Green synthesis of nickel nanoparticles using Ocimum sanctum and their application in dye and pollutant adsorption

Nickel nanoparticles as an eco-friendly adsorbent was biosynthesized using Ocimum sanctum leaf extract. The physiochemical properties of green synthesized nickel nanoparticles (NiGs) were characterized by UV-Vis spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). NiGs were used as adsorbent for the removal of dyes such as crystal violet (CV), eosin Y (EY), orange II (OR) and anionic pollutant nitrate (NO₃^-), sulfate (SO₄^2-) fromaqueous solution. Adsorption capacity of NiGswas examined in batchmodes at different pH, contact time, NiG dosage, initial dye and pollutant concentration. The adsorption process was pH dependent and the adsorption capacity increased with increase in contact time and with that of NiG dosage,whereas the adsorption capacity decreased at higher concentrations of dyes and pollutants. Maximum percentage removal of dyes and pollutants were observed at 40, 20, 30, 10 and 10 mg·L^-1 initial concentration of CV, EY, OR, NO₃^- and SO₄^2- respectively. The maximum adsorption capacities in Langmuir isotherm were found to be 0.454, 0.615, 0.273, 0.795 and 0.645 mg·g^-1 at pH 8, 3, 3, 7 and 7 for CV, EY, OR, NO₃^- and SO₄^2- respectively. The higher coefficients of correlation in Langmuir isotherm suggested monolayer adsorption. The mean energies (E), 2.23, 3.53, 2.50, 5.00 and 3.16 kJ·mol^-1 for CV, EY, OR, NO₃^- and SO₄^2- respectively, calculated from the Dubinin-Radushkevich isotherm showed physical adsorption of adsorbate onto NiGs. Adsorption kinetics data was better fitted to pseudo-second-order kinetics with R² > 0.870 for all dyes and pollutants. NiGs were found to be an effective adsorbent for the removal of dyes and pollutants from aqueous solution and can be applied to treat textile and tannery effluents.