AuPt Nanoparticles Research Articles

Design and synthesis of target-responsive hydrogel for portable visual quantitative detection of uranium with a microfluidic distance-based readout device

Due to uranium's increasing exploitation in nuclear energy and its toxicity to human health, it is of great significance to detect uranium contamination. In particular, development of a rapid, sensitive and portable method is important for personal health care for those who frequently come into contact with uranium ore mining or who investigate leaks at nuclear power plants. The most stable form of uranium in water is uranyl ion (UO22+). In this work, a UO22+ responsive smart hydrogel was designed and synthesized for rapid, portable, sensitive detection of UO22+. A UO22+ dependent DNAzyme complex composed of substrate strand and enzyme strand was utilized to crosslink DNA-grafted polyacrylamide chains to form a DNA hydrogel. Colorimetric analysis was achieved by encapsulating gold nanoparticles (AuNPs) in the DNAzyme-crosslinked hydrogel to indicate the concentration of UO22+. Without UO22+, the enzyme strand is not active. The presence of UO22+ in the sample activates the enzyme strand and triggers the cleavage of the substrate strand from the enzyme strand, thereby decreasing the density of crosslinkers and destabilizing the hydrogel, which then releases the encapsulated AuNPs. As low as 100nM UO22+ was visually detected by the naked eye. The target-responsive hydrogel was also demonstrated to be applicable in natural water spiked with UO22+. Furthermore, to avoid the visual errors caused by naked eye observation, a previously developed volumetric bar-chart chip (V-Chip) was used to quantitatively detect UO22+ concentrations in water by encapsulating Au-Pt nanoparticles in the hydrogel. The UO22+ concentrations were visually quantified from the travelling distance of ink-bar on the V-Chip. The method can be used for portable and quantitative detection of uranium in field applications without skilled operators and sophisticated instruments.

Optimum Alloying of Bimetallic Platinum-Gold Nanoparticles Used As an Efficient and Robust Counter Electrode Material of Dye-Sensitized Solar Cells

This study reports on the synthesis of bimetallic PtAu nanoparticles (NPs) on the transparent conducting oxide electrode by using dry plasma reduction under atmospheric pressure without using any toxic chemicals and at a low temperature, which are first employed as counter electrodes (CEs) for efficient dye-sensitized solar cells (DSCs). High resolution scanning electron microscopy (HRSEM) and x-ray photoelectron spectroscopy (XPS) are utilized for analyzing the morphology and the chemical composition of bimetallic PtAu NPs. The highest catalytic activity of the bimetallic PtAu NP CE is found through an optimization of the volume ratio of Au and Pt precursors used for synthesis of NPs. As a result, the highest electrocatalytic performance, which corresponds to the lowest charge transfer resistance of 0.88 Ω, is obtained at the Au and Pt precursor molar ratio of 1. The DSC employing Pt0.5Au0.5 alloy CE achieved a maximum efficiency of 8.0% among all cells under study. The efficiency is higher than those of 7.4%, and 0.1% for Pt NPs and Au NPs – based DSCs, respectively. The obtained results establish a base for the potential use of PtAu alloy CEs in efficient and robust DSCs.

