Postsynthetic Tuning of Metal-Organic Frameworks for Targeted Applications

MOFs-Based Aerogels and Their Derivatives for Water Treatment: A Review

Metal-organic frameworks (MOFs) are a class of environmental nano-materials composed of metal ions and organic ligands with remarkable physical and chemical properties, such as huge specific surface area as well as abundant pore volume. Based on their unique structures and properties, MOFs have demonstrated potential applications in the fields of adsorption, gas storage, separation membranes, and catalysis, and have become popular candidates in water treatment technologies. However, MOFs particles in powder form are prone to agglomeration and adhesion effects in water, which leads to problems such as difficult separation and secondary pollution. As an ideal carrier for MOFs, aerogels exhibit a unique three-dimensional interconnected pore structure, which endows aerogels with high porosity properties and excellent adsorption capacity. Researchers have skillfully combined MOFs with aerogels to create a new type of MOF aerogel composites (MOFACs). These composites are converted into highly porous and high-strength carbon aerogels through a high-temperature pyrolysis process in an inert environment. These carbon aerogels not only retain the high catalytic efficiency of MOFs, but also inherit the advantages of aerogels in terms of light weight, low density and easy handling. This paper reviews various types of MOFACs, each of which possesses different chemical compositions and physical properties, thus adapting to different applications. The paper also discusses the applications of MOFACs and carbon aerogels in water treatment for catalysis, selective adsorption and solid phase microextraction.

Mechanochromic Luminescence Behavior in Multivariate Metal-Organic Frameworks Based on Linker Effects

Mechanochromic luminescence molecules show great appeal in the realm of intelligent luminescent materials but face great challenges from aggregation-caused quenching and/or amorphization during mechanical processing. Integrating aggregation-induced emission (AIE) luminogens into the architecture of highly crystalline metal-organic frameworks (MOFs) could potentially address these issues. In this work, two isomorphic Zn-MOFs ({[Zn(TCPE)0.5(Lx)0.5]·guests}n, where H4TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene, L1 = triethylenediamine, and L2 = piperazine) are synthesized via a multiligand assembly approach. The mechanochromic luminescence behaviors observed in these Zn-MOFs have been thoroughly analyzed, with a focus on the influence of linker effects. Under mechanical grinding, the lattice contraction of Zn-MOFs is accompanied by the distortion of the benzene rings within TCPE4-, leading to altered intramolecular twisted charge transfer within the Zn-MOFs, which subsequently changes their luminescence properties. The potential application of this luminescence behavior in light-emitting diodes was preliminarily explored.

Unlocking coordination sites of metal-organic frameworks for high-density and accessible copper nanoparticles toward electrochemical nitrate reduction to ammonia

Ordered pore engineering of metal-organic framework (MOF)-based catalysts by soft-template strategies can facilitate the mass transfer of reactants during heterogeneous electrocatalysis. Besides, the abundant open coordination sites generated by the removal of surfactants also open up a new avenue for incorporating active moieties within the framework; however, such studies are still limited. Herein, a mesoporous cerium-based MOF, MUiO-66(Ce), is synthesized by introducing a pluronic triblock copolymer as a template, where abundant open coordination sites are found to be present on the hexa-cerium nodes. By providing rich Ce-OH/Ce-OH2 sites, plenty of copper moieties are installed on the framework (denoted as Cu-MUiO-66(Ce)). After the in situ reduction process, a high density of copper nanoparticles is confined within MUiO-66(Ce), and Cu@MUiO-66(Ce) is thus obtained. With a high loading of active copper sites and efficient diffusion of reactants, the Cu@MUiO-66(Ce)-modified electrode can achieve an ammonia production rate of 1.875 mg h-1 mgcatalyst -1 and a faradaic efficiency of 88.7% for nitrate-to-ammonia reduction. Findings here shed light on the importance of pore engineering of MOF-based catalysts for unlocking open coordination sites and facilitating the mass transfer to enhance the electrocatalytic activity.

In situ generated hydrogen-bonding microenvironment in functionalized MOF nanosheets for enhanced CO2 electroreduction

The microenvironment around catalytic sites plays crucial roles in enzymatic catalysis while its precise control in heterogeneous catalysts remains challenging. Herein, the coordinatively unsaturated metal nodes of Hf-based metal-organic framework nanosheets are simultaneously codecorated with catalytically active Co(salen) units and adjacent pyridyl-substituted alkyl carboxylic acids via a post modification route. By varying pyridyl-substituted alkyl carboxylic acids, the spatial positioning of the N atom in pyridine group relative to adjacent Co(salen) can be precisely controlled. Notably, the 3-(pyridin-4-yl)propionic acid, with para-position pyridine N atom, maximally improves the electrocatalytic CO2 reduction performance of Co(salen) unit, far superior to other counterparts. Mechanism investigations reveal that the pyridine unit of 3-(pyridin-4-yl)propionic acid is optimally positioned relative to Co(salen) and undergoes in situ reduction to pyridinyl radical under working potentials. This greatly facilitates the stabilization of *COOH intermediate via hydrogen-bonding interaction, lowering the formation energy barrier of *COOH and therefore boosting CO2 electroreduction.

pH-responsive ZIF-8 nanoplatform co-loaded with DSF and ICG for multiple synergistic antitumor therapy

Disulfiram (Allensworth et al.), an "old drug" for the treatment of chronic alcohol dependence, has received extensive attention due to its potential antitumor activity for new medical applications. However, the application of DSF in cancer therapy was limited by its extremely terrible solubility in water. Meanwhile, Cu2+ was used to enhance the antitumor activity of DSF in most of the current studies, while few studies related to the combination of Zn2+ and DSF. Herein, we developed a pH-responsive hyaluronic acid/polyethylene glycol-graft-polyglutamic acid (HPG) modified zeolitic imidazolate framework-8 (ZIF-8) nanoparticle system (ID@ZIF-8@HPG) to achieve the co-delivery of Zn2+/indocyanine green (ICG)/DSF and the improvement of the solubility of DSF, which conducted an efficient anticancer effectiveness through its chemotherapy/photothermal/photodynamic multiple synergistic antitumor effects. The obtained ID@ZIF-8@HPG demonstrated acid-sensitive and photothermal-sensitive release behavior, which contributed to the release of DSF from nanoparticles within tumor cells upon laser irradiation of the tumor site and was beneficial to reduce the toxicity produced by chemotherapy. In vitro experiments demonstrated that ID@ZIF-8@HPG could be better taken up by tumor cells, resulting in excellent photothermal and photodynamic properties. In addition, ID@ZIF-8@HPG exhibited outstanding intratumor retention capacity and powerful tumor cell-killing ability while maintaining favorable biocompatibility. In summary, this study presents a promising nanoparticle delivery platform for cancer treatment, broadening the application of ZIF-8 in the field of tumor combination therapy.

