Removal of hazardous azo dye from water using synthetic nano adsorbent: Facile synthesis, characterization, adsorption, regeneration and design of experiments

The low cost, facile, feasible and potential route was applied to synthesize nickel(II) oxide nanoparticles for adsorptive removal of hazardous azo dye from aqueous solutions. The synthesized nickel(II) oxide nanoparticles were characterised by advanced analytical techniques such as X-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping analysis, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The nanomaterial was utilised to probe the removal process of methyl orange dye from the aqueous solution by batch adsorption approach. The influence of pertinent factors, i.e. pH, contact time, initial concentration, dose and temperature on the efficiency of azo dye removal were tested. Moreover, isotherm, kinetics and thermodynamic studies were conducted which illustrate that the adsorption followed by Freundlich isotherm and pseudo-second-order kinetic model. The results show that the adsorption was fast and 95.22% methyl orange was removed at pH 6 with 0.05 g dose. The response surface methodology was used by availing three levels and three factorial Box-Behnken design to optimise the adsorption process. The low p-value and high R² validated the significance of the mathematical model. The three-dimensional (3D) and contour plots display the effect of various factors into the response. The optimum conditions for dye removal were optimised by Taguchi L9 (3^3) orthogonal array experimental design. The regeneration capacity and of the nickel(II) oxide nanoparticles proves its importance in industrial wastewater treatment.