The Different Behavior of Rutile and Anatase Nanoparticles in Forming Oxy Radicals Upon Illumination with Visible Light: An EPR Study

Photoexcited TiO2 has been found to generate reactive oxygen species, yet the precise mechanism and chemical nature of the generated oxy species especially regarding the different crystal phases remain to be elucidated. Visible light‐induced reactions of a suspension of titanium dioxide (TiO2) in water were investigated using electron paramagnetic resonance (EPR) coupled with the spin‐trapping technique. Increased levels of both hydroxyl (˙OH) and superoxide anion (˙O2−) radicals were detected in TiO2 rutile and anatase nanoparticles (50 nm). The intensity of signals assigned to the ˙OH and ˙O2− radicals was larger for the anatase phase than that originating from rutile. Moreover, illumination with visible (nonUV) light enhanced ˙O2− formation in the rutile phase. Singlet oxygen was not detected in water suspension of TiO2 neither in rutile nor in anatase nanoparticles, but irradiation of the rutile phase with visible light revealed a signal, which could be attributed to singlet oxygen formation. The blue part of visible spectrum (400–500 nm) was found to be responsible for the light‐induced ROS in TiO2 nanoparticles. The characterization of the mechanism of visible light‐induced oxy radicals formation by TiO2 nanoparticles could contribute to its use as a sterilization agent.

[1]  J. West,et al.  Correlating nanoscale titania structure with toxicity: a cytotoxicity and inflammatory response study with human dermal fibroblasts and human lung epithelial cells. , 2006, Toxicological sciences : an official journal of the Society of Toxicology.

[2]  K. Jan,et al.  Ultrafine titanium dioxide particles in the absence of photoactivation can induce oxidative damage to human bronchial epithelial cells. , 2005, Toxicology.

[3]  Pedro J J Alvarez,et al.  Comparative eco-toxicity of nanoscale TiO2, SiO2, and ZnO water suspensions. , 2006, Water research.

[4]  Garry R. Buettner,et al.  Spin trapping: ESR parameters of spin adducts. , 1987, Free Radical Biology & Medicine.

[5]  Reinhard Schmidt,et al.  Physical mechanisms of generation and deactivation of singlet oxygen. , 2003, Chemical reviews.

[6]  Rachel Lubart,et al.  Enhanced Antibacterial Activity of Nanocrystalline ZnO Due to Increased ROS‐Mediated Cell Injury , 2009 .

[7]  E. Kasahara,et al.  Irradiation of titanium dioxide generates both singlet oxygen and superoxide anion. , 1999, Free radical biology & medicine.

[8]  Peter R. Ogilby,et al.  A Singlet Oxygen Image with 2.5 μm Resolution , 2002 .

[9]  Awadhesh N Jha,et al.  Hydroxyl radicals (*OH) are associated with titanium dioxide (TiO(2)) nanoparticle-induced cytotoxicity and oxidative DNA damage in fish cells. , 2008, Mutation research.

[10]  Jun-Jie Yin,et al.  Oxidative damage to nucleic acids photosensitized by titanium dioxide. , 1997, Free radical biology & medicine.

[11]  Yoshinori Murakami,et al.  Singlet oxygen formation in photocatalytic TiO2 aqueous suspension , 2004 .

[12]  Akira Fujishima,et al.  Titanium dioxide photocatalysis , 2000 .

[13]  T. Konovalova,et al.  Generation of superoxide anion and most likely singlet oxygen in irradiated TiO2 nanoparticles modified by carotenoids , 2004 .

[14]  D. Dvoranová,et al.  Reactive oxygen species produced upon photoexcitation of sunscreens containing titanium dioxide (an EPR study). , 2005, Journal of photochemistry and photobiology. B, Biology.

[15]  Y. Nosaka,et al.  Photocatalytic reactivity for O2•- and OH• radical formation in anatase and rutile TiO2 suspension as the effect of H2O2 addition , 2007 .

[16]  B. Ohtani,et al.  Mechanism of photocatalytic production of active oxygens on highly crystalline TiO2 particles by means of chemiluminescent probing and ESR spectroscopy , 2001 .

[17]  E. Janzen,et al.  Spin trapping: ESR parameters of spin adducts. , 1988, Free radical biology & medicine.

[18]  E. Kasahara,et al.  Ultraviolet irradiation of titanium dioxide in aqueous dispersion generates singlet oxygen , 2001, Redox report : communications in free radical research.

[19]  Toshihiro Daimon,et al.  Formation of singlet molecular oxygen associated with the formation of superoxide radicals in aqueous suspensions of TiO2 photocatalysts , 2008 .

[20]  R. Tyrrell,et al.  Singlet oxygen: a primary effector in the ultraviolet A/near-visible light induction of the human heme oxygenase gene. , 1993, Cancer research.

[21]  D. Murphy,et al.  EPR study of spin-trapped free radical intermediates formed in the heterogeneously-assisted photodecomposition of acetaldehyde† , 1997 .

[22]  S. Matsuzawa,et al.  An approach to estimating photocatalytic activity of TiO2 suspension by monitoring dissolved oxygen and superoxide ion on decomposing organic compounds , 2007 .

[23]  B. R. Misra,et al.  Vasoactive intestinal peptide, a singlet oxygen quencher. , 1990, The Journal of biological chemistry.

[24]  Y. Nosaka,et al.  Formation and Behavior of Singlet Molecular Oxygen in TiO2 Photocatalysis Studied by Detection of Near-Infrared Phosphorescence , 2007 .

[25]  E. Corey,et al.  Water induced dismutation of superoxide anion generates singlet molecular oxygen. , 1987, Biochemical and biophysical research communications.

[26]  G. Buettner.  Spin trapping: ESR parameters of spin adducts. , 1987, Free radical biology & medicine.