Green Synthesis and Particle Size Control of High-Purity Alumina Based on Hydrolysis of Alkyl Aluminum

This study introduces a green synthesis strategy for producing high-purity alumina (≥99.99%) through the controlled hydrolysis of aluminum isopropoxide, coupled with a novel impurity removal protocol to address persistent challenges in conventional methods, such as residual silicon/iron impurities and particle agglomeration. The experimental results indicate that La₂O₃, 1-(2-pyridylazo)-2-naphthol (PAN), and phenolphthalein exhibit effective removal capabilities for silicon/iron impurities. The addition of 1 wt% La₂O₃ reduces silicon content from 99.7 ppm to 16.4 ppm, whereas 0.6 wt% PAN and 0.2 wt% phenolphthalein, employed as iron-binding agents, lower iron content from 66.4 ppm to 20.7 ppm and 9.7 ppm, respectively. Through optimized dropwise hydrolysis and subsequent calcination at 1200 °C for 4 h, nanosized alumina powders with uniform morphology and controlled particle sizes (274-832 nm) were successfully synthesized. The proposed method offers a scalable and efficient pathway for synthesizing high-purity alumina with tailored particle characteristics.