Turning seawater or sewage into drinkable water depends on the filtering power of thin polyamide membranes. Microbes glom onto and muck up these membranes, disrupting their ability to remove salts and contaminants. But attaching graphene oxide nanosheets to the polyamide materials reduces bacterial growth, according to a new study (Environ. Sci. Technol. Lett. 2013, DOI: 10.1021/ez4001356). These functionalized membranes may require less cleaning and last longer than those in use today.
Certain nanomaterials, such as graphene oxide, kill microbes by an as-yet-unknown mechanism. In previous studies, researchers made antimicrobial membranes by mixing graphene oxide into the polyamides during casting. The problem with that, according to Menachem Elimelech of Yale University, is graphene oxide ends up inside the membrane where it’s useless for slaying microbes. Since nanomaterials are expensive and may impact the environment, Elimelech wanted to develop an antimicrobial membrane that requires as little graphene oxide as possible.
To that end, Elimelech and colleagues attached 30- to 650-nm-wide sheets of graphene oxide just to the surface of a polyamide membrane using amide coupling chemistry. “Whenever you alter the surface chemistry, you almost always affect the membrane performance,” Elimelech says. But that wasn’t so this time: The functionalized membrane let water through just as well as the untreated membrane.
The researchers tested the functionalized membrane’s antimicrobial activity by covering it with an Escherichia coli-laced broth for an hour. Then, they attempted to grow on agar plates any bacteria that had stuck to the membrane. Compared to untreated membranes, those modified with graphene oxide produced 65% fewer bacterial colonies. To boost lethality, Elimelech plans to alter the number and size of graphene oxide sheets on the membrane’s surface in future experiments.