Interfacial adsorption and recovery of Lithium ions using sulfonated graphene oxide and Ti₃C₂T_x MXene nanocomposite hydrogels

Recovery of lithium from different water resources like brine water and wastewater, as well as from other waste sources such as lithium-ion battery waste, has emerged as a promising strategy for sustainable lithium production. Herein, we designed nanocomposite-based adsorbents with a form of hydrogels containing sulfonated graphene oxides, Ti₃C₂T_x MXene, and alginate, aiming at lithium-selective adsorption and recovery. In particular, two-dimensional (2D) sulfonated graphene oxides in hydrogel adsorbent provide sulfonic acid groups allowing interfacial lithiation via ion exchange process. The co-existence of Ti₃C₂T_x MXene facilitates the surface coordination of lithium ions, thereby boosting the lithium-selective adsorptivity. The resulting nanocomposite-based hydrogels exhibit exceptional adsorptivity of 46 mg/g and lithium removal efficiency of more than 91.8 %. Moreover, lithium adsorption is found to be endothermic and can be well defined with pseudo-second-order kinetic model and Langmuir model, indicating chemical adsorption and monolayer adsorption. These hydrogels maintain high adsorptivity even in salt mixtures and show stable regenerability over multiple adsorption-desorption cycles. As a practical framework of the hydrogel adsorbent for lithium recovery, incorporating ionic liquid in hydrogel adsorbents has achieved superior lithium selectivity, specifically 7.4 and 4.3 times higher against magnesium and sodium ions, respectively, compared to hydrogels without ionic liquid. 2D nanocomposite hydrogels as adsorbents, with advantages of their scalability and chemical tunability, may be a potential platform possibly for practical direct extraction of lithium from aqueous lithium resources, including brine and produced water.