Fabrication of pH-sensitive thin-film nanocomposite nanofiltration membranes with enhanced performance by incorporating amine-functionalized graphene oxide

Abstract

To determine the influence of positively charged graphene-based nanofillers on the nanofiltration (NF) performance as well as strengthen the nanofiller stability in a polypiperazine-amide (PPA) matrix, graphene oxide (GO) was first modified with ethylenediamine (EDA) and polyethylenimine (PEI) to obtain two kinds of aminated graphene oxide (AGO) nanofillers with a positive charge. The characterization results of AGO nanofillers indicated that EDA and PEI were successfully grafted onto GO via amide bonds without destroying the original GO structure. Then, novel thin film nanocomposite (TFN) NF membranes were fabricated by incorporating AGO nanofillers into the PPA skin layer using the interfacial polymerization (IP) method. With the addition of 60 ppm GO-EDA or 40 ppm GO-PEI, the TFN-GO-EDA-60 and TFN-GO-PEI-40 NF membranes showed optimal individual permselectivities ascribed to the formation of thinner, smoother and stronger hydrophilic nanocomposite skin layers. While retaining a rejection level of sodium sulfate >98%, the water fluxes of TFN-GO-EDA-60 and TFN-GO-PEI-40 membranes reached 59.6 and 62.1 L·m−2·h−1, corresponding to 154.4 and 160.9%, respectively, of that of the TFC-blank membrane. Furthermore, both the TFN-GO-EDA-60 and TFN-GO-PEI-40 NF membranes exhibited excellent anti-fouling capabilities, chlorine resistances as well as mechanical stabilities compared with TFC-blank membrane. However, their anti-fouling performance and salt rejection varied with the solution pH due to the positively charged AGO nanofillers. Moreover, GO-PEI demonstrated a greater potential for enhancing the performance of TFN NF membranes compared with that of GO-EDA.