Effect of Graphene Oxide Functionalization on the Performance of Ultrafiltration Mixed-Matrix Membranes

Abstract

Membrane separation technology contributes significantly to solving the global water crisis due to the advances in the materials of desalination and water treatment membranes. Nevertheless, improving the flux, rejection, and fouling resistance of polymeric membranes remain important requirements to further increase their reliability and decrease the cost associated with their frequently required cleaning. In this thesis, graphene oxide (GO) was functionalized with amine (NH2) and carboxyl (COOH) functional groups to enhance its hydrophilicity and antifouling characteristics. Subsequently, nanocomposites polysulfone (PS) and different concentrations of functionalized graphene oxide (f-GO) were formulated and used to fabricate mixed matrix ultrafiltration membranes via phase inversion process. The developed membranes were characterized and tested for separation of water-oil emulsion. An array of characterization techniques was utilized to confirm GO functionalization including XPS, EDX, Raman, XRD, SEM, and TEM. The morphology of the fabricated membranes was also characterized by AFM and SEM to study the porosity, roughness and channeling structure of f-GO membranes. The mechanical properties of the membranes were analyzed using dynamic mechanical analysis (DMA) and the effect of f-GO on the membrane hydrophilicity was probed by contact angle measurements. Our results confirmed the functionalization of GO to f-GO leading to significant increase in hydrophilicity as indicated by ~ 13° decrease in water contact angle. Moreover, Young’s modulus of f-GO membranes displayed enhancement of up to 93% and 88% for GO/NH2 and GO/COOH, respectively. The concentration of f-GO dictates the porosity, roughness and water flux, which all increase at small f-GO concentrations (0.05 – 0.2 wt. %), but then decrease with higher loading (0.4 and 0.8 wt. %). An increase of 97% and 44% of the pure water permeability was attained for 0.2%GO/COOH and 0.2%GO/NH2 and high oil rejection of 97.92 % was achieved by 0.1% GO/COOH. A preliminary antifouling test using BSA was carried on the optimum f-GO membranes and the results indicated f-GO membranes have strong fouling resistance characteristics compared to control membrane with BSA flux recovery ratio of 0.9 and 0.72 for 0.2%GO/COOH and 0.2%GO/NH2. BSA rejection was also improved from 73% for the control membrane to 79% and 87% for 0.2% GO/COOH and 0.2% GO/NH2, respectively. Finally, high concentration of f-GO has an adverse effect on the characteristics and performance of membranes, the optimal concentration is between 0.1 and 0.2 wt.% f-GO due to positive impacts it has on membrane’s flux, rejection, and fouling resistance.