新型晶须状氧化钛担载Au的CO催化氧化性能

从钛钾比较高的二钛酸钾晶须出发,通过离子交换和热处理等步骤制备了具有不同微观结构的晶须状TiO2,然后通过均相沉积-沉淀法在制得的TiO2上担载1%的Au.采用X射线衍射、扫描电镜、低温N2吸附-脱附及透射电镜等技术对催化剂样品进行了表征,并测定了其催化CO氧化反应性能.结果表明,600℃处理所得晶须状TiO2载体(T(600))具有丰富的介孔结构,比表面积为59 m2/g,平均孔径为11 nm,担载Au后其孔道结构保持良好,而800℃处理所得晶须状TiO2样品(T(800))孔结构完全坍塌,但仍保持纯锐钛矿晶型.在相同担载条件下Au/T(800)上的Au颗粒尺寸明显小于Au/T(600)上的,但两者催化CO氧化反应活性相差不大,CO完全转化温度分别为80和70℃,活性均比Au/P25的高.     

Synthesis and properties of silver and gold nanocomposites in poly-1-vinyl-1,2,4-triazole matrix

Novel multifunctional hybrid nanocomposites with silver and gold nanoparticles stabilized by original polymer matrix based on poly-1-vinyl-1,2,4-triazole were synthesized and studied using UV and IR spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The obtained nanocomposites comprise silver or gold nanoparticles of spherical and elliptical shape with size 3–20 nm and 1–10 nm, respectively.     

A novel hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on chitosan-graphene oxide/cysteamine-modified gold electrode

A novel strategy to fabricate a hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on chitosan-graphene oxide nanocomposites/cysteamine-modified gold (Au) electrode was reported. The chitosan-graphene oxide nanocomposites were first assembled on a cysteamine-modified Au electrode to produce chitosan-graphene oxide/cysteamine/Au electrode. Then Ag nanoparticles were electrodeposited on the modified Au electrode and formed Ag nanoparticles/chitosan-graphene oxide/cysteamine/Au electrode. The chitosan-graphene oxide nanocomposites and the electrodeposited Ag nanoparticles were characterized by atomic force microscopy and scanning electron microscopy. The results showed the Ag nanoparticles were uniformly dispersed on the chitosan-graphene oxide/cysteamine/Au electrode. The cyclic voltammagrams and amperometric method were used to evaluate electrocatalytic properties of the Ag nanoparticles/chitosan-graphene oxide/cysteamine/Au electrode. The results showed that the modified electrode displayed good electrocatalytic activity to the reduction of hydrogen peroxide with a detection limit of 0.7 μM hydrogen peroxide based on a signal-to-noise ratio of 3. The sensor has good reproducibility, wide linear range, and long-term stability.     

Ternary Ag/Polyaniline/Au nanocomposites: Preparation,characterization and electrochemical properties

Ternary Ag/Polyaniline/Au nanocomposites were synthesized successfully by immobilizing of Au nanoparticles (NPs) on the surface of Ag/Polyaniline (PANI) nanocomposites. Ag/PANI nanocomposites were prepared via in situ chemical polymerization of aniline in the presence of 4-aminothiophenol (4-ATP) capped silver colloidal NPs. Then, uniform gold (Au) NPs were assembled on the surface of resulted Ag/PANI nanocomposites through electrostatic interaction to get Ag/Polyaniline/Au nanocomposites. The nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), ultraviolet visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Moreover, Ag/PANI/Au nanocomposites were immobilized on the surface of a glassy carbon electrode and showed enhanced electrocatalytic activity for the reduction of H₂O₂ compared with Ag/PANI.     

Preparation and characterization of metal-chitosan nanocomposites

Various metal-chitosan nanocomposites were synthesized, including silver (Ag), gold (Au), platinum (Pt), and palladium (Pd) in aqueous solutions. Metal nanoparticles were formed by reduction of corresponding metal salts with NaBH4 in the presence of chitosan. And chitosan molecules adsorbing onto the surface of as-prepared metal nanoparticles formed the corresponding metal-chitosan nanocomposites. Transmission electron microscopy (TEM) images and UV-vis spectra of the nanocomposites revealed the presence of metal nanoparticles. Comparison of all the resulting particles size, it shows that silver nanoparticles are much larger than others (Au, Pt and Pd). In addition, the difference in particles size leads to develop different morphologies in the films cast from prepared metal-chitosan nanocomposites. Polarized optical microscopy (POM) images show a batonet-like structure for Ag-chitosan nanocomposites film, while for the films cast from other metal (Au, Pt, and Pd)-chitosan nanocomposites, some branched-like structures with a few differences among them were observed under POM observation.     

Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles

Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (St?ber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.     

