Synthesis of Highly Crystalline Al–Li Layered Double Hydroxide by Homogeneous Precipitation Method

Abstract

The formation of Al–Li layered double hydroxide (LDH) by a homogeneous precipitation method using urea as a precipitant has been investigated as a function of solution composition, aging temperature and time. When the mixed aqueous solution of Al(NO₃)₃ and LiNO₃ containing urea was heated, the solution pH was gradually increased with the thermal hydrolysis of urea and a white precipitate began to form at pH 5.7–6.1 in the temperature range of 80–90 °C. The crystallinity of the solid products was found to be influenced by the reaction conditions.
A quite highly crystallined Al–Li LDH, with a basal spacing of 7.83 Å, was obtained from the mixed solution of Al/Li molar ratio of less than 0.10 (0.166 mol dm⁻³ Li⁺) and urea concentration of more than 1.0 mol dm⁻³ at above 85 °C for 3–5 h. The typical LDH product has a chemical composition of Al_2.17Li_1.00(OH)_6.83(CO₃)_0.34 · yH₂O and is an aggregate of hexagonal plate-like shape particle with lateral dimensions of about 2 μm. From the analytical results of the solid products obtained during the aging, it was found that amorphous aluminium hydroxide was precipitated first and then LDH was gradually crystallized by the reaction of the aluminium hydroxide precipitate with Li⁺ ion in the solution.