Dendrimer-Encapsulated Nanoparticles: New Synthetic and Characterization Methods and Catalytic Applications

In this article we describe the synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles (DENs). These materials are synthesized using a template approach in which metal ions are extracted into the interior of dendrimers and then subsequently reduced chemically to yield nearly size-monodisperse particles having diameters in the 1-2 nm range. Monometallic, bimetallic (alloy and core@shell), and semiconductor nanoparticles have been prepared by this route. The dendrimer component of these composites serves not only as a template for preparing the nanoparticle replica, but also as a stabilizer for the nanoparticle. In this perspective, we report on progress in the synthesis, characterization, and applications of these materials since our last review in 2005. Significant advances in the synthesis of core@shell DENs, characterization, and applications to homogeneous and heterogeneous catalysis (including electrocatalysis) are emphasized.U.S. Department of Energy, Office of Basic Energy Sciences DE-FG02-09ER16090U.S. National Science Foundation 0847957Robert A. Welch Foundation F-0032Chemistr

Selective Mono-Hydrogenation of Polyunsaturated Hydrocarbons: Traditional and Nanoscale Catalysis

Selective hydrogenation of olefins is an important process in both chemical and pharmaceutical industries. This chapter reviews intriguing catalytic studies accomplished by employing a variety of catalysts such as metal complexes, supported materials, supported metal complexes, and nanosized materials for polyene hydrogenation. In addition, new research area involving unsupported colloidal nanoparticle catalysts, which exhibit an excellent activity and selectivity toward the polyene hydrogenation is introduced. The high activity of colloidal metal nanoparticle catalysts often allows the reactions to be completed under mild conditions, at atmospheric pressure, and room temperature. These colloidal nanoparticle catalysts also offer an advantage of facile separation and multiple recycling without significant losses in activity and selectivity. This chapter provides important fundamental understandings on the influence of chemical environments (solvents, ligands, dopants, etc.) and compositions (metal complex, metals, alloys, etc.) toward the catalytic activity and selectivity of various catalysts in homogeneous, heterogeneous, and semi-heterogeneous conditions. The systematic evaluation discussed in this chapter would pave a way to further develop chemo-, regio-, and stereo-selective catalysts for polyene hydrogenation

Gold, Palladium and Mesoporous Oxide-based Nanocatalysts for redox processes and sustainable catalysis : synthesis and catalytic evaluation

Abstract: Transition metals' exceptional ability and properties at the nanoscale level transcend their corresponding bulk metals in chemical transformation both in the laboratories and the industries. However, the nanoparticles are prone to particle growth and agglomeration at this nanoscale state, inhibiting their excellent performance and compromising their uniqueness. Hence, the stability of the particles presents a significant factor in governing their innovative attributes. Therefore, organic polymers, such as polyvinylpyrrolidone (PVP) and dendrimer, were considerably employed as soft templates to ensure stability and prevent the agglomeration of these nanoparticles in a homogeneous phase. These synthesized nanoparticles include AuPVP, PdPVP, AuPdPVP nanoparticles, and CuDENs. Although conventional homogeneous catalysts possess a vast tendency to enhance high conversion and product selectivity in chemical reactions, nevertheless, they present limiting phenomenon of recoverability, recyclability, and deactivation at high temperatures. Therefore, to circumvent these limitations, we fabricated metal nanoparticles through the dispersion of metals onto an insoluble and solid mesoporous silica and metal oxide support by adapting a dual templating approach, followed by a galvanic replacement protocol. In addition, inverse micelle, sol-gel, and wet impregnation methods were also employed to design ideal heterogeneous catalysts such as Cun@SiO2, Au@SiO2, Pd@SiO2, CoMMO, and MnMMO, which are capable of high operating procedures, easy recoverability, and reusability for oxidation and reduction reactions. Different analytical techniques were used to characterize and obtain the properties of these catalysts. These techniques include nitrogen sorption with Brunauer-Emmett-Teller (BET) and Barret-Joyner-Halenda (BJH) to examine the surface area, pore size, and pore volume distribution, high-resolution transmission electron microscopy (H-TEM) for internal morphologies, powder X-ray diffraction (p-XRD), for the diffraction patterns of the materials. While thermogravimetric analysis (TG) was performed to determine the sample’s thermal stability, Fourier transform infrared spectroscopy (FT-IR) identified the specific functional groups present. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) obtained the surface morphologies and identification of metal composition. In addition, hydrogen-temperature programmed reduction (H2-TPR) was used to examine the reducibility of the catalyst...Ph.D. (Chemistry

