Au-Pt Alloy Research Articles

Bacterial Adhesion of Streptococcus mutans to Dental Material Surfaces.

The aim of this study was to investigate and understand bacterial adhesion to different dental material surfaces like amalgam, Chromasit, an Co-Cr alloy, an IPS InLine ceramic, yttrium stabilized tetragonal polycrystalline zirconia (TPZ), a resin-based composite, an Au-Pt alloy, and a tooth. For all materials, the surface roughness was assessed by profilometry, the surface hydrophobicity was determined by tensiometry, and the zeta potential was measured by electrokinetic phenomena. The arithmetic average roughness was the lowest for the TPZ ceramic (Ra = 0.23 µm ± 0.02 µm), while the highest value was observed for the Au-Pt alloy (Ra = 0.356 µm ± 0.075 µm). The hydrophobicity was the lowest on the TPZ ceramic and the highest on the Co-Cr alloy. All measured streaming potentials were negative. The most important cause of tooth caries is the bacterium Streptococcus mutans, which was chosen for this study. The bacterial adhesion to all material surfaces was determined by scanning electron microscopy. We showed that the lowest bacterial extent was on the amalgam, whereas the greatest extent was on tooth surfaces. In general, measurements showed that surface properties like roughness, hydrophobicity and charge have a significant influence on bacterial adhesion extent. Therefore, dental material development should focus on improving surface characteristics to reduce the risk of secondary caries.

A displacement dealloying route to dilute nanoporous PtAu alloys for highly active formic acid electro-oxidation

Functional nanoporous metals and alloys can be fabricated by chemical or electrochemical dealloying routes in corrosive media, followed by customized surface functionalization. The present work describes how a combination of displacement reaction and dealloying can provide a facile one-pot procedure to nanoporous alloys such as PtAu, and the resulted electrocatalysts are characterized by highly dispersed Pt atoms or small clusters embedded within a high surface area Au matrix. These dilute alloy electrocatalysts with low Pt contents exhibit remarkable activity toward formic acid oxidation via a favorable dehydrogenation mechanism. At 0.6 V versus reversible hydrogen electrode, they can demonstrate over 70-fold enhancement in Pt mass activity than that of the commercial Pt/C.

Au‐Promoted Pt nanoparticles supported on MgO/SBA‐15 as an efficient catalyst for selective oxidation of glycerol

AbstractA systematic study of Au‐promoted and unpromoted Pt/MgO/SBA‐15 catalyst is developed to separate the promoter effect from electron transfer effect between Au and Pt. Multi‐characterizations revealed that Au and Pt metals in these bimetallic catalysts mainly exist in the form of alloy, and the main role of Au is to reduce the size of AuPt alloy nanoparticles, thus enhancing the adsorption and activation of intermediate products. Through the optimization of various factors (including MgO content, Au/Pt molar ratio, reaction temperature and time), the Au1Pt2/MgO/SBA‐15 (0.05) catalyst exhibits excellent catalytic activity and glyceric acid selectivity for the selective oxidation of glycerol. Density functional theory calculation confirmed that the synergistic effect between Pt and Au active sites could facilitate the oxidation of primary hydroxyl group by promoting the activation of CH bond and the oxidation of aldehyde group. The results may give insights on designing effective Pt based bimetallic catalyst for selective oxidation of glycerol.

Reconciling of Experimental and Theoretical Insights on the Electroactive Behavior of C/Ni Nanoparticles with Aupt Alloys for Hydrogen Evolution Efficiency and Non-Enzymatic Sensor

Reconciling of Experimental and Theoretical Insights on the Electroactive Behavior of C/Ni Nanoparticles with Aupt Alloys for Hydrogen Evolution Efficiency and Non-Enzymatic Sensor

Improved photocatalytic degradation and reduction performance of Bi2O3 by the decoration of AuPt alloy nanoparticles

