Selective separation of lithium using brown algae-inspired alginate hydrogel incorporated with phosphonate metal organic framework*

The separation of Li⁺ from brine with a high Mg/Li ratio is of great importance. In this study, we fabricated a new phosphonate metal organic framework (pMOF)-incorporated alginate hydrogel inspired by the Li⁺ adsorption mechanism of brown algae. Firstly, the Li⁺ adsorption by brown algae was investigated. Based on the result, fabricated biomimetic pMOF-incorporated alginate hydrogel was used to separate Li⁺. The pMOF incorporated Cu²⁺-based alginate hydrogel increased Li⁺ adsorption, while decreasing Mg²⁺ adsorption. The effect of size confinement by Cu²⁺-pMOF was utilized to selectively adsorb Li⁺. By contrast, the pMOF incorporated Al³⁺-based alginate hydrogel greatly increased Mg²⁺ adsorption, whereas Li⁺ adsorption was decreased. This reverse adsorption behavior might be attributed to partial dehydration, depending on the dehydration energy. The fabricated alginate hydrogels could be reused by washing them with ethanol/DI water due to weak electrostatic force. The present study would help selective separation of Li⁺.