Ph Responsive Membraens for Water Treatment

Nanofiltration membranes are frequently used for water treatment. Development of responsive nanofiltration membranes where the membrane properties can be altered by changing environmental conditions could lead to the development of multi-functional membranes. Here nanofiltration membranes have been modified by growing acrylic acid nanobrushes from the surface of the membrane and pores. 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 may be grafted from the surface and pores of large pore nanofiltration membranes without significantly impacting the permeate flux. Furthermore, swelling of the grafted nanobrushes at pH values above their pKa leads to a decrease in permeate flux. This results in nanofiltration membranes with properties that can be altered by changing the feed pH. In particular we show how rejection and flux may be varied by adjusting the feed pH. Complimentary modeling studies indicate that the pKa of the tethered polyacrylic acid brushes is affected by graft density and polymer molecular weight.