Tenon-and-Mortise Structure-Inspired MOF/PVDF Composites with Enhanced Piezocatalytic Performance via Dipole-Engineering Strategy

Fabricating poly(vinylidene fluoride) (PVDF) and its composite ferroelectrics are essential for the development of next-generation lightweight, portable, wearable, and implantable intelligent devices. However, integrating and maximizing spontaneous polarization and interfacial electromechanical conversion efficiency remain major challenges in the contemporary PVDF-based composites field. Herein, inspired by the tenon-and-mortise structure associated with ancient Chinese architecture, an amino-anchored metal-organic framework (MOF)/PVDF piezoelectric composite using a dipole-engineering strategy to deliver enhanced piezocatalytic performance is constructed. Homogeneous and long-range ordered hydrogen-bond networks have been formed with the PVDF matrix after introducing periodically arranged amino anchors into the NH2-HU MOF. The NH2-HU10wt%/PVDF composite exhibits a 40% greater β-phase content and a remnant polarization value more than 550% higher than that of the bare PVDF fibers. These amino anchors synergistically enhance both the local electric field and collaborative dipole alignment resulting in a piezocatalytic bactericidal performance of 97.4% when irradiated under clinical ultrasound conditions. Moreover, the enhanced polarizability within the MOF/PVDF composite simultaneously improves its responsiveness to X-rays via its periodic amino anchoring networks, thereby doubling CT imaging efficacy for implants at lower voltages. Integrating piezoelectric MOFs and polymer matrices through molecular design presents a viable approach for optimizing ferroelectric properties and expanding piezoelectric-composite applications.

Comparison of Hydrogen Bonded Organic Framework with Reduced Graphene Oxide-Pd Based Nanocatalyst: Which One Is More Efficient for Entrapment of Nitrophenol Pollutants?

In this study, a Pd nanoparticles@hydrogen-bonded organic framework (Pd NPs@HOF) thin film was fabricated at the toluene-water interface. The HOF was formed through the interaction of trimesic acid (TMA) and melamine (Mel) in the water phase, while Pd(0) was produced from the reduction of [PdCl2(cod)] in the organic phase. The as-synthesized Pd NPs@HOF thin film was demonstrated to be an effective catalyst for the selective reduction of p-nitrophenol and o-nitrophenol to p-aminophenol and o-aminophenol. The porous network of the Pd NPs@HOF introduced strong active sites between Mel, TMA, and Pd(0). Kinetic studies showed that the Pd NPs@HOF catalyst exhibited an enhanced rate of p-nitrophenol and o-nitrophenol reduction in comparison with Pd@reduced-graphene oxide (r-GO) with rates that were 1.7 times faster for p-nitrophenol and 1.5 times faster for o-nitrophenol or even 10 times faster than some Pd-based catalysts, with a maximum conversion of 97.1% which was attributed to the higher porosity and greater surface-to-volume ratio of the Pd NPs@HOF material. Furthermore, π-π stacking interactions enhance the catalytic activity of the Pd NPs@HOF catalyst by increasing the active sites, stabilizing the NPs and trapping the nitrophenols, facilitating the electron transfer, and providing the synergistic effect. Also, contributions of hydrogen bonding, van der Waals forces, electrostatic interactions, and π-σ noncovalent interactions are reasons for better performance of Pd NPs@HOF than Pd/r-GO catalyst with the reduced functional groups.

Single-Atom Pt Loaded on MOF-Derived Porous TiO2 with Maxim-Ized Pt Atom Utilization for Selective Hydrogenation of Halonitro-benzene

The location control of single atoms relative to supports is challenging for single-atom catalysts, leading to a large proportion of inaccessible single atoms buried under supports. Herein, a "sequential thermal transition" strategy is developed to afford single-atom Pt preferentially dispersed on the outer surface of TiO2. Specifically, a Ti-MOF confining Pt nanoparticles is converted to PtNPs and TiO2 composite coated by carbon (PtNPs&TiO2@C-800) at 800 °C in N2. Subsequent thermal-driven atomization of PtNPs at 600 °C in air produce single-atom Pt decorated TiO2 (Pt1/TiO2-600). The resulting Pt1/TiO2-600 exhibits superior p-chloroaniline (p-CAN) selectivity (99 %) to PtNPs/TiO2-400 (45 %) and much better activity than Pt1@TiO2-600 with randomly dispersed Pt1 both outside and inside TiO2 in the hydrogenation of p-chloronitrobenzene (p-CNB). Mechanism investigations reveal that Pt1/TiO2-600 achieves 100 % accessibility of Pt1 and preferably adsorbs the -NO2 group of p-CNB while weakly adsorbs -Cl group of p-CNB and p-CAN, promoting catalytic activity and selectivity.

Rational design and synthesis of atomically precise nanocluster-based nanocomposites: a step towards environmental catalysis

Atomically precise metal nanoclusters (NCs) and metal-organic frameworks (MOFs) possess distinct properties that can present challenges in certain applications. However, integrating these materials to create new composite functional materials has gained significant interest due to their unique characteristics through a range of applications, particularly in catalysis. Considering MOFs as hosts and NCs as guests, several synergistic effects have been observed in composites, particularly in environmental catalytic reactions. However, the precise role of encapsulated NCs within the MOF pore structure is still in its infancy. Besides, stabilizing NCs, whether through intact ligands or without ligands via the MOF host, presents challenges that are currently being investigated. This feature article reviews recent advancements in the synthesis of NC@MOF composites, focusing on cutting-edge strategies for selecting MOFs and the roles of NC ligands, as well as characterization and catalytic applications.

Full-Color Emissive Zirconium-Organic Frameworks Constructed via in Situ "One-Pot" Single-Site Modification for Tryptophan Detection and Energy Transfer

Organic linker-based luminescent metal-organic frameworks (LMOFs) have received extensive studies due to the unlimited species of emissive organic linkers and tunable structure of MOFs. However, the multiple-step organic synthesis is always a great challenge for the development of LMOFs. As an alternative strategy, in situ "one-pot" strategy, in which the generation of emissive organic linkers and sequential construction of LMOFs happen in one reaction condition, can avoid time-consuming pre-synthesis of organic linkers. In the present work, we demonstrate the successful utilization of in situ "one-pot" strategy to construct a series of LMOFs via the single-site modification between the reaction of aldehydes and o-phenylenediamine-based tetratopic carboxylic acid. The resultant MOFs possess csq topology with emission covering blue to near-infrared. The nanosized LMOFs exhibit excellent sensitivity and selectivity for tryptophan detection. In addition, two component-based LMOFs can also be prepared via the in situ "one-pot" strategy and used to study energy transfer. This work not only reports the construction of LMOFs with full-color emissions, which can be utilized for various applications, but also indicates that in situ "one-pot" strategy indeed is a useful and powerful method to complement the traditional MOFs construction method for preparing porous materials with tunable functionalities and properties.

