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.
Highlights
An extensive study of spontaneous alloying has been carried out by Mori and co-workers, reporting the rapid alloying of Cu,[10] Zn,6 Pb11 and Sb12 with gold
Scheme 1 Schematic representation of the time alloying process. (a) Metal small nanoparticles (sNPs) stabilized with weak ligands produce AuPt nanoalloys. (b) When Au sNPs are stabilized with thiol groups Pt and Au sNPs remain segregated even if Pt sNPs have a weak capping agent. (c) When 20 nm size Au nanoparticles stabilized with weak capping agents are used the particles remain segregated even if Pt sNPs have a weak capping agent
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
Summary
Spontaneous formation of Au–Pt alloyed nanoparticles using pure nano-counterparts as Cite this: Nanoscale, 2015, 7, 10152 starters: a ligand and size dependent process†. In this work we investigate the formation of PtAu monodisperse alloyed nanoparticles by ageing pure metallic Au and Pt small nanoparticles (sNPs), nanoparticle size
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