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

Upcycling of Hazardous Metals and PET Waste derived Metal-Organic Frameworks: A Review in Recent Progress and Prospects

An intense increase in non-biodegradable plastics and waste metals is an immediate threat to the world and needs to be addressed urgently. There are several strategies deployed to control, eliminate,...

Strategies for induced defects in metal-organic frameworks for enhancing adsorption and catalytic performance

Metal-organic frameworks (MOFs) have emerged among porous materials. The designable structure and specific functionality make them stand out for diverse applications. In conceptual MOF, the metal ions/clusters and organic ligands...

Applications of novel composite UiO-66-NH2/Melamine with phosphorous acid tags as a porous and efficient catalyst for the preparation of novel spiro-oxindoles

A new approach for the incorporation of phosphorous acid tags into a metal organic framework based on UiO-66-NH2/Melamine was introduced. This new catalyst was applied to the preparation of novel spiro-oxindoles under mild and green conditions.

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

Crystallographic characterization of a heterogeneous ethylene polymerization catalyst elucidates a chromium–carbon bond after alkyl aluminum activation and provides mechanistic insights.

Generating Catalytic Sites in UiO-66 through Defect Engineering

UiO-66 is regarded as an epitome of metal-organic frameworks (MOFs) because of its stability. Defect engineering has been used as a toolbox to alter the performance of MOFs. UiO-66 is among the most widely explored MOFs because of its capability to bear a high number of defects without undergoing structural collapse. Several representative works in the field of MOF-based defect engineering are available based on UiO-66. In this review, more emphasis is given toward the construction of catalytic sites by engineering defects in UiO-66 as a representative including all the detailed synthesis procedures for inducing defects, and the characterization techniques used to analyze these defects in UiO-66 are discussed. Furthermore, a comprehensive review for the defects themselves and the support using defects in catalysis is provided to accentuate the importance of defect engineering.

Templated synthesis of zirconium(IV)-based metal-organic layers (MOLs) with accessible chelating sites

Metal-organic layers (MOLs) are of great interest in heterogeneous catalysis, particularly materials that can accommodate extraneous metal centres. Here, we demonstrate a two-step preorganisation/delamination synthetic strategy using CuI as a template to prepare Zr-based MOLs with accessible 'syn' bis-pyrazolyl chelating sites (named UAM-2·ns) that are poised for quantitative post-synthetic metalation with late transition metals.

Ultrathin nanosheet-assembled nickel-based metal-organic framework microflowers for supercapacitor applications

Herein, we propose a solvent-assisted approach for preparing Ni-MOF microflowers with high specific capacitance and excellent rate capability as an electrode material for supercapacitors. The high electrochemical performance of this Ni-MOF is attributed to the fast ion transport and low electrical resistance resulting from its hierarchical flower-like structure, and the capacitance contribution from nickel hydroxide species.

Advances in Oxidative Desulfurization of Fuel Oils over MOFs-Based Heterogeneous Catalysts

Catalytic oxidative desulfurization (ODS) of fuel oils is considered one of the most promising non-hydrodesulfurization technologies due to the advantages of mild reaction conditions, low cost and easy removal of aromatic sulfur compounds. Based on this reason, the preparation of highly efficient ODS catalysts has been a hot research topic in this field. Recently, metal-organic frameworks (MOFs) have attracted extensive attention due to the advantages involving abundant metal centers, high surface area, rich porosity and varied pore structures. For this, the synthesis and catalytic performance of the ODS catalysts based on MOFs materials have been widely studied. Until now, many research achievements have been obtained along this direction. In this article, we will review the advances in oxidative desulfurization of fuel oils over MOFs-based heterogeneous catalysts. The catalytic ODS performance over various types of catalysts is compared and discussed. The perspectives for future work are proposed in this field.

