Forward osmosis membrane doped with water-based zirconium fumarate MOFs to enhance dye pollutant removal and membrane antifouling performance

Metal-organic frameworks (MOFs) can be applied to enhance the property of forward osmosis membranes. However, organic solvents can easily remain in organic synthetic metal-organic frame materials and cause membrane fouling and a decrease in membrane permeability. In this study, water-based Zr-fumarate MOFs were synthesized and doped into the membrane active layer by interfacial polymerization to provide a water-based MOF-doped thin-film composite membrane (TFC membrane). It was found that doping the water-based MOFs effectively improved membrane hydrophilicity, and nanowater passages were introduced in the active layer to improve permeability. The water flux of the water-based MOF-doped TFC membranes was increased by 21% over that of the original membrane, and the selectivity performance of the membrane was improved while keeping the salt rejection basically unchanged. Additionally, the water-based MOF-doped TFC membrane showed good removal efficiency (R_d > 94%) and strong antipollution performance in the treatment of dye pollutants.

From crystal phase mixture to pure metal-organic frameworks - Tuning pore and structure properties

In this study, a sonochemical route for the preparation of a new Hf-MIL-140A metal-organic framework from a mixture of UiO-66/MIL-140A is presented. The sonochemical synthesis route not only allows the phase-pure MIL-140A structure to be obtained but also induces structural defects in the MIL-140A structure. The synergic effect between the sonochemical irradiation and the presence of a highly acidic environment results in the generation of slit-like defects in the crystal structure, which increases specific surface area and pore volume. The BET-specific surface area in the case of sonochemically derived Zr-MIL-140A reaches 653.3 m2/g, which is 1.5 times higher than that obtained during conventional synthesis. The developed Hf-MIL-140A structure is isostructural to Zr-MIL-140A, which was confirmed by synchrotron X-ray powder diffraction (SR-XRD) and by continuous rotation electron diffraction (cRED) analysis. The obtained MOF materials have high thermal and chemical stability, which makes them promising candidates for applications such as gas adsorption, radioactive waste removal, catalysis, and drug delivery.

Identification of Dynamic Active Sites Among Cu Species Derived from MOFs@CuPc for Electrocatalytic Nitrate Reduction Reaction to Ammonia

Direct electrochemical nitrate reduction reaction (NITRR) is a promising strategy to alleviate the unbalanced nitrogen cycle while achieving the electrosynthesis of ammonia. However, the restructuration of the high-activity Cu-based electrocatalysts in the NITRR process has hindered the identification of dynamical active sites and in-depth investigation of the catalytic mechanism. Herein, Cu species (single-atom, clusters, and nanoparticles) with tunable loading supported on N-doped TiO2/C are successfully manufactured with MOFs@CuPc precursors via the pre-anchor and post-pyrolysis strategy. Restructuration behavior among Cu species is co-dependent on the Cu loading and reaction potential, as evidenced by the advanced operando X-ray absorption spectroscopy, and there exists an incompletely reversible transformation of the restructured structure to the initial state. Notably, restructured CuN4&Cu4 deliver the high NH3 yield of 88.2 mmol h-1 gcata-1 and FE (~ 94.3%) at - 0.75 V, resulting from the optimal adsorption of NO3- as well as the rapid conversion of *NH2OH to *NH2 intermediates originated from the modulation of charge distribution and d-band center for Cu site. This work not only uncovers CuN4&Cu4 have the promising NITRR but also identifies the dynamic Cu species active sites that play a critical role in the efficient electrocatalytic reduction in nitrate to ammonia.

Applications of Metal-Organic Frameworks and Their Derivatives in Electrochemical CO2 Reduction

Electrochemically reducing CO2 to more reduced chemical species is a promising way that not only enables the conversion of intermittent energy resources to stable fuels, but also helps to build a closed-loop anthropogenic carbon cycle. Among various electrocatalysts for electrochemical CO2 reduction, multifunctional metal-organic frameworks (MOFs) have been employed as highly efficient and selective heterogeneous electrocatalysts due to their ultrahigh porosity and topologically diverse structures. Up to now, great progress has been achieved in the design and synthesis of highly active and selective MOF-related catalysts for electrochemical CO2 reduction reaction (CO2RR), and their corresponding reaction mechanisms have been thoroughly studied. In this review, we summarize the recent progress of applying MOFs and their derivatives in CO2RR, with a focus on the design strategies for electrocatalysts and electrolyzers. We first discussed the reaction mechanisms for different CO2RR products and introduced the commonly applied electrolyzer configurations in the current CO2RR system. Then, an overview of several categories of products (CO, HCOOH, CH4, CH3OH, and multi-carbon chemicals) generated from MOFs or their derivatives via CO2RR was discussed. Finally, we offer some insights and perspectives for the future development of MOFs and their derivatives in electrochemical CO2 reduction. We aim to provide new insights into this field and further guide future research for large-scale applications.

Facile immunochromatographic assay based on metal-organic framework-decorated polydopamine for the determination of hydrochlorothiazide adulteration in functional foods

Herein, a novel immunochromatographic assay (ICA) based on metal-organic framework-decorated polydopamine (MOF@PDA) was firstly developed for the determination of hydrochlorothiazide (HCTZ) adulteration in functional foods. The coupling rate of MOF@PDA carrier to HCTZ antibody was as high as 91.7 %. The detection limits of the developed MOF@PDA-ICA in functional tablets and capsules were 5.93 and 4.72 μg/kg, the linear ranges were 11.2-91.91 μg/kg and 9.11-86.78 μg/kg, respectively. The sensitivity was 27-fold higher than that of the reported ICA. The recovery was 82.5-116.6 %, and coefficient of variation was 6.9-14.2 %. The results can be achieved and analyzed in 8 min with the smartphone-based detection device. The parallel tests of 23 commercial functional tablets and capsules showed that the results of the MOF@PDA-ICA were consistent with that of the LC-MS/MS (R² > 0.99). Therefore, our method is facile, sensitive, portable, and can provide a reliable technical mean for the detection of HCTZ adulteration in functional foods.

Inorganic nanoparticles as scaffolds for bioorthogonal catalysts

Bioorthogonal transition metal catalysts (TMCs) transform therapeutically inactive molecules (pro-drugs) into active drug compounds. Inorganic nanoscaffolds protect and solubilize catalysts while offering a flexible design space for decoration with targeting elements and stimuli-responsive activity. These "drug factories" can activate pro-drugs in situ, localizing treatment to the disease site and minimizing off-target effects. Inorganic nanoscaffolds provide structurally diverse scaffolds for encapsulating TMCs. This ability to define the catalyst environment can be employed to enhance the stability and selectivity of the TMC, providing access to enzyme-like bioorthogonal processes. The use of inorganic nanomaterials as scaffolds TMCs and the use of these bioorthogonal nanozymes in vitro and in vivo applications will be discussed in this review.

Dual-monomer molecularly imprinted electrochemical sensor based on amino-functionalized MOFs and graphene for trace determination of taurine

A molecularly imprinted electrochemical sensor (MIECS) for trace determination of taurine was developed. The sensor was constructed by electropolymerizing dopamine and o-phenylenediamine as dual monomers on the surface of amino-functionalized iron-based MOFs and graphene composite-modified electrode. The porous structure and large specific surface area of amino-functionalized iron-based MOFs not only increase the number of imprinted sites, but also facilitate the binding of molecularly imprinted films. The presence of dual monomers can increase the binding sites during the formation of imprinted films. The linear range of this sensor for taurine detection is 1.00 × 10^-14-1.00 × 10^-8 mol L^-1 with a determination limit of 3.20 × 10^-15 mol L^-1. The proposed MIECS was successfully applied to quantify the amount of taurine in human serum sample with good recovery values from 97.3 to 113%.

