中空型的Ag/Pd和Ag/Pt纳米立方的一锅合成及其光学性能表征

本文通过改进的多元醇法成功制备了尺寸可控、均一的立方形银纳米材料, 然后在不经过任何后处理的情况下通过置换反应一锅合成了中空型的银/钯(Ag/Pd)和银/铂(Ag/Pt)纳米立方体, 并用透射电子显微镜(TEM)和紫外可见吸收(UV-visible)光谱对所合成的Ag纳米立方和空心的Ag/Pd 和Ag/Pt纳米立方进行了表征。     

Fabrication of Rh based solid-solution bimetallic alloy nanoparticles with fully-tunable composition through femtosecond laser irradiation in aqueous solution

Many late transition binary alloy nanoparticles (NPs) have been fabricated through a wide variety of techniques. Various steps are involved in the fabrication of such NPs. Here, we used a simple and green route to fabricate solid-solution Rh–Pd and Rh–Pt bimetallic alloy NPs through femtosecond laser irradiation in a solution without any chemicals like reducing agents. X-ray diffraction (XRD) peaks of NPs obtained in the solutions with different ratios of Rh–Pd and Rh–Pt ions monotonically varied from the position of pure Rh to those of Pd and to Pt which respectively indicated that these NPs were alloy. Composition of fabricated NPs was fully tuned over the entire range of Rh_1?x –Pd _x , and Rh_1?x –Pt _x with varying the mixing ratio of metal ions in the solution. Studies of Rh–Pd and Rh–Pt solid-solution system suggest that the alloy formation occurs through the nucleation of Rh and then followed by the diffusion of Rh, Pd and Rh, Pt to form a homogeneous alloy. The variety of average size of the alloy NPs for different compositions could be attributed to different reduction rate and surface energies of metal ions. Our result implies that femtosecond laser irradiation in aqueous solution is one of the potential methodologies to form multimetallic solid-solution alloy NPs with fully tunable composition.     

PdPt Nanocubes: A High‐Performance Catalyst for Hydrolytic Dehydrogenation of Ammonia Borane

An effective way to improve the catalytic activity of metal‐based nanostructured materials is to control the size, shape, or composition. Here, the bimetallic PdPt nanoparticles (NPs) show significant dependency on the shape for catalytic hydrolysis of ammonia borane. The catalytic activity of PdPt cubic nanoparticles (cNPs) is found to be the best compared with the activities of spherical nanoparticles (sNPs) of Pd, Pt, and PdPt and cNPs of Pd under the same reaction conditions. The turnover frequency (50.02 min^?1) of PdPt cNPs for ammonia borane hydrolysis is among the values of the most active catalysts. This high catalytic performance of PdPt cNPs encourages the approach of shape and composition control for various catalytic applications.     

Structural optimization of Au–Pd bimetallic nanoparticles with improved particle swarm optimization method

Due to the dependence of the chemical and physical properties of the bimetallic nanoparticles(NPs) on their structures,a fundamental understanding of their structural characteristics is crucial for their syntheses and wide applications. In this article, a systematical atomic-level investigation of Au–Pd bimetallic NPs is conducted by using the improved particle swarm optimization(IPSO) with quantum correction Sutton–Chen potentials(Q-SC) at different Au/Pd ratios and different sizes. In the IPSO, the simulated annealing is introduced into the classical particle swarm optimization(PSO) to improve the effectiveness and reliability. In addition, the influences of initial structure, particle size and composition on structural stability and structural features are also studied. The simulation results reveal that the initial structures have little effects on the stable structures, but influence the converging rate greatly, and the convergence rate of the mixing initial structure is clearly faster than those of the core-shell and phase structures. We find that the Au–Pd NPs prefer the structures with Au-rich in the outer layers while Pd-rich in the inner ones. Especially, when the Au/Pd ratio is 6:4, the structure of the nanoparticle(NP) presents a standardized Pd_(core) Au_(shell) structure.     