Aptamer grafted nanoparticle as targeted therapeutic tool for the treatment of breast cancer

Breast carcinomas repeat their number and grow exponentially making it extremely frequent malignancy among women. Approximately, 70-80% of early diagnosed or non-metastatic conditions are treatable while the metastatic cases are considered ineffective to treat with current ample amount of therapy. Target based anti-cancer treatment has been in the limelight for decades and is perceived significant consideration of scientists. Aptamers are the 'coming of age' therapeutic approach, selected using an appropriate tool from the library of sequences. Aptamers are non-immunogenic, stable, and high-affinity ligand which are poised to reach the clinical benchmark. With the heed in nanoparticle application, the delivery of aptamer to the specific site could be enhanced which also protects them from nuclease degradation. Moreover, nanoparticles due to robust structure, high drug entrapment, and modifiable release of cargo could serve as a successful candidate in the treatment of breast carcinoma. This review would showcase the method and modified method of selection of aptamers, aptamers that were able to make its way towards clinical trial and their targetability and selectivity towards breast cancers. The appropriate usage of aptamer-based biosensor in breast cancer diagnosis have also been discussed.

Resistive Memory Devices Based on Reticular Materials for Electrical Information Storage

Recently, reticular materials, such as metal-organic frameworks and covalent organic frameworks, have been proposed as an active insulating layer in resistive switching memory systems through their chemically tunable porous structure. A resistive random access memory (RRAM) cell, a digital memristor, is one of the most outstanding emergent memory devices that achieves high-density electrical information storage with variable electrical resistance states between two terminals. The overall design of the RRAM devices comprises an insulating layer sandwiched between two metal electrodes (metal/insulator/metal). RRAM devices with fast switching speeds and enhanced storage density have the potential to be manufactured with excellent scalability owing to their relatively simple device architecture. In this review, recent progress on the development of reticular material-based RRAM devices and the study of their operational mechanisms are reviewed, and new challenges and future perspectives related to reticular material-based RRAM are discussed.

The Molecular Path Approaching the Active Site in Catalytic Metal-Organic Frameworks

How molecules approach, bind at, and release from catalytic sites is key to heterogeneous catalysis, including for emerging metal-organic framework (MOF)-based catalysts. We use in situ synchrotron X-ray scattering analysis to evaluate the dominant binding sites for reagent and product molecules in the vicinity of catalytic Ni-oxo clusters in NU-1000 with different surface functionalization under conditions approaching those used in catalysis. The locations of the reagent and product molecules within the pores can be linked to the activity for ethylene hydrogenation. For the most active catalyst, ethylene reagent molecules bind close to the catalytic clusters, but only at temperatures approaching experimentally observed onset of catalysis. The ethane product molecules favor a different binding location suggesting that the product is readily released from the active site. An unusual guest-dependence of the framework negative thermal expansion is documented. We hypothesize that reagent and product binding sites reflect the pathway through the MOF to the active site and can be used to identify key factors that impact the catalytic activity.

Photoinduced Delamination of Metal-Organic Framework Thin Films by Spatioselective Generation of Reactive Oxygen Species

Metal-organic frameworks (MOFs) built from different building units offer functionalities going far beyond gas storage and separation. In connection with advanced applications, e.g., in optoelectronics, hierarchical MOF-on-MOF structures fabricated using sophisticated methodologies have recently become particularly attractive. Here, we demonstrate that the structural complexity of MOF-based architectures can be further increased by employing highly spatioselective photochemistry. Using a layer-by-layer, quasi-epitaxial synthesis method, we realized a photoactive MOF-on-MOF hetero-bilayer consisting of a porphyrinic bottom layer and a tetraphenylethylene (TPE)-based top layer. Illumination of the monolithic thin film with visible light in the presence of oxygen gas results in the generation of reactive oxygen species (¹O₂) in the porphyrinic bottom layer, which lead to a photocleavage of the TPE units at the internal interface. We demonstrate that this spatioselective photochemistry can be utilized to delaminate the top layers, yielding two-dimensional (2D) MOF sheets with well-defined thickness. Experiments using atomic force microscopy (AFM) demonstrate that these platelets can be transferred onto other substrates, thus opening up the possibility of fabricating planar MOF structures using photolithography.

