Catalysis by Metal Organic Frameworks: Perspective and Suggestions for Future Research

Chemical Vapor Deposition of Edge-on Oriented 2D Conductive Metal-Organic Framework Thin Films

We demonstrated the synthesis of a conductive two-dimensional metal-organic framework (MOF) thin film by single-step all-vapor-phase chemical vapor deposition (CVD). The synthesized large-area thin film of Cu₃(C₆O₆)₂ has an edge-on-orientation with high crystallinity. Cu₃(C₆O₆)₂ thin film-based microdevices were fabricated by e-beam lithography and had an electrical conductivity of 92.95 S/cm. Synthesis of conductive MOF thin films by the all-vapor-phase CVD will enable fundamental studies of physical properties and may help to accomplish practical applications of conductive MOFs.

Selective Photocatalytic Dehydrogenation of Formic Acid by an In Situ-Restructured Copper-Postmetalated Metal-Organic Framework under Visible Light

Formic acid is considered as one of the most promising liquid organic hydrogen carriers. Its catalytic dehydrogenation process generally suffers from low activity, low reaction selectivity, low stability of the catalysts, and/or the use of noble-metal-based catalysts. Herein we report a highly selective, efficient, and noble-metal-free photocatalyst for the dehydrogenation of formic acid. This catalyst, UiO-66(COOH)₂-Cu, is built by postmetalation of a carboxylic-functionalized Zr-MOF with copper. The visible-light-driven photocatalytic dehydrogenation process through the release of hydrogen and carbon dioxide has been monitored in real-time viaoperando Fourier transform infrared spectroscopy, which revealed almost 100% selectivity with high stability (over 3 days) and a conversion yield exceeding 60% (around 5 mmol·g_cat^–1·h^–1) under ambient conditions. These performance indicators make UiO-66(COOH)₂-Cu among the top photocatalysts for formic acid dehydrogenation. Interestingly, the as-prepared UiO-66(COOH)₂-Cu hetero-nanostructure was found to be moderately active under solar irradiation during an induction phase, whereupon it undergoes an in-situ restructuring process through intraframework cross-linking with the formation of the anhydride analogue structure UiO-66(COO)₂-Cu and nanoclustering of highly active and stable copper sites, as evidenced by the operando studies coupled with steady-state isotopic transient kinetic experiments, transmission electron microscopy and X-ray photoelectron spectroscopy analyses, and Density Functional Theory calculations. Beyond revealing outstanding catalytic performance for UiO-66(COO)₂-Cu, this work delivers an in-depth understanding of the photocatalytic reaction mechanism, which involves evolutive behavior of the postmetalated copper as well as the MOF framework over the reaction. These key findings pave the way toward the engineering of new and efficient catalysts for photocatalytic dehydrogenation of formic acid.

Molecular identification and quantification of defect sites in metal-organic frameworks with NMR probe molecules

The defects in metal-organic frameworks (MOFs) can dramatically alter their pore structure and chemical properties. However, it has been a great challenge to characterize the molecular structure of defects, especially when the defects are distributed irregularly in the lattice. In this work, we applied a characterization strategy based on solid-state nuclear magnetic resonance (NMR) to assess the chemistry of defects. This strategy takes advantage of the coordination-sensitive phosphorus probe molecules, e.g., trimethylphosphine (TMP) and trimethylphosphine oxide (TMPO), that can distinguish the subtle differences in the acidity of defects. A variety of local chemical environments have been identified in defective and ideal MOF lattices. The geometric dimension of defects can also be evaluated by using the homologs of probe molecules with different sizes. In addition, our method provides a reliable way to quantify the density of defect sites, which comes together with the molecular details of local pore environments. The comprehensive solid-state NMR strategy can be of great value for a better understanding of MOF structures and for guiding the design of MOFs with desired catalytic or adsorption properties.

Defects in porous materials can alter the pore structure and chemical properties. Here authors demonstrate an approach for studying defects in metal-organic frameworks using ³¹P NMR and probe molecules.

