Deposition of gold nanoparticles on silica spheres by electroless metal plating technique

A previously proposed method for metal deposition with silver [Kobayashi et al., Chem. Mater. 13 (2001) 1630] was extended to uniform deposition of gold nanoparticles on submicrometer-sized silica spheres. The present method consisted of three steps: (1) the adsorption of Sn(2+) ions took place on surface of silica particles, (2) Ag(+) ions added were reduced and simultaneously adsorbed to the surface, while Sn(2+) was oxidized to Sn(4+), and (3) Au(+) ions added were reduced and deposited on the Ag surface. TEM observation, X-ray diffractometry, and UV-vis absorption spectroscopy revealed that gold metal nanoparticles with an average particle size of 13 nm and a crystal size of 5.1 nm were formed on the silica spheres with a size of 273 nm at an Au concentration of 0.77 M.     

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile. Most importantly, the hollow bimetallic nanospheres (Au/Pt and Pd/Pt) obtained here exhibit an area of greater electrochemical activity than other Pt hollow or solid nanospheres. In addition, the approximately 6 nm hollow urchinlike Pt nanospheres can achieve a potential of up to 0.57 V for oxygen reduction, which is about 200 mV more positive than that obtained by using a approximately 6 nm Pt nanoparticle modified glassy carbon (GC) electrode. Rotating ring-disk electrode (RRDE) voltammetry demonstrates that approximately 6 nm hollow Pt nanospheres can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated H(2)SO(4) (0.5 M). Finally, compared to the approximately 6 nm Pt nanoparticle catalyst, the approximately 6 nm hollow urchinlike Pt nanosphere catalyst exhibits a superior electrocatalytic activity toward the methanol oxidation reaction at the same Pt loadings.     

Synthesis of Au, Au/Ag, Au/Pt and Au/Pd nanoparticles using the microwave-polyol method

Gold, Au/Ag, Au/Pt and Au/Pd bimetallic nanoparticles with varying mol fractions were synthesized in ethylene glycol and glycerol, using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It was found that bimetallic colloids of Au/Ag, Au/Pd and Au/Pt form an alloy either on co-reduction of respective metal ions or on mixing individual sols.     

Complex Langmuir-Blodgett films of SiO2 and ZnO nanoparticles with advantageous optical and photocatalytical properties

Multifunctional Langmuir-Blodgett (LB) films were fabricated on the surface of glass substrates using sol-gel derived ZnO and SiO2 particles. ZnO particles of 6 and 110 nm diameter were synthesized according to the methods of Meulenkamp and Seelig et al. (Meulenkamp, E. A. J. Phys. Chem. B 1998, 102, 5566; Seelig, E. W.; Tang, B.; Yamilov, A.; Cao, H.; Chang, R. P. H. Mater. Chem. Phys. 2003, 80, 257). Silica particles of 37 and 96 nm were prepared by the Stober method (Stober, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62). Alternate deposition of monoparticulate Langmuir films of SiO2 and ZnO nanoparticles provided complex (six- and nine-layered) LB films with both antireflective and photocatalytic properties. The LB films were investigated with scanning electron microscopy (morphology and structure) and UV-vis spectroscopy (optical properties and stability). The photocatalytic activity was measured by immersing the UV-irradiated films into an aqueous solution of Methyl Orange and following the photodegradation of the dye by optical spectroscopy. Adding ZnO particles to the silica films slightly lowered the antireflection property but ensured strong photocatalytic activity. Both the photocatalytic activity and antireflection properties were proved to be sensitive to the sequence of the silica and ZnO layers, with optimum properties in the case of nine-layered films with a repeated (SiO2-ZnO-ZnO) structure.     

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.     

Electrooxidation of Several Organic Compounds on Simply Prepared Metallic Nanoparticles: A Comparative Study

The electrooxidation of several fuel compounds was studied using metallic nanoparticles of Au, Pd, Pt, AuPd and AuPt synthesized by direct electrodeposition by applying a constant potential of ‐200 mV (vs. Ag/AgCl) to pencil graphite in an acidic medium. Scanning electron microscope (SEM) images and X‐ray diffraction (XRD) data show that monometallic (Au, Pd and Pt) and alloys of bimetallic nanoparticles of AuPd and AuPt have been formed. The catalytic performance of the prepared electrodes was investigated in a neutral medium (100 mM phosphate buffer, pH 7) by cyclic voltammetry. Amongst all fuels, the highest current densities were obtained by the electrooxidation of formic acid (ca. 9.8 mA cm^?2) and formaldehyde (ca. 9.7 mA cm^?2) on the AuPt catalyst.     

