Effect of structure-directing agents on facile hydrothermal preparation of hierarchical γ-Al₂O₃ and their adsorption performance toward Cr(VI) and CO₂

Hierarchical flower-like and sphere-like mesoporous γ-Al₂O₃ microparticles were successfully prepared by a facile hydrothermal method followed by a calcination process using sodium aluminate as aluminum source, urea as precipitating agent, and Pluronic F127 (EO₁₀₆PO₇₀EO₁₀₆), polyacrylic acid sodium (PAAS), and mixed F127-PAAS as structure-directing agents (SDAs), respectively. Effects of the SDAs on the phase structure, morphology, textural properties, surface alkaline, and the adsorption performance toward Cr(VI) and CO₂ of the as-prepared samples were comparatively studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N₂ adsorption-desorption, CO₂ temperature programmed desorption (CO₂-TPD), and UV-Vis spectrophotometric method. The results indicate that the sphere-like γ-Al₂O₃ obtained by using F127 as the SDA shows the best adsorption performance toward Cr(VI) with a high adsorption rate of 95% and adsorption capacity of 5.7mg/g when the adsorption reaches equilibrium for 4h at room temperature. However, the flower-like γ-Al₂O₃ obtained by using PAAS as the SDA has the biggest CO₂ adsorption capacity of 1.04mmol/g at room temperature. This work provides a simple and practical way to prepare potentially bifunctional γ-Al₂O₃ adsorbent for the removal of pollutants in water and air treatment from cheap sodium aluminate by using different SDAs.