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Spontaneous formation of Au-Pt alloyed nanoparticles using pure nano-counterparts as starters: a ligand and size dependent process.

Usón L, Sebastian V, Mayoral A, Hueso JL, Eguizabal A, Arruebo M, Santamaria J - Nanoscale (2015)

Bottom Line: PtAu alloyed nanoparticles were obtained after 150 h of reaction at room temperature if a weak capping agent was used for the stabilization of the nanoparticles.It was also found that Au atoms diffuse towards Pt sNPs, producing a surface enriched in Au atoms.This study shows that even pure nanoparticles are prone to be modified by the surrounding nanoparticles to give rise to new nanomaterials if atomic diffusion is feasible.

View Article: PubMed Central - PubMed

Affiliation: Institute of Nanoscience of Aragon (INA) and Department of Chemical Engineering and Environmental Technology, University of Zaragoza, C/Mariano Esquillor, s/n, I+D+i Building, 50018, Zaragoza, Spain. victorse@unizar.es jesus.santamaria@unizar.es.

ABSTRACT
In this work we investigate the formation of PtAu monodisperse alloyed nanoparticles by ageing pure metallic Au and Pt small nanoparticles (sNPs), nanoparticle size <5 nm, under certain conditions. We demonstrate that those bimetallic entities can be obtained by controlling the size of the initial metallic sNPs separately prepared and by selecting their appropriate capping agents. The formation of this spontaneous phenomenon was studied using HR-STEM, EDS, ionic conductivity, UV-Vis spectroscopy and cyclic voltammetry. Depending on the type of capping agent used and the size of the initial Au sNPs, three different materials were obtained: (i) AuPt bimetallic sNPs showing a surface rich in Au atoms, (ii) segregated Au and Pt sNPs and (iii) a mixture of bimetallic nanoparticles as well as Pt sNPs and Au NPs. Surface segregation energies and the nature of the reaction environment are the driving forces to direct the distribution of atoms in the bimetallic sNPs. PtAu alloyed nanoparticles were obtained after 150 h of reaction at room temperature if a weak capping agent was used for the stabilization of the nanoparticles. It was also found that Au atoms diffuse towards Pt sNPs, producing a surface enriched in Au atoms. This study shows that even pure nanoparticles are prone to be modified by the surrounding nanoparticles to give rise to new nanomaterials if atomic diffusion is feasible.

No MeSH data available.


Cyclic voltammetry (sweep rate 50 mV s–1) at 298 K and 0.5 M H2SO4 of Pt and Au sNPs stabilized with THPC and physically mixed and analysed after 15 days. Cyclic voltammograms show that the onset of oxide adsorption on Au is positively shifted by more than 600 mV vs. Pt, indicating that Pt is much more oxophilic than Au.
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fig6: Cyclic voltammetry (sweep rate 50 mV s–1) at 298 K and 0.5 M H2SO4 of Pt and Au sNPs stabilized with THPC and physically mixed and analysed after 15 days. Cyclic voltammograms show that the onset of oxide adsorption on Au is positively shifted by more than 600 mV vs. Pt, indicating that Pt is much more oxophilic than Au.

Mentions: The surface properties associated with the nanoscale alloying or phase segregation of the bimetallic nanoparticles can also be addressed by measurements of the electrochemical properties. In fact, the electrochemical properties of Au and Pt nanoparticles are different since Au nanoparticles are inactive for hydrogen adsorption.32 Then, the electrochemical characterization of the bimetallic Au–Pt sNPs obtained after the physical mixture of pure sNPs can give some insight into the atomic distribution of Au and Pt. The cyclic voltammograms (CVs) of the monometallic and bimetallic sNPs in 0.5 M H2SO4 are displayed in Fig. 6. In the CVs of the Pt sNPs, characteristic current peaks that can be assigned to the hydrogen adsorption/desorption on the Pt surface are identified at around 0 and 0.2 V vs. RHE, indicating the effective removal of surfactants and organic materials from the surface of the Pt sNPs by the previous electrochemical cleaning process. Oxidation/reduction of Pt events can be located at potentials around 0.6–1.1 V vs. RHE in the same voltammogram.