SnO2负载Au和M-Au(M=Pt,Pd)催化剂及其低温催化氧化CO性能

以SnO₂为载体, 采用沉积沉淀法(DP)、共沉淀法(CP)和浸渍法(IM)制备了金负载Au/SnO₂催化剂, 同时采用沉积沉淀法制备了M-Au/SnO₂(M=Pd, Pt)双金属负载催化剂. 通过X射线衍射(XRD)、BET比表面积测定、透射电镜(TEM)和X射线光电子能谱(XPS)等技术对样品进行表征, 并测定其对CO的催化活性. 结果表明: 与CP法和IM 法相比, DP法制备的Au/SnO₂-DP 催化剂, Au 颗粒(<5 nm)较小, 分布均匀; Au/SnO₂-DP 中的Au 是以金属态Au0存在, 而Au/SnO₂-CP 和Au/SnO₂-IM 中, 金以Au⁰和Au³⁺的混合价态存在, 在Au/SnO₂-DP和M-Au/SnO₂中的Au、Pt、Pd和SnO₂之间存在相互作用; Au/SnO₂-DP 催化性能明显优于Au/SnO₂-CP 和Au/SnO₂-IM. Au与Pt 和Pd的双金属复合催化剂催化活性明显提高. 不同方法制备Au/SnO₂催化活性的差别主要是由于Au颗粒大小和Au氧化态的不同而产生. 而M-Au/SnO₂活性提高, 可能是由于Au与Pt 和Pd之间的相互作用.     

Radiochemical neutron activation analysis for determination of Au,Ag, Pt and Pd in geological samples

A procedure for separation of Au, Ag, Pt, and Pd in geological samples has been developed. After irradiation, samples were fused with Na₂O₂ and silver was separated by filtering through a PbCl₂ filter in 4M nitric acid solution. Au, Pt and Pd were concentrated with rhodium and thiourea as rhodium sulfide and the separation process of these elements was carried out by a chromatographic method. Au, Pt and Pd were retained on a Dowex-1×8 anion column in 1M HCl. Pd was eluted from the column by using a mixture of 75% HCl acid-25% acetone. Au was eluted by using a mixture of 10% HCl-90% acetone. In the gold fraction, Pt was also determined through the photopeak of¹⁹⁹Au radionuclide (158 keV). The method was simple and rapid.     

Gold nanoparticles assembling on smooth silver spheres for surface-enhanced Raman spectroscopy

A simple and cost-effective chemical method was introduced to assemble gold (Au) nanoparticles on smooth silver (Ag) spheres for realizing surface-enhanced Raman scattering (SERS) enhancement by the replacement reaction between chloroauric acid and Ag spheres. In addition, the Ag-Au core-shell spheres were fabricated when a certain amount of chloroauric acid was used in the reaction solution. We found that the Ag particles decorated with small Au nanoparticles demonstrated the strongest SERS enhancement, while Ag-Au core-shell spheres showed the weakest enhancement.     

Absorption and scattering of light by Pt, Pd, Ag, and Au nanodisks: absolute cross sections and branching ratios

