UV and Visible Light-Driven Production of Hydroxyl Radicals by Reduced Forms of N, F, and P Codoped Titanium Dioxide

The photocatalytic activities of reduced titanium dioxide (TiO₂) materials have been investigated by measuring their ability to produce hydroxyl radicals under UV and visible light irradiation. Degussa P25 TiO₂ was doped with nitrogen (N), fluorine (F), and/or phosphorus (P) and then subjected to surface modification employing a thermo-physicochemical process in the presence of reducing agent sodium borohydride (NaBH₄). The reduced TiO₂ materials were characterized by a number of X-ray, spectroscopic and imaging methods. Surface doping of TiO₂ was employed to modulate the band gap energies into the visible wavelength region for better overlap with the solar spectrum. Hydroxyl radical generation, central to TiO₂ photocatalytic water purification applications, was quantitated using coumarin as a trap under UV and visible light irradiation of the reduced TiO₂ materials. At 350 nm irradiation, the yield of hydroxyl radicals generated by the reduced forms of TiO₂ was nearly 90% of hydroxyl radicals generated by the Degussa P25 TiO₂. Hydroxyl radical generation by these reduced forms of TiO₂ was also observed under visible light irradiation (419 and 450 nm). These results demonstrated that simple surface modification of doped TiO₂ can lead to visible light activity, which is important for more economical solar-driven applications of TiO₂ photocatalysis.