A highly sensitive and specific luminescent MOF determines nitric oxide production and quantifies hydrogen sulfide-mediated inhibition of nitric oxide in living cells

The synthesis of a novel carboxylate-type organic linker-based luminescent MOF (Zn(H₂L) (L₁)) (named PUC2) (H₂L = 2-aminoterephtalic acid, L₁ = 1-(3-aminopropyl) imidazole) is reported by the solvothermal method and comprehensively characterized using single-crystal XRD, PXRD, FTIR, TGA, XPS, FESEM, HRTEM, and BET. PUC2 selectively reacts with nitric oxide (^▪NO) with a detection limit of 0.08 µM, and a quenching constant (0.5 × 10⁴ M^-1) indicating a strong interaction with ^▪NO. PUC2 sensitivity remains unaffected by cellular proteins or biologically relevant metals (Cu²⁺/ Fe³⁺/Mg²⁺/ Na⁺/K⁺/Zn²⁺), RNS/ROS, or H₂S to score ^▪NO in living cells. Lastly, we used PUC2 to demonstrate that H₂S inhibition increases ^▪NO production by ~ 14-30% in various living cells while exogenous H₂S suppresses ^▪NO production, indicating that the modulation of cellular ^▪NO production by H₂S is rather generic and not restricted to a particular cell type. In conclusion, PUC2 can successfully detect ^▪NO production in living cells and environmental samples with considerable potential for its application in improving the understanding of the role of ^▪NO in biological samples and study the inter-relationship between ^▪NO and H₂S.

MOF-based nanozyme grafted with cooperative Pt(IV) prodrug for synergistic anticancer therapy

Manipulating Fenton chemistry in tumor microenvironment (TME) for the generation of reactive oxygen species is an effective strategy for chemodynamic therapy. However, this is usually restricted by limited intracellular content of H₂O₂ and insufficient acidic environment at the tumor site. Herein, a ferric metal-organic framework (MOF) is covalently grafted with a prodrug of cisplatin (Pt(IV) prodrug) and loaded with a biocatalyst glucose oxidase (GOx) to afford a nanozyme MOF-Pt(IV)@GOx for cascade reactions. In this system, the attached Pt(IV) prodrug on MOF plays a significant role in the cooperative enhancement of GOx loading and chemotherapy. The high concentration of glutathione in TME reduces Fe(III) to Fe(II) for Fenton reaction, and converts Pt(IV) prodrug to cisplatin for DNA targeting and H₂O₂ production. Meanwhile, glucose oxidation catalyzed by GOx not only consumes glucose for starvation therapy, but also promotes the intracellular acidity and H₂O₂ supply in TME, which are in favor of Fenton reaction. Both in vitro and in vivo studies demonstrate that MOF-Pt(IV)@GOx enables remarkable anticancer efficacy due to the synergistic trimodal therapy consisting of ferroptosis, starvation therapy, and chemotherapy.

MOFs-alginate/polyacrylic acid/poly (ethylene imine) heparin-mimicking beads as a novel hemoadsorbent for bilirubin removal in vitro and vivo models

Metal-organic frameworks (MOFs) have a potential application in blood purification, but their microcrystalline nature has hampered their industrial application. Here, novel MOFs-polymer beads based on UiO, sodium alginate, polyacrylic acid, and poly (ethylene imine) were prepared and applied as a whole blood hemoadsorbent for the first time. The amidation among polymers immobilized UiO66-NH₂ into the network of the optimal product (SAP-3), and the NH₂ of UiO66-NH₂ significantly increased the removal rate (70 % within 5 min) of SAP-3 on bilirubin. The adsorption of SAP-3 on bilirubin mainly obeyed the pseudo-second-order kinetic, Langmuir isotherm and Thomas models with a maximum adsorption capacity (q_m) of 63.97 mg·g^-1. Experimental and density functional theory simulation results show that bilirubin was mainly adsorbed by UiO66-NH₂via electrostatic force, hydrogen bonding, and π-π interactions. Notably, the adsorption in vivo show that the total bilirubin removal rate in the whole blood of the rabbit model was up to 42 % after 1 h of adsorption. Given its excellent stability, cytotoxicity, and hemocompatibility, SAP-3 has a great potential in hemoperfusion therapy. This study proposes an effective strategy for settling the powder property of MOFs and could provide experimental and theoretical references for application of MOFs in blood purification.

Synthesis, Structure and Near Infrared Fluorescence Property of a New Nd-MOF Based on a Triangular Benzylamine Ligand

A new 3D metal-organic framework (Nd-MOF) {[Nd₂L₂]·2NH₂(CH₃)₂·3H₂O} was successfully established via a solvothermal method with Nd³⁺ ion and 5-(bis(4-carboxybenzyl) amino)-isophthalicacid (H₄L), and has also been characterized by X-ray diffraction, powder X-ray diffraction (PXRD), IR and photoluminescence(PL)spectrum. The neodymium ions are free of coordinated solvents, and the Nd-MOF exhibits strong near-infrared (NIR) fluorescence. Besides, Its NIR fluorescence property shows low temperature resistance, which is favorable for being used in the low temperature environment. Besides, the fluorescence lifetime of Nd-MOF is 6.03 μs, and the quantum yield is 1.2%. The small quantum yield may owe to large energy gap between the T1 of the ligand H₄L and the resonance energy level ⁴F_3/2 of the Nd³⁺ ion, or due to large crystal size of the Nd-MOF.

A novel spectroscopic technique for studying metal-organic frameworks based on Mie scattering

Metal-organic frameworks (MOFs) are promising candidates for a wide range of applications, and spectroscopic techniques are important tools for analyzing their structures and properties. Here, we propose a novel and general scattering spectroscopic approach to study various MOFs such as zeolitic imidazolate frameworks (ZIF-67 and ZIF-8), HKUST-1, Co-based MOF (Co-MOF), and Ni-based MOF (Ni-MOF) based on their inherent Mie scattering properties. We show that by using a dark-field microscope, the inherent scattering colors and spectra can be obtained, which are mainly from the high-order magnetic and electric resonant modes. The scattering capacities are dependent on the chemical structures for producing polarized charges and internal circular displacement currents. Additionally, all the MOFs are capable of responding to solvent guests due to their high porosity, and the scattering peaks are in a linear correlation with solvent refractive indices, displaying scattering solvatochromic behaviors. Our results open up a powerful and universal avenue for visually studying the host-guest interactions in MOFs.

Glyco-conjugated metal-organic framework biosensor for fluorescent detection of bacteria

Metal-organic frameworks (MOFs) are hybrid materials constructed by the linkage between an inorganic secondary building unit and an organic linker. A number of MOFs are luminescent in nature and can be structurally tuned for desirable geometry, surface functionality, and porosity. Luminescent MOFs have been endorsed for various biosensing applications. Lectins and carbohydrates have been used for the development of simple and convenient biosensing and bioimaging tools. Lectins are mostly present on the surface of microorganisms where they aid in pathogenesis. Due to this, they can be potential targets for a microbial biosensor. The present study, for the first time, explores the usage of a carbohydrate-conjugated FeMOF (Glyco-MOF) bioprobe for the selective determination of Pseudomonas aeruginosa and Escherichia coli. NH₂-MIL-53(Fe) MOF was synthesized via a room temperature protocol and separately conjugated with galactose and mannose sugars via glutaraldehyde chemistry. The synthesized bioprobe is validated for structural integrity, luminescent nature, stability, and analyte assay. Electron microscopy studies validated the unhindered MOF's morphology and structural integrity, after bioconjugation. The synthesized bioprobes were able to detect P. aeruginosa and E. coli up to respective detection limits of 202 and 8 CFU/mL, respectively. The bioprobes are selective even in co-presence of possible interferants as well as being environmentally stable.

