Enhanced photo-induced catalytic activity of Cu ion doped ZnO - Graphene ternary nanocomposite for degrading organic dyes

A ternary photocatalyst Cu doped (0 to 10 wt%) ZnO-hybridized Graphene nanocomposite (GZCu) was prepared by hydrothermal method. A detailed analysis by XRD, RAMAN, FTIR and FESEM showed a formation of ZnO nanorods with hexagonal wurtzite structure on graphene sheets. Optical band gap has been decreased from 3.12 eV for GZnO (undoped ZnO) to 2.89 eV for GZCu. Subsequently, intensity of PL emission and PL lifetime have also been decreased with increasing Cu ion content in ZnO. Photocatalytic studies under UV and Sunlight irradiations were done on the photodegradation of organic dyes such as methyl orange (MO). The GZCu with 0.5 wt % Cu showed the highest photodegradation of MO. The maximum MO degradation was 85.7 and 89.1% under UV and Sunlight irradiation respectively for GZCu and this was 12% and 11% higher than the same shown by undoped GZnO. The enhanced degradation observed at lower Cu doping (0.5 wt %) in ZnO was attributed to the optimum doping concentration which is responsible for reduced charge recombination, increased PL lifetime and increased ^[rad]OH radical generation during the photocatalytic reaction. Photocatalytic experiments under different pH conditions showed that the photocatalyst could effectively degrade cationic dye in basic medium, because under basic conditions the catalyst's surface become negatively charged, whereby more adsorption of the cationic dye took place on its surface and resulted in enhanced degradation.