when used as photocatalysts due to their high surface area, adaptable topologies, and functional ability. In this article, we summarize current developments in the use of MOFs as photocatalysts for a variety of applications, such as CO2 reduction, water splitting, pollutant degradation, and hydrogen production. We discuss the fundamental properties of MOFs that make them ideal for photocatalytic applications, as well as strategies for improving their performance. The opportunities and challenges presented by this rapidly expanding field are also highlighted.

γ-Cyclodextrin Metal-Organic Frameworks: Do Solvents Make a Difference?

Conventionally, methanol is the solvent of choice in the synthesis of gamma-cyclodextrin metal-organic frameworks (γ-CD-MOFs), but using ethanol as a replacement could allow for a more food-grade synthesis condition. Therefore, the aim of the study was to compare the γ-CD-MOFs synthesised with both methanol and ethanol. The γ-CD-MOFs were characterised by scanning electron microscopy (SEM), surface area and pore measurement, Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD). The encapsulation efficiency (EE) and loading capacity (LC) of the γ-CD-MOFs were also determined for curcumin, using methanol, ethanol and a mixture of the two as encapsulation solvent. It was found that γ-CD-MOFs synthesised by methanol and ethanol do not differ greatly, the most significant difference being the larger crystal size of γ-CD-MOFs crystallised from ethanol. However, the change in solvent significantly influenced the EE and LC of the crystals. The higher solubility of curcumin in ethanol reduced interactions with the γ-CD-MOFs and resulted in lowered EE and LC. This suggests that different solvents should be used to deliberately manipulate the EE and LC of target compounds for better use of γ-CD-MOFs as their encapsulating and delivery agents.

The rise of metal-organic framework based micromotors

Micromotors (MMs) are micro and nanoscale devices capable of converting energy into autonomous motion. Metal-organic frameworks (MOFs) are crystalline materials that display exceptional properties such as high porosity, internal surface areas, and high biocompatibility. As such, MOFs have been used as active materials or building blocks for MMs. In this highlight, we describe the evolution of MOF-based MMs, focusing on the last 3 years. First, we covered the main propulsion mechanisms and designs, from catalytic to fuel-free MOF-based MMs. Secondly, we discuss recent applications of new fuel-free MOFs MM to give a critical overview of the current challenges of this blooming research field. The advantages and challenges discussed provide a useful guide for the design of the next generation MOF MMs toward real-world applications.

Polyamidoamine Dendrimers Functionalized Water-Stable Metal-Organic Frameworks for Sensitive Fluorescent Detection of Heavy Metal Ions in Aqueous Solution

In this work, polyamidoamine (PAMAM)-functionalized water-stable Al-based metal-organic frameworks (MIL-53(Al)-NH2) were proposed with enhanced fluorescence intensity, and used for the sensitive detection of heavy metal ions in aqueous solution. The size and morphology of MIL-53(Al)-NH2 were effectively optimized by regulating the component of the reaction solvents. PAMAM dendrimers were subsequently grafted onto the surface with glutaraldehyde as a cross-linking agent. It was found that the size and morphology of MIL-53(Al)-NH2 have great influence on their fluorescence properties, and PAMAM grafting could distinctly further improve their fluorescence intensity. With higher fluorescence intensity, the PAMAM-grafted MIL-53(Al)-NH2 showed good linearity (R2 = 0.9925-0.9990) and satisfactory sensitivity (LOD = 1.1-8.6 μmol) in heavy metal ions determination. Fluorescence enhancement and heavy metal ions detection mechanisms were discussed following the experimental results. Furthermore, analogous water-stable Materials of Institute Lavoisier (MIL) metal-organic frameworks such as MIL-53(Fe)-NH2 were also proved to have similar fluorescence enhancement performance after PAMAM modification, which demonstrates the universality of the method and the great application prospects in the design of PAMAM-functionalized high-sensitivity fluorescence sensors.

Stimuli-Responsive Design of Metal-Organic Frameworks for Cancer Theranostics: Current Challenges and Future Perspective

Scientific fraternity revealed the potential of stimuli-responsive nanotherapeutics for cancer treatment that aids in tackling the major restrictions of traditionally reported drug delivery systems. Among stimuli-responsive inorganic nanomaterials, metal-organic frameworks (MOFs) have transpired as unique porous materials displaying resilient structures and diverse applications in cancer theranostics. Mainly, it demonstrates tailorable porosity, versatile chemical configuration, tunable size and shape, and feasible surface functionalization, etc. The present review provides insights into the design of stimuli-responsive multifunctional MOFs for targeted drug delivery and bioimaging for effective cancer therapy. Initially, the concept of cancer, traditional cancer treatment, background of MOFs, and approaches for MOFs synthesis have been discussed. After this, applications of stimuli-responsive multifunctional MOFs-assisted nanostructures that include pH, light, ions, temperature, magnetic, redox, ATP, and others for targeted drug delivery and bioimaging in cancer have been thoroughly discussed. As an outcome, the designed multifunctional MOFs showed an alteration in properties due to the exogenous and endogenous stimuli that are beneficial for drug release and bioimaging. The several reported types of stimuli-responsive surface-modified MOFs revealed good biocompatibility to normal cells, promising drug loading capability, target-specific delivery of anticancer drugs into cancerous cells, etc. Despite substantial progress in this field, certain crucial issues need to be addressed to reap the clinical benefits of multifunctional MOFs. Specifically, the toxicological compatibility and biodegradability of the building blocks of MOFs demand a thorough evaluation. Moreover, the investigation of sustainable and greener synthesis methods is of the utmost importance. Also, the low flexibility, off-target accumulation, and compromised pharmacokinetic profile of stimuli-responsive MOFs have attracted keen attention. In conclusion, the surface-modified nanosized design of inorganic diverse stimuli-sensitive MOFs demonstrated great potential for targeted drug delivery and bioimaging in different kinds of cancers. In the future, the preference for stimuli-triggered MOFs will open a new frontier for cancer theranostic applications.

