Bimetallic Alloy Nanocrystals Research Articles

Fast detection of ppm n-pentanol by PtAu alloy nanocrystals decorated flower-like WO3

Rapid detection of n-pentanol is of great significance. Herein, we presented an excellent n-pentanol gas sensor based on bimetallic PtAu alloy nanocrystals (NCs) modified flower-like WO3. PtAu NCs with relatively uniform size were synthesized through a reduction method in oleylamine solution. The sensitive materials of flower-like WO3 with different mass percentages of PtAu NCs were prepared by impregnation. WO3 with the loading amount of 0.5 wt% showed a response of 162 (Ra/Rg) for 20 ppm n-pentanol at 200 °C, which was 105 times higher than that for pure WO3. PtAu adding enhanced the response due to the sensitization and their synergistic effect. It is noteworthy that PtAu-modified WO3 exhibited ultrafast response/recovery speed (tres = 1 s, trec = 3 s) to n-pentanol, as far as we know it is the fastest n-pentanol sensor based on semiconductor until now. Flower-like WO3 3D nanostructures allow fast diffusion of gas molecules, resulting in the high rates of gas adsorption and desorption. At the same time, with the help of the bimetal catalysis, the reaction was further promoted. This work can provide a new solution strategy for fast detection and real-time monitoring of n-pentanol in chemical plants.

Elucidating growth mechanism and shape evolution of highly branched PtNi alloy nanocrystals and their electrocatalytic performance

Due to the difficulty in controlling thermodynamics and kinetics of the growth for branched bimetallic metal alloy nanocrystals in a solution system, understanding the growth mechanisms of this class of nanostructures is critical for their shape-controlled synthesis. Herein, we report an approach to control over shape of branched PtNi alloy nanocrystals by tuning the molar ratio of Pt to Ni in an oleyamine solution. The detailed analyses confirmed that the morphologies of PtNi alloy nanocrystals evolve from dendrites (less than 5 at% Ni) to multipods (5–10 at% Ni) to star shapes (10–20 at% Ni) and finally to polyhedrons (100 at% Ni) as the nickel content in PtNi alloy nanocrystals increase. During the morphology evolution, the growth mechanism changes from oriented attachment growth to a new mechanism combining oriented attachment and anisotropic overgrowth, then to kinetically controlled overgrowth and finally to thermodynamic control growth. More importantly, we find that the growth of branched PtNi alloy nanocrystals is always along the [220] direction, and the growth direction determines the number of branches in nanocrystals. Electrochemical results show that highly branched PtNi alloy nanocrystals exhibit significantly enhanced electrocatalytic activity and durability compared with commercial Pt catalysts. These in-depth findings will provide new hints to precisely control synthesis of highly branched PtNi nanocrystals.

Atmosphere-Induced Transient Structural Transformations of Pd-Cu and Pt-Cu Alloy Nanocrystals.

We have investigated the transformations of colloidal Pd–Cu and Pt–Cu bimetallic alloy nanocrystals (NCs) supported on γ-Al2O3 when exposed to a sequence of oxidizing and then reducing atmospheres, in both cases at high temperature (350 °C). A combination of in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption spectroscopy was employed to probe the NC surface chemistry and structural/compositional variations in response to the different test conditions. Depending on the type of noble metal in the bimetallic NCs (whether Pd or Pt), different outcomes were observed. The oxidizing treatment on Pd–Cu NCs led to the formation of a PdCuO mixed oxide and PdO along with a minor fraction of CuOx species on the support. The same treatment on Pt–Cu NCs caused a complete dealloying between Pt and Cu, forming separate Pt NCs with a minor fraction of PtO NCs and CuOx species, the latter finely dispersed on the support. The reducing treatment that followed the oxidizing treatment largely restored the Pd–Cu alloy NCs, although with a residual fraction of CuOx species remaining. Similarly, Pt–Cu NCs were partially restored but with a large fraction of CuOx species still located on the support. Our results indicate that the noble metal present in the bimetallic Cu-based alloy NCs has a strong influence on the dealloying/migrations/realloying processes occurring under typical heterogeneous catalytic reactions, elucidating the structural/compositional variations of these NCs depending on the atmospheres to which they are exposed.

