Thermoresponsive Al3+-crosslinked poly(N-isopropylacrylamide)/alginate composite for green recovery of lithium from Li-spiked seawater

With the rapid increase in the demand for lithium as an energy-critical element, the recovery of Li+ ions from seawater is a worldwide challenging issue. Herein, we propose a new facile and fast selective recovery approach of Li+ using an Al3+-crosslinked poly(N-isopropylacrylamide) (PNIPAAm)/alginate (Alg) (PNP/Alg(Al)) adsorbent. The in situ TEM images indicate that Alg–Al3+ coordination is reorganized via the rearrangement of PNIPAAm and Alg networks, as the temperature increases. The reorganization eventually leads to the formation of polycrystalline structure. The in situ FTIR results exhibit that PNP/Alg(Al) composite has peculiar phase transitions, which includes a retrogressive phase change from hydrophobic to hydrophilic. The synergetic effect of the strong repulsion force of Al3+ ions and the attractive force of negatively charged polymeric chains enables the efficient adsorption of Li+ ions with a low affinity from Li-spiked seawater. 7.3% of Li+ ions are recovered from Li-spiked seawater although the concentration of Li-spiked seawater is very high. In addition, Li+ ions can be extracted from PNP/Alg(Al) composite with the use of a small thermal energy. The proposed thermoresponsive IPN gel provides a strong potential in practical applications for Li+ recovery as an innovative energy-material strategy.