Remarkably stable metal-organic frameworks on an inert substrate: M-TCNQ on graphene (M = Ni, Fe, Mn)

Potential applications of 2D metal-organic frameworks (MOF) require the frameworks to be monophase and well-defined at the atomic scale, to be decoupled from the supporting substrate, and to remain stable at the application conditions. Here, we present three systems meeting this elusive set of requirements: M-TCNQ (M = Ni, Fe, Mn) on epitaxial graphene/Ir(111). We study the systems experimentally by scanning tunneling microscopy, low energy electron microscopy and X-ray photoelectron spectroscopy. When synthesized on graphene, the 2D M-TCNQ MOFs are monophase with M₁(TCNQ)₁ stoichiometry, no alternative structure was observed with slight variation of the preparation protocol. We further demonstrate a remarkable chemical and thermal stability of TCNQ-based 2D MOFs: all the studied systems survive exposure to ambient conditions, with Ni-TCNQ doing so without any significant changes to its atomic-scale structure or chemical state. Thermally, the most stable system is Fe-TCNQ which remains stable above 500 °C, while all the tested MOFs survive heating to 250 °C. Overall, the modular M-TCNQ/graphene system combines the atomic-scale definition required for fundamental studies with the robustness and stability needed for applications, thus we consider it an ideal model for research in single atom catalysis, spintronics or high-density storage media.

Copper-based metal-organic frameworks for biomedical applications

Metal-organic frameworks (MOFs) are a class of important porous, crystalline materials composed of metal ions (clusters) and organic ligands. Owing to the unique redox chemistry, photochemical and electrical property, and catalytic activity of Cu^2+/+, copper-based MOFs (Cu-MOFs) have been recently and extensively explored in various biomedical fields. In this review, we first make a brief introduction to the synthesis of Cu-MOFs and their composites, and highlight the recent synthetic strategies of two most studied representatives, three-dimensional HKUST-1 and two-dimensional Cu-TCPP. The recent advances of Cu-MOFs in the applications of cancer treatment, bacterial inhibition, biosensing, biocatalysis, and wound healing are summarized and discussed. Furthermore, we propose a prospect of the future development of Cu-MOFs in biomedical fields and beyond.

Fabricating defect-rich metal-organic frameworks via mixed linker-induced crystal transformation

Defect-rich hcp UiO-66-NO₂ was synthesized via mixed linker-induced crystal transformation from fcu UiO-66-NO₂/NH₂. The defect concentration and porosity of hcp UiO-66-NO₂ can be fine-tuned by varying the BDC-NH₂/BDC-NO₂ ratio, which in turn endowed hcp UiO-66-NO₂ with superior catalytic performance in the ring-opening reaction of epoxides with alcohols.

Photoresponsive Metal-Organic Frameworks as Adjustable Scaffolds in Reticular Chemistry

The easy and remote switching of light makes this stimulus an ideal candidate for a large number of applications, among which the preparation of photoresponsive materials stands out. The interest of several scientists in this area in order to achieve improved functionalities has increase parallel to the growth of the structural complexity of these materials. Thus, metal-organic frameworks (MOFs) turned out to be ideal scaffolds for light-responsive ligands. This review is focused on the integration of photoresponsive organic ligands inside MOF crystalline arrays to prepare enhanced functional materials. Besides the summary of the preparation, properties and applications of these materials, an overview of the future outlook of this research area is provided.

Conductive Co-triazole metal-organic framework exploited as an oxygen evolution electrocatalyst

A Co-triazole metal-organic framework (Co-trz) endowed with electrical conductivity was synthesized effortlessly via a microwave-based method. Providing a high density of catalytic centers with electrically conductive features, as suggested by DFT calculations, the framework exhibited a low overpotential for the oxygen evolution reaction (OER) with good kinetics. A mechanistic reaction pathway was proposed based on monitoring alterations in the oxidation state and local coordination environment of Co centers upon the occurrence of the OER. Due to its performance and its chemical and electrochemical robustness, the framework was highlighted as a promising MOF electrocatalyst for the OER.

