Cellulose nanofiber intermediary to fabricate highly-permeable ultrathin nanofiltration membranes for fast water purification

Highly-permeable nanofiltration membranes are highly desired in water production and dissolved solutes removal due to environmental and energy concerns. Here a facile approach is presented to prepare ultrathin polymeric nanofiltration membrane using surface modification of ultrafine cellulose nanofiber (UCN) membrane via interfacial polymerization. The hydrophilic UCN membrane endows an interconnected nanoporous microstructure containing free spaces for the growth of the crosslinked-PEI layer creating narrow permeation channels that are responsible for the transport of water moleucles. The resultant membranes comprising an ultrathin selective layer intertwined with cellulose nanofiber matrix are smooth and allow fast permeation of water. Typically, the 77.4 nm-thick membrane with a mean pore size of about 0.45 nm and molecular weight cut-off of 824 g mol(-1) has a high pure water flux of 32.7 L m(-2) h(-1) bar(-1) that is an order of magnitude higher than those of previously reported similar nanofiltration membranes. The membranes are also positively charged and display high permeation flux and sufficient rejections for inorganic salts and organic dyes in the water purification. Further performance evaluation using model synthetic wastewater demonstrates the membranes have a great potential in the wastewater treatment. This approach presents a promising strategy for the development of highly-permeable nanofiltration membranes for fast water purification and high-efficient separation of small molecules.