Controllable synthesis of FeMn bimetallic ferrocene-based metal-organic frameworks to boost the catalytic efficiency for removal of organic pollutants

A series of FeMn bimetallic ferrocene-based metal-organic frameworks (FeMn-Fc-MOFs) with various molar ratios of Fe and Mn (1:9, 2:8, 4:6, 6:4) were successfully synthesized using a simple hydrothermal synthesis method and employed as an efficient activator on persulfate (PS) activation for water decontamination. Characterizations demonstrated that Fe and Mn were smoothly introduced into ferrocene-based MOFs and various molar ratios of Fe:Mn had some influence on crystallinity and surface structure of FeMn-Fc-MOFs. Within 120 min, Fe₄Mn₆-Fc-MOFs demonstrated the best catalytic activity among the different molar ratios, and acid orange 7(AO7) degradation rate was up to 92.0%. In addition, electrochemical experiments revealed that Fe₄Mn₆-Fc-MOFs possessed superior electron transfer capability than other FeMn-Fc-MOFs, leading to better catalytic performance. Moreover, quenching tests and electron paramagnetic resonance (EPR) detection indicated that hydroxyl radicals and sulfate radicals were both responsible for AO7 decomposition. Notably, the redox cycle of Fe(II)/Fe(III) and Mn(II)/Mn(IV) was discovered in the Fe₄Mn₆-Fc-MOFs/PS system, which was considered as the limiting process for the cleavage of the O-O bond in PS to generate active radicals. Ultimately, the Fe₄Mn₆-Fc-MOFs exhibits an excellent universality and good cycling stability for 5 continuous runs. This paper broadens the application of ferrocene-based MOFs on heterogeneous PS activation in environmental catalysis.

Metal-organic frameworks doped with metal ions for efficient sterilization: Enhanced photocatalytic activity and photothermal effect

Photocatalytic and photothermal disinfection is a promising strategy for addressing the challenges of environmental microbial contamination. In this work, we choose a metal-organic framework (MOF), ZIF-8, as an inexpensive and ideal model for metal ion doping, and manipulate the band structure, thermal vibration in molecules, charge distribution, and robustness of the metal-ligand coordination bond of the metal-ion-doped ZIFs for their use in photo-disinfection. The effects of their absorption edge, rate of the photo-induced temperature rise, transient photocurrent response, photo-generated reactive oxygen species (ROS) type, and crystal stability on the photo-disinfection performance are systematically studied by varying the metal ion type (Co²⁺, Ni²⁺, or Cu²⁺) and doping concentration (1-100%). The results show that the efficiency of light harvesting and photogenerated carrier separation is facilitated in all doped ZIFs. The photothermal conversion gradually improves with the increasing concentration of doped Co²⁺/Cu²⁺. Remarkably, the photo-generated ROS type changes from the original singlet oxygen (¹O₂) to multiple ROS (¹O₂ and •O₂^-) due to the introduction of Co(II) sites. Consequently, compared with pristine ZIF-8 and other doped ZIFs, Co²⁺-doped ZIF-8 with a 5% doping concentration shows the highest sterilization efficiency (6.6 log₁₀ CFU mL^-1) against Escherichia coli (E. coli) under simulated sunlight within one hour by virtue of the enhanced photothermal effect and the generation of multiple ROS. This work provides insights into the application of metal-ion-doped MOF photocatalysts to the disinfection of environments with pathogenic microorganisms.

A novel fluorescence aptasensor based on PCN-223 as an efficient quencher for sensitive determination of prostate-specific antigen

A novel fluorescence aptasensor based on PCN-223 as an efficient quencher was developed to sensitively detect prostate-specific antigen (PSA). The 5-carboxytetramethylrhodamine (TAMRA)-labeled PSA aptamer was adsorbed on PCN-223 by π-π stacking and hydrogen-bonding interactions, which contributed to fluorescence quenching because of the photoinduced electron transfer from TAMRA to PCN-223. In addition, the amount of quenched fluorescence of the PSA-binding aptamer complex-PCN-223 was lower than that of TAMRA aptamer-PCN-223 without PSA (at excitation/emission peaks of 545/582 nm), which can be explained by the fact that the PSA-binding aptamer complexes contributed to the separation of the aptamer from PCN-223. ∆F value of fluorescence intensities for TAMRA aptamer-PCN-223 with and without PSA showed a good linear relationship with PSA concentration over a range of 0.1 to 24 ng mL^-1, with a detection limit of 0.05 ng mL^-1. Compared with three metal-organic frameworks (MOFs) of UiO-66-NH₂, ZIF-67, and Ni₃(HITP)₂ as quenchers, PCN-223 as a Zr-MOF exhibited the highest ∆F value for PSA detection. The advantage of PCN-223 could be attributed to its carboxyl, benzene, and porphyrin groups, the large specific surface area and good biocompatibility. This proposed aptasensor can be successfully used to detect PSA in sera of prostate cancer patients. The PSA detection results of this aptasensor were consistent with those which were obtained from hospital by Archtecti2000sr automatic chemiluminescence immunoanalyzer. The proposed aptasensor has potential clinical detection application.

Fe3O4 supported UiO-66 (Zr) metal-organic framework for removal of drug contaminants from water: fuzzy logic modeling approach

The increase in production and consumption of pharmaceuticals and personal care products causes environmental problems. In this study, naproxen and clofibric acid adsorption were studied using Fe₃O₄-supported UiO-66 (Zr) metal-organic framework (Mag-UiO-66). The adsorption processes were carried out in batch mode at pH value 3.0. The optimum adsorbent quantities, equilibrium periods, pseudo-first-order (PFO), pseudo-second-order (PSO), and intra-particles diffusion kinetic models were calculated. Non-linear Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Sips isotherm equations were applied to experimental data. Thermodynamic analyses of naproxen and clofibric acid adsorption were also carried out in this study. The Langmuir isotherm q_m values were found as 14.15 mg/g for naproxen at 308 K and 41.87 mg/g for clofibric acid at 298 K. Both of the adsorption processes were exothermic. MISO (multi-input single-output) fuzzy logic models for removal of both naproxen and clofibric acid adsorptions were designed based on the experimental data to estimate the removal uptake values. It is noteworthy that the results obtained through designed fuzzy logic models matched well with the experimental data and the findings of this study emphasize the validity of designed fuzzy logic models.

Catalytic metal-organic framework-melamine foam composite as an efficient material for the elimination of organic pollutants

Water-insoluble organic pollutants in environment, such as sea oil spill, industrial reagents, and the abused organic pesticides, bring great risks to global water systems, which thus requires effective approaches for organic pollutant elimination. In this study, we report a catalytic metal-organic framework (MOF)-melamine foam (MF) composite material (DDT-UiO-66-NH₂@MF) showing excellent oil-water separation performance and enzyme-like degradation ability toward organophosphorus pesticides. The fabrication of DDT-UiO-66-NH₂@MF is based on the immobilization of a MOF-derived nanozyme (UiO-66-NH₂) on MF sponge, and followed by the hydrophobic modification of UiO-66-NH₂ by 1-dodecanethiol (DDT). The obtained DDT-UiO-66-NH₂@MF thus displayed superhydrophobic/superhydrophilic property with a high water contact angle (WCA = 144.6°) and specific adsorption capacity toward various oils/organic solvents (62.2-119.8 g/g), which leads to a continuous oil-water separation on a simple device. In the meanwhile, owing to the enzyme-like property of UiO-66-NH₂, DDT-UiO-66-NH₂@MF also displayed good ability to hydrolyze paraoxon under mild conditions, which facilitates the elimination of toxic pesticide residuals in water systems. This work provides a simple, efficient, and green approach for the separation and treatment of water-insoluble organic pollutants, as well as expands the use of MOFs-MF sponge composite materials in environmental sustainability.

