A highly permeable UiO-66-NH2/polyethyleneimine thin-film nanocomposite membrane for recovery of valuable metal ions from brackish water

Abstract A positively charged thin film nanocomposite (TFN) membrane was synthetized based on the nano-gel UiO-66-NH2 for fractionation of monovalent and multivalent ions from saline water. The addition of nano-gel UiO-66-NH2 in the aqueous phase containing polyethyleneimine (PEI) led to the fabrication of a nanofiltration (NF) membrane with a looser structure, which can enhance the water permeability. The resulting TFN/PEI membranes were found to have a high rejection of 97.4 % and 88.1 % to MgCl2 and MgSO4 and a very low rejection of 4.1 % and 6.1 % for LiCl and NaCl with a permeability above 38 L/m2.h.bar. The TFN/PEI-3 membrane with 1 wt% nano-gel UiO-66-NH2 in PA layer had an optimal selectivity and permeability for fractionation of Mg2+/Li+ in MgCl2/ LiCl solution and Mg2+/Na+ in MgSO4/ NaCl solution. An efficient separation of Mg2+/Li+ with separation factor of 33, accompanied by a permeability as high as 30.6 L/m2.h.bar, was obtained. Moreover, the high hydrophilicity of the UiO-66-NH2-based TFN/PEI membrane led to a reasonable value of 82.6 % flux recovery after three cycles of filtration of a 2000 ppm Mg2+/Li+ mixed solution. These results demonstrate that this UiO-66-NH2-based TFN/PEI membrane with high permeability and selectivity can be an appropriate candidate for lithium extraction in practice.