MOFs as Versatile Catalysts: Synthesis Strategies and Applications in Value-Added Compound Production

Catalysts played a crucial role in advancing modern human civilization, from ancient times to the industrial revolution. Due to high cost and limited availability of traditional catalysts, there is a need to develop cost-effective, high-activity, and nonprecious metal-based electrocatalysts. Metal-organic frameworks (MOFs) have emerged as an ideal candidate for heterogeneous catalysis due to their physicochemical properties, hybrid inorganic/organic structures, uncoordinated metal sites, and accessible organic sections. MOFs are high nanoporous crystalline materials that can be used as catalysts to facilitate polymerization reactions. Their chemical and structural diversity make them effective for various reactions compared to traditional catalysts. MOFs have been applied in gas storage and separation, ion-exchange, drug delivery, luminescence, sensing, nanofilters, water purification, and catalysis. The review focuses on MOF-enabled heterogeneous catalysis for value-added compound production, including alcohol oxidation, olefin oligomerization, and polymerization reactions. MOFs offer tunable porosity, high spatial density, and single-crystal XRD control over catalyst properties. In this review, MOFs were focused on reactions of CO2 fixation, CO2 reduction, and photoelectrochemical water splitting. Overall, MOFs have great potential as versatile catalysts for diverse applications in the future.

Palladium nanoparticles supported on ionic liquid and glucosamine-modified magnetic iron oxide as a catalyst in reduction reactions

A magnetic nanocomposite comprising imidazolium ionic liquid and glucosamine is successfully synthesized and used for stabilization of Pd nanoparticles. This new material, Fe₃O₄@SiO₂@IL/GA-Pd, is fully characterized and applied as a catalyst in the reduction of nitroaromatic compounds to desired amines at room temperature. Also, the reductive degradation of organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) is studied and compared with another previous publications. The survey of the stabilization of the palladium catalytic entities is described demonstrating the separation ability and recycling of them. In addition, TEM, XRD, and VSM analyses of the recycled catalyst confirmed its stability.

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

Enzyme-immobilized metal-organic frameworks: From preparation to application

As a class of widely used biocatalysts, enzymes possess advantages including high catalytic efficiency, strong specificity and mild reaction condition. However, most free enzymes have high requirements on the reaction environment and are easy to deactivate. Immobilization of enzymes on nanomaterial-based substrates is a good way to solve this problem. Metal-organic framework (MOFs), with ultra-high specific surface area and adjustable porosity, can provide a large space to carry enzymes. And the tightly surrounded protective layer of MOFs can stabilize the enzyme structure to a great extent. In addition, the unique porous network structure enables selective mass transfer of substrates and facilitates catalytic processes. Therefore, these enzyme-immobilized MOFs have been widely used in various research fields, such as molecule/biomolecule sensing and imaging, disease treatment, energy and environment protection. In this review, the preparation strategies and applications of enzymes-immobilized MOFs are illustrated and the prospects and current challenges are discussed.

Beyond Frameworks: Structuring Reticular Materials across Nano-, Meso-, and Bulk Regimes

Reticular materials are of high interest for diverse applications, ranging from catalysis and separation to gas storage and drug delivery. These open, extended frameworks can be tailored to the intended application through crystal-structure design. Implementing these materials in application settings, however, requires structuring beyond their lattices, to interface the functionality at the molecular level effectively with the macroscopic world. To overcome this barrier, efforts in expressing structural control across molecular, nano-, meso-, and bulk regimes is the essential next step. In this Review, we give an overview of recent advances in using self-assembly as well as externally controlled tools to manufacture reticular materials over all the length scales. We predict that major research advances in deploying these two approaches will facilitate the use of reticular materials in addressing major needs of society.

Rational Design of Multisite Trielement Ru-Ni-Fe Alloy Nanocatalysts with Efficient and Durable Catalytic Hydrogenation Performances

The co-decomposition of non-noble metals into Ru nanoparticles (NPs) would provide multiple active centers as well as synergistically alter the reaction pathway, enhancing the catalytic hydrogenation performance. Herein, a facile route for synthesizing trielement Ru-Ni-Fe alloy NPs was proposed. The catalytic hydrogenation performance of NPs was measured using p-nitrophenol as a model. The synergistic effect of these three elements (Ru, Ni, and Fe) and synergistic catalysis of multiple crystal faces greatly improved the catalytic hydrogenation performance of Ru₄₄Ni₂₈Fe₂₈ alloy NPs. Ru with more vacant orbitals showed a strong coordination with BH₄^- for the generation of active H species. Ni played a major role in transporting electrons and active H species, increasing the accessibility of catalytically active sites. Fe could cooperate with BH₄^- to produce active H species and promote electrons transfer. Ru₄₄Ni₂₈Fe₂₈ alloy NPs could be reused and applied for the fabrication of films at the oil-water (ethyl acetate-water) interface. The densely packed Ru₄₄Ni₂₈Fe₂₈ NP films were good Raman substrates for monitoring the complete conversion of 4-nitrothiophenol into 4-aminothiophenol. The rational design of Ru₄₄Ni₂₈Fe₂₈ will broaden the application range of Ru-based catalysts and provide new insights into the rational design of other multisite alloy catalysts.