Bactericidal activity of Ag-doped multi-walled carbon nanotubes and the effects of extracellular polymeric substances and natural organic matter

The objective of this study was to determine the bactericidal mechanisms of Ag-doped multi-walled carbon nanotube (MWCNT) nanoparticles (Ag-0/MWCNTs) to Escherichia coli DH5 alpha. The contributions of silver ion dissolution, reactive species, and direct contact on bacteria inactivation were systematically determined. The relatively higher survival rate of bacteria exposed to 0.02 mg L-1 Ag+ ions (the maximum concentration of Ag+ ions dissolved from Ag-0/MWCNTs) suggested that the antibacterial property of Ag-0/MWCNTs was not caused by silver ion dissolution. The effects of each reactive species ((OH)-O-center dot, H2O2, O-center dot(2)-, h(+), and e(-)) on the disinfection process were investigated by using multiple scavengers, and the results showed that (OHb)-O-center dot, (OHs)-O-center dot, and h(+) play important roles in bactericidal actions. The significance of (OHb)-O-center dot, (OHs)-O-center dot, and h(+) in the disinfection process was further confirmed in the partition systems combined with scavenger. The antibacterial effects of these reactive species mainly arose through direct contact of the nanocomposites with the bacteria. The effects of extracellular polymeric substances (EPS) and natural organic matter (NOM) on the inactivation of bacteria were also investigated. The lower antibacterial effect observed for EPS-rich bacteria relative to EPS-poor bacteria demonstrated the protective effects of EPS in the disinfection system. The decreased bacterial toxicity effect acquired by the addition of humic acid (as the model NOM) in the disinfection system demonstrated the influence of NOM on the bacterial toxicity of nanocomposites, where the sorption of NOM onto the surface of the nanocomposites contributed to the decreased antibacterial effects. (c) 2012 Elsevier B.V. All rights reserved.