SYNTHESIS, CHARACTERIZATION, AND PROPERTIES OF METALLIC COPPER NANOPARTICLES

Nanoscale particles of metallic copper clusters have been prepared by two methods, namely the thermal reduction and sonochemical reduction o f copper(II) hydrazine carboxylate Cu(N2H3COO)(2) . 2H(2)O complex in an aqueous medium. Both reduction processes-take place under an argon atmosphere over a period of 2-3 h. The FT-IR, powder X-ray diffraction , and UV-visible studies support the reduction products of Cu2+ ions a s metallic copper nanocrystallites. The powder X-ray analysis of the t hermally derived products show the formation of pure metallic copper, while the sonochemical method yields a mixture of metallic copper and copper oxide(Cu2O). The formation of Cu2O along with the copper nanopa rticles in the sonochemical process can be attributed to the partial o xidation of copper by in situ generated H2O2 under the sonochemical co nditions. However, the presence of a mixture of ee an argon/hydrogen ( 95:5) atmosphere yields pure copper metallic nanoparticles, which coul d be due to the scavenging action of the hydrogen towards the OH. radi cals that are produced in solution during ultrasonic irradiation. The synthesized copper nanoparticles exhibit a distinct absorption peak in the region of 550-650nm. The transmission electron microscopy studies of the thermally derived copper show the presence of irregularly shap ed particles (200-250 nm) having sharp edges and facets. On the other hand, the sonochemically derived copper powder shows the presence of p orous aggregates(50-70nm) that contain an irregular network of small n anoparticles. The copper nanoparticles are catalytically active toward an ''Ullmann reaction''-that is, the condensation of aryl halides to an extent of 80-90% conversion. The time course of catalysis was studi ed for condensation of iodobenzene at 200 degrees C for a period of 1- 5 h. The catalytic ability of copper nanoparticles produced by the the rmal and sonochemical methods was compared with that of commercial cop per powders.