Low-Tortuosity Adsorption Networks Triggered by Micelle-Enhanced Swelling Enable Efficient Lithium Extraction from Seawater

Abstract

Lithium-ion sieve (LIS) hydrogels offer a solution to powder loss and poor site accessibility of LIS in lithium extraction through swelling. However, their adsorption efficiency is constrained by the inherently slow diffusion of lithium ions (Li+) through tortuous pathways within the hydrogel matrix. Herein, we regulate Li+ transport channels in LIS hydrogels by engineering dynamic adsorption networks through swelling enhancement with anionic surfactants. By integrating pulsed-field gradient nuclear magnetic resonance (PFG-NMR) diffusion experiments with molecular dynamics simulations, we demonstrate that rapid swelling creates low-tortuosity percolation channels, which significantly accelerate Li+ diffusion and enhance active-site accessibility during adsorption. So, the LIS hydrogel achieves a Li+ adsorption capacity of 52.79 mg g–1 HMO, approaching the theoretical capacity, with a high adsorption rate constant of 5.85 mg mg–1 h–1. The LIS hydrogel retains over 80% of its capacity after 20 cycles while reducing Mn2+ dissolution loss. In natural Bohai seawater, it shows high Li+ selectivity and delivers a Li+ adsorption capacity of 12.45 mg g–1 HMO in a 15-day scaled-up extraction test. The accelerated swelling by anionic surfactant micelles also enhances photothermal lithium extraction efficiency by modulating water states. This work provides a general and robust strategy for designing high-efficiency adsorbents for the reversible extraction of strategic metals from natural seawater.