Chemical Evolution of Pt–Zn Nanoalloys Dressed in Oleylamine

Abstract

We report on the shape, composition (from Pt95Zn5 to Pt77Zn23), and surface chemistry of Pt–Zn nanoparticles obtained by reduction of precursors M2+(acac)2 – (M2+: Pt2+ and Zn2+) in oleylamine, which serves as both solvent and ligand. We show first that the addition of phenyl ether or benzyl ether determines the composition and shape of the nanoparticles, which point to an adsorbate-controlled synthesis. The organic (ligand)/inorganic (nanoparticles) interface is characterized on the structural and chemical level. We observe that the particles, after washing with ethanol, are coated with oleylamine and the oxidation products of the latter, namely, an aldimine and a nitrile. After exposure to air, the particles oxidize, covering themselves with a few monolayer thick ZnO film, which is certainly discontinuous when the particles are low in zinc. Pt–Zn particles are unstable and prone to losing Zn. We have strong indications that the driving force is the preferential oxidation of the less noble metal. Finally, we show that adsorption of CO on the surface of nanoparticles modifies the oxidation state of amine ligands and attribute it to the displacement of hydrogen adsorbed on Pt. All the structural and chemical information provided by the combination of electron microscopy and X-ray photoelectron spectroscopy allows us to give a fairly accurate picture of the surface of nanoparticles and to better understand why Pt–Zn alloys are efficient in certain electrocatalytic reactions such as the oxidation of methanol.

Controlled Preparation and Anti‐Sulfate Electrocatalysis of Self‐Assembled Multidimensional PtZn Quasi‐Cubic Nanodendrites

“…This was already reported previously for the study on composition and surface chemistry of PtZn alloy nanoparticles by Alter Zakhtser et al. [ 53 ]…”

“…Furthermore, the reason of why the zinc content was extremely low in PtZn‐FL could also be explained because Zn preferred to combine with facets which have more exposed surface atoms to provide stable deposition sites for Zn atoms. Since the (100) facet of Pt, that was believed to have more exposed surface atoms than the (111) facet, [ 53 ] was hindered by Br – , Zn had to deposit on the (111) facet of Pt that is not an ideal facet for deposition of Zn, and thus gave rise to the less zinc content. With the reaction going on 20 h, the appearance of the products without CTAB became spiny‐ball shaped (with average size of 34–47 nm).…”

“…In particular, as the reaction temperature was controlled at relative low temperature (190 °C) aimed to prolong the reaction period (20 h), it becomes convenient to catch intermediate products at different stages for tracking the crystal growth and investigating of the formation process of the PtZn‐ND. [ 52,53 ] In addition, other crucial factors that have significant influences on crystal growth, such as the amount of hexadecyltrimethyammonium bromide (CTAB), the ratio of oleylamine (OAM) to oleic acid (OA), the replacement for CTAB with NaBr, were also comparatively studied to obtain a deep understanding of the regulation mechanism of the PtZn‐ND. Meanwhile, the distribution behavior of Pt and Zn in the PtZn‐ND was proposed via comparing influences of the surface energy, strain energy and formation mechanism.…”

Anisotropic growth of ZnO nanoparticles driven by the structure of amine surfactants: the role of surface dynamics in nanocrystal growth

“…39 In this context, the use of amines with long fatty chains as surfactants, like the archetypal oleylamine, 40 is very popular to achieve good control of the morphology of NCs. The high boiling point of oleylamine, above 360 °C, allowed using it in thermolytic reduction processes whether in a "heat up" approach, [41][42][43][44][45][46][47][48][49] or through the so-called "hot-injection" [48][49][50][51] technique. Hexadecylamine, dodecylamine and octylamine are also extensively used under milder conditions for the formation of metallic, II-VI or III-V semiconductor NCs.…”

Bimetallic Nanoparticles Associating Noble Metals and First-Row Transition Metals in Catalysis

“…Furthermore, Zakhtser et al also describe the leaching of zinc when PtZn nanoparticles (NPs) were left for several days at room temperature in non-degassed toluene, a phenomenon which leads to the formation of a Pt-enriched surface. 3 These observations highlight the dynamic behavior of bimetallic nano-alloys that can eventually be segregated or can give rise to the isolation of one atom of an element at the surface of another, leading to a large complexity of situations, some aspects of which we will discuss here. Using selected recent examples, we will underscore the importance of such bimetallic compounds in catalysis and electrochemistry and give evidence for their atomic mobility and for the electronic influence of one metal on the other.…”