Modulator-Mediated Functionalization of MOF-808 as a Platform Tool to Create High-Performance Mixed-Matrix Membranes

Advancements in MOF-based resistive gas sensors: synthesis methods and applications for toxic gas detection

Gas sensors are essential tools for safeguarding public health and safety because they allow the detection of hazardous gases. To advance gas-sensing technologies, novel sensing materials with distinct properties are needed. Metal-organic frameworks (MOFs) hold great potential because of their extensive surface areas, high porosity, unique chemical properties, and capabilities for preconcentration and molecular sieving. These attributes make MOFs highly suitable for designing and creating innovative resistive gas sensors. This review article examines resistive gas sensors made from pristine, doped, decorated, and composite MOFs. The first part of the review focuses on the synthesis strategies of MOFs, while the second part discusses MOF-based resistive gas sensors that operate based on changes in resistance.

Determination of five alternaria toxins in peppermint by dispersive solid-phase extraction coupled with ultra-high performance liquid chromatography-tandem mass spectrometry based on MOF-808-TFA

An efficient and rapid ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MSMS) method was developed for simultaneous determination of 5 alternaria toxins (ATs) in edible and medicinal plant - peppermint using MOF-808-trifluoroacetic acid (MOF-808-TFA) as the adsorbent. Characterization methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption demonstrated that the synthesized MOF-808-TFA had a regular ortho-octahedral configuration and high specific surface area. Under the optimal conditions, the 5 ATs showed good linearity (R2 ≥ 0.9993) in their respective concentration ranges. The limits of quantifications (LOQs) of the method ranged from 0.21 to 0.48 μg/L, and the recoveries were 77.8-118.2 %, with the relative standard deviations (RSDs) less than 8.9 %.

Photoclick surface modification of MOF-808 for galactose-mediated targeted chemotherapy

Controllable surface modification of nanoparticulate drug delivery vectors is key to enhancing specific desirable properties such as colloidal stability, targeting, and stimuli-responsive cargo release. Metal-organic frameworks (MOFs) have been proposed as potential delivery devices, with surface modification achieved by various bioconjugate "click" reactions, including copper-catalysed and strain-promoted azide-alkyne cycloaddition. Herein, we show that photo-induced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) can be used to surface-modify tetrazole-appended Zr MOFs with maleimides, and vice versa, with the extent of this traceless surface functionalisation controlled by the length of photoirradiation. This "photoclick" surface modification protocol is exemplified by the decorating of carboplatin-loaded MOF-808 with galactose units to target asialoglycoprotein receptors of specific cancer cell types. Targeting towards HepG2 cells, which overexpress these receptors, is indicated by enhanced endocytosis and cytotoxicity in both two- and three-dimensional cell cultures compared to other cell lines. The study shows both the power of the NITEC protocol for functionalisation of MOFs, and also the benefits of carbohydrate targeting in drug delivery vectors, with scope for significant additional work diversifying the surface targeting units available for nanoparticle functionalisation under these mild, biocompatible "photoclick" conditions.

A fluorescent sensor based on pentafluoropropanoic acid-functionalized UiO-66-NH2 for enhanced selectivity and sensitivity of dicloran detection

A pentafluoropropionic acid-functionalized fluorescent metal-organic framework material (UiO-66-NH2-PFPA) is prepared by a simple post-synthetic modification (PSM) strategy for the sensitive and selective detection of dichloran (DCN). The results of fluorescence experiments demonstrate that the sensitivity of UiO-66-NH2-PFPA (limit of detection, LOD = 0.478 μM) to DCN is nearly 10.93 times higher than that of UiO-66-NH2 (LOD = 5.225 μM) and the material has good selectivity and anti-interference ability. After the addition of DCN, the blue fluorescence of UiO-66-NH2-PFPA is obviously quenched. Therefore, the possible quenching mechanism is further discussed in combination with relevant experiments and density functional theory calculations. Moreover, the sensor is applied to the detection of DCN in fruit samples with a satisfactory recovery of 101.1-107.9%, which implies that UiO-66-NH2-PFPA is expected to be a candidate material for the detection of DCN in food.

