Photocatalytic degradation reactions of aquatic nitrogenous organic compounds using pure and modified titania

TiO₂ photocatalyst has been very successful in mineralizing aquatic organic pollutants because of the strong oxidation potential of its valence band holes. A study on the photocatalytic degradation reactions of aquatic NH₃, alkylamines, and alkylammoniums using pure and surface-modified TiO₂ was carried out. By using TiO₂ deposited with nano-Pt particles, NH₃ was oxidized selectively to N₂. While the pure TiO₂ almost quantitatively transformed ammonia into nitrite and nitrate, Pt/TiO₂ converted NH₃ into N₂ with reducing the total nitrogen concentration in the suspension. The Pt surface stabilized intermediate NH_x species and facilitated their recombination into dinitrogen. The photocatalytic method converted NH₃ to N₂ in a single step. The H-atom abstraction by OH radicals initiated successive demethylation processes to generate tri-, di-, and monomethylammonium/amine as an intermediate and NH₃/NH₄⁺ as a final product. The OH radical behaviors and the product distribution were closely related and the reaction with OH radicals took place on the TiO₂ surface and in the solution bulk. Results of the study of tetramethylammonium (TMA, (CH₃)₄N⁺) ions in water using both naked-TiO₂ and fluorinated-TiO₂ were elucidated. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).