Synthesis of palladium nanoparticles in water-in-oil microemulsions

Palladium nanoparticles have been synthesized by the reduction of Pd(NH3)(4 )Cl-2 with hydrazine in the cationic water-in-oil (w/o) microemulsions of w ater/cetyl-trimethyl-amonium bromide (CTAB), n-butanol/isooctane at 25 degr eesC. By the analyses of electron diffraction pattern and X-ray diffraction , the resultant particles were characterized to be the pure palladium cryst alline with a face-centered cubic (fcc) structure. The investigation on the microemulsion compositions indicated that the average diameter of palladiu m nanoparticles was affected mainly by the interfacial property, not the si ze of microemulsion droplets. At a higher ratio of CTAB to n-butanol, small er particles could be obtained. When Pd(NH3)(4)Cl-2 concentration was fixed , the average diameter of palladium nanoparticles decreased with the increa se in hydrazine concentration and then approached to a constant value when the concentration ratio of hydrazine to Pd(NH3)(4)Cl-2 was above 7. At a su fficiently high hydrazine concentration, the average diameter of palladium nanoparticles was independent of Pd(NH3)(4)Cl-2 concentration. In addition, it was surprisingly found that the magnetic susceptibility of the resultan t palladium nanoparticles was significantly higher than that of bulk pallad ium. (C) 2001 Elsevier Science B.V. All rights reserved.