Improvement of anti-corrosion performance of an epoxy coating using hybrid UiO-66-NH2/carbon nanotubes nanocomposite

In this study, a porous nanocontainer from UiO-66-NH₂/CNTs nanocomposite with an excellent barrier characteristics was constructed through amine-functionalized Zr-based metal organic framework. The characterization of the prepared nano-materials were performed using different analyses such as FTIR, XRD, SEM, EDS, TEM, and BET and the results proved the successful synthesize of UiO-66-NH₂/CNTs nanocomposite. The corrosion protection performance of the coated panels was investigated by electrochemical impedance spectroscopy (EIS), salt spray, and contact angle measurement. The EIS results revealed that unmodified and UiO-66-NH₂ containing coating in 3.5 wt.% NaCl electrolyte were failed after 45 days but the corrosion was negligible in UiO-66-NH₂/CNTs coating due to high pore resistance values even after 45 days. Salt spray and contact angle measurements confirmed that UiO-66-NH₂/CNTs containing coating acts as an efficient barrier against wet saline environment even at long exposure times. This is attributed to uniform dispersion in the epoxy matrix and formation of a uniform nanocomposite coating.

Catalytic Degradation of Polyethylene Terephthalate Using a Phase-Transitional Zirconium-Based Metal-Organic Framework

Polyethylene terephthalate (PET) is utilized as one of the most popular consumer plastics worldwide, but difficulties associated with recycling PET have generated a severe environmental crisis with most PET ending its lifecycle in landfills. We report that zirconium-based metal-organic framework (Zr-MOF) UiO-66 deconstructs waste PET into the building blocks terephthalic acid (TA) and mono-methyl terephthalate (MMT) within 24 hours at 260 °C (total yield of 98 % under 1 atm H₂ and 81 % under 1 atm Ar). Extensive structural characterization studies reveal that during the degradation process, UiO-66 undergoes an intriguing transformation into MIL-140A, which is another Zr-MOF that shows good catalytic activity toward PET degradation under similar reaction conditions. These results illustrate the diversity of applications for Zr-MOFs and establish MOFs as a new class of polymer degradation catalysts with the potential to address long-standing challenges associated with plastic waste.

Effect of Loading on the Water Stability of the Metal-Organic Framework DMOF-1 [Zn(bdc)(dabco)0.5]

In this work, the degradation of the metal-organic framework (MOF) DMOF-1 as a function of water adsorption was investigated. As the quantity of water vapor adsorbed by DMOF-1 increases, degradation of the MOF from hydrolysis accelerates. Degradation was attributed to clustering of water molecules in the void space of DMOF-1, as seen in NVT Monte Carlo simulations. Our molecular simulations strongly suggest that degradation of DMOF-1 by water is driven by water adsorption at defect sites in the MOF. Interestingly, it was observed that DMOF-1 can remain stable if it adsorbs less water than the 1 mmol/g necessary to initiate degradation within the framework. Even though the rate of hydrolysis increases at higher temperatures, the degradation threshold for DMOF-1 remains 1 mmol/g regardless of temperature. This suggests that at sufficiently elevated temperatures (above ∼50 °C) DMOF-1 is stable toward water vapor at all relative humidities.

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

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

Epoxidation vs. dehydrogenation of allylic alcohols: heterogenization of the VO(acac)2 catalyst in a metal-organic framework

Allylic alcohol epoxidation and dehydrogenation reactivity is distinguished when VO(acac)₂ is used in solution or anchored in a metal-organic framework (MOF). The chemical mechanism depends on the electronic profile of alkene substituents when the vanadyl complex is used in the homogenous phase. However, confinement effects imparted by MOF channels allow gaining control of the chemoselectivity toward the dehydrogenation product.

Mechanism of peroxymonosulfate activation and the utilization efficiency using hollow (Co, Mn)3O4 nanoreactor as an efficient catalyst for degradation of organic pollutants

Development of efficient catalysts for peroxymonosulfate (PMS) activation and further understanding its mechanism on organic pollutants degradation is of significant importance for advanced oxidation processes (AOPs). Herein, hollow (Co, Mn)₃O₄ catalysts were synthesized by calcination of Co, Mn containing metal-organic frameworks (MOFs) and further used to evaluate the effectiveness of organic pollutants (Bisphenol A (BPA), atrazine (ATZ), and diethyl phthalate (DEP)) degradation by PMS activation. The PMS utilization efficiency in (Co, Mn)₃O₄/PMS system (36.4%) was estimated to be 28.0% and 43.8% higher than that of Co₃O₄/PMS and Mn₅O₈/PMS system, respectively. Notably, the metal leaching in (Co, Mn)₃O₄/PMS system was significantly suppressed. The utilization efficiency also reveals an inverse proportionality relationship with BPA mineralization but decreases with increasing initial pH value. A synergy between oxides of Co and Mn was perceived to enhance PMS utilization efficiency and BPA degradation. The results indicate enhanced catalytic performance with (Co, Mn)₃O₄ compared to Co₃O₄ derived from Co-MOF and other reported catalysts, with 99% of BPA degradation within 4 min. The oxidation mechanism was then proposed based on the electron paramagnetic resonance (EPR) and XPS results. Our findings might have contributed to designing heterogeneous catalysts for efficient PMS utilization in AOPs.