Exploring and expanding the Fe-terephthalate metal-organic framework phase space by coordination and oxidation modulation

The synthesis of phase pure metal-organic frameworks (MOFs) - network solids of metal clusters connected by organic linkers - is often complicated by the possibility of forming multiple diverse phases from one metal-ligand combination. For example, there are at least six Fe-terephthalate MOFs reported to date, with many examples in the literature of erroneous assignment of phase based on diffraction data alone. Herein, we show that modulated self-assembly can be used to influence the kinetics of self-assembly of Fe-terephthalate MOFs. We comprehensively assess the effect of addition of both coordinating modulators and pH modulators on the outcome of syntheses, as well as probing the influence of the oxidation state of the Fe precursor (oxidation modulation) and the role of the counteranion on the phase(s) formed. In doing so, we shed light on the thermodynamic landscape of this phase system, uncover mechanistics of modulation, provide robust routes to phase pure materials, often as single crystals, and introduce two new Fe-terephthalate MOFs to an already complex system. The results highlight the potential of modulated self-assembly to bring precision control and new structural diversity to systems that have already received significant study.

A facile fabrication of a hierarchical ZIF-8/MWCNT nanocomposite for the sensitive determination of rutin

In this paper, a novel type of zeolitic imidazolate framework-8 (ZIF-8) polyhedron/multi-walled carbon nanotube (MWCNT) modified electrode was successfully prepared for effective on-site detection of rutin. The morphology and microstructure of the ZIF-8/MWCNT nanocomposite were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical performance of the ZIF-8/MWCNT based electrode for the determination of rutin was studied by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPV). The as-prepared sensor illustrates better electrocatalytic activity and lower background current than the MWCNT modified electrode for the oxidation of rutin. Besides, the ZIF-8/MWCNTs sensor offers a remarkable linear response for rutin concentrations from 0.1 to 15 μM. The detection limit (LOD) was calculated to be 0.26 nM (S/N = 3). Also, the ZIF-8/MWCNT electrode showed high anti-interference ability towards common interfering species. More importantly, the fabricated electrode was quickly evaluated for determination of rutin in medicine tablets with satisfactory recoveries and the obtained results successfully achieved good consistency with the data from high performance liquid chromatography (HPLC). Finally, the method shows an enhanced electrocatalytic property and sensitivity for the analysis of rutin, which may provide an economical and promising electrochemical sensor for practical on-site detection of rutin.

Coordination-induced band gap reduction in a metal-organic framework

Herein, we report on the synthesis of a microporous, three‐dimensional phosphonate metal–organic framework (MOF) with the composition Cu₃(H₅‐MTPPA)₂ ⋅ 2 NMP (H₈‐MTPPA=methane tetra‐p‐phenylphosphonic acid and NMP=N‐methyl‐2‐pyrrolidone). This MOF, termed TUB1, has a unique one‐dimensional inorganic building unit composed of square planar and distorted trigonal bipyramidal copper atoms. It possesses a (calculated) BET surface area of 766.2 m²/g after removal of the solvents from the voids. The Tauc plot for TUB1 yields indirect and direct band gaps of 2.4 eV and 2.7 eV, respectively. DFT calculations reveal the existence of two spin‐dependent gaps of 2.60 eV and 0.48 eV for the alpha and beta spins, respectively, with the lowest unoccupied crystal orbital for both gaps predominantly residing on the square planar copper atoms. The projected density of states suggests that the presence of the square planar copper atoms reduces the overall band gap of TUB1, as the beta‐gap for the trigonal bipyramidal copper atoms is 3.72 eV.

Elemental Depth Profiling of Intact Metal-Organic Framework Single Crystals by Scanning Nuclear Microprobe

The growing field of MOF–catalyst composites often relies on postsynthetic modifications for the installation of active sites. In the resulting MOFs, the spatial distribution of the inserted catalysts has far-reaching ramifications for the performance of the system and thus needs to be precisely determined. Herein, we report the application of a scanning nuclear microprobe for accurate and nondestructive depth profiling of individual UiO-66 and UiO-67 (UiO = Universitetet i Oslo) single crystals. Initial optimization work using native UiO-66 crystals yielded a microbeam method which avoided beam damage, while subsequent analysis of Zr/Hf mixed-metal UiO-66 crystals demonstrated the potential of the method to obtain high-resolution depth profiles. The microbeam method was further used to analyze the depth distribution of postsynthetically introduced organic moieties, revealing either core–shell or uniform incorporation can be obtained depending on the size of the introduced molecule, as well as the number of carboxylate binding groups. Finally, the spatial distribution of platinum centers that were postsynthetically installed in the bpy binding pockets of UiO-67-bpy (bpy = 5,5′-dicarboxyy-2,2′-bipyridine) was analyzed by microbeam and contextualized. We expect that the method presented herein will be applicable for characterizing a wide variety of MOFs subjected to postsynthetic modifications and provide information crucial for their optimization as functional materials.