Synthesis of Thiol Functionalized MOF-808 and its Efficiency for Mercury Removal

A thiol-functionalized MOF-808 was produced and used to remove mercury by post-synthetic modification using 6-mercaponicotinic acid (6mna). Parent MOF-808 was impregnated for varied periods in the 6mna solution to create modified MOF-808 materials, known as MOF-808-6mna-x, where x refers to the impregnation time. Diffraction and several spectroscopic techniques were employed to quantify and confirm the coordination of 6mna into MOF-808 framework. The amount of grafted 6man and the ability for adsorption of mercury (Hg) was shown to be linearly associated; the functionalized MOF-808-6mna-36 demonstrated improved Hg(II) removal, with an adsorption capacity of 250 mg/g.

Luminescence Nanothermometry: Investigating Thermal Memory in UiO-66-NH2 Nanocrystals

Metal-organic frameworks (MOFs), a diverse and rapidly expanding class of crystalline materials, present many opportunities for various applications. Within this class, the amino-functionalized Zr-MOF, namely, UiO-66-NH2, stands out due to its distinctive chemical and physical properties. In this study, we report on the new unique property where UiO-66-NH2 nanocrystals exhibited enhanced fluorescence upon heating, which was persistently maintained postcooling. To unravel the mechanism, the changes in the fluorescence signal were monitored by steady-state fluorescence spectroscopy, lifetime measurements, and a fluorescence microscope, which revealed that upon heating, multiple mechanisms could be contributing to the observed enhancement; the MOFs can undergo disaggregation, resulting in a fluorescent enhancement of the colloidally stable MOF nanocrystals and/or surface-induced phenomena that result in further fluorescence enhancement. This observed temperature-dependent photophysical behavior has substantial applications. It not only provides pathways for innovations in thermally modulated photonic applications but also underscores the need for a better understanding of the interactions between MOF crystals and their environments.

Highly Performing Sodium Metal Batteries Reinforced by a Self-Regulated Dual-Layered Solid Electrolyte Interphase via a Metal-Organic Framework

Sodium-metal batteries, heralded for high energy density and cost-effectiveness, are compromised by an unstable solid electrolyte interphase (SEI) and dendrite formation, which hinder practical applications. Herein, a zirconium-based metal-organic framework nanostructure coating (ZMOF-NSC) was constructed in a low-loss, flexible manner. Comprehensive studies show that ZMOF-NSC, with its periodically ordered nanochannels and organized pore structures, enhances ion transport and decreases the Na+ migration energy barrier, thus ensuring uniform ion flux and achieving uniform spherical deposition. Additionally, ZMOF-NSC facilitates partial desolvation, catalyzing the formation of an inorganic-rich, dual-layered SEI that effectively protects the anode and suppresses dendrite formation. Consequently, the ZMOF-NSC@Na symmetric battery exhibits an impressive lifespan of over 2500 h, demonstrating extended operational longevity. The Na3V2(PO4)3∥ZMOF-NSC@Na batteries demonstrate exceptional cycling stability with 81% capacity retention after 2000 cycles at 10 C, maintaining stability over 3000 cycles at 20 C. Moreover, the NVP∥ZMOF-NSC@Na battery achieves an energy density of 370 Wh kg-1 and a power density of 10,484 W kg-1, indicating superior durability and performance. This significant finding highlights the significant potential of structured MOFs to induce a dual-layered SEI, advancing the commercialization of durable, dendrite-free sodium metal batteries. The precise design of self-assembled pore structures and surface active sites in MOFs demonstrates significant potential in advancing the commercialization of durable, dendrite-free electrodes of metal-based rechargeable batteries.

Morphology Regulation of UiO-66-2I Supporting Systematic Investigations of Shape-Dependent Catalytic Activity for Degradation of an Organophosphate Nerve Agent Simulant

