The synthesis and characterization of NiO/WO3 Nanocomposites using Vernonia amygdalina plant extract for Adsorption of Cr (VI) and Pb (II) Containing Industrial Wastewater Effluent: The Case of Gulele subcity, Addis Ababa, Ethiopia

Abstract

The contamination of water by potentially toxic elements is considered a global problem. It calls for a safe, economic and technological approach in order to curb and prevent the devastating effect of the menace on both human and the aquatic life. In the light of this background, the adsorption potential of nickel oxide nanoparticles, tungesten oxide nanopartcles and their composites for the removal of chromium and lead from industrial wastewater was studied. The synthesized nanomaterials were characterized by FTIR, XRD, SEM and UV vis for the determination of functional group, morphology, bandgap energy, respectively. The band gap energy (Eg) was found to be 2.51 eV; 2.61eV and 2.46 eV for NiO NPs, WO3 NPs and NiO/WO3 NCs, respectively. Fourier transform infrared (FT-IR) spectroscopy indicated the functional groups present in NiO NPs, WO3 NPs and NiO/WO3 NCs. Scanning electron microscope (SEM) image depicted the synthesized NiO/WO3 NCs. The effect of concentration, catalytic load, temperatures, contact time and pH on the removal efficiency of both metal ions was investigated. The maximum removal adsorption was found to be 88.7%, 89.89%, 92.68% for Pb (II) and 91.22%, 90.70%, 91.59% for Cr (VI) onto NiO NPs, WO3 NPs and NiO/WO3 NCs, respectively. The Langmuir isotherm model showed a better fit to the equilibrium data than the Freundlich isotherm model while the adsorption mechanism of both metal ions to the nanomaterials surface agrees well with pseudo second order kinetic model. The results showed that NiO/WO3 NCs has excellent adsorption properties and thus can be used as an effective low-cost adsorbent for the removal of lead and chromium ions from industrial wastewater.