复合空心立方银/金属纳米材料的制备及其SERS表征

本文用一锅法, 以立方银纳米材料为模板, 通过置换反应成功制备了空心的立方银/钯(Ag/Pd)、银/铂(Ag/Pt)和银/金(Ag/Au)纳米材料, 并将它们作为基底(以KSCN作为探针), 检测其SERS信号。     

Synthesis of bimetallic systems using replacement reactions

Series of bimetallic systems were prepared by replacement reactions and characterized by XRD and XPS. The results suggest that the ad-metals are monolayer dispersed on the surface of sub-metal in Pd(Pt, Cu)/Co(Ni) systems, while in Pd(Pt, Au)/Cu systems surface solid solution is formed. In Ag(Au)/Co(Ni) and Ag/Cu systems no interaction between the metals is observed just as in the simple mixture of the respective crystallites. The outermost electronic configurations, the atomic radius of the metals, and the low-preparation temperature seem to be important factors for the different states of these bimetallic catalysts.     

Multi-component electrocatalyst for low-temperature fuel cells synthesized via sonochemical reactions

This review presents recent advances in multi-component electrocatalysts for low-temperature fuel cells (FCs) synthesized via sonochemical reactions. As a feasible approach to develop novel electrocatalysts that can overcome the many problems of the prevailing Pt electrocatalysts, Pt- or Pd-based alloy and core–shell M@Pt nanoparticles (NPs) have been pursued. Synthesizing NPs with desirable properties often turn out to be challenging. Sonochemistry generates extreme conditions via acoustic cavitation, which have been utilized in the syntheses of various Pt and Pd NPs and Pt- and Pd-based alloy NPs. Especially, it has been reported that several M@Pt core–shell NPs can be synthesized by sonochemistry, which is hard to achieve by other methods. The principles of sonochemistry are presented with examples. Also alloy NPs and core–shell NPs synthesized by sonochemistry and those by other methods are compared.     

Metal–Organic Framework Supported Palladium Nanoparticles: Applications and Mechanisms

Heterogeneous palladium (Pd)‐based catalysts are extensively applied to improve the catalytic performance and/or expand the reaction scope in many catalytic processes, involving the cross‐coupling, hydrogenation, reduction, and oxidation reactions. Among them, metal–organic framework (MOF)‐supported Pd nanoparticles (Pd NPs) are becoming the most popular one for their excellent catalytic performance and reusable property. To motivate the development of this technology, the applications of MOF‐supported Pd NPs (Pd NPs/MOFs) in heterogeneous catalysis are critically summarized herein, including the hydrogenation reduction of nitro‐ and polyunsaturated compounds, synthesis of carbon–carbon (C? C) bonds compounds, chromium (Cr(VI)) reduction, dehalogenation, alcohol oxidation, CO₂ conversion, and CO oxidation. The influences of base, solvents, electron character of substitutes, and type of halogen on the catalytic performance are comprehensively discussed. Finally, the application prospects of Pd NPs/MOFs and existing shortcomings in the catalytic field are proposed.     

One-step sonochemical syntheses of Ni@Pt core–shell nanoparticles with controlled shape and shell thickness for fuel cell electrocatalyst

We demonstrate a facile one-step method to synthesize Ni@Pt core–shell nanoparticles (NPs) with a control over the shape and the Pt-shell thickness of the NPs. By adjusting the relative reactivity of the Pt and Ni reagents in ultrasound-assisted polyol reactions, two Ni@Pt NP samples of the same composition (Ni/Pt = 1) and size (3–4 nm) but with different particle shape (octahedral vs. truncated octahedral) and different Pt-shell thicknesses (1–2 vs. 2–3 monolayer) are obtained. The control is achieved by using different Ni reagents, Ni(acac)₂ (acac = acetylacetonate) and Ni(hfac)₂ (hfac = hexafluoroacetylacetonate). A reaction mechanism that can explain all of the observations is proposed. The Ni@Pt NPs show up to threefold higher mass activity than pure Pt NPs in oxygen reduction reaction. Between the two Ni@Pt NP samples, the one composed of octahedral NPs with the thicker Pt-shell has higher activity than the other.     

