In-liquid plasma discharge for synthesis of copper oxide (CuO) nanospindles

Plasma generation inside liquid has been rapidly raising due to its potential application in nanomaterial synthesis. Copper oxide (CuO) nanoparticle is a p-type metal oxide semiconductor having band gap 1.2 eV. Due to its unique electrical, optical, magnetic and catalytic properties, its application also increases in recent years, such as in solar cells, sensors, water treatment, biomedical applications etc. We have developed a liquid plasma discharge reactor. Characterization of the plasma in such a system is very challenging. Plasma is generated by applying a potential difference between two copper electrodes inside distilled water. As soon as, a critical voltage is applied between the two electrodes, the tips of the electrodes become very hot and the water layer on the surface of the electrodes tends to evaporate i.e. a gaseous medium is created, which leads to the formation of a plasma channel between the two electrodes. Copper oxide nanospindles are produced due to the evaporation of atomic copper from the electrodes, followed by the rapid oxidation of the evaporated particles by the reactive radicals present in water medium due to plasma generation. Characterizations of compositional, structural and stability of CuO nanospindle has been carried out by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Dynamic light scattering (DLS) analyzer respectively. UV-Visible spectrometer is used to calculate the indirect band gap of the CuO nanospindles and it is found to be 1.58 eV. Transmission Electron Microscopy (TEM) images demonstrate that the lattice fringe width of CuO nanospindle crystal planes match with the XRD data. Moreover, TEM images shows that the nanospindles have a very strong tendency to aggregate to form CuO nanoflowers. (author)