Diffusion Controlled Features of Microwave Assisted ZnS/ZnO Nanocomposite with Reduced Band Gap

Abstract

ZnS and ZnO are both wide band gap semiconductors. Their nanocomposites have high potential for photocatalytic activity and useful for different applications such as optical sensor, photoconductor, catalysts and anode material for solar cells. In the present investigations an effort has been made to synthesize ZnS/ZnO nanocomposites by inducing microwave treatment before hydrothermal process in order to increase the reaction rate of ZnS/ZnO and to reduce the optical band gap and particle size of the material. X-ray diffraction data revealed the formation of ZnS as well as ZnO phases. W-H plot and Size-Strain plot revealed information of size and strain present in the material. UV–vis spectroscopy analysis showed a reduced band gap of 3.14 eV and the refractive index of 2.36 for the material. Microstructural and morphological investigations as carried out by TEM and FESEM showed spherical shaped particles having average crystallite size of about 26 nm. Elemental compositional analysis of the material depicted the presence of zinc, oxygen and sulphur. FTIR study revealed the formation of Zn-S bond and presence of adsorbed oxygen in the as-synthesized material. The electrochemical studies include cyclic voltammetry (CV) and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS). Cyclic voltammetry depicted the diffusion-controlled behaviour of the ZnS/ZnO nanocomposites and the reduction in specific capacitance with increasing scan rate. PEIS studies were analyzed by Nyquist and Bode plot which also confirmed the diffusion behaviour of material by Randle’s Circuit and its parameters. ZnS/ZnO showed diffusion controlled features indicating that the excitons control the current in the material and thus has a good prospect for solar cell applications.