Efficient Synthesis of Bimetallic Pt3Zn Alloy Nanocrystals with Different Shapes and their Enhanced Electrocatalytic Activity

AbstractHighly uniform dispersed bimetallic Pt3Zn alloy nanocrystals (NCs) with unique geometries are obtained via a facile one‐pot synthesis process by regulating different reductants. To investigate the morphology and composition of the prepared catalysts, the transmission electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy are utilized. Electrochemical measurements reveal that the Pt3Zn NCs significantly exhibited larger electrochemically active surface areas and excellent catalytic activity towards electro‐oxidation of methanol and ethanol in comparison to the commercial Pt/C. The optimized Pt3Zn (AA) NCs exhibit excellent mass activities in both methanol oxidation reaction (1251.4 mA mgPt−1) and ethanol oxidation reaction (975.7 mA mgPt−1) in acidic media, which are respectively 4.28 times and 3.02 times higher than those of commercial Pt/C. Moreover, the Pt3Zn NCs show a higher stability and better resistance to the COads poisoning. The activity enhancements are attributed to electronic effects and a bifunctional mechanism.

Synthesis and Activation of Pt–Cu Alloy Nanocrystals with Controlled Structure and Exposed Facets for Ethylene Glycol Oxidation

The ability to control the shape, structure and faceting characteristics of bimetallic alloy nanocrystals (NCs) has been vital for designing a catalyst with excellent activity and durability in fuel cells. However, it has remained a significant challenge to synthesize platinum–copper (Pt–Cu) alloy NCs with controlled structure and exposed facets. Herein, Pt–Cu alloy NCs with different shapes, structures and facets were synthesized via a one-step direct chemical co-reduction method employing various glucose concentrations. The results showed that the prepared Pt–Cu alloy NCs exhibited very interesting facet-dependent electrocatalytic properties for ethylene glycol oxidation. In comparison with other prepared Pt–Cu alloy NCs and commercial Pt/C, Pt–Cu alloy NPs with (111)-dominant facets showed higher electrocatalytic activity and durability for ethylene glycol oxidation. Alloy NPs showing prominent electrocatalytic performance were attributed to the predominant (111) facets on NP surfaces serving as catalytic active sites, in addition to added Cu providing unique electronic and synergistic effects. The present work highlighted that these NPs with (111)-dominant facets were indeed promising candidates as electrocatalysts with excellent activity and superior durability.

One-pot synthesis of Ag-rich AgPd alloy nanoactiniae and their enhanced electrocatalytic activity toward oxygen reduction

Abstract The electro-catalytic properties can be effectively optimized by designing bimetallic alloy nanoparticles with high-content less-active metal to enhance the competence of more-active noble metal. Herein, a one-pot hydrothermal approach is demonstrated for the controllable synthesis of Ag-rich Ag9Pd1 alloy nanoactiniae with obviously enhanced electro-catalytic activity (2.23 mA cm−2 at 0.85 V) and stability for oxygen reduction reaction. In alkaline solution, the ORR onset potential and half-wave potential of the Ag9Pd1 alloy nanoactiniae can reach a value of 1.02 V and 0.89 V, respectively, which origin from strong ligand and ensemble effects between Pd element and Ag element. The nanocrystals are uniformly alloyed, displaying a Ag9Pd1 combination, as displayed by an assembly of X-ray diffraction (XRD) spectrum, energy dispersive X-ray (EDX) analysis, and cyclic voltammetry (CV). This concept of tuning bimetallic alloy nanocrystals with low concentrations of more precious metal may be a promising approach to be applicable to a wide range of alloy nanocrystals.

Synthesis of PtAu Alloy Nanocrystals in Micelle Nanoreactors Enabled by Flash Heating and Cooling

AbstractA microwave‐assisted flash heating and cooling strategy has been developed for the rapid synthesis of bimetallic alloy nanocrystals made of immiscible metals in microemulsion micelle nanoreactors. The promising oxygen reduction reaction (ORR) catalysts of PtAu alloy nanocrystals with tunable compositions have been successfully synthesized by using the new strategy. The water‐in‐oil (w/o) microemulsion micelles contain strong microwave‐absorbing species (including metal ion precursors, reducing reagent, water, n‐butanol) and they are surrounded with cyclohexane that barely absorbs microwave. The selective absorption of microwave energy in the micelles enables the rapid production of well‐mixed PtAu alloy melt at extremely high local temperatures while the micelle walls are cooled with the cold pool of cyclohexane to freeze the PtAu alloy melt into PtAu alloy nanocrystals with a uniform distribution of metal atoms. Such flash heating inside micelle containers followed by the flash cooling on the micelle walls results in a non‐equilibrium thermodynamic condition to benefit the formation of alloy nanocrystals composed of two immiscible metals.

