Modification of energy level diagram of nano-crystalline ZnO by its composites with ZnWO4 suitable for sunlight assisted photo catalytic activity

Abstract

In this paper we report single step synthesis of ZnO - ZnWO4 nanocomposites using thermal plasma route, where thermal plasma plume having sufficiently high thermal flux was impinged onto zinc -tungsten precursor and the species so evaporated were made to interact with oxygen in gas phase to get the final product. X-ray diffraction and Raman spectroscopic techniques were used to ascertain the composite phases. X-Ray Diffraction and Raman Spectroscopic analysis witnessed the formation of ZnO-ZnWO4 nano-composites, with monoclinic wolframite structure of tungstate while wurtzite structure of ZnO. Optical properties of the as synthesized product were recorded and analyzed using UV–vis and Photo-luminescence spectroscopic techniques. Retarding field diode method was used to determine work function of the ZnO-ZnWO4 composites under investigation, where gold sample was used as a reference. Subsequently, the photocatalytic efficiency of such ZnO-ZnWO4 nano-composites was analyzed by assessing the degradation of Crystal Violet dye. Experimentally measured values of surface work-function of the composites were analyzed and corelated with photocatalytic response. The degradation of Crystal Violet up to 82.07 % was achieved for 5 wt. % of W in the composite as compared to a value of 25.14 % for the pure ZnO nanoparticles under the exposure to sunlight radiations.