The Antifouling Mechanism and Efficacy of Graphene Nanomaterials in Composite Coatings against Marine Diatoms.

The urgent need for sustainable antifouling solutions in marine environments has intensified the search for alternatives to toxic biocides. One promising approach involves embedding graphene nanomaterials into polymer composites. While graphene's antifouling properties have been extensively studied in solution, its mechanisms within solid composites remain unclearparticularly whether its effects are primarily chemical, such as oxidative stress, or physical, such as mechanical disruption. This study investigates the antifouling mechanisms of native, unmodified graphene and graphene oxide embedded in epoxy composite coatings targeting marine diatoms under laboratory conditions. Both graphene-based coatings significantly outperformed pure epoxy in reducing diatom adhesion in flow-through systems, using both monocultures and mixed algal cultures, with efficacy increasing alongside filler concentration. A comprehensive suite of characterizationsincluding surface energy analysis, reactive oxygen species (ROS) measurements, and scanning and transmission electron microscopywas employed to elucidate the mode of action. Unlike commercial antifouling coatings, the high surface energy of these composites rules out fouling release as the dominant mechanism. ROS measurements indicated minimal oxidative stress, suggesting that chemical toxicity is not the primary driver. Microscopy revealed membrane disruption as the main cause of cell death, primarily through contact-mediated phospholipid damage. Furthermore, cellular assays showed higher cell mortality on graphene-containing surfaces compared with those with graphene oxide, reinforcing the role of mechanical disruption. Overall, these findings demonstrate that graphene nanomaterials confer antifouling activity primarily through direct contact interactions, highlighting their potential for durable, nontoxic marine coatings. However, to fully leverage the biocidal properties of graphene and graphene oxide, efficient removal of dead foulants remains a critical challenge.