Zn(II)-Based Mixed-Ligand-Bearing Coordination Polymers as Multi-Responsive Fluorescent Sensors for Detecting Dichromate, Iodide, Nitenpyram, and Imidacloprid

Coordination polymers (CPs) are organo-inorganic porous materials consisting of metal ions or clusters and organic linkers. These compounds have attracted attention for use in the fluorescence detection of pollutants. Here, two Zn-based mixed-ligand-bearing CPs, [Zn₂(DIN)₂(HBTC^2-)₂] (CP-1) and [Zn(DIN)(HBTC^2-)]·ACN·H₂O (CP-2) (DIN = 1,4-di(imidazole-1-yl)naphthalene, H₃BTC = 1,3,5-benzenetricarboxylic acid, and ACN = acetonitrile), were synthesized under solvothermal conditions. CP-1 and CP-2 were characterized by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, and powder X-ray diffraction analysis. Solid-state fluorescence analysis revealed an emission peak at 350 nm upon excitation at 225 and 290 nm. Fluorescence sensing tests showed that CP-1 was highly efficient, sensitive, and selective for detecting Cr₂O₇^2- at 225 and 290 nm, whereas I^- was only detected well at an excitation of 225 nm. CP-1 detected pesticides differently at excitation wavelengths of 225 and 290 nm; the highest quenching rates were for nitenpyram at 225 nm and imidacloprid at 290 nm. The quenching process may occur via the inner filter effect and fluorescence resonance energy transfer.

Engineering Metal-Organic-Framework (MOF)-Based Membranes for Gas and Liquid Separation

Separation is one of the most energy-intensive processes in the chemical industry, and membrane-based separation technology contributes significantly to energy conservation and emission reduction. Additionally, metal-organic framework (MOF) materials have been widely investigated and have been found to have enormous potential in membrane separation due to their uniform pore size and high designability. Notably, pure MOF films and MOF mixed matrix membranes (MMMs) are the core of the "next generation" MOF materials. However, there are some tough issues with MOF-based membranes that affect separation performance. For pure MOF membranes, problems such as framework flexibility, defects, and grain orientation need to be addressed. Meanwhile, there still exist bottlenecks for MMMs such as MOF aggregation, plasticization and aging of the polymer matrix, poor interface compatibility, etc. Herein, corresponding methods are introduced to solve these problems, including inhibiting framework flexibility, regulating synthesis conditions, and enhancing the interaction between MOF and substrate. A series of high-quality MOF-based membranes have been obtained based on these techniques. Overall, these membranes revealed desired separation performance in both gas separation (e.g., CO₂, H₂, and olefin/paraffin) and liquid separation (e.g., water purification, organic solvent nanofiltration, and chiral separation).

Opportunities from Metal Organic Frameworks to Develop Porous Carbons Catalysts Involved in Fine Chemical Synthesis

In the last decade, MOFs have been proposed as precursors of functional porous carbons with enhanced catalytic performances by comparison with other traditional carbonaceous catalysts. This area is rapidly growing mainly because of the great structural diversity of MOFs offering almost infinite possibilities. MOFs can be considered as ideal platforms to prepare porous carbons with highly dispersed metallic species or even single-metal atoms under strictly controlled thermal conditions. This review briefly summarizes synthetic strategies to prepare MOFs and MOF-derived porous carbons. The main focus relies on the application of the MOF-derived porous carbons to fine chemical synthesis. Among the most explored reactions, the oxidation and reduction reactions are highlighted, although some examples of coupling and multicomponent reactions are also presented. However, the application of this type of catalyst in the green synthesis of biologically active heterocyclic compounds through cascade reactions is still a challenge.

BioMOF-Based Anti-Cancer Drug Delivery Systems

A variety of nanomaterials have been developed specifically for biomedical applications, such as drug delivery in cancer treatment. These materials involve both synthetic and natural nanoparticles and nanofibers of varying dimensions. The efficacy of a drug delivery system (DDS) depends on its biocompatibility, intrinsic high surface area, high interconnected porosity, and chemical functionality. Recent advances in metal-organic framework (MOF) nanostructures have led to the achievement of these desirable features. MOFs consist of metal ions and organic linkers that are assembled in different geometries and can be produced in 0, 1, 2, or 3 dimensions. The defining features of MOFs are their outstanding surface area, interconnected porosity, and variable chemical functionality, which enable an endless range of modalities for loading drugs into their hierarchical structures. MOFs, coupled with biocompatibility requisites, are now regarded as highly successful DDSs for the treatment of diverse diseases. This review aims to present the development and applications of DDSs based on chemically-functionalized MOF nanostructures in the context of cancer treatment. A concise overview of the structure, synthesis, and mode of action of MOF-DDS is provided.