Synthesis of ZnS and rGO/ZnS Nanocomposite, Application for Photodegradation of Methylene Blue and Heavy Metal Ions Detection in Water.

The ZnS quantum dots (QDs) and rGO/ZnS nanocomposite were prepared by a simple photochemical method. The structure and morphology of the ZnS QDs and rGO/ZnS nanocomposite samples were characterized by XRD, TEM, RAMAN, FTIR, FESEM, EDAX, and optical transmission techniques. X-ray diffraction results confirmed the formation of cubic zinc blende ZnS QDs and rGO/ZnS nanocomposite. TEM images showed that the synthesized QDs were spherical in shape. Photoluminescence spectra of the specimens revealed a broad emission with a peak centered at 490 nanometers (nm) related to surface defects. In this work, the prepared ZnS QDs were employed as a quenched fluorescence sensor for the fast and simple detecting heavy metal ions in water and indicated good performance for detecting lead ion (Pb⁺²) with high selectivity. It was noticed that, the photoluminescence spectral intensity of ZnS QDs gradually decreased in the presence of Lead ion (Pb⁺²), and the light emission was completely quenched in the presence of 60 nanomolar (nM) lead ion (Pb⁺²). Also, the removal of organic dye methylene blue (MB), as an organic pollutant, from aqueous solution through photodegradation process by ZnS quantum dots as well as rGO/ZnS nanocomposite as photocatalyst in the presence of UV light was investigated. The rGO/ZnS nanocomposite showed better performance for photodegradation of methylene blue compared to other samples. In addition, various radical scavengers utilized to find out the parameter which had the main effect in the MB photodegradation process by rGO/ZnS nanocomposite under UV light. The results of the radical scavenger experiment confirmed that surface electrons of rGO/ZnS nanocomposites had an essential role in the photodegradation process.