C?H bond activation of ethylene by bare neutral palladium and platinum atoms: a theoretical investigation

The reactions of bare neutral palladium (Pd) and platinum (Pt) atoms with ethylene on both singlet and triplet surfaces were investigated at B3LYP and CCSD (T) levels of theory. The calculated potential energy profiles clearly show that Pt has higher reactivity than Pd toward ethylene. For both Pd and Pt, the reactions on singlet surfaces are energetically more favorable than those on triplet surfaces. However, notable barriers lie on the singlet and triplet surfaces for Pd +ethylene. This result rationalizes the experimental observation that Pd mainly forms π‐complex with ethylene. But under high‐energy condition, the reaction can proceed to yield dehydrogenation products, Pd‐CCH. and Pd (HCCH). For Pt, triplet‐singlet surface crossing was suggested to occur in the region where Pt forms π‐complex with ethylene to lead the reactions to the energetically more favorable singlet surfaces. For both the two metals, π‐complex and C? H bond insertion species are the reaction intermediates and the H.‐elimination products are the final products. Copyright © 2010 John Wiley & Sons, Ltd.     

Engineering Multifunctional Gold Decorated Dendritic Mesoporous Silica/Tantalum Oxide Nanoparticles for Intraperitoneal Tumor‐Specific Delivery

Nonspecific high‐energy radiation for treatment of metastatic ovarian cancer is limited by damage to healthy organs, which can be mitigated by the use of radiosensitizers and image‐guided radiotherapy. Gold (Au) and tantalum oxide (TaO_x) nanoparticles (NPs), by virtue of their high atomic numbers, find utility in the design of bimetallic NP systems capable of high‐contrast computed tomography (CT) imaging as well as a potential radiosensitizing effect. These two radio‐dense metals are integrated into dendritic mesoporous silica NPs (dMSNs) with radial porous channels for high surface‐area loading of therapeutic agents. This approach results in stable, monodispersed dMSNs with a uniform distribution of Au on the surface and TaO_x in the core that exhibits CT attenuation up to seven times greater than iodine or monometallic dMSNs without either TaO_x or Au. Tumor targeting is assessed in a metastatic ovarian cancer mouse model. Ex vivo micro‐CT imaging of collected tumors shows that these NPs not only accumulate at tumor sites but also penetrate inside tumor tissues. This study demonstrates that after intraperitoneal administration, rationally designed bimetallic NPs can simultaneously serve as targeted contrast agents for imaging tumors and to enhance radiation therapy in metastatic ovarian cancer.     

Novel synthesis, structure and catalysis of inverted core/shell structured Pd/Pt bimetallic nanoclusters

The catalytic properties of Pd-core/Pt-shell (inverted core/shell) structured bimetallic nanoclusters, synthesized by a successive addition method using sacrificial hydrogen, were investigated for hydrogenation of methyl acrylate. Partial deposition of Pt atoms on the surface of Pd nanoclusters can enhance the catalytic activity of the Pd atoms remaining in the surface of the inverted core/shell structured Pd/Pt bimetallic nanoclusters. Received 29 November 2000     

Nucleation and Growth of Magnetron-Sputtered Ag Nanoparticles as Witnessed by Time-Resolved Small Angle X-Ray Scattering

Kinetic aspects of the synthesis of Ag nanoparticles (NPs) by magnetron sputtering are studied by in situ and time-resolved small angle X-ray scattering (SAXS). Part of the NPs are found to become confined within a capture zone at 1–10 mm from the surface of the target and circumscribed by the plasma ring. Three regimes of the NP growth are identified: 1) early growth at which the average NP diameter rapidly increases to 90 nm; 2) cycling instabilities at which the SAXS signal periodically fluctuates either due to expelling of large NPs from the capture zone or due to the axial rotation of the NP cloud; and 3) steady-state synthesis at which stable synthesis of the NPs is achieved. The NP confinement within the capture zone is driven by the balance of forces, the electrostatic force being dominant. On reaching the critical size, large NPs acquire an excessive charge and become expelled from the capture zone via the electrostatic interactions. As a result, significant NP deposits are formed on the inner walls of the aggregation chamber as well as in the central area of the target.     