Nanoporous {Y2}-Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization-Knoevenagel Condensation

Stable metal-organic frameworks containing periodically arranged nanosized pores and active Lewis acid-base active sites are considered as ideal candidates for efficient heterogeneous catalysis. Herein, the exquisite combination of [Y₂(CO₂)₇(H₂O)₂] cluster (abbreviated as {Y₂}) and multifunctional linker of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H₆TDP) led to a nanoporous framework of {[Y₂(TDP)(H₂O)₂]·5H₂O·4DMF}_n (NUC-53, NUC = North University of China), which is a rarely reported binuclear three-dimensional (3D) framework with hierarchical tetragonal-microporous (0.78 nm) and octagonal-nanoporous (1.75 nm) channels. The inner walls of these channels are aligned by {Y₂} clusters and plentifully coexisted Lewis acid-base sites of Y^III ions and N_pyridine atoms. Furthermore, NUC-53 has a quite large void volume of ∼65.2%, which is significantly higher than most documented 3D rare-earth-based MOFs. The performed catalytic experiments exhibited that activated NUC-53 showed a high catalytic activity on the cycloaddition reactions of CO₂ with styrene oxide under mild conditions with excellent turnover number (TON: 1980) and turnover frequency (TOF: 495 h^-1). Moreover, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile could be efficiently prompted by the heterogeneous catalyst of NUC-53. These findings not only pave the way for the construction of nanoporous MOF based on rare-earth clusters with a variety of catalytic activities but also provide some new insights into the catalytic mechanism.

Supramolecular Frameworks and a Luminescent Coordination Polymer from New β-Diketone/Tetrazole Ligands

Mixed multidentate linkers with donor groups of different types can be fruitfully exploited in the self-assembly of coordination polymers (CPs) and Metal-Organic Frameworks (MOFs). In this work we develop new ligands containing a β-diketone chelating functionality, to better control the stereochemistry at the metal center, and tetrazolyl multidentate bridging groups, a combination not yet explored for networking with metal ions. The new ligands, 1,3-bis(4-(1H-tetrazol-5-yl)phenyl)-1,3-propanedione (H3L1) and 1-phenyl-3-(4-(1H-tetrazol-5-yl)phenyl)-1,3-propanedione (H2L2), are synthesized from the corresponding nitrile precursors by [2+3] dipolar cycloaddition of azide under metal-free catalytic conditions. Crystal structure analysis evidences the involvement of tetrazolyl fragments in multiple hydrogen bonding giving 2D and 1D supramolecular frameworks. Reactivity of the new ligands with different metal salts indicates good coordinating ability, and we report the preparation and structural characterization of the tris–chelate complex [Fe(HL1)3]3− (1) and the homometallic 2D CP [ZnL2(DMSO)] (2). In compound 1 only the diketonate donor is used, whereas the partially deprotonated tetrazolyl groups are involved in hydrogen bonding, giving rise to a 2D supramolecular framework of (6,3)IIa topological type. In compound 2 the ligand is completely deprotonated and uses both the diketonate donor (chelating) and the tetrazolate fragment (bridging) to coordinate the Zn(II) ions. The resulting neutral 2D network of sql topology shows luminescence in the solid state, which is red shifted with respect to the free ligand. Interestingly, it can be easily exfoliated in water to give a luminescent colloidal solution.

