(245f) Responsive Membranes for Water Treatment
Numerous membrane processes such as reverse osmosis, nanofiltration, ultrafiltration, microfiltration and membrane distillation find applications in water treatment. Membrane processes often require far less energy than alternative unit operation making them particularly attractive for water treatment applications. Unfortunately membrane fouling often limits the use of membrane separations for water treatment. Development of advanced antifouling membranes will be essential if the potential for low energy membrane separations are to be realized for water treatment. Our research focuses on the development of new multi-functional mem¬branes i.e., membranes that carry out two or more functions cooperatively to achieve desired per¬formance. Here results will be presented for surface modification of commercially available nanofiltration membranes. Polymer brushes have been grown from the surface of the membrane using UV initiated and atom transfer radical polymerization. Nanofiltration membranes modified by growing acrylic acid nanobrushes from the surface of the membrane and pores respond to changes in feed pH. If the pH of the feed is above the pKa of the grafted nanobrushes, the carboxylic groups will be deprotonated and swell. Filtration experiments confirm that polyacrylic acid nanobrushes swell at pH values above their pKa leading to a decrease in permeate flux. This results in nanofiltration membranes with properties that can be altered by changing the feed pH. Rejection as a function of pH has also been determined. Growth of N-isopropylacrylamide (PNIPAM) from polyamide nanofiltration membranes lead to membrane surfaces that switch between a hydrophobic and hydrophilic conformation by switching above and below the lower critical solution temperature. Finally we have developed magnetically responsive nanofiltration membranes. Superparamagnetic particles have been attached to the ends of polymer brushes grown from the surface of the nanofiltration membranes. In an oscillating magnetic field, the ends of the brushes rotate like the cilia of microorganisms. This movement creates mixing at the nano-scale, which we have shown suppress fouling of the membrane by particulate matter. These three examples of responsive nanofiltration membranes indicate the tremendous potential for advanced multifunctional membranes for water treatment applications.