Nanocomposite membranes containing positively polarized gold nanoparticles for facilitated olefin transport

Positively polarized gold nanoparticles have been demonstrated for use as stable olefin carriers for facilitated olefin transport membranes. The formation and size of gold nanoparticles stabilized by 4-dimethylaminopyridine (DMAP) were monitored using X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy. Nanocomposite membranes that deliver high separation performance for olefin/paraffin mixtures were prepared by dispersing gold nanoparticles stabilized by DMAP in a polymer matrix, poly(vinyl pyrrolidone) (PVP). X-ray photoelectron spectroscopy (XPS) and zeta potential measurements revealed that gold nanoparticles stabilized by DMAP exhibited a high positive polarity, which is responsible for the reversible interaction between the gold nanoparticles and olefin molecules. Compared to neat PVP membranes, the composite membranes consisting of PVP and the polarized gold nanoparticles showed stable and enhanced separation of olefin/paraffin mixtures.     

Sonochemical Processes and Formation of Gold Nanoparticles within Pores of Mesoporous Silica

Mesoporous silica with gold nanoparticles inside its pores was prepared by the soaking and ultrasound-induced reduction method. This new composite was characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and high-resolution transmission electron microscopy (HRTEM) techniques. The results showed that nearly spherical-shaped gold nanoparticles, with mean size in diameter of 5.2 nm, are located in the pores, most of which are less than 6 nm in diameter. The ultrasonic irradiation time dependence of optical absorption for the soaked porous solid sample, as suggested by the variation in absorbance at 310 and 544 nm, indicated the reduction of Au (III) ions, and the nucleation and aggregation of gold nanoparticles within pores of mesoporous silica. Additionally, the reaction rates estimated phenomenologically by the absorbance decay at 310 nm for both the porous sample and the corresponding soaking solution presented the enhancement of the sonochemical reduction rate of Au (III) ions within pores of mesoporous silica. It is assumed that the extensive liquid-solid interfacial zones in the pores, due to the high specific surface areas and great porosity of the mesoporous solid, are the major regions where the efficient sonochemical reduction induced by the cavitation takes place. Copyright 2001 Academic Press.     

Synthesis and characterization of polyethylene/clay–silica nanocomposites: A montmorillonite/silica‐hybrid‐supported catalyst and in situ polymerization

A novel approach to the preparation of polyethylene (PE) nanocomposites, with montmorillonite/silica hybrid (MT‐Si) supported catalyst, was developed. MT‐Si was prepared by depositing silica nanoparticles between galleries of the MT. A common zirconocene catalyst [bis(cyclopentadienyl)zirconium dichloride/methylaluminoxane] was fixed on the MT‐Si surface by a simple method. After ethylene polymerization, two classes of nanofillers (clay layers and silica nanoparticles) were dispersed concurrently in the PE matrix and PE/clay–silica nanocomposites were obtained. Exfoliation of the clay layers and dispersion of the silica nanoparticles were examined with transmission electron microscopy. Physical properties of the nanocomposites were characterized by tensile tests, dynamic mechanical analysis, and DSC. The nanocomposites with a low nanofiller loading (<10 wt %) exhibited good mechanical properties. The nanocomposite powder produced with the supported catalyst had a granular morphology and a high bulk density, typical of a heterogeneous catalyst system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 941–949, 2004     

Study of Aggregation of Gold Nanoparticles in Chitosan

In this work it is reported the synthesis of gold nanoparticles supported in situ in chitosan by solvated metal atom dispersion technique in order to study the inclusion of Au nanoparticles in the biopolymer matrix. To study their aggregation along time and compare with the synthesis of Au/2-propanol colloid by chemical liquid deposition technique. Studies of Au nanoparticles aggregation along time, supported nanoparticles and colloidal nanoparticles morphology were also carried out. The characterization of Au nanoparticles was performed by transmission electron microscopy, field-emission and scanning electron microscopy, infrared spectroscopy, X-ray diffraction, light scattering and ultraviolet–visible spectroscopy. Metal colloid showed fractal agglomeration type and delay time after the synthesis, the agglomeration size increased to flocculate. Au nanoparticles supported in chitosan showed the same shape as colloids and fractal aggregation was mostly distributed on the matrix.     

ABS/clay nanocomposites obtained by a solution technique: Influence of clay organic modifiers

Acrylonitrile-butadiene-styrene (ABS) polymer/clay nanocomposites were produced using an intercalation-adsorption technique from polymer in solution: polymer/clay suspensions were subjected to ultrasonic processing to increase the effectiveness of mixing. Several kinds of organically modified layered silicates (OMLS) were used to understand the influence of the surfactant nature on the intercalation-exfoliation mechanism. We show that only imidazolium-treated montmorillonite (DMHDIM-MMT) is stable at the processing temperature of 200 °C, used for hot-pressing, whereas alkyl-ammonium modified clays show significant degradation.The morphology of ABS based polymer nanocomposites prepared in this work was characterized by means of wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Dynamic-mechanical analysis (DMA) was used to determine the storage modulus and damping coefficient as a function of temperature, and to investigate the correlations between mechanical properties and morphology of the nanocomposites. The thermal stability was assessed by means of thermogravimetric analysis (TGA). DMA and TGA show that the nanocomposites based on imidazolium-modified clay out-perform the nanocomposites based on quaternary-ammonium-modified clays in terms of mechanical properties and thermal stability.     