Sandwich-type biosensor for the detection of α2,3-sialylated glycans based on fullerene-palladium-platinum alloy and 4-mercaptophenylboronic acid nanoparticle hybrids coupled with Au-methylene blue-MAL signal amplification

α2,3-sialylated glycans (α2,3-sial-Gs) are one of the significant tumour biomarkers for the early diagnosis of cancer. In this work, a neoteric sandwich-type biosensor was developed for detecting α2,3-sial-Gs using 4-mercaptophenylboronic acid (4-MPBA) to construct a novel molecular recognition system by the coordination of a boron atom of 4-MPBA to the amide group of Neu5Ac in the α2,3-sial-Gs structure. Amino-functionalized fullerene coupled with palladium-platinum bimetallic alloy nanocrystals (n-C60-PdPt) was synthesized to modify the surface of a glassy carbon electrode (GCE) because the n-C60 nanomaterial affords a large surface area for the on-site reduction of bimetallic alloy nanoparticles and an excellent capacity for electron transfer. Abundant 4-MPBA were immobilized on the n-C60-PdPt, since the 4-MPBA has the mercapto group can combine with PdPt alloy through strong adsorption. Maackia amurensis lectin (MAL) was covalently immobilized on Au-poly (methylene blue) (Au-PMB) acting as the signal amplification components, which was used to recognize the α2, 3-sial-Gs specifically like a second antibody linked on Au-PMB. The differential pulse voltammetry (DPV) current response of the biosensor in 5mL of PBS (0.1M, pH = 7.4) was recorded, and the proposed sandwich-type biosensor showed a wide linear range of 10 fg mL−1 −100ngmL−1 as well as, a low detection limit of 3fgmL−1 (S/N = 3). Furthermore, the proposed method exhibited good recovery and stability, indicating its potential for use in clinical studies.

One-pot fabrication of single-crystalline octahedral Pd-Pt nanocrystals with enhanced electrocatalytic activity for methanol oxidation

This study reports the synthesis of octahedral Pd-Pt bimetallic alloy nanocrystals through a facile, one-pot, templateless, and seedless hydrothermal method in the presence of glucose and hexadecyl trimethyl ammonium bromide. The morphologies, compositions, and structures of the Pd-Pt nanocrystals were fully characterized by various physical techniques, thereby demonstrating their highly alloying octahedral nanostructures. The formation or growth mechanism of the Pd-Pt bimetallic alloy nanocrystals was explored and is discussed here based on the experimental observations. In addition, the synthesized Pd-Pt nanocrystals were applied to the methanol oxidation reaction (MOR) in alkaline media, which proved that the as-prepared catalysts exhibit enhanced electrocatalytic activity for MOR. Pd1Pt3 exhibited the best stability and durability, and its mass activity was 3.4 and 5.2 times greater than those of Pt black and Pd black catalysts, respectively. The facile synthetic process and excellent catalytic performance of the as-prepared catalysts demonstrate that they have the potential to be used in direct methanol fuel cell techniques.

Controlling the alloy composition of PtNi nanocrystals using solid-state dewetting of bilayer films

We demonstrate that solid-state dewetting of bilayer films is an effective way for obtaining bimetallic alloy nanocrystals of controlled composition. When a Pt–Ni bilayer film were annealed near 700 °C, Pt and Ni atoms inter-diffused to form a PtNi bimetallic alloy film. Upon annealing at higher temperatures, the bilayer films transformed into <111> oriented PtNi alloy nanocrystals in small-rhombicuboctahedron shape through solid-state dewetting process. The Pt content of the nanocrystals and the alloy films, estimated by applying the Vegard's law to the relaxed lattice constant, was closely related to the thickness of each layer in the as-grown bilayer films which can be readily controlled during bilayer deposition.

Synthesis of composition-tunable octahedral Pt–Cu alloy nanocrystals by controlling reduction kinetics of metal precursors

In this paper, we reported a solvothermal method for the synthesis of octahedral Pt–Cu bimetallic alloy nanocrystals (NCs) with tunable composition. Inspired by the result from our previous exploration on octahedral Pt–Cu alloy NCs that Cu contents can be tuned from 10% to 50%, we further tuned the Cu portion from 50%to75% by simply introducing n-butylamine in the reaction system. It is believed that n-butylamine plays a key role in breaking through a thermodynamic constraint in the formation of Pt–Cu alloy nanocrystals (NCs). The synergistic effect of underpotential deposition-like Cu reduction and the different complexion abilities of amine group of n-butylamine with two metal species effectively tuned the reduction kinetics, by which each reduced Pt atom is able to catalyze reduction of more Cu atoms and be fully covered with 12Cu atoms in the Pt–Cu alloy crystal, while Cu precursor is not able to be reduced solely and bind solely with Cu atoms, resulting in the successful tuning of Cu composition from 50% to 75%. In addition, we investigated the electro-catalytic activity of Pt–Cu bimetallic alloy NCs with different composition in electro-oxidation of methanol. The as-prepared PtCu3 NCs exhibit excellent electro-catalytic performance and stability in comparison with commercial Pt black and other compositional Pt–Cu alloy NCs.

