A comparative study on the influences of sulfonated- and phosphorated-graphene oxide on polyvinylidene fluoride cation-exchange membranes for electrodialysis

The -SO3H and -PO3H2 groups were grafted on graphene oxide (GO) by adding sulfuric acid and phosphoric acid at the same weight percentage, respectively. The physicochemical properties of the sulfonated GO (SGO) and phosphorated GO (PGO) were compared using different techniques. SGO and PGO were individually incorporated into the PVDF matrix (at the same wt%) to compare their effects on the properties of the resulting PVDF/ SGO and PVDF/PGO cation-exchange membranes (CEMs). Membranes' characteristics including ionic conductivity and water content, area resistance, and the rate at which Na+ ions diffuse throughout the membranes changed considerably by altering the type of ion exchange sites, and more desirable values were obtained using PGO. Nevertheless, PVDF/SGO provided an ion exchange capacity (IEC) of 5.5 meq g- 1, while it was about 1.7 times lower than PVDF/PGO (9.4 meq g- 1). It also provided a promising ionic conductivity (17.24 mS cm- 1), transport number (93.65 %), permselectivity (89.58 %), and low area resistance (2.7 Omega cm2), which exceeded those of the commercial CEMs such as Ralex. Moreover, PVDF/SGO exhibited desirable mechanical characteristics, and a low weight loss (2.4 %) and low resistance change (22.2 %) after 9 h being submerged in the Fenton reagent, however, these parameters were better for PVDF/PGO.