Near‐field optical enhancement by lead‐sulfide quantum dots and metallic nanoparticles for SERS

There is a growing interest in using quantum dots (QDs) and metallic nanoparticles (NPs), both for luminescence enhancement and surface‐enhanced Raman scattering (SERS). Here, we study the electromagnetic‐field enhancement that can be generated by lead‐sulfide (PbS) QDs using three‐dimensional finite‐element simulations. We investigate the field enhancement associated with combinations of PbS QDs with metallic NPs and substrates. The results show that high field enhancement can be achieved by combining PbS QDs with metallic NPs of larger sizes. The ideal size for Ag NPs is 25 nm, providing a SERS enhancement factor of ~5*10⁸ for light polarization parallel to the NP dimer axis and a gap of 0.6 nm. For Au NPs, the bigger the size, the higher is the field for the studied diameters, up to 50 nm. The near‐field values for PbS QDs above metallic substrates were found to be lower compared to the case of PbS QD‐metal NP dimers. This study provides the understanding for the design and application of QDs for the enhancement of near‐field phenomena. Copyright © 2013 John Wiley & Sons, Ltd.     

Liénard-type chemical oscillator

Using first-principles calculation, we have studied the properties of a series of M _x Co_1?x /Co(0001) (M = Pd, Pt) bimetallic surface alloys with atom M ratios from 0.25 to 1.0, then the effect of alloyed M metal on the properties of S adsorbed on these surfaces are discussed. Our calculations show that the alloying of metal Pd, Pt on Co(0001) weakens the S-M (M = Pd, Pt, Co) bond strength compared to monometallic surfaces and the site preference of sulfur atom is dependent on the alloyed metal M and its surface concentration. Moreover, bimetallic surface electronic structure modifications with and without sulfur are analyzed in comparison with clean Co(0001), and the correlation between the sulfur adsorption energy and the bimetallic surface d-band center is presented.     

Imaging the Hydrated Microbe‐Metal Interface Using Nanoscale Spectrum Imaging

PdAu nanocrystals are synthesised by Geobacter sulfurreducens, a dissimilatory metal‐reducing bacterium, and the resulting bimetallic nanocrystal‐decorated microbes are imaged using a range of advanced electron microscopy techniques. Specifically, the first example of elemental mapping of fully hydrated biological nanostructures using scanning transmission electron microscope (STEM) energy dispersive X‐ray (EDX) spectrum imaging within an environmental liquid‐cell is reported. These results are combined with cryo‐TEM and ex situ STEM imaging and EDX analysis with the aim of better understanding microbial synthesis of bimetallic nanoparticles. It is demonstrated that although Au and Pd are colocalized across the cells, the population of nanoparticles produced is bimodal, containing ultrasmall alloyed nanocrystals with diameters <3 nm and significantly larger core‐shell structures (>200 nm in diameter) which show higher Pd contents and exhibit a Pd enriched shell only a few nanometers thick. The application of high‐resolution imaging techniques described here offers the potential to visualize the microbe‐metal interface during the bioproduction of a range of functional materials by microbial “green” synthesis routes, and also key interfaces underpinning globally relevant environmental processes (e.g., metal cycling).     