Monitoring a MOF Catalyzed Reaction Directly in Blood Plasma

Herein, we establish a method to quantitatively monitor a metal-organic framework (MOF)-catalyzed, biomedically relevant reaction directly in blood plasma, specifically, the generation of nitric oxide (NO) from the endogenous substrate S-nitrosoglutathione (GSNO) catalyzed by H3[(Cu4Cl)3-(BTTri)8] (CuBTTri). The reaction monitoring method uses UV-vis and 1H NMR spectroscopies along with a nitric oxide analyzer (NOA) to yield the reaction stoichiometry and catalytic rate for GSNO to NO conversion catalyzed by CuBTTri in blood plasma. The results show 100% loss of GSNO within 16 h and production of 1 equiv. of glutathione disulfide (GSSG) per 2 equiv. of GSNO. Only 78 ± 10% recovery of NO(g) was observed, indicating that blood plasma can scavenge the generated NO before it can escape the reaction vessel. Significantly, to best apply and understand reaction systems with biomedical importance, such as NO release catalyzed by CuBTTri, methods to study the reaction directly in biological solvents must be developed.

Thermochemical Investigation of Oxyanion Coordination in a Zirconium-Based Metal-Organic Framework

Porous materials possess high internal surface areas and void fractions that make them valuable in several applications, including gas storage, heterogeneous catalysis, and water purification. Despite the plentiful effort allocated to porous materials research annually, few methods exist to directly monitor and characterize chemical events occurring within a pore's confines. The crystalline nature of zeolites, covalent organic frameworks (COFs), and metal-organic frameworks (MOFs) permit structural characterization by X-ray diffraction; yet, quantifying the thermodynamics of chemical processes and transformations remains tedious and error ridden. Herein, we employ isothermal titration calorimetry (ITC) to determine the full thermodynamic profile of oxyanion adsorption in a zirconium-based MOF, NU-1000. To further validate this method, which we recently introduced to the field, we replicated ITC experiments as bulk adsorption measurements to demonstrate the correlation between the extracted stoichiometric parameter from ITC thermograms and the MOF uptake capacity. Moreover, based on the calculated association constants, we accurately predicted which analytes might be able to displace others. For example, dihydrogen phosphate can displace selenate and sulfate because of its higher association constant (ΔGphosphate = -5.41 kcal/mol; ΔGselenate = -4.98 kcal/mol; ΔGsulfate = -4.77 kcal/mol). We monitored the exchange processes by titrating oxyanion-functionalized MOF samples with a more strongly binding analyte.

Heterogenizing a Homogeneous Nickel Catalyst Using Nanoconfined Strategy for Selective Synthesis of Mono- and 1,2-Disubstituted Benzimidazoles

A homogeneous Ni-phenanthroline catalyst was successfully immobilized into the cavities of a metal-organic framework, ZIF-8. The as-synthesized heterogeneous catalyst, Ni-Phen@ZIF, represents the first MOF based catalyst that enables dehydrogenative coupling of alcohols with aromatic diamines for selective synthesis of both mono- and 1,2-disubstituted benzimidazoles. The catalyst survived under harsh basic conditions, characterized by SEM, TEM, BET, PXRD, and EDX elemental mappings. The presence of the nanoconfined Ni-phenanthroline complex and the formation of extra Lewis acid sites during catalysis in the Ni-Phen@ZIF structure, confirmed by TPD analysis and kinetic experiments, might be responsible for higher activity and selectivity.

Using Machine Learning and Data Mining to Leverage Community Knowledge for the Engineering of Stable Metal-Organic Frameworks

Although the tailored metal active sites and porous architectures of MOFs hold great promise for engineering challenges ranging from gas separations to catalysis, a lack of understanding of how to improve their stability limits their use in practice. To overcome this limitation, we extract thousands of published reports of the key aspects of MOF stability necessary for their practical application: the ability to withstand high temperatures without degrading and the capacity to be activated by removal of solvent molecules. From nearly 4000 manuscripts, we use natural language processing and image analysis to obtain over 2000 solvent-removal stability measures and 3000 thermal degradation temperatures. We analyze the relationships between stability properties and the chemical and geometric structures in this set to identify limits of prior heuristics derived from smaller sets of MOFs. By training predictive machine learning (ML, i.e., Gaussian process and artificial neural network) models to encode the structure-property relationships with graph- and pore-structure-based representations, we are able to make predictions of stability orders of magnitude faster than conventional physics-based modeling or experiment. Interpretation of important features in ML models provides insights that we use to identify strategies to engineer increased stability into typically unstable 3d-transition-metal-containing MOFs that are frequently targeted for catalytic applications. We expect our approach to accelerate the time to discovery of stable, practical MOF materials for a wide range of applications.

