Synthesis and lithium adsorption behavior of nanostructured lithium manganese oxide ion sieve by two‐step hydrothermal oxidation

Abstract Li + adsorption from brine water by lithium manganese oxide ion sieve (LMO) has become one of the most promising methods due to the high efficiency and selectivity towards lithium ion. However, the dissolution loss of Mn affects its structural stability and thus seriously limits its practical application. In this study, a novel approach of two‐step hydrothermal oxidation technique where H 2 O 2 and NaClO as the oxidants for the first step and the second step oxidation, respectively, is developed to fabricate nanostructured LMO (N‐LMO) with particle size of 20–45 nm. Influences of synthesis conditions in the first‐step H 2 O 2 oxidation and the second‐step NaClO oxidation on the lithium adsorption of N‐HMO prepared by N‐LMO acid leaching were investigated. Selectivity behavior towards lithium ion of N‐HMO was also studied. FTIR, FESEM, XPS, and XRD were used to characterize the structure and morphology of N‐LMO. Porous and nanostructures produced by two‐step hydrothermal oxidation increase the exposure of adsorption sites, which significantly accelerates the deintercalation and intercalation of Li + from vacancies in the framework. N‐HMO has high Li + adsorption capacity of 31.5 mg/g. Adsorption capacity for Li + remains at 85.7% after 5 recycles, indicating stable structure and good cycling performance of N‐HMO in the process of adsorption–desorption, due to the fact that the second‐step NaClO oxidation can transform some Mn 3+ into Mn 4+ . The distribution coefficient (K d ) of Li + (874.21) is significantly higher than those of other competing metal ions (Na + : 23.17, K + : 22.51, Ca 2+ : 30.89, Mg 2+ : 70.22). Moreover, the concentration factor C F of Li + (608.3) is much higher than that of other metal ions, indicating that lithium adsorption is hardly interfered by other competitive metal ions, and thus lithium is recovered from brine with high selectivity. This research develops an efficient and novel strategy for the synthesis of nanostructured LMO with simple and mild conditions via a two‐step hydrothermal oxidation method, eliminating the requirement for complicated, time‐consuming and high‐energy consumption for conventional calcination method, and the prepared N‐HMO has great potential application in recovering lithium ion from brine sources due to its high structural stability and high selectivity towards lithium ion.