Recent Advances in Polyoxometalate-Catalyzed Reactions

Nanotechnology monitors a leading agricultural controlling process, especially by its miniature dimension. The application of nanotechnology to agriculture and food industries is resonant increased encumbrance because of the potential benefits ranging from enhanced food quality, safety to reduced agricultural inputs and enriched absorbing nanoscale nutrients from the soil. Agriculture, food and natural resources are a part of those challenges like sustainability, susceptibility, human health and healthy life. The ambition of nanomaterials in agriculture is to reduce the amount of spread chemicals, minimize nutrient losses in fertilization and increased yield through pest and nutrient management. Nanotechnology has the prospective to improve the agriculture and food industry with novel nanotools for the controlling of rapid disease diagnostic, enhancing the capacity of plants to absorb nutrients among others. The significant interest of using nanotechnology in agriculture includes specific applications like nanofertilizers and nanopesticides to trail products and nutrients levels to increase the productivity without decontamination of soils, waters and protection against several insect pest and microbial diseases. Nanotechnology may act as sensors for monitoring soil quality of agricultural field and thus it maintain the health of agricultural plants.This study provides a review of the current challenges of sustainability, food security and climate change that are exploring by the researchers in the area of nanotechnology in the improvement of agriculture.

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Nanotechnology in Sustainable Agriculture: Recent Developments, Challenges, and Perspectives.

Polyoxometalate (POM)-based metal–organic framework (MOF) materials contain POM units and generally generate MOF materials with open networks. POM-based MOF materials, which utilize the advantages of both POMs and MOFs, have received increasing attention, and much effort has been devoted to their preparation and relevant applications over the past few decades. They have good prospects in catalysis owing to the electronic and physical properties of POMs that are tunable by varying constituent elements. In this review, we present recent developments in porous POM-based MOF materials, including their classification, synthesis strategies, and applications, especially in the field of catalysis.

Recent advances in porous polyoxometalate-based metal-organic framework materials.

Polyoxometalates (POMs) are a subset of metal oxides with unique physical and chemical properties, which can be reliably modified through various techniques and methods to develop sophisticated materials and devices. In parallel with the large number of new crystal structures reported in the literature, the application of these POMs towards multifunctional materials has attracted considerable attention. This critical review summarizes recent progress on POM-based molecular and composite materials, and particularly highlights the emerging areas that are closely related to surface, electronic, energy, environment, life science, etc. (171 references).

Recent advances on polyoxometalate-based molecular and composite materials

The design of artificial catalysts able to compete with the catalytic proficiency of enzymes is an intense subject of research. Non-covalent interactions are thought to be involved in several properties of enzymatic catalysis, notably (i) the confinement of the substrates and the active site within a catalytic pocket, (ii) the creation of a hydrophobic pocket in water, (iii) self-replication properties and (iv) allosteric properties. The origins of the enhanced rates and high catalytic selectivities associated with these properties are still a matter of debate. Stabilisation of the transition state and favourable conformations of the active site and the product(s) are probably part of the answer. We present here artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes.

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Supramolecular catalysis. Part 2: artificial enzyme mimics

A “smart” core–shell complex is designed to combine a catalytic reaction and automatic separation through remote light control. Here, we present the induced amphiphilic behavior of a surfactant-encapsulated polyoxometalate complex with photoresponsive azobenzene units on the periphery. The reversible phase transfer of the complex shuttle between two incompatible phase termini, driven by a photoisomerization-induced polarity change, further facilitates the separation and recycle of the catalyst.

A photo-driven polyoxometalate complex shuttle and its homogeneous catalysis and heterogeneous separation.