Greener organic synthetic methods: Sonochemistry and heterogeneous catalysis promoted multicomponent reactions

Ultrasound is an essential technique to improve organic synthesis from the point of view of green chemistry, as it can promote better yields and selectivities, in addition to shorter reaction times when compared to the conventional methods. Heterogeneous catalysis is another pillar of sustainable chemistry being the recycling and reuse of the catalysts one of its great advantage. In the other hand, multicomponent reactions provide the synthesis of structurally diverse compounds, in a one-pot fashion, without isolation and purification of intermediates. Thus, the combination of these protocols has proved to be a powerful tool to obtain biologically active organic compounds with lower costs, time and energy consumption. Herein, we provide a comprehensive overview of advances on methods of organic synthesis that have been reported over the past ten years with focus on ultrasound-assisted multicomponent reactions under heterogeneous catalysis. In particular, we present pharmacologically important N- and O-heterocyclic compounds, considering their synthetic methods using green solvents, and catalyst recycling.

"Shake 'n Bake" Route to Functionalized Zr-UiO-66 Metal-Organic Frameworks

We report a novel synthetic procedure for the high-yield synthesis of metal-organic frameworks (MOFs) with fcu topology with a UiO-66-like structure starting from a range of commercial ZrIV precursors and various substituted dicarboxylic linkers. The syntheses are carried out by grinding in a ball mill the starting reagents, namely, Zr salts and the dicarboxylic linkers, in the presence of a small amount of acetic acid and water (1 mL total volume for 1 mmol of each reagent), followed by incubation at either room temperature or 120 °C. Such a simple "shake 'n bake" procedure, inspired by the solid-state reaction of inorganic materials, such as oxides, avoids the use of large amounts of solvents generally used for the syntheses of Zr-MOF. Acidity of the linkers and the amount of water are found to be crucial factors in affording materials of quality comparable to that of products obtained under solvo- or hydrothermal conditions.

Fine-Tuning Window Apertures in ZIF-8/67 Frameworks by Metal Ions and Temperature for High-Efficiency Molecular Sieving of Xylenes

Separation of structurally similar components from their mixtures is one of the most promising applications of metal-organic frameworks (MOFs). A high efficiency of such molecular sieving requires fine tuning of the MOF structure. In this work, we investigate subtle metal- and temperature-induced changes in window dimensions of zeolitic imidazolate frameworks (ZIF-8(Zn) and ZIF-67(Co)) and apply such structural tuning for efficient separation of xylene isomers (p-, m-, and o-xylenes). The use of Co instead of Zn favorably modifies window geometry: it accelerates the diffusion of all components by a factor of 2-3 while maintaining closely the same separation efficiency as that of ZIF-8(Zn). Outstanding selectivity above 18:1 and faster isolation of demanded p-xylene from the ternary mixture using ZIF-67(Co) have been demonstrated at room temperature, opening new horizons for its energy-efficient xylene separation. More generally, our findings suggest the prospective ways to tune various MOFs for target liquid-state separations.

ZnO-Co3O4/N-C Cage Derived from the Hollow Zn/Co ZIF for Enhanced Degradation of Bisphenol A with Persulfate