Abstract In this work, AuPt alloy nanoparticles were attached onto the surface of Bi2O3 particles to obtain AuPt/Bi2O3 composite. The existence of AuPt bimetallic alloy and their homogeneous distribution on Bi2O3 surface were fully confirmed by XPS characterization and HRTEM observation. The surface plasmon resonance (SPR) effect of noble metals was detected using Ultraviolet–visible diffuse reflectance spectra. The photocatalytic degradation and reduction ability of products were estimated using Acid orange 7 (AO7), phenol and Cr(VI) as the target reactant under simulated sunlight irradiation, indicating that AuPt/Bi2O3 composite possesses remarkable higher photocatalytic activity compared with bare, Au and Pt decorated Bi2O3. In addition, AuPt/Bi2O3 composite is proved to be a stable photocatalysts. The effective separation and migration of photoinduced electrons and holes in AuPt/Bi2O3 sample is demonstrated employing electrochemical and photoluminescence detection. The AuPt/Bi2O3 composite not only has suitable schottky barrier height for trapping the photogenerated charges but also exhibits surface plasmon resonance (SPR) effect, which leads to enhanced photocatalytic activity.

Nanoporous Au-Cu-Pt As a Superior Electro-Catalyst for the Methanol Oxidation Reaction

Among fuel cells, the direct methanol fuel cell (DMFC) has attracted great attention and has been considered a very promising power source because of the ease of methanol transportation and its high energy density. A major limiting factor hindering DMFC’s commercial application is the poor catalytic performance in the anode (methanol oxidation reaction). The methanol oxidation reaction (MOR) requires (OH-) from water dissociation as an oxygen donor for the reaction; however, the slow water dissociation on Pt limits the rate of MOR. In addition to the sluggish catalytic activity, the other major impediment for Pt catalysts is the generation of carbon monoxide (CO) during the MOR process.In order to improve the catalytic performance of MOR catalysts, a variety of catalyst design strategies have been devised. The interesting way of carrying out the MOR catalytic process is the non-CO pathway which takes place on Pt-Au bimetallic catalysts, thus eliminating CO poisoning. However, the overall activity of Pt-Au alloys in MOR is relatively low, which ultimately limits the application of Pt-Au catalysts.In this study, a nanoporous (np) Au-Cu-Pt thin-film catalyst with a fine structure and tunable composition is synthesized by using a facile method involving successive electrodeposition and de-alloying. SEM, SEM-EDX and ICP have been used for morphology characterization and composition assessment. Pb under-potential deposition (UPD), H UPD and CO stripping tests have been employed to determine the electrochemical active surface area (ECSA) and to probe the Pt active sites specifically. Also, cyclic voltammetry (CV) tests have been performed to assess the catalytic performance in MOR. Finally, long-term CV and chronoamperometry (constant potential) tests have been used to study and evaluate the durability of accordingly synthesized catalyst for MOR.The prepared np Au-Cu-(8% in the precursor alloy)Pt catalyst exhibits outstanding mass and specific activity toward the MOR, which is approximately six- and nine-times higher than the activity of a commercial Pt/C(40%) counterpart, respectively. A negative 75 mV onset potential shift upon the MOR anodic scan on the np Au-Cu-(8 %)Pt catalyst in comparison with Pt/C(40%) corroborates its higher catalytic activity. Furthermore, the alloy catalyst demonstrates better durability than the Pt/C(40%) counterpart in a three-hour constant potential test and exhibits full post-factum recovery of its cycling activity. In addition, it retains more than 60% of its original activity after 3000 cycles of an accelerated degradation test.Reference:Xie, Y., Li, C., Razek, S.A., Fang, J. and Dimitrov, N., 2020. Synthesis of Nanoporous Au− Cu− Pt Alloy as a Superior Catalyst for the Methanol Oxidation Reaction. ChemElectroChem, 7(2), pp.569-580.

Reversing the Thermodynamics of Galvanic Replacement Reactions by Decreasing the Size of Gold Nanoparticles.

