Low temperature synthesis of nanosized boehmite powder from sodium aluminate by template-free hydrothermal method

Abstract

This study introduces a novel procedure for efficiently precipitating crystalline nanosized boehmite (γ-AlO(OH)) through the reaction of sodium aluminate (NaAlO₂) solutions, derived from aluminum foil, with nitric acid. The effects of reaction pH, temperature, and aging time on the morphology of the synthesized γ-AlO(OH) were thoroughly investigated. Samples were synthesized under varying conditions, including aging ranging from 4 to 24 h, temperatures between 70 and 110 °C, and pH levels from 7.5 to 11. Characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and BET surface area and pore volume analysis were employed. The XRD results confirmed that most of the samples were predominantly single-phase γ-AlO(OH). The research emphasized that variations in synthesis parameters had a substantial impact on the crystallite size, surface area, and pore volume of γ-AlO(OH). Specifically, higher pH levels, elevated temperatures, and extended aging times resulted in larger crystallite sizes, which consequently decreased both the surface area and pore volume. At 90°C and a 12-hour aging time, the sample prepared at pH 7.5 exhibited the highest pore volume (0.56 cm³/g) with a surface area of 208.2 m²/g, while the sample at pH 11 had the largest surface area 272.2 m²/g (pore volume 0.45 cm³ g⁻¹) and high purity. Pure boehmite was consistently produced within the pH range of 7.5–11, although bayerite impurities were observed at pH 9.5 when the reaction temperature was between 85 and 90°C.