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

Surface derivatization of titanium dioxide nanoparticles with a Fe(III)-porphyrin has been carried out following a new procedure whereby the complex, rather than the surface, contains the aminopropylsilane functional group. This avoids the problems of surface deactivation by silane groups, reported in earlier investigations, on analogous systems. Characterization of the light-transparent dispersions by laser flash photolysis, W-vis spectroscopy and photo-electrochemical methods has shown that the nature of the solvent is an important parameter in determining the redox processes involving the grafted porphyrin. In particular, one observes marked effects on the stability of the Fe(II)-porphyrin formed upon capture of the photogenerated electrons. The photocatalytic activity of the composite systems was assessed in the process of monooxygenation of cyclohexane and cyclohexene by molecular oxygen. The bonded porphyrin enhances the yield and the formation of the monooxygenation products with respect to total degradation to CO, for both the examined substrates. On this basis, we can claim an increase in the efficiency and selectivity with the composite photocatalytic system. In the case of cyclohexane, we observed, in addition, that the iron-porphyrin complex also changes the selectivity of the process, increasing the alcohol to ketone ratio. (C) 2000 Elsevier Science B.V. All rights reserved.