Copper-aided photosterilization of microbial cells on TiO 2 film under irradiation from a white light fluorescent lamp

Abstract

The copper-aided photosterilization of Escherichia coli was examined on TiO 2 thin films under a lighting condition with less UV rays from a white light fluorescent lamp. It was found that the coexistence of Cu 2+ and H 2O 2 in liquid phase exerted the synergistic effect on killing E. coli cells though these chemical species were individually at nontoxic levels to the cells (less than 10 mmol/m 3). At an incident light intensity of I 0 = 28 W/m 2, the addition of Cu 2+ (10 mmol/m 3) to liquid phase on TiO 2 film gave the apparent deactivation rate constant of k′ = 12 × 10 −2 min −1, the value of which was about 5 times as large as that on TiO 2 film in the absence of Cu 2+. This result suggested that in the liquid phase, Cu 2+ was reduced to Cu + by receiving electron from photo-excited TiO 2, and then Cu + reacted with photocatalysis-derived H 2O 2 to produce OH via Fenton-type reaction. The deactivation tests were also examined using a modified film preparation made from copper-incorporated TiO 2. On this film, the k′ value was 23 × 10 −2 min −1 at I 0 = 28 W/m 2, which was respectively about two and nine times as large as those on the original TiO 2 film with and without Cu 2+ addition (10 mmol/m 3). The enhancement of biocidal activity on the modified TiO 2 film was considered to arise from promoted OH formation by the aid of copper component anchored in TiO 2 solid phase.