Chiral Metal-Organic Frameworks

In the past two decades, metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) assembled from metal ions or clusters and organic linkers via metal-ligand coordination bonds have captivated significant scientific interest on account of their high crystallinity, exceptional porosity, and tunable pore size, high modularity, and diverse functionality. The opportunity to achieve functional porous materials by design with promising properties, unattainable for solid-state materials in general, distinguishes MOFs from other classes of materials, in particular, traditional porous materials such as activated carbon, silica, and zeolites, thereby leading to complementary properties. Scientists have conducted intense research in the production of chiral MOF (CMOF) materials for specific applications including but not limited to chiral recognition, separation, and catalysis since the discovery of the first functional CMOF (i.e., d- or l-POST-1). At present, CMOFs have become interdisciplinary between chirality chemistry, coordination chemistry, and material chemistry, which involve in many subjects including chemistry, physics, optics, medicine, pharmacology, biology, crystal engineering, environmental science, etc. In this review, we will systematically summarize the recent progress of CMOFs regarding design strategies, synthetic approaches, and cutting-edge applications. In particular, we will highlight the successful implementation of CMOFs in asymmetric catalysis, enantioselective separation, enantioselective recognition, and sensing. We envision that this review will provide readers a good understanding of CMOF chemistry and, more importantly, facilitate research endeavors for the rational design of multifunctional CMOFs and their industrial implementation.

Exploring mechanistic routes for light alkane oxidation with an iron-triazolate metal-organic framework

In this work, we computationally explore the formation and subsequent reactivity of various iron-oxo species in the iron-triazolate framework Fe₂(μ-OH)₂(bbta) (H₂bbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) for the catalytic activation of strong C-H bonds. With the direct conversion of methane to methanol as the probe reaction of interest, we use density functional theory (DFT) calculations to evaluate multiple mechanistic pathways in the presence of either N₂O or H₂O₂ oxidants. These calculations reveal that a wide range of transition metal-oxo sites - both terminal and bridging - are plausible in this family of metal-organic frameworks, making it a unique platform for comparing the electronic structure and reactivity of different proposed active site motifs. Based on the DFT calculations, we predict that Fe₂(μ-OH)₂(bbta) would exhibit a relatively low barrier for N₂O activation and energetically favorable formation of an [Fe(O)]²⁺ species that is capable of oxidizing C-H bonds. In contrast, the use of H₂O₂ as the oxidant is predicted to yield an assortment of bridging iron-oxo sites that are less reactive. We also find that abstracting oxo ligands can exhibit a complex mixture of both positive and negative spin density, which may have broader implications for relating the degree of radical character to catalytic activity. In general, we consider the coordinatively unsaturated iron sites to be promising for oxidation catalysis, and we provide several recommendations on how to further tune the catalytic properties of this family of metal-triazolate frameworks.

Artificial Monovalent Metal Ion-Selective Fluidic Devices Based on Crown Ether@Metal-Organic Frameworks with Subnanochannels

Precise regulation of ion transport through nanoscale pores will profoundly impact diverse fields from separation to energy conversion but is still challenging to achieve in artificial ion channels. Herein, inspired by the exquisite ion selectivity of biological Na⁺ channels, we have successfully fabricated hierarchically grown metal-organic frameworks (MOFs) on an asymmetrical substrate assisted by atomically thin nanoporous graphene. Efficient separation of monovalent metal ions is realized by encapsulating 18-crown-6 into MOF crystals. The resulting 18-crown-6@ZIF-67/ZIF-8 device, with subnanochannels and specific K⁺ binding sites, shows an ultrahigh Li⁺ conductivity of 1.46 × 10^-2 S cm^-1 and selectivities of 9.56 and 6.43 for Li⁺/K⁺ and Na⁺/K⁺, respectively. The Li⁺ conductivity is around 1-2 orders of magnitude higher than reported values for the other MOF materials. It is the first time that MOFs with subnanochannels realize selective transport of Na⁺ (ionic diameter of 1.9 Å) over K⁺ (2.6 Å) based on subangstrom differences in their ionic diameter. Our work opens new avenues to develop crown ether@MOF platforms toward efficient ion transistors, fluidic logic devices, and biosensors.

MOFSimplify, machine learning models with extracted stability data of three thousand metal-organic frameworks

We report a workflow and the output of a natural language processing (NLP)-based procedure to mine the extant metal–organic framework (MOF) literature describing structurally characterized MOFs and their solvent removal and thermal stabilities. We obtain over 2,000 solvent removal stability measures from text mining and 3,000 thermal decomposition temperatures from thermogravimetric analysis data. We assess the validity of our NLP methods and the accuracy of our extracted data by comparing to a hand-labeled subset. Machine learning (ML, i.e. artificial neural network) models trained on this data using graph- and pore-geometry-based representations enable prediction of stability on new MOFs with quantified uncertainty. Our web interface, MOFSimplify, provides users access to our curated data and enables them to harness that data for predictions on new MOFs. MOFSimplify also encourages community feedback on existing data and on ML model predictions for community-based active learning for improved MOF stability models.

