Functional metal–organic frameworks for catalytic applications

Pseudomorphic replication for surface patterning with porphyrinic metal-organic frameworks

An unexplored strategy for controlled surface patterning with porphyrinic metal-organic frameworks (MOFs), integrating atomic layer deposition (ALD) and pseudomorphic replication (PMR), is presented. Surface patterning with a sub-micrometer size resolution is enabled by translating ALD-patterned Al2O3 into a MOF pattern in the presence of a porphyrinic linker.

Cu-incorporated NH2-MIL-125(Ti): a versatile visible-light-driven platform for enhanced photocatalytic H2 generation and CO2 photoconversion

Here, we present for the first time an efficient platform for simultaneous H2 generation and CO2 conversion into HCOOH, utilizing a Cu-incorporated NH2-MIL-125(Ti) material with triethanolamine as the sacrificial agent. When subjected to light, Cu-NH2-MIL-125(Ti) exhibits a remarkable enhancement in H2 generation, with a 30-fold increase under UV-Vis light and an 8-fold increase under visible irradiation compared to the pristine MOF. The study on the CO2 photoreduction ability of Cu-NH2-MIL-125(Ti) indicated successful conversion into formic acid yielding 62.4 μmol gcat-1 under visible irradiation. This notable improvement in photocatalytic activity can be attributed to the heightened light absorption capacity and efficient charge transportation and separation mechanisms inherent in Cu-NH2-MIL-125(Ti). Furthermore, the stability of the Cu-NH2-MIL-125(Ti) photocatalyst remains steady even after 24 hours of continuous irradiation. The theoretical simulations suggest that Cu introduction effectively reduces the bandgap while leaving the position and composition of the valence band unaffected.

NH2-MIL-125(Ti) and its functional nanomaterials - a versatile platform in the photocatalytic arena

Titanium (Ti)-based MOFs are promising materials known for their porosity, stability, diverse valence states, and a lower conduction band (CB) than Zr-MOFs. These features support stable ligand-to-metal charge transfer (LMCT) transitions under photoirradiation, enhancing photocatalytic performance. However, Ti-MOF structures remain a challenge owing to the highly volatile and hydrophilic nature of ionic Ti precursors. The discovery of MIL-125 marked a breakthrough in Ti-cluster coordination chemistry. Combining it with NH2 chromophores to form NH2-MIL-125 enhanced its structural design and extended its activity into the visible light region. This review delves into the high-performance photocatalytic properties of NH2-MIL-125, focusing on its applications in H2O2 and H2 production, CO2 and N2 reduction, drug and dye degradation, photocatalytic sensors, and organic transformation reactions. The discussion considers the influence of the Ti precursor, coordination environment, synthesis process, and charge transfer mechanisms. Numerous strategic methods have been discussed to improve the performance of NH2-MIL-125 by incorporating linker modification, metal node modification, encapsulation of active species, and post-modification for enhancing light absorption ability, promoting charge separation, and improving photocatalytic efficiency. Moreover, future perspectives include methods to investigate how the efficiency of NH2-MIL-125-based materials can be planned in promoting research by highlighting their versatility and potential impacts in the area of photocatalysis.

Metal-organic framework catalysed multicomponent reactions towards the synthesis of Pyrans

Metal-Organic Frameworks (MOFs) gaining increasing interest in heterogeneous catalysis owing to their advantageous properties such as superior porosity, high surface area, ample catalytic sites. Their properties can be tailored by varying the metal ions or metal clusters (nodes) and organic linkers. Magnetically active nano core-shell MOF composites are also discovered for easy separation and reuse of catalyst. MOF catalysed multicomponent reactions (MCRs) satisfy several green chemistry principles and thus can be considered as a sturdy step towards sustainable chemical synthesis. In this article, synthesis of biologically potent pyran scaffolds through MOF catalysed MCR approaches have been reviewed. Preparation of MOF catalyst, its catalytic performance in pyran synthesis, reusability has been discussed with reaction for each example.

A Chemically Robust 2D Ni-MOF as an Efficient Heterogeneous Catalyst for One-Pot Synthesis of Therapeutic and Bioactive 2-Amino-3-Cyano-4H-Pyran Derivatives

Despite possessing numerous catalytic advantages of MOFs, developing 2D frameworks having excellent chemical stability along with new catalytic properties remains a grand challenge. Herein, by employing a mixed ligand synthetic approach, we have constructed a 2D Ni-MOF, IITKGP-52, which exhibits excellent framework robustness in open air, water, as well as over a wide range of aqueous pH solutions (2-12). Benefitting from its robustness and abundant Lewis acidic open metal sites (OMSs), IITKGP-52 is explored in catalyzing the heterogeneous three-component condensation reaction for the tandem synthesis of bioactive 2-amino-3-cyano-4H-pyran derivatives with low catalytic loading, greater compatibility for a wide range of substrates, excellent recyclability and superior catalytic efficiency than the previously employed homo and heterogeneous systems. IITKGP-52 inaugurates the employment of MOF-based catalysts for one-pot synthesis of therapeutic and bioactive 2-amino-3-cyano-4H-pyran derivatives.

Recent advances in heterogeneous porous Metal-Organic Framework catalysis for Suzuki-Miyaura cross-couplings

Suzuki-Miyaura coupling (SMC), a crucial C-C cross-coupling reaction, is still associated with challenges such as high synthetic costs, intricate work-ups, and contamination with homogeneous metal catalysts. Research intensely focuses on strategies to convert homogeneous soluble metal catalysts into insoluble powder solids, promoting heterogeneous catalysis for easy recovery and reuse as well as for exploring greener reaction protocols. Metal-Organic Frameworks (MOFs), recognized for their high surface area, porosity, and presence of transition metals, are increasingly studied for developing heterogeneous SMC. The molecular fence effect, attributed to MOF surface functionalization, helps preventing catalyst deactivation by aggregation, migration, and leaching during catalysis. Recent reports demonstrate the enhanced catalytic activity, selectivity, stability, application scopes, and potential of MOFs in developing greener heterogeneous synthetic methodologies. This review focuses on the catalytic applications of MOFs in SMC reactions, emphasizing developments after 2016. It critically examines the synthesis and incorporation of active metal species into MOFs, focusing on morphology, crystallinity, and dimensionality for catalytic activity induction. MOF catalysts are categorized based on their metal nodes in subsections, with comprehensive discussion on Pd incorporation strategies, catalyst structures, optimal SMC conditions, and application scopes, concluding with insights into challenges and future research directions in this important emerging area of MOF applications.