Here, we describe the surprising reactivity between surface-attached (a) 0.9, 1.6, and 4.1 nm diameter weakly stabilized Au nanoparticles (NPs) and aqueous 1.0 × 10-4 M Ag+ solution, and (b) 1.6 and 4.1 nm diameter weakly stabilized Au NPs and aqueous 1.0 × 10-5 M PtCl42-, which are considered to be antigalvanic replacement (AGR) reactions because they are not thermodynamically favorable for bulk-sized Au under these conditions. Anodic Stripping Voltammetry (ASV) and Scanning Transmission Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (STEM-EDS) mapping provide quantitation of the extent of Ag and Pt replacement as a function of Au NP diameter. The extent of the reaction increases as the Au NP size decreases. The percentage of Ag in the AuAg alloy following AGR based on ASV is 17.8 ± 0.6% for 4.1 nm diameter Au NPs, 87.2 ± 2.9% for 1.6 nm Au NPs, and an unprecedented full 100% Ag for 0.9 nm diameter Au NPs. STEM-EDS mapping shows very close agreement with the ASV-determined compositions. In the case of PtCl42-, STEM-EDS mapping shows AuPt alloy NPs with 3.9 ± 1.3% and 41.1 ± 8.7% Pt following replacement with 4.1 and 1.6 nm diameter Au NPs, respectively, consistent with qualitative changes to the ASV. The size-dependent AGR correlates well with the negative shift in the standard potential (E0) for Au oxidation with decreasing NP size.

Boosted aromatics production with para-xylene selectivity using Au-lean Au–Pt/H-ZSM-5 bimetallic naphtha reforming composite catalysts

This study discloses for the first time Au-lean Au–Pt/H-ZSM-5 catalysts for naphtha reforming reactions. Addition of 1 to 5 wt% Au to the Au-Pt bimetallic catalyst boosts aromatic production. Total metal content was 0.3 wt%. The effect of Au/Pt weight ratios of 0/100, 1/99, 2/98 and 5/95 on the product composition for a reaction temperature of 490 °C (4 bar pressure at a WHSV of 5.7 h−1) has been studied. Au/Pt weight ratio of 1/99 results in the maximum aromatics production and naphthenes conversion. This ratio results in maximum para-xylene formation (15.1 wt% of total aromatics) and iso-pentane formation. The catalysts have been characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature programmed reduction (TPR) and CO adsorption analyses. The Au/Pt weight ratio of 1/99 results in the minimal bimetallic aggregate particle size (2.65 nm). Based on TPR analysis, it is stated that the optimal Au-Pt/H-ZSM-5 catalyst consists of an Au-lean Au-Pt alloy beside Pt metal.

Electrocatalysis of Methanol on the Platinum‐Gold Bimetallic Microstructures Codeposited with Silicate Sol‐gel on Indium Tin Oxide Electrode

AbstractA facile one‐step electrochemical codeposition of platinum‐gold (PtAu) alloy materials embedded in N‐[3‐(trimethoxysilyl)propyl] ethylenediamine (EDAS) silicate sol‐gel on indium‐tin‐oxide electrode (ITO/EDAS‐PtAu) is reported. The x‐ray diffraction patterns, X‐ray photoelectron spectroscopy analysis, scanning electron microscopy, energy dispersive X‐ray analysis, elemental mapping, line scan spectra and cyclic voltammetric studies showed the formation of PtAu bimetallic microstructures at the ITO/EDAS‐PtAu electrodes. The electrochemically codeposited PtAu alloy microstructures materials showed profound enhancement for methanol oxidation reaction in alkaline medium. The observed results revealed that the present facile synthetic methodology for the preparation of PtAu alloy microstructures materials embedded in silicate sol‐gel (ITO/EDAS‐PtAu) modified electrode is a promising approach and the modified electrode showed enhanced mass activity and stability towards methanol oxidation reaction.