Measurement(s)	thermal decomposition
Technology Type(s)	thermogravimetry

Polyaromatic Carboxylate Ligands Based Zn(II) Coordination Polymers for Ultrasound-Assisted One-Pot Tandem Deacetalization–Knoevenagel Reactions

Solvothermal reactions between the polyaromatic group containing carboxylic acid pro-ligands 5-{(pyren-1-ylmethyl)amino}isophthalic acid (H2L1) and 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H2L2) with Zn(NO3)2·6H2O led to the formation of the new 1D coordination polymer [Zn(L1)(NMF)]n (1) and four other coordination polymers, [Zn(L1)(DMF)]n (2), [Zn(L1)(4,4′-Bipy)]n (3), [Zn(L2)(DMF)(H2O)2]n·n(H2O) (4) and [Zn2(L2)2(DMF)(CH3OH)]n (5), which were previously reported by our group. Single crystal X-ray diffraction analyses revealed that the CP 1 has a one-dimensional (1D) double-chain-type structure similar to that of CP 2. For CP 3, the assembly of the Zn(II) ion with a deprotonated L12− ligand and 4,4′-bipyridine produces a 3D network. CP 4 and 5 exhibit 1D linear and 2D layered-type structures. The ultrasound-assisted tandem reactions promoted by CPs have not yet been well studied. Thus, in the present work, we have investigated the catalytic activities of the newly synthesized CP 1, as well as of the other CPs 2–5, towards the tandem deacetalization–Knoevenagel condensation reactions of various acetals under ultrasonic irradiation. They proved to be highly efficient, with special emphasis on catalyst 1, which completely converted the substrate (benzaldehyde dimethyl acetal) into the desired product (2-benzylidenemalononitrile) after 2 h. The stability of the catalysts, namely regarding the action of ultrasonic radiation, was demonstrated by their reuse, where only a slight loss of activity was observed after four cycles. Heterogeneity was also demonstrated, and no leaching was detected over the various cycles.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

State of the art on the ultrasonic-assisted removal of environmental pollutants using metal-organic frameworks

The environmental and health issues of drinking water and effluents released into nature are among the major area of contention in the past few decades. With the growth of ultrasound-based approaches in water and wastewater treatment, promising materials have also been considered to employ their advantages. Metal-organic frameworks (MOFs) are among the porous materials that have received great attention from researchers in recent years. Features such as high porosity, large specific surface area, electronic properties like semi-conductivity, and the capacity to coordinate with the organic matter have resulted in a substantial increase in scientific researches. This work deals with a comprehensive review of the application of MOFs for ultrasonic-assisted pollutant removal from wastewater. In this regard, after considering features and synthesis methods of MOFs, the mechanisms of several ultrasound-based approaches including sonocatalysis, sonophotocatalysis, and sono-adsorption are well assessed for removal of different organic compounds by MOFs. These methods are compared with some other water treatment processes with the application of MOFs in the absence of ultrasound. Also, the main concern about MOFs including environmental hazards and water stability is fully discussed and some techniques are proposed to reduce hazardous effects of MOFs and improve stability in humid/aqueous environments. Economic aspects for the preparation of MOFs are evaluated and cost estimates for ultrasonic-assisted AOP approaches were provided. Finally, the future outlooks and the new frontiers of ultrasonic-assisted methods with the help of MOFs in global environmental pollutant removal are presented.

Effect of Unsaturated Metal Site Modulation in Highly Stable Microporous Materials on CO2 Capture and Fixation

