Effective removal of congo red dye from aqueous solution using biosynthesized zinc oxide nanoparticles

Abstract

Zinc oxide behave as an excellent semiconducting material for its high band gap. Present research demonstrate the green synthetic route of ZnO nanoparticles from leaf extracts of Hibiscus rosa-sinensis. The synthesised nanoparticles was characterised by UV–vis, SEM, TEM, XRD and pHZPC studies. TEM study clearly revealed that synthesised nanoparticles are spherical in shape with average size 100 nm. The XRD study revealed that the nano ZnO is crystalline in nature. On the other hand, the active functional groups was assigned by FTIR study. Finally, the congo red dye was removed from aqueous solution by using nano ZnO through batch study. The optimum adsorption conditions were obtained as concentration (4 mg/L), adsorbent dosage (0.05 g) and contact time (20 min) for the present study. Results also revealed that the adsorption of dye is nicely fitted with Langmuir isotherm followed by Freundlich isotherm. The kinetics of congo red dye better agreement with pseudo-second-order kinetics. The thermodynamics of the dye adsorption study suggest that the adsorption is exothermic in nature and entropy driven. Finally it can be suggested that nanoZnO could be an effective semiconductor towards adsorption of cong red dye.