Lithium selective adsorption on 1-D MnO2 nanostructure ion-sieve

β-MnO2, spinel-type Li4Mn5O12 and pure cubic phase MnO2 nanorod, with the size about 20–140 nm in diameter and 0.8–4 μm in length, were synthesized via a combination of hydrothermal synthesis and low temperature solid-phase reaction, more favorable to control the nanocrystalline structure with well-defined pore size distribution and high surface area than the traditional high temperature calcination process. Further, the MnO2 ion-sieves with lithium selective adsorption property were prepared by the acid treatment process to completely extract lithium from the spinel Li4Mn5O12 precursor with little change to the Mn–O lattice structure and the 1-D nanorod morphology. 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 powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), N2 adsorption–desorption at 77 K, and Li+ selective adsorption measurements. The lithium selective adsorption capacity was improved remarkably to 6.62 mmol g−1 at equilibrium and about 5 mmol g−1 at the initial lithium concentration of only 5.0 mmol l−1, which is significant for lithium extraction from aqueous solutions with very low lithium content.