Proton-Mediated Dynamic Nestling of DNA Payloads Within Size-Matched MOFs Nanochannels for Smart Intracellular Delivery

With sequence-programmable biological functions and excellent biocompatibility, synthetic functional DNA holds great promise for various biological applications. However, it remains a challenge to simultaneously retain their biological functions while protecting these fragile oligonucleotides from the degradation by nucleases abundant in biological circumstances. Herein, a smart delivery system for functional DNA payloads is developed based on proton-mediated dynamic nestling of cytosine-rich DNA moieties within the precisely size-matched nanochannels of highly crystalline metal-organic frameworks (MOFs): At neutral pH, cytosine-rich DNA strands exhibit a flexible single-stranded state and can be accommodated by MOFs nanochannels with a size of ca. 2.0 nm; while at acidic conditions, the protonation of cytosine-rich strands weakens their interaction with the nanochannels, and the tendency to form four-stranded structures drives these DNA strands out of the nanochannels. Results confirm the successful protection of DNA payloads from enzymatic hydrolysis by the MOFs nanochannels, and the delicate coupling of the endocytosis processes and the proton-responsive Cytosine-rich DNA/MOFs systems realized the efficient intracellular delivery of DNA payloads. Furthermore, with a complementary sequence to the telomere overhangs, direct imaging of telomeres and the nucleus is successfully achieved with the proton-mediated DNA/MOFs system.

Differentiated Intra-Ligand Charge Transfer Boosting Multicolor Responsive MOF Heterostructures as Robust Anti-Counterfeiting Labels

Metal-organic framework (MOF) heterostructures with hybrid architectures and abundant functional sites possess great potential applications in advanced information security, yet still suffer from the harsh stimuli mechanisms with restrained emission control. Herein, the differentiated design strategy on intra-ligand charge transfer is first reported to realize smart-responsive multicolor MOF heterostructures as robust anticounterfeiting labels. Designed similar MOF blocks with the differentiated intra-ligand charge transfer are integrated via time-dependent epitaxial growth to form multicolor MOF heterostructures. Different numbers of electron-donating groups in MOF blocks offer distinct space regulation on the torsion of charge transfer ligands, which trigger the diverse responsive emissions under the same mild stimuli, thus generating multiple tunable color patterns in heterostructures. These spatial-resolved MOF heterostructures with stable multicolor responsive modes permit the encoding of fingerprint information, which further functions as robust anti-counterfeiting labels with high-security convert states. These results offer a promising route for the function-oriented exploitation of smart-responsive MOF heterosystems for advanced information anticounterfeiting.

Defect-Engineered Metal-Organic Frameworks as Bioinspired Heterogeneous Catalysts for Amide Bond Formation

The synthesis of amides from amines and carboxylic acids is the most widely carried out reaction in medicinal chemistry. Yet, most amide couplings are still conducted using stoichiometric reagents, leading to significant waste; few synthetic catalysts for this transformation have been adopted industrially due to their limited scope and/or poor recyclability. The majority of catalytic approaches focus on a single activation mode, such as enhancing the electrophilicity of the carboxylic acid partner using a Lewis acid. In contrast, nature effortlessly forges and breaks amide bonds using precise arrays of Lewis/Brønsted acidic and basic functional groups. Drawing inspiration from these systems, herein we report a simple defect engineering strategy to colocalize Lewis acidic Zr sites with other catalytically active species within porous metal-organic frameworks (MOFs). Specifically, the combination of pyridine N-oxide and Zr open metal sites within the defective framework MOF-808-py-Nox produces a heterogeneous catalyst that facilitates amide bond formation with broad functional group compatibility from amines and carboxylic acids, esters, or primary amides. Extensive density functional theory (DFT) calculations using cluster models support that the formation of a hydrogen-bonding network at the defect sites facilitates amide bond formation in this material. MOF-808-py-Nox can be recycled at least five times without losing significant crystallinity, porosity, or catalytic activity and can be employed in continuous flow. This defect engineering strategy can be potentially generalized to produce libraries of catalytically active MOFs with different combinations of colocalized functional groups.

Development of polyoxometalate-loaded MOFs for heterogeneous catalysis and enhanced dye adsorption

This study focuses on the enhancement of MIL-117 functionality by incorporating a well-known polyoxometalate (POM), tetrabutylammonium octamolybdate [(n-C4H9)4N]4[Mo8O26]. Using an encapsulation method with conventional heating, Mo8O264- anions were for the first time successfully integrated into MIL-117 tubular channels (Mo8O26@MIL-117). Comprehensive characterization of the material through FTIR, XRD, BET, FE-SEM, EDX, and XPS confirmed the uniform distribution of Mo8O264- within MIL-117 without compromising its structural integrity. The Mo8O26@MIL-117 composite demonstrates exceptional catalytic performance in oxidative C-N bond formation and Paal-Knorr pyrrole synthesis, achieving high yields under optimized conditions with diverse amine substrates. Characterization and stability assessments confirm Mo8O26@MIL-117 as a robust and recyclable catalyst, maintaining structural integrity and catalytic activity over multiple cycles, highlighting its potential for sustainable applications in synthetic chemistry. The composite material was also evaluated for its efficacy in dye removal, specifically targeting methylene blue (MB) and Rhodamine B (RHB) from aqueous solutions. Mo8O26@MIL-117 exhibited superior adsorption capacity for MB compared to MIL-117 alone, demonstrating high efficiency even at elevated concentrations. The composite showed improved selectivity towards MB over RHB, highlighting its potential for selective dye removal in wastewater treatment applications.

Recovery of Berry Natural Products Using Pyrene-Based MOF Solid Phase Extraction

This work introduces a novel method of recovering bioactive berry natural products (BNPs) using solid phase extraction with metal-organic frameworks (MOF-SPE). Two pyrene-based MOFs with different structural topologies, Al-PyrMOF and Zr-NU-1000, were evaluated for their ability to capture and desorb BNPs, including ellagic acid, quercetin, gallic acid, and p-coumaric acid. Time-dependent BNP uptake via dispersive SPE revealed that NU-1000 outperformed Al-PyrMOF in capturing all BNPs. Our findings show NU-1000 demonstrated a higher and more consistent BNP capture profile, achieving over 90 % capture of all BNPs within 36 h, with only a 9 % variation between the most and least effectively captured BNPs. In contrast, Al-PyrMOF, displayed a staggered uptake profile, with a significant 53 % difference in capture efficiency between the most and least effectively captured BNP. However, when a BNP mixture was used at a loading concentration of 50 μg/mL, Al-PyrMOF outperformed NU-1000, capturing over 70 % of all BNPs. Al-PyrMOF also exhibited improved BNP recovery, with a minimum of two-fold greater amount recovered for all BNPs. Further testing with a BNP mixture at a concentration of 15 μg/mL demonstrated that Al-PyrMOF efficiently concentrated all BNPs, achieving a maximum extraction factor of 2.71 observed for quercetin. These findings highlight the use of Al-PyrMOF as a MOF-SPE sorbent for recovering bioactive BNPs.

Metal-organic framework-based membranes for ion separation/selection from salt lake brines and seawater

Nanofiltration (NF) technologies have evolved into a stage ready for industrial commercialization. NF membranes with unique separation characteristics are widely used for ion selection in water environments. Although many materials have been synthesized and functionalized for specific ion separation, the permeability-selectivity trade-off is still a major challenge. Metal-organic frameworks (MOFs), as a class of promising materials to meet industrial demands, are gaining increasing attention. Many experimental and theoretical studies have been conducted on the applications of MOF-based membranes in ion selection. This review focuses on MOF-based NF membranes for ion separation/selection from seawater and salt lake brines, including their applications in industry. First, a brief discussion on the development of membrane technology for ion selection is given, with the principles of ion separation via NF membranes, industrial implementations, and technical difficulties being discussed. Next, the benefits and challenges of using MOF membranes in NF processes are elaborated, including the basic properties of MOFs, approaches to fabricate MOF membranes for efficient ion selection and challenges in constructing industrially viable membranes. Finally, state-of-the-art studies on key characteristics of MOFs for NF membrane fabrication are presented. It indicates that the utilization of MOF-based membranes has significant potential to improve ion separation performance. However, the lack of sufficient data under industrial conditions highlights the need for further development in this area.

