(711e) Magnetically Responsive Self-Cleaning Nanofiltration Membranes

Magnetically responsive nanofiltration (NF) membranes with superparamagnetic nanoparticles attached to the chain ends of the grafted polymer nanolayers have been shown to be effective in breaking concentration polarization at the membrane-liquid interface under an appropriate external oscillating magnetic field. NF270 is one of the most commonly used NF membranes for removing low molecular weight species and divalent or trivalent salt ions from the feed solutions. Earlier studies for magnetically responsive NF membranes have focused on 500 ppm NaCl and 2000 ppm MgSO₄ model salt solutions only. Here the effects of the frequency of the oscillating field, salt ion type and its concentration on the performance of NF270 are systematically investigated. Salt solutions investigated include NaCl, CaCl₂, MgCl₂, MgSO₄ and Na₃PO₄ as well as their mixtures with concentration ranging from 500 to 5000 ppm. In addition, the effects of grafting degree including both chain length and chain density are also studied. Our studies show that the higher the salt concentration, the higher the valence of the salt ions and the higher the grafting degree, the stronger the effects of the magnetic field on permeate flux and salt rejection.