Bimetallic alloy nanocrystals encapsulated in ZIF-8 for synergistic catalysis of ethylene oxidative degradation.

Highly dispersed PtPd alloy nanocrystals (NCs) were firstly successfully encapsulated in microporous zeolitic imidazolate framework ZIF-8 (PtPd@ZIF-8) with tunable compositions by a "bottle around ship" approach. The PtPd@ZIF-8 catalyst showed excellent synergistic photocatalytic activity in the transformation of the adsorbed ethylene into CO2 and H2O at room temperature.

Chirality-specific growth of single-walled carbon nanotubes on solid alloy catalysts.

Carbon nanotubes have many material properties that make them attractive for applications. In the context of nanoelectronics, interest has focused on single-walled carbon nanotubes (SWNTs) because slight changes in tube diameter and wrapping angle, defined by the chirality indices (n, m), will shift their electrical conductivity from one characteristic of a metallic state to one characteristic of a semiconducting state, and will also change the bandgap. However, this structure-function relationship can be fully exploited only with structurally pure SWNTs. Solution-based separation methods yield tubes within a narrow structure range, but the ultimate goal of producing just one type of SWNT by controlling its structure during growth has proved to be a considerable challenge over the last two decades. Such efforts aim to optimize the composition or shape of the catalyst particles that are used in the chemical vapour deposition synthesis process to decompose the carbon feedstock and influence SWNT nucleation and growth. This approach resulted in the highest reported proportion, 55 per cent, of single-chirality SWNTs in an as-grown sample. Here we show that SWNTs of a single chirality, (12, 6), can be produced directly with an abundance higher than 92 per cent when using tungsten-based bimetallic alloy nanocrystals as catalysts. These, unlike other catalysts used so far, have such high melting points that they maintain their crystalline structure during the chemical vapour deposition process. This feature seems crucial because experiment and simulation both suggest that the highly selective growth of (12, 6) SWNTs is the result of a good structural match between the carbon atom arrangement around the nanotube circumference and the arrangement of the catalytically active atoms in one of the planes of the nanocrystal catalyst. We anticipate that using high-melting-point alloy nanocrystals with optimized structures as catalysts paves the way for total chirality control in SWNT growth and will thus promote the development of SWNT applications.

Titania‐Photocatalyzed Transfer Hydrogenation Reactions with Methanol as a Hydrogen Source: Enhanced Catalytic Performance by Pd–Pt Alloy at Ambient Temperature

AbstractHydrogenation reactions are of great importance in scientific research and in industry productions. Herein, we designed a novel system to realize photocatalytic transfer hydrogenation by using solar light as the energy input and methanol as the hydrogen source. In this reaction, titania loaded with Pd–Pt bimetallic alloy nanocrystals as a cocatalyst exhibited photocatalytic performance that was remarkably superior to that exhibited by titania with Pd or Pt alone as the cocatalyst. This work has shed light on the rational design of multifunctional catalysts through selecting appropriate bimetallic alloys as efficient cocatalysts.

Component‐Controlled Synthesis of Small‐Sized Pd‐Ag Bimetallic Alloy Nanocrystals and Their Application in a Non‐Enzymatic Glucose Biosensor

