Reaction TiO2 photocatalysis

In early works, the reactivity associated widi TiO2 photocatalysis was assigned to free OH radicals, but more recently die oxidative species has been identified as bound HO radicals and photogenerated holes. Reaction of the substrate with these species would require either die direct adsorption of organic compounds to the semiconductor interface or Fickian diffusion of the substrate to the semiconductor surface under depletion conditions. However, these two pathways imply different mechanisms, and in some cases different reaction products or intermediates. 

Figure 5 Reaction pathways proposed for the TiO2 photocatalysis of dichlofenthion and bromophos methyl in aqueous media. (From Ref. 48.)...

In this chapter, an attempt has been made to address fundamental mechanistic and kinetic aspects of TiO2 photocatalysis of organophosphorus compounds. Comparisons between homogeneous (radiolysis) and heterogeneous (photocatalysis) hydroxyl-generating processes have helped to elucidate the reaction pathways and led to number of important mechanistic conclusions. From the various kinetic parameters, the overall rates and efficiencies for the degradation of organophosphorus compounds can be predicted and may find direct application in evaluation and implementation of semiconductor photocatalysis. 

The photocatalysis of TCE on the TiO2-coated optical microfibers in the presence of oxygen was further investigated by in situ C MAS NMR spectroscopy 191 ). The major products are phosgene and carbon dioxide, with small quantities of DCAA and trichloroacetaldehyde remaining on the catalyst at the end of the reaction. Solid-state NMR spectroscopy has also been applied successfully for the investigation of the photocatalytic degradation of dichloromethane (192,193). 

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