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Differences in the gas-phase photocatalytic degradation of NH3 and ethanol in the presence of water over two commercial TiO2 materials with different structural characteristics (Evonik's P25 (P25) and Sigma Aldrich's anatase (SA)) were established here using FTIR. The materials were characterized using different techniques including BET, XRD, UV–vis DRS and XPS. The interaction of CO probe molecule with the oxides was evaluated via calorimetry and by in-situ DRIFTS coupled to on-line mass spectrometry. This allowed us to determine differences in the surface properties of the two TiO2 materials. NOx− surface species became evident during the photodegradation of adsorbed NH3 over both SA and P25. However, while surface bidentate nitrate species remained strongly bound to P25, the surface species were fully eliminated from SA. Differences in the photocatalytic degradation of ethanol over P25 and SA were also determined. Ethanol adsorption and its evolution were largely independent of the presence of oxygen for SA, but oxygen affected these processes for P25.

The kinetics and adsorption aspects of the photocatalytic degradation of three cresolic isomers were studied in aqueous suspension containing TiO 2 (Degussa P-25). The Langmuir–Hinshelwood model (L–H) was applied to the kinetic results. Degradation kinetic constants were similar for the three compounds ( o -cresol, 0.0188 ppm/s; m -cresol, 0.0166 ppm/s; p -cresol, 0.0182 ppm/s). However, the adsorption pattern of p -cresol is different from those of the other organics. Results from adsorption experiments carried out in darkness were modelized by using Langmuir and Freundlich isotherms. In general, the studied cresols showed little adsorption on TiO 2 surface. The adsorbed species on the catalyst surface were identified by FITR spectroscopy. According to these results, only p -cresol forms cresolates. An important correlation between Langmuir constants and FTIR results was observed.

The photocatalytic degradation of catechol, resorcinol, m-cresol, o-cresol and phenol has been studied individually, in dual mixtures and in the presence of hydrogen peroxide to determine possible competition for adsorption and photoactive centres and for the radicals photogenerated. The obtained results have shown that in the presence of hydrogen peroxide degradation rates are determined by the localization of specific adsorption centres more than by the amount of adsorbed molecules or the number of aromatic ring activating positions generated by substituents. The interaction of catechol with the hydroxyls responsible for the formation of the more photoactive OH radicals slows down the degradation of the other phenolics. Additionally, the interaction of each compound with the surface of TiO2 results in the change of the photoadsorption of oxygen. Consequently, degradation rates of the mixtures are also determined by the photoadsorption of oxygen.

The photocatalytic degradation of three dihydroxybenzenes (hydroquinone, catechol and resorcinol) by TiO 2 and Cu-TiO 2 has been studied. Degradation rates depend on the molecule catalyst surface interaction type. FTIR studies have shown that Cu presence modifies the organics interactions with the catalysts surface. Therefore, catalysts have shown different types of behaviour with each compound. Resorcinol interaction with Cu-TiO 2 may produce a hydroxyphenolate thus reducing the number of activating centres in the aromatic ring. However, catechol interaction provides a catecholate bidentate which virtually deactivates the aromatic ring, hence reducing its degradation by OH radicals attacks. Hydroquinone interaction with Cu-TiO 2 occurs by means of a hydrogen bond, while with TiO 2 this interaction is established through the formation of a hydroxyphenolate monodentate. This justifies the improved catalytic behaviour of Cu-TiO 2 . Studies in presence of H 2 O 2 have shown the existence of similar degradation mechanisms, but degradation rates have been notably higher.

Solar TiO2-photocatalysis was applied to waters from a natural wastewater treatment plant located in the Universidad de Las Palmas de Gran Canaria. Degussa P-25 TiO2 and its mixture with activated carbon (AC–TiO2) were used as catalysts. The presence of ozone and certain ions such as phosphates on the photocatalytic degradation of organic matter was also studied. Disinfection experiments have provided interesting results, particularly when using the catalyst AC–TiO2 and ozone, since total disinfection was achieved in less than 60 min. No bacterial reappearance at 24 or 48 h was observed. Additionally, this catalyst gave important TOC and some ions concentrations reductions. Studies in catalyst reuse revealed that the catalyst AC–TiO2 showed almost no deactivation.