Transformations, photocatalytic

Minero, C., Mariella, G., Maurino, V., and Pelizzetti, E. (2000) Photocatalytic transformation of organic compounds in the presence of inorganic anions. 1. Hydroxyl-mediated and direct electron-transfer reactions of phenol on a titanium dioxide-fluoride system. Langmuir,... 

Formula (69) is in agreement with experimental data according to which the velocity of a photocatalytic reaction g at low radiation doses (Cl B) increases together with increase of dose rate, and at fairly high radiation doses (Cl B) reaches saturation, i.e., ceases to be dependent on the intensity of illumination (45). (Note that it is in this region of saturation that the high levels of excitation, which we discussed above and at which formula (67) is transformed into (68), are attained.)... 

The applications of polyoxometalates in catalytic dehalogenation of halocar-bons have been succinctly reviewed by Hill and coworkers [188]. This reaction involves the photocatalytic transformation of organic halides coupled with the oxidation of sacrificial organic reductants (secondary alcohols or tertiary amides) (Eq. (9)) [189, 190] ... 

Fig. 7 SEM images of nanopillars of titanium oxide produced by controlled anodic process and model of virus and bacteria transformation by photocatalytic processes using nanopillars of titanium oxide.242...

C. Minero, V. Maurino, E. Pelizzetti, Mechanism of the photocatalytic transformation of organic compounds, in V. Ramamurthy, K.S. Schanze (eds.), Semiconductor Photochemistry and Photophysics, Vol 10 of Molecular and Supramolecular Photochemistry, Marcel Dekker, New York, 2003, pp. 211-229. 

T.C.-K. Yang, S.-F. Wang, S.H.-Y. Tsai and S.-Y. Lin, Intrinsic photocatalytic oxidation of the dye adsorpbed on Ti02 photocatalysts by diffuse reflectance infrared Fourier transform spectroscopy. Appl. Cat. B Envir., 30 (2001) 293-301. 

The key requirement for a SET step in the photocatalytic process seems to be the surface complexation of the substrate, according to an exponential dependence of the probability of electronic tunneling from the distance between the two redox centers [66]. However, as was pointed out in the preceding section on the key role of back reactions, the presence of a SET mechanism could be a disadvantage from an applicative point of view. If the formed SET intermediate (e.g., a radical cation) strongly adsorbs and/or does not transform irreversibly [e.g., by loss of CO from a carboxylic acid or fast reaction with other species (e.g., superoxide or oxygen)], it can act as a recombination center, lowering the overall photon efficiency of the photocatalytic process. 

The possible accumulation of intermediates during the photocatalytic oxidation of aromatic contaminants has been studied with a variety of techniques, including temperature-progranuned desorption (TPD), oxidation (TPO), and hydrogenation (TPH), Fourier transform infrared analysis (FTIR), and extraction of adsorbed species with a variety of solvents. 

Mixtures of isomeric allylic chlorides are formed when 1,1-disubstituted allenes react with HC1.1,3-Disubstituted allenes yield products of both central and terminal carbon attacks. In contrast, selective transformations occur with HBr. The gas-phase, photocatalytic addition of HBr gives selectively vinylic bromides129 [Eq. (6.20)], while hydrobromination in solution phase yields allylic bromides130 [Eq. (6.21)] ... 

---