Localized surface plasmons (LSPs) of metallic nanoparticles decay either radiatively or via an electron-hole pair cascade. In this work, the authors have experimentally and theoretically explored the branching ratio of the radiative and nonradiative LSP decay channels for nanodisks of Ag, Au, Pt, and Pd, with diameters D ranging from 38 to 530 nm and height h=20 nm, supported on a fused silica substrate. The branching ratio for the two plasmon decay channels was obtained by measuring the absorption and scattering cross sections as a function of photon energy. The former was obtained from measured extinction and scattering coefficients, using an integrating sphere detector combined with particle density measurements obtained from scanning electron microscopy images of the nanoparticles. Partly angle-resolved measurements of the scattered light allowed the authors to clearly identify contributions from dipolar and higher plasmonic modes to the extinction, scattering, and absorption cross sections. Based on these experiments they find that absorption dominates the total scattering cross section in all the examined cases for small metallic nanodisks (D<100 nm). For D>100 nm absorption still dominates for Pt and Pd nanodisks, while scattering dominates for Au and Ag. A theoretical approach, where the metal disks are approximated as oblate spheroids, is used to account for the trends in the measured cross sections. The field problem is solved in the electrostatic limit. The spheroid is treated as an induced dipole for which the dipolar polarizability is calculated based on spheroid geometry and the (bulk) dielectric response function of the metal the spheroid consists of and the dielectric medium surrounding it. One might expect this model to be inappropriate for disks with D>100 nm since effects due to the retardation of the incoming field across the metallic nanodisk and contributions from higher plasmonic modes are neglected. However, this model describes quite well the energy dependence of the dipolar resonance, the full width at half maximum, and the total extinction cross section for all four metallic systems, even when 100相似文献   

Heteropolymetallic Architectures as Snapshots of Transmetallation Processes at Different Degrees of Transfer

Novel heteropolymetallic architectures have been built by integrating Pd, Au and Ag systems. The dinuclear [(CNC)(PPh₃)Pd-^G11M(PPh₃)](ClO₄) (^G11M=Au ( 3 ), Ag ( 4 ); CNC=2,6-diphenylpyridinate) and trinuclear [{(CNC)(PPh₃)Pd}₂^G11M](ClO₄) (^G11M=Au ( 6 ), Ag ( 5 )) complexes have been accessed or isolated. Structural and DFT characterization unveil striking interactions of one of the aryl groups of the CNC ligand(s) with the ^G11M center, suggesting these complexes constitute models of transmetallation processes. Further analyses allow to qualitatively order the degree of transfer, proving that Au promotes the highest one and also that Pd systems favor higher degrees than Pt. Consistently, Energy Decomposition Analysis calculations show that the interaction energies follow the order Pd−Au > Pt−Au > Pd−Ag > Pt−Ag. All these results offer potentially useful ideas for the design of bimetallic catalytic systems.     

Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy

Electrical properties of contacts formed between conducting polymers and noble metal nanoparticles have been examined using current-sensing atomic force microscopy (CS-AFM). Contacts formed between electrochemically prepared pi-conjugated polymer films such as polypyrrole (PPy), poly(3-methylthiophene) (P3MeT), as well as poly(3,4-ethylenedioxythiophene) (PEDOT) and noble metal nanoparticles including platinum (Pt), gold (Au), and silver (Ag) have been examined. The Pt nanoparticles were electrochemically deposited on a pre-coated PPy film surface by reducing a platinum precursor (PtCl62-) at a constant potential. Both current and scanning electron microscopic images of the film showed the presence of Pt islands. The Au and Ag nanoparticles were dispersed on the P3MeT and PEDOT film surfaces simply by dipping the polymer films into colloid solutions containing Au or Ag particles for specified periods (5 to approximately 10 min). The deposition of Au or Ag particles resulted from either their physical adsorption or chemical bonding between particles and the polymer surface depending on the polymer. When compared with PPy, P3MeT and PEDOT showed a stronger binding to Au or Ag nanoparticles when dipped in their colloidal solutions for the same period. This indicates that Au and Ag particles are predominantly linked with the sulfur atoms via chemical bonding. Of the two, PEDOT was more conductive at the sites where the particles are connected to the polymer. It appears that PEDOT has better aligned sulfur atoms on the surface and is strongly bonded to Au and Ag nanoparticles due to their strong affinity to gold and silver. The current-voltage curves obtained at the metal islands demonstrate that the contacts between these metal islands and polymers are ohmic.     

