Graphene‐Based Bacterial Filtration via Electrostatic Adsorption
Advanced Materials Interfaces
ditions lack clean water, fecal-oral diseases can proliferate rapidly. Diarrhea may not seem deadly to those who have access to improved sanitation, but it kills 750 000 children every year that is more than malaria, AIDS, and measles combined.  aterborne pathogens are also of great concern in the hospital environment, as the water temperatures and the complex structure of hospital water systems are suitable for bacterial growth and biofilm formation. [3, 4] These pathogens in connected
... es (such as sinks, showers, ice machines, water baths, eyewash stations, and dental units) can lead to severe infections, especially with the rising number of multidrug-resistant bacteria. [5, 6] he faucet micropore filters that are used to prevent this outcome must be replaced after a few weeks of use, making them very costly. Novel antibacterial technologies may offer practical and cost-effective prevention strategies for these concerns.  These flexible, singleatom-thick, nano-micrometer sized sheets feature an extremely large surface area. [10, 11] Among the variety of different graphene materials, graphene oxide (GO) is frequently used due to its inexpensive preparation from graphite      as well as its hydrophilic functional groups, which enhance its dispersibility in polar solvents and offer multiple options for chemical post-modification. [17, 18] n a previous work we demonstrated that polymer post-modification of micrometer-sized GO can be used to create polycationic microsheets.  These flexible GO microsheets matched the size and surface-charge density of opposite charged E. coli bacterial cells. Incubating them with gram-positive methicillinresistant Staphylococcus aureus (MRSA) and gram-negative Escherichia coli (E. coli) led to wrapping and immobilization of bacterial cells in both cases.  Based on multivalent electrostatic attraction, these GO derivates (GOX) also showed antibacterial activity when they were attached to a carrier material. [20, 21] lthough many polycationic polymers like chitosan, [22, 23] polyethylene imine, [24, 25] ε-polylysine,  polysiloxanes, [27, 28] polyionenes [29, 30] as well as modified GO materials with various conjugated moieties like mannose,  lactose,  quaternary ammonium compounds [33, 34] and zwitterionic systems  have been shown to bind and inhibit bacteria, investigation Flexible graphene oxide (GO) microsheets with attached positively charged polymers, termed GOX microsheets, are efficient at bacterial adsorption, as they bind electrostatically to bacterial membranes' negative surface charge. The authors explore an antimicrobial water filter application for GOX's extremely high surface area and its previously described efficient bacterial adsorption. Cellulose-fiber carrier material is functionalized with GOX microsheets to create an adsorption-based bacteria filtration material. The morphology and charge density (7.8 × 10 19 g -1 ) of the prepared GOX fibers are determined by scanning electron microscopy and dye adsorption assay, and widefield fluorescence microscopy is used to visualize the adsorption of stained Escherichia coli bacterial cells on the fibers. GOX fibers are tested in filtration setups to investigate their bacteria removal performance. The experimental results, with 100 mg of GOX fibers filtering 2.4 × 10 9 colony-forming units (CFU) from an E. coli bacterial culture with 99.5% bacterial reduction, demonstrate the fibers' high bacteria loading capacity. The electrostatic adsorption-based filtration mechanism allows the filter to be operated at higher flow rates than micropore membrane filters, while maintaining 3-log bacterial reduction. GOX filter materials removing bacteria via adsorption are a high flow rate alternative to current water filtration processes that rely on size-exclusion.