MECHANOCHEMICAL SYNTHESIS OF NiO NANOPARTICLES: INSIGHT INTO THE NATURE OF PREFERRED GROWTH ORIENTATION

Abstract

Nickel oxide ( NiO ) nanoparticles were synthesized by calcination at 400°C to 700°C for 8 h of the precursor obtained via mechanochemical reaction of Ni ( NO 3)2 ⋅ 6 H 2 O with citric acid as a dispersant. The nanoparticles were characterized by thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The kinetics of different surfaces of the nanocrystals under nonisothermal conditions was investigated. The activation energies for different lattice planes of NiO nanoparticles were determined using the Arrhenius equation, revealing their preferred orientation. The growth of NiO obeyed the general theory that nanoparticles with the largest surface energy tend to form. XRD data reveal that the NiO nanoparticles possess preferred (111) or (200) orientations that reflect their complex activity. The nature of preferred growth orientation was found to be negative diffusion activity among different lattice surfaces, which indicates that oxygen atoms diffuse from low oxygen concentration on the lattice surface to high concentration on the lattice surface.