Hierarchical spheres of Mg–Al LDH for the removal of phosphate ions: effect of alumina polymorph as precursor

Abstract

In order to tailor the morphology of the layered double hydroxide (LDHs) particles, we focused on a synthesis method that involves the use of Al₂O₃ as a precursor, employing Al₂O₃ with different crystal structures (e.g., α-Al₂O₃, θ-Al₂O₃, and γ-Al₂O₃) as well as amorphous Al₂O₃. A three-dimensional network of plate-shaped LDH particles was formed when θ-Al₂O₃ and γ-Al₂O₃ were used, even though α-Al₂O₃ barely reacts to form the LDH phase. Finally, adsorption tests involving HPO₄²⁻ ions confirmed that the fabricated LDH particles exhibited high ion-removal rates. The LDH particles prepared with θ-Al₂O₃ and γ-Al₂O₃ could remove the hydrogen phosphate ions (HPO₄²⁻) in a concentration of 0.40 mmol g⁻¹ completely within 10 min; this is approximately 20 times shorter than the time taken by the LDH particles prepared from amorphous Al₂O₃.