Systematic Control of Size and Morphology in the Synthesis of Gold Nanoparticles

The synthesis of gold nanoparticles (Au NPs) capped by poly(1‐vinylpyrrolidin‐2‐one (PVP, average  = 10 000 kDa) yields moderately dispersed (6–8.5 nm) product with limited morphological control while larger NPs (15–20 nm) are reliably prepared using trisodium citrate (Na₃Cit) as a reductant/capping agent. Excellent size control in the intermediate 10 nm regime is achieved by hybridizing these methodologies, with highly monodisperse, polycrystalline Au NPs forming. For a Na₃Cit:PVP:Au ratio of 3.5:3.5:1, anisotropic NPs with an aspect ratio of 1.8:1 suggest the systematic agglomeration of NP pairs. Enhanced control of NP morphology is allowed by the 1,2‐tetradecanediol reduction of Au^III in the presence of straight chain, molecular anti‐agglomerants. Last, ligand substitution is used to controllably grow preformed Au seeds. In spite of the extended growth phase used, the replacement of phosphine by 1‐pentadecylamine affords highly monodisperse, cuboidal NPs containing a single clearly visible twinning plane. The allowance of particle growth parallel to this close‐packed plane explains the remarkable particle morphology.     

The Cellular Interactions of PEGylated Gold Nanoparticles: Effect of PEGylation on Cellular Uptake and Cytotoxicity

Poly(ethylene glycol) (PEG) is frequently used to coat various medical nanoparticles (NPs). As PEG is known to minimize NP interactions with biological specimens, the question remains whether PEGylated NPs are intrinsically less toxic or whether this is caused by reduced NP uptake. In the present work, the effect of gold NP PEGylation on uptake by three cell types is compared and evaluated the effect on cell viability, oxidative stress, cell morphology, and functionality using a multiparametric methodology. The data reveal that PEGylation affects cellular NP uptake in a cell‐type‐dependent manner and influences toxicity by different mechanisms. At similar intracellular NP numbers, PEGylated NPs are found to yield higher levels of cell death, mostly by induction of oxidative stress. These findings reveal that PEGylation significantly reduces NP uptake, but that at similar functional (= cell‐associated) NP levels, non‐PEGylated NPs are better tolerated by the cells.     

Synthesis of a Au‐on‐Pd Heteronanostructure Stabilized by Citrate and its Catalytic Application

The preparation of Au‐on‐Pd heteronanostructure (HNS) using citrate‐stabilized polycrystalline Pd nanoparticles (NPs) as the seeds is described. The resulting Au‐on‐Pd HNS is characterized and it is found that the formation of Au‐on‐Pd HNS depends greatly on a ratio between Pd seeds and AuCl₄^? ions added and the optimal molar ratio is 10:1. If fewer AuCl₄^? ions are added (Pd/Au ratio is 100:1), the growth of Au NPs only occurs on part of the Pd seeds’ surface. The addition of more AuCl₄^? ions (Pd/Au ratio is 5:1) hinders the growth of Au NPs on the Pd seeds’ surface. To demonstrate the catalytic performance, the electrochemistry oxidation of ethanol and the reduction of p‐nitrophenol by NaBH₄ are chosen to examine the catalytic activity of Au‐on‐Pd HNS. Pd seeds, Au NPs, and poly(vinyl pyrrolidone) (PVP)‐stabilized PdAu nanoalloy are used as the references for comparison. In the first reaction, the catalytic reactivity of Au‐on‐Pd HNS is better than that of corresponding pure Pd or Au NPs, while the opposite occurs for the latter reaction. The catalytic activity of Au‐on‐Pd HNS is much higher than that of PVP‐stabilized PdAu nanoalloy.     

SERS study of Ag nanoparticles electrodeposited on patterned TiO2 nanotube films

In this work, Ag nanoparticles (NPs) were deposited on patterned TiO₂ nanotube films through pulse‐current (PC) electrodeposition, and as a result patterned Ag NPs films were achieved. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X‐ray diffraction (XRD) were used, respectively, to study the morphology, uniformity, and phase structure of the patterned Ag NP films. The size and density of the as‐deposited Ag NPs could be controlled by changing the deposition charge density, and it was found that the patterned Ag NP films produced under a charge density of 2.0 C cm⁻² gave intense UV–vis and Raman peaks. Two‐dimensional surface‐enhanced Raman scattering (SERS) mapping of rhodamine 6G (R6G) on the patterned Ag NP films demonstrated a high‐throughput, localized molecular adsorption and micropatterned SERS effect. Copyright © 2010 John Wiley & Sons, Ltd.