Effect of pH on solvothermal synthesis of β-Ni(OH)2 and NiO nano-architectures: Surface area studies, optical properties and adsorption studies

Abstract

We report here a simple and modified solvothermal synthesis of NiO nanoparticles by using nickel nitrate hexahydrate [Ni(NO3)2⋅6H2O], hexamethylenetetramine [C6H12N4], sodium hydroxide [NaOH] and ethanol [C2H5OH] as refluxing solvent. Nickel hydroxide [β-Ni(OH)2] nanostructures were first formed which were then calcined at 400°C to obtain nickel oxide (NiO) nanoparticles. The nano-powder was investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy and Brunauer–Emmett–Teller surface area studies. The size of the NiO nanoparticles was estimated by X-ray powder diffraction pattern, which was in close agreement with the particle size obtained by transmission electron microscopy analysis. Scanning electron microscopy studies revealed that the synthesized nickel oxide nanostructures showed various morphologies and the morphologies can be easily tailored by adjusting the pH value. The chemical structure information of the products was studied by Fourier transform infrared spectroscopy. Electronic spectra were used to clarify qualitatively the change in absorption band positions on changing the particle size of NiO. The values of the optical band gap of the NiO nanoparticles increases from 2.9 to 3.5eV as the particle size decreases and indicated a direct transition. The specific surface area of NiO nanoparticles was found to increase from 58.3 to 131.4m2/g with decrease in the particle size from 20nm to 5nm. It also exhibited excellent adsorption of Co(II) and Pb(II), demonstrating a promising application in waste water treatment.