Spectroscopic Techniques to Characterize and Develop Sensing Methods for Titanium Dioxide Nanoparticles in Water
Titanium dioxide nanoparticles are being used in ever increasing amounts and applications in many consumer products and industrial processes including water treatment. These nanoparticles have not been shown to be toxic to humans via ingestion, but it is worthwhile to develop a portable and rapid detection method to quantify the concentration of nanoparticles in treated drinking water. Current detection methods include single particle inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectrometry, tunneling electron microscopy and scanning electron microscopy. While extremely sensitive, these techniques are expensive and sometimes require extensive sample preparation before analysis. A preliminary study on how chelating ligands influence the dispersion and ζ-potential of TiO2 nanoparticles was performed. Two studies were designed to find ligands that would fluoresce when bound to TiO2 by measuring the level of adsorption but were unsuccessful. They did however show which ligands best improve the suspension of TiO2 in water. It is important to develop new and inexpensive methods to quickly determine if nanoparticles are present in a water sample and at what concentrations. Current detection techniques typically require expensive analytical equipment and often complex sample preparation. Herein, we develop a simple and relatively portable method that exploits the photocatalytic reactivity of titanium dioxide nanoparticles to detect and quantify these materials in various matrices including synthetic distilled, soft, and hard waters. Three nanomaterials are used in this study, all titanium dioxide with various crystalline structure and sizes from 18 nm up to 30 nm. The developed method is adequate for quantifying titanium dioxide nanomaterials in water at levels measured in contaminated environmental samples and used in current toxicological studies. The detection technique employs TiO2 as a hydroxyl radical generator. These hydroxyl radicals then attack terephthalic acid (TPA) to form 2-hydroxyterephthalic acid (2-hTPA). 2-hTPA has an excitation maximum at 368 nm and an emission maximum of 425 nm. This will provide a method to detect nanoparticles in water using a field portable system which is inexpensive, rapid, and easily configurable. This study provided an assay to detect P25, anatase, and rutile nanoparticles in simulated drinking water at levels as low as 0.6 ppb for P25 in distilled water, 2.1 ppb for P25 in soft water, 64.3 ppb for P25 in hard water, 13.9 ppb for anatase in distilled water, and 453.6 ppb for rutile in distilled water. Furthermore, the study provided a conversion factor between nanoparticles of different crystalline structure to provide a method of calculating a P25-equivalent TiO2 concentration in simulated drinking water. Lastly, TiO2 will be studied using single particle ICP-MS in a two-week aging study in synthetic water matrices including distilled, soft and hard drinking water. This study was designed to quantify the effect of how increasing concentrations of dissolved organic solids affect the size distribution and particle number of nanoparticles over an extended period of time. However, the nanoparticles used in the study were slowly removed from suspension by adhering to the inner walls of the test tubes used to contain each sample solution. However, some insights are made on the changes over time in nanoparticle sizes, the influence of dissolved inorganics on these particles, and the influence of particle size and type.
Turley, Reagan Scott, "Spectroscopic Techniques to Characterize and Develop Sensing Methods for Titanium Dioxide Nanoparticles in Water" (2020). ETD Collection for University of Texas, El Paso. AAI27963991.