Nanofiltration Membranes Prepared by Layer-by-Layer Self-Assembly of Polyelectrolyte

Ultrathin composite nanofiltration (NF) membranes fabricated by layer-by-layer (LbL) assembly technique, which can precisely control structures and compositions, has received a rapid development. In this paper, a review is presented on LbL assembly methods, types of polyelectrolytes and influencing factors of LbL assembly NF membranes in recent years. Three different approaches for LbL assembly are mainly introduced, including the conventional electrostatic deposition method, the pressure-driven LbL assembly and the electric field enhanced LbL assembly. The types of the self-assembled polyelectrolyte materials, which can be classified into homopolymer, copolymer, and organic-inorganic hybrid polyelectrolytes are carried out. Separation performances of NF membrane influenced by various factors, such as the charge character, the charge density and the ionization degree of the polyelectrolyte are discussed. The applications of LbL assembly NF membrane for water-treatment and substances separation from organic solvent are summarized. At the same time, some propose of speeding up the assembly process, improving the performance and development orientation of NF membranes are presented.