Solar-driven fast and selective extraction of lithium from seawater enabled by unidirectional photothermal conversion and confined crystallization with facile synthesis of nanoarray evaporator

Lithium extraction from seawater offers a promising solution to mitigating the shortage of terrestrial lithium resources. Photothermal evaporation, which received tremendous attention recently, shows vast potential for this purpose by rapidly rising the lithium concentration of seawater while separating other ions. In order to improve the efficacy of photothermal evaporation-driven lithium extraction, it is necessary to develop evaporation structures with high solar conversion and reasonable structure design. Here, we first developed the facile synthesis approach of hierarchically ordered polypyrrole nanoarrays as the high-performance solar absorber, and then proposed a strategy of unidirectionally channeling photothermal seawater fluid through the nanostructured evaporator to enable linear enrichment, confined salt crystallization and hence lithium extraction. The evaporator achieves evaporation rates up to 1.87 kg m -2 h -1 and selectively concentrates lithium by several orders of magnitude while rejecting NaCl in the form of site-specific salt precipitation. Finally, a Li/Na ratio of >4000 is achieved by our approach. Besides experimental validations, a transport model is employed to interpretate the concentration and separation process. Our strategy also shows the advantages of scalability and feasibility, making it an effective practical solution for lithium extraction from seawater.