Spontaneous formation of Au-Pt alloyed nanoparticles using pure nano-counterparts as starters: a ligand and size dependent process.

Usón L, Sebastian V, Mayoral A, Hueso JL, Eguizabal A, Arruebo M, Santamaria J - Nanoscale (2015)

Cyclic voltammetry (sweep rate 50 mV s–1) at 298 K and 0.5 M H2SO4 of Pt and Au sNPs stabilized with THPC and physically mixed and analysed after 15 days. Cyclic voltammograms show that the onset of oxide adsorption on Au is positively shifted by more than 600 mV vs. Pt, indicating that Pt is much more oxophilic than Au.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4447060&req=5

fig6: Cyclic voltammetry (sweep rate 50 mV s–1) at 298 K and 0.5 M H2SO4 of Pt and Au sNPs stabilized with THPC and physically mixed and analysed after 15 days. Cyclic voltammograms show that the onset of oxide adsorption on Au is positively shifted by more than 600 mV vs. Pt, indicating that Pt is much more oxophilic than Au.
Mentions: The surface properties associated with the nanoscale alloying or phase segregation of the bimetallic nanoparticles can also be addressed by measurements of the electrochemical properties. In fact, the electrochemical properties of Au and Pt nanoparticles are different since Au nanoparticles are inactive for hydrogen adsorption.32 Then, the electrochemical characterization of the bimetallic Au–Pt sNPs obtained after the physical mixture of pure sNPs can give some insight into the atomic distribution of Au and Pt. The cyclic voltammograms (CVs) of the monometallic and bimetallic sNPs in 0.5 M H2SO4 are displayed in Fig. 6. In the CVs of the Pt sNPs, characteristic current peaks that can be assigned to the hydrogen adsorption/desorption on the Pt surface are identified at around 0 and 0.2 V vs. RHE, indicating the effective removal of surfactants and organic materials from the surface of the Pt sNPs by the previous electrochemical cleaning process. Oxidation/reduction of Pt events can be located at potentials around 0.6–1.1 V vs. RHE in the same voltammogram.

Bottom Line: PtAu alloyed nanoparticles were obtained after 150 h of reaction at room temperature if a weak capping agent was used for the stabilization of the nanoparticles.It was also found that Au atoms diffuse towards Pt sNPs, producing a surface enriched in Au atoms.This study shows that even pure nanoparticles are prone to be modified by the surrounding nanoparticles to give rise to new nanomaterials if atomic diffusion is feasible.

View Article: PubMed Central - PubMed

Affiliation: Institute of Nanoscience of Aragon (INA) and Department of Chemical Engineering and Environmental Technology, University of Zaragoza, C/Mariano Esquillor, s/n, I+D+i Building, 50018, Zaragoza, Spain. victorse@unizar.es jesus.santamaria@unizar.es.

ABSTRACT
In this work we investigate the formation of PtAu monodisperse alloyed nanoparticles by ageing pure metallic Au and Pt small nanoparticles (sNPs), nanoparticle size <5 nm, under certain conditions. We demonstrate that those bimetallic entities can be obtained by controlling the size of the initial metallic sNPs separately prepared and by selecting their appropriate capping agents. The formation of this spontaneous phenomenon was studied using HR-STEM, EDS, ionic conductivity, UV-Vis spectroscopy and cyclic voltammetry. Depending on the type of capping agent used and the size of the initial Au sNPs, three different materials were obtained: (i) AuPt bimetallic sNPs showing a surface rich in Au atoms, (ii) segregated Au and Pt sNPs and (iii) a mixture of bimetallic nanoparticles as well as Pt sNPs and Au NPs. Surface segregation energies and the nature of the reaction environment are the driving forces to direct the distribution of atoms in the bimetallic sNPs. PtAu alloyed nanoparticles were obtained after 150 h of reaction at room temperature if a weak capping agent was used for the stabilization of the nanoparticles. It was also found that Au atoms diffuse towards Pt sNPs, producing a surface enriched in Au atoms. This study shows that even pure nanoparticles are prone to be modified by the surrounding nanoparticles to give rise to new nanomaterials if atomic diffusion is feasible.

No MeSH data available.