Metal-organic framework with pore contraction and modification by diethylammonium cations for record SO2/CO2 separation

A robust MOF with diethylammonium cations in its pores, enhances pore partitioning and modifies the environment, enabling selective and dense SO2 packing through hydrogen bonds. It achieves a reversible SO2 uptake with a high adsorption enthalpy and record IAST selectivity of 1182 for SO2/CO2 at 298 K and 1 bar.

Strategies for the Preparation of Single-Atom Catalysts Using Low-Dimensional Metal-Organic Frameworks

As single-atom catalysts are important energy materials, their preparation and synthesis methods have become particularly important. The unique structures of low-dimensional metal-organic frameworks and their derivatives provide various strategies for preparing single-atom catalysts. This paper summarizes various strategies for the preparation of single-atom catalysts based on low-dimensional metal-organic frameworks and their derivatives.

Synergistic Effects of MOFs and Noble Metals in Photocatalytic Reactions: Mechanisms and Applications

Photocatalytic technology can efficiently convert solar energy to chemical energy and this process is considered as one of the green and sustainable technology for practical implementation. In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their unique advantages and have been widely applied in the field of photocatalysis. Among them, noble metals have contributed significant advances to the field as effective catalysts in photocatalytic reactions. Importantly, noble metals can also form a synergistic catalytic effect with MOFs to further improve the efficiency of photocatalytic reactions. However, how to precisely control the synergistic effect between MOFs and noble metals to improve the photocatalytic performance of materials still needs to be further studied. In this review, the synergistic effects of MOFs and noble metal catalysts in photocatalytic reactions are firstly summarized in terms of noble metal nanoparticles, noble metal monoatoms, noble metal compounds, and noble metal complexes, and focus on the mechanisms and advantages of these synergistic effects, so as to provide useful guidance for the further research and application of MOFs and contribute to the development of the field of photocatalysis.

Atomically Dispersed Metal Catalysts for the Conversion of CO2 into High-Value C2+ Chemicals

The conversion of carbon dioxide (CO2) into value-added chemicals with two or more carbons (C2+) is a promising strategy that cannot only mitigate anthropogenic CO2 emissions but also reduce the excessive dependence on fossil feedstocks. In recent years, atomically dispersed metal catalysts (ADCs), including single-atom catalysts (SACs), dual-atom catalysts (DACs), and single-cluster catalysts (SCCs), emerged as attractive candidates for CO2 fixation reactions due to their unique properties, such as the maximum utilization of active sites, tunable electronic structure, the efficient elucidation of catalytic mechanism, etc. This review provides an overview of significant progress in the synthesis and characterization of ADCs utilized in photocatalytic, electrocatalytic, and thermocatalytic conversion of CO2 toward high-value C2+ compounds. To provide insights for designing efficient ADCs toward the C2+ chemical synthesis originating from CO2, the key factors that influence the catalytic activity and selectivity are highlighted. Finally, the relevant challenges and opportunities are discussed to inspire new ideas for the generation of CO2-based C2+ products over ADCs.

Multi-channel electron transfer induced by polyvanadate in metal-organic framework for boosted peroxymonosulfate activation

Catalytic peroxymonosulfate (PMS) activation processes don't solely rely on electron transfer from dominant metal centers due to the complicated composition and interface environment of catalysts. Herein the synthesis of a cobalt based metal-organic framework containing polyvanadate [V4O12]4- cluster, Co2(V4O12)(bpy)2 (bpy = 4,4'-bipyridine), is presented. The catalyst demonstrates superior degradation activity toward various micropollutants, with higher highest occupied molecular orbital (HOMO), via nonradical attack. The X-ray absorption spectroscopy and density functional theory (DFT) calculations demonstrate that Co sites act as both PMS trapper and electron donor. In situ spectral characterizations and DFT calculations reveal that the terminal oxygen atoms in the [V4O12]4- electron sponge could interact with the terminal hydrogen atoms in PMS to form hydrogen bonds, promoting the generation of SO5* intermediate via both dynamic pull and direct electron transfer process. Further, Co2(V4O12)(bpy)2 exhibits long-term water purification ability, up to 40 h, towards actual wastewater discharged from an ofloxacin production factory. This work not only presents an efficient catalyst with an electron sponge for water environmental remediation via nonradical pathway, but also provides fundamental insights into the Fenton-like reaction mechanism.

Zirconium-based metal-organic frameworks and their roles in electrocatalysis

Due to their exceptional chemical stability in water and high structural tunability, zirconium(IV)-based MOFs (Zr-MOFs) have been considered attractive materials in the broad fields of electrocatalysis. Numerous studies published since 2015 have attempted to utilise Zr-MOFs in electrocatalysis, with the porous framework serving as either the active electrocatalyst or the scaffold or surface coating to further enhance the performance of the actual electrocatalyst. Herein, the roles of Zr-MOFs in electrocatalytic processes are discussed, and some selected examples reporting the applications of Zr-MOFs in various electrocatalytic reactions, including several studies from our group, are overviewed. Challenges, limitations and opportunities in using Zr-MOFs in electrocatalysis in future studies are discussed.

Anchoring Ultrafine β-Mo2C Clusters Inside Porous Co-NC Using MOFs for Electric-Powered Coproduction of Valuable Chemicals

Electroredox of organics provides a promising and green approach to producing value-added chemicals. However, it remains a grand challenge to achieve high selectivity of desired products simultaneously at two electrodes, especially for non-isoelectronic transfer reactions. Here a porous heterostructure of Mo2C@Co-NC is successfully fabricated, where subnanometre β-Mo2C clusters (<1 nm, ≈10 wt%) are confined inside porous Co, N-doped carbon using metalorganic frameworks. It is found that Co species not only promote the formation of β-Mo2C but also can prevent it from oxidation by constructing the heterojunctions. As noted, the heterostructure achieves >96% yield and 92% Faradaic efficiency (FE) for aldehydes in anodic alcohol oxidation, as well as >99.9% yield and 96% FE for amines in cathodal nitrocompounds reduction in 1.0 M KOH. Precise control of the reaction kinetics of two half-reactions by the electronic interaction between β-Mo2C and Co is a crucial adjective. Density functional theory (DFT) gives in-depth mechanistic insight into the high aldehyde selectivity. The work guides authors to reveal the electrooxidation nature of Mo2C at a subnanometer level. It is anticipated that the strategy will provide new insights into the design of highly effective bifunctional electrocatalysts for the coproduction of more complex fine chemicals.