The zeolitic imidazolate framework (ZIF)-67 microcrystal was employed as a precursor to synthesize the hollow ZIF-8/ZIF-67 composite via the epitaxial growth of ZIF-8 on ZIF-67, in situ self-sacrifice, and excavation of ZIF-67. The hollow ZIF-8/ZIF-67 composite was successfully transformed to the ZnO-Co₃O₄/N-C cage by thermal treatment, which was further used as the catalyst for the oxidative degradation of bisphenol A (BPA) in the presence of potassium persulfate (PS). In comparison with the Co₃O₄/N-C and Co₃O₄ obtained from pure ZIF-67 and cobalt nitrate, the ZnO-Co₃O₄/N-C cage demonstrated a more than four fold-higher activity and robust reusability. Based on structural analysis, the enhanced catalytic performance could be ascribed to the small, highly dispersed cobalt oxide particles, the hollow structure that facilitated the transportation of the molecules, and the synergistic effect between cobalt oxide and nitrogen-doped carbon in the composite. Besides, the effect of dosage of PS, BPA, and the co-existing components such as chloride ion, methanol, and t-butyl alcohol was carefully investigated to propose the possible mechanism. This study would give new insights into the design of functional composite materials from metal organic frameworks and the development of their application in environmental pollution disposal.

Crystalline Hydrogen-Bonding Networks and Mixed-Metal Framework Materials Enabled by an Electronically Differentiated Heteroditopic Isocyanide/Carboxylate Linker Group

Mixed-metal solid-state framework materials are emerging candidates for advanced applications in catalysis and chemical separations. Traditionally, the syntheses of mixed-metal framework systems rely on postsynthetic ion exchange, metalloligands, or metal-deposition techniques for the incorporation of a second metal within a framework material. However, these methods are often incompatible with the incorporation of low-valent metal centers, which preferentially bind to electronically "soft" ligands according to the tenets of hard/soft acid/base theory. Here we present the electronically differentiated isocyanide/carboxylate heteroditopic linker ligand 1,4-CNAr^Mes2C₆H₄CO₂H (TIB^Mes2H; TIB = terphenyl isocyanide benzoate; Ar^Mes2 = 2,6-(2,4,6-Me₃C₆H₂)₂C₆H₂), which is capable of selective binding of low-valent metals via the isocyano group and complexation of hard Lewis acidic metals through the carboxylate unit. This heteroditopic ligand also possesses an encumbering m-terphenyl backbone at the isocyanide function to foster coordinative unsaturation. The treatment of TIB^Mes2H with [Cu(NCMe)₄]PF₆ in a 3:1 ratio results in preferential binding of the isocyanide group to the Cu(I) center as assayed by multinuclear NMR and IR spectroscopies. IR spectroscopy also provides strong evidence for the formation of a copper(I) tris(isocyanide) complex, wherein the carboxylic acid group remains unperturbed. The addition of TIB^Mes2 to [Cu(NCMe)₄]PF₆ in a 4:1 ratio results in crystallization of the hydrogen-bonding network, [Cu(TIB^Mes2H)₄]PF₆, in which the formation of R₂²(8) hydrogen bonds results in a 7-fold interpenetrated diamondoid lattice structure. The preassembly of a copper(I) tris(isocyanide) complex using TIB^Mes2H, followed by deprotonation and the introduction of ZnCl₂, generates a novel and unusual zwitterionic solid-state phase (denoted as Cu/Zn-^ISOCN-5; ^ISOCN = isocyanide coordination network) consisting of a coordinatively unsaturated [Cu(CNR)₃]⁺ cationic secondary building unit (SBU) and an anionic, paddlewheel-type Zn(II)-based SBU of the formulation [Cl₂Zn₂(O₂CR)₃]^-. Inductively coupled plasma mass spectrometry analysis provided firm evidence for a 2:1 Zn-to-Cu ratio in the network, thereby indicating that the isocyanide and carboxylate groups selectively bind soft and hard Lewis acidic metal centers, respectively. The extended structure of Cu/Zn-^ISOCN-5 is a densely packed, noninterpenetrated AB-stacked layer network with modest surface area. However, it is thermally robust, and its formation and compositional integrity validate the use of an electronically differentiated linker for the formation of mixed-metal frameworks incorporating low-valent metal centers.