Hybrid Metal-Organic Frameworks (MOFs) for Various Catalysis Applications

Porous materials have been gaining popularity in catalysis applications, solving the current ecological challenges. Metal-organic frameworks (MOFs) are especially noteworthy for their high surface areas and customizable chemistry, giving them a wide range of potential applications in catalysis remediation. The review study delves into the various applications of MOFs in catalysis and provides a comprehensive summary. This review thoroughly explores MOF materials, specifically focusing on their diverse catalytic applications, including Lewis catalysis, oxidation, reduction, photocatalysis, and electrocatalysis. Also, this study emphasizes the significance of high-performance MOF materials, which possess adjustable properties and exceptional features, as a novel approach to tackling technological challenges across multiple sectors. MOFs make it an ideal candidate for catalytic reactions, as it enables efficient conversion rates and selectivity. Furthermore, the tunable properties of MOF make it possible to tailor its structure to suit specific catalytic requirements. This feature improves performance and reduces costs associated with traditional catalysts. In conclusion, MOF materials have revolutionized the field of catalysis and offer immense potential in solving various technological challenges across different industries.

Construction of pyrimidine derivatives-copper enzyme mimics as colorimetric sensing elements for efficient detection of phenolic compounds and hydrogen peroxide

As concerns about environmental pollution grow, the rapid identification and quantification of pollutants have become increasingly vital. In this work, a series of pyrimidine derivatives-Cu enzyme mimics (Cytosine-Cu, Cytidine-Cu, and CMP-Cu) with laccase- and peroxidase-like activity were prepared through the coordination of Cu2+ with different pyrimidine derivatives (PDs). The PDs-Cu enzyme mimics contain high levels of Cu+ and N - Cu coordination structures, which provide sufficient catalytic sites for the substrates. Compared with natural enzymes and other nanozymes, PDs-Cu demonstrate superior substrate affinity, catalytic efficiency, stability, and resistance to interference. It was found that PDs-Cu enzyme mimics have different catalytic activities towards different phenolic compounds. Therefore, a three-channel colorimetric sensor array (CSA) was successfully developed utilizing PDs-Cu as the sensing elements. The CSA can accurately identify different phenolic compounds and their mixtures in seawater and simulated wastewater. Additionally, a colorimetric method for detecting H2O2 in eye drops was developed, featuring a detection range of 0.1-10.0 μM and a limit of quantification of 0.1 μM. This research not only provides a flexible protocol for regulating the catalytic activity of enzyme mimics, but also provides important inspiration for the development of methods for rapid identification and detection of contaminants in the environmental water.

Bismuth Nanoparticles and Single Iron Atoms on Carbon Derived from a Covalent Organic Framework Synergistically Catalyze the Oxygen Reduction Reaction

The utilization of catalysts comprising metal nanoparticle has been beneficial for enhancing the performance of oxygen reduction reaction (ORR). However, the inadequate intrinsic activity of these catalysts still presents a significant challenge, limiting their overall effectiveness. This issue can be addressed by introducing single atoms, which can create a synergistic effect with the nanoparticles to catalyse and thereby improve performance. Nevertheless, the synergistic catalysis of nanoparticles and single atoms is still under investigation. In this study, we fabricated a core-shell structured carbon framework incorporating Fe single atoms and Bi nanoparticles through the pyrolysis of COF and MOF core-shell structures. Introducing Fe single atoms into ZIF-8, with Fe-ZIF-8 as the core and Bi-containing COF as the shell, resulted in higher ORR activity. The catalyst exhibited a half-wave potential of 0.867 V and a high current density of 6.68 mA cm-2 in 0.1 M KOH, which were comparable to those of Pt/C equivalent. This study provides new research concepts for exploring the application of single atoms and nanoparticles in catalytic oxygen reduction reactions through synergistic effects.

Distillery-Waste-Derived C-SiO2 Catalyst Support Reinforces Phenol Adsorption and Selective Hydrogenation

Selective hydrogenation of lignin-derived phenolic compounds is an essential process for developing the sustainable chemical industry and reducing dependence on nonrenewable resources. Herein, a composite C-SiO2 material (DGC) was prepared via the stepwise pyrolysis and steam activation of the distiller's grains, a fermentation solid waste from the Chinese liquor industry. After Ru loading, Ru/DGC was used for the catalytic hydrogenation of phenol to cyclohexanol. Steam activation remarkably increased the hydrophilicity and specific surface area of DGC, introducing oxygen-containing functional groups on the surface of DGC, thereby promoting the adsorption of Ru3+ and phenol. Additionally, the large specific surface area facilitated the dispersion of the active metal. Furthermore, the steam activation of DGC promoted the graphitization of the carbon matrix and formed Si-H/Si-OH bonds on the SiO2 surface. The benzene ring of phenol interacted with the carbon matrix via π-π stacking, and the hydroxyl group of phenol interacted with SiO2 via hydrogen bonding. The synergistic interactions of phenol at the C-SiO2 interface enhanced phenol adsorption to promote the hydrogenation. Consequently, 100 % of phenol was hydrogenated to cyclohexanol at 60 °C within 30 min. Furthermore, the optimized catalyst exhibited high activity for phenol hydrogenation even after four reuse cycles. The outstanding stability of the catalyst and its requirement for mild reaction conditions favor its large-scale industrial applications.