Gold-Platinum Nanostructures Formed By Thermal Dewetting

Introduction Bimetallic core-shell nanoparticles, including Au-Pt nanoparticles (NPs), exhibit interesting electrocatalytic properties for fuel cell reactions.1 For this application, the ability to control the size of the NPs, as well as their composition and surface crystallinity, has been shown to be important to enhance the utilization efficiency of the catalysts.2 NP arrays have been previously achieved by fabrication methods such as “top-down” or “bottom-up” approaches, which typically involve lithography and self-assembly, respectively. Top-down methods are often costly and time consuming, while bottom-up methods suffer from poor long range (> µm) order. The present study has focused on the formation of bimetallic nanostructures on Ta templates, where the large surface energy difference between a metallic thin film (Au and Pt) and the air-formed oxide on the Ta surface cause the dewetting of a sputter-coated metallic film to form NPs. This approach has been previously used to form Au NPs of controllable size, with a linear relationship observed between the metal film thickness prior to dewetting and the NP diameter.3 Here, we have attempted to form useful Au/Pt nanostructures and the electrochemistry of these materials, formed using a range of fabrication conditions, will be discussed in detail. Methods and Results Solid-state dewetting of thin metal films on oxide substrates is a known method of fabricating metal NP arrays over relatively large dimensions (e.g., cm2) without requiring costly lithography processes.4,5 Recent work in our group has demonstrated the ability to form ordered Au NP arrays on Ta templates, which are covered by a thin, air-formed Ta oxide film. This was achieved by the sputter-deposition of a thin film (3-4 nm) of Au, followed by thermal annealing at 450 oC for 30 minutes.4 This method was then adapted to form Au-Pt nanostructures, where two metal films (3-4 nm each of Au and Pt) were sequentially sputtered (Au then Pt, or Pt then Au) on chemically polished Ta templates, and then thermally annealed at 450 oC or 600 oC for 90 minutes. These Au-Pt nanostructures were characterized by FESEM (field emission scanning electron microscopy) to determine the extent of dewetting. It was observed that higher annealing temperatures of 600 oC (well below the melting point of both Au and Pt) were needed to further dewet the thin metal films (Figure 1 (a) and (b)), as heating at 450 oC was only able to partially dewet these Au-Pt films (Figure 1 (c) and (d)). The electrochemical behaviour of these bimetallic nanostructures was investigated by cyclic voltammetry (CV) in 0.5 M H2SO4 solution and then compared to the response from the individual Au vs. Pt thin films. The CVs show that the bimetallic thin films (before annealing) exhibit characteristics of both metals, indicating that the second sputter-coated metal does not form a conformal coating on the first sputter-coated film. After annealing at 450 oC, the CVs exhibit only Au characteristics, regardless of the deposition sequence. This suggests that, regardless of the order of sputter-coating, Au is coating the Pt structures after thermal annealing (i.e., these are Pt@Au nanostructures), in contrast to the Pt enrichment observed at the surface of Au@Pt core-shell NPs, formed by the electrochemical reduction of ionic precursors in solution. The characteristics of the nanostructures were shown to be optimized by varying the fabrication conditions (film thickness and annealing conditions), which also aided in understanding the mechanism of dewetting of these thin bimetallic films. Acknowledgements We gratefully acknowledge financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC). References Luo, J.; Maye, M.M.; Kariuki, N.N.; Wang, L.; Njoki, P.; Lin, Y.; Schadt, M.; Naslund, H.R.; Zhong, C.J. Catal. Today. 2005, 17, 291-297.Ataee-Esfahani, H.; Wang, L.; Nemoto, Y.; Yamauchi, Y. Chem. Mater. 2010, 22, 6310-6318.Kojima, Y.; Kato, T. Nanotechnology . 2008, 19, 255605.El-Sayed, H. A.; Molero, H. M.; Birss, V. I. Nanotechnology. 2012, 23, 435602.Wang, D.; Schaff, P. J.Mater.Sci: Mater Electron. 2011, 22,1067-1070. Figure 1

고효율 염료감응형 태양전지를 위한 탄소나노튜브 기반 나노 하이브리드 상대전극

In this study, we present an excellent approach for easily and uniformly immobilizing Pt, Au and bimetallic PtAu nanoparticles (NPs) on a multi-walled carbon nanotube (MWNT)-coated layer through dry plasma reduction. The NPs are sta- bly and uniformly immobilized on the surface of MWNTs and the nanohybrid materials are applied to counter electrode (CE) of dye-sensitized solar cells (DSCs). The electrochemical properties of CEs are examined through cyclic voltammogram, electrochemical impedance spectroscopy, and Tafel measurements. As a result, both electrochemical catalytic activity and electrical conductivity are highest for PtAu/MWNT electrode. The DSC employing PtAu/MWNT CE exhibits power conversion efficiency of 7.9%. The efficiency is better than those of devices with MWNT (2.6%), AuNP/MWNT (2.7%) and PtNP/MWNT (7.5%) CEs.

