Importance of S-Doped Porous Carbon Acidity and Visible Light Photoactivity for Its Antibacterial Activity

Bactericidal activity of sulfur-doped carbon has been investigated against a common Gram-negative bacterium, Escherichia coli K-12 (E. coli), in aqueous solution. Under dark conditions, 1 h contact of carbon with bacteria resulted in a 3–4 log decrease from the initial concentration of 7 log. When exposed to visible light, a 6–7 log decrease in E. coli was observed. The bactericidal activity under dark conditions was linked to the effects of functional groups, particularly sulfonic groups, which released protons that contributed to bacterial death. Even though under visible light no reactive oxygen species (ROS) were detected in electron paramagnetic resonance (EPR) and scavenger experiments, the enhanced bactericidal activity was due to the generation of holes in the carbon matrix. The photoactivity of sulfur-doped carbon is attributed to hole generation in aqueous solution under visible light, further enhancing its bactericidal effect. Bacterial death was not affected by the surface area or the porous structure of carbons.