Influence of ZnO concentration on the optical and photocatalytic properties of Ni-doped ZnS/ZnO nanocomposite

Photocatalysts consisting of nickel-doped ZnS/ZnO core shell nanocomposites with varying concentrations of ZnO was synthesized through chemical precipitation method. The catalyst was deployed in photocatalytic degradation of indigo carmine dye as a model organic pollutant. Characterization of the samples was achieved through the use of X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, UV-vis spectroscopy and energy dispersive spectroscopy. The composites consist of wurtzite ZnO phase deposited on cubic ZnS. Optical absorption, crystallite sizes and photocatalytic degradation efficiency increased with increasing ZnO concentration. Bandgap values of ZnS also decreased appreciably with increase in ZnO concentration. Ni-doped ZnS/(0.5 M ZnO) was identified as the most efficient catalyst with 91% dye degradation efficiency at a rate of 15.38 × 10^-3 min^-1 in 180 min. Meanwhile, the pristine ZnS degraded 25% of the dye at the rate of 1.53×10^-3 min^-1 within the same time. The Ni-doped Zns/(0.5MZnO) was used to degrade the dye on the basis of influence of factors such as solution temperature, hydrogen peroxide (H₂O₂) and ethanol contents. Dye degradation increased with increase in temperature, but decreased with ethanol content. H₂O₂ content initially caused enhanced dye degradation but the efficiency decreased with higher H₂O₂ content.