Thermoresponsive Al^(3+)-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 Al^(3+)-crosslinked poly(N-isopropylacrylamide)(PNIPAAm)/alginate(Alg)(PNP/Alg(Al)) adsorbent.The in situ TEM images indicate that Alg-Al^(3+)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 Al^(3+) 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.