Fullerol-titania charge-transfer-mediated photocatalysis working under visible light

Chemistry. 2009 Oct 19;15(41):10843-50. doi: 10.1002/chem.200901704.


The development of visible-light-active photocatalysts is being investigated through various approaches. In this study, C(60)-based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water-soluble fullerol (C(60)(OH)(x)) instead of C(60), we demonstrate that the adsorbed fullerol activates TiO(2) under visible-light irradiation through the "surface-complex CT" mechanism, which is largely absent in the C(60)/TiO(2) system. Although fullerene and its derivatives have often been utilized in TiO(2)-based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible-light sensitizer of TiO(2) is not well established. Fullerol/TiO(2) exhibits marked visible photocatalytic activity not only for the redox conversion of 4-chlorophenol, I(-), and Cr(VI), but also for H(2) production. The photoelectrode of fullerol/TiO(2) also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO(2) and C(60)/TiO(2), which confirms that the visible-light-induced electron transfer from fullerol to TiO(2) is particularly enhanced. The surface complexation of fullerol/TiO(2) induced a visible absorption band around 400-500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO(2). The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol(*+)) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO(2) cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO(2) cluster) as the origin of the visible-light absorption.