Phosphonate-based nerve agents, as a kind of deadly chemical warfare agent, are a persistent and evolving threat to humanity. Zirconium-based metal-organic frameworks (Zr-MOFs) are a kind of highly porous crystalline material that includes Zr-OH-Zr sites and imitates the active sites of the phosphotriesterase enzyme, representing significant potential for the adsorption and catalytic hydrolysis of phosphonate-based nerve agents. In this work, we present a new Zr-MOF, UiO-66-2I, which attaches two iodine atoms in the micropore of the MOF and exhibits excellent catalytic activity on the degradation of a nerve agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP), as the result of the formation of halogen bonds between the phosphate ester bonds and iodine groups. Furthermore, various morphologies of UiO-66-2I, such as blocky-shaped nanoparticles (NPs), two-dimensional (2D) nanosheets, hexahedral NPs, stick-like NPs, colloidal microspheres, and colloidal NPs, have been obtained by adding acetic acid (AA), formic acid (FA), propionic acid (PA), valeric acid (VA), benzoic acid (BA), and trifluoroacetic acid (TFA) as modulators, respectively, and show different catalytic hydrolysis activities. Specifically, the catalytic activities follow the trend UiO-66-2I-FA (t1/2 = 1 min) > UiO-66-2I-AA-NP (t1/2 = 4 min) ≈ UiO-66-2I-VA (t1/2 = 4 min) > UiO-66-2I-BA (t1/2 = 5 min) > UiO-66-2I-PA (t1/2 = 15 min) > UiO-66-2I-TFA (t1/2 = 18 min). The experimental results show that the catalytic hydrolysis activity of Zr-MOF is regulated by the crystallinity, defect quantity, morphologies, and hydrophilicity of these samples, which synergistically affect the accessibility of catalytic sites and the diffusion of phosphate in the pores of Zr-MOFs.

New generation mixed matrix membrane for CO2 separation: Transition from binary to quaternary mixed matrix membrane

Contemporary advances in material development associated with membrane gas separation refer to the cost-effective fabrication of high-performance, defect-free mixed matrix membranes (MMMs). For clean energy production, natural gas purification, and CO2 capture from flue gas systems, constituting a functional integration of polymer matrix and inorganic filler materials find huge applications. The broad domain of research and development of MMMs focused on the selection of appropriate materials, inexpensive membrane fabrication, and comparative study with other gas separation membranes for real-world applications. This study addressed a comprehensive review of the advanced MMMs wrapping various facets of membrane material selection; polymer and filler particle morphology and compatibility between the phases and the relevance of several fillers in the assembly of MMMs are analyzed. Further, the research on binary MMMs, their problems, and solutions to overcome these challenges have also been discussed. Finally, the future directions and scope of work on quaternary MMM are scrutinized in the article.

Copper single-site engineering in MOF-808 membranes for improved water treatment

MOF-808, a metal-organic framework containing Zr6O8 clusters, can serve as a secure anchoring point for stabilizing copper single-sites with redox activity, thus making it a promising candidate for catalytic applications. In this study, we target the incorporation of Cu-MOF-808 into a mixed-matrix membrane for the degradation of tyrosol, an emerging endocrine-disrupting compound commonly found in water sources, through Fenton reactions, developing innovative technologies for water treatment. We successfully demonstrate the effectiveness of this approach by preparing catalytic membranes with minimal metal leaching, which is one of the primary challenges in developing copper-based Fenton heterogeneous catalysts. Furthermore, we utilized advanced synchrotron characterization techniques, combining X-ray absorption spectroscopy and pair distribution function analysis of X-ray total scattering, to provide evidence of the atomic structure of the catalytic copper sites within the membranes. Additionally, we observed the presence of weak interactions between the MOF-808 and the organic polymer, potentially explaining their enhanced stability.

Recent Progress in 2D Metal-Organic Framework-Related Materials

2D metal-organic frameworks-based (2D MOF-related) materials benefit from variable topological structures, plentiful open active sites, and high specific surface areas, demonstrating promising applications in gas storage, adsorption and separation, energy conversion, and other domains. In recent years, researchers have innovatively designed multiple strategies to avoid the adverse effects of conventional methods on the synthesis of high-quality 2D MOFs. This review focuses on the latest advances in creative synthesis techniques for 2D MOF-related materials from both the top-down and bottom-up perspectives. Subsequently, the strategies are categorized and summarized for synthesizing 2D MOF-related composites and their derivatives. Finally, the current challenges are highlighted faced by 2D MOF-related materials and some targeted recommendations are put forward to inspire researchers to investigate more effective synthesis methods.

