Measuring Kinetics of Photoactive Titanium Dioxide Nanoparticles in Natural Systems

Although nanoparticle use dates back to the nineteenth century, relatively little is known about their environmental impact. Titanium dioxide (TiO2) nanoparticles possess unique ultraviolet light (UV) absorbing capabilities and photoactive properites. These characteristics give TiO2 nanoparticles several useful industry applications including its use in food, pharmaceuticals, cosmetics, and protective coatings. This widespread use of TiO2 makes the environmental risks it poses a great concern because of its ability to generate potentially toxic reactive oxygen species (ROS) after UV exposure.  Quantifying the rates of ROS production mediated by different morphologies of TiO2 is an important step toward acquiring more knowledge of its photoactive capabilities in environmental media. Experiments simulated different types of TiO2 nanoparticles in a natural environment during sunlight exposure. Coumarin was used to measure the relative rate of production of hydroxyl radicals (OH·), which are the most reactive type of ROS. Three morphologies of TiO2 nanoparticles were tested: P25, TM3, and TM4. Preliminary results indicate that TM3 has the highest rate of OH· production at 2.48x10-6 s-1, although the rate also possesses the highest margin of error at 1.35x10-5. P25 has a rate approximately four times that of TM4, 1.643x10-5 s-1 and 4.07x10-6 s-1, respectively. Both have relatively small margins of error at 1.202x10-7 and 2.03x10-7, respectively. Alternative measurement experiments must be conducted to verify the results.