Influence of borohydride concentration on the synthesized Au/graphene nanocomposites for direct borohydride fuel cell

Au/graphene nanocomposites are prepared via a one-pot chemical reduction process at room temperature, using graphene oxide (GO) and chloroauric acid (HAuCl₄) as precursors. The obtained Au/graphene nanocomposites are characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). TEM shows that the Au nanoparticles with size of approximately 8.7 nm disperse randomly on the surface of graphene. XPS confirms that the Au/graphene nanocomposites show a higher atomic percentage of C/O (6.3/1), in contrast to its precursor GO (2.2/1). Electrochemical studies reveal that the Au/graphene nanocomposites have electrochemically active surface area of 9.82 m² g^?1. Besides, the influence of borohydride concentration on the as-prepared Au/graphene nanocomposites is investigated in details by cyclic voltammetry, chronoamperometry, and chronopotentiometry. The results indicate that high concentration of borohydride can significantly improve the electrochemical performance of the Au/graphene catalyst.     

Aerosol assisted chemical vapor deposition using nanoparticle precursors: a route to nanocomposite thin films

Gold nanoparticle and gold/semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapor deposition (CVD). A preformed gold colloid in toluene was used as a precursor to deposit gold films onto silica glass. These nanoparticle films showed the characteristic plasmon absorption of Au nanoparticles at 537 nm, and scanning electron microscopic (SEM) imaging confirmed the presence of individual gold particles. Nanocomposite films were deposited from the colloid concurrently with conventional CVD precursors. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)(6)], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O(i)Pr)(4)]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. Titania/gold composite films were intensely colored and showed dichromism: blue in transmitted light and red in reflected light. They showed metal-like reflection spectra and plasmon absorption. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirmed the presence of metallic gold, and SEM imaging showed individual Au nanoparticles embedded in the films. X-ray diffraction detected crystalline gold in the composite films. This CVD technique can be readily extended to produce other nanocomposite films by varying the colloids and precursors used, and it offers a rapid, convenient route to nanoparticle and nanocomposite thin films.     

Effect of the synthesis temperature of porous carbon-metal oxide composites on the gold particle morphology

The state of gold deposited from a chloride solution on the surface of the porous magnetite-carbon composite obtained from modified birch saw dust at 400 and 800°C was studied by electron microscopy, X-ray photoelectron spectroscopy, and XRD analysis. The shape and size of the deposited gold crystallites depend on the synthesis temperature of the composite. The deposited gold crystallites were mainly ray-shaped at the synthesis temperature of 400°C and spheroid at 800°C.     

Surface modification of gold nanoparticles with polyhedral oligomeric silsesquioxane and incorporation within polymer matrices

A new approach to achieve polymer‐mediated gold ferromagnetic nanocomposites in a polyhedral oligomeric silsesquioxane (POSS)‐containing random copolymer matrix has been developed. Stable and narrow distributed gold nanoparticles modified by 3‐mercaptopropylisobutyl POSS to form Au‐POSS nanoparticles are prepared by two‐phase liquid‐liquid method. These Au‐POSS nanoparticles form partial particle aggregation by blending with poly(n‐butyl methacrylate) (PnBMA) homopolymer because of poor miscibility between Au‐POSS and PnBMA polymer matrix. The incorporation the POSS moiety into the PnBMA main chain as a random copolymer matrix displays well‐dispersed gold nanoparticles because the POSS‐POSS interaction enhances miscibility between gold nanoparticles and the PnBMA‐POSS copolymer matrix. This gold‐containing nanocomposite exhibits ferromagnetic phenomenon at room temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 811–819, 2009     

Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth

We report on the use of Neem (Azadirachta indica) leaf broth in the extracellular synthesis of pure metallic silver and gold nanoparticles and bimetallic Au/Ag nanoparticles. On treatment of aqueous solutions of silver nitrate and chloroauric acid with Neem leaf extract, the rapid formation of stable silver and gold nanoparticles at high concentrations is observed to occur. The silver and gold nanoparticles are polydisperse, with a large percentage of gold particles exhibiting an interesting flat, platelike morphology. Competitive reduction of Au3+ and Ag+ ions present simultaneously in solution during exposure to Neem leaf extract leads to the synthesis of bimetallic Au core-Ag shell nanoparticles in solution. Transmission electron microscopy revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core-shell structure. The rates of reduction of the metal ions by Neem leaf extract are much faster than those observed by us in our earlier studies using microorganisms such as fungi, highlighting the possibility that nanoparticle biological synthesis methodologies will achieve rates of synthesis comparable to those of chemical methods.     