Synthesis of Reduced Graphene Oxide-Supported PtAu Catalysts and Their Electrocatalytic Activity for Formic Acid Oxidation

In this paper, we demonstrate that, a one-pot synthesis of a reduced graphene oxide (RGO)-supported freely assembled binary alloy catalyst (PtAu/RGO) under alkaline conditions. The synthesized PtAu/RGO catalyst has been characterized by powder X-ray diffraction (pXRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). It was found that graphene oxide (GO) was successfully reduced to RGO and that the PtAu nanoparticles exhibited alloy structure about 3.60 ± 0.20 nm in diameter and uniformly distributed on RGO surface. Further, the electrocatalytic activity of the catalyst was examined toward formic acid (FA) oxidation, which exhibited better catalytic activity toward FA The electrocatalytic activity of PtAu/RGO (Pt mass loading: 20%) was examined with the solution of 0.1 M H2SO4 + 0.5 M HCOOH. The catalytic activity of PtAu/RGO was compared with the Pt/RGO (Pt mass loading: 20%) and commercial Pt/CB (Pt mass loading: 20%). Figure 1 shows that the linear sweep voltammograms of (a) Pt/RGO, (b) PtAu/RGO and (c) Pt/CB in 0.5 M HCOOH containing 0.1 M H2SO4 aqueous solution. It could be observed from the Fig. 5, two oxidation peaks can be clearly observed, the peak I is related to the direct oxidation of HCOOH to CO2, whereas the peak II is correspond to the oxidation of the COads generated from the dissociative adsorption step. The peak I current densities are in the order of PtAu/RGO > Pt/RGO > commercial Pt/CB, which indicates that the RGO can effectively enhance the activity of PtAu and Pt catalysts, which may be due to the strong interaction between PtAu or Pt NPs and RGO surface. In contrast, the peak II current densities are in the order of PtAu/RGO < Pt/RGO < commercial Pt/CB, indicating that the presence of RGO in PtAu/RGO hold back the formation of poisoning intermediate COadsduring the FA oxidation. Based on the present and previously reported results, it can be considered that the uniform distribution of NPs and electronic interaction between PtAu NPs and RGO could enhance the catalytic activity. To sum up, freely assembled PtAu/RGO nanocomposites were synthesized under alkaline conditions. On the basis of pXRD, TEM, STEM, XPS, the GO was converted to RGO and PtAu NPs were highly dispersed and uniformly distributed through out the surface. The PtAu/RGO catalyst exhibited higher catalytic activity for FA oxidation compared to the other catalysts Pt/RGO and commercial Pt/CB. This work provides a simple and fast approach to synthesize a novel RGO based catalyst with high electrocatalytic activity. Figure 1. Linear sweep voltammograms of (a) Pt/RGO, (b) PtAu/RGO and (c) Pt/CB in 0.5 M HCOOH containing Ar-saturated 0.1 M H2SO4 aqueous solution at 2000 rpm. Figure 1

Altered Cell Cycle Arrest by Multifunctional Drug-Loaded Enzymatically-Triggered Nanoparticles.

