Consequences of Nitrogen Doping and Oxygen Enrichment on Titanium Local Order and Photocatalytic Performance of TiO2 Anatase

Extended X-ray absorption fine structure (EXAFS) investigation of the oxygen-rich titania formed-via the thermal treatment of N-doped TiO2 has revealed that the removal of N-dopants is responsible for the creation of defect sites in the titanium environment, thus triggering at high temperatures (500-800 degrees C) the capture of atmospheric oxygen GIN followed by its diffusion toward the vacant sites and formation of interstitial oxygen species. The effect of the dopants on Ti coordination number and Ti-O-int, and Ti-N-int; bond distances has been estimated. The photocatalytic p-cresol degradation tests have demonstrated that the interband states formed by the N-dopants contribute to a greater extent to the visible-light activity than the oxygen interstitials do. However, under the UV irradiation the oxygen-rich titania shows higher efficiency in the pollutant degradation, while the N-dopants in N-TiO2 play the role of recombination sites. The presence of the surface nitrogen species in TiO2 is highly beneficial for the application in partial photooxidation reactions, where N-TiO2 demonstrates a superior selectivity of 5-hydroxymethyl furfural (HMF) oxidation to 2,5-furandicarboxaldehyde (FDC). Thus, this work underlines the importance of a rational design of nonmetal doped titania for photocatalytic degradation and partial oxidation applications, and it establishes the role of bulk defects and surface dopants on the TiO2 photooxidation performance.