Porous lithium ion sieves nanofibers: General synthesis strategy and highly selective recovery of lithium from brine water

Lithium ion sieves (LIS) have gained great interest in lithium recovery. However, the synthesis of high stability, selectivity, and adsorption capacity of LIS is still a great challenge. Here, a general strategy combining electrospinning and calcination techniques is developed to fabricate a series of porous titanium-based LIS nanofibers. The porous structure created by calcination increases the exposure of the adsorption sites, which significantly accelerates the deintercalation and intercalation of Li+ from and into the vacancies in the framework. All of samples have good Li+ adsorption capacity and high selectivity for Li+. As a proof of concept, porous H4Ti5O12 nanofibers (P-HTO-NF) transformed from the electrospun porous Li4Ti5O12 nanofibers (P-LTO-NF) are systematically investigated in lithium recovery. P-HTO-NF possesses a superior adsorption capacity (59.1 mg/g), which is nearly close to the theoretical value (63.77 mg/g). The Freundlich isotherm model can well describe the adsorption isotherm data. The adsorption equilibrium can reach within 30 min (C-0 = 300 mg/L, pH = 11, S/L = 60 mg/60 mL). The equilibrium distribution coefficient (K-d, mL/g) for Li+ (232) is extremely higher than that for competing ions (1.41 for Na+, 1.17 for K+, 0.88 for Mg2+, 0.58 for Ca2+) (C-0 = 40 mg/L for Li+, pH = 8), indicative of a highly selective recovery of lithium from brine water. The LIS show excellent stability with a low Ti dissolution and the adsorption capacity for Li+ remains 86.5% after 6 cycles. Our work provides a universal strategy for the synthesis of porous LIS.