Polymer-Infiltrated Metal-Organic Frameworks for Thin-Film Composite Mixed-Matrix Membranes with High Gas Separation Properties

Thin-film composite mixed-matrix membranes (TFC-MMMs) have potential applications in practical gas separation processes because of their high permeance (gas flux) and gas selectivity. In this study, we fabricated a high-performance TFC-MMM based on a rubbery comb copolymer, i.e., poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl] ethyl methacrylate)-co-poly(oxyethylene methacrylate) (PBE), and metal-organic framework MOF-808 nanoparticles. The rubbery copolymer penetrates through the pores of MOF-808, thereby tuning the pore size. In addition, the rubbery copolymer forms a defect-free interfacial morphology with polymer-infiltrated MOF-808 nanoparticles. Consequently, TFC-MMMs (thickness = 350 nm) can be successfully prepared even with a high loading of MOF-808. As polymer-infiltrated MOF is incorporated into the polymer matrix, the PBE/MOF-808 membrane exhibits a significantly higher CO₂ permeance (1069 GPU) and CO₂/N₂ selectivity (52.7) than that of the pristine PBE membrane (CO₂ permeance = 431 GPU and CO₂/N₂ selectivity = 36.2). Therefore, the approach considered in this study is suitable for fabricating high-performance thin-film composite membranes via polymer infiltration into MOF pores.

Experimental observation of metal-organic framework-polymer interaction forces and intercalation

We attach a MOF crystallite to an atomic force microscope cantilever to realize a system for rapidly and quantitatively studying the interaction between single-crystal MOFs and polymer films. Using this method, we find evidence of polymer intercalation into MOF pores. This approach can accelerate composite design.

Fluorinated metal-organic frameworks for gas separation

Fluorinated metal-organic frameworks (F-MOFs) as fast-growing porous materials have revolutionized the field of gas separation due to their tunable pore apertures, appealing chemical features, and excellent stability. A deep understanding of their structure-performance relationships is critical for the synthesis and development of new F-MOFs. This critical review has focused on several strategies for the precise design and synthesis of new F-MOFs with structures tuned for specific gas separation purposes. First, the basic principles and concepts of F-MOFs as well as their structure, synthesis and modification and their structure to property relationships are studied. Then, applications of F-MOFs in adsorption and membrane gas separation are discussed. A detailed account of the design and capabilities of F-MOFs for the adsorption of various gases and the governing principles is provided. In addition, the exceptional characteristics of highly stable F-MOFs with engineered pore size and tuned structures are put into perspective to fabricate selective membranes for gas separation. Systematic analysis of the position of F-MOFs in gas separation revealed that F-MOFs are benchmark materials in most of the challenging gas separations. The outlook and future directions of the science and engineering of F-MOFs and their challenges are highlighted to tackle the issues of overcoming the trade-off between capacity/permeability and selectivity for a serious move towards industrialization.

Metal-Organic Frameworks (MOFs)-Based Mixed Matrix Membranes (MMMs) for Gas Separation: A Review on Advanced Materials in Harsh Environmental Applications

The booming of global environmental awareness has driven the scientific community to search for alternative sustainable approaches. This is accentuated in the 13th sustainable development goal (SDG13), climate action, where urgent efforts are salient in combating the drastic effects of climate change. Membrane separation is one of the indispensable gas purification technologies that effectively reduces the carbon footprint and is energy-efficient for large-scale integration. Metal-organic frameworks (MOFs) are recognized as promising fillers embedded in mixed matrix membranes (MMMs) to enhance gas separation performance. Tremendous research studies on MOFs-based MMMs have been conducted. Herein, this review offers a critical summary of the MOFs-based MMMs developed in the past 3 years. The basic models to estimate gas transport, preparation methods, and challenges in developing MMMs are discussed. Subsequently, the application and separation performance of a variety of MOFs-based MMMs including those of advanced MOFs materials are summarized. To accommodate industrial needs and resolve commercialization hurdles, the latest exploration of MOF materials for a harsh operating condition is emphasized. Along with the contemplation on the outlook, future perspective, and opportunities of MMMs, it is anticipated that this review will serve as a stepping stone for the coming MMMs research on sustainable and benign environmental application.

MOF/Polymer Mixed-Matrix Membranes Preparation: Effect of Main Synthesis Parameters on CO2/CH4 Separation Performance

Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO₂/CH₄ separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO₂ permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.

One-pot synthesis of bimetallic metal–organic frameworks (MOFs) as acid–base bifunctional catalysts for tandem reaction

Bimetallic MIL-101(Al/Fe)–NH₂ exhibits enhanced acid–base bifunctional catalytic activity due to its synergistic mechanism and hierarchical pore system.