Enhanced water stability and catalytic activity of Fe-based metal-organic frameworks with co-ligands for 2,4-dichlorophenol degradation

Fe-based metal-organic frameworks (MOFs) have good photocatalytic performance, environmental friendliness, low cost, and abundance. However, their applications are limited by low water stability, particularly in the presence of light irradiation and oxidizing agents. In this study, we present a MIL-53(Fe)-based MOF using 1,4-naphthalene dicarboxylic (1,4-NDC) and 1,4-benzenedicarboxylic (H2BDC) acid co-ligands, denoted MIL-53(Fe)-Nx, where Nx represents the ratio of 1,4-NDC. This MOF exhibits high water stability and good photocatalytic activity because of the hydrophobicity of naphthalene. The removal and mineralization rates for 100 mg/L 2,4-dichlorophenol reached 100% and 22%, respectively, within 60 min. After three cycles of use, the Fe leached into the solution from the catalysts was significantly lower than the maximum permissible limit indicated in the European Union standard. Of note, 1,4-NDC can be used to make a rigid MOF, thereby improving the crystallinity, porosity, and hydrophobicity of the resultant materials. It also significantly reduced the bandgap energy and improved the charge separation efficiency of the catalysts. This study provides a route to enhance the water stability of Fe-based MOFs via a mixed-ligand strategy to expand their applications in pollutant control.

Defect-Engineered Metal-Organic Frameworks as Nanocarriers for Pharmacotherapy: Insights into Intracellular Dynamics at The Single Particle Level

Nanoscale Metal-Organic Frameworks (nanoMOFs) are widely implemented in a host of assays involving drug delivery, biosensing catalysis, and bioimaging. However, the cell pathways and cell fate remain poorly understood. Here, a new fluorescent nanoMOF integrating ATTO 655 into surface defects of colloidal UiO-66 is synthesized, allowing to track the spatiotemporal localization of Single nanoMOF in live cells. Density functional theory reveals the stronger binding of ATTO 655 to the Zr6 cluster nodes compared with phosphate and Alendronate Sodium. Parallelized tracking of the spatiotemporal localization of thousands of nanoMOFs and analysis using machine learning platforms reveals whether nanoMOFs remain outside as well as their cellular internalization pathways. To quantitatively assess their colocalization with endo/lysosomal compartments, a colocalization proxy approach relying on the nanoMOF detection of particles in one channel to the signal in the corresponding endo/lysosomal compartments channel, considering signal versus local background intensity ratio and signal-to-noise ratio is developed. This strategy mitigates colocalization value inflation from high or low signal expression in endo/lysosomal compartments. The results accurately measure the nanoMOFs' colocalization from early to late endosomes and lysosomes and emphasize the importance of understanding their intracellular dynamics based on single-particle tracking for optimal and safe drug delivery.

Decorating the Node of a Zirconium-Based Metal-Organic Framework to Tune Adsorption Behavior and Surface Permeation

Surface barriers are commonly observed in nanoporous materials. Although researchers have explored methods to repair defects or create flawless crystals to mitigate surface barriers, these approaches may not always be practical or readily achievable in targeted metal-organic frameworks (MOFs). In our study, we propose an alternative approach focusing on the introduction of diverse ligands onto a MOF-808 node to finely adjust its adsorption and mass transport characteristics. Significantly, our findings indicate that while adsorption curves can be inferred based on the MOF's chemical composition and the probing molecule, surface permeabilities exhibit variations dependent on the specific probe utilized and the incorporated ligand. Our investigation, considering van der Waals forces exclusively between the adsorbate (e.g., n-hexane, propane, and benzene) and the adsorbent, revealed that augmenting these interactions can indeed improve surface permeation to a certain extent. Conversely, strong adsorption resulting from hydrogen bonding interactions, particularly with water in modified MOFs, led to compromised permeation within the MOF crystals. These outcomes provide valuable insights for the porous materials community and offer guidance in the development of adsorbents with enhanced affinity and superior mass transport properties for gases and vapors.

Lutein Loaded in β-Cyclodextrin Metal-Organic Frameworks for Stability and Solubility Enhancements

Lutein (Lut) is a recognized nutritional supplement known for its antioxidative and anti-inflammatory properties, crucial in mitigating ocular disease. However, enhancements to Lut stability and solubility remain challenges to be addressed in the healthcare industry. Herein, we fabricated and evaluated a food-grade highly porous β-cyclodextrin metal-organic framework (β-CD-MOF) for its ability to encapsulate Lut. Lut stability considerably improved when loaded into β-CD-MOF to form a Lut@β-CD-MOF complex, which exhibited better stability than Lut loaded into the γ-cyclodextrin metal-organic framework (Lut@γ-CD-MOF), Lut@β-CD, and commercial product (Blackmores™) at 40°C, 60°C, and 70°C, respectively. The solubility of Lut@β-CD-MOF in water increased by 26.8-fold compared to raw Lut at 37°C. Lut@β-CD-MOF exhibited greater hydrophilicity, as determined by measuring the water contact angle. Molecular docking and other characterizations of Fourier transform infrared spectroscopy and powder X-ray diffraction confirmed that Lut was successfully encapsulated in the chamber formed by the three cyclodextrins in β-CD-MOF. Thermogravimetric analysis and Raman spectroscopy demonstrated that Lut distributed in the β-CD-MOF cavity deeply improved Lut stability and solubility. In conclusion, our findings underscored the function of β-CD-MOF in enhancing Lut stability and solubility for formulation applications.

A robust aluminum-octacarboxylate framework with topology for selective capture of sulfur dioxide

The high structural diversity and porosity of metal-organic frameworks (MOFs) promote their applications in selective gas adsorption. The development of robust MOFs that are stable against corrosive SO2 remains a daunting challenge. Here, we report a highly robust aluminum-based MOF (HIAM-330) built on a 4-connected Al3(OH)2(COO)4 cluster and 8-connected octacarboxylate ligand with a (4,8)-connected scu topology. It exhibits a fully reversible SO2 uptake of 12.1 mmol g-1 at 298 K and 1 bar. It is capable of selective capture of SO2 over other gases (CO2, CH4, and N2) with high adsorption selectivities of 60, 330, and 3537 for equimolar mixtures of SO2/CO2, SO2/CH4, and SO2/N2, respectively, at 298 K and 1 bar. Breakthrough measurements verified the capability of HIAM-330 for selective capture of SO2 (2500 ppm) over CO2 or N2. High-resolution synchrotron X-ray powder diffraction of SO2 loaded HIAM-330 revealed the binding domains of adsorbed SO2 molecules and host-guest interactions.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

The use of collective variables and enhanced sampling in the simulations of existing and emerging microporous materials

Microporous materials, including zeolites, metal-organic frameworks, and cage compounds, offer diverse functionalities due to their unique dynamics and guest confinement properties. These materials play a significant role in separation, catalysis, and sensing, but their complexity hinders exploration using traditional atomistic simulations. This review explores collective variables (CVs) paired with enhanced sampling as a powerful approach to enable efficient investigation of key features in microporous materials. We highlight successful applications of CVs in studying adsorption, diffusion, phase transitions, and mechanical properties, demonstrating their crucial role in guiding material design and optimisation. The future of CVs lies in integration with techniques like machine learning, allowing for enhanced efficiency and accuracy. By tailoring CVs to specific materials and developing multi-scale approaches we can further unlock the intricacies of these fascinating materials. Simulations are a cornerstone in unravelling the complexities of microporous materials and are crucial for our future understanding.