Conversion of isobutane to n-butane over bifunctional PtAu-solid superacids catalyst

A platinum-substituted alumina-promoted sulfated zirconia (PtAu/SZA) was prepared and used for the conversion of isobutane to n-butane, aiming to optimize the ethylene feedstock in the steam thermal cracking process and increase the ethylene yield. PtAu bimetallic catalysts showed higher catalytic activity than Pt-alone catalyst, and the enhancement is attributed to PtAu alloying. By diluting and separating Pt with PtAu alloy agglomerates, continuous Pt agglomerates disappear and hydrogen dissociation on Pt is enhanced. In addition, the reduction temperature of Pt is decreased with the increase in Au content, while the reduction temperature of sulfate was increased which will delay the loss of sulfate according to the results of H2-TPR and NH3-TPD. However, the acidity of the catalyst decreases with the increase in Au, which is due to that PtAu alloy covers the acid sites on the surface. Overall, we found that the Pt0.5Au0.3/SZA showed the highest yield to n-butane (34.69%).

Agglomerates of Au-Pt bimetallic nanoparticles: synthesis and antibacterial activity

The extraction of bimetallic Au-Pt nanoparticles is interesting due to their multiple applications in catalytic processes, electronic devices, photothermal therapies, among others. On the other hand, the tendency of nanoparticles forming agglomerates may modify the behavior of the material, and thus their applications. This study shows a highly reproducible novel synthesis method, which only uses two organic agents (sucrose and ascorbic acid) as the reducing and stabilizing agents from nano-agglomerates of Au-Pt at room temperature. The TEM images show agglomerates with a mass fractal structure. We identified crystalline FCC, corresponding to the Au-Pt alloy. Furthermore, the coexistence of gold and platinum nanoparticles was shown through the EDS analysis. The UV-Vis spectrum showed that the resonance plasmon identified coincides with a great approximation to the results reported in the literature. Additionally, the agglomerates exhibited excellent antibacterial activity against bacteria Escherichia coli.

A simulation study on the orientational phase transformation behavior of Au-Pt alloy for different concentration of Pt

In this study, the AuxPt100-x (x = 90, 50, 10) model alloy system was modelled molecular dynamic (MD) simulation for different atomic concentration percentage of platinum (Pt). The potential energy function was used the Embedded Atom Method (EAM). The bond-type index method of Honeycutt–Andersen (HA) and cluster-type index methods (CTIM-1 and CTIM-2) was used to detect the crystal/amorphous-type polyhedrons. The phase transformation behavior of the model alloy system was examined by using local order symmetry based on bond orientational parameter. In addition, the structural development of system at a defined temperature was investigated by radial distribution function (RDF). The melting point of system was obtained by potential energy function and HA method during the heating. In this process, the α′, the α″ and the α′+ α″ phase regions for Au-Pt system was determined by bond orientational order parameter. The modelling results were compared with experimental results and the results demonstrate that the simulation calculations are in reasonable agreement with the experimental data.

Bimetallic PtAu alloy nanomaterials for nonenzymatic selective glucose sensing at low potential

Electrochemical nonenzymatic glucose sensing meets the challenge of excellent selectivity and the minimum poisoning effect of the electrode. Bimetallic alloys based on Pt have distinct synergistic characteristics and offer remarkable anti-poisoning capability and electrocatalytic performance for sensitive and selective glucose sensing at low potential. Bimetallic PtAu alloy nanomaterials loaded into nanocarbon carrier (PtAu/C) were successfully fabricated. The morphology and structure of PtAu bimetallic alloy were observed. The voltammetric response of the PtAu/C modified electrodes towards glucose oxidation in NaOH revealed significant enhanced compared with Pt/C or Au/C. PtAu (1:1)/C with 0.4 wt% content of Pt was used for selective glucose detection at a low potential of −0.33 V (vs. SCE). Interfering substances revealed inert and ignorable analytical influence on glucose detection. Furthermore, DPV was applied for sensitive determination of glucose. A linear relationship was found between peak current and glucose concentration within the range of 0.01–10 mM with the limit of detection (LOD) of 3 μM. Validation in human serum samples indicated that the PtAu (1:1)/C (0.4 wt% Pt) modified electrode accurately detected glucose. The PtAu bimetallic alloy exhibited a bright prospect for the glucose analysis of real samples.

The Influence of Recycling on the Properties of Interface between Ceramic and Dental Alloys.

