Nitrogen-containing TiO2 photocatalysts: Part 2. Photocatalytic behavior under sunlight excitation

A series of nanosized N-containing TiO2-based materials with Anatase-type structure and synthesized by a microemulsion method were tested in the photocatalytic degradation of methylcyclohexene, a representative example of volatile organic compound (VOC) present in urban atmospheres. A combined diffuse reflectance infrared (DRIFTS) and X-ray absorption (XAS) spectroscopic study allows to analyze the nature and number of N-containing species and other defects (particularly oxygen vacancies) present in the solid catalysts. The structural characterization was used to interpret the UV–vis spectra of the solids and the resulting joint information allows to rationalize the photocatalytic activity differences observed through the samples under sunlight-type excitation. We founded that our samples contain substitutional and interstitial N-containing impurities and a significant number of oxygen vacancies. Photocatalytic activity is correlated with an optimum of oxygen vacancies, above and below which a decrease of the steady state reaction rate is observed. The physico-chemical bases of this behavior are discussed on the light of the above mentioned experimental results.