Nanostructured Adsorbents for Selective Lithium Recovery: Mechanisms, Fabrication, Performance Evaluation, and Applications in Desalination

Abstract

The growing demand for lithium in energy storage systems necessitates the development of selective and scalable extraction technologies, particularly from complex saline water resources. This dissertation systematically investigates nanostructured Lithium/Aluminum-layered double hydroxide (Li/Al-LDH)–based adsorbents through mechanistic modulation, structural engineering, and process integration to enhance lithium recovery performance. Poly(acrylic acid)-modified LDH (PAA@LDH) was first developed to regulate surface electronic density and interfacial charge distribution. Under optimized conditions (2.5 wt% PAA, 333 K), the lithium adsorption capacity increased from 2.08 mg/g to 3.41 mg/g in low-concentration produced water, with rapid equilibrium achieved within 40 min. Density functional theory (DFT) calculations revealed enhanced electron cloud density and reduced equipotential charge, confirming a charge-transfer-driven adsorption mechanism. To overcome diffusion limitations of powder adsorbents, electrospun lithium porous nanosorbent fibers (Li-PNFs) were fabricated by embedding LDH into a polyacrylonitrile matrix. The optimized fibers exhibited a uniform diameter of approximately 546 nm, tensile strength of 2.48 MPa, and yield stress of 0.09 MPa, ensuring mechanical robustness. The hierarchical porous structure enabled a significantly enhanced static lithium adsorption capacity of 13.45 mg/g, reaching equilibrium within 60 min. DFT analysis further revealed strong Li⁺ binding energy of up to -5.72 eV, indicating favorable adsorption thermodynamics. To bridge material performance with scalable operation, a continuous fixed-bed system was implemented. Under optimized conditions, the Li-PNFs achieved a lithium capture efficiency of 23.83% in a single-pass continuous experiment. Breakthrough behavior was successfully predicted using the Clark and Thomas models, demonstrating reliable dynamic adsorption modeling. Finally, a dual-functional MoS2–LDH@Sponge composite was developed to integrate photothermal evaporation with lithium-selective adsorption. The bilayer architecture achieved broadband light absorption (>97%) and demonstrated a dynamic hydration-controlled adsorption mechanism. Photothermal stimulation initially enhanced ion transport and interfacial evaporation, followed by hydration-shell restructuring that modulated lithium mobility. This work establishes a multi-scale framework that couples electronic modulation, nanoscale architecture, continuous process engineering, and solar-driven energy input for sustainable lithium recovery.