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

Interaction of DNA bases with silver nanoparticles: Assembly quantified through SPRS and SERS

Colloidal silver nanoparticles were prepared by reducing silver nitrate with sodium borohydride. The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported here describes the interaction between nanoscale silver particles and various DNA bases (adenine, guanine, cytosine, and thymine), which are used as molecular linkers because of their biological significance. In colloidal solutions, the color of silver nanoparticles may range from red to purple to orange to blue, depending on the degree of aggregation as well as the orientation of the individual particles within the aggregates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and absorption spectroscopy were used to characterize the assemblies. DNA base-induced differential silver nanoparticle aggregation was quantified from the peak separation (relates to color) of surface plasmon resonance spectroscopy (SPRS) and the signal intensity of surface-enhanced Raman scattering (SERS), which rationalize the extent of silver–nucleobase interactions. © 2008 Published by Elsevier Inc

Decoration of Carbon Nitride Surface with Bimetallic Nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via Galvanic Exchange for Hydrogen Evolution Reaction

Here, we propose the synthesis of AgPt, AgPd, and AgAu bimetallic nanoparticles (NPs) on a carbon nitride (C₃N₄) surface via a galvanic exchange technique for the hydrogen evolution reaction (HER). Prior to the synthesis of C₃N₄/AgPt, AgPd, and AgAu, Ag NPs were synthesized on a C₃N₄ surface. For the synthesis of Ag NPs, initially Ag⁺ ions were adsorbed and then reduced by NaBH₄ resulting in the decoration of Ag NPs. These Ag NPs were then subjected to galvanic exchange where sacrificial Ag was replaced by Pt²⁺, Pd²⁺, and Au³⁺ to fabricate AgPt, AgPd, and AgAu NPs. The galvanic exchange reaction occurs on a solid substrate, which favored slow exchange of Ag and resulted in the transformation of Ag into AgPt, AgPd, and AgAu alloys. The synthesized heterostructures were characterized with the help of PXRD, XPS, TEM, FESEM, and EDS techniques. All the materials were applied for hydrogen evolution using 0.5 M H₂SO₄ solution. C₃N₄/AgPt shows efficient electrocatalytic activity as it requires only −150 mV potential to attain current density of 10 mA/cm². Bimetallic catalysts synthesized through galvanic exchange proved very efficient as compared to monometallic C₃N₄/Ag

Exploitation of electrostatic field force for immobilization and catalytic reduction of o-nitrobenzoic acid to anthranilic acid on resin-bound silver nanocomposites

A new solid-phase catalyst has been designed and reported here for the catalytic reduction of o-nitrobenzoic acid to anthranilic acid. Electrostatic field force helps immobilization, in turn deposition of silver nanoparticles onto solid resin surfaces and reduction of o-nitrobenzoic acid through effective catalysis. While characterization of catalyst particles has been performed by different physical methods (XRD, XPS, SEM, TEM, and EDX) in a worthwhile fashion, selective reduction of o-nitrobenzoic acid has also been achieved conveniently (95%). Different thermodynamic parameters for the reduction reaction have been presented from varied experimental conditions. Novelty of this work lies with the catalytic efficiency of nanometer size silver particles immobilized solid-phase matrix for one step synthesis of anthranilic acid over bulk silver

Effect of bromide and chloride ions for the dissolution of colloidal gold

Gold organosol has been synthesized in toluene employing two-phase (water–toluene) extraction of AuCl4− followed by its reduction with sodium borohydride in presence of cationic surfactants with variable counter ions. The influence of the counterions of the phase transfer reagent and stabilizing ligand on the photochemical stability of the gold colloids in toluene has been investigated. The counterions of the surfactants, i.e. bromide or chloride ions at times generate the corresponding radicals under UV-irradiation, which oxidize the gold clusters. It is explored that photodiscoloration process is faster for bromide system as compared to chloride. The slower discoloration in presence of only chloride system has been explained in the light of electron affinity of chlorine and stability of chlorocomplex. The photodiscoloration is facilitated in chloroform. It has further been observed that HCl oxidizes the gold nanoparticles under ambient condition. Finally the thermal activation facilitates the oxidation process in presence of bromide ions

Dipole-dipole plasmon interactions in self-assembly of gold organosol induced by glutathione

Assemblies of gold nanoparticles in an organic medium have been synthesized to study the plasmon–plasmon interactions amongst the gold nanoparticles. A pH-sensitive biomolecule, glutathione (GSH), has been introduced as a molecular linker of the parent gold nanoparticles to obtain small nanoparticle aggregates. The optical spectra of gold nanoparticles shifted to the red region indicate dipole–dipole interactions in the gold particle assembly. The aggregates have been characterized by UV-Vis, FTIR, HRTEM and XRD techniques. A controlled method of aggregating gold nanoparticles in organic solvents has been achieved successfully under controlled pH conditions with different concentrations of the molecular linker, GSH. The pH dependent anchoring of GSH onto gold surfaces has been proved beyond doubt to bring about nanoparticle aggregation

Oxidation mechanism of thin Cu films: A gateway towards the formation of single oxide phase

Controlled thermal oxidations of thin copper films at relatively lower temperatures (up to 500°C) leading towards the formation of a single phase of copper oxide are investigated where the oxidation temperature, duration, oxygen partial pressure, film thickness and the crystallographic orientations play very crucial roles to significantly control the final phase of the copper oxide. Thin Cu films of thicknesses 100-1000 nm were deposited on glass and silicon substrates using the vacuum assisted thermal evaporation technique. Oxidations of those Cu films were performed at different temperatures for variable durations in air ambient as well as oxygen ambient conditions. Four probe resistivity measurement, x-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM) and x-ray photoemission spectroscopy (XPS) techniques have been used to characterize the oxide films. At a thermodynamic equilibrium, it has been observed that the oxide phase is solely determined by the oxidation temperature, however, the oxygen partial pressure can significantly alter this temperature range. In case of thermal oxidation in air, the initial oxidation of the copper films starts at about 150 °C, but a well ordered crystalline phase of the cuprous oxide (Cu2O) is observed only above 200 °C. However, the cupric oxide (CuO) phase starts to appear only above 320 °C. The details of the oxidation mechanism of the Cu film are explained with a probable schematic model in terms of thermal diffusion as well as the chemical reactivity

Dendrimerencapsulated nanoparticles: New synthetic and characterization methods and catalytic applications. Chem Sci 2011

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