Synthesis of benzo-12-crown-4 ether immobilized silica for lithium-ion adsorption

To develop an adsorbent for Li⁺ recovery from seawater and/or spent lithium batteries, a benzo-12-crown-4 ether (B12C4) moiety was immobilized with silica (immobilization yield: 0.70 meq g⁻¹). Compared to pure silica, the resulting adsorbent (FB12C4-SG) had a reduced Brunauer–Emmett–Teller surface area (500 vs. 180 m² g⁻¹) and pore volume (0.75 vs. 0.26 cm³ g⁻¹). The Li⁺ adsorption reached equilibrium at 31 mg g⁻¹ after 2 h (1000 ppm Li⁺ solution). The adsorption behavior was well explained by pseudo-second-order kinetics and the Langmuir adsorption model (maximum adsorption capacity: 33 mg g⁻¹). The material exhibited a Li⁺/Na⁺ adsorption selectivity factor of 4.2 and high chemical stability under acidic regeneration conditions (1.0 N HCl solution).