<p>This work explores how the pH of the synthesis affects the morphology and structure of cobalt oxide (Co₃O₄) nanoparticles made using the microwave technique. The impact of alkalinity on phase formation and particle evolution was demonstrated by samples made at different pH values. X-ray diffraction (XRD) verified a single-phase cubic spinel Co₃O₄ structure, while Fourier Transform Infrared (FTIR) spectra showed distinctive Co–O vibrations. The morphological transition from irregular small particles at lower pH to well-faceted nanostructures at higher pH was demonstrated by Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM) analyses, suggesting enhanced crystal growth in alkaline conditions. The compositional sensitivity to the synthesis environment was reflected in the energy-dispersive X-ray (EDX) data, which showed pH-dependent elemental changes. Overall, the nucleation, development, and compositional behaviour of Co₃O₄ nanoparticles are efficiently controlled by careful pH control during microwave synthesis.</p> Graphical abstract <p></p>