A group of researchers at Dagestan State University has managed to synthesise cuprite nanoparticles using an electrochemical method. They report their discovery in an article currently in print, issue #7–8 of the Russian Nanotechnologies.
Cuprous oxide – Cu2O, or cuprite — is a rather promising material for solar power engineering. In its main form, cuprite electrons — just like all other semiconductors — fill the valence band with excitation (energy transferring externally) resulting in a shift into the conductivity band. At that, electrons cannot have the intermediate energy for both zones; the width of this forbidden zone for cuprite reaches 2.0–2.2 eV. In turn, visible light photons have from 1.6 to 3.1 eV which means that their interaction with the electrons allows them to transfer the energy sufficient for a shift into the conductivity band. Due to this ability, cuprite can effectively turn solar radiation into electricity which, together with its inexpensive price, makes Cu2O a rather promising photovoltaic material.
Copper electrodes are used as anodes and cathodes for electrolysis with the current flowing between them through a saturated sodium chlorides water solution. The copper electrode dissolves in the process with a reddish Cu2O sediment forming there. These properties of copper were used by the researchers at Dagestan State University. They paid special attention to experimenting with additional conditions of the synthesis. The study was conducted according to the Federal Task Program “Scientific and Pedagogical Resources of Innovative Russia for 2009-2013.
Cuprite synthesis was undertaken at various levels of hydrogen pressure. In all cases, the scanning electron microscopy and X-ray structural analysis proved that Cu2O particles of high purity were generated. However, the specific surface area that can be quantified by the degree of chromium adsorption decreases with the pressure growth as the average particle size goes up from 8 to 36 nanometer. The known fact is that the surface area is inversely proportional to the particle size.
In addition, Cu2O particles have good photocatalystic properties. Their presence results in the formation of active oxygen-containing agents that destroy dye molecules. Dark-blue chrome azo dye was used for photocatalysis experiments. Exposure to ultraviolet or daylight made the dye lose its colour, with the increase of the external pressure of the oxidiser — oxygen — the speed of decolouration grew as well. The resultant dependence between the decolouration speed and the oxygen pressure has a knee around the 0.4 megapascal which might suggest a side-effect of a film consisting of CuO bivalent copper oxide on the surface on the nanoparticles.
Thus, Russian researchers found the method of effective generation of Сu2O photoactive nanoparticles. In addition, they studied the effect of external pressure on the size of nanoparticles and their photocatalystic properties.
Source of information:
А. B. Isaev, N. А. Zakargaeva, Z. М. Aliev: “The Electrochemical Synthesis of Сu2O nanoparticles Under Pressure and the Study of Their Photocatalystic Activity.” The Russian Nanotechnologies, vol. 6, #7–8 (in print).