cRGD-targeting matrix metalloproteinase (MMP)-sensitive nanoparticles [PLGA-PEG1K-cRGD/PLGA-peptide-PEG5K (NPs-cRGD)] were successfully developed. Au-Pt(IV) nanoparticles, PTX, and ADR were encapsulated into NPs-RGD separately. The effects of the drug-loaded nanoparticles on the cell cycle were investigated. Here, we showed that higher cytotoxicity of drug-loaded nanoparticles was related to the cell cycle arrest, compared to that of free drugs. The NPs-cRGD studied here did not disrupt cell cycle progression. The cell cycle of Au-Pt(IV)@NPs-cRGD showed a main S phase arrest in all phases of the cell cycle phase, especially in G0/G1 phase. PTX@NPs-cRGD and ADR@NPs-cRGD showed a higher ratio of G2/M and S phase arrest than the free drugs, respectively. Cells in G0/G1 and S phases of the cell cycle had a higher uptake ratio of NPs-cRGD. A nutrient deprivation or an increase in the requirement of nutrients in tumor cells could promote the uptake of nanoparticles from the microenvironments. In vivo, NPs-cRGD could efficiently accumulate at tumor sites. The inhibition of tumor growth coupled with cell cycle arrest is in line with that in vitro. On the basis of our results, we propose that future studies on nanoparticle action mechanism should consider the cell cycle, which could be different from free drugs. Understanding the actions of cell cycle arrest could affect the application of nanomedicine in the clinic.

Electrochemical Cycling Induced Surface Segregation of AuPt Nanoparticles in HClO4 and H2SO4

The surface composition of bimetallic nanoparticles is critical to their electrochemical performance. The most effective existing approach for changing surface composition is the thermal treatment, which induces the surface segregation of the metal with low surface energy. Some studies have shown that the surface segregation in bimetallic nanoparticles may also occur under the electrochemical conditions. However, the effect of the electrolyte in this process has not been investigated. This article presents a comparative study on the difference between cycling AuPt nanoparticles in HClO4 and H2SO4. The nanoparticles were electrochemically cycled in Ar-saturated HClO4 and H2SO4 and the electrochemical surface composition of nanoparticles was analyzed by cyclic voltammetry method. The size evolution was investigated by transition electron microscope (TEM). Energy-dispersive X-ray spectroscopy (EDX) mapping analysis confirmed no phase separation on AuPt nanoparticles. It is found that cycling in H2SO4 shows higher degree of surface segregation of Au than doing same in HClO4. The enhanced surface segregation of Au is believed due to the stronger adsorption of bi-sulfate anions on Au. In addition, the cycled nanoparticles with various surface composition exhibited different activities toward electrooxidation of methanol. This work indicates that electrolytes may affect the surface segregation of bimetallic nanoparticles.

The preparation of large surface area lanthanum based perovskite supports for AuPt nanoparticles: tuning the glycerol oxidation reaction pathway by switching the perovskite B site.

Gold and gold alloys, in the form of supported nanoparticles, have been shown over the last three decades to be highly effective oxidation catalysts. Mixed metal oxide perovskites, with their high structural tolerance, are ideal for investigating how changes in the chemical composition of supports affect the catalysts' properties, while retaining similar surface areas, morphologies and metal co-ordinations. However, a significant disadvantage of using perovskites as supports is their high crystallinity and small surface area. We report the use of a supercritical carbon dioxide anti-solvent precipitation methodology to prepare large surface area lanthanum based perovskites, making the deposition of 1 wt% AuPt nanoparticles feasible. These catalysts were used for the selective oxidation of glycerol. By changing the elemental composition of the perovskite B site, we dramatically altered the reaction pathway between a sequential oxidation route to glyceric or tartronic acid and a dehydration reaction pathway to lactic acid. Selectivity profiles were correlated to reported oxygen adsorption capacities of the perovskite supports and also to changes in the AuPt nanoparticle morphologies. Extended time on line analysis using the best oxidation catalyst (AuPt/LaMnO3) produced an exceptionally high tartronic acid yield. LaMnO3 produced from alternative preparation methods was found to have lower activities, but gave comparable selectivity profiles to that produced using the supercritical carbon dioxide anti-solvent precipitation methodology.

Sensitive electrochemical detection of nitric oxide based on AuPt and reduced graphene oxide nanocomposites.

