Graphene Oxide-Functionalized Membranes: The Importance of Nanosheet Surface Exposure for Biofouling Resistance.

Surface functionalization using two-dimensional (2D) graphene oxide (GO) materials is a promising technique to enhance the biofouling resistance of membranes used in water purification and reuse. However, the role of GO exposure, which is crucial for the contact-mediated toxicity mechanism, has not been well evaluated or elucidated in previous studies. Herein, we employ bioinspired polydopamine chemistry to fabricate GO-functionalized membranes through two strategies: coating and blending. The two types of GO-functionalized membranes displayed comparable roughness, hydrophilicity, water permeability, and solute retention properties but different degrees of GO nanosheet exposure on the membrane surface. When in contact with the model bacterium, Escherichia coli, the GO-coated membrane exhibited enhanced biofouling resistance compared to that of the GO-blended membrane, as evidenced by lower viable cells in static adsorption experiments, and lower water flux decline and higher flux recovery in dynamic biofouling experiments. Moreover, the development of biofilm on the GO-coated membrane was also inhibited to a greater extent than on the GO-blended membrane. Taken together, our findings indicate the paramount importance of GO exposure on the membrane surface in conferring antibacterial activity and biofouling resistance, which should be considered in the future design of antibiofouling membranes using 2D nanomaterials.