A time resolved, in-situ X-ray diffraction study of the de-intercalation of anions and lithium cations from [LiAl₂(OH)₆]nX·qH₂O (X = Cl⁻, Br⁻, NO₃⁻, SO₄²⁻)

The layered double hydroxides (LDHs), [LiAl2(OH)6]nX·qH2O (Xn− = Cl−, Br−, NO3−, SO42−) spontaneously lose both Li+ cations and Xn− anions to give crystalline Al(OH)3 on stirring in water. The kinetics of this topochemical de-intercalation reaction have been studied using time-resolved, in-situ energy dispersive X-ray powder diffraction. The temperature dependence of the rate of the de-intercalation reaction yields activation energies of 94 ± 15 kJ mol−1 for mono-dispersed [LiAl2(OH)6]Cl·1.5H2O crystallites (particle size 5–10 µm) and 117 ± 15 kJ mol−1 for poly-dispersed [LiAl2(OH)6]Cl·1.5H2O crystallites (particle size 1–30 µm). The rate of ion de-intercalation was found to decrease as the H2O/LDH ratio decreased. The rate of the de-intercalation has also been shown to be dependent on the interlayer anion, with the reaction rates NO3− > Cl − > Br−. In the case of SO42− rapid de-intercalation only goes to 40% completion.