Influence of morphology in the catalytic activity of bioconjugated platinum nanostructures

Abstract: Platinum nanoparticles stabilized by a protein, bovine serum albumin, have been synthesized successfully with two different morphologies such as cuboctahedra and nanorods. They have been characterized by the use of different techniques such as XPS, PCS, TEM, and STEM-HAADF. These nanoparticles have been applied as catalysts for the hydrogenation of allyl alcohol in an aqueous solution. A key finding of this article is the superior catalytic activity of the nanorods compared to the cuboctahedral particles. This difference in the catalytic activity was justified because of the variation in the amount of protein to stabilize the nanorods. A model for the nanorods and equations that describe the proportion of atoms in the different sites of the particle (face, vertex, edge, or interior) is used to calculate the percentage of atoms that are located on the nanorod surface. The stability of these particles as catalysts was also studied. The results showed that Pt nanorods and Pt cuboctahedra particles were degraded after 24 h of reactio

Leveraging Dendrimer Macromolecules for the Encapsulation and Stabilisation of Nano-Sized Ruthenium Catalysts: Evaluation of Catalytic Reaction Kinetics in the Reduction of Pollutants Organic Dyes, Oxidation of Alcohols and Alkenes as Well as Hydrogenation Reactions

Encapsulation of nano-sized metal catalysts within the dendrimers macromolecules’ frameworks has been well documented thus far. Dendrimers are described as symmetric, monodispersed macromolecules resembling a tree-like branched structure and have been utilised as both a template and stabilising agent for the fabrication of metal (noble and non-noble) nano-catalysts. For this purpose, different types of dendrimers can be employed. The use of dendrimers for metal catalysts stabilisation or encapsulation offers several advantages in catalysis. For example, the dendrimer template allows the synthesis of catalytically active monodispersed nanoparticles and the dendrimers template itself does not passivate the metal active atoms during the catalytic process. Additionally, dendrimers have the potential to act as a “vehicle” that can be leveraged for the fabrication of heterogeneous catalysts. For example, surface groups of the dendrimers can be functionalised to chemically link the dendrimer-encapsulated nanoparticles (DENs) with solid supports such as silica. A significant number of studies on the synthesis and catalytic evaluation of dendrimer-metal nanocomposite materials (e.g. Ruthenium-based) onvarious reactions can be found in the literature. This chapter, however, will particularly focus on the recent developments on the synthesis, characterisation and catalytic applications of dendrimer-derived (colloidal and supported) Ruthenium catalysts

Nanoparticle Building Blocks for Functional Structures

A major goal in material science is achieving a desired function using structures fabricated with designed building blocks. Advanced synthetic and self-assembly techniques allow various nanomaterials to become promising building blocks, providing the control of the interaction between building blocks. The unique properties of nanomaterials can be transferred to structured systems. Among nanomaterials, inorganic nanoparticles such as gold nanoparticles (AuNPs), magnetic particles, and quantum dots (QDs) provide useful physical properties stemming from their inorganic core, large surface areas, and oriented surface functionalities. My research has focused on fabricating functional systems using gold nanoparticles (AuNPs), manipulating the interaction between AuNPs, bio-entities, and small molecules. To construct complicated three-dimensional structures and embed functions, emulsion templates for the fabrication of the capsule structures and various supramolecular chemistry between AuNPs or AuNP and enzyme were employed. My research consisted of 2 approaches: first, through both the design of the monolayer at the molecular level and the emulsion template, (1) enzyme-immobilized microparticles having high immobilization efficiency and reusability were fabricated; (2) correlations between the mechanical properties of the AuNP monolayer film and the binding affinities between nanoparticle components were investigated; and (3) stable 100 nm sized nanoparticle-dendrimer hybrid capsules as a drug delivery carrier were fabricated and evaluated in vivo. Second, by encapsulating various hydrophobic catalysts in the hydrophobic pockets of the monolayer of water-soluble AuNPs, (4) water-soluble nanoreactors were developed. By incorporating host-guest elements on the surface of water-soluble nanoreactors, (5) artificial enzymes capable of catalyzing bio-orthogonal chemical reactions inside living cells which can be regulated by the addition of host or guest molecules were fabricated. As can be seen, engineering of the AuNP surface at the molecular level opens new avenues for the fabrication of numerous functional materials