Facile synthesis of size-tunable copper and copper oxide nanoparticles using reverse microemulsions

The synthesis of pure metal and metal-oxide nanoparticles of a desired size remains a significant challenge. We describe a novel, simple and convenient method for the synthesis of copper and copper(II) oxide nanoparticles with tailored sizes at room temperature from a common copper(II) salt (CuSO4 center dot 5H(2)O) in TX-100/n-hexanol/cyclohexane/water by a reverse microemulsion route. It was found that reduction with hydrazine hydrate (reduction potential 1.15 V) in an inert N-2 environment gives copper nanoparticles whereas reaction with sodium borohydrate (reduction potential 1.24 V) in aerobic condition gives copper(II) oxide nanoparticles. Several parameters were modulated to examine their effects on the structural properties of nanoparticles, namely the size and morphology of the nanoparticles. The size of the copper and copper(II) oxide nanoparticles can be easily controlled by changing the molar ratio of water to surfactant or by altering the concentration of the reactants. The nanoparticles were characterized using a variety of analytical techniques like X-ray diffraction (XRD), quasi elastic light scattering (QELS), UV-visible absorption spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDAX). Our studies reveal that the nanoparticles are spherical in shape and have an average size distribution of 5-100 nm. Our protocol provides a rapid and low cost procedure for the synthesis of both copper and copper(II) oxide nanoparticles in the same microemulsion pool. The nanoparticles so formed have been successfully used for catalyzing various chemical reactions.