Environmental Toxicity of Titanium Dioxide Nanoparticles Kristen O’Connor CHM 4020
Nanotechnology and Nanoparticles The objects that are classified under nanotechnology include those that are larger than atoms but are smaller than what can be seen with the human eye. 1 nm is 100,000 times smaller than a single strand of human hair 1 nm = distance of 10 hydrogen atoms in close contact
Titanium Dioxide Nanoparticles • Common characteristics: TEM image of P25 • High UV absorbance • Transparency to invisible light • Iridescent quality • Photocatalysis • Resistance to discoloration • High refractive index • Of all the TiO2 produced, 70% is used as pigments in paints, glazes, enamels, plastics, foods, pharmaceuticals, toothpastes, and cosmetics.
Why TiO2 Nanoparticles in Sunscreen? - Clear or tramslucent application - Highly UV absorbent • Size functionality: • 100 and 200 nm in diameter are opaque • 60 nm produce a clear solution • Photochemical excitation: UV light strikes molecule, stimulated to a higher energy level, returns to original energy state, excess energy is emitted as light (infrared region or blue range of visible)
Coated TiO2 Coating assists with: • Dispersing particles (sunscreen lotions) • Preventing aggregation • Increasing photo stability • Suppressing toxicity effects of TiO2core: • Photo-oxidation reactions or • Production of reactive oxygen species (ROS) • Common coatings: aluminum, silicon, polymers
ROS Generation TiO2: N-type semiconductor photocatalyst Anataseand Rutile band gap energies: 3.26 and 3.00 eV P25 band gap energies: between 3.2 and 3.0 eV, 388 – 414 nm Hydroxyl, hydrogen peroxide, and superoxide radicals - Oxidative stress - Inflammation - Damage to DNA, membranes, and proteins 500 nm small DNA breakage 20 nm completely destroys super- coiledDNA
Photocatalytic ROS Experiment • Removal of UV-A (320-400 nm) radiation significantly decreased the amount of ROS produced • Removal of UV-B (280-320 nm) had no impact on the amount of ROS produced • Photocatalytic ROS production of TiO2 was dependent on the solar radiation spectrum and concentration
Conclusion The global production of nanoscaleTiO2: - 2000 tons in 2005 1300 tons used in cosmetics and sunscreens - 5000 tons in 2010 - Expected to continue increasing until 2025 The increasing use of TiO2 nanoparticles could result in environmental impacts including high concentrations in water sources that could result in human exposure as well as phototoxicity and ROS generation
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