Sol-Gel Synthesis, Structure, and Adsorption Properties of LiMgxMn(2 – x)O4 (0 ≤ x ≤ 0.7) Oxides

Abstract

Lithium manganese oxides with a spinel structure LiMg_xMn_{(2 – x)}O₄ doped with Mg²⁺ ions in the range 0 ≤ x ≤ 0.7, were obtained by sol-gel synthesis. Phase composition and morphology of obtained oxides were studied by X-ray powder diffraction and scanning electron microscopy. It is shown, that in the studied range 0 ≤ x ≤ 0.7 Mg-doped lithium manganese oxides saved the structure of the original cubic spinel LiMn₂O₄, while an increase in parameter a was observed from 8.175 to 8.309 Å and average crystallite size practically unchanged (30–36 nm). Samples of the initial LiMn₂O₄ spinel and Mg-doped spinel consisted of prismatic particles of submicron (0.1–0.2 µm) and micron (1.0–3.0 µm) sizes, respectively. The effect of the adsorbent dose (0.05–0.3 g/L) and pH (3.0–13.0) of the solution on the adsorption efficiency was studied. The adsorption isotherms of samples LiMg_0.3Mn_1.7O₄ were described by the Langmuir monomolecular adsorption equation. An increase in the temperature of the model solution from 25 to 45°C was accompanied by an increase in the maximum adsorption of the LiMg_0.3Mn_1.7O₄ samples from 10.50 to 10.98 mmol/g, which indicates the endothermic nature of the adsorption process. The kinetics of adsorption was well described by a pseudo-second order equation, which indicates the occurrence of chemical interaction during the adsorption process.