Polymer Protected and Gel Immobilized Gold and Silver Nanoparticles in Catalysis

This mini-review is focused on preparation of polymer protected gold (AuNPs) and silver (AgNPs) nanoparticles that are immobilized on the surface of inorganic supporters and within hydrogel and/or cryogel matrices. A series of water soluble polymers such as poly(N-vinylpyrrolidone), poly(acrylic acid), branched polyethyleneimine, and amphoteric cryogel based on the copolymer of N,N-dimethylaminoethylmethacrylate and methacrylic acid poly(DMAEM-MAA) were used for reduction and stabilization of metal nanoparticles. The catalytic properties of polymer protected AuNPs and AgNPs were evaluated with respect to hydrogen peroxide decomposition, hydrogenation of 4-nitrophenol and oxidation of cyclohexane.     

Modulation of Fluorescence of a Terbium-Complex-Containing Polymer by Gold Nanoparticles through Energy Transfer

A terbium complex-containing polymer (P-Tb) is prepared via free radical polymerization in solution. The copolymer exhibits the characteristic fluorescence bands of Tb³⁺ complex as well as a strong and broad band at near 400 nm. The fluorescence of P-Tb can be modulated by gold nanoparticles, with the gradual addition of gold nanoparticles into the DMF/toluene solution of P-Tb. The intensity of the characteristic emissions steadily decreases whereas the broad band at ca. 400 nm experiences fluorescence enhancement. For the solid films of P-Tb with varied amount of gold nanoparticles, both the characteristic emissions and the broad band suffers fluorescence quenching. The absorption of gold nanoparticle solution exhibits a prominent red-shift upon addition of P-Tb, suggesting there exists strong binding between the Tb/β-diketone complexes and gold nanoparticles. It is thought that the energy transfer is the driving force for the change in fluorescence intensity; and, the difference in polymer chain conformation in solution and in the solid state leads to different fluorescence behaviors for solution and solid samples.     

Catalysis of Gold Nanoparticles Deposited on Metal Oxides

Gold in bulk is chemically inert and has often been regarded to be poorly active as a catalyst. However, when gold is small enough—with particle diameters below 10 nm—it turns out to be surprisingly active for many reactions, such as CO oxidation and propylene epoxidation. This is especially so at low temperatures. Here, a summary of the catalysis of Au nanoparticles deposited on base metal oxides is presented. The catalytic performance of Au is defined by three major factors: contact structure, support selection, and particle size, the first of which being the most important because the perimeter interfaces around Au particles act as the site for reaction.     

Catalysis by Gold Nanoparticles: Epoxidation of Propene

Supported nano-gold catalysts have attracted rapidly growing interest due to their potential applicability to various reactions of industrial and environmental significance. In this article, we focus on the advances related to the direct vapor-phase oxidation of propene to propene oxide in the presence of molecular oxygen and hydrogen over gold catalysts supported on Ti-incorporated silica materials prepared by different methods. The importance of catalyst preparation and pretreatment method, nature of support material, Au particle size and loading amount is emphasized. Possibilities to enhance the catalyst performance by using promoters and by silylation are also discussed.     

Organic Molecular Probes in Heterogeneous Catalysis. Hydrogenation of Norbornadiene on Gold

A few important examples are described to show that well-chosen molecular probes in organic reactions on heterogeneous catalysts can reveal much about the nature of the active sites and reaction mechanisms. This approach using norbornadiene in hydrogenation casts much light on the reasons why highly dispersed gold is an active selective catalyst. In the new polar mechanism, H₂ undergoes heterolytic fission in the very act of addition to adsorbed alkene, in contrast to the conventional Horiuti-Polanyi mechanism based on prior homolytic dissociation of H₂ on the metal surface.     

Biphasic Hydrogenation of Olefins by Functionalized Ionic Liquid‐Stabilized Palladium Nanoparticles

Palladium nanoparticles in the size range of 5–6 nm were prepared conveniently by reducing palladium(II) with atmospheric pressure hydrogen and stabilized by 2,2′‐dipyridylamine‐functionalized imidazolium cations according to our approach. The efficient catalytic conversion of cyclohexene into cyclohexane by the functionalized ionic liquid‐stabilized palladium nanoparticles has been performed under very mild hydrogen pressure (0.1 MPa) and at 35 °C. It was found that the concentration of palladium and the reaction temperature considerably affected the size and degree of aggregation of Pd nanoparticles in ionic liquid, which further changed the performance of the catalyst activity. The synthesized nanocatalysts can be recycled at least five times without any loss of the activity. Finally, the scope of substrates was also investigated. The excellent catalytic activity of the present system can be attributed to good stabilization and high dispersion of palladium nanoparticles.     