Small‐sized monodisperse Pd‐Ag alloy nanocrystals (NCs) are synthesized via a solid‐liquid and solid‐solid phase chemical route, i.e., sequential reduction of Pd(NO3)2 and AgNO3 solid precursors in the liquid mixture of dodecylamine and 1‐octadecene, followed by fusion of formed Pd and Ag NCs at 250 °C. By controlling the addition sequence and molar ratio of the metallic precursors, a series of Pd‐Ag alloy NCs, including Pd5Ag, Pd2Ag, PdAg, PdAg2, and PdAg5, is obtained. The alloy NCs are highly crystallized and exhibit a strong atomic ensemble in addition to component‐dependent electronic effects. Pd2Ag NCs have unique structure and electronic properties, showing a much faster electron transfer process at a modified glassy carbon electrode interface compared with that of other alloys. Therefore, the Pd2Ag NCs are chosen as the electrocatalyst to evaluate the performance of Pd‐Ag nanoalloy and a novel non‐enzymatic glucose biosensor is fabricated. The biosensor exhibits an acceptable reproducibility, a good stability and low interferences, which can be used to examine glucose in clinic blood serum samples. This work provides a simple multiphasic reaction system to synthesize binary alloy NCs with well‐controlled componential ratio and opens the avenue to utilize them in biosensing or other advanced technological fields.

Alloy Nanocrystals: Kinetically Controlled Growth of Polyhedral Bimetallic Alloy Nanocrystals Exclusively Bound by High‐Index Facets: Au–Pd Hexoctahedra (Small 5/2013)

Manipulating the nanocrystal (NC) growth kinetics via control of the amount of reductant is the key synthetic lever to control the morphology of Au–Pd NCs. The alloys, which have a hexoctahedral structure enclosed exclusively by high-index {541} facets, are prepared on page 660 by S. W. Han and co-workers via the simultaneous reduction of Au and Pd precursors without seeds or additional metal ions as structure-regulating agents. These NCs exhibit higher catalytic performances toward the electro-oxidation of ethanol than Au–Pd alloy NCs bound by low-index facets.

Kinetically Controlled Growth of Polyhedral Bimetallic Alloy Nanocrystals Exclusively Bound by High‐Index Facets: Au–Pd Hexoctahedra

Au-Pd alloy nanocrystals (NCs) with a hexoctahedral structure, enclosed exclusively by high-index {541} facets, are prepared via the simultaneous reduction of Au and Pd precursors without added seeds or additional metal ions as structure-regulating agents. Manipulating the NC growth kinetics via control of the relative amount of reductant is the key synthetic lever for controlling the morphology of the Au-Pd NCs. The hexoctahedral Au-Pd NCs exhibit higher catalytic performance toward the electro-oxidation of ethanol than low-index-faceted Au-Pd NCs.

Synthesis of spatially uniform metal alloys nanocrystals via a diffusion controlled growth strategy: The case of Au-Pd alloy trisoctahedral nanocrystals with tunable composition

Rational synthesis of bimetallic alloy nanocrystals (NCs) is still a great challenge. Especially, spatially uniform alloy NCs are very difficult to achieve because of the different reduction rates of the individual alloy components. Herein we propose a facile wet chemical synthetic strategy to prepare uniform bimetallic alloy NCs with tunable composition by controlling the growth of alloy NCs under diffusion controlled conditions. Using this strategy, we successfully synthesized trisoctahedral (TOH) Au-Pd alloy NCs enclosed by {hhl} high-index facets with uniform spatial distributions and different compositions. Significantly, using our strategy, the composition of the as-prepared Au-Pd alloy NCs is identical to the ratio of the two metal precursors in the reaction solution over a wide range. Investigation of the composition-dependent electrochemical behavior of the as-prepared TOH Au-Pd alloy NCs showed that the TOH Au-Pd alloy NCs containing 14.1 atom% Pd exhibited the best activity. Open image in new window

Shape control of bimetallic nanocatalysts through well-designed colloidal chemistry approaches

Synthesis of bimetallic nanomaterials with well controlled shape is an important topic in heterogeneous catalysis, low-temperature fuel cell technology, and many other fields. Compared with monometallic counterparts, bimetallic nanocatalysts endow scientists with more opportunities to optimize the catalytic performance by modulating the charge transfer between different metals, local coordination environment, lattice strain and surface element distribution. Considering the current challenges in shape controlled synthesis of bimetallic nanocatalysts, this tutorial review highlights some significant achievements in preparing bimetallic alloy, core-shell and heterostructure nanocrystals with well-defined morphologies, summarizes four general routes and some key factors of the bimetallic shape control scenarios, and provides some general ideas on how to design synthetic strategies to control the shape and exposing facets of bimetallic nanocrystals. The composition and shape dependent catalytic behaviours of bimetallic nanocrystals are reviewed as well.

Polyhedral Bimetallic Alloy Nanocrystals Exclusively Bound by {110} Facets: Au–Pd Rhombic Dodecahedra

Polyhedral Bimetallic Alloy Nanocrystals Exclusively Bound by {110} Facets: Au–Pd Rhombic Dodecahedra