Since nitric oxide (NO) plays a critical role in many biological processes, its precise detection is essential toward an understanding of its specific functions. Here we report on a facile and environmentally compatible strategy for the construction of an electrochemical sensor based on reduced graphene oxide (rGO) and AuPt bimetallic nanoparticles. The prepared nanocomposites were further employed for the electroanalysis of NO using differential pulse voltammetry (DPV) and amperometric methods. The dependence of AuPt molar ratios on the electrochemical performance was investigated. Through the combination of the advantages of the high conductivity from rGO and highly electrocatalytic activity from AuPt bimetallic nanoparticles, the AuPt-rGO based NO sensor exhibited a high sensitivity of 7.35 μA μM(-1) and a low detection limit of 2.88 nM. Additionally, negligible interference from common ions or organic molecules was observed, and the AuPt-rGO modified electrode demonstrated excellent stability. Moreover, this optimized electrochemical sensor was practicable for efficiently monitoring the NO released from rat cardiac cells, which were stimulated by l-arginine (l-arg), showing that stressed cells generated over 10 times more NO than normal cells. The novel sensor developed in this study may have significant medical diagnostic applications for the prevention and monitoring of disease.

A sensitive electrochemiluminescent immunosensor based on 3D-flower-like MoS2microspheres and using AuPt nanoparticles for signal amplification

We herein report the synthesis of MoS2which was three-dimensional flower-like microspheres, and then the prepared GOx–AuPt and MoS2–luminol were applied in a sandwich-type ECL immunosensor for prostate-specific antigen detection.

Shape-controlled synthesis of porous AuPt nanoparticles and their superior electrocatalytic activity for oxygen reduction reaction

Control of structure and morphology of Pt-based nanomaterials is of great importance for electrochemical energy conversions. In this work, we report an efficient one-step synthesis of bimetallic porous AuPt nanoparticles (PAuPt NPs) in an aqueous solution. The proposed synthesis is performed by a simple stirring treatment of an aqueous reactive mixture including K2PtCl4, HAuCl4, Pluronic F127 and ascorbic acid at a pH value of 1 without organic solvent or high temperature. Due to their porous structure and bimetallic composition, as-made PAuPt NPs exhibit excellent electrocatalytic activity for oxygen reduction reaction.

Characterization of Au and Bimetallic PtAu Nanoparticles on PDDA-Graphene Sheets as Electrocatalysts for Formic Acid Oxidation.

Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20–50 and 5–10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°–3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

Electrocatalytic oxidation of small organic molecules on Pt-Au nanoparticles supported by POMAN-MWCNTs

Poly (o-methoxyaniline) and multi-wall carbon nanotube composite (POMAN-MWCNT) films were deposited onto the platinum (Pt) electrode surface by cyclic voltammetry (CV). Then, platinum and gold (Au) nano-particles were deposited by CV and the double potential deposition method to modify the composite film on the Pt electrode. The morphology of the composite film was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and its electrocatalytic activity toward methanol and formaldehyde oxidation was studied by CV and other electrochemical methods. The results demonstrated that Pt-Au/POMAN-MWCNTs obtained by the double potential deposition method had a much higher catalytic activity and better anti-poisoning property for electrooxidation of methanol and formaldehyde. The improved catalytic performance could be attributed to the uniformly distribution of duel-metal nanoparticles and the synergistic effect between Pt and Au metals. The abstract should briefly state the problem or purpose of the research, indicate the methodology used, summarize the principal findings and major conclusions.

