CuO-MMT nanocomposite: effective photocatalyst for the discoloration of methylene blue in the absence of H2O2

Copper oxide (CuO) nanoparticles are of particular interest because of their interesting properties and promising applications in photocatalysis and purification of water. In this work, CuO-montmorillonite (CuO-MMT) nanocomposite was synthesized by a thermal decomposition method and characterized by diffuse reflectance spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The resultant particles were nearly spherical, and particle size in MMT was in the range of similar to 3-5 nm. The powder X-ray reflection patterns indicate that MMT has a d-spacing higher (1.22 nm) than CuO-MMT nanocomposite (0.97 nm). The shrinkage probably is related to the conformation of CuO nanoparticles on the clay surface. The diffuse reflectance spectrum of CuO-MMT showed band around 340-360 nm corresponding to presence of [Cu-O-Cu] n-type clusters over the support surface. The band gaps of the resulting CuO nanoparticles and CuO-MMT nanocomposite were widened from 1.70 to 1.80 eV for an indirect allowed band gap and from 3.70 to 3.82 eV for a direct allowed inter band transition owing to the quantum size effect, respectively. The nanocomposite exhibited an enhanced and stable photoactivity for the discoloration of methylene blue (MB) aqueous solution under visible light. The result showed that MB discoloration was observed after 20 min light irradiation in the absence of H2O2. The several parameters were examined, such as the catalyst amount, pH and initial concentration of MB. The mechanism of separation of the photogenerated electrons and holes of the CuO-MMT nanocomposite was discussed.