Antiadherent AgBDC Metal-Organic Framework Coating for Escherichia coli Biofilm Inhibition

Surface microbial colonization and its potential biofilm formation are currently a major unsolved problem, causing almost 75% of human infectious diseases. Pathogenic biofilms are capable of surviving high antibiotic doses, resulting in inefficient treatments and, subsequently, raised infection prevalence rates. Antibacterial coatings have become a promising strategy against the biofilm formation in biomedical devices due to their biocidal activity without compromising the bulk material. Here, we propose for the first time a silver-based metal-organic framework (MOF; here denoted AgBDC) showing original antifouling properties able to suppress not only the initial bacterial adhesion, but also the potential surface contamination. Firstly, the AgBDC stability (colloidal, structural and chemical) was confirmed under bacteria culture conditions by using agar diffusion and colony counting assays, evidencing its biocide effect against the challenging E. coli, one of the main representative indicators of Gram-negative resistance bacteria. Then, this material was shaped as homogeneous spin-coated AgBDC thin film, investigating its antifouling and biocide features using a combination of complementary procedures such as colony counting, optical density or confocal scanning microscopy, which allowed to visualize for the first time the biofilm impact generated by MOFs via a specific fluorochrome, calcofluor.

Recent progress of metal-organic frameworks as sensors in (bio)analytical fields: towards real-world applications

The deployment of metal-organic frameworks (MOFs) in a plethora of analytical and bioanalytical applications is a growing research area. Their unique properties such as high but tunable porosity, well-defined channels or pores, and ease of post-synthetic modification to incorporate additional functional units make them ideal candidates for sensing applications. This is possible because the interaction of analytes with a MOF often results in a change in its structure, eventually leading to a modification of the intrinsic physicochemical properties of the MOF which is then transduced into a measurable signal. The high porosity allows for the adsorption of analytes very efficiently, while the tunable pore sizes/nature and/or installation of specific recognition groups allow modulating the affinity towards different classes of compounds, which in turn lead to good sensor sensitivity and selectivity, respectively. Some figures are given to illustrate the potential of MOF-based sensors in the most relevant application fields, and future challenges and opportunities to their possible translation from academia (i.e., laboratory testing of MOF sensing properties) to industry (i.e., real-world analytical sensor devices) are critically discussed.

Synthesis and potential applications of cyclodextrin-based metal-organic frameworks: a review

Metal-organic frameworks are porous polymeric materials formed by linking metal ions with organic bridging ligands. Metal-organic frameworks are used as sensors, catalysts for organic transformations, biomass conversion, photovoltaics, electrochemical applications, gas storage and separation, and photocatalysis. Nonetheless, many actual metal-organic frameworks present limitations such as toxicity of preparation reagents and components, which make frameworks unusable for food and pharmaceutical applications. Here, we review the structure, synthesis and properties of cyclodextrin-based metal-organic frameworks that could be used in bioapplications. Synthetic methods include vapor diffusion, microwave-assisted, hydro/solvothermal, and ultrasound techniques. The vapor diffusion method can produce cyclodextrin-based metal-organic framework crystals with particle sizes ranging from 200 nm to 400 μm. Applications comprise food packaging, drug delivery, sensors, adsorbents, gas separation, and membranes. Cyclodextrin-based metal-organic frameworks showed loading efficacy of the bioactive compounds ranging from 3.29 to 97.80%.

Structure-performance correlation guided cerium-based metal-organic frameworks: Superior adsorbents for fluoride removal in water

Fluoride in the hydrosphere exceeds the standard, which could be critically hazardous to human health and the natural environment. The adsorption method is a mature and effective way to remove pollutants in water, including fluoride. In this study, we synthesized three kinds of cerium-based metal-organic frameworks (Ce-MOFs) with different structures and properties by modulating the organic ligands (i.e., trimesic acid (BTC), 1,2,4,5-benzenetetracarboxylic acid (PMA), and terephthalic acid (BDC)) via the solvothermal method. The adsorption kinetics of Ce-MOFs on fluoride well fit the pseudo second order model, and their adsorption isotherms also conform to Langmuir isothermal model. The thermodynamic study reveals that the adsorption process is a spontaneous endothermic reaction. The maximum saturated adsorption capacities of Ce-BTC, Ce-PMA, and Ce-BDC are 70.7, 159.6, and 139.5 mg g^-1, respectively. Ce-MOFs have stable and excellent adsorption capacity at pH = 3-9. Coexisting anions (Cl^-, SO₄^2-, and NO₃^-) do not affect the performance of Ce-MOFs for fluoride removal. Moreover, Ce-MOFs also show their broad prospect as superior fluoride adsorbents because of their excellent performance and reusability in real water samples. Organic ligands have a remarkable influence on the defluoridation performance of Ce-MOFs. This work will provide a feasible idea for designing MOFs as superiors adsorbents for defluoridation.

Core-shell architectured NH2-UiO-66@ZIF-8/multi-walled carbon nanotubes nanocomposite-based sensitive electrochemical sensor towards simultaneous determination of Pb2+ and Cu2

Amino functionalized zirconium-based metal-organic framework (NH₂-UiO-66) and zinc-based zeolitic imidazolate framework (ZIF-8) were integrated to develop a core-shell architectured hybrid material (NH₂-UiO-66@ZIF-8, NU66@Z8). The morphology and structure evolutions of core-shell NU6@Z8 were investigated by FE-SEM, XRD, FTIR, and XPS. The NU66@Z8 combined with carboxylated multi-walled carbon nanotubes (CMWCNT) was deposited on a glassy carbon electrode (GCE) for fabricating an electrochemical platform towards detecting Pb²⁺ and Cu²⁺. The NU66@Z8/CMWCNT/GCE revealed significantly improved electrochemical performance for determination of Pb²⁺ and Cu²⁺ compared with the individual components, which can be attributed to the strong adsorption capacity, unique core-shell structure, and large electrochemical active surface area of NU66@Z8/CMWCNT. Under the optimal conditions, the developed sensor exhibited excellent sensing capability with a low limit of detection (Pb²⁺,1 nM; Cu²⁺, 10 nM) and a wide determination range (Pb²⁺,0.003-70 μM; Cu²⁺, 0.03-50 μM). The sensor showed high selectivity towards common interfering ions and good repeatability. The real sample recoveries of proposed sensor were in the range 95.0-103% for Pb²⁺ (RSD ≤ 5.3%) and 94.2-106% for Cu²⁺ (RSD ≤ 5.9%), suggesting that the NU66@Z8/CMWCNT is suitable for examining trace heavy metals in natural environment.

Deciphering the underlying mechanism of MOF-808-based abiotic catalysis enhancing biodegradability of waste activated sludge: Insights from the effects on bioconversion of extracellular organic substances into methane

Extracellular organic substances (EOSs) usually control sludge biodegradability. Metal-organic framework-808 (MOF-808), a catalyst with a high ability of catalytic hydrolysis and proton transfer, has great potential to enhance biodegradability of EOSs. In this study, the underlying mechanism of MOF-808 enhancing the biodegradability of EOSs via abiotic catalysis was investigated. Experimental results showed that protein-like and humic acid-like substances were the main organic components in EOSs, and the MOF-808 enhanced the disintegration of protein-like substances rather than humic acid-like substances. Analyses of the changes in the functional group, the secondary structure of protein-like substances, and the electron transfer of catalytically degraded EOS samples revealed that the MOF-808 enhanced the hydrolysis of EOSs protein-like substances, loosened their secondary structure, and improved the electron transfer in EOSs. Further analyses of the MOF-808 before and after the catalysis reaction revealed that the coordination of Zr sites with protein-like substance-specific active sites (such as ZrN) in the MOF-808 substantially contributed to the high-efficiency catalysis. Biochemical methane potential assays confirmed that MOF-808-based abiotic catalysis promoted the generation efficiency of methane from the EOSs. These findings can elucidate the abiotic catalytic effect of MOF-808 on sludge biodegradability during the anaerobic digestion process.