Two-dimensional metal-organic framework for post-synthetic immobilization of graphene quantum dots for photoluminescent sensing

Immobilization of graphene quantum dots (GQDs) on a solid support is crucial to prevent GQDs from aggregation in the form of solid powder and facilitate the separation and recycling of GQDs after use. Herein, spatially dispersed GQDs are post-synthetically coordinated within a two-dimensional (2D) and water-stable zirconium-based metal-organic framework (MOF). Unlike pristine GQDs, the obtained GQDs immobilized on 2D MOF sheets show photoluminescence in both suspension and dry powder. Chemical and photoluminescent stabilities of MOF-immobilized GQDs in water are investigated, and the use of immobilized GQDs in the photoluminescent detection of copper ions is demonstrated. Findings here shed the light on the use of 2D MOFs as a platform to further immobilize GQDs with various sizes and distinct chemical functionalities for a range of applications.

Advancing stroke therapy: the potential of MOF-based nanozymes in biomedical applications

In this study, we explored the growing use of metal-organic framework (MOF)-based Nanozymes in biomedical research, with a specific emphasis on their applications in stroke therapy. We have discussed the complex nature of stroke pathophysiology, highlighting the crucial role of reactive oxygen species (ROS), and acknowledging the limitations of natural enzymes in addressing these challenges. We have also discussed the role of nanozymes, particularly those based on MOFs, their structural similarities to natural enzymes, and their potential to improve reactivity in various biomedical applications. The categorization of MOF nanozymes based on enzyme-mimicking activities is discussed, and their applications in stroke therapy are explored. We have reported the potential of MOF in treating stroke by regulating ROS levels, alleviation inflammation, and reducing neuron apoptosis. Additionally, we have addressed the challenges in developing efficient antioxidant nanozyme systems for stroke treatment. The review concludes with the promise of addressing these challenges and highlights the promising future of MOF nanozymes in diverse medical applications, particularly in the field of stroke treatment.

Hydrogen-bonded organic frameworks for membrane separation

Hydrogen-bonded organic frameworks (HOFs) are a new class of crystalline porous materials that are formed through the interconnection of organic or metal-organic building units via intermolecular hydrogen bonds. The remarkable flexibility and reversibility of hydrogen bonds, coupled with the customizable nature of organic units, endow HOFs with mild synthesis conditions, high crystallinity, solvent processability, and facile self-healing and regeneration properties. Consequently, these features have garnered significant attention across various fields, particularly in the realm of membrane separation. Herein, we present an overview of the recent advances in HOF-based membranes, including their advanced fabrication strategies and fascinating applications in membrane separation. To attain the desired HOF-based membranes, careful consideration is dedicated to crucial factors such as pore size, stability, hydrophilicity/hydrophobicity, and surface charge of the HOFs. Additionally, diverse preparation methods for HOF-based membranes, including blending, in situ growth, solution-processing, and electrophoretic deposition, have been analyzed. Furthermore, applications of HOF-based membranes in gas separation, water treatment, fuel cells, and other emerging application areas are presented. Finally, the challenges and prospects of HOF-based membranes are critically pointed out.

Reversible Postsynthetic Modification in a Metal-Organic Framework

Postsynthetic modification (PSM) of metal-organic frameworks (MOFs) provides access to functional materials and advanced porous solid engineering. Herein, we report the reversible PSM of a multivariate isoreticular MOF by applying dynamic furan-maleimide Diels-Alder (DA) chemistry. The key step involves incorporating a furan group into the MOF via "click" PSM, which can then undergo repeated cycles of modification and de-modification with maleimides. The structural integrity, crystallinity, and porosity of the furan-appended MOF remained intact even after three consecutive PSM/de-modification cycles using three different functionalized maleimides.

Water-stable metal-organic frameworks (MOFs): rational construction and carbon dioxide capture

Metal-organic frameworks (MOFs) are considered to be a promising porous material due to their excellent porosity and chemical tailorability. However, due to the relatively weak strength of coordination bonds, the stability (e.g., water stability) of MOFs is usually poor, which severely inhibits their practical applications. To prepare water-stable MOFs, several important strategies such as increasing the bonding strength of building units and introducing hydrophobic units have been proposed, and many MOFs with excellent water stability have been prepared. Carbon dioxide not only causes a range of climate and health problems but also is a by-product of some important chemicals (e.g., natural gas). Due to their excellent adsorption performances, MOFs are considered as a promising adsorbent that can capture carbon dioxide efficiently and energetically, and many water-stable MOFs have been used to capture carbon dioxide in various scenarios, including flue gas decarbonization, direct air capture, and purified crude natural gas. In this review, we first introduce the design and synthesis of water-stable MOFs and then describe their applications in carbon dioxide capture, and finally provide some personal comments on the challenges facing these areas.

Understanding and Controlling Molecular Compositions and Properties in Mixed-Linker Porphyrin Metal-Organic Frameworks

Porphyrin-based metal-organic frameworks (MOFs) are attractive materials for photo- and thermally activated catalysis due to their unique structural features related to the porphyrin moiety, guest-accessible porosity, and high chemical tunability. In this study, we report the synthetic incorporation of nonplanar β-ethyl-functionalized porphyrin linkers into the framework structure of PCN-222, obtaining a solid-solution series of materials with different modified linker contents. Comprehensive analysis by a combination of characterization techniques, such as NMR, UV-vis and IR spectroscopy, powder X-ray diffraction, and N2 sorption analysis, allows for the confirmation of linker incorporation. A detailed structural analysis of intrinsic material properties, such as the thermal response of the different materials, underlines the complexity of synthesizing and understanding such materials. This study presents a blueprint for synthesizing and analyzing porphyrin-based mixed-linker MOF systems and highlights the hurdles of characterizing such materials.

Advances in metal-organic frameworks for water remediation applications

Rapid industrialization and agricultural development have resulted in the accumulation of a variety of harmful contaminants in water resources. Thus, various approaches such as adsorption, photocatalytic degradation and methods for sensing water contaminants have been developed to solve the problem of water pollution. Metal-organic frameworks (MOFs) are a class of coordination networks comprising organic-inorganic hybrid porous materials having organic ligands attached to inorganic metal ions/clusters via coordination bonds. MOFs represent an emerging class of materials for application in water remediation owing to their versatile structural and chemical characteristics, such as well-ordered porous structures, large specific surface area, structural diversity, and tunable sites. The present review is focused on recent advances in various MOFs for application in water remediation via the adsorption and photocatalytic degradation of water contaminants. The sensing of water pollutants using MOFs via different approaches, such as luminescence, electrochemical, colorimetric, and surface-enhanced Raman spectroscopic techniques, is also discussed. The high porosity and chemical tunability of MOFs are the main driving forces for their widespread applications, which have huge potential for their commercial use.

