Crystallite-engineered NiO nanoparticles via co-precipitation for high-performance ethanol gas sensing

Nickel oxide (NiO) nanoparticles, noted for their high catalytic activity, chemical stability, and low cost, were synthesized via a simple and scalable co-precipitation method. This approach provides advantages such as operational simplicity, environmental compatibility, and suitability for large-scale production. X-ray diffraction (XRD) confirmed the formation of a cubic crystal structure, with crystallite sizes estimated using the Scherrer, Williamson–Hall, and Modified Debye–Scherrer models. Fourier-transform infrared (FTIR) spectroscopy verified the presence of NiO and associated functional groups. SEM/EDX analysis revealed a non-agglomerated morphology with uniform elemental distribution, while Raman spectroscopy identified surface optical (SO) phonon and magnon modes that varied with crystallite size. TEM images showed irregular aggregates with particle sizes ranging from 30 to 80 nm. X-ray photoelectron spectroscopy (XPS) confirmed Ni²⁺ and O²⁻ states with binding energies of 854.12 eV and 529.22 eV, respectively. Thermogravimetric and differential thermal analyses (TGA-DTA) demonstrated good thermal stability and favorable phase-formation behavior. Gas-sensing studies revealed excellent ethanol sensitivity, with the highest response at 100 ppm. Given ethanol’s importance in environmental monitoring, industrial safety, and health protection, these results indicate that co-precipitated NiO nanoparticles are promising candidates for low-cost, high-performance ethanol gas sensors.