Non-noble MNP@MOF materials: synthesis and applications in heterogeneous catalysis

Transition metals have a long history in heterogeneous catalysis. Noble or precious transition metals have been widely used in this field. The advantage of noble and precious metals is obvious in 'heterogeneous catalysis'. However, the choice of Earth abundant metals is a sustainable alternative due to their abundance and low cost. Preparing these metals in the nanoscale dimension increases their surface area which also increases the catalytic reactions of these materials. Nevertheless, metals are unstable in the nanoparticle form and tend to form aggregates which restrict their applications. Loading metal nanoparticles (MNPs) into highly porous materials is among the many alternatives for combating the unstable nature of the active species. Among porous materials, highly crystalline metal-organic frameworks (MOFs), which are an assembly of metal ions/clusters with organic ligands, are the best candidate. MOFs, on their own, possess catalytic activity derived from the linkers and metal ions or clusters. The catalytic properties of both non-noble metal nanoparticles (MNPs) and MOFs can be improved by loading non-noble MNPs in MOFs yielding MNP@MOF composites with a variety of potential applications, given the synergy and based on the nature of the MNP and MOF. Here, we discussed the synthesis of MNP@MOF materials and the applications of non-noble MNP@MOF materials in heterogeneous catalysis.

Remodelling a shp: Transmetalation in a Rare-Earth Cluster-Based Metal-Organic Framework

Postsynthetic modification of metal-organic frameworks (MOFs) is an important strategy for accessing MOF analogues that cannot be easily synthesized de novo. In this work, the rare-earth (RE) cluster-based MOF Y-CU-10 with shp topology was modified through transmetalation using a series of RE ions, including La(III), Nd(III), Eu(III), Tb(III), Er(III), Tm(III), and Yb(III). In all cases, metal exchange higher than 70% was observed, with reproducible results. All transmetalated materials were fully characterized and compared to the parent MOF Y-CU-10 with regard to crystallinity, surface area, and morphology. Additionally, single-crystal X-ray diffraction measurements were performed to provide further evidence of transmetalation occurring in the nonanuclear cluster nodes of the MOF.

AIE-MOF materials for biological applications

Metal-Organic Frameworks (MOFs), coming under the realm of coordination chemistry, are unparalleled and the most studied among the group of porous materials. Structurally, these are well-defined three-dimensional crystalline products that can be tuned for various potential applications with a range of physico-chemical properties. More recently, aggregation-induced emission (AIE) and AIE of MOF material has attracted tremendous attention due to promising applications in biology. However, a chapter summarizing the work in AIE-MOFs materials has never been reported till date. A comprehensive review on the AIE and MOFs separately is beyond the reach of this chapter. Hence, we have summarized overview of recent developments in the syntheses and biological applications such as cell imaging, heparin detection, and drug delivery. In the end, conclusion, prospects and challenges in the arena of AIE-MOF materials are also highlighted.

A Two Step Postsynthetic Modification Strategy: Appending Short Chain Polyamines to Zn-NH2-BDC MOF for Enhanced CO2 Adsorption

Functionalizing metal-organic frameworks (MOFs) with amines is a commonly used strategy to enhance their performance in CO₂ capture applications. As such, in this work, a two-step strategy to covalently functionalize NH₂-containing MOFs with short chain polyamines was developed. In the first step, the parent MOF, Zn₄O(NH₂-BDC)₃, was exposed to bromoacetyl bromide (BrAcBr), which readily reacts with pendant -NH₂ groups on the 2-amino-1,4-benzenedicarboxylate (NH₂-BDC^2-) ligand. ¹H NMR of the digested MOF sample revealed that as much as 90% of the MOF ligands could be functionalized in the first step. Next, the MOF samples 60% of the ligands functionalized with acetyl bromide, Zn₄O(NH₂-BDC)_1.2(BrAcNH-BDC)_1.8, was exposed to several short chain amines including ethylenediamine (ED), diethylenetriamine (DETA), and tris(2-aminoethyl)amine (TAEA). Subsequent digested ¹H NMR analysis indicated that a total of 30%, 28%, and 19% of the MOF ligands were successfully grafted to ED, DETA, and TAEA, respectively. Next, the CO₂ adsorption properties of the amine grafted MOFs were studied. The best performing material, TAEA-appended-Zn₄O(NH₂-BDC)_1.2(BrAcNH-BDC)_1.8, exhibits a zero-coverage isosteric heat of CO₂ adsorption of -62.5 kJ/mol, a value that is considerably higher than the one observed for the parent framework, -21 kJ/mol. Although the boosted CO₂ affinity only leads to a slight increase in the CO₂ adsorption capacity in the low-pressure regime (0.15 bar), which is of interest in postcombustion carbon dioxide capture, the CO₂/N₂ (15/85) selectivity at 313 K is 143, a value that is ∼35 times higher than the one observed for Zn₄O(NH₂-BDC)₃, 4.1. Such enhancements are attributed to accessible primary amines, which were grafted to the MOF ligand. This hypothesis was further supported via in situ DRIFTS measurements of TAEA-Ac-Zn₄O(NH₂-BDC)_1.2(BrAcNH-BDC)_1.8 after exposure to CO₂, which revealed the chemisorption of CO₂ via the formation of hydrogen bonded carbamates/carbamic acid and CO₂^δ- species; the latter are adducts formed between CO₂ and [amineH]⁺Br^- salts that are produced during the amine grafting step.

