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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.


Cs-corrected STEM-HAADF images, particle size distribution and representative EDS analysis of single PtAu sNPs obtained by the physical mixture of Au and Pt sNPs stabilized with THPC at several times: (a) 16 h and (b) spontaneous alloying after 10 days.
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fig2: Cs-corrected STEM-HAADF images, particle size distribution and representative EDS analysis of single PtAu sNPs obtained by the physical mixture of Au and Pt sNPs stabilized with THPC at several times: (a) 16 h and (b) spontaneous alloying after 10 days.

Mentions: In a previous study,23 we showed that the use of tetrakis-(hydroxymethyl) phosphonium chloride solution (THPC) as the simultaneous reducing and stabilizing agent at room temperature in aqueous phase renders a variety of monometallic, bimetallic and trimetallic noble metal clusters. Tris(hydroxymethyl) phosphine oxide (THPO) is the cleavage product of THPC in alkaline solution, and it adsorbs onto the surface of the colloidal NPs as a protecting ligand during the reduction of noble metal precursors.24Fig. 1a and b show a representative selection of the spherical aberration (Cs) corrected STEM-HAADF images of Pt and Au small nanoparticles (sNPs) obtained at room temperature after 4 days of reaction time following this approach. In the case of the Pt clusters, well-crystallized structures of 1.8 nm were observed which could be indexed matching the Fm3m space group of Pt. On the other hand, gold nanoparticles with a relatively wide size distribution between 4 and 6 nm (Fig. 1b), with decahedral morphology, presented a certain tendency to coarsen at room temperature though this process could be avoided if they were kept under 4 °C.23,25 PtAu bimetallic sNPs were obtained if platinum and gold precursors were simultaneously mixed before the reduction process was induced by the THPC decomposition under alkaline conditions (see Fig. 1c). The particle size, chemical composition and atomic distribution were well controlled using this easy synthesis procedure.23 Finally, when preformed Pt and Au sNPs were mixed in equimolar concentrations, Au sNPs tended to coarse while Pt sNPs were stable (Fig. 2a). After several days of aging at room temperature, PtAu nanoalloyed sNPs with a Pt/Au atomic ratio of 1.2 were obtained (Fig. 2b).


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)

Cs-corrected STEM-HAADF images, particle size distribution and representative EDS analysis of single PtAu sNPs obtained by the physical mixture of Au and Pt sNPs stabilized with THPC at several times: (a) 16 h and (b) spontaneous alloying after 10 days.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: Cs-corrected STEM-HAADF images, particle size distribution and representative EDS analysis of single PtAu sNPs obtained by the physical mixture of Au and Pt sNPs stabilized with THPC at several times: (a) 16 h and (b) spontaneous alloying after 10 days.
Mentions: In a previous study,23 we showed that the use of tetrakis-(hydroxymethyl) phosphonium chloride solution (THPC) as the simultaneous reducing and stabilizing agent at room temperature in aqueous phase renders a variety of monometallic, bimetallic and trimetallic noble metal clusters. Tris(hydroxymethyl) phosphine oxide (THPO) is the cleavage product of THPC in alkaline solution, and it adsorbs onto the surface of the colloidal NPs as a protecting ligand during the reduction of noble metal precursors.24Fig. 1a and b show a representative selection of the spherical aberration (Cs) corrected STEM-HAADF images of Pt and Au small nanoparticles (sNPs) obtained at room temperature after 4 days of reaction time following this approach. In the case of the Pt clusters, well-crystallized structures of 1.8 nm were observed which could be indexed matching the Fm3m space group of Pt. On the other hand, gold nanoparticles with a relatively wide size distribution between 4 and 6 nm (Fig. 1b), with decahedral morphology, presented a certain tendency to coarsen at room temperature though this process could be avoided if they were kept under 4 °C.23,25 PtAu bimetallic sNPs were obtained if platinum and gold precursors were simultaneously mixed before the reduction process was induced by the THPC decomposition under alkaline conditions (see Fig. 1c). The particle size, chemical composition and atomic distribution were well controlled using this easy synthesis procedure.23 Finally, when preformed Pt and Au sNPs were mixed in equimolar concentrations, Au sNPs tended to coarse while Pt sNPs were stable (Fig. 2a). After several days of aging at room temperature, PtAu nanoalloyed sNPs with a Pt/Au atomic ratio of 1.2 were obtained (Fig. 2b).

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.