Designing magnetic field responsive nanofiltration membranes

Abstract

Base, thin film composite polyamide, nanofiltration membranes have been modified using surface initiated atom transfer radical polymerization to graft poly(2-hydroxyethyl methacrylate) (polyHEMA) chains from the surface of the membrane. A modified Gabriel synthesis procedure was used to attach superparamagnetic (Fe3O4) nanoparticles to the chain ends. Chain density and chain length were independently varied by adjusting the initiator density and polymerization time. Membranes were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements.The performance of modified membranes was investigated by determining deionized water fluxes as well as permeate fluxes and salt rejection for aqueous feed streams containing 500ppm CaCl2 and 2000ppm MgSO4. All experiments were conducted in dead end mode. Modified membranes display a reduced permeate flux and increased salt rejection compared to unmodified membranes in the absence of a magnetic field. Since both grafted chain density and chain length are expected to affect membrane performance differently, the decrease in permeate flux and increase in salt rejection is not directly proportional to the increase in grafted polymer weight. Modified membranes display both increased permeate fluxes and increased salt rejection in the presence of an oscillating magnetic field compared to their performance in the absence of an oscillating magnetic field. Magnetically responsive membranes could represent a new class of fouling resistant membranes.