Infrared crystallography for framework and linker orientation in metal-organic framework films

Pore alignment and linker orientation influence diffusion and guest molecule interactions in metal-organic frameworks (MOFs) and play a pivotal role for successful utilization of MOFs. The crystallographic orientation and the degree of orientation of MOF films are generally determined using X-ray diffraction. However, diffraction methods reach their limit when it comes to very thin films, identification of chemical connectivity or the orientation of organic functional groups in MOFs. Cu-based 2D MOF and 3D MOF films prepared via layer-by-layer method and from aligned Cu(OH)2 substrates were studied with polarization-dependent Fourier-transform infrared (FTIR) spectroscopy in transmission and attenuated total reflection configuration. Thereby, the degrees for in-plane and out-of-plane orientation, the aromatic linker orientation and the initial alignment during layer-by-layer MOF growth, which is impossible to investigate by laboratory XRD equipment, was determined. Experimental IR spectra correlate with theoretical explanations, paving the way to expand the principle of IR crystallography to oriented, organic-inorganic hybrid films beyond MOFs.

Towards improving the capacity of UiO-66 for antibiotic elimination from contaminated water

Antibiotics are found in natural waters, raising concern about their human and environmental toxicity and the wide occurrence of antibiotic resistant bacteria. The antibiotic resistance crisis is attributed to the overuse and misuse of these medications. Particularly, sulfamethazine (SMT), an antibiotic commonly used in pigs and cattle for the treatment of bacterial diseases, has been detected in the natural environment (soil and water). Among all the technologies developed to combat the deteriorating water quality and control antimicrobial resistance, heterogeneous photocatalysis should be highlighted for the degradation of refractory organic compounds. Here, we described the SMT adsorption and photodegradation capacity of a highly porous and robust zirconium-based MOF UiO-66 under realistic conditions, and its potential recyclability. Further, its SMT removal capacity was improved by functionalizing the MOF porosity (28.5% of SMT adsorption in 24 h for nanoUiO-66-NH2), and nanosizing the MOF (100% SMT photodegradation in only 4 h for nanoUiO-66). Finally, the safety of the formed by-product during SMT photodegradation was confirmed, reinforcing the potential of the application of UiO-66 in water remediation.

Synthetic approaches for accessing rare-earth analogues of UiO-66

Rare-earth (RE) analogues of UiO-66 with non-functionalised 1,4-benzenedicarboxylate linkers are synthesised for the first time, and a series of synthetic approaches is provided to troubleshoot the synthesis. RE-UiO-66 analogues are fully characterised, and demonstrate a high degree of crystallinity, high surface area and thermal stability, consistent with the UiO-66 archetype.

Defect Engineering of Nanoscale Hf-Based Metal-Organic Frameworks for Highly Efficient Iodine Capture

With the rapid development of the nuclear industry, how to deal with radioactive iodine waste in a timely and effective manner has become an important issue to be solved urgently. Herein, the defect-engineering strategy has been applied to develop a metal-organic framework (MOF)-based solid adsorbent by using the classical UiO-type Hf-UiO-66 as an example. After simple acid treatment, the produced defect-containing Hf-UiO-66 (DHUN) not only retains its topological structure, high crystallization, and regular shape but also shows a great increase in the Brunauer-Emmett-Teller value and pore size in comparison with the original Hf-UiO (HUN). These formed defects within DHUN have been demonstrated to be important for the great enhancement of the iodine capture and following application in computed tomography imaging in vitro. This present work gives a new insight into the control and formation of defect sites, and this simple and efficient defect-engineering strategy also shows great promise for the development of novel solid adsorbents and other functional MOF materials.