Synthesis of platinum ultrafine particles in AOT reverse micelles

The synthesis of platinum ultrafine particles by the reduction of H2PtCl6 w ith hydrazine in AOT/isooctane reverse micellar solutions has been studied. By high-resolution electron microscope, electron diffraction pattern, and XRD analyses, the resultant particles have been found to be pure platinum o f fee structure. Their sizes were observed to increase with the increases i n the molar ratio of water to AOT (omega(O)) and in the concentration of H2 PtCl6, while they decreased with the increase of hydrazine concentration. A t a constant omega(O) value, the size of platinum ultrafine particles was n ot affected significantly when the concentration ratio of hydrazine to H2Pt Cl6 was above 10, the AOT concentration increased from 0.1 to 0.6 M, and th e temperature varied from 15 to 35 degrees C. Furthermore, the kinetic stud y of particle formation indicated that the nucleation time needed several m inutes. The time for the growth of platinum ultrafine particles to their fi nal size after nucleation was about one to several hours. It was observed t hat the formation rates increased with the increase of omega(O) value and t he concentrations of AOT and H2PtCl6, but they were not affected by hydrazi ne concentration when the concentration ratio of hydrazine to H2PtCl6 was a bove 10. (C) 1999 Academic Press.