Purpose The purpose of this study was to evaluate the effect of recycling on the properties of interface between 2 dental alloys and their corresponding porcelains. Materials and Methods Noble alloy (Pd-Cu-Ga) and high-noble alloy (Au-Pt) were used in this study. Metal matrices (cylinders Φ4 mm × 4 mm with pedestal Φ5 mm × 1 mm) were prepared by arc melting in argon after recasting 1-3 times. Corresponding porcelain with overall dimensions of Φ4 mm × 2 mm was veneered on each metal cylinder. There were 22 specimens in each alloy group. Specifically, two specimens of each group were chosen randomly for interfacial morphology and diffusion analyses by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The remaining 20 specimens were divided into 2 groups with or without thermal cycling. The bond strength was evaluated by shear test, and the data were analyzed by two-way analysis of variance (ANOVA). The failure mode of shear test specimen was observed with a stereoscopic microscopy and subjected to the exact probability test (α = 0.05). Results According to the results from SEM, no obvious difference was observed in the interfacial morphology of both Pd-Cu-Ga and Au-Pt alloys among different recasting specimens. EDS analysis revealed that no significant difference was found in the width of elemental diffusion among 2 test alloys after recycling 1-3 times. Notably, in Pd-Cu-Ga alloy groups, the peak of Ga in thrice recasting was lower than those in first and second recastings. And there was no significant difference (P > 0.05) in the metal-ceramic shear bond strength of Pd-Cu-Ga and Au-Pt alloys after recycling 1-3 times, with or without thermal cycling. The results of failure modes observed on specimens were not affected by the recycling and thermal cycling in the 2 tested alloys. Conclusions Within the limitations of this study, the Pd-Cu-Ga and Au-Pt alloys can be recycled 2 times without significant changes on the properties of metal-ceramic interface, with or without thermal cycling.

Efficient Plasmon-Mediated Energy Funneling to the Surface of Au@Pt Core-Shell Nanocrystals.

The structure and ultrafast photodynamics of ∼8 nm Au@Pt core-shell nanocrystals with ultrathin (<3 atomic layers) Pt-Au alloy shells are investigated to show that they meet the design principles for efficient bimetallic plasmonic photocatalysis. Photoelectron spectra recorded at two different photon energies are used to determine the radial concentration profile of the Pt-Au shell and the electron density near the Fermi energy, which play a key role in plasmon damping and electronic and thermal conductivity. Transient absorption measurements track the flow of energy from the plasmonic core to the electronic manifold of the Pt shell and back to the lattice of the core in the form of heat. We show that strong coupling to the high density of Pt(d) electrons at the Fermi level leads to accelerated dephasing of the Au plasmon on the femtosecond time scale, electron-electron energy transfer from Au(sp) core electrons to Pt(d) shell electrons on the sub-picosecond time scale, and enhanced thermal resistance on the 50 ps time scale. Electron-electron scattering efficiently funnels hot carriers into the ultrathin catalytically active shell at the nanocrystal surface, making them available to drive chemical reactions before losing energy to the lattice via electron-phonon scattering on the 2 ps time scale. The combination of strong broadband light absorption, enhanced electromagnetic fields at the catalytic metal sites, and efficient delivery of hot carriers to the catalyst surface makes core-shell nanocrystals with plasmonic metal cores and ultrathin catalytic metal shells promising nanostructures for the realization of high-efficiency plasmonic catalysts.

Spin Hall effect investigated by spin Hall magnetoresistance in Pt100−xAux/CoFeB systems

We studied spin Hall effect (SHE) in Pt100-xAux with various Au compositions x for Pt-Au/CoFeB systems by means of spin Hall magnetoresistance (SMR). We synthesized low resistive, flat, and highly (111)-textured Pt-Au alloy films by sputtering using low pressure Kr gas. We found that spin Hall angle (θSH), spin Hall conductivity (σSH), and spin diffusion length (λS) increase by alloying Pt with Au at certain x. The enhancement of σSH is consistent with the theoretically predicted increase in the intrinsic spin Hall conductivity, however quantitatively, there are some discrepancies in θSH and λS between our result and the experimental and theoretical results in the literatures 19 and 20. The discrepancy between our results and previous results would be related to the difference of the nanostructure in Pt-Au alloys related to the scattering from film surfaces and grain boundaries and the degree of phase separation in Pt-Au alloy systems.

