Unveiling the sonozonation synthesis of NiO nanoparticles: The effect of reaction time

This work investigated the effects of treatment duration and magnetic stirring, compared with sonozonation, on the defect chemistry and multifunctional properties of nickel oxide nanoparticles (NiONPs). The primary aim was to determine how synthesis duration (1, 3, and 5 h) and the sonozonation process influence the nanoparticle structural, electrical, thermal, and magnetic properties of NiONPs. The findings indicated a specific fragmentation-growth process exclusive to sonozonation. The particle size initially dropped from 20.37 nm at 1 h to a minimum value of 12.92 nm at 3 h, before increasing to 21.5 nm at 5 h. Hexagonal-like morphology was observed in all samples. Using XRD and EDX, the multiphase presence of NiO, NiOOH, and Ni₂O₃ was confirmed in all samples, revealing a notable bulk oxygen deficiency in the SO-3 h, sample, which exhibited 82.68 atomic% of Ni. The SO-1 h sample exhibited the maximum coercive field (H_c) of 587.189 Oe and a squareness ratio (SQR) of 0.054. The SO-3 h sample analysis confirms optimum conditions for magnetization, resulting in a peak magnetization (M) of 0.585 emu/g and the narrowest band gap, 2.82 eV. Sonozonation enhanced defect engineering and resulted in a maximum oxygen vacancy (V_o) concentration of 31.0% for SO-5 h. The Stirr-5 h sample showed increased surface non-stoichiometry with an O_def / O_lat ratio of 1.688 and a wider optical band gap of 3.17 eV. Sonozonation is presumably effective for bulk stoichiometric modification, while magnetic stirring produces surface vacancies and widens the band gap. The current study shows improved p-type oxides for high-performance magnetic storage media and high-efficiency catalytic surfaces.