Comparative study on graphene oxide and sulfonated graphene oxide reinforced polyethersulfone-based cation-exchange membrane

Abstract

In this research, polyethersulfone/sulfonated graphene oxide (PES/SGO) heterogeneous cation exchange membranes were fabricated by the mold casting method. The sulfonation of GO was carried out using the diazonium salt of sulfanilic acid. The properties of the synthesized GO and SGO were compared in terms of chemical structure, morphology, surface charge, crystallinity, and thermal stability. The variations in surface morphology and roughness, hydrophilicity, dimensional stability, and ionic conductivity of the PES-based membranes as a function of GO and SGO content were investigated. Results revealed that SGO enjoyed a higher level of oxygenated groups contributing to its higher surface charge. SGO also tolerated a higher temperature before being fully decomposed due to the presence of the sulfur-containing groups. A finer nanostructured morphology was observed in the SGO-containing membranes, resulting in a considerably lower surface roughness of these membranes than the corresponding GO-based membranes. The membrane comprising 10 wt% SGO showed the lowest surface roughness of 88 nm, and the highest water uptake of 16.66 %, ion-exchange capacity of 1.12 meq g-1, and the lowest charge transfer resistance of 3.6 Ω and area resistance of 0.9 Ωcm2. This was accompanied with a considerable increment in the permselectivity and cation (Na+) transport number of this membrane to 95.9 % and 97.5 %, respectively, due to the higher surface adhesion energy of 94.57 J m-2 and higher Na+ flux of 4.43×10-7 mol m-2 s-1, which were significantly higher than that obtained for the corresponding PES-based membrane containing 10 wt% GO. Furthermore, a lower weight loss and resistance change were observed for PES/SGO after being exposed to the Fenton reagent for 9 h, indicating the impact of the sulfonated groups on the oxidative stability enhancement of the membrane.