Highly flexible interconnected Li⁺ ion-sieve porous hydrogels with self-regulating nanonetwork structure for marine lithium recovery

Li⁺ ion-sieve (LIS) films, foams, or granules have been fabricated to immobilize LIS to overcome powder loss for Li extraction from seawater. However, the practical application is still restricted by their low swelling ability and poor flexibility to withstand harsh marine environment for a long time. Here, a highly elastic interconnected porous LIS nanocomposite hydrogel with tunable pore structure and flexibility, as well as good swelling property, is prepared by using LIS (viz. λ-MnO₂) as a pore self-modifier during the in-situ fabrication of polypyrrole (PPy) and polyvinyl alcohol (PVA) interpenetrating hydrogel (denoted as λ-MnO₂@IG). In addition to physical confinement interactions, the strong coordination/chelation and electrostatic interactions between λ-MnO₂ nanoparticles and polymer chains enable well-dispersed λ-MnO₂ nanoparticles to be confined in a rich network structure. Even at a marine environment (pH 8.3), the λ-MnO₂@IG hydrogel exhibits superior Li⁺ adsorption performance (20.6 mg g⁻¹ HMO), outperforming most adsorbents containing LIS. Specially, the porous hydrogel is easily recyclable and exhibits super-stable cyclic Li extraction performance, which are directly attributable to the further-improved pore structure in continuous regeneration process. This study provides a self-regulating strategy to design LIS porous hydrogels with controllable porosity, high flexibility, good swelling ability, and excellent cycle stability to address the growing Li⁺ demanding challenges.