pH-responsive nanofiltration membranes by surface modification

▶ High flux (NF 270) nanofiltration membranes have been successfully surface modified using UV initiated free radical polymerization. ▶ Polyacrylic acid nanobrushes have been grafted to the membrane surface. ▶ Contact angle, ATR-FTIR and XPS analysis indicate that increasing reaction time and monomer concentration leads to greater amounts of grafted polymer. ▶ Grafting leads to pH responsive nanofiltration membrane. ▶ Modified membranes display a pH dependant water flux and glucose rejection. Fouling of nanofiltration membranes remains a major concern that often limits process viability. One method to minimize fouling is to modify the filtration surface and perhaps the pores of the membrane in order to minimize adsorption of dissolved solutes. Here nanofiltration membranes have been modified by growing acrylic acid nanobrushes from the surface of the membrane. If the pH of the feed is above the pKa of the grafted nanobrushes, the carboxylic groups will be deprotonated and swell. Dead end filtration experiments confirm that polyacrylic acid nanobrushes may be grafted from the surface of high flux nanofiltration membranes without significantly impacting the filtrate flux. Furthermore, swelling of the grafted nanobrushes at pH values above their pKa leads to a decrease in filtrate flux. Rejection of glucose has also been investigated. For the base membrane, glucose rejection was not affected by feed pH over the range 3–7. However for modified membranes a significant change in rejection was observed as a function of pH. Thus pH-responsive nanofiltration membranes may be designed by surface modification.