A directional growth strategy for high layer charge Li/Al-LDHs to reinforce Li⁺ extraction in low-grade salt lake brines

Novel Li/Al-LDHs with high layer charges (HCLDHs) were synthesized in the light of the inter-layer effect on Li+ adsorption. Compared with conventional low-charge Li/Al-LDHs (LCLDHs), HCLDHs exhibited a distinct micromorphology characterized by a preferential growth orientation along the c-axis and a significantly reduced lateral diameter. Adsorption experiments showed that HCLDHs possessed superior Li+ adsorption performance in various brines, specifically with a Li+ adsorption capacity of 9.72 mg/g in Qarhan old brine, surpassing that of LCLDHs by 2 mg/g. All-around characterizations and finite element analysis calculations uncovered that the reduced lateral dimensions facilitated the exposure of more accessible Li+ adsorption sites, while the high positive charge of the host layers decreased the electrostatic repulsion toward Li+ by attracting anions and increased the surrounding ionic strength. Surface photovoltage (SPV) and x-ray absorption fine structure (XAFS) further proved the structural stability of HCLDHs, which ensured the maintenance of a high Li+ adsorption capacity during adsorption-desorption cycles.