Inactivation of E. coli mediated by high surface area CuO accelerated by light irradiation >360 nm

CuO powders with different specific surface areas are reported hereby to inactivate E. coli in aqueous solution in the dark under visible light irradiation λ > 360 nm. The inactivation of E. coli mediated by the CuO suspensions was investigated as a function of the solution parameters: specific surface area of the Cu-oxides (40–77 m2/g), amount of CuO, light intensity and fate of the Cu1+-ion within the inactivation process. The specific surface area of the CuO was observed to play an important role during the E. coli inactivation kinetics. The light induced inactivation of E. coli in CuO suspensions (1 g/L) was complete within 4 h. The cytotoxicity of E. coli when using CuO (77 m2/g) was found for CuO concentrations as low as 0.2 g/L. A reaction mechanism is suggested for the Fenton-like reactions due to the Cu-ions/CuO action and the reactive oxygen species (ROS) generated in solution. These highly oxidative radicals decompose Orange II and methylene blue (MB) dyes in aqueous solution of CuO. The CuO in contact with the bacterial suspension shows a change in its surface oxidation state from Cu2+ to Cu1+. The outermost layer of the catalyst (5–7 nm) becomes mainly Cu2O (80%) and CuO (20%) as observed by X-ray photoelectron spectroscopy (XPS). A shift of the Cu 2p3/2 peak from the initial position at 933.6–932.6 eV upon contact of the E. coli with CuO was observed concomitant with the disappearance of the Cu2+ shake-up satellite lines at 942.3 and 962.2 eV. The XPS surface composition of copper catalyst is reported at different stages of E. coli inactivation and it was observed that the reduced copper oxide remains stable during the 4 h needed to inactivate the E. coli suspension.