On the thermal stability and surface and catalytic properties of Cu-Ni nanoparticles

Abstract

There is an increased interest in nanoparticle research due to the distinct behaviour of nanoparticles and their compact counterparts with the same chemical composition. The distinct properties include different catalytic activities and phase transformation temperatures. The presented paper deals with the thermal stability and surface and catalytic properties of bimetallic Cu-Ni nanoparticles (NPs). Samples with selected compositions of nanoparticles with a diameter of 8 – 21 nm were prepared via the solvothermal method from copper(II) acetylacetonate and nickel(II) acetylacetonate in an organic solvent mixture of oleylamine and octadec-1-ene. The nanoparticles were characterized by dynamic light scattering (DLS), ultraviolet and visible light spectroscopy (UV-VIS), scanning and transmission electron microscopy (SEM, TEM) equipped with elemental analysis using energy dispersive X-ray spectroscopy (EDX). The elemental composition was characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES). The catalytic properties of the Cu-Ni NPs and the catalytic decomposition of the organic envelope were investigated by Knudsen effusion mass spectrometry (KEMS). Carbon dioxide evolution and creation of decomposition products were observed by mass spectrometry (MS). The optimum efficiency of the catalytic process was observed for Cu-Ni NPs with a copper content of 40-50 %. The thermal stability of the Cu-Ni NPs was monitored using differential scanning calorimetry (DSC) and their melting point depression was evaluated to range from 35.9 to 28.4°C. The results include a description of the processes occurring during the heating of nanoparticles above their melting temperature and during cooling. In addition, new findings were made about the catalytic decomposition of the stabilising organic ligands on the Cu-Ni NPs and the solidus curve of the Cu-Ni phase diagram was determined for Cu-Ni NPs of an average size of 12 nm.