Influence of calcination temperature on nickel oxide nanoparticles synthesized by thermal treatment

Recently, semiconductor nanoparticles have received immense interests due to their peculiar and outstanding physical and chemical properties which are different from their bulk counterparts. Nanostructures nickel and its oxides have potential applications in battery electrodes, catalysts, piezoresistors,thermistors, gas sensors, stain glass, and ceramic additives. Nickel oxide (NiO) nanoparticles have a wide direct band gap (3.56 eV) is a stable material and exhibits p-type semiconducting behavior. They also can be superparamagnetic and factor increased from 2.28167 to 2.29367 with increase of calcination temperature from 500 to 800 oC.superanti-feromagnetic in their properties. Several methods have been used and developed for synthesizing crystalline NiO nanoparticles in recent years, including chemical reaction,electrodeposition, sputtering, pulsed laser deposition, oxidation of nickel at high temperatures, solution growth techniques, spray pyrolysis, and sol–gel route. In many of these methods, the main objectives are to produce controlled nanoscale materials, high purity, low cost, and environmentally friendly for particular technological applications. However, most of these synthesis methods have some drawbacks to meet these objectives due to complicated procedures involved, longer reaction times, high reaction temperatures, and toxic chemical precursors used. In the present work, crystalline nickel oxide (NiO) nanoparticles have been synthesized using a simple thermal treatment method from a well-mixed solution containing only nickel nitrate as a metal precursor, polyvinyl pyrrolidone as a capping agent, and deionized water as a solvent before proceeded by drying at 80 oC for 24 h, grounding, and calcination at different temperatures range from 500 to 800 oC. The morphological, structural, optical and magnetic properties of the obtained nanoparticles were studied using various techniques. The surface electron microscopy (SEM) images showed that surface morphology of the samples consists of monocrystalline grains with almost uniform shape. The X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectra exhibited that the samples were amorphous at room temperature but transformed into a crystalline structure during calcination. The XRD spectra showed that the average particle size and the degree of crystallinity increased with increasing calcination temperature. The average particle sizes from the transmission electron microscopy (TEM) images were about 15 and 35 nm at calcination temperatures of 500 and 800 oC respectively. The elemental composition of the samples was determined by energy dispersed X-ray spectroscopy (EDX) which confirmed the presence of Ni and O in the final products. The optical properties were determined by UV–Vis reflection spectrophotometer and showed a decrease in the band gap from 3.60 to 3.51 eV with increase of calcination temperature from 500 to 800 oC. The magnetic properties were also investigated by electron spin resonance (ESR) spectroscopy, which confirmed the presence of unpaired electrons. The resonant magnetic field decreased from 296.4 to 289.7 Oe and the g-factor increased from 2.28167 to 2.29367 with increase of calcination temperature from 500 to 800 oC.

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