Fabrication of high performance cation-exchange membrane based on sodium tripolyphosphate (NaTPP)-grafted graphene oxide for electrodialysis

Graphene oxide (GO) was modified by sodium tripolyphosphate (NaTPP) via a grafting method and applied as a nanofiller for fabricating mixed matrix polyvinylidene fluoride (PVDF)-based cation-exchange membranes. The influences of NaTPP loading level on the chemical structure of GO were investigated using different techniques. Adding NaTPP to GO led to an increase in the surface charge and level of sp(3) domains, and a decrease in the interlayer d-spacing and crystallinity of the resulting GO-NaTPP. Generally, GO-NaTPP-based membranes provided smoother surface morphology, higher surface wettability, higher ionic and water content, and lower area resistance compared to the GO-containing membranes. The best membrane exhibited a high water uptake of 46.2 +/- 1.3 % and ion exchange capacity (IEC) of 3.8 +/- 0.1 meq g(-1), leading to the easier diffusion of Na+ ions within the membrane. This resulted in the favorable membrane area resistance of 1.3 +/- 0.32 omega cm(2), which was about 87.48 % lower than that of the GO-containing membrane. The oxidative and mechanical stability of the membranes was significantly boosted by adding GO-NaTPP, in which the best membrane exhibited a low weight loss of 1.37 %, and a low resistance change of 17.49 % after being immersed in the Fenton reagent for 9 h.