Effect of ionic liquid on the synthesis and electrocatalytic property of platinum-based bimetallic nanoparticles

Because of their many distinct advantages, the application of ionic liquids (ILs) for the synthesis and tailoring of nanoscale metal catalysts represents a burgeoning direction in materials chemistry. We herein depict the using of ammonium dibutyl phosphate ([AD]PO4), an organic soluble ionic liquid as an additive for the synthesis of Pt-based nanoparticles at elevated temperature in oleylamine. The experimental results reveal that not only the size/morphology, but also the electrocatalytic property of the platinum (Pt)-based bimetallic nanoparticles could be significantly tuned by a small amount of ionic liquid added in the reaction systems. For the silver (Ag)-Pt bimetallic system, core-shell Ag-Pt nanoparticles with dense or dendritic Pt shells are obtained at IL/oleylamine volume ratio of 0.25/10 and 0.5/10, while for gold (Au)-Pt bimetalic system, although the tuning of IL on the size/morphology of the particles are not apparent, the core-shell Au-Pt nanoparticles synthesized at IL/oleylamine volume ratio of 0.5/20 exhibit superior catalytic activity and durability for methanol oxidation reaction (MOR), compared to those prepared at other volume ratios. (C) 2015 Elsevier B.V. All rights reserved.

One-pot synthesis of highly dispersed PtAu nanoparticles–CTAB–graphene nanocomposites for nonenzyme hydrogen peroxide sensor

A simple and efficient approach was developed to fabricate an amperometric sensor for hydrogen peroxide (H2O2) determination based on one-pot synthesis of highly dispersed PtAu nanoparticles–CTAB–graphene nanocomposites. In this study, graphene oxide was first functionalized with a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB); then PtAu nanoparticles (NPs) were deposited on graphene (GR) via a simple chemical co-reduction method. A large amounts of highly dispersed bimetallic PtAu nanoparticles could be well loaded on the surface of the graphene, as revealed by transmission electron microscopy (TEM). In addition, PtAuNPs–CTAB–GR nanocomposites were also characterized by electrochemical methods including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experimental results demonstrated that constructed sensor exhibited good catalytic activity toward H2O2, and obtained a wide linear range from 5.0×10−9 to 4.8×10−6mol/L with a limit of detection (LOD) of 1.7×10−9mol/L (S/N=3). Moreover, it could also be applied to real samples analysis. The excellent performance of this H2O2 sensor could be ascribed to graphene being used as effective load matrix for the deposition of PtAuNPs and synergistic effect of bimetallic PtAuNPs and graphene nanomaterials.

Bimetallic nanoparticles for arsenic detection.

Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As(III) detection. We show that trace amounts of As(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb(-1). The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic.

Enhancing the performance of catalytic AuPt nanoparticles in nonaqueous lithium-oxygen batteries.

The deposition of catalytic AuPt (1 : 1) nanoparticles (NPs) into hollow mesoporous nitrogen-doped carbon microspheres (HMCMS) was found to significantly improve the effectiveness of the catalysis of oxygen reactions in nonaqueous lithium-oxygen batteries (LOBs); surpassing the performance of unsupported AuPt NPs or HMCMS in discharge and charge overpotentials (lower), specific capacity and rate performance (higher), and cycle life (longer). Specifically at a typical current density of 100 mA g(-1), a LOB with the AuPt/HMCMS cathode catalyst could provide discharge and charge capacities of 6028 and 6000 mA h g(-1) respectively and a charge-discharge voltage gap of only 1.27 V. The discharge capacity decreased by 5% when the current density was doubled, and by 23% when the current density was quintupled. The AuPt/HMCMS LOB could be cycled 75 times for a depth of discharge (DOD) of 1000 mA h g(-1) without exceeding the charge cut-off voltage of 4.4 V. These measurements indicate that the HMCMS is an outstanding catalyst support to use for increasing the effectiveness of oxygen electrocatalysts in the LOBs.