In situ facile loading of noble metal nanoparticles on polydopamine nanospheres via galvanic replacement reaction for multifunctional catalysis

Noble metal nanoparticles(Pd,Ag,Pt,Au) with small and relatively uniform sizes were loaded on polydopamine nanospheres through in situ galvanic replacement reaction in aqueous solution.No additional reductant,surfactant or organic solvent was needed.X-ray photoelectron spectroscopy results revealed that the amount of quinone increased,while the amount of phenolic hydroxyl decreased on PDA nanospheres,indicating that the galvanic displacement reaction occurred between catechol groups and noble metal ions.The as-prepared PDA/Pd exhibited high catalytic activity and excellent stability in styrene hydrogenation.Moreover,PDA spheres retains the photo-thermal effect to serve as a nano-sized heater to accelerate the catalytic reactions under near-infrared illumination.     

Trimetallic Au@PdPt core-shell nanoparticles with ultrathin PdPt skin as highly stable electrocatalysts for the oxygen reduction reaction in acid solution

To design efficient and low-cost core-shell electrocatalysts with an ultrathin platinum shell, the balance between platinum dosage and durability in acid solution is of great importance. In the present work, trimetallic Au@PdPt core-shell nanoparticles(NPs)with Pd/Pt molar ratios ranging from 0.31:1 to 4.20:1 were synthesized based on the Au catalytic reduction strategy and the subsequent metallic replacement reaction. When the Pd/Pt molar ratio is 1.19:1(designated as Au@Pd_(1.19) Pt_1 NPs), the superior electrochemical activity and stability were achieved for oxygen reduction reaction(ORR) in acid solution. Especially, the specific and mass activities of Au@Pd_(1.19) Pt_1 NPs are 1.31 and 6.09 times higher than those of commercial Pt/C catalyst. In addition, the Au@Pd_(1.19) Pt_1 NPs presented a good durability in acid solution. After 3000 potential cycles between 0.1 and 0.7 V(vs. Ag/AgCl), the oxygen reduction activity is almost unchanged. This study provides a simple strategy to synthesize highperformance trimetallic ORR electrocatalyst for fuel cells.     

A density functional theory approach to mushroom-like platinum clusters on palladium-shell over Au core nanoparticles for high electrocatalytic activity

Recently, it was found that Pt clusters deposited on Pd shell over Au core nanoparticles (Au@Pd@Pt NPs) exhibit unusually high electrocatalytic activity for the electro-oxidation of formic acid (P. P. Fang, S. Duan, et al., Chem. Sci., 2011, 2, 531-539). In an attempt to offer an explanation, we used here carbon monoxide (CO) as probed molecules, and applied density functional theory (DFT) to simulate the surface Raman spectra of CO at this core-shell-cluster NPs with a two monolayer thickness of Pd shell and various Pt cluster coverage. Our DFT results show that the calculated Pt coverage dependent spectra fit the experimental ones well only if the Pt clusters adopt a mushroom-like structure, while currently the island-like structure is the widely accepted model, which follows the Volmer-Weber growth mode. This result infers that there should be a new growth mode, i.e., the mushroom growth mode as proposed in the present work, for Au@Pd@Pt NPs. We suggest that such a mushroom-like structure may offer novel active sites, which accounts for the observed high electrocatalytic activity of Au@Pd@Pt NPs.     

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry

In this paper, we demonstrated an effective enviromentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen-metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine, without any label step. Furthermore, the cyclic voltammograms showed Pt NPs networks have good electrocatalytic ability for the reduction of O₂.     

From homogeneous dispersion to micelles-a molecular dynamics simulation on the compromise of the hydrophilic and hydrophobic effects of sodium dodecyl sulfate in aqueous solution

