Mesopore-confined AlLi-LDHs/SBA-15 with interfacial electronic reconstruction and hydration-shell sieving: Breaking the capacity–selectivity trade-off for lithium extraction from high Mg2+/Li+ brines

3.25 mg g −1 capacity at ultrahigh Mg 2+ /Li + ratio of 474.6 and excellent cycling use. • AlLi-LDHs were confined in SBA-15 pores via solvent evaporation-induced strategy. • Si-O-Al/Li interface increases electron density, boosting electrostatic adsorption. • Hydration-shell sieving effect excludes Mg 2+ , Na + , K + for selective Li + adsorption. The sustainable extraction of lithium from salt lake brines featuring high Mg 2+ /Li + ratios poses a severe technical bottleneck that limits the high-efficiency utilization of global lithium resources. Herein, a novel pore-confined AlLi-LDHs/SBA-15 adsorbent (SEI-AL/SBA-15-B) is rationally constructed via a solvent evaporation-induced method to break this limitation, which directs the exclusive and uniform growth of AlLi-LDH nanosheets inside the ordered mesochannels of SBA-15 rather than on the external surface. This architecture delivers three synergistic effects: (i) physical confinement suppresses nanosheet agglomeration, maximizing accessible active sites; (ii) interfacial Si-O-Al/Li covalent bonds reconstruct the local electronic structure, lowering the DFT-calculated adsorption energy of Li + (H 2 O) 4 from −1.61 eV (pristine AlLi-LDHs) to −3.06 eV; and (iii) a hydration-shell sieving effect, governed by the interplay of geometric radius and dehydration energy, efficiently excludes competing Mg 2+ , Na + and K + . The optimized adsorbent achieves a Li + uptake of 10.52 mg g −1 within 1 h in 800 mg/L LiCl solution (equilibrium capacity 12.11 mg g −1 at 4 h). Impressively, a capacity of 3.25 mg g −1 is preserved at an ultrahigh Mg 2+ /Li + mass ratio (474.6), which surpasses most reported AlLi-LDHs adsorbents. Normalization to the active LDH mass shows that SEI-AL/SBA-15-B exhibits a 2.85-fold higher capacity than pristine AlLi-LDHs, proving that the enhanced performance originates from improved active-site utilization rather than higher LDH loading. The adsorbent also demonstrates excellent stability over eight adsorption–desorption cycles. This work establishes mesopore confinement engineering as a powerful platform to overcome the inherent limitations of layered double hydroxide adsorbents, enabling sustainable lithium extraction from high Mg 2+ /Li + ratio salt lake brines. AlLi-LDHs were confined within SBA-15 mesopores by solvent evaporation-induced method to form SEI-AL/SBA-15 composite adsorbent. The mesoporous confinement effect suppresses the agglomeration of AlLi-LDHs, reconstructs the Si-O-Al/Li interfacial electronic structure to enhance electrostatic adsorption and coordination bonding capability, and reinforces size sieving by blocking large-sized competing hydrated ions. These synergistic effects enable SEI-AL/SBA-15-B high lithium adsorption capacity and ultrahigh selectivity in brine. Download: Download high-res image (140KB) Download: Download full-size image