High Capacity Adsorption and Degradation of a Nerve Agent Simulant and a Pesticide by a Nickel Pyrazolate Metal-Organic Framework

The development of materials that enable the efficient removal of toxic compounds is important for the improvement of current protective materials or decontamination technologies. Current materials rely either on agent removal by adsorption or by effecting (catalytic) degradation. Ideally, both of these mechanisms are combined in a single material in order to target a more broad spectrum of toxic agents and to improve the performance of the materials. Recent attempts to combine materials with either adsorptive or catalytic properties into a composite material are promising, although the overall performance often suffers from competition for the agent between the adsorptive and catalytic domains in the composites. In this work, we propose that metal-organic frameworks (MOFs) could feature both adsorptive properties as well as catalytic properties in a single structural domain, thereby avoiding a reduction in the overall performance originating from competitive agent interactions. We showcase this concept using the MOF Ni3(BTP)2, which exhibits strong affinity and high capacity for the storage of a nerve agent simulant and a pesticide. Moreover, it is demonstrated that the adsorbed agents are efficiently degraded and that the nontoxic degradation products are rapidly expelled from the MOF pores. Its ability to catalyze the hydrolytic degradation of both organophosphate and organophosphorothioate compounds highlights another unique feature of this material. The presented concept illustrates the feasibility for developing materials that target a broader spectrum of agents via adsorption, catalysis, or both and by their broader reactivity toward different types of agents.

Blocking Accretion Enables Dimension Reduction of Metal-Organic Framework for Photocatalytic Performance

The evolution and formation process of two-dimensional metal-organic frameworks (MOFs) primarily arise from the anisotropic growth of crystals, leading to variations in photocatalytic performance. It is crucial to achieve a synergistic combination of anisotropic electron transfer direction and dimension reduction strategies. In this study, a novel approach that effectively blocks crystal growth accretion through the coordination of solvent molecules is presented, achieving the successful synthesis of impurity-free two-dimensional nanosheet Zn-PTC with exceptional hydrogen evolution reaction (HER) performance (15.4 mmol g-1  h-1 ). The structural and photophysical characterizations validate the successful prevention of crystal accretion, while establishing correlation between structural anisotropy and intrinsic charge transfer mode through transient spectroscopy. These findings unequivocally demonstrate that electron transfer along the [001] direction plays a pivotal role in the redox performance of nano-Zn-PTC. Subsequently, by coupling the photocatalytic performance and density functional theory (DFT) simulation calculations, the carrier diffusion kinetics is explored, revealing that effective dimension reduction along the ligand-to-metal charge transfer (LMCT) direction is the key to achieving superior photocatalytic performance.

Accelerating structure reconstruction to form NiOOH in metal-organic frameworks (MOFs) for boosting the oxygen evolution reaction

Structural reconstruction of electrocatalysts to generate metal hydroxide/oxyhydroxide species is critical for an efficient oxygen evolution reaction (OER), but the controllable regulation of the reconstruction process still remains a challenge. Given the designable nature of metal-organic frameworks (MOFs), herein, we have reported a localized structure disordering strategy to accelerate the structural reconstruction of Ni-BDC to generate NiOOH for boosting the OER. The Ni-BDC nanosheets were modified by Fe3+ and urea to form cracks, which could promote the accessibility of the Ni sites by the electrolyte and thus promote the reconstruction to form NiOOH. In addition, the interaction between Ni2+ and Fe3+ allows the electron flow from Ni2+ to Fe3+, further enhancing the NiOOH generation. As a result, the optimized sample exhibits excellent OER activity with a small overpotential of 251 mV at 10 mA cm-2, which is superior to most of the MOF-based OER catalysts reported previously. This work provides a controllable strategy to regulate the structural reconstruction for promoting the OER, which could provide important guidance for the development of more efficient OER electrocatalysts.

Multivariate metal-organic frameworks generated through post-synthetic modification: impact and future directions

Reticular chemistry has proven to be invaluable over time, thanks to the structural versatility, and tailored porosity observed in structures like metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and metal-organic polyhedra (MOPs). Despite the wide array of ligands and metals available for synthesizing MOFs, they are still somewhat constrained by the reliance on de novo conditions and the focus on generating MOFs with single ligand and metal. To surpass these limitations, researchers have established strategies to generate multivariate (MTV) MOF structures incorporating more than one ligand/metal into the crystal lattice. MTV-MOFs have demonstrated enhanced properties by virtue of the additional functionalities incorporated within their structures. One approach to developing MTV-MOFs is through post-synthetic modification (PSM), where new functionalities are introduced after the initial synthesis, thereby achieving the enhanced properties of MTV-MOFs even in cases where the new functionalities are incompatible with MOF synthesis.

Prediction of the capture and utilization of atmospheric acidic gases by azo-based square-pillared fluorinated MOFs

More than the permissible limit of acidic gases like CO2, SO2, and NO2 in the atmosphere are responsible for the formation of acid rain, the greenhouse effect and many other undesirable environmental hazards. So, the capture and utilization of these gases are essential for mankind. Herein, we proposed an azo-based square pillared MOF, [Ni(MF5)(1,2-bis(4-pyridy)diazene)2]n, with the CUS metal site, i.e. M = Al/Fe, for the selective capture and conversion of acidic gas molecules into commodity chemicals such as cyclic carbonate, sulphite and nitrite. With the aid of Density Functional Theory (DFT), [Ni(MF5)(1,2-bis(4-pyridy)diazene)2]n has been optimized, and the specific force field is derived via guest-host interaction. The Grand Canonical Monte Carlo (GCMC) simulation has been used to explore the guest-host interactions over a wide range of pressures, and their respective stability under pre-humidification is evaluated. The adsorption prediction reveals that MFFIVE-Ni-apy have a higher adsorptive capacity (37.1 mmol g-1), and especially ALFFIVE-Ni-apy possesses a higher affinity towards guest molecules (CO2, SO2) rather than FEFFIVE-Ni-apy. Additionally, the adsorption of gases in the presence of humidity reveals that ALFFIVE-Ni-apy has an optimal adsorption capacity for all investigated acidic gases even at 38.5 RH%. The absorbed acidic gases on MFFIVE-Ni-apy were used for the theoretical investigations on cycloaddition with the aid of DFT as an application perspective of the toxic gases instead of expelling into atmosphere. The Climbing Image Nudged Elastic Band (CI-NEB) approach was used to discover the transition state in this scenario, in which the cycloaddition of adsorbed CO2, SO2, and NO2 gases with epoxides leads to the formation of cyclic carbonates, sulphites, and nitrates, respectively.

Postsynthetic Modification of the Nonanuclear Node in a Zirconium Metal-Organic Framework for Photocatalytic Oxidation of Hydrocarbons

Heterogeneous catalysis plays an indispensable role in chemical production and energy conversion. Incorporation of transition metals into metal oxides and zeolites is a common strategy to fine-tune the activity and selectivity of the resulting solid catalysts, as either the active center or promotor. Studying the underlying mechanism is however challenging. Decorating the metal-oxo clusters with transition metals in metal-organic frameworks (MOFs) via postsynthetic modification offers a rational approach to construct well-defined structural models for better understanding of the reaction mechanism. Therefore, it is important to expand the materials scope beyond the currently widely studied zirconium MOFs consisting of Zr6 nodes. In this work, we report the design and synthesis of a new (4,12)-connected Zr-MOF with ith topology that consists of rare Zr9 nodes. FeIII was further incorporated onto the Zr9 nodes of the framework, and the resulting MOF material exhibits significantly enhanced activity and selectivity toward the photocatalytic oxidation of toluene. This work demonstrates a delicate ligand design strategy to control the nuclearity of Zr-oxo clusters, which further dictates the number and binding sites of transition metals and the overall photocatalytic activity toward C-H activation. Our work paves the way for future exploration of the structure-activity study of catalysts using MOFs as the model system.

