Superabsorbent polymer microparticles incorporating with crown ether for swelling-enhanced selective and rapid...

Superabsorbent polymer (SAP) microparticles incorporating 2-hydroxymethyl-12-crown-4 were developed to combine Li⁺-selective coordination with rapid hydrogel swelling. The materials were prepared in the presence of Li⁺-crown ether complexes within an acrylic acid-acrylamide (AA-AAm) network, resulting in coordination environments within the swollen hydrogel structure. Single-particle swelling measurements showed that the microparticles reached equilibrium within ∼5 min, enabling rapid solution ingress and transport of Li⁺ into the hydrogel network. In batch adsorption experiments, the modified SAPs achieved a lithium adsorption capacity of ∼1200 μmol g^-1 at 20 ppm Li⁺ (pH 7), significantly higher than non-functionalized SAPs and a rigid methacrylic acid-ethylene glycol dimethacrylate (MAA-EGDMA)-based IIP included as a literature-class benchmark for field contextualization. The materials also exhibited preferential Li ⁺ uptake over Mg²⁺ and Co²⁺ under both single-ion and competitive conditions and retained higher adsorption capacity under acidic conditions (pH 4.5). These results suggest that incorporation of crown ether functionality within a fast-swelling hydrogel matrix enhances Li⁺ uptake and selectivity through a combined effect of ion transport and coordination interactions.