Extractant Assisted Synthesis of Polymer Stabilized Platinum and Palladium Metal Nanoparticles for Sensor Applications

Abstract

Extractant‐assisted synthesis of platinum and palladium polymer‐stabilized metal nanoparticles (PSMNP) was carried out for the first time. The synthesis included the following sequential steps: a) loading of extractant (tributyl‐phosphine oxide, TBPO) with the desired metal ion; b) preparation of a membrane “cocktail” by mixing a metal‐containing extractant, solution of the polymer (PVC or polysulfone) and plastisizer; c) membrane deposition and metal reduction inside the membrane (intermatrix synthesis of PSMNP) by using either a chemical or an electrochemical reduction technique. The electro conductivity of the resulting polymer‐metal nanocomposite membrane appeared by several orders of magnitude higher than that of the metal‐free polymer. The mass‐exchange properties of PSMNP‐containing membranes were shown to depend on both the type of the polymer and the membrane deposition technique.     

EDTA导致柠檬酸钠稳定的金纳米粒子的聚集与CTAB的解聚集作用

室温下用柠檬酸钠做保护剂,硼氢化钠作为还原剂制备粒径为4 nm的金溶液,并通过紫外-可见分光光度计(UV-Vis),原子力显微镜(AFM)对其进行表征和分析。在溶液中加入不同含量的乙二胺四乙酸二钠(EDTA),结果表明,EDTA可以使金纳米粒子形成聚集体,通过实验证明,十六烷基三甲基溴化铵(CTAB)对柠檬酸钠保护的金纳米聚集体有强烈的解聚集作用。     

Green Synthesis of Gold Nanoparticles in Pomegranate Seed Oil Stabilized Using Laser Ablation

In this paper, gold nanoparticles were synthesized in pomegranate seed oil using a laser ablation. The nano fluids were characterized using UV–Vis spectroscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. The nanoparticles were formed inside the pomegranate seed oil in spherical form, and the particle size ranged from 12 to 4 nm, and the gold nanoparticles were capped with COO^? of carboxylic acid groups of fatty acid in pomegranate seed oil.     

Effects of Reaction Parameters in Catalysis of Glycerol Oxidation by Citrate-Stabilized Gold Nanoparticles

Abstract  

This work describes a catalytic oxidation of glycerol using citrate-stabilized gold nanoparticles (citrate-AuNPs) having a mean diameter of 22 ± 3 nm. A careful product analysis was performed by mean of high-performance liquid chromatography, liquid chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. Effects of reaction temperature, oxygen pressure, catalyst and reactant concentration, and NaOH/glycerol molar ratio on glycerol conversion, and product yields were investigated. The glycerol conversion and glyceric acid yield were optimum when the oxidation was performed using 0.6 M glycerol and NaOH at 80 °C under 3 bar of O₂ pressure in the presence of 50 ppm citrate-AuNPs catalyst for 3 h.     

Magnetically Stabilized Bed for Selective Hydrogenation of Benzene

The characteristics of a magnetically stabilized bed (MSB) were studied by cold‐model experiments, using water as liquid phase, hydrogen as gas phase, and γ‐Fe₂O₃ magnetic powder as solid phase. The fluidized state of different bed positions was investigated by testing the transmissible laser current. Effects of magnetic field intensity and gas flow rate on layer expansion states of the MSB were analyzed by color diagrams. A Ru‐Zn‐B amorphous alloy was prepared by chemical reduction. Selective hydrogenation of benzene was carried out in the MSB by adjusting the contact time between the catalysts and reactants through variations of reaction temperature, magnetic field current, and liquid hourly space velocity.     