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.

Boosting the catalysis of cesium phosphomolybdate encapsulated in hierarchical porous UiO-66 by microenvironment modulation for epoxidation of alkenes

The chemical microenvironment of polyoxometalates (POMs) encapsulated in metal-organic frameworks (MOFs) presents a significant influence on their catalytic performance, which can be easily regulated by the linker functional group alteration or metal substitution in MOFs. Herein, a series of cesium phosphomolybdate (CsPM) encapsulated in hierarchical porous UiO-66-X composites (CsPM@HP-UiO-66-X, X = H, 2CH3, or 2OH, where X represents the alterable group grafted onto the linker benzene ring) were successfully synthesized through a one pot modulated solvothermal method. The catalytic performances of the obtained materials were explored in alkene epoxidation reaction with tert-butyl hydroperoxide (t-BuOOH). CsPM@HP-UiO-66-2CH3 showed relatively high catalytic activity, stability, and epoxidation selectivity in cyclooctene epoxidation among the CsPM@HP-UiO-66-X composites. Moreover, CsPM@HP-UiO-66-2CH3 was effective in the epoxidation of numerous alkenes, especially cyclic alkenes. The superior catalytic activity of CsPM@HP-UiO-66-2CH3 is mainly attributed to the modulation of the microenvironment surrounding CsPM active sites by introducing a hydrophobic methyl group. Meanwhile, the size-matched effect, the introduction of cesium cations, and the strong metal-support interactions (SMSIs) between CsPM and HP-UiO-66-2CH3 play a crucial role in the stability of CsPM@HP-UiO-66-2CH3.

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.

A promising sensing platform for explosive markers: Zeolite-like metal-organic framework based monolithic composite as a case study

Preconcentration for on-site detection or subsequent determination is a promising technique for selective sensing explosive markers at low concentrations. Here, we report divinylbenzene monolithic polymer in its blank form (neat-DVB) and as a composite incorporated with sodalite topology zeolite-like metal-organic frameworks (3-ZMOF@DVB), as a sensitive, selective, and cost-effective porous preconcentrator for aliphatic nitroalkanes in the vapor phase as explosive markers at infinite dilution. The developed materials were fabricated as 18 cm gas chromatography (GC) monolithic capillary columns to study their separation performance of nitroalkane mixture and the subsequent physicochemical study of adsorption using the inverse gas chromatography (IGC) technique. A strong preconcentration effect was indicated by a specific retention volume adsorption/desorption ratio equal to 3 for nitromethane on the neat-DVB monolith host-guest interaction, and a 14% higher ratio was observed using the 3-ZMOF@DVB monolithic composite despite the low percentage of 0.7 wt.% of sod-ZMOF added. Furthermore, Incorporating ZMOF resulted in a higher percentage of micropores, increasing the degree of freedom more than bringing stronger adsorption and entropic-driven interaction more than enthalpic. The specific free energy of adsorption (ΔGS) values increased for polar probes and nitroalkanes, denoting that adding ZMOFs earned the DVB monolithic matrix a more specific character. Afterward, Lewis acid-base properties were calculated, estimating the electron acceptor (KA) and electron donor (KB) constants. The neat-DVB was found to have a Lewis basic character with KB/KA = 7.71, and the 3-ZMOF@DVB had a less Lewis basic character with KB/KA = 3.82. An increased electron-accepting nature can be directly related to incorporating sod-ZMOF into the DVB monolithic matrix. This work considers the initial step in presenting a portable explosives detector or preconcentrating explosive markers trace prior to more sophisticated analysis. Additionally, the IGC technique allows for understanding the factors that led to the superior adsorption of nitroalkanes for the developed materials.

Covalent connections between metal-organic frameworks and polymers including covalent organic frameworks

Hybrid composite materials combining metal-organic frameworks (MOFs) and polymers have emerged as a versatile platform for a broad range of applications. The crystalline, porous nature of MOFs and the flexibility and processability of polymers are synergistically integrated in MOF-polymer composite materials. Covalent bonds, which form between two distinct materials, have been extensively studied as a means of creating strong molecular connections to facilitate the dispersion of "hard" MOF particles in "soft" polymers. Numerous organic transformations have been applied to post-synthetically connect MOFs with polymeric species, resulting in a variety of covalently connected MOF-polymer systems with unique properties that are dependent on the characteristics of the MOFs, polymers, and connection modes. In this review, we provide a comprehensive overview of the development and strategies involved in preparing covalently connected MOFs and polymers, including recently developed MOF-covalent organic framework composites. The covalent bonds, grafting strategies, types of MOFs, and polymer backbones are summarized and categorized, along with their respective applications. We highlight how this knowledge can serve as a basis for preparing macromolecular composites with advanced functionality.

Bioinspired microenvironment modulation of metal-organic framework-based catalysts for selective methane oxidation

Inspiration from natural enzymes enabling creationary catalyst design is appealing yet remains extremely challenging for selective methane (CH4) oxidation. This study presents the construction of a biomimetic catalyst platform for CH4 oxidation, which is constructed by incorporating Fe-porphyrin into a robust metal-organic framework, UiO-66, furnished with saturated monocarboxylic fatty acid bearing different long alkyl chains. The catalysts demonstrate the high efficiency in the CH4 to methanol (CH3OH) conversion at 50 °C. Moreover, the selectivity to CH3OH can be effectively regulated and promoted through a fine-tuned microenvironment by hydrophobic modification around the Fe-porphyrin. The long-chain fatty acids anchored on the Zr-oxo cluster of UiO-66 can not only tune the electronic state of the Fe sites to improve CH4 adsorption, but also restrict the amount of H2O2 around the Fe sites to reduce the overoxidation. This behavior resembles the microenvironment regulation in methane monooxygenase, resulting in high CH3OH selectivity.

Selective CO2 reduction to CH3OH over atomic dual-metal sites embedded in a metal-organic framework with high-energy radiation

The efficient use of renewable X/γ-rays or accelerated electrons for chemical transformation of CO2 and water to fuels holds promise for a carbon-neutral economy; however, such processes are challenging to implement and require the assistance of catalysts capable of sensitizing secondary electron scattering and providing active metal sites to bind intermediates. Here we show atomic Cu-Ni dual-metal sites embedded in a metal-organic framework enable efficient and selective CH3OH production (~98%) over multiple irradiated cycles. The usage of practical electron-beam irradiation (200 keV; 40 kGy min-1) with a cost-effective hydroxyl radical scavenger promotes CH3OH production rate to 0.27 mmol g-1 min-1. Moreover, time-resolved experiments with calculations reveal the direct generation of CO2•‒ radical anions via aqueous electrons attachment occurred on nanosecond timescale, and cascade hydrogenation steps. Our study highlights a radiolytic route to produce CH3OH with CO2 feedstock and introduces a desirable atomic structure to improve performance.