Comparative evaluation of copper oxide nano-photocatalyst characteristics by formation of composite with TiO2 and ZnO

In this paper, the effect of composite formation of CuO-Cu2O with TiO2 and ZnO on photocatalytic degradation of methylene blue (MB) dye was studied under visible light irradiation. The X-ray diffraction (XRD) and Raman results revealed that both Cu2O and CuO phases were obtained. Field emission scanning electron microscopy (FESEM) results showed the uniform coverage of copper oxides with TiO2 and ZnO nanoparticles which will be beneficial for charge carriers transform between different phases and copper oxides. The highly decreased photoluminescence (PL) intensity of CuO-Cu2O-ZnO photocatalyst indicated better charge separation compared to those of other samples. However, diffuse reflectance spectroscopy (DRS) results showed the increased band gap energy from 1.6 to about 2.6 and 2.7 eV by the addition of ZnO and TiO2 over CuO-Cu2O, respectively. Relatively complete degradation of 5 mg L-1 of MB solution was obtained by CuO-Cu2O-ZnO photocatalyst after 180 min visible light irradiation. A study on the kinetics and mechanism of the photodegradation process showed the rate-determining step was the formation of hydroxyl radicals. The activation energy for photodegradation of MB by CuO-Cu2O was 17.7 kJ mol(-1), which can be reduced to 8.8 kJ mol(-1) by adding ZnO. Study on the thermodynamics of photocatalysis in the temperature range of 288-318 K using the activated complex theory revealed the endothermic and nonspontaneous features of the photocatalytic process.