Synthesis and characterization of nickel oxide nanoparticles

In this study, nickel oxide (NiO) nanoparticles were synthesized using the chemical precipitation method, and the effects of synthesis parameters on nanoparticle properties were investigated in detail. The response surface methodology-based Box-Behnken design was employed to investigate three key parameters—temperature, stirring speed, and reactant molar ratio—and their influence on the average particle size of the NiO nanoparticles was analyzed. The aim of this research was to identify the optimal synthesis conditions to control the specific properties of the nanoparticles and gain better control over the process. In the initial step, nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) was used as the precursor and sodium hydroxide (NaOH) as the precipitating agent to synthesize nickel hydroxide (Ni(OH)₂). The synthesis was conducted in a stirred and temperature-controlled reactor to ensure homogeneous precipitation and to study the effects of process parameters on the morphology of the nanoparticles. Precipitation experiments were carried out both under microwave-assisted and conventional conditions to analyze the impact of microwave irradiation on particle size, surface area, and pore structure. To achieve diverse morphological characteristics, various surfactants, including CTAB (cetyltrimethylammonium bromide), SDS (sodium dodecyl sulfate), PVP (polyvinylpyrrolidone), NP10 (nonionic surfactant), Tween 80, and PEG (polyethylene glycol), were incorporated into the precipitation process. The effects of these surfactants on the surface morphology, size distribution, and porosity of the NiO nanoparticles were investigated. The role of surfactants in particle aggregation, agglomeration tendencies, and changes in surface area was also examined. After precipitation, the synthesized nickel hydroxide (Ni(OH)₂) nanoparticles were calcined at different temperatures (300, 400, 500, and 600 °C) to convert them into nickel oxide (NiO) nanoparticles. At this stage, the influence of calcination temperature on particle size, surface area, and pore structure was studied. For characterization, FTIR (Fourier Transform Infrared Spectroscopy) was used to analyze the chemical structure, and XRD (X-ray Diffraction) was applied for phase analysis. The surface morphology of the nanoparticles was observed using SEM (Scanning Electron Microscopy), while particle size distributions were determined through zetasizer and SEM analysis. Additionally, BET analysis was conducted to evaluate surface area and porosity. The characterization results confirmed the successful synthesis of NiO nanoparticles using the chemical precipitation method. Among the investigated parameters, the reactant molar ratio was identified as the most influential factor on the average particle size, followed by stirring speed. Particle size analysis revealed that the synthesized NiO nanoparticles were polydisperse and exhibited a tendency to agglomerate. SEM images showed that the nanoparticles were smaller than 50 nm, but significant agglomeration resulted in larger clusters. Calcination experiments indicated that particle size was largest at 300 °C, but TGA (Thermogravimetric Analysis) revealed that calcination was incomplete at this temperature. As the calcination temperature increased, the particle size decreased, but a subsequent increase was observed at 600 °C. These findings suggested that the suitable calcination temperature for NiO nanoparticle synthesis lies between 400 and 500 °C. Microwave-assisted precipitation altered the pore structure and size of the particles, leading to a reduction in BET surface area under these conditions. In conclusion, this study provides a detailed evaluation of the effects of microwave irradiation and synthesis parameters on the properties of NiO nanoparticles. It identifies the optimal synthesis conditions and contributes valuable insights to the literature. The findings demonstrate that the surface properties, morphology, and physical structure of NiO nanoparticles can be effectively controlled by adjusting the synthesis parameters.