Sustainable synthesis of α-alumina nanoparticles: a comparative study of base-mediated crystallization via co-precipitation

Abstract

Alpha-alumina (α-Al₂O₃) nanoparticles (NPs) were synthesized via a controlled co-precipitation method using three different bases: sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonium hydroxide (NH₄OH). The influence of each base on the structural, optical, and surface properties of the synthesized nanoparticles was systematically investigated. Characterization techniques, including powder X-ray diffraction (PXRD), dynamic light scattering (DLS), UV-Vis spectroscopy, and zeta potential analysis, were employed. Crystallite sizes, estimated using multiple models, ranged from 54.67 nm to 94.74 nm, with NH₄OH yielding the smallest size and the highest specific surface area (28.36 m² g⁻¹). Rietveld refinement confirmed complete α-phase formation for the NaOH- and NH₄OH-derived samples, while the KOH-derived sample exhibited minor potassium oxide impurities. UV-Vis analysis revealed a wide band gap (5.4–5.5 eV), and zeta potential measurements indicated enhanced colloidal stability for samples synthesized using NaOH and NH₄OH. Thermogravimetric and differential scanning calorimetry confirmed α-phase formation between 1047 and 1121 °C. Transmission electron microscopy revealed spherical morphology and nanoscale particle size. These findings highlight the critical role of base selection in tuning the physicochemical properties of α-alumina and demonstrate the effectiveness of NH₄OH in producing fine, phase-pure, and stable α-Al₂O₃ nanoparticles suitable for applications in high-temperature ceramics, electronics, and photocatalysis.