Ultrathin two-dimensional (2D) manganese-based metal-organic framework nanosheets for selective photocatalytic oxidation of thioether

The efficiency of photocatalysts depends largely on the accessibility of reaction species to the active centre, the electron transfer and geometric matching between the active surface of the catalyst and reaction species. In this work, we successfully synthesized and designed one two-dimensional Mn(II) MOF with [Mn2(H2L1)(H2O)2(DMF)2]n·(CH3CH2OH)n (HSTC 3) by using MnCl2·4H2O and 5,5'-(anthracene-9,10-diyl)diisophthalic acid (H4L1), in which the adjacent layers are stacked with weak interactions, and the huge gap leads to the interpenetration between layers to form a 2D + 2D → 3D interpenetration frame. Based on the particularity of the structure of HSTC 3, ultrasonic wall breaking methods were tried to successfully peel HSTC 3 into nanosheets (HSTC 3-NS), thus achieving a significant improvement in a series of optoelectronic properties due to exposure to more active centres for HSTC 3-NS. These results significantly enhance the photocatalytic selective oxidation of thioether. This study provides a new insight into the post-synthesis modification of MOF photocatalyst and their application in photocatalytic organic synthesis.

A comprehensive study about functionalization and de-functionalization of MOF-808 as a defect-engineered Zr-MOFs for selective catalytic oxidation

In metal-organic frameworks (MOFs), confined space as a chemical nanoreactor is as essential as coordinatively unsaturated metal site catalysis. The properties of MOFs can be adjusted through the incorporation of functional groups and open metal sites in frameworks that can modify the catalytic performance. In this regard, a set of defect-engineered MOFs, Ex-MOF-808(NH2, NO2, H) and Mix-MOF-808(NH2, NO2, H), were synthesized by ultrasonic-assisted linker exchange approach (Ex-MOFs) and solvothermal mixing ligand method (Mix-MOFs), respectively. Further, the relationship between the preparation method, structural properties, and catalytic efficiency of the prepared materials in the selective oxidation of methyl phenyl sulfide (MPS) has been investigated. By analyzing zeta potential, it was found that in the exchange method, the amount of defect and functional groups on the surface of MOFs are more than in the mixing method, which also affects the catalytic activity. In our contribution, mix-MOF-808(NO2) carrying nitro groups at their organic linkers, which has a well-dispersion of nitro groups at the framework exhibits selective conversion of MPS to sulfone (91 %). Furthermore, the performance of stable heterogeneous catalysts was investigated for three cycles, which demonstrated their great potential for advanced catalytic oxidation.

Zeolitic imidazolate frameworks (ZIFs): Advanced nanostructured materials to enhance the functional performance of food packaging materials

Zeolite imidazole framework (ZIF) materials are a class of metallic organic framework (MOF) materials that have several potential applications in the food and other industries. They consist of metal ions or clusters of metal ions coordinated with imidazole-based organic linkers, creating a three-dimensional solid structure with well-defined pores and channels. ZIFs possess several important features, including high porosity, tunable pore sizes, high surface areas, adjustable surface chemistries, and good stabilities. These characteristics make them highly versatile materials that can be used in a variety of applications, including smart and active food packaging. Based on their controllable compositions, dimensions, and pore sizes, the properties of ZIFs can be tailored for a diverse range of applications, including energy storage, sensing, separation, encapsulation, and catalysis. In this article, we focus on recent progress and potential applications of ZIFs in food packaging materials. Previous studies have shown that ZIFs can significantly improve the optical, mechanical, barrier, thermal, sustainability, and preservative properties of packaging materials. Moreover, ZIFs can be used as carriers to encapsulate, protect, and control the release of bioactive agents in packaging materials. ZIFs are capable of selectively adsorbing and releasing molecules based on their size, shape, and surface properties. These unique characteristics make them particularly suitable for smart or active food packaging applications. By selectively removing gases (such as oxygen, carbon dioxide, water, or ethylene) ZIFs can improve the shelf life and quality of packaged foods. In addition, they can be employed to control the growth of spoilage microorganisms and minimize oxidation reactions, thereby enhancing the freshness and extending the shelf life of foods. They may also be used to create sensors capable of detecting and indicating food spoilage. For instance, ZIFs that change color or release specific compounds when spoilage products are present can provide visual or chemical indications of food deterioration. This feature is especially valuable in ensuring the safety and quality of packaged food, as it enables consumers and retailers to easily identify spoiled products. ZIFs can be functionalized using various additives, including antioxidants, antimicrobials, pigments, and flavors, which can improve the preservative and sensory properties of packaged foods. Moreover, ZIF-based packaging materials offer sustainability benefits. Unlike traditional plastic packaging, ZIFs are biodegradable and can easily be disposed of without causing harm to the environment, thereby reducing the adverse effects of plastic waste materials. The application of ZIFs in smart/active food packaging offers exciting possibilities for enhancing the shelf life, quality, and safety of foods. With further research and development, ZIF-based packaging could become a sustainable alternative to plastic-based packaging in the food industry. An important aim of this review article is to stimulate further research on the development and application of ZIFs within food packaging materials.

Real Active Site Identification of Co/Co3O4 Anchoring Ni-MOF Nanosheets with Fast OER Kinetics for Overall Water Splitting

Doping metals and constructing heterostructures are pivotal strategies to enhance the electrocatalytic activity of metal-organic frameworks (MOFs). Nevertheless, effectively designing MOF-based catalysts that incorporate both doping and multiphase interfaces poses a significant challenge. In this study, a one-step Co-doped and Co3O4-modified Ni-MOF catalyst (named Ni NDC-Co/CP) with a thickness of approximately 5.0 nm was synthesized by a solvothermal-assisted etching growth strategy. Studies indicate that the formation of the Co-O-Ni-O-Co bond in Ni NDC-Co/CP was found to facilitate charge density redistribution more effectively than the Co-O-Ni bimetallic synergistic effect in NiCo NDC/CP. The designating Ni NDC-Co/CP achieved superior oxygen evolution reaction (OER) activity (245 mV @ 10 mA cm-2) and robust long stability (100 h @ 100 mA cm-2) in 1.0 M KOH. Furthermore, the Ni NDC-Co/CP(+)||Pt/C/CP(-) displays pregnant overall water splitting performance, achieving a current density of 10 mA cm-2 at an ultralow voltage of 1.52 V, which is significantly lower than that of commercial electrolyzer using Pt/C and IrO2 electrode materials. In situ Raman spectroscopy elucidated the transformation of Ni NDC-Co to Ni(Co)OOH under an electric field. This study introduces a novel approach for the rational design of MOF-based OER electrocatalysts.

