Biomolecule assisted morphology-controllable synthesis of Zinc Sulphide nanomaterials for efficient photocatalytic activity under solar irradiation

Abstract

Tuning the optical and morphological properties of Zinc Sulphide (ZnS) nanomaterials (NMs) may be executed based on its synthetic approaches with experimental parameters that may improve the photocatalytic degradation efficiency as compared to bulk ZnS. A bio-molecule (Citrus limetta juice) assisted synthetic method was employed with the variation of precursors and stabilizer ratio for manipulating the morphology of as-synthesized ZnS NMs. Field emission scanning electron microscopic analysis confirmed the structure of nanospheres/nanoflowers/nanotubes of ZnS NMs, corresponding to different sulphur ratios and amount of Citrus limetta juice-extract. Chemical composition of the ZnS NMs was substantiated by X-ray photoelectron spectroscopy. The photocatalytic degradation ability of the ZnS NMs toward major water pollutants: Rhodamine B and Methyl orange, indicated the correlation between morphological and photocatalytic properties. Highest defect emission due to Sulphur interstices and lowest band edge emission due to less electron-hole pair recombination, as-observed through Photoluminescence spectroscopy, accounted for maximum degradation of dyes by ZnS nanospheres as compared to nanoflowers/nanotubes, which may be attributed to the high separation efficiency of electron-hole pairs and high surface-to-volume ratio. Electrochemical impedance spectroscopy established the highest electrical conductivity of ZnS nanospheres. 85% degradation of RhB and 82% degradation of MO under sunlight were achieved with ZnS nanospheres. Reusability and radical scavenging studies revealed reduction of ∼10% degradation efficiency after 3rd cycle and super oxide radical ions as the prominent reactive species during degradation processes, respectively.