Amines as dual function ligands in the two-phase synthesis of stable AuxCu(1−x) binary nanoalloys

Abstract

The synthesis of Au_xCu_(1−x) nanoalloys (NAs) by a two-phase method employing amines acting simultaneously as coordinating ligands, phase transfer agents as well as nanoparticle (NP) stabilisers, is presented. The value of x was varied between 0 and 1 and dodecylamine (DDA) and hexadecylamine (HDA) were used as ligands. The nanoparticles were characterised by elemental analysis, UV-vis and IR spectroscopies, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning TEM (STEM) and X-ray photoelectron spectroscopy (XPS). Alloying with Au imparts significant stability to Cu nanoparticles. Interestingly, some degree of surface segregation for Cu in the synthesised Au_xCu_(1−x) NAs is revealed from the TEM analysis, contrary to expectations based on previously calculated segregation energies. XRD analysis demonstrates a high degree of crystallinity of the cores although the crystallite sizes obtained from the Scherrer equation are smaller than TEM measurements. A mild heat treatment is sufficient to enhance the overall particle crystallinity resulting in crystallite size estimates from XRD comparable to those obtained from TEM.