Photodegradation of Sulforhodamine-B Dye in Platinized Titania Dispersions under Visible Light Irradiation:  Influence of Platinum as a Functional Co-catalyst

The photooxidative degradation of sulforhodamine-B dye (SRB) taking place in visible-light illuminated platinized titania dispersions is revisited to examine the influence of metallic platinum doped on TiO2 particles (Degussa P25 titania) by photocatalytic deposition from a hexachloroplatinic acid solution. The various TiO2/Pt specimens were characterized by transmission electron microscopy (TEM), UV−vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The self-photosensitized degradation of SRB mediated by TiO2/Pt specimens is 3-fold faster than that occurring on TiO2 alone under visible light irradiation and under otherwise identical conditions. That is, the TiO2/Pt system exhibited greater catalytic activity than P25 TiO2 alone, which earlier proved to be an effective photocatalyst in the degradation of dyes under visible illumination. A reaction mechanism is proposed on the basis of a series of experiments that included spin−trap electron spin resonance (ESR) spectral results, measurement of quantities of H2O2 formed, chemical oxygen demand (CODCr), and total organic carbon (TOC) data. The platinum dopant acