Tuning Li/Al-LDHs nucleation and active sites toward enhanced lithium extraction

Abstract

Lithium–aluminum layered double hydroxides (Li/Al-LDHs) have achieved successful industrial-scale application in lithium extraction from salt lakes due to their excellent structural stability, high selectivity and environmental friendliness. However, they suffer from limited adsorption capacity. Herein, this issue can be effectively resolved by precise regulation of the LDH nucleation strategy, thereby controlling oxygen species content. The Li/Al-LDHs are synthesized via a one-pot precipitation method, and the nucleation conditions, including Al/Li ratio, crystallization temperature and terminal pH, are systematically optimized through crystal growth analysis, adsorption performance evaluation, and structural stability characterization. The results confirm that the adsorption capacity of Li/Al-LDHs is critically dependent on the pH value attained at equilibrium. Notably, the terminal pH simultaneously governs Al(OH)₃ nucleation and Li⁺ intercalation through oxygen speciation control. The elevated active oxygen content (38.65%) enhances hydrophilicity (contact angle 22.5°) and strengthens lithium-ion diffusion kinetics. The density functional theory (DFT) calculation further indicates that high levels of active oxygen (37.5%) facilitate low formation energy (−3.527 eV) and adsorption energies (−0.739 eV), confirming the correlation between the structure and Li active sites. What's more, the prepared Li/Al-LDHs show outstanding lithium adsorption performance with a maximum adsorption capacity of 13.42 mg g⁻¹ in East Taijinar salt-lake brine. The separation coefficients of Na⁺, K⁺, and Mg²⁺ are 395.86, 140.89, and 121.69, respectively. This study provides vital insights for advancing high-performance aluminum-based lithium adsorbents.