Tunable localized surface plasmon resonance by self-assembly of trimetallic and bimetallic alloy nanoparticles via Ag sublimation from Ag/Au/Pt tri-layers

In this work, various configurations, size, density and composition of AgAuPt and AuPt alloy NPs are demonstrated via the solid-state dewetting (SSD) of Ag/Au/Pt tri-layers on the transparent c-plane sapphire (0001) and the corresponding LSPR characteristics are thoroughly investigated along with the FDTD simulation. The SSD is adapted to convert the sputtered Ag/Au/Pt tri-layers into the definite alloy NPs based on the diffusion, interdiffusion and energy minimization process. The resulting AgAuPt and AuPt NPs demonstrate much stronger plasmonic characteristics as compared to their counterparts with the tunable LSPR bands in the UV and VIS regions along with the various plasmon resonance modes such as dipolar (DR), quadrupolar (QR), multipolar (MR) and higher order (HO). Furthermore, the Ag atom sublimation demonstrates a significant role in the dewetting process, which significantly alters the size, shape and composition of alloy NPs, giving a rise to the development of AuPt NPs. In specific, the LSPR response attenuates with the sublimation, however, as the AuPt NPs in this study are significantly improved in terms of composition and configuration, i.e. shape, size and spacing, the LSPR responses are much stronger and dynamic as compared to the pure Pt NPs on sapphire in the previous studies.

Highly active PtAu alloy surface towards selective formic acid electrooxidation

Highly active PtAu alloy surface towards selective formic acid electrooxidation

Electrodeposition of AuPt Alloy Nanostructures on a Biotemplate with Hierarchically Assembled M13 Virus Film Used for Methanol Oxidation Reaction

Herein, we report an electrode surface with a hierarchical assembly of wild-type M13 virus nanofibers (M13) to nucleate the AuPt alloy nanostructures by electrodeposition. M13 was pulled on the electrode surface to produce a virus film, and then a layer of sol–gel matrix (SSG) was wrapped over the surface to protect the film, thereby a bio-template was constructed. Blending of metal binding domains of M13 and amine groups of the SSG of the bio-template were effectively nucleate and directed the growth of nanostructures (NSs) such as Au, Pt and AuPt alloy onto the modified electrode surface by electrodeposition. An electrocatalytic activity of the modified electrode toward methanol oxidation in alkaline medium was investigated and found an enhanced mass activity (534 mA/mgPt) relative to its controlled experiments. This bio-templated growth of NSs with precise composition could expedite the intention of new alloy materials with tuneable properties and will have efficacy in green energy, catalytic, and energy storage applications.

Controllable Synthesis of Surface Pt-Rich Bimetallic AuPt Nanocatalysts for Selective Hydrogenation Reactions.

Bimetallic nanocatalysts, with efficient and controllable catalytic performance, have a promising application in chemical production. In this study, surface Pt-rich bimetallic AuPt nanoparticles with different Pt/Au ratios were prepared and tested in selective hydrogenation reactions of substituted nitroaromatics. Au nanoparticles were first prepared with n-butyllithium as a rapid reducer, which were further used as seeds in the slow growth process of Pt atoms. Because of the employed sequential reduction method and the following atom diffusion, surface Pt-rich bimetallic AuPt nanoparticles were obtained. Compared with the uniform AuPt alloy nanocatalysts synthesized by the co-reduction method with n-butyllithium as the reducer and monometallic Pt nanocatalysts, the obtained surface Pt-rich AuPt bimetallic nanocatalysts presented an enhanced catalytic selectivity or activity. The performance enhancement is assigned to the optimized Au/Pt interaction in the surface Pt-rich bimetallic nanostructures. This work demonstrates that the optimization of the stoichiometry and construction of bimetallic materials is a feasible method to synthesize controllable and efficient nanocatalysts.