Scalable synthesis of Al-doped CuO ceramic nanoparticles using a citrate-based sol-gel approach

Abstract

Al-doped CuO nanoparticles with Al concentrations of 0%, 1%, 3%, and 5% are successfully synthesized via a citrate-based sol–gel method followed by sintering at 1000 °C. X-ray diffraction (XRD) analysis confirmed the formation of single-phase monoclinic CuO (space group C2/c), with characteristic peaks indexed to the (110), (−111), (111), (−113), (−311), and (004) planes. A systematic shift of diffraction peaks toward higher 2θ values and a reduction in crystallite size from 17.74 nm (S1) to 15.30 nm (S4) are observed, indicating lattice contraction due to Al³⁺ substitution. FTIR spectra revealed characteristic Cu–O vibrations in the range of 500–600 cm^-1, along with enhanced O–H stretching bands (~3200–3500 cm^-1), confirming increased surface hydroxylation with Al doping. Raman analysis showed typical CuO modes at ~298, ~348, and ~633 cm^-1, with noticeable peak broadening and shifts in doped samples, indicating increased lattice disorder. Thermal analysis (TGA/DTG/DSC) demonstrated multi-stage weight loss, with total mass loss increasing from ~4.5% (S1) to ~6.9% (S4). DTG peaks shifted from ~150°C to ~135°C (moisture removal) and from ~380°C to ~330°C (decomposition), indicating reduced thermal stability with increasing Al content. Archimedes measurements showed a decrease in apparent porosity from ~25% (S1) to ~15% (S4) and an increase in bulk density from ~4.7 g/cm³ to ~5.3 g/cm³, confirming enhanced densification. Morphological analysis indicated improved particle uniformity with increasing Al concentration. These results demonstrate that Al doping effectively modifies the structural, thermal, and microstructural properties of CuO, making the materials suitable for advanced applications in catalysis, sensing, and electronic devices. CP-OES analysis showed a composition-dependent Cu²⁺ ion release, with the lowest release at 3% Al doping, suggesting optimal structural stability among the investigated samples.