Formation mechanism of Pd/PVP nanoparticles: effect of ultrasonic irradiation time

Abstract

The effects of ultrasonic irradiation time on the palladium nanoparticles (Pdns) formation mechanism have been investigated using UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Pdns colloids have been prepared by ultrasonic irradiation of Pd(NO3)2 solutions at different irradiation times (from 30 to 180 minutes). The obtained results show that the rate of sonochemical reduction of Pd(II) ions has been found to be dependent upon the irradiation time. The kinetic of Pdns formation can also be correlated with the rate of sonochemical reduction ofPd(II) ions, as well as with the role of PVP molecules. The results suggest a three-step mechanism to describe the Pdns formation as a function of ultrasound irradiation time. During the first step, the Pd(II) ions are rapidly reduced to Pd(0) atoms, and when the concentration of Pd(0) atoms is sufficient for nucleation, the formation of primary particles occurs which are stabilised by a maximal number of PVP molecules. During the second step, these particles grow progressively by adsorption of the Pd(0) atoms and the obtained particles are coordinated to all available PVP molecules. The third step corresponds to decrease of the bounded PVP to the particle surface and the growth of the large particles at the expense of the unstable small ones. Keywords: Palladium nanoparticles, ultrasound irradiation, formation mechanism, UV-visible spectroscopy, FT-IR spectroscopy, TEM.