Phororedox and photocatalytic processes on Fe(III)-porphyrin surface modified nanocrystalline TiO2

Surface derivatization of titanium dioxide nanoparticles with a Fe(III)-por phyrin has been carried out following a new procedure whereby the complex, rather than the surface, contains the aminopropylsilane functional group. T his avoids the problems of surface deactivation by silane groups, reported in earlier investigations, on analogous systems. Characterization of the li ght-transparent dispersions by laser flash photolysis, W-vis spectroscopy a nd photo-electrochemical methods has shown that the nature of the solvent i s an important parameter in determining the redox processes involving the g rafted porphyrin. In particular, one observes marked effects on the stabili ty of the Fe(II)-porphyrin formed upon capture of the photogenerated electr ons. The photocatalytic activity of the composite systems was assessed in t he process of monooxygenation of cyclohexane and cyclohexene by molecular o xygen. The bonded porphyrin enhances the yield and the formation of the mon ooxygenation products with respect to total degradation to CO, for both the examined substrates. On this basis, we can claim an increase in the effici ency and selectivity with the composite photocatalytic system. In the case of cyclohexane, we observed, in addition, that the iron-porphyrin complex a lso changes the selectivity of the process, increasing the alcohol to keton e ratio. (C) 2000 Elsevier Science B.V. All rights reserved.