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.

Starfruit-Shaped Zirconium Metal-Organic Frameworks: From 3D Intermediates to 2D Nanosheet Petals with Enhanced Catalytic Activity

We present the fabrication of a novel Starfruit-shaped metal-organic framework (SMOF) composed of zirconium and Tetra(4-carboxyphenyl)porphine linkers. The SMOF exhibits a unique morphology with edge-sharing two-dimensional (2D) nanosheet petals. Our investigation unravels a captivating transformation process, wherein three-dimensional (3D) shuttle-shaped MOFs form initially and subsequently evolve into 2D nanosheet-based SMOF structures. The distinct morphology of SMOF showcases superior catalytic activity in detoxifying G-type nerve agent and blister agent simulants, surpassing that of its 3D counterparts. This discovery of the 3D-to-2D transition growth pathway unlocks exciting opportunities for exploring novel strategies in advanced MOF nanostructure development, not only for catalysis but also for various other applications.

Versatile Structural Engineering of Metal-Organic Frameworks Enabling Switchable Catalytic Selectivity

The structure engineering of metal-organic frameworks (MOFs) forms the cornerstone of their applications. Nonetheless, realizing the simultaneous versatile structure engineering of MOFs remains a significant challenge. Herein, a dynamically mediated synthesis strategy to simultaneously engineer the crystal structure, defect structure, and nanostructure of MOFs is proposed. These include amorphous Zr-ODB nanoparticles, crystalline Zr-ODB-hz (ODB = 4,4'-oxalyldibenzoate, hz = hydrazine) nanosheets, and defective d-Zr-ODB-hz nanosheets. Aberration-corrected scanning transmission electron microscopy combined with low-dose high-angle annular dark-field imaging technique vividly portrays these engineered structures. Concurrently, the introduced hydrazine moieties confer self-reduction properties to the respective MOF structures, allowing the in situ installation of catalytic Pd nanoparticles. Remarkably, in the hydrogenation of vanillin-like biomass derivatives, Pd/Zr-ODB-hz yields partially hydrogenated alcohols as the primary products, whereas Pd/d-Zr-ODB-hz exclusively produces fully hydrogenated alkanes. Density functional theory calculations, coupled with experimental evidence, uncover the catalytic selectivity switch triggered by the change in structure type. The proposed strategy of versatile structure engineering of MOFs introduces an innovative pathway for the development of high-performance MOF-based catalysts for various reactions.

Heterogenization of molecular catalysts within porous solids: the case of Ni-catalyzed ethylene oligomerization from zeolites to metal-organic frameworks

The last decade has seen a tremendous expansion of the field of heterogenized molecular catalysis, especially with the growing interest in metal-organic frameworks and related porous hybrid solids. With successful achievements in the transfer from molecular homogeneous catalysis to heterogenized processes come the necessary discussions on methodologies used and a critical assessment on the advantages of heterogenizing molecular catalysis. Here we use the example of nickel-catalyzed ethylene oligomerization, a reaction of both fundamental and applied interest, to review heterogenization methodologies of well-defined molecular catalysts within porous solids while addressing the biases in the comparison between original molecular systems and heterogenized counterparts.

One-pot synthesis of bimetallic Fe-Cu metal-organic frameworks composite for the elimination of organic pollutants via peroxymonosulphate activation

A series of bimetallic of FeCu metal-organic frameworks (MOFs) have been synthesised using a solvothermal process by varying the ratio between the two metals. Further, the bimetallic MOF catalysts were characterised by X-ray powder diffraction, scanning electron microscopy, and infrared spectroscopy techniques. Their catalytic properties for activation of peroxymonosulphate (PMS) have been tested by the removal of a model dye, rhodamine B. As a result, NH2-Fe2.4Cu1-MOF demonstrated the highest degradation, the effect of the ratio NH2-Fe2.4Cu1-MOF/PMS has been studied, and the main reactive species have been assessed. The application of these MOFs in powder form is difficult to handle in successive batch or flow systems. Thus, this study assessed the feasibility of growing NH2-Fe2,4Cu1-MOF on polyacrylonitrile (PAN) spheres using the one-pot solvothermal synthesis method. The optimisation of the catalytic activity of the synthesised composite (NH2-Fe2.4Cu1-MOF@PAN) has been evaluated by response surface methodology using a central composite face-centred experimental design matrix and selecting as independent variables: time, PMS concentration, and catalyst dosage. Based on the results, the optimisation of the operational conditions has been validated. At 2.5 mM PMS, 90 min, and 1.19 g·L-1 of catalyst dosage, maximum degradation (80.92%) has been achieved, which doubles the removal values obtained in previous studies with other MOFs. In addition, under these conditions, the catalyst has been proven to maintain its activity and stability for several cycles without activity loss.

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.

