(387b) Responsive Membranes for Water Treatment

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 operations 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 is to be realized for water treatment.  Our research focuses on the development of new multi-functional mem­branes, i.e., membranes that carry out two or more functions cooperatively to achieve desired per­formance. Here results will be presented for surface modification of commercially available nanofiltration membranes in order to make them responsive to an oscillating magnetic field. 

Commercially available nanofiltration membranes (NF 270) have been modified using atom transfer radical polymerization to grow poly(2-hydroxyethyl methacrylate) chains from the surface of the membrane. Next a Gabriel synthesis reaction was used to convert the alkyl halide end group of the polymer chains to primary amines. Carboxylic acid coated iron oxide nanoparticles were then attached to the chain ends through an amide linkage. Successful surface modification of the membranes has been monitored using X-ray photoelectron spectroscopy.

Movement of the magnetically responsive brushes has been visualized using particle image velocimetry. Our data indicate that this motion is sufficient to cause mixing up to a distance of 0.5 mm from the membrane surface.  Dead end filtration experiments have been conducted using feed streams consisting of aqueous solutions of MgSO₄ and CaCl₂. The presence of an oscillating magnetic field has little effect on the flux for unmodified membranes though the rejection increases slightly.  Since the ionic species in solution can also respond to the oscillating magnet field this could lead to a decrease in concentration polarization and hence higher rejection.  Importantly our results indicate improved fluxes and rejection for modified membranes in the presence of an oscillating magnetic field. These results demonstrate successful modification of nanofiltration membranes in order to make them responsive to an oscillating magnetic field. Further, the movement of the polymer chains induces mixing at low Reynolds number and is also expected to suppress fouling.