Layer-by-layer self-assembled chitosan/PAA nanofiltration membranes

Polyelectrolyte composite nanofiltration membranes were prepared using layer-by-layer self-assembly of chitosan and poly(acrylic acid) on a microporous polyethersulfone substrate. Membranes with a layer-by-layer structure were formed by sequential depositions of cationic chitosan and anionic poly(acrylic acid) alternately. The impacts of parameters involved in the membrane preparation process on the separation performance of the resulting membrane were investigated. The membranes showed good separation performance with an over 90% rejections to sulfate salts (i.e., MgSO4 and Na2SO4) and nearly 60% rejections to chloride salts (i.e., MgCl2 and NaCl). In spite of commonly observed trade-off relationship between salt rejection and water permeability, the membrane fabrication conditions can be tailored to enhance the overall performance of the nanofiltration membranes. The LbL self-assembled membranes may not afford a long-term use for nanofiltration of aqueous solutions due to extensive membrane swelling over a prolonged period of operation, and thermal and chemical post-treatments (i.e., heat treatment and chemical crosslinking) can be used to improve the membrane stability.