Uniform arrays of gold nanoparticles with different surface roughness for surface enhanced Raman scattering

Uniform arrays of coarse and smooth gold nanoparticles with diameter about 130 nm were successfully synthesized through seed-mediated growth method, separately. Scanning and transmission electron microscopy (SEM and TEM) and X-ray diffraction (XRD) have been used to study the formation and structure of the nanocomposites. The high enhancement factor for surface-enhanced Raman scattering of coarse and smooth gold nanoparticles were estimated to be about 3.1 × 10⁶ and 2.0 × 10⁶, respectively. It is evident that the coarse gold nanostructures has higher influence factor than the smooth gold nanostructures. Therefore, these unique properties of the coarse Au nanoparticles appear to be very promising for applications as high-performance SERS substrates.     

Graphene oxide-based supramolecular hydrogels for making nanohybrid systems with Au nanoparticles

In the presence of a small amount of a proteinous amino acid (arginine/tryptophan/histidine) or a nucleoside (adenosine/guanosine/cytidine), graphene oxide (GO) forms supramolecular stable hydrogels. These hydrogels have been characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) analysis, Raman spectroscopy, and rheology. The morphology of the hydrogel reveals the presence of nanofibers and nanosheets. This suggests the supramolecular aggregation of GO in the presence of an amino acid/nucleoside. Rheological studies of arginine containing a GO-based hydrogel show a very high G' value (6.058 × 10(4) Pa), indicating the rigid, solid-like behavior of this gel. One of these hydrogels (GO-tryptophan) has been successfully utilized for the in situ synthesis and stabilization of Au nanoparticles (Au NPs) within the hydrogel matrix without the presence of any other external reducing and stabilizing agents to make Au NPs containing the GO-based nanohybrid material. The Au NPs containing the hybrid hydrogel has been characterized by using UV/vis spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). In this study, gold salt (Au(3+)) has been bioreduced by the tryptophan within the hydrogel. This is a facile "green chemical" method of preparing the GO-based nanohybrid material within the hydrogel matrix. The significance of this method is the in situ reduction of gold salt within the gel phase, and this helps to decorate the nascently formed Au NPs almost homogeneously and uniformly on the surface of the GO nanosheets within the gel matrix.     

Fe3O4/Polypyrrole/Au nanocomposites with core/shell/shell structure: synthesis, characterization, and their electrochemical properties

Uniform Fe3O4 nanospheres with a diameter of 100 nm were rapidly prepared using a microwave solvothermal method. Then Fe304/polypyrrole (PPy) composite nanospheres with well-defined core/shell structures were obtained through chemical oxidative polymerization of pyrrole in the presence of Fe3O4; the average thickness of the coating shell was about 25 nm. Furthermore, by means of electrostatic interactions, plentiful gold nanoparticles with a diameter of 15 nm were assembled on the surface of Fe3O4/PPy to get Fe3O4/PPy/Au core/shell/shell structure. The morphology, structure, and composition of the products were characterized by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), X-ray powder diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The resultant nanocomposites not only have the magnetism of Fe3O4 nanoparticles that make the nanocomposites easily controlled by an external magnetic field but also have the good conductivity and excellent electrochemical and catalytic properties of PPy and Au nanoparticles. Furthermore, the nanocomposites showed excellent electrocatalytic activities to biospecies such as ascorbic acid (AA).     

Catalysis with TiO2/gold nanocomposites. Effect of metal particle size on the Fermi level equilibration

Photoexcited semiconductor nanoparticles undergo charge equilibration when they are in contact with metal nanoparticles. Such a charge distribution has direct influence in dictating the energetics of the composite by shifting the Fermi level to more negative potentials. The transfer of electrons to Au nanoparticles has now been probed by exciting TiO(2) nanoparticles under steady-state and laser pulse excitation. Equilibration with the C(60)/C(60)(-) redox couple provides a means to determine the apparent Fermi level of the TiO(2)-Au composite system. The size-dependent shift in the apparent Fermi level of the TiO(2)-Au composite (20 mV for 8-nm diameter and 40 mV for 5-nm and 60 mV for 3-nm gold nanoparticles) shows the ability of Au nanoparticles to influence the energetics by improving the photoinduced charge separation. Isolation of individual charge-transfer steps from UV-excited TiO(2) --> Au --> C(60) has provided mechanistic and kinetic information on the role of metal in semiconductor-assisted photocatalysis and size-dependent catalytic activity of metal-semiconductor nanocomposites.