Hydrothermal synthesis and adsorption behavior of H₄Ti₅O₁₂ nanorods along [100] as lithium ion-sieves

The adsorption method is a promising route to recover Li⁺ from waste lithium batteries and lithium-containing brines. To achieve this goal, it is vital to synthesize a stable and high adsorption capacity adsorbent. In this work, Li₄Ti₅O₁₂ nanorods are prepared by two hydrothermal processes followed by a calcination process. Then the prepared Li₄Ti₅O₁₂ nanorods are treated with different HCl concentrations to obtain a H₄Ti₅O₁₂ adsorbent with 5 μm length along the [100] direction. The maximum amount of extracted lithium can reach 90% and the extracted titanium only 2.5%. The batch adsorption experiments indicate that the H₄Ti₅O₁₂ nanorod maximum adsorption capacity can reach 23.20 mg g^-1 in 24 mM LiCl solution. The adsorption isotherms and kinetics fit a Langmuir model and pseudo-second-order model, respectively. Meanwhile, the real adsorption selectivity experiments show that the maximum Li⁺ adsorption capacity reaches 1.99 mmol g^-1, which is far higher than Mg²⁺ (0.03 mmol g^-1) and Ca²⁺ (0.02 mmol g^-1), implying these nanorods have higher adsorption selectivity for Li⁺ from Lagoco Salt Lake brine. The adsorption capacity for Li⁺ remains 91% after five cycles. With the help of XPS analyses, the adsorption mechanism of Li⁺ on the H₄Ti₅O₁₂ nanorods is an ion exchange reaction. Therefore, this nanorod adsorbent has a potential application for Li⁺ recovery from aqueous lithium resources.