Ultrasensitive Electrochemiluminescence Immunoassay for Protein Specific Detection Based on Dendrimer-Encapsulated Gold Nanoparticles Labels

A sensitivity-enhanced electro chemiluminescence immunoassay (ECLIA) was fabricated by covalently immobilizing a monoclonal prostate specific antigen (PSA) antibody (anti-PSA, Ab2) and a luminophore (luminol) on dendrimer-encapsulated gold nanoparticles (Den/AuNPs) as electrochemiluminescence labels. The primary antibody was immobilized on Fe₃O₄@SiO₂ NP support, and the antibody-loaded Fe₃O₄@SiO₂ NP was placed onto an indium tin oxide working electrode in a home made electrochemiluminescence (ECL) cell. PSA and Ab2/Luminol/Den/AuNP was successively injected into the cell, and conjugated to form a sandwich-type immunocomplex. Under optimized experimental conditions, the proposed ECLIA provided a linear response range from 0.001 to 100.0 ng/mL with a low detection limit of 0.3 pg/mL. The PSA assay results in clinical serum samples were in good agreement with the commercially available electro chemiluminescence assay. The ECL immunosensor has the advantages of high sensitivity, specificity and stability and may be a promising technique for tumor marker detection.     

Catalytic Activity of Ruthenium Nanoparticles Supported on Carbon Nanotubes for Hydrogenation of Soybean Oil

Ruthenium catalysts supported on multiwalled carbon nanotubes (MCNTs) with different loadings (1% wt, 3% wt, 5% wt) were prepared by reduction with H₂ or NaBH₄ for selective hydrogenation of soybean oil at 338 K and initial pressure of 1.066 MPa. These catalysts were characterized using transmission electron microscopy (TEM), X-ray powder diffraction (XRD), N₂ adsorption–desorption, and H₂-temperature programmed desorption (TPD) techniques. Ru particles were dispersed more homogeneously on the surface of the nanotubes after being reduced with H₂ than with NaBH₄. The catalysts with 3% and 5% Ru loadings had higher hydrogenation activity. The NaBH₄-reduced catalyst had higher cis-isomer selectivity.     

Carbene Transfer – A New Pathway for Propargylic Esters in Gold Catalysis

Gold carbenes generated via 1,2‐migration of a propargylic ester group can be transferred over a tethered alkyne. The use of aromatic backbones leads after a 1,7‐carbene transfer to a benzyl‐stabilized carbene as intermediate. A 1,2‐shift of a methyl group delivers vinyl‐substituted β‐naphthol derivatives as the final products.

     

Gold Nanoparticles Stabilized by Task-Specific Oligomeric Ionic Liquid for Styrene Epoxidation Without Using VOCs as Solvent

An oligomer of ionic liquid containing imidazolium and disulfide groups, which is miscible with the ionic liquid of [Bmim]PF₆, was synthesized and used to stabilize gold nanoparticles. As such, epoxidation of styrene could be catalyzed by the oligomeric ionic liquid-stabilized gold nanoparticles in the nonvolatile [Bmim]PF₆ without using any VOC as solvent. Under optimum reaction conditions, a styrene conversion of 100% with the selectivity to styrene oxide of 90% was obtained.     

Interactions Between Gold Nanoparticles and Polymer Bearing 3-Styryl Thiophene Chromophores

The interactions between gold nanoparticles and a novel acrylate copolymer bearing 3-styryl thiophene chromophores were studied spectrally and electrochemically. The emission intensity of the polymer solution can be quenched by gold nanoparticles. Collisional quenching is likely the main mechanism for the deactivation process and heterogeneous electron transfer takes place in the process. For the solid polymer film, the presence of gold nanoparticles reduces the emission intensity of the single chromophore as well as the intensity of the excimers. Cyclic voltammetry (CV) investigations indicate that the polymer solution exhibits no oxidation wave. However, in the presence of gold nanoparticles, either by directly addition to the polymer solution or by deposition on the ITO electrode, the polymer solutions possess distinct CV oxidation peak(s), indicating that the gold nanoparticles may mediate the contact and enhance the electron transfer between the electrode and chromophores.     

Enhancement of the Antitumour Activity for the Synthesised Dodecylcysteine Surfactant using Gold Nanoparticles

In this paper, the surfactant dodecylcysteine hydrochloride was synthesised. The surface parameters of the synthesised surfactant were studied using a surface tension technique. The surface parameters show a good surface activity of the prepared surfactant in aqueous solution. The self-assembling behaviour of the synthesised surfactant comparing with that of cysteine compound on the prepared gold nanoparticles was confirmed using transmission electron microscope (TEM) measurements. The effect of self-assembling of this surfactant on the size of gold nanoparticles was studied using TEM images. The antitumour activity of the prepared surfactant without and with the gold nanoparticles was investigated. The results show that the antitumour activity of the prepared surfactant was enhanced with the presences of the gold nanoparticles.