Metal-Organic Frameworks Functionalized Separators for Robust Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are one of the promising energy storage systems, which consist of electrode materials, electrolyte, and separator. The first two have been significantly received ample development, while the prominent role of the separators in manipulating the stability of the electrode has not attracted sufficient attention. In this work, a separator (UiO-66-GF) modified by Zr-based metal organic framework for robust AZIBs is proposed. UiO-66-GF effectively enhances the transport ability of charge carriers and demonstrates preferential orientation of (002) crystal plane, which is favorable for corrosion resistance and dendrite-free zinc deposition. Consequently, Zn|UiO-66-GF-2.2|Zn cells exhibit highly reversible plating/stripping behavior with long cycle life over 1650 h at 2.0 mA cm^-2, and Zn|UiO-66-GF-2.2|MnO₂ cells show excellent long-term stability with capacity retention of 85% after 1000 cycles. The reasonable design and application of multifunctional metal organic frameworks modified separators provide useful guidance for constructing durable AZIBs.

Metabolic pathways reveal the effect of fungicide loaded metal-organic frameworks on the growth of wheat seedlings

Metal-organic frameworks (MOF) are an emerging class of hybrid inorganic-organic porous materials used in various fields, especially in molecule delivery system. As iron is an essential micronutrient for plant growth, iron-based MOF (Fe-MOF) is developed for agricultural application as fungicide carriers. However, fungicides may have various effect on the plant growth, which may be different from Fe-MOF. When they are combined with the carriers, the effects on target plants will change. In this work, tebuconazole-loaded Fe-MOF was prepared and used to treat wheat seedlings. The physiological, biochemical and metabolic levels of wheat roots and shoots were shown by a comparative study. Related metabolic pathways were analyzed by non-targeted metabolomic method. Many metabolites in wheat roots and shoots showed an upward trend after Fe-MOF treatment, but tebuconazole had a negative impact on these indicators. Related metabolic pathways in Fe-MOF and tebuconazole treatment were different, and the related pathway of tebuconazole-loaded Fe-MOF was closer to that of Fe-MOF. The metabolic pathways study revealed that the negative impact from tebuconazole was mitigated when wheat seedlings were treated with tebuconazole-loaded Fe-MOF. This research firstly explores the mechanism of MOF as carriers to help plant reduce the negative effects from fungicide by regulating metabolic pathways.

A novel metal-organic frameworks composite-based label-free point-of-care quartz crystal microbalance aptasensing platform for tetracycline detection

A novel label-free point-of-care quartz crystal microbalance (QCM) aptasensing platform based on metal-organic frameworks (MOFs) and gold nanoparticles (AuNPs) was fabricated for tetracycline (TC) detection. MOFs (HKUST-1) and AuNPs were modified onto the sensing interface of QCM sensor to enhance the sensing performance of the QCM aptasensor. TC aptamer with sulfhydryl group was fixed through Au-S bond. The recognition performance of the aptasensor was predicted and verified by the computer simulation. At the optimal conditions, the frequency change of the sensor was adopted for quantitative detection of TC. The prepared QCM aptasensor exhibited a wide linear range from 1 × 10^-10 g mL^-1 to 1 × 10^-5 g mL^-1 with low limit of detection (0.8 × 10^-11 g mL^-1). High sensitivity, good selectivity, acceptable recoveries (87.6-91.4%) in real samples were obtained. For the first time, MOFs were utilized in the construction of QCM aptasensing platform, providing a promising application way of MOFs in the QCM sensing.

Construction of efficient electrochemiluminescence resonance energy transfer sensor based on SnO2/SnS2QDs-Ru@IRMOF-3 composite for sensitive detection of procalcitonin

An efficient electrochemiluminescence resonance energy transfer (ECL-RET) method is proposed which combines the luminescent materials of tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) (energy donor) and tin dioxide and tin disulfide quantum dots (SnO₂/SnS₂QDs) (energy acceptor) into the isoreticular metal - organic framework-3 (IRMOF-3) material to form a composite. In this mode, the distance between the energy donor and the acceptor was greatly shortened, reducing the energy loss, and thereby effectively improving RET efficiency and further significantly improving the ECL signal. The obtained composite (SnO₂/SnS₂QDs-Ru@IRMOF-3) was combined with sandwich immunoreaction to construct an ECL immunosensor for the sensitive detection of procalcitonin (PCT). Under the optimized experimental conditions with a working potential of - 1.48 V (vs Ag/AgCl), the proposed PCT biosensor exhibited a linear concentration range of 1 × 10^-4-200 ng mL^-1, with a detection limit of 0.029 pg mL^-1 (S/N = 3). The biosensor was used to detect PCT in actual samples. The biosensor has broad application prospects in biological analysis and clinical diagnosis due to its high sensitivity, good selectivity, and good stability.

Enhanced carbon dioxide biomethanation with hydrogen using anaerobic granular sludge and metal-organic frameworks: Microbial community response and energy metabolism analysis

In this work, metal-organic frameworks (MOFs) were prepared to evaluate its impact on carbon dioxide (CO₂) biomethanization during anaerobic degradation (AD). The results showed that MOFs significantly improved the CO₂ biomethanation efficiency, especially in the AD reactors using a concentration of 1.0 g/L MOFs. Furthermore, MOFs promoted direct interspecific electron transfer and alleviated the hydrogen competition of bacteria. Meanwhile, hydrogenotrophic methanogens were enriched in the AD reactors with MOFs. After the addition of MOFs, there was 3.28 times and 3.41 times increase in the abundance of metabolic functions related to methanogenesis by CO₂ reduction with hydrogen and dark hydrogen oxidation, respectively. There was an increased abundance of all genes that encode the key enzymes used in methane metabolism. However, functional genes involved in nitrate reduction had their expressions inhibited. The work may offer a contribution to helping the industry achieve the carbon capture and utilization policy.

Application of MOF-based nanotherapeutics in light-mediated cancer diagnosis and therapy

Light-mediated nanotherapeutics have recently emerged as promising strategies to precisely control the activation of therapeutic reagents and imaging probe both in vitro and in vivo, largely ascribed to their unique properties, including minimally invasive capabilities and high spatiotemporal resolution. Nanoscale metal-organic frameworks (NMOFs), a new family of hybrid materials consisting of metal attachment sites and bridging ligands, have been explored as a new platform for enhanced cancer diagnosis and therapy due to their tunable size, modifiable surface, good biocompatibility, high agent loading and, most significantly, their ability to be preferentially deposited in tumors through enhanced permeability and retention (EPR). Especially the light-driven NMOF-based therapeutic platform, which not only allow for increased laser penetration depth and enhanced targeting, but also enable imaging-guided or combined treatments. This review provides up-to-date developments of NMOF-based therapeutic platforms for cancer treatment with emphasis on light-triggered therapeutic strategies and introduces their advances in cancer diagnosis and therapy in recent years.

Sensing performance and mechanism of carbon dots encapsulated into metal-organic frameworks

Metal-organic frameworks (MOFs) can be combined with nanomaterials and the combined composites have excellent optical properties. Carbon dots (CDs) with tiny particle size, non-toxic and rich surface functional groups are novel fluorescent materials. Carbon dots@metal-organic frameworks (CDs@MOFs) are synthesized by encapsulating CDs into MOFs. CDs@MOFs are promising composites for the preparation of a new generation of fluorescence sensors, which combine the hybrid properties of MOFs and the special optical properties of CDs. Urged as such, we are encouraged to categorize according to the sensing mechanisms. These include fluorescence resonance energy transfer (FRET), aggregation-caused quenching (ACQ), static quenching, dynamic quenching, photo-induced electron transfer (PET), inner filter effect (IFE) and so on. Based on the above mechanisms, CDs@MOFs can specifically interact with target analytes to generate fluorescence quenching. This review covers the research progress of CDs@MOFs in recent five years (with 103 refs), synthetic design of CDs@MOFs and introduces the sensing mechanism. The current challenges and future research directions are discussed briefly. The sensing mechanism and applications of CDs@MOFs.

