Ultraviolet irradiation of titanium dioxide in aqueous dispersion generates singlet oxygen

Abstract

We previously reported that irradiation of titanium dioxide (TiO2) in ethanol generates both singlet oxygen (1O2) and superoxide anion (O2*-) as measured by EPR spectroscopy. The present study describes the production of reactive oxygen species upon irradiation of TiO2 in aqueous suspension as determined by EPR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TMP) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). Photoproduction of 1O2 by suspended TiO2, detected as 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (4-oxo-TEMPO), was measured in water and deuterium oxide (D2O) in the presence or absence of sodium azide (NaN3) and under air or argon atmospheres. Production of a DMPO-OH adduct was examined in 4-oxo-TMP containing medium in the presence or absence of dimethyl sulfoxide (DMSO). The signal for the DMPO spin adduct of superoxide anion was not observed in aqueous conditions. Kinetic analysis revealed that 1O2 was produced at the surface of irradiated TiO2 in aqueous suspension as was observed in ethanol. Kinetic analysis revealed that the formation of DMPO-OH adduct reflects oxidation of DMPO by 1O2 rather than the trapping of the hydroxyl radical produced by the reaction of photo-exited TiO2 and water. The production of large amounts of 1O2 by TiO2 in aqueous suspension as compared to those in ethanol and possible formation of hydroxyl radical in aqueous suspension but not in alcohol, suggest that irradiation of TiO2 in aqueous environments is biologically more important than that in non-aqueous media.

A surface science perspective on TiO2 photocatalysis

“…However, the observed PSD signal over time generally exhibited a multi-exponential form. Thompson 728,834,[867][868][869][870][871][872][873][874][875], with two groups examining this phenomenon in detail. Nosaka's group [872][873][874] used transient spectroscopy and phosphorescent markers to follow 1 O 2 formation over a variety of TiO 2 samples.…”

Ultrafine titanium dioxide nanoparticles induce cell death in human bronchial epithelial cells

“…Due to their photocatalytic activity, one of the environmental applications of TNPs involves effective catalysis of decomposing organic contaminants found in water and aqueous wastes [11,12]. The mechanism of this reaction involves the absorption of UVA by TNPs to catalyse the production of reactive oxygen species (ROS), mainly hydroxyl radicals, superoxide ions, and hydrogen peroxide in aqueous phase [13][14][15][16]. Recent advances in the photocatalytic capability of TNPs have also shed light on novel applications for photodynamic therapy for endobronchial cancers [17].…”

Effects of Cu x TiO y nanometer particles on biological toxicity during zebrafish embryogenesis

“…Additionally, anatase (10 and 20 nm) TiO 2 particles, in the absence of photo-activation, induced oxidative DNA damage, lipid peroxidation, micronuclei formation, and increased hydrogen peroxide and nitric oxide production in a human bronchial epithelial cell line [9]. While there is ample evidence of the formation of reactive oxygen species (ROS) when TiO 2 is exposed to UV light [19][20][21], there is disagreement as to the exact nature of the species produced and their involvement in cell death. Possible ROS that could be formed are hydroxyl radicals ( • OH), superoxide radical anions (O 2− ), hydrogen peroxide (H 2 O 2 ) and singlet oxygen.…”