Template-free synthesis of hierarchical spindle-like γ-Al2O3 materials and their adsorption affinity towards organic and inorganic pollutants in water

Abstract

Hierarchical spindle-like γ-Al₂O₃ materials were prepared in the form of fray ended bundles of twisted nanoflakes by a non-template hydrothermal synthesis and sequential calcination route using aluminium nitrate or aluminium chloride as precursors and urea as precipitating agent. The microstructures, morphologies and textural properties of the resulting materials were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and N₂ adsorption–desorption techniques. It was found that the spindle-like γ-Al₂O₃ particles are composed of at least three levels of hierarchical organization: polycrystalline γ-Al₂O₃ at the nanoscale, oriented nanoflakes and uniform spindle-like assemblies. The hierarchical γ-Al₂O₃ particles prepared from aluminium nitrate show a slightly smaller size, fewer self-organized nanoplatelets and better textural properties than γ-Al₂O₃ prepared from aluminium chloride, due to the larger aqueous ionic radius of NO₃⁻ than that of Cl⁻. The reported experiments allowed us to propose the mechanism of formation of the spindle-like assemblies, which involves self-transformation of metastable amorphous aluminium hydroxide particles and their sequential cooperative assembly. The as-prepared γ-Al₂O₃ was found to be effective adsorbent for the removal of selective pollutants from wastewater as a result of its unique hierarchical structure and high specific surface area, indicating a promising potential of this material for environmental remediation.