Construction of gradient hydrogel-based lithium ion channels enhanced by Hofmeister effects

Autonomous extraction of low-concentration lithium is of great importance for alleviating the shortage of lithium resources. Inspired by the unidirectional ion transport of biomimetic ion channels, we designed gradient weak polyelectrolyte hydrogels-based lithium ion channels for autonomous enrichment of low-concentration lithium ions. In order to increase the chain density and stabilize the gradient structure distribution, the hydrogels were optimized through Hofmeister effect based on ion-water and ion-polymer interactions. After Na 2 SO 4 regulation, the gradient P(MAA-AM) hydrogels demonstrate superior elastic properties, stronger mechanical property and higher internal potential. Especially, the gradient P(MAA-AM) hydrogels are more conductive towards Li + than other cations, exhibiting a higher lithium selectivity. Owing to the enhanced chain density and the optimized gradient distribution, the obtained hydrogel-based channels demonstrate outstanding lithium enrichment performance via the synergistic effect of electrostatic attraction and lithium bonds. At an ultra-low Li-ion concentration of 1 mg/L, the gradient hydrogel displays a high lithium enrichment efficiency of up to 75 %. The designed gradient polyelectrolyte hydrogel-based lithium ions channels may have potential applications for the autonomous and selective enrichment of low-concentration lithium ions. • A pH-responsive gradient hydrogel-based lithium-ion channel was constructed. • Na 2 SO 4 -regulated hydrogels exhibit enhanced mechanical strength, viscoelasticity, and internal potential. • Gradient hydrogels exhibit high lithium-ion conductivity and selectivity. • Autonomous enrichment and release achieved for low-concentration lithium.