The structural and functional diversity of surfactant systems has attracted simulation works in atomistic, coarse grain, and mesoscopic models (Bandyopadhyay, S.; et al. Langmuir 2000, 16, 942; Senapati, S.; et al. J. Phys. Chem. B 2003, 107, 12906; Maiti, P. K.; et al. Langmuir 2002, 18, 1908; Srinivas, G.; et al. J. Phys. Chem. B 2004, 108, 8153; Groot, R. D.; et al. J. Chem. Phys. 1999, 110, 9739; Rekvig, L.; et al. Langmuir 2003, 19, 8195). However, atomistic models have suffered from their tremendous computational cost and are, so far, not able to simulate the structural behaviors in sufficient spatio-temporal scales (Shelley, J. C.; Shelley, M. Y. Curr. Opin. Colloid Interface Sci. 2000, 5, 101). The other two approaches are not microscopic enough to describe the configurations of the surfactants that determine their behaviors (Shelley and Shelley). In this study, we propose to simplify atomistic models based on the observation that the compromise of the hydrophilic and hydrophobic effects (Li, J.; Kwauk, M. Chem. Eng. Sci. 2003, 58, 521-535) and molecular structures of surfactants are the dominant factors shaping their structures in the systems. With this simplification, we are able to simulate with moderate computing cost the whole process of micelle formation from an initially uniform dispersion of sodium dodecyl sulfate (SDS) in aqueous solution. The resulting micelle structures are different from those predicted by atomistic simulations that started with a predefined micelle configuration at the same surfactant concentrations. However, if we use their initial micelle configuration, micelle structures the same as theirs are obtained. Analyses show that our results are more realistic and that the results of the atomistic simulations suffer from artificial initial conditions. Therefore, our model may serve as a reasonable simplification of atomistic models in terms of the general structure of micelles.     

Origin of bulklike structure and bond length disorder of Pt37 and Pt6Ru31 clusters on carbon: comparison of theory and experiment

We describe a theoretical analysis of the structures of self-organizing nanoparticles formed by Pt and Ru-Pt on carbon support. The calculations provide insights into the nature of these metal particle systems-ones of current interest for use as the electrocatalytic materials of direct oxidation fuel cells-and clarify complex behaviors noted in earlier experimental studies. With clusters deposited via metallo-organic Pt or PtRu(5) complexes, previous experiments [Nashner et al. J. Am. Chem. Soc. 1997, 119, 7760; Nashner et al. J. Am. Chem. Soc. 1998, 120, 8093; Frenkel et al. J. Phys. Chem. B 2001, 105, 12689] showed that the Pt and Pt-Ru based clusters are formed with fcc(111)-stacked cuboctahedral geometry and essentially bulklike metal-metal bond lengths, even for the smallest (few atom) nanoparticles for which the average coordination number is much smaller than that in the bulk, and that Pt in bimetallic [PtRu(5)] clusters segregates to the ambient surface of the supported nanoparticles. We explain these observations and characterize the cluster structures and bond length distributions using density functional theory calculations with graphite as a model for the support. The present study reveals the origin of the observed metal-metal bond length disorder, distinctively different for each system, and demonstrates the profound consequences that result from the cluster/carbon-support interactions and their key role in the structure and electronic properties of supported metallic nanoparticles.     

Thermodynamic considerations and computer simulations on the formation of core-shell nanoparticles under electrochemical conditions

We report on thermodynamic modeling and computer simulations on the electrochemical generation of metallic and bimetallic nanoparticles (NPs) by means of quenched molecular dynamics (QMD). The present results suggest that the spontaneous formation of core-shell NPs depends on several factors, i.e. size and shape of the core, chemical composition of the system, and under-/oversaturation conditions. Homo- and heteroatomic prototypical systems were considered. The former systems were Au and Pt. The latter were Ag(core)/Au(shell), Pt(core)/Au(shell), Au(core)/Ag(shell) and Au(core)/Pt(shell).     

The determination of gold,platinum, palladium and rhodium by atomic absorption spectrophotometry with an ultrasonic nebulizer and a multi-element high-intensity hollow-cathode lamp with selective modulation

The use of a multi-element high-intensity hollow-cathode lamp with selective modulation and a 2-MHz ultrasonic nebulizer for the determination of Au, Pt, Pd and Rh by atomic absorption spectroscopy is described. The sensitivities for the various elements in aqueous and organic media were studied. Only some organic solutions could be nebulized satisfactorily; a solution containing 95% acetone proved to be the best. For aqueous solutions, the detection limits (concn. giving 0.004 O.D.) were as follows: Au, 0.03 p.p.m.; Pd, 0.02 p.p.m.; Pt. 0.3 p.p.m.; and Rh, 0.09 p.p.m. For a 95% acetone solution the detection limits were: Au, 0.009 p.p.m.; Pd, 0.012 p.p.m.; Pt, 0.20 p.p.m. and Rh, 0.06 p.p.m. The coefficients of variation for aqueous and organic media were satisfactory.