Antimicrobial Hierarchically Porous Graphene Oxide Sponges for Water Treatment

Water treatment technologies based on graphene oxide (GO) sponges show promise due to their high surface area and versatile chemistry, yielding an excellent adsorption affinity for different contaminants. However, the bacteria removal capacity and the intrinsic antimicrobial properties of GO sponges are not well understood. While GO has been successfully functionalized with antibiotics or metal biocides, these antimicrobials present cytotoxicity concerns. Natural antimicrobial agents such as antimicrobial enzymes, peptides, and polymers hold promise in this respect due to their relatively low cost, biocompatibility, and ability to readily functionalize GO by covalent bond formation with oxygen-containing functional groups. In this work, the antimicrobial enzyme lysozyme, antimicrobial peptide nisin, and antimicrobial polyamide ε-poly-l-lysine were used to covalently functionalize the surface of a hierarchically porous GO sponge. The antimicrobial activity of the functionalized material was demonstrated against two model organisms: the Gram-positive B. subtilis and Gram-negative E. coli. The performance of the porous material in a simulated filtration context was evaluated using packed column experiments, and an improved bacterial retention of both strains by the functionalized sponge was demonstrated. Furthermore, samples of spent sponge after filtration were evaluated with a membrane integrity assay demonstrating antimicrobial activity in a continuous flow mode.