Comparative study for removal of toxic hexavalent chromium by zinc oxide nanoparticles, chitosan, chitin and zinc-chitosan nano-biocomposite

Abstract

Hexavalent chromium is classified as a human carcinogen and its removal is crucial from wastewater. A comparative study was done to remove Cr (VI) from an aqueous solution by synthesized nanoparticles such as chitin, chitosan, zinc oxide (at various temperatures 500 °C, 600 °C and 700 °C), and ZnO-chitosan composite. Among all the synthesized materials the maximum uptake of chromium (VI) was observed in ZnO-chitosan nano-biocomposite (ZnO-CS NC). The adsorption variables like initial concentration, adsorbent dosage, adsorption time, and pH were examined. The batch adsorption studies revealed the best result in 20 ppm concentration dosage of 0.5 g/l, pH 3 at 60 min. The characterization of nanoparticles and nanocomposite was done by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared (FTIR) techniques Langmuir isotherm models were best fitted due to the highest R2 value. Among all adsorbent, ZnO-chitosan nano-biocomposite was best adsorbent for chromium (VI) removal. ZnO-chitosan adsorption capacity and adsorption efficiency were 69.5 mg/g and 96.5% respectively. ZnO nanoparticles showed the potential for antibacterial activity. Electrostatic attraction between chromium and ZnO-chitosan biocomposite was the main cause for the removal of chromium from aqueous solution and it could be a promising material for sustainable treatment of wastewater.