Manoj B. Gawande

Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis

The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications in catalysis. The synthesis part discusses numerous preparative protocols for Cu and Cu-based nanoparticles, whereas the application sections describe their utility as catalysts, including electrocatalysis, photocatalysis, and gas-phase catalysis. We believe this critical appraisal will provide necessary background information to further advance the applications of Cu-based nanostructured materials in catalysis.

Core–shell nanoparticles: synthesis and applications in catalysis and electrocatalysis

Core-shell nanoparticles (CSNs) are a class of nanostructured materials that have recently received increased attention owing to their interesting properties and broad range of applications in catalysis, biology, materials chemistry and sensors. By rationally tuning the cores as well as the shells of such materials, a range of core-shell nanoparticles can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems. Various synthetic methods for preparing different classes of CSNs, including the Stöber method, solvothermal method, one-pot synthetic method involving surfactants, etc., are briefly mentioned here. The roles of various classes of CSNs are exemplified for both catalytic and electrocatalytic applications, including oxidation, reduction, coupling reactions, etc.

Solvent‐Free and Catalysts‐Free Chemistry: A Benign Pathway to Sustainability

In the past decade, alternative benign organic methodologies have become an imperative part of organic syntheses and chemical reactions. The various new and innovative sustainable organic reactions and methodologies using no solvents or catalysts and employing alternative energy inputs such as microwaves, sonication, conventional and room temperature heating conditions, mechanochemical mixing, and high-speed ball milling are discussed in detail. Environmentally benign and pharmaceutically important reactions such as multicomponent, condensation, and Michael addition reactions; ring opening of epoxides; and oxidation and other significant organic reactions are discussed. An overview of benign reactions through solvent- and catalyst-free (SF-CF) chemistry and a critical perspective on emerging synergies between SF-CF organic reactions are discussed.

Role of mixed metal oxides in catalysis science—versatile applications in organic synthesis

A variety of mixed metal oxides (MMOs), containing alkali, alkaline, rare earth and noble metals, and their applications are presented. In this mini review, we summarize versatile applications of mixed metal oxides in organic synthesis. A variety of reactions such as reduction, oxidation, multicomponent, Mannich, alkylation, condensation, deprotection, cycloaddition, hydroxylation, dehydration, dehydrogenation, transesterification, reactions involving biomimetic oxygen-evolving catalysts and other important C–C bond forming reactions are well presented on the surface of mixed metal oxides under a variety of reaction conditions. The scope of MMOs in important organic reactions, industrial applications, and green chemistry and recent applications of MMOs are well presented in this review.

Magnetite-supported sulfonic acid: a retrievable nanocatalyst for the Ritter reaction and multicomponent reactions

Magnetite-sulfonic acid (Nanocat-Fe-OSO3H), prepared by the wet-impregnation method, serves as a magnetically retrievable sustainable catalyst for the Ritter and multicomponent reactions. The as synthesized catalyst can be used in several reaction cycles without any loss of activity.

Regio‐ and Chemoselective Reduction of Nitroarenes and Carbonyl Compounds over Recyclable Magnetic FerriteNickel Nanoparticles (Fe3O4Ni) by Using Glycerol as a Hydrogen Source

Reduction by magnetic nano-Fe(3)O(4)-Ni: a facile, simple and environmentally friendly hydrogen-transfer reaction that takes place over recyclable ferrite-nickel magnetic nanoparticles (Fe(3)O(4)-Ni) by using glycerol as hydrogen source allows aromatic amines and alcohols to be synthesized from the precursor nitroarenes and carbonyl compounds.

Fe3O4 (iron oxide)-supported nanocatalysts: synthesis, characterization and applications in coupling reactions

The use of magnetic nanoparticles as a solid support material for the development of magnetically retrievable catalytic systems has led to a dramatic expansion of their potential applications as they enable environmentally-friendly and sustainable catalytic processes. These quasi-homogeneous catalysts possess numerous benefits such as ease of isolation and separation from the desired reaction mixtures using an external magnet and excellent recyclability. Consequently, much effort has been directed towards the synthesis of magnetically isolable nano-sized particles by developing methods such as co-precipitation, thermal decomposition, microemulsion, hydrothermal techniques etc. Further, in order to render them suitable for catalytic applications, several protection strategies such as surfactant/polymer, silica and carbon coating of magnetic nanoparticles or embedding them in a matrix/support have been reported in the literature. This review focuses on the substantial progress made in the fabrication of nanostructured catalysts with special emphasis on the protection and functionalization of the magnetite nanoparticles (Fe3O4). Finally, considering the importance of coupling chemistry in the field of organic synthesis, a broad overview of the applications of these magnetite nanoparticle-based catalysts in several types of coupling reactions has been presented. The future of catalysis lies in the rational design and development of novel, highly active and recyclable nanocomposite catalysts which would eventually pave the pathway for the establishment of green and sustainable technologies.

