Abstract: Pure β-MnO₂ oxide was synthesized by hydrothermal synthesis of MnSO₄H₂O and (NH₄)₂S₂O₈. Spinel-type Li₄Mn₅O₁₂ precursors were synthesized via low temperature solid-phase reaction. Furthermore, MnO₂ ion-sieves with Li⁺ selective adsorption property were prepared by the acid treatment process to completely extract Li⁺ from the spinel Li₄Mn₅O₁₂ precursor. The effects of hydrothermal and solid-phase reaction process on the nanostructure, chemical stability and ion-exchange property of the ion-sieve material were examined with XRD, HRTEM, SAED, and Li⁺ selective adsorption measurements. The results show that Li₄Mn₅O₁₂ precursor and final MnO₂ ion-sieve are effectively controlled within low-dimensional structure, indicating that low temperature solid-phase reaction is more favorable to control the nanocrystalline structure than traditional high-temperature calcination process. The Li⁺ selective adsorption capacity is improved remarkably to 6.6 mmol/g at equilibrium and about 5.0 mmol/g at the initial Li⁺ concentration of only 5.0 mmol/L, which is significant for lithium extraction from aqueous solutions with very low lithium content.

Key words: low-dimensional, ion-sieve, Li₄Mn₅O₁₂, adsorption, lithium