High flux hyperbranched starch-graphene oxide piperazinamide composite nanofiltration membrane

Polypiperazinamide membranes are most commonly used membranes for nanofiltration (NF) of solution. These membranes suffer low flux due to the relatively flexible hydrophobic backbone. Hydrophilic graphene oxide (GO) was incorporated in the top layer of these membranes to improve flux. However, GO is expensive therefore, the GO was modified with starch, a benign and inexpensive hydrophilic matrix to minimize the economic burden. Starch functionalized GO was added in the polypiperazinamide network to give high-flux hyperbranched starch functionalized graphene oxide composite (HGOST) nanofiltration membranes. GO-starch composites were integrated in the polyamide (PA) top layer by esterification. Abundant oxygen functional groups in starch and graphene oxide decreased contact angle to 22.18 degrees. Permeance of the membranes increased to 79.6 L m(-2) h(-1) (LMH) with the addition of HGOST to the top layer, with slight increase in the ionic rejection. The use of starch decreased the amount of graphene oxide needed to improve performance by about 80%. Hydrophilic nature of starch-GO composite, its compatibility with the polypiperazinamide matrix and enhance surface negative charge on the membrane in combination with a thin top layer are responsible for enhanced performance. Excellent stability was obtained due to bonding between starch, GO and polypiperazinamide layer. Membranes displayed excellent rejection of charged and neutral dyes as well. The inclusion of GO-starch composites shows good promise for enhancing the performance of polyamide membranes.