The Many Faces of Graphene as Protection Barrier. Performance under Microbial Corrosion and Ni Allergy Conditions.

In this work we present a study on the performance of CVD (chemical vapor deposition) graphene coatings grown and transferred on Ni as protection barriers under two scenarios that lead to unwanted metal ion release, microbial corrosion and allergy test conditions. These phenomena have a strong impact in different fields considering nickel (or its alloys) is one of the most widely used metals in industrial and consumer products. Microbial corrosion costs represent fractions of national gross product in different developed countries, whereas Ni allergy is one of the most prevalent allergic conditions in the western world, affecting around 10% of the population. We found that grown graphene coatings act as a protective membrane in biological environments that decreases microbial corrosion of Ni and reduces release of Ni2+ ions (source of Ni allergic contact hypersensitivity) when in contact with sweat. This performance seems not to be connected to the strong orbital hybridization that Ni and graphene interface present, indicating electron transfer might not be playing a main role in the robust response of this nanostructured system. The observed protection from biological environment can be understood in terms of graphene impermeability to transfer Ni2+ ions, which is enhanced for few layers of graphene grown on Ni. We expect our work will provide a new route for application of graphene as a protection coating for metals in biological environments, where current strategies have shown short-term efficiency and have raised health concerns.

Suppressing bacterial interaction with copper surfaces through graphene and hexagonal-boron nitride coatings.

Understanding biological interaction with graphene and hexagonal-boron nitride (h-BN) membranes has become essential for the incorporation of these unique materials in contact with living organisms. Previous reports show contradictions regarding the bacterial interaction with graphene sheets on metals. Here, we present a comprehensive study of the interaction of bacteria with copper substrates coated with single-layer graphene and h-BN. Our results demonstrate that such graphitic coatings substantially suppress interaction between bacteria and underlying Cu substrates, acting as an effective barrier to prevent physical contact. Bacteria do not "feel" the strong antibacterial effect of Cu, and the substrate does not suffer biocorrosion due to bacteria contact. Effectiveness of these systems as barriers can be understood in terms of graphene and h-BN impermeability to transfer Cu(2+) ions, even when graphene and h-BN domain boundary defects are present. Our results seem to indicate that as-grown graphene and h-BN films could successfully protect metals, preventing their corrosion in biological and medical applications.