Synthesis of palladium nanoparticles in water-in-oil microemulsions

Palladium nanoparticles have been synthesized by the reduction of Pd(NH3)4Cl2 with hydrazine in the cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB), n-butanol/isooctane at 25°C. By the analyses of electron diffraction pattern and X-ray diffraction, the resultant particles were characterized to be the pure palladium crystalline with a face-centered cubic (fcc) structure. The investigation on the microemulsion compositions indicated that the average diameter of palladium nanoparticles was affected mainly by the interfacial property, not the size of microemulsion droplets. At a higher ratio of CTAB to n-butanol, smaller particles could be obtained. When Pd(NH3)4Cl2 concentration was fixed, the average diameter of palladium nanoparticles decreased with the increase in hydrazine concentration and then approached to a constant value when the concentration ratio of hydrazine to Pd(NH3)4Cl2 was above 7. At a sufficiently high hydrazine concentration, the average diameter of palladium nanoparticles was independent of Pd(NH3)4Cl2 concentration. In addition, it was surprisingly found that the magnetic susceptibility of the resultant palladium nanoparticles was significantly higher than that of bulk palladium.