Green synthesis of ZnS nanoparticles and fabrication of ZnS–chitosan nanocomposites for the removal of Cr(vi) ion from wastewater

Abstract

Abstract A modified homogeneous precipitation method has been used to synthesize ZnS nanoparticles. Starch and polyvinyl alcohol (PVA) were utilized as capping molecules, and later, the ZnS–PVA-capped nanoparticles were then incorporated with chitosan to form ZnS–chitosan nanocomposites for the removal of Cr(vi) ion from wastewater. The optical measurements of the synthesized ZnS nanoparticles showed the band gap which was blue-shifted when compared with the bulk ZnS material. The crystalline structures were determined by X-ray diffraction, and the crystalline sizes were estimated from the Scherer formula. XRD spectra confirmed the formation of hexagonal phase for the uncapped ZnS nanoparticles with an average crystalline size of 3.71 nm whereas the starch- and PVA-capped ZnS nanoparticles showed the formation of cubic phase structures with crystalline sizes of 3.26 and 2.88 nm. The TEM image showed spherical particles with regular morphologies and significantly narrow size distributions. The calculated average particle diameters were in good agreement with the estimated XRD result. The removal of Cr(vi) ion from wastewater was studied through the adsorption process. The effect of pH, dosage, and contact time was investigated. More than 95% of the metal ion recovery was achieved through using ZnS–chitosan nanocomposites.