Adsorption of microorganisms on single-walled carbon nanotubes and other porous media.

摘要

Waterborne outbreaks resulting from contamination of drinking water systems with biothreat pathogens are a cause of major public health concern in many countries today. State of the art technologies, which are primarily designed to treat sewage based contaminations, are not very effective against biothreat agents. Most of the biothreat agents are colorless, tasteless and odorless and are likely to be undetected by existing sensory systems. These two drawbacks (ineffectiveness in treatment and inability to detect) have made the water treatment plants highly vulnerable for bioterrorism attacks. Carbon nanotube technology has a great potential to make important advancement in water security and protection from biothreat agents. Carbon nanotubes can be used as adsorbent media for effective removal of multiple pathogens from contaminated water, they can also be used as potential biosensors for simultaneous concentration and detection of multiple pathogens in water.; In this research the results of batch adsorption studies of three different microorganisms on single-walled carbon nanotubes, activated carbon and NanoCeram(TM) are presented and the feasibility of using carbon nanotubes for removal of microorganisms are reported. Batch adsorption experiments are conducted to determine adsorption kinetics and adsorption equilibrium of pure cultures of Bacillus subtilis (B.subtilis), Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) on SWCNT aggregates. Adsorption of mixed cultures of E.coli and S.aureus on single-walled carbon nanotube aggregates is also tested. The diffusivities of the pure cultures of bacteria in single walled carbon nanotubes obtained are 1.26*10-10 cm2/s for B.subtilis, 1.09*10-10 cm2/s for E.coli, and 1.64*10-9 cm2/s for S.aureus. The Henry's constant for B.subtilis adsorption on SWCNT is 788,550. This is significantly higher than those obtained for activated carbon 28,631, and NanoCeram(TM) 20,853.; Henry's constants obtained for E.coli and S.aureus are 1.0*106 and 1.10*108 respectively. High Henry's constant of adsorption means high adsorption affinity. Diffusivities of both the bacterial species in single-walled carbon nanotubes are also calculated. It was found that smaller size S. aureus, the smallest microorganism of the three, on the average diffuses 13 times faster than B.subtilis and 15 times faster than E.coli and has a 5-10 times faster diffusion rate than E. coli. In addition, S.aureus about 100 times higher adsorption affinity for SWCNT than the other two. The combined high adsorption affinity and fast adsorption kinetics for S.aureus suggest that even unmodified single-wall carbon nanotubes can selectively differentiate S. aureus from B. subtilis and E. coli in water.; In addition to the adsorption studies, extensive electron microscopy and confocal microscopy analysis is performed with bacterial samples adsorbed on carbon nanotubes. The microscopic analysis qualitatively confirmed the adsorption results and provides direct visualization of the adsorbed bacteria on carbon nanotube aggregates. Both E.coli and S.aureus form biofilms on carbon nanotube aggregates and have a strong tendency to connect with each other rather than with the carbon surface.