A type of interesting immobilized supramolecular catalysts based on surfactant-encapsulated polyoxometalates has been developed for oxidation reactions. Through a sol-gel process with tetraethyl orthosilicate, hydroxyl-terminated surfactant-encapsulated polyoxometalate complexes have been covalently and uniformly bound to a silica matrix with unchanged complex structure. The formed hybrid catalysts possess a defined hydrophobic nano-environment surrounding the inorganic clusters, which is conducive to compatibility between the polyoxometalate catalytic centres and organic substrates. The supramolecular synergy between substrate adsorption, reaction, and product desorption during the oxidation process has been found to have an obvious influence on the reaction kinetics, with the activity of the catalyst being greatly improved. The supramolecular catalysts performed effectively in the selective oxidation of several different kinds of organic compounds, such as alkenes, alcohols, and sulfides, and the main products were the corresponding epoxides, ketones, sulfoxides, and sulfones. More significantly, the catalyst could be easily recovered by simple filtration, and the catalytic activity was well retained for at least five cycles. Finally, the present strategy has proved to be a general route for the fabrication of supramolecular hybrid catalysts containing common polyoxometalates suitable for various purposes.

Surfactant-Encapsulated Polyoxometalates as Immobilized Supramolecular Catalysts for Highly Efficient and Selective Oxidation Reactions

silica microspheres, [ 6 ] and polymers, [ 7 ] as well as small molecules, [ 3 , 8 ] were used to induce aggregation and dispersion in solution in response to the light stimulus. However, the integration of the smart response with specialized functions in a single system still remains a challenge. Polyoxometalates (POMs) as a class of nanoscale inorganic polyanionic clusters possess versatile properties in catalysis, redox reactions, medicines, etc . [ 9 ] The surface modifi cation with organic cations through electrostatic interactions makes possible the ready integration of various additional functional properties into POMs, [ 10 ] in addition to the improvement of the solubility in weakly polar solvents and the structural stability for diverse chemical environments as well as the promotion of catalytic reaction effi ciency. [ 11 ] In contrast to that only giant POMs are found to show self-assembling behavior in water, [ 12 ] most of these surfactant-encapsulated POM (SEP) and covalent hybrid complexes can self-assemble in organic media and the states at which they exist are dominated by the nature of solvents, [ 11a , 13 ] the amphiphilicity and structure of surfactants, as well as the size and charge density of POMs. [ 14 ] Up to

Photo‐Responsive Self‐Assembly of an Azobenzene‐Ended Surfactant‐Encapsulated Polyoxometalate Complex for Modulating Catalytic Reactions

Managing the blues: Chiral heteropoly blues of achiral polyoxometalate clusters were created through an intermolecular interaction with a chiral organic compound Controllable chiroptical switching of the cluster complexes was possible through reversible photochromism of the polyoxometalates (see picture)

Chiral Heteropoly Blues and Controllable Switching of Achiral Polyoxometalate Clusters

A cationic dendritic molecule that has alkyl chains has been synthesized and employed to encapsulate anionic polyoxometalates through electrostatic interactions. The prepared surfactant-encapsulated polyoxometalate (SEP) complexes were used as building blocks to fabricate self-assemblies in solution and the solid state. Monodispersion, lamellar, and columnar assemblies of SEP complexes have been characterized in detail. With increasing the number of peripheral cationic dendrons on inorganic clusters, the SEPs undergo changes from globular assemblies to monodispersions in solution and from lamellar assemblies to hexagonal columnar structures in the solid state, depending on the amounts of cationic dendrons in the complexes. The structural evolvement was simulated through consideration of the size and shape of the cationic dendron and polyanionic clusters, and the experimental results are in good agreement with the interpretation of the simulations. The present research demonstrates a new kind of dendritic complex and provides a route for controlling their assembling states by simply alternating the number of cationic dendrons in the complexes.

Yizhan Wang

Papers

A photo-driven polyoxometalate complex shuttle and its homogeneous catalysis and heterogeneous separation.

Surfactant-Encapsulated Polyoxometalates as Immobilized Supramolecular Catalysts for Highly Efficient and Selective Oxidation Reactions

Photo‐Responsive Self‐Assembly of an Azobenzene‐Ended Surfactant‐Encapsulated Polyoxometalate Complex for Modulating Catalytic Reactions

Chiral Heteropoly Blues and Controllable Switching of Achiral Polyoxometalate Clusters

Self‐Assembly and Structural Evolvement of Polyoxometalate‐Anchored Dendron Complexes