Carbon‐Shell‐Confined Functional Silica Xerogels for Concurrent Lithium Dual‐Mode Optical Detection and Seawater Recovery

ABSTRACT

Rational material designs for lithium extraction from unconventional dilute resources have attracted attention to meet the rising demand. Here, a new multifunctional composite is developed that not only extracts lithium but also enables its concurrent optical detection. The material design integrates silica xerogel confined within hollow carbon spheres as a high‐surface‐area matrix, heteroatom‐doped CDs as a fluorescence tag, and a covalently attached benzophenone‐derived ligand as the lithium‐binding site. This design also demonstrates an alternative detection paradigm in which a non‐fluorogenic receptor coupled with matrix‐confined CDs is used for optical signal transduction. In the presence of major seawater ions (Na ⁺ , Mg ²⁺ , Ca ²⁺ , K ⁺ ), the composite demonstrates selective dual‐mode detection: naked‐eye colorimetric and turn‐on red luminescence with ultra‐high sensitivity (LOD: 1.5 nM). The turn‐on emission arises from disruption of the photoinduced electron transfer (PET) process upon Li ⁺ binding, which restores the intrinsic emission of the CDs. The flexible benzophenone‐derived ligand enhances Li ⁺ binding stability, as supported by density functional theory (DFT) investigations. The adsorbent exhibits high lithium uptake (110 mg g ⁻¹ ), fast adsorption kinetics, and good recyclability, meeting key requirements for direct lithium extraction (DLE). Real seawater‐system testing for lithium quantification and extraction highlights its potential for advancing integrated lithium detection‐extraction technologies.