Structural Evolution of AuPt and AuPd Nanoparticles Fabricated by Microwave Assisted Synthesis: A Comparative Study

ABSTRACTBimetallic nanoparticles (NPs), particularly Au/Pd and Au/Pt, have attracted extensive attention due to their wide-spread application in catalysis, optoelectronics and energy recuperation.[1] Here we have attempted the fabrication of Au/Pt and Au/Pd bimetallic NPs by an energy-efficient eco-friendly microwave methodology. The microwave-assisted reactions enable considerably large product yields over conventional colloidal methods due to (a) almost two-fold increased reaction kinetics, (b) localized superheating at reaction sites and rapid rise of initial temperature.[2] Au NPs (sizes 20 ± 3 nm) are fabricated in the first step followed by the reduction of [PdCl2(NH3)2] or [K2PtCl6]in tetraethylene glycol at 180 ºC for 2 min. Controlling and understanding the atomic structure and elemental distributions of these NPs are crucial for their optimized performances. So, we address the fundamental question of the most likely arrangement of Au and Pd or Pt atoms in these bimetallic NPs prepared under similar conditions by complementary characterizations using UV-Vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-Vis spectroscopy reveals the formation of an alloy shell. The extent of depression of the plasmon peak of Au and its blue-shift reveals substantial deposition of Pd atoms on an Au core and significant alloying in comparison to Au/Pt NPs. XRD reveals the gradual shift of the diffraction peak from the position of Au to the position of Pd or Pt with change in composition. XRD supports the formation of a thick alloy shell in these NPs. However, the TEM images reveal a very interesting result. With increase in Pt concentration, the size of the dispersed NPs decreases from 20 ± 3 nm to about 16 nm (± 1 nm) and there is evolution of a bimodal particle size distribution with small particles about 1-2 nm diameters. On the contrary, with increasing Pd concentration, the particle size of the dispersed particles increases to about 32 nm (± 1 nm). This discrepancy of particle size evolution for the two systems arises due to the differences in surface energies (Pt &gt; Pd &gt; Au atoms). Pt atoms tend to diffuse towards the core with the formation of Au nano-islands which eventually segregates leading to a reduction in particle size and bimodal distribution. At higher concentration of Pt, Pt and Au atoms tend to nucleate separately also contribute to the bimodal distribution. While for Au/Pd NPs, we have an Au core with an alloyed shell having higher Pd concentration. This is further supported by experimental evidence by selective etching and dissolution of Au by potassium-iodide solution. Furthermore, the Au/Pd bimetallic NPs are found to possess better catalytic activities in the reduction of 4-nitrophenol to 4-aminophenol than Au/Pt and monometallic NPs.

Oxygen reduction reaction activity and structural stability of Pt-Au nanoparticles prepared by arc-plasma deposition.

The oxygen reduction reaction (ORR) activity and durability of various Au(x)/Pt100 nanoparticles (where x is the atomic ratio of Au against Pt) are evaluated herein. The samples were fabricated on a highly-oriented pyrolytic graphite substrate at 773 K through sequential arc-plasma depositions of Pt and Au. The electrochemical hydrogen adsorption charges (electrochemical surface area), particularly the characteristic currents caused by the corner and edge sites of the Pt nanoparticles, decrease with increasing Au atomic ratio (x). In contrast, the specific ORR activities of the Au(x)/Pt100 samples were dependent on the atomic ratios of Pt and Au: the Au28/Pt100 sample showed the highest specific activity among all the investigated samples (x = 0-42). As for ORR durability evaluated by applying potential cycles between 0.6 and 1.0 V in oxygen-saturated 0.1 M HClO4, Au28/Pt100 was the most durable sample against the electrochemical potential cycles. The results clearly showed that the Au atoms located at coordinatively-unsaturated sites, e.g. at the corners or edges of the Pt nanoparticles, can improve the ORR durability by suppressing unsaturated-site-induced degradation of the Pt nanoparticles.

A sensitive electrochemical immunosensor for the detection of squamous cell carcinoma antigen by using PtAu nanoparticles loaded on TiO2colloidal spheres as labels

A sensitive sandwich-type electrochemical immunosensor for detection of squamous cell carcinoma antigen (SCCA) was developed by using PtAu nanoparticles loaded on TiO2colloidal spheres (PtAu/TiO2) as secondary-antibody (Ab2) labels.