Abstract
In the present work, we provide evidence for visible light irradiation of the Au/TiO2 nanoparticles’ surface plasmon resonance band (SPR) leading to electron injection from the Au nanoparticles to the conduction band of TiO2. The Au/TiO2 SPR band is shown to greatly enhance the light absorption of TiO2 in the visible region. Evidence is presented for the light absorption by the Au/TiO2 plasmon bands leading to the dissolution of Au nanoparticles. This dissolution occurs concomitantly with the injection of the hot electrons generated by the Au plasmon into the conduction band of TiO2. The electron injection from the Au nanoparticles into TiO2 was followed by femtosecond spectroscopy. The formation of Au ions was further confirmed by the spectral shift of the transient absorption spectra of Au/TiO2. The spectral changes of the SPR band of Au/TiO2 nanoparticles induced by visible light were detected by spectrophotometer, and the morphological transformation of Au/TiO2 was revealed by electron microscopy techniques as well. Subsequently, the fate of the Au ions was sorted out during the growth and biofilm formation for some selected Gram-negative bacteria. This study compares the bactericidal mechanism of Au ions and Ag ions, which were found to be substantially different depending on the selected cell used as a probe.
Highlights
TiO2 photocatalysis induced by UV light possess powerful antimicrobial properties against bacteria, including multiresistant bacterial strains, viruses, and fungi
Moderate bacterial inactivation kinetics were induced by TiO2, as shown in Figure 1, due to the TiO2 surface states’ excitation under visible light irradiation [31]
A higher acceleration in the E. coli AB1157 CFU bacterial inactivation kinetics is seen in Figure 1 for suspensions of Au/TiO2 under visible light, as compared to TiO2
Summary
TiO2 photocatalysis induced by UV light possess powerful antimicrobial properties against bacteria, including multiresistant bacterial strains, viruses, and fungi. TiO2 photocatalysts need UV-light photons with energies ≥3.2 eV. The photogenerated electron–hole pairs lead to the generation of reactive oxygen species (ROS) in aqueous solution, leading to the degradation of contaminants and microorganisms [1,2]. Photocatalytic systems with biocidal effects under visible light are have not been widely reported and their mechanism of bacterial inactivation is only partially understood [3]. The photocatalytic/biocidal activity of Au/TiO2 nanocomposites is higher compared to bare TiO2 when excited by UV light. Electrons and holes are generated in TiO2 due to the interband transition induced by the UV quanta absorption. Au promotes the electron/hole separation and leads to ROS formation [4,5]
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