Silica-nanosphere-based organic–inorganic hybrid nanomaterials: synthesis, functionalization and applications in catalysis

The design and development of organic–inorganic hybrid nanomaterials and their applications in catalysis – an important area in sustainable chemistry – have captivated the attention of several researchers worldwide, as they enable environmentally friendly and benign catalytic processes. In recent years, novel approaches have been adopted to design highly selective nanostructured catalysts by controlling the interaction between the active catalytic species and the support material. There are extensive reports wherein silica nanoparticles (NPs) have been employed as solid supports for the fabrication of organic–inorganic hybrid nanocatalysts, possessing several outstanding features such as high activity and selectivity, excellent stability, efficient recovery and recyclability. Moreover, such quasi-homogeneous catalytic systems are free from diffusion problems that are generally associated with bulk catalytic systems, as these NPs can be dispersed in a wide range of organic solvents, eventually facilitating the accessibility of the substrates to the metal centres. This review attempts to summarise recent progress in the development of hybrid materials based on silica NPs, with special emphasis on the various fabrication strategies employed in previously published reports. Furthermore, a broad overview of the applications of these heterogeneous nanocatalysts in numerous organic transformations, including oxidation, reduction, condensation, amination, coupling, polymerization, addition and many more, is presented. It is believed that the successful applications of such versatile nanocatalytic systems would play a key role in establishing sustainable technologies.

Magnetically recyclable magnetite–ceria (Nanocat-Fe-Ce) nanocatalyst – applications in multicomponent reactions under benign conditions

A novel magnetite nanoparticle-supported ceria catalyst (Nanocat-Fe-Ce) has been successfully prepared by a simple impregnation method and was characterized by XRD, SIMS, FEG-SEM-EDS, and TEM. The exact nature of Nanocat-Fe-Ce was confirmed by X-ray photoelectron spectroscopy and it is noted that CeO2 nanoparticles are supported on magnetite, with evidence of secondary ion mass spectrometry. Catalytic activity of the nano-catalyst was explored for the synthesis of dihydropyridines under benign conditions; a greener protocol is described that provides a simple and efficient method for the synthesis of functionalized 1,4-dihydropyridines using a recyclable nanocatalyst. Notably, 5.22 mol% of the catalyst is sufficient to catalyze the multicomponent reaction in ethanolic medium at room temperature. Importantly, the catalyst could be easily separated from the reaction mixture by using an external magnet and recycled several times without loss of activity.

The Rise of Magnetically Recyclable Nanocatalysts

Magnetic nanoparticles (MNPs) have attracted a great deal of interest in recent years, owing to their remarkably different and unique properties, which include a high surface area, easy recovery, and nanosize. The unique functional surface of MNPs allows the immobilization of homogeneous species, including metals, organoligands/organocatalysts, and N-heterocyclic carbenes (NHC). 2] Traditionally, in various catalytic processes, nanoparticles have been stabilized on the surface of various supports such as porous materials (e.g. silicates, zeolites, alumina, carbons, etc.), until recent developments in nanoscience and nanotechnology paved the way to the synthesis of magnetic nanocatalysts, which are often an excellent choice in heterogeneous catalysis. From a sustainable chemistry viewpoint, MNPs were initially employed as relevant alternatives to conventional inert supports, to facilitate catalyst separation and recovery using simple magnets. In this way, time-consuming and tedious filtration/separation/isolation protocols could be significantly simplified into a one/two-step method for the catalyst recovery and reuse (Scheme 1). Advances in the field of MNPs further expanded their potential into design of novel nanomaterials based on fundamental understanding. The design of MNPs involved a number of strategies such as surface modification, grafting, self-assembly, and nanocasting, which together offered significant new alternatives. These MNPs possess an important advantage compared to conventional supported systems: 1) versatility ; 2) ease and simplicity of separation; 3) improved catalyst reusability (more stable catalysts) and reduction of waste; 4) enhanced catalytic activities ; 5) different selectivities to products; 6) access to previously challenging chemistries (e.g. aqueous processes). 7] Various types of MNPs have also been developed in recent years for important catalytic applications. These include magnetite-supported organocatalysts, metal nanoparticles (Pd, Ni, Cu, Ni, Co, Au, etc.), NHC and chiral catalysts which have been extensively investigated in various organic transformations (Scheme 2 and 3). The advantages of these MNPs from the sustainable chemistry perspective are clear. Expensive and hardly reusable organoligands/organocatalysts can be