Anti-fouling Nanofiltration Membranes
Membrane technologies with molecular-scale fractionation capability are of interest for advanced separations in the food, chemical and pharmaceutical industries. Molecular sieving membranes offer potential advantages of scalability, speed and cost efficiency compared with competing technologies such as chromatography, electrophoresis, distillation and crystallization. A membrane whose pore size could be actively tuned to control the size of permeate species during filtration would be particularly valuable as a “one size fits all” molecular fractionation tool. Key to the success of such separations is the ability of the membrane to resist adsorption of molecules from the feed solution that could modify the effective pore size.
In this project we employ amphiphilic comb polymers as a thin coating on the surface of a conventional UF membrane to create thin film composite nanofiltration (NF) membranes with molecular-level fractionation ability. Molecules of polyvinylidene fluoride -graft -polyoxyethylene methacrylate, PVDF -g -POEM, self-assemble into continuous nanophase domains of semicrystalline PVDF interweaved with hydrophilic nanochannels lined with poly(ethylene oxide), PEO, providing a mechanism for fast water transport along with a steric barrier to molecular adsorption. The molecular sieving capability of such membranes was demonstrated through the separation of like-charged organic dye molecules differing in dimension by only a few angstroms. The fractionation of Au nanoparticles to achieve a well-defined cutoff diameter and low size dispersity was further shown. By controlling the degree of swelling of the PEO chains lining the nanochannels, the size cut-off can be tuned to a given separation. Current efforts seek to extend this approach to other comb chemistries.
These NF membranes are also of interest for water treatement, due to the foul-resistant nature of the coating and the high quality of the effluent. No evidence of fouling is seen in dead-end filtration studies on feed solutions containing = 1000 mg/L concentrations of bovine serum albumin, sodium alginate, or humic acid, while retentions for these model foulants were >99.9%, 92% and 99%, respectively. By contrast, filtration of the same foulant solutions using the PVDF UF base membrane showed rapid and irreversible fouling, and substantially lower retentions (69, 60 and 37%, respectively). These membranes thus hold promise for applications where high concentrations of biofoulants are present, such as membrane bioreactors.Collaborators:
Dr. Rich Salinaro (Pall Corp.)
Prof. Eberhard Morgenroth (UIUC)
Professor Menachem Elimelech (Yale Univ.)
Prof. Francesco Stellacci (MIT)
Office of Naval Research
WaterCAMPWS at U.I.U.C. (an NSF STC)