Atomic Layers of Graphene for Microbial Corrosion Prevention.

Graphene is a promising material for many biointerface applications in engineering, medical, and life-science domains. Here, we explore the protection ability of graphene atomic layers to metals exposed to aggressive sulfate-reducing bacteria implicated in corrosion. Although the graphene layers on copper (Cu) surfaces did not prevent the bacterial attachment and biofilm growth, they effectively restricted the biogenic sulfide attack. Interestingly, single-layered graphene (SLG) worsened the biogenic sulfide attack by 5-fold compared to bare Cu. In contrast, multilayered graphene (MLG) on Cu restricted the attack by 10-fold and 1.4-fold compared to SLG-Cu and bare Cu, respectively. We combined experimental and computational studies to discern the anomalous behavior of SLG-Cu compared to MLG-Cu. We also report that MLG on Ni offers superior protection ability compared to SLG. Finally, we demonstrate the effect of defects, including double vacancy defects and grain boundaries on the protection ability of atomic graphene layers.

Hexagonal Boron Nitride for Sulfur Corrosion Inhibition.

Corrosion by sulfur compounds is a long-standing challenge in many engineering applications. Specifically, designing a coating that protects metals from both abiotic and biotic forms of sulfur corrosion remains an elusive goal. Here we report that atomically thin layers (∼4) of hexagonal boron nitride (hBN) act as a protective coating to inhibit corrosion of the underlying copper (Cu) surfaces (∼6-7-fold lower corrosion than bare Cu) in abiotic (sulfuric acid and sodium sulfide) and biotic (sulfate-reducing bacteria medium) environments. The corrosion resistance of hBN is attributed to its outstanding barrier properties to the corrosive species in diverse environments of sulfur compounds. Increasing the number of atomic layers did not necessarily improve the corrosion protection mechanisms. Instead, multilayers of hBN were found to upregulate the adhesion genes in Desulfovibrio alaskensis G20 cells, promote cell adhesion and biofilm growth, and lower the protection against biogenic sulfide attack when compared to the few layers of hBN. Our findings confirm hBN as the thinnest coating to resist diverse forms of sulfur corrosion.

Electricity from methanol using indigenous methylotrophs from hydraulic fracturing flowback water.

Methanol solvents that are used in hydraulic fracturing often return back to the surface in the form of recalcitrant flowback water. Here, the indigenous methylotrophic bacteria from flowback water were enriched and used to generate electricity from methanol in a two-compartment microbial fuel cell (CH3OH-MFC). An identical MFC based on a tryptone-yeast extract (TY-MFC) was used as a control. CH3OH-MFC yielded a 2.7-fold thicker biofilm dominated by electrogenic species (81%) and higher power density (76 mW/m2) compared with TY-MFC (50 mW/m2). Illumina MiSeq sequencing of the 16S rRNA gene in TY-MFC revealed classes from Actinobacteria, Bacteroidia and γ-proteobacteria. The CH3OH-MFC yielded α-proteobacteria, ß-proteobacteria, γ-proteobacteria and Bacteroidia, with a dominant fraction of Rhodobacter sphaeroides (~29%). We discuss the potential pathways used by R. sphaeroides to maintain syntrophic cooperation with other bacterial and archaeal members to sustain CH3OH oxidation. Finally, we establish that a pure culture of R. sphaeroides 2.4.1 generates electricity directly from methanol.