Spontaneous Chemical Ordering in Bimetallic Nanoparticles

Abstract

The real composition of nanostructure strongly determines its properties. Especially, in some cases the bulk composition of material could be different than the surface composition due to the surface segregation. Surface segregation is a common process caused by different surface energy of elements. Moreover the surface (in the sense of first atomic layer) composition is very important knowledge in many science fields e.g. semiconductors functionalization, environmental protection or pollution remediation. One of such a surface science is heterogeneous catalysis. In this field surface composition is extremely important because chemical reaction occurs only at catalyst surface. The X-ray Photoelectron Spectroscopy is surface sensitive technique, which could determine samples' composition. In this method, depending on the material, major amount of signal is collected from the first 5 nm of the sample. Nevertheless for nanostructures like core-shell nanoparticles such an XPS analysis is more challenging due to the diameter of nanoparticles which is usually around 5 nm. Although with more complex analysis, which includes Inelastic Mean Free Path model for each element building nanoparticle, we can more effectively describe observed segregation [1]. Figure1. XPS quantitative analysis for Pt-Rh nanoparticles in function of nominal platinum content. Two data sets are shown black line-determined from higher energetic Pt 4f doublet and red line-determined from higher energetic Pt 4d doublet. Increased Pt content in topmost layer can be observed. In this report we determined composition and described surface segregation in bimetal alloy-PtRh nanoparticles. We determined surface composition using monochromatic XPS measurement and we compared it with total composition obtained by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Thanks to determining the actual surface composition in this material we could properly correlate catalytic properties of this material to Rhodium content on the surface. Our results demonstrate the strength of X-ray Photoelectron Spectroscopy technique in such interdisciplinary studies.

Comparative Physicochemical and Electrochemical Characterization of the Structure and Composition of Thin Pd Binary and Ternary Codeposits with Pt, Ru, and Rh

“…These points require more detailed comments [ 64 ]: The good agreement with Vegard’s law suggests that the alloy phase is the only one present in the samples, i.e., that the deposits are highly homogeneous. However, the literature data show that such a conclusion should be drawn with care (see Januszewska et al [ 65 ] and the references therein). In particular, there are evidences that even in homogenous systems, the deviations from Vegard’s law are observed, and vice versa, Vegard’s law can be very well fulfilled in the case of heterogeneous materials.…”

Palladium Nanoparticles in Polyols: Synthesis, Catalytic Couplings, and Hydrogenations

“…Jurczakowski and co-workers prepared PdPt nanoparticles in neat EG by co-reduction of PdCl 2 and K 2 PtCl 4 in the absence of any other reagent, leading to nanoparticles highly aggregated as proven by TEM analyses. 99 These materials were used to study the spontaneous segregation of PdPt nanoalloys, mainly evidenced by the enhanced hydrogen solubility under ambient conditions together with XPS studies, proving a higher segregation trend than their bulk counterparts. These experimental results confirm the theoretical DFT studies reported by Barcaro et al concerning the multi-shell segregation of PdPt nano-alloys.…”