Porous lanthanide metal-organic frameworks with metallic conductivity

Metallic charge transport and porosity appear almost mutually exclusive. Whereas metals demand large numbers of free carriers and must have minimal impurities and lattice vibrations to avoid charge scattering, the voids in porous materials limit the carrier concentration, provide ample space for impurities, and create more charge-scattering vibrations due to the size and flexibility of the lattice. No microporous material has been conclusively shown to behave as a metal. Here, we demonstrate that single crystals of the porous metal-organic framework Ln_1.5(2,3,6,7,10,11-hexaoxytriphenylene) (Ln = La, Nd) are metallic. The materials display the highest room-temperature conductivities of all porous materials, reaching values above 1,000 S/cm. Single crystals of the compounds additionally show clear temperature-deactivated charge transport, a hallmark of a metallic material. Lastly, a structural transition consistent with charge density wave ordering, present only in metals and rare in any materials, provides additional conclusive proof of the metallic nature of the materials. Our results provide an example of a metal with porosity intrinsic to its structure. We anticipate that the combination of porosity and chemical tunability that these materials possess will provide a unique handle toward controlling the unconventional states that lie within them, such as charge density waves that we observed, or perhaps superconductivity.

Preparation of metal-organic framework @molecularly imprinted polymers for extracting strobilurin fungicides from agricultural products

The core-shell metal-organic framework coated with molecularly imprinted polymers (ZIF-8@MIPs) were successfully synthesized by surface imprinting technique, and applied as adsorbents for solid-phase extraction of strobilurin fungicides. The obtained hybrid complex was characterized in detail, and their adsorbing and recognition performance were evaluated. The results showed that ZIF-8@MIPs presented typically core-shell structure with MIP shell (about 20 nm), and exhibited larger adsorption capacity (102.5 mg g^-1) and fast adsorption ability (only 5 min). Under the optimized conditions, a sensitive, efficient and reliable method for determining six strobilurin fungicides in different agricultural products based on ZIF-8@MIPs coupling with high performance liquid chromatography-tandem mass spectrometry was established. This method showed good linearity with correlation coefficients higher than 0.9990. With spiked at three different concentration levels in agricultural products (apple, pear, banana, Chinese cabbage, cabbage, cucumber), the good recoveries (83.5-129.0%) with relative standard deviations from 0.5 to 10.2% were obtained. The limit of detections and the limit of quantifications were 0.01-1.12 ng g^-1 and 0.03-3.73 ng g^-1, respectively. Those results demonstrated good potential application of ZIF-8@MIPs for enriching and separating trace strobilurin fungicides in agricultural samples.

Effective defluoridation of water using nanosized UiO-66-NH2 encapsulated within macroreticular polystyrene anion exchanger

Environmental concerns associated with the efficient defluoridation of contaminated water remain a substantial challenge. In this work, a new nanocomposite, UiO-66-NH₂@PS⁺, was successfully fabricated via in situ precipitation of a water-stable metal-organic framework (UiO-66-NH₂) inside a commercial polystyrene anion exchanger PS⁺. The as-formed nanocomposite UiO-66-NH₂@PS⁺ was characterized using various morphological methods, which demonstrated that nanosized UiO-66-NH₂ was homogenously dispersed within the inner pores of PS⁺. Batch adsorption experiments indicated that UiO-66-NH₂@PS⁺ exhibited outstanding adsorption performance for fluoride over a broad pH range of 3.0-8.0. The saturated adsorption capacity of fluoride at 298 K was 27.5 and 32.8 mg/g for pH 6.5 and 4.5 with the adsorbent dosage of 0.5 g/L and initial concentration of 5-80 mg/L. Moreover, the utilization rate of active adsorption sites of UiO-66-NH₂ was greatly improved after encapsulation. The XPS study indicated that the integrated effects of specific inner-sphere coordination and ligand exchange between fluoride and UiO-66-NH₂ might be the dominant adsorption mechanism. Fixed-bed tests indicated that the UiO-66-NH₂@PS⁺ column could successively produce clean water with bed volumes of 350 and 70 ([F^-] <1.5 mg/L) from simulated fluoride-pollution water at pH 4.5 and 8.0, with a liquid velocity of 20 mL/h, and an empty bed contact time (EBCT) of 15 min, which was higher than that of the other materials. In addition, the exhausted UiO-66-NH₂@PS⁺ was regenerated and reused for 5 times through complete regeneration, highlighting the potential feasibility of defluorination in practical applications.

Turn-on fluorescence determination of sulfide based on site-occupying modulation of MOF-copper nanocluster interaction

A tunable interaction between Fe-MOFs (MIL-53(Fe) and kojic acid (KA)-functional copper nanoclusters (Cu NCs) has been studied. When introducing MIL-53(Fe), the Fe-O bonds can be formed between the KA on the surface of Cu NCs and MIL-53(Fe), which will induce the electron transfer from Cu NCs to MIL-53(Fe) and fluorescence quenching of Cu NCs. By introducing S^2- it occupies the Fe-site of MIL-53(Fe) and impede the interaction between Cu NCs and MIL-53(Fe), rendering a "turn-on" fluorescence signal. Thus, the KA-Cu NC/MIL-53(Fe) pair is designed as fluorescence sensing for S^2-, which displays a low detection limit of 18.6 nM and a wide linear detection range from 0.05 to 5 µM by fitting the fluorescence intensity at maximum wavelength of 500 nm with excitation at 400 nm. It was also applied to monitor S^2- in water samples and food additives with satisfactory results, demonstrating the practicability and reliability of the sensing strategy based on the tuable MOF-Cu NC interactions.

Cyclodextrin-based metal-organic framework nanoparticles as superior carriers for curcumin: Study of encapsulation mechanism, solubility, release kinetics, and antioxidative stability

In this paper, we propose a facile program of preparing nanoscale γ-cyclodextrin-based metal-organic frameworks (Nano-CD-MOFs) for the encapsulation of curcumin. Such Nano-CD-MOFs not only possess excellent mono-dispersity and crystalline structure, but also perform superior loading capacity. The results of N₂ adsorption-desorption, XRD, DSC, and microtopography are utilized to confirm the presence status of encapsulated curcumin and further reveal the encapsulation mechanism of Nano-CD-MOFs. Curcumin-loaded Nano-CD-MOFs (Cur-Nano-CD-MOFs) dramatically increase curcumin solubility and a top-down uniform dispersion in the dissolution process. The perfect fitting of First-order and Korsmeyer-Peppas models suggests that the release performance of Nano-CD-MOFs is controlled by the loaded quantity of curcumin and related to Fickian diffusion. Moreover, the antioxidative stability of Cur-Nano-CD-MOFs is considerably enhanced even after 120 min of persistent ultraviolet irradiation. Therefore, we suggest that such Nano-CD-MOFs can be promoted as an advanced carrier for the delivery of curcumin or other nutraceuticals.

A "bottle-around-ship" method to encapsulated carbon nitride and CdTe quantum dots in ZIF-8 as the dual emission fluorescent probe for detection of mercury (II) ion

A facile and efficient "bottle-around-ship" approach for preparing the ratiometric fluorescent probe has been developed by encapsulating the red-colored fluorescence CdTe quantum dots (QDs) and blue-colored fluorescence graphitic carbon nitride quantum dots (g-CNQDs) into the zeolitic imidazolate metal-organic frameworks (ZIF-8) in one step. At a single excitation of 360 nm, the obtained probe ZIF-8@g-CNQD/CdTe shows the dual-emission peaked at 450 and 633 nm, respectively. The red emission of CdTe QDs is selectively quenched by the Hg²⁺, whereas the blue fluorescence of g-CNQDs as an internal reference is insensitive, resulting in an apparent color transformation from pink to blue for special recognition of Hg²⁺. By this approach, the relative fluorescence intensity ratio (F₆₃₃/F₄₅₀) decreased linearly with increasing Hg²⁺ concentration in the 0.2-3.5 μM range with a low limit of detection (LOD) of ~ 46 nM. Therefore, we demonstrate that this "bottle-around-ship" process provides a new strategy for the construction of ratiometric fluorescent Hg²⁺ probes with good simplicity, high efficiency, and excellent stabilities. Moreover, the obtained Hg²⁺ fluorescent probe shows good results in the detection of actual samples.

