Rongcai Xie

Visible-Light-Induced Bactericidal Activity of Titanium Dioxide Codoped with Nitrogen and Silver

Titanium dioxide nanoparticles codoped with nitrogen and silver (Ag(2)O/TiON) were synthesized by the sol-gel process and found to be an effective visible light driven photocatalyst. The catalyst showed strong bactericidal activity against Escherichia coli (E. coli) under visible light irradiation (λ > 400 nm). In X-ray photoelectron spectroscopy and X-ray diffraction characterization of the samples, the as-added Ag species mainly exist as Ag(2)O. Spin trapping EPR study showed Ag addition greatly enhanced the production of hydroxyl radicals (•OH) under visible light irradiation. The results indicate that the Ag(2)O species trapped e(CB)(-) in the process of Ag(2)O/TiON photocatalytic reaction, thus inhibiting the recombination of e(CB)(-) and h(VB)(+) in agreement with the stronger photocatalytic bactericidal activity of Ag(2)O/TiON. The killing mechanism of Ag(2)O/TiON under visible light irradiation is shown to be related to oxidative damages in the forms of cell wall thinning and cell disconfiguration.

Memory antibacterial effect from photoelectron transfer between nanoparticles and visible light photocatalyst

A novel visible light photocatalyst system was developed, consisting of palladium oxide (PdO) nanoparticles well dispersed on a nitrogen-doped titanium oxide (TiON) matrix. Clear evidence of photoelectron transfer between PdO nanoparticles and the TiON matrix was obtained for the first time. The optoelectronic coupling between PdO and TiON introduces enhanced photocatalytic bacterial disinfection under visible light illumination by electron trapping on a PdO nanoparticle, and a unique catalytic memory effect on bacterial disinfection due to the discharging of trapped electrons on PdO nanoparticles in the dark when the illumination is switched off. Thus, a unique robust catalytic disinfection system is created, which is driven by solar/visible light illumination, enables the continuous operation in day and night, and could be adapted to a broad range of environmental applications.

Enhanced photocatalytic disinfection of microorganisms by transition-metal-ion-modification of nitrogen-doped titanium oxide

In this article, palladium modification and silver modification were used as examples to demonstrate the disinfection effects on microorganisms in aqueous environment of photocatalytic transition-metal-ion-modified nitrogen-doped titanium oxide (TiON/M) materials. Transition metal ion modification was applied to TiON to take advantage of the coupling between transition metal ion addition and TiON semiconductor matrix under visible light illumination. The coupling promotes the separation of electron and hole pairs produced by photon excitation, thus it could reduce the intrinsic charge carrier recombination from anion-doping, which largely limits the photoactivity of TiON under visible light illumination. Large enhancements on the hydroxyl radical production and the photocatalytic disinfection efficiency on microorganisms under visible light illumination were observed for TiON with both palladium and silver modifications. The superior photocatalytic performance under visible light illumination suggests that the transition metal ion modification is an effective approach to reduce the massive charge carrier recombination from anion-doping and to enhance the photocatalytic performance of anion-doped TiO 2 . The resulting photocatalytic materials have the potential for a wide range of environmental applications.