Visible light photocatalysis by a Titania–Rhodium(III) complex

Titania hybrid photocatalysts containing 0.5, 1.0, 2.0, and 5.0 wt% of rhodium(III) were prepared by chemisorption of RhCl3 × 3H2O onto anatase hydrate powder (TH). Analytical data suggest that a titania–trichlororhodate complex is produced containing a [TiO2]–O–Rh bond. Similar results are found in the case of modification by RhBr3 × 3H2O. Diffuse reflectance spectra exhibit an absorption shoulder throughout the visible region down to 700 nm. Photoelectrochemical measurements indicate that the quasi-Fermi level of electrons is gradually shifted to more anodic potentials with increasing rhodium loading reaching a value of −0.34 V at pH 7 (vs. NHE) in the case of 5.0%RhCl3/TH. This is more anodic by 210 mV as compared to unmodified TH. Upon visible light irradiation this photocatalyst induces a fast mineralization of 4-chlorophenol whereas cyanuric acid, which is known to be mineralized in the presence of the analogous Pt(IV) modified titania, is not degraded.