Hetero-Interfaces on Cu Electrode for Enhanced Electrochemical Conversion of CO2 to Multi-Carbon Products

Electrochemical CO₂ reduction reaction (CO₂RR) to multi-carbon products would simultaneously reduce CO₂ emission and produce high-value chemicals. Herein, we report Cu electrodes modified by metal-organic framework (MOF) exhibiting enhanced electrocatalytic performance to convert CO₂ into ethylene and ethanol. The Zr-based MOF, UiO-66 would in situ transform into amorphous ZrO_x nanoparticles (a-ZrO_x), constructing a-ZrO_x/Cu hetero-interface as a dual-site catalyst. The Faradaic efficiency of multi-carbon (C2+) products for optimal UiO-66-coated Cu (0.5-UiO/Cu) electrode reaches a high value of 74% at - 1.05 V versus RHE. The intrinsic activity for C2+ products on 0.5-UiO/Cu electrode is about two times higher than that of Cu foil. In situ surface-enhanced Raman spectra demonstrate that UiO-66-derived a-ZrO_x coating can promote the stabilization of atop-bound CO* intermediates on Cu surface during CO₂ electrolysis, leading to increased CO* coverage and facilitating the C-C coupling process. The present study gives new insights into tailoring the adsorption configurations of CO₂RR intermediate by designing dual-site electrocatalysts with hetero-interfaces.

Biomimetic metal-organic frameworks navigated biological bombs for efficient lung cancer therapy

The rising risk of lung cancer has become a primary global concern with high mortality and mobility. Presently, clinically used anticancer drugs show limited efficacy and significant side effects. A new generation of anticancer weapons is in great demand for lung cancer therapy. Herein, we have developed a novel style of biomimetic zeolitic imidazolate framework-8 (ZIF-8) based on the merits of cell membranes derived from human bone marrow mesenchymal stem cells (hBMSCs), which can navigate biological bombs herpes simplex virus type I thymidine kinase-encoded plasmids (pHSVtk) and ganciclovir (GCV) to treat lung cancer. The biological bomb-loaded structure can kill transfected lung cancer cells and neighboring lung cancer cells through the "bystander effect," which induces efficient suppression of lung cancer both in vitro and in vivo. The biomimetic nanoparticles show an enhanced circulation lifetime and drug accumulation in the tumor tissues and significantly inhibit the tumors. We have developed a straightforward approach to deliver biological bombs with biomimetic metal-organic frameworks for efficient lung cancer therapy. To the best of our knowledge, this is the first report of such a strategy for lung cancer therapy.

Metal-organic frameworks as a good platform for the fabrication of multi-metal nanomaterials: design strategies, electrocatalytic applications and prospective

MOF-derived multi-metal nanomaterials are attracting numerous attentions in widespread applications such as catalysis, sensors, energy storage and conversion, and environmental remediation. Compared to the monometallic counterparts, the presence of foreign metal is expected to bring new physicochemical properties, thus exhibiting synergistic effect for enhanced performance. MOFs have been proved as a good platform for the fabrication of polymetallic nanomaterials with requisite features. Herein, various design strategies related to constructing multi-metallic nanomaterials from MOFs are summarized for the first time, involving metal nodal substitution, seed epitaxial growth, ion-exchange strategy, guest species encapsulation, solution impregnation and combination with extraneous substrate. Afterwards, the recent advances of multi-metallic nanomaterials for electrocatalytic applications, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are systematically discussed. Finally, a personal outlook on the future trends and challenges are also presented with hope to enlighten deeper understanding and new thoughts for the development of multi-metal nanomaterials from MOFs.

Hybrid liposome/metal-organic framework as a promising dual-responsive nanocarriers for anticancer drug delivery

In this work, liposome-coated iron (III) benzene-1,3,5-tricarboxylate (Fe-BTC) metal-organic framework is examined as a promising pH/Ultrasound dual-responsive nanocarriers for doxorubicin (DOX) delivery. The successful coating of the MOF particles (Lip-Fe-BTC) with the phospholipid bilayer (PBL) was established by direct fusion into the synthesized liposomes. The liposome coating was verified using several techniques, including dynamic light scattering (DLS) and transmission electron microscopy (TEM). The DLS measurements showed an increase in the average particle diameter of liposomes from 150 nm to 163.1 nm for Lip-Fe-BTC particles. The Fe-BTC particles had the highest average particle diameter (287.3 nm). These results demonstrated that the PBL reduced the aggregation of the particles and improved their dispersity in the release medium. The TGA results demonstrated the MOF's excellent thermal stability. Furthermore, the nanocarrier's loading efficiency and capacity were determined to be ~90% and ~13.5 wt%, respectively. The in-vitro DOX release experiments demonstrated that the DOX-loaded Fe-BTC and liposome-coated Fe-BTC particles showed good pH and US dual-responsive capability, making them promising nanocarriers for drug delivery. The application of US enhanced DOX release from both Fe-BTC and liposome-coated Fe-BTC. In the case of Fe-BTC-DOX particles, the application of US enhanced the DOX release to around 38% and 67%, at pH levels of 7.4 and 5.3, respectively. Similarly, DOX release from the Lip-Fe-BTC-DOX particles reached ~35% and ~53%, at pH levels of 7.4 and 5.3, respectively. The MTT assay showed the biocompatibility and low cytotoxicity of these nanocarriers below 100 µg/ml.

Enhancement of antitumor immunotherapy using mitochondria-targeted cancer cell membrane-biomimetic MOF-mediated sonodynamic therapy and checkpoint blockade immunotherapy

Immunotherapeutic interventions represent a promising approach to treating cancer, with strategies such as immune checkpoint blockade (ICB), immunogenic sonodynamic therapy (SDT), and immune adjuvant T cell delivery having exhibited clinical promise. In this report, we describe the use of cancer cell membrane-coated triphenylphosphonium (TPP) decorated nano-metal-organic framework (nMOF) constructs [Zr-TCPP(TPP)/R837@M] that were used to generate homologous, mitochondria-targeted platforms with a high rate of sonosensitizer loading. This construct was utilized to simultaneously promote tumor antigen presentation via enhancing SDT while synergistically promoting dendritic cell (DC) maturation through the delivery of the Toll-like receptor agonist R837. In vitro, these functionalized nMOFs were readily internalized by homologous tumor cells in which they were efficiently targeted to the mitochondria, promoting DC activation through the induction of immunogenic cell death (ICD) following ultrasound exposure. Moreover, this nanoplatform was able to achieve in vivo synergy with anti-CTLA-4 ICB to reverse immunosuppression tumor microenvironment (TME), thus achieving more robust antitumor efficacy capable of suppressing metastatic disease progression and facilitating the development of durable antitumor memory responses. Together, these results highlight a promising approach to achieving enhanced SDT activity while overcoming an immunosuppressive TME, thereby achieving more robust antitumor immunity.

Electrocatalytic methane oxidation to formate on magnesium based metal-organic frameworks

The electrochemical methane oxidation reaction is a potential approach for upgrading the nature-abundant methane (CH₄) into value-added chemicals, while the activity and selectivity have remained substantially low due to the extremely inert chemical property of CH₄. Inspired by the methane mono-oxygenase in nature, we demonstrated Mg-substituted metal-organic frameworks (Mg-MOF-74) containing a uniform distribution of Mg-oxo-Mg nodes as efficient catalytic sites. Compared to MgNi-MOF-74 and Mg(OH)₂ without the Mg-oxo-Mg nodes, the Mg-MOF-74 presented a much enhanced CH₄ electrooxidation performance, with a unique selectivity of producing formate. The maximum Faradaic efficiency of all liquid products reached 10.9% at 1.60 V versus reversible hydrogen electrode (RHE), corresponding to the peak production rate of 126.6 μmol·h^-1·g^-1.

