(671e) An Improved Method for Surface Modification of Porous Water Purification Membranes with Bioinspired Coatings

The surfaces of polysulfone and polyethersulfone ultrafiltration membranes were coated with polydopamine, a bioinspired surface modification agent that mimics the adhesive proteins found in secretions of mussels.  The polydopamine coating yielded hydrophilic membranes that, under constant transmembrane pressure fouling conditions, have previously shown enhanced flux relative to unmodified membranes.  When evaluated under constant permeate flux fouling, however, modified membranes exhibited higher transmembrane pressures than their unmodified analogs.  This increased transmembrane pressure in the coated membranes was ascribed to the decrease in membrane permeance resulting from applying the polydopamine coating.  The membrane permeance could be tuned by varying polydopamine deposition time and, even at the shortest deposition times studied here of a few minutes, a substantial increase in membrane hydrophilicity could be achieved.  Therefore, polydopamine permits independent tuning of the membrane permeance and hydrophilicity.  Polydopamine was deposited on a membrane of relatively high permeance until the pure water permeance of the modified membrane matched that of an unmodified membrane having lower native permeance, permitting a comparison of the fouling performance of a modified and unmodified membrane with the same pure water permeance.  When unmodified and modified membranes of the same initial permeance were compared at constant flux fouling conditions, the modified membranes consistently exhibited lower transmembrane pressures and similar organic rejections to the unmodified membranes.  Because many porous water purification membranes are operated at constant flux in industrial settings, an interesting methodology for membrane surface modification may be to surface modify a membrane of high permeance until the desired permeance is achieved, rather than by surface modification of a membrane that natively has the desired water transport characteristics, since the surface modification procedures almost invariably lead to lower pure water permeance.