Removal of Ni(II), Cu(II), Pb(II), and Cd(II) from Aqueous Phases by Silver Nanoparticles and Magnetic Nanoparticles/Nanocomposites

The intake of heavy metals into the body, even at very low concentrations, may cause a decrease in central nervous system functions; deterioration of blood composition; and liver, kidney, and lung damage. Therefore, heavy metal ions must be removed from water. In this study, silver, magnetic iron/copper, and iron oxide nanoparticles were synthesized using Lathyrus brachypterus extract and then Fe/Cu-AT, Fe3O4-AT, Fe/Cu-CS, and Fe3O4-CS magnetic nanocomposite beads were synthesized using alginate and chitosan. The removal of Cd(II), Pb(II), Ni(II), and Cu(II) ions from aqueous phases using synthesized nanoadsorbents was investigated by single and competitive (double and quaternary) adsorption techniques. The kinetic usability of the magnetic iron oxide chitosan (Fe3O4-CS) nanocomposite beads with the highest removal efficiency was evaluated. Based on experimental results, the order of removal was found to be 98.39, 75.52, 51.54, and 45.34%, and it was listed as Pb(II) > Cu(II) > Cd(II) > Ni(II), respectively. The Dubinin-Radushkevich, Freundlich, Langmuir, and Temkin isotherm models were used, and experimental results revealed that the experimental data fit the Langmuir model better. The maximum adsorption capacities (qm) obtained from the Langmuir isotherm model of Fe3O4-CS were found to be 8.71, 23.75, 18.57, and 12.38 mg/g for Ni(II), Pb(II), Cu(II), and Cd(II) ions, respectively. When the kinetic data were applied to the Lagergren, Ho-McKay, and Elovich models, it was observed that the adsorption kinetics mostly conformed to the Ho-McKay second-order rate equation. The binary and quaternary competitive adsorption data showed that Fe3O4-CS were selective toward Cu(II) and Pb(II). The reusability of the Fe3O4-CS nanoadsorbent was performed as three cycles with the same concentration. The adsorption capacities were found to be 95.81, 70.65, 50.50, and 42.75%, in turn for Pb(II), Cu(II), Cd(II), and Ni(II) ions after three cycles, which revealed that the Fe3O4-CS nanoadsorbent can be used after three cycles without losing its efficiency.

Th6-Based Multicomponent Heterometallic Metal-Organic Frameworks Featuring 6,12-Connected Topology for Iodine Adsorption

Its high coordination number and tendency to cluster make Th4+ suitable for constructing metal-organic frameworks (MOFs) with novel topologies. In this work, two novel thorium-based heterometallic MOF isomers (IHEP-17 and IHEP-18) were assembled from a Th6 cluster, a multifunctional organic ligand [4-(1H-pyrazol-4-yl)benzoic acid (HPyba)], and Cu2+/Ni2+ cations via the one-pot solvothermal synthesis strategy. The framework features a 6,12-connected new topology net and contains two kinds of supramolecular cage structures, Th36M4 and Th24M2, suitable for guest exchange. Both MOF materials can efficiently adsorb I2. X-ray photoelectron spectroscopy, Raman spectroscopy, and single-crystal X-ray diffraction indicate that the adsorbed iodine is uniformly distributed within the Th36M4 cage but not the Th24M2 cage in the form of I3-.

MOF-based catalysts: insights into the chemical transformation of greenhouse and toxic gases

Metal-organic framework (MOF)-based catalysts are outstanding alternative materials for the chemical transformation of greenhouse and toxic gases into high-add-value products. MOF catalysts exhibit remarkable properties to host different active sites. The combination of catalytic properties of MOFs is mentioned in order to understand their application. Furthermore, the main catalytic reactions, which involve the chemical transformation of CH4, CO2, NOx, fluorinated gases, O3, CO, VOCs, and H2S, are highlighted. The main active centers and reaction conditions for these reactions are presented and discussed to understand the reaction mechanisms. Interestingly, implementing MOF materials as catalysts for toxic gas-phase reactions is a great opportunity to provide new alternatives to enhance the air quality of our planet.

Interfacial chemistries in metal-organic framework (MOF)/covalent-organic framework (COF) hybrids

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been attracting tremendous attention in various applications due to their unique structural properties. Recent interest has been focused on their combination as hybrids to enable the engineering of new classes of frameworks with complementary properties. This review gives a comprehensive summary on the interfacial chemistries in MOF/COF hybrids, which play critical roles in their hybridization. The challenges and perspectives in the field of MOF/COF hybrids are also provided to inspire more efforts in diversifying this hybrid family and their cross-disciplinary applications.

Ligand leaching enabling improved electrocatalytic oxygen evolution performance

Design and fabrication of cost-effective (pre-)catalysts are important for water splitting and metal-air batteries. In this direction, various metal-organic frameworks (MOFs) have been investigated as pre-catalysts for oxygen evolution. However, the activation process and the complex reconstruction behaviour of these MOFs are not well understood. Herein, square-like MOF nanosheets in which carbon nanotubes were embedded were prepared by introducing an amine ligand to coordinate with Ni ions and then reacting with [Fe(CN)₆]^3-. The formed MOF nanosheets containing nickel and iron species were then activated by NaBH₄, inducing the leaching of ligands and the formation of tiny active species in situ loaded on carbon nanotubes. The prepared catalyst shows superior oxygen evolution performance with an ultralow overpotential of 231 mV for 10 mA cm^-2, a fast reaction kinetics with a small Tafel slope of 52.3 mV dec^-1, and outstanding catalysis stability. The excellent electrocatalytic performance for oxygen evolution can be attributed to the structural advantage of in situ derived small sized active species and one-dimensional conductive networks. This work provides a new thought for the enhancement of the electrocatalytic performance of MOF materials.