Persulfate activation by ferrocene-based metal-organic framework microspheres for efficient oxidation of orange acid 7

Ferrocene-based metal-organic framework with different transition metals (M-Fc-MOFs, M = Fe, Mn, Co) was synthesized by a simple hydrothermal method and used as a heterogeneous catalyst for persulfate activation. The samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray electron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Meanwhile, the influences of factors such as catalyst dosage, persulfate concentration, and pH on the degradation of acid orange 7 (AO7) were studied in detail. The results showed that hollow cobalt-based ferrocenyl metal-organic framework microspheres (Co-Fc-MOFs) exhibited the best catalytic performance, which is closely related to the synergy of Fc/Fc⁺ and Co(II)/Co(III) cycles in persulfate activation. Free radical quenching studies indicated that both sulfate and hydroxyl appeared to contribute to the degradation of AO7.

Electrochemically reduced graphene oxide/Cu-MOF/Pt nanoparticles composites as a high-performance sensing platform for sensitive detection of tetracycline

A promising sensing platform was constructed based on an electrochemically reduced graphene oxide (ErGO)/copper metal-organic framework (Cu-MOF)/platinum nanoparticles (ErGO/Cu-MOF/PtNPs) modified glassy carbon electrode for the detection of tetracycline. The ErGO/Cu-MOF/PtNPs composite electrode possessed an excellent electrochemical performance to tetracycline detection mainly due to the synergistic effect of ErGO, Cu-MOF and PtNPs. The electrochemical kinetics and catalytical mechanism of tetracycline were systematically studied, showing that tetracycline's electrocatalytic oxidation reaction was an absorption-controlled two-step process involving two electrons and one proton transfer, respectively. Low concentration of tetracycline was detected by amperometry with the a linear range of 1 ~ 200 μM (R² = 0.9900) and a detection limit of 0.03 μM (S/R = 3). The proposed sensor was successfully applied to the detection of tetracycline in the real water samples with recoveries of 93.5% ~ 106%, and relative standard deviations (RSD) of 4.65% ~ 5.21% (n = 3). Furthermore, acceptable stability, repeatability and reproducibility were verified for continuous determination of tetracycline under optimized conditions. The ErGO/Cu-MOF/PtNPs composite electrode also demonstrated better anti-interference performance compared to other types of antibiotics than that of similar structural tetracyclines. Therefore, the proposed ErGO/Cu-MOF/PtNPs composites might provide a potential sensing platform for detecting analogous tetracyclines or total tetracyclines in the environment.

In situ electrochemical reductive construction of metal oxide/metal-organic framework heterojunction nanoarrays for hydrogen peroxide sensing

Transition metal oxide/metal-organic framework heterojunctions (TMO@MOF) that combine the large specific surface area of MOFs with TMOs' high catalytic activity and multifunctionality, show excellent performances in various catalytic reactions. Nevertheless, the present preparation approaches of TMO@MOF heterojunctions are too complex to control, stimulating interests in developing simple and highly controllable methods for preparing such heterojunction. In this study, we propose an in situ electrochemical reduction approach to fabricating Cu₂O nanoparticle (NP)@CuHHTP heterojunction nanoarrays with a graphene-like conductive MOF CuHHTP (HHTP is 2,3,6,7,10,11-hexahydroxytriphenylene). We have discovered that size-controlled Cu₂O nanoparticles could be in situ grown on CuHHTP by applying different electrochemical reduction potentials. Also, the obtained Cu₂O NP@CuHHTP heterojunction nanoarrays show high H₂O₂ sensitivity of 8150.6 μA·mM^-1·cm² and satisfactory detection performances in application of measuring H₂O₂ concentrations in urine and serum samples. This study offers promising guidance for the synthesis of MOF-based heterojunctions for early cancer diagnosis.

Ultralight Magnetic and Dielectric Aerogels Achieved by Metal-Organic Framework Initiated Gelation of Graphene Oxide for Enhanced Microwave Absorption

Metal-organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels. The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents. The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal-organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal-oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe₃O₄@C/rGO and Ni-doped Fe₃O₄@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (- 58.1 dB and 6.48 GHz) and 2.8 mm (- 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

Recent advancements in metal-organic frameworks composites based electrochemical (bio)sensors

Metal-organic frameworks (MOFs) are a novel class of crystalline materials which find widespread applications in the field of microporous conductors, catalysis, separation, biomedical engineering, and electrochemical sensing. With a specific emphasis on the MOF composites for electrochemical sensor applications, this review summarizes the recent construction strategies on the development of conductive MOF composites (post-synthetic modification of MOFs, in situ synthesis of functional materials@MOFs composites, and incorporating electroactive ligands). The developed composites are revealed to have excellent electrochemical sensing activity better than their pristine forms. Notably, the applicable functionalized MOFs to electrochemical sensing/biosensing of various target species are discussed. Finally, we highlight the perspectives and challenges in the field of electrochemical sensors and biosensors for potential directions of future development.

MicroRNA-21 electrochemiluminescence biosensor based on Co-MOF-N-(4-aminobutyl)-N-ethylisoluminol/Ti3C2Tx composite and duplex-specific nuclease-assisted signal amplification

A novel electrochemiluminescence (ECL) biosensor for the determination of microRNA-21 (miRNA-21) was developed, based on a hybrid luminescent Co-MOF-ABEI/Ti₃C₂T_x composite as an ECL luminophore combined with a duplex-specific nuclease (DSN)-assisted signal amplification strategy. The synthesized Co-MOF-ABEI/Ti₃C₂T_x composite carrying N-(4-aminobutyl)-N-ethylisoluminol (ABEI) exhibited strong and stable ECL in the presence of reactive oxygen species (ROS). The ECL biosensor was fabricated by adsorbing Co-MOF-ABEI/Ti₃C₂T_x onto a glassy carbon electrode and covalently coupling the probe DNA onto the surface of the Co-MOF-ABEI/Ti₃C₂T_x-modified electrode. In the presence of the target miRNA-21, the DSN selectively cleaved the complementary DNA section (S1) to miRNA-21, resulting in the release of the transduction section (S2) and the reuse of miRNA-21 in the subsequent amplification cycle. The interaction of the stem-loop structure of the probe DNA with the Co-MOF-ABEI/Ti₃C₂T_x-modified glassy carbon electrode with S2 strands led to the opening of the annular part of the probe DNA. Then, the opened guanine (G)-rich sequences of probe DNA were exposed and folded into a hemin/G-quadruplex DNAzyme in the presence of hemin. The catalysis of H₂O₂ to ROS by the hemin/G-quadruplex DNAzyme significantly enhanced ECL intensity, and this intensity was logarithmically proportional to the concentration of target miRNA-21 between 0.00001 and 10 nM, having a limit of detection of 3.7 fM. The designed ECL biosensor can  detect miRNA-21 extracted from HeLa cells, indicating its promising application in clinical diagnosis and disease prognosis analysis.

State of the Art and Prospects in Metal-Organic Framework-Derived Microwave Absorption Materials

Microwave has been widely used in many fields, including communication, medical treatment and military industry; however, the corresponding generated radiations have been novel hazardous sources of pollution threating human's daily life. Therefore, designing high-performance microwave absorption materials (MAMs) has become an indispensable requirement. Recently, metal-organic frameworks (MOFs) have been considered as one of the most ideal precursor candidates of MAMs because of their tunable structure, high porosity and large specific surface area. Usually, MOF-derived MAMs exhibit excellent electrical conductivity, good magnetism and sufficient defects and interfaces, providing obvious merits in both impedance matching and microwave loss. In this review, the recent research progresses on MOF-derived MAMs were profoundly reviewed, including the categories of MOFs and MOF composites precursors, design principles, preparation methods and the relationship between mechanisms of microwave absorption and microstructures of MAMs. Finally, the current challenges and prospects for future opportunities of MOF-derived MAMs are also discussed.