We have designed and synthesized two unprecedented microporous three-dimensional metal-organic frameworks, {[Cd₆(TPOM)₃(L)₆]·12DMF·3H₂O}_n (1) and {[Zn₂(TPOM)(L)₂]·2DMF·H₂O}_n (2), based on a flexible quadritopic ligand, tetrakis(4-pyridyloxymethylene)methane (TPOM), and a bent dicarboxylic acid, 4,4'-(dimethylsilanediyl)bis-benzoic acid (H₂L). The networks of 1 and 2 share a 4-c uninodal net NbO topology but exhibit different metal environments due to coordination preferences of Cd(II) and Zn(II). The Cd(II) center in 1 is six-coordinated, whereas the Zn(II) center in 2 is only four-coordinated, making the latter an unsaturated metal center. Such modulation of coordination atmosphere of metal centers in MOFs with the same topology is possible due to diverse binding of the carboxylate groups of L^2-. Both 1 and 2 have relatively high thermal stability and exhibit permanent porosity after the removal of guest solvent molecules based on variable temperature powder X-ray diffraction and gas adsorption analysis. These materials exhibit similar gas adsorption properties, especially highly selective CO₂ uptake/capture over other gases (N₂ and CH₄). However, because of the presence of an unsaturated Lewis acidic metal site, 2 acts as a very efficient heterogeneous catalyst toward the chemical conversion of CO₂ to cyclic carbonates under mild conditions, whereas 1 shows very less activity. This work provides experimental evidence for the postulate that an unsaturated metal site in MOFs enhances adsoprtion of CO₂ and promotes its conversion via the Lewis-acid catalysis.

Catalytic Performance and Electrophoretic Behavior of an Yttrium-Organic Framework Based on a Tricarboxylic Asymmetric Alkyne

A new Y-based metal-organic framework (MOF) GR-MOF-6 with a chemical formula of {[YL(DMF)₂]·(DMF)}_n {H₃L = 5-[(4-carboxyphenyl)ethynyl] isophthalic acid; DMF = N,N-dimethylformamide} has been prepared by a solvothermal route. Structural characterization reveals that this novel material is a three-dimensional MOF in which the coordination of the tritopic ligand to Y(III) metal ions leads to an intercrossing channel system extending over three dimensions. This material has proven to be a very efficient catalyst in the cyanosilylation of carbonyls, ranking second in catalytic activity among the reported rare earth metal-based MOFs described so far but with the lowest required catalyst loading. In addition, its electrophoretic behavior has been studied in depth, providing a zero-charge point between pH 4 and 5, a peak electrophoretic mobility of -1.553 μm cm V^-1 s^-1, and a ζ potential of -19.8 mV at pH 10.

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

A defining characteristic of nearly all catalytically functional MOFs is uniform, molecular-scale porosity. MOF pores, linkers and nodes that define them, help regulate reactant and product transport, catalyst siting, catalyst accessibility, catalyst stability, catalyst activity, co-catalyst proximity, composition of the chemical environment at and beyond the catalytic active site, chemical intermediate and transition-state conformations, thermodynamic affinity of molecular guests for MOF interior sites, framework charge and density of charge-compensating ions, pore hydrophobicity/hydrophilicity, pore and channel rigidity vs. flexibility, and other features and properties. Collectively and individually, these properties help define overall catalyst functional behaviour. This review focuses on how porous, catalyst-containing MOFs capitalize on molecular-scale confinement, containment, isolation, environment modulation, energy delivery, and mobility to accomplish desired chemical transformations with potentially superior selectivity or other efficacy, especially in comparison to catalysts in homogeneous solution environments.

A two-dimensional thin Co-MOF nanosheet as a nanozyme with high oxidase-like activity for GSH detection

A two-dimensional thin Co-MOF (ZIF-67) nanosheet with high oxidase-like activity was applied for sensitive visual GSH detection.

Zirconium oxo clusters as discrete molecular catalysts for the direct amide bond formation

A discrete dodecanuclear Zr oxo cluster catalyzed the direct formation of amide bonds without the need of water scavenging or dry reactions conditions showcasing the potential of these molecular clusters to become a new class of efficient catalysts.

Dye contaminated wastewater treatment through metal–organic framework (MOF) based materials

A complete discussion of MOFs and MOF composites such as MOF-based membranes, magnetic MOFs, and metal–organic gels (MOGs) used for dye removal along with their adsorption efficiency has been done.

Designing and Construction of Polyaromatic Group Containing Cd(II)-based Coordination Polymers for Solvent-free Strecker-type Cyanation of Acetals

In the present work, we have synthesized and characterized two novel Cd(II) coordination polymers, [Cd4(L1)4(DMF)6]n.3n(DMF) (1) and [Cd2(L2)2(DMF)3]n.2n(DMF) (2), and studied their catalytic application. They were synthesized via solvothermal reaction...