An introductory review on advanced multifunctional materials

This review summarizes the applications of some of the advanced materials. It included the synthesis of several nanoparticles such as metal oxide nanoparticles (e.g., Fe₃O₄, ZnO, ZrOSO₄, MoO_3-x, CuO, AgFeO₂, Co₃O₄, CeO₂, SiO₂, and CuFeO₂); metal hydroxide nanosheets (e.g., Zn₅(OH)₈(NO₃)₂·2H₂O, Zn(OH)(NO₃)·H₂O, and Zn₅(OH)₈(NO₃)₂); metallic nanoparticles (Ag, Au, Pd, and Pt); carbon-based nanomaterials (graphene, graphene oxide (GO), graphitic carbon nitride (g-C₃N₄), and carbon dots (CDs)); biopolymers (cellulose, nanocellulose, TEMPO-oxidized cellulose nanofibers (TOCNFs), and chitosan); organic polymers (e.g. covalent-organic frameworks (COFs)); and hybrid materials (e.g. metal-organic frameworks (MOFs)). Most of these materials were applied in several fields such as environmental-based technologies (e.g., water remediation, air purification, gas storage), energy (production of hydrogen, dimethyl ether, solar cells, and supercapacitors), and biomedical sectors (sensing, biosensing, cancer therapy, and drug delivery). They can be used as efficient adsorbents and catalysts to remove emerging contaminants e.g., inorganic (i.e., heavy metals) and organic (e.g., dyes, antibiotics, pesticides, and oils in water via adsorption. They can be also used as catalysts for catalytic degradation reactions such as redox reactions of pollutants. They can be used as filters for air purification by capturing carbon dioxide (CO₂) and volatile organic compounds (VOCs). They can be used for hydrogen production via water splitting, alcohol oxidation, and hydrolysis of NaBH₄. Nanomedicine for some of these materials was also included being an effective agent as an antibacterial, nanocarrier for drug delivery, and probe for biosensing.

3D Lanthanide Neodymium Porphyrin Metal-Organic Framework for Photocatalytic Oxidation of Styrene

A novel three-dimensional lanthanide porphyrin-based MOF (Nd-PMOFs) was synthesized by using tetracarboxyphenyl porphyrin as the ligand and the lanthanide Nd as the coordination metal. Its specific crystal structure information was obtained by single-crystal diffraction with the space group C2/c and the empirical formula C₇₂H₄₅N₆Nd₂O_15.25. This new Nd porphyrin-based MOF with an organic framework formed by a unique coordination method enables the effective separation of photogenerated electrons and holes under photoluminescence, giving it excellent photocatalytic property which could be verified by the characterization data. The photocatalytic performance was examined by taking tert-butyl hydroperoxide as the oxidant and Nd-PMOFs as the catalyst for photocatalytic oxidation of styrene to benzaldehyde with 91.4% conversion and 81.2% benzaldehyde selectivity under optimal reactions, which surpasses most of the results reported in the literature. Several styrenes with other substituents were screened to explore the general applicability of Nd-PMOF for photocatalysis of styrene, among which Nd-PMOFs also exhibited excellent photocatalytic performance. This work offers the possibility to apply lanthanide organometallic frameworks, which are widely used in fluorescent materials, to photocatalysis. In addition, it also provides a new method for the catalytic generation of benzaldehyde from styrene that is consistent with the needs of modern green development.

Molecular Catalysis of Energy Relevance in Metal-Organic Frameworks: From Higher Coordination Sphere to System Effects

The modularity and synthetic flexibility of metal-organic frameworks (MOFs) have provoked analogies with enzymes, and even the term MOFzymes has been coined. In this review, we focus on molecular catalysis of energy relevance in MOFs, more specifically water oxidation, oxygen and carbon dioxide reduction, as well as hydrogen evolution in context of the MOF-enzyme analogy. Similar to enzymes, catalyst encapsulation in MOFs leads to structural stabilization under turnover conditions, while catalyst motifs that are synthetically out of reach in a homogeneous solution phase may be attainable as secondary building units in MOFs. Exploring the unique synthetic possibilities in MOFs, specific groups in the second and third coordination sphere around the catalytic active site have been incorporated to facilitate catalysis. A key difference between enzymes and MOFs is the fact that active site concentrations in the latter are often considerably higher, leading to charge and mass transport limitations in MOFs that are more severe than those in enzymes. High catalyst concentrations also put a limit on the distance between catalysts, and thus the available space for higher coordination sphere engineering. As transport is important for MOF-borne catalysis, a system perspective is chosen to highlight concepts that address the issue. A detailed section on transport and light-driven reactivity sets the stage for a concise review of the currently available literature on utilizing principles from Nature and system design for the preparation of catalytic MOF-based materials.

Boosting Activity and Selectivity of UiO-66 through Acidity/Alkalinity Functionalization in Dimethyl Carbonate Catalysis

The acid-base properties of supports have an enormous impact on catalytic reactions to regulate the selectivity and activity of supported catalysts. Herein, a train of Pd-X-UiO-66 (X = NO₂ , NH₂ , and CH₃ ) catalysts with different acidity/alkalinity functional groups and encapsulated Pd(II) species is first developed, whose activities in dimethyl carbonate (DMC) catalysis are then investigated in details. Thereinto, the Pd-NO₂ -UiO-66 catalyst with acidity functionalization exhibits the best catalytic behavior: the DMC selectivity stemmed from methyl nitrite (MN) is up to 68%, the conversion of CO is 73.4%. The obtained experimental results demonstrate that the NO₂ group not only affected the interaction between X-UiO-66 and Pd(II) active sites but also play an indispensable role in the adsorption and activation of MN and CO, which remarkably promote the formation of the COOCH₃ ^* intermediate and DMC product.

CuO-decorated MOF derived ZnO polyhedral nanostructures for exceptional H2S gas detection

Considering that H₂S is a hazardous gas that poses a significant risk to people's lives, research into H₂S gas sensors has garnered a lot of interest. This work reports a CuO/ZnO multifaceted nanostructures(NS) created by heat treating Cu²⁺/ZIF-8 impregnation precursors, and their microstructure and gas sensing characteristics were examined using various characterization techniques (XRD, XPS, SEM, TEM, and BET). The as-prepared hollow CuO/ZnO multifunctional nanostructures had a high gas response value (425@50 ppm H₂S gas), quick response and recovery times (57/191s @20 ppm), a low limit of detection (1.6@500 ppb H₂S), good humidity resistance and highly selective towards H₂S gas. The hollow CuO/ZnO multifaceted nanostructures possessed enhanced gas sensing capabilities which may be related to their porous hollow nanostructures, the manufactured p-CuO/n-ZnO heterojunctions, and the spillover effect between CuO and H₂S.

Role of the Support Effects in Single-Atom Catalysts

In recent years, single-atom catalysts (SACs) have received a significant amount of attention due to their high atomic utilization, low cost, high reaction activity, and selectivity for multiple catalytic reactions. Unfortunately, the high surface free energy of single atoms leads them easily migrated and aggregated. Therefore, support materials play an important role in the preparation and catalytic performance of SACs. Aiming at understanding the relationship between support materials and the catalytic performance of SACs, the support effects in SACs are introduced and reviewed herein. Moreover, special emphasis is placed on exploring the influence of the type and structure of supports on SAC catalytic performance through advanced characterization and theoretical research. Future research directions for support materials are also proposed, providing some insight into the design of SACs with high efficiency and high loading.

Enzyme-Linked Metal Organic Frameworks for Biocatalytic Degradation of Antibiotics

Metal organic frameworks (MOFs) are multi-dimensional network of crystalline material held together by bonding of metal atoms and organic ligands. Owing to unique structural, chemical, and physical properties, MOFs has been used for enzyme immobilization to be employed in different catalytic process, including catalytic degradation of antibiotics. Immobilization process other than providing large surface provides enzyme with enhanced stability, catalytic activity, reusability, and selectivity. There are various approaches of enzyme immobilization over MOFs including physical adsorption, chemical bonding, diffusion and in situ encapsulation. In situ encapsulation is one the best approach that provides extra stability from unfolding and denaturation in harsh industrial conditions. Presence of antibiotic in environment is highly damaging for human in particular and ecosystem in general. Different methods such as ozonation, oxidation, chlorination and catalysis are available for degradation or removal of antibiotics from environment, however these are associated with several issues. Contrary to these, enzyme immobilized MOFs are novel system to be used in catalytic degradation of antibiotics. Enzyme@MOFs are more stable, reusable and more efficient owing to additional support of MOFs to natural enzymes in well-established process of photocatalysis for degradation of antibiotics aimed at environmental remediation. Prime focus of this review is to present catalytic degradation of antibiotics by enzyme@MOFs while outlining their synthetics approaches, characterization, and mechanism of degradation. Furthermore, this review highlights the significance of enzyme@MOFs system for antibiotics degradation in particular and environmental remediation in general. Current challenges and future perspective of research in this field are also outlined along with concluding comments.

Graphical Abstract

Synergistic Effect of FeII and MnII Ions in Cyano-Bridged Heterometallic Coordination Polymers on Catalytic Selectivity of Benzene Oxygenation to Phenol

A cyano-bridged heterometallic coordination polymer with partial deficiencies of CN^- ligands, [Mn^II(H₂O)_8/3]_3/2[Fe^II(CN)₅(NH₃)], forms open metal sites both on Mn^II and Fe^II ions by liberation of monodentate ligands such as NH₃ and H₂O. [Mn^II(H₂O)_8/3]_3/2[Fe^II(CN)₅(NH₃)] exhibits high catalytic activity and selectivity of benzene oxygenation to phenol in the presence of m-chloroperoxybenzoic acid as an oxidant. The postcatalytic spectroscopy of [Mn^II(H₂O)_8/3]_3/2[Fe^II(CN)₅(NH₃)] and catalysis comparison with a physical mixture of [Mn^II(H₂O)₃]₂[Fe^II(CN)₆] and [Fe(H₂O)_3/2]_4/3[Fe(CN)₆], which has open metal sites on both Mn^II and Fe ions separately, indicated that the high activity resulted from high oxidation ability and phenol adsorption ability of Fe^II and Mn^II ions, respectively.

Catalytic Oxidation of Benzoins by Hydrogen Peroxide on Nanosized HKUST-1: Influence of Substituents on the Reaction Rates and DFT Modeling of the Reaction Path

In this research, the oxidation of a series of benzoins, R-C(=O)-CH(OH)-R, where R = phenyl, 4-methoxyphenyl, 4-bromophenyl, and 2-naphthyl, by hydrogen peroxide in the presence of nanostructured HKUST-1 (suspension in acetonitrile/water mixture) was studied. The respective benzoic acids were the only products of the reactions. The initial average reaction rates were experimentally determined at different concentrations of benzoin, H₂O₂ and an effective concentration of HKUST-1. The sorption of the isotherms of benzoin, dimethoxybenzoin and benzoic acid on HKUST-1, as well as their sorption kinetic curves, were measured. The increase in H₂O₂ concentration expectedly led to an acceleration of the reaction. The dependencies of the benzoin oxidation rates on the concentrations of both benzoin and HKUST-1 passed through the maxima. This finding could be explained by a counterplay between the increasing reaction rate and increasing benzoin sorption on the catalyst with the increase in the concentration. The electronic effect of the substituent in benzoin had a significant influence on the reaction rate, while no relation between the size of the substrate molecule and the rate of its oxidation was found. It was confirmed by DFT modeling that the reaction could pass through the Baeyer-Villiger mechanism, involving an attack by the HOO^- anion on the C atom of the activated C=O group.

Heterometallic palladium-iron metal-organic framework as a highly active catalyst for cross-coupling reactions

Palladium-based metal-organic frameworks (Pd-MOFs) are an emerging class of heterogeneous catalysts extremely challenging to achieve due to the facile leaching of palladium and its tendency to be reduced. Herein, Pd(ii) was successfully incorporated in the framework of a MOF denoted as MUV-22 using a solvent assisted reaction. This stable MOF, with square-octahedron (soc) topology as MIL-127, and a porosity of 710 m² g^-1, is highly active, selective, and recyclable for the Suzuki-Miyaura allylation of aryl and alkyl boronates as exemplified with the coupling between cinnamyl bromide and Me-Bpin, a typically reluctant reagent in cross-coupling reactions.

High-Symmetry Co/Ni Triazine Polycarboxylate Diverse Frameworks Constructed by Mx(COO)y Building Blocks: Characterization and Catalytic Performance Evaluation of p-Nitrophenol

Three new triazine compounds [Co_1.5(H₃TDPAT)(H₂O)₃]·6H₂O (1), [Co₂(TCPT)(μ₂-H₂O)₂]·OH (2), and [Ni₃(TCPT)]·3OH (3) were designed and synthesized via the reaction of the symmetrical triazine ligand connected by C-N-C and C-O-C bonds with triazine poly(carboxylic acid)s ligands as the side arms: H₆TDPAT (H₆TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) and H₃TCPT (H₃TCPT = 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine) as well as the corresponding metal salts under the solvothermal condition. Three triazine polycarboxylate frameworks were characterized by elemental analysis, infrared spectroscopy, ultraviolet spectroscopy, thermogravimetric analysis, X-ray powder diffraction, and solid fluorescent spectra in detail. The structural analysis results showed that the three-dimensional porous cage framework of compound 1 was constructed by three different polyhedral cages connected with [Co(COO)₄(H₂O)₂] building blocks. One of the compounds, 2, is formed by twin propeller Co₂(μ₂-H₂O)(COO)₃ building blocks connecting two-dimensional layers and the intermolecular π-π interactions involved the triazine rings between the layers. While the structure of compound 3 is similar to that of 2, assembly is by Ni(COO)₃ building blocks and adjacent layers of the face-to-face π-π interaction between the triazine rings. In order to explore functional properties, the catalytic reduction of p-nitrophenol (PNP) of compounds 1-3 was investigated. They exhibit excellent catalytic activity of more than 95% for reduction of PNP with a dose of 2.5 mg of the compounds.

Metal-Organic Frameworks as Photocatalysts for Solar-Driven Overall Water Splitting

Metal-organic frameworks (MOFs) have been frequently used as photocatalysts for the hydrogen evolution reaction (HER) using sacrificial agents with UV-vis or visible light irradiation. The aim of the present review is to summarize the use of MOFs as solar-driven photocatalysts targeting to overcome the current efficiency limitations in overall water splitting (OWS). Initially, the fundamentals of the photocatalytic OWS under solar irradiation are presented. Then, the different strategies that can be implemented on MOFs to adapt them for solar photocatalysis for OWS are discussed in detail. Later, the most active MOFs reported until now for the solar-driven HER and/or oxygen evolution reaction (OER) are critically commented. These studies are taken as precedents for the discussion of the existing studies on the use of MOFs as photocatalysts for the OWS under visible or sunlight irradiation. The requirements to be met to use MOFs at large scale for the solar-driven OWS are also discussed. The last section of this review provides a summary of the current state of the field and comments on future prospects that could bring MOFs closer to commercial application.

A Review of Noble Metal Catalysts for Catalytic Removal of VOCs

Volatile organic compounds (VOCs) are important precursors for the formation of secondary pollutants, such as fine particulate matter (PM) and ozone (O3), which will lead to severe atmospheric environmental problems to restrict the sustainable development of the social economy. Catalytic oxidation is a safe, eco-friendly, and simple method for eliminating VOCs, which can be converted into CO2 and H2O without the generation of other harmful substances. The fabrication and development of catalysts are very crucial to enhance the catalytic oxidation efficiency of the removal of VOCs. The noble metal catalyst is one of the commonly used catalysts for the catalytic oxidation of VOCs because of the high reaction activity, good stability, poisoning-resistant ability, and easy regeneration. In this review, the research progress of noble metal (Pt, Pd, Au, Ag, and Ir) catalysts for the removal of VOCs in recent years was summarized with the discussion of the influence factors in the preparation process on the catalytic performance. The reaction mechanisms of the removal of VOCs over the corresponding noble metal catalysts were also briefly discussed.

Enhanced catalytic activity of MOF-74 via providing additional open metal sites for cyanosilylation of aldehydes

The preparation of metal-organic frameworks (MOFs) having many open metal sites is an excellent approach for the development of highly active MOF-based catalysts. Herein, well-defined rice-shaped MOF-74 microparticles having structural defects are prepared by incorporating two analogous organic linkers [2,5-dihydroxy-1,4-bezenedicarboxylic acid (DHBDC) and 2-hydroxy-1,4-benzenedicarboxylic acid (HBDC)] within the MOF-74 structure. The replacement of some of DHBDC in MOF-74 by HBDC causes the structural defects (excluding some of the bridged hydroxyl groups), and these structural defects provide the additional open metal sites within MOF-74. Finally, the additional open metal sites within MOF-74 result in the enhanced catalytic activity for the cyanosilylation of several aldehydes. A series of MOF-74s is prepared with various incorporated amounts of HBDC, and the optimum ratio between DHBDC and HBDC in MOF-74 to achieving the best catalytic performance is determined. In addition, the defected MOF-74 displays an excellent recyclability for the catalytic reaction.

MOF/POM hybrids as catalysts for organic transformations

Insertion of molecular metal oxides, e.g. polyoxometalates (POMs), into metal-organic frameworks (MOFs) opens up new research opportunities in various fields, particularly in catalysis. POM/MOF composites have strong acidity, oxygen-rich surface, and redox capacity due to typical characteristics of POMs and the large surface area, highly organized structures, tunable pore size, and shape are due to MOFs. Such hybrid materials have gained a lot of attention due to astonishing structural features, and hence have potential applications in organic catalysis, sorption and separation, proton conduction, magnetism, lithium-ion batteries, supercapacitors, electrochemistry, medicine, bio-fuel, and so on. The exceptional chemical and physical characteristics of POMOFs make them useful as catalysts in simple organic transformations with high capacity and selectivity. Here, the thorough catalytic study starts with a brief introduction related to POMs and MOFs, and is followed by the synthetic strategies and applications of these materials in several catalytic organic transformations. Furthermore, catalytic conversions like oxidation, condensation, esterification, and some other types of catalytic reactions including photocatalytic reactions are discussed in length with their plausible catalytic mechanisms. The disadvantages of the POMOFs and difficulties faced in the field have also been explored briefly from our perspectives.