Photosensitization of crystalline and amorphous titanium dioxide by platinum(IV) chloride surface complexes

Anatase, rutile, and amorphous titania powders were surface-modified by gri nding with PtCl4 and H-2[PtCl6]. Only the anatase modification afforded hyb rid photocatalysts capable of degradation of 4-chlorophenol (4-CP) with vis ible light, with sufficient stability towards decomplexation. Grinding with K-2[PtCl4] produced materials of only low photocatalytic activity. Most ef ficient photocatalysts contained up to 2 wt% of Pt-IV: At higher surface lo ading the excess fraction of the complex is desorbed into the aqueous solut ion. Scavenging experiments with benzoic acid and tetranitromethane reveale d that hydroxyl radicals are produced by the primary reduction of oxygen by conduction band electrons generated through electron injection from a post ulated surface platinum(III) complex. It is proposed that the latter is for med from a charge-transfer ligand-to-metal (CTLM) excited state through hom olysis of the Pt-Cl bond. Accordingly, the primary oxidation of 4-CP may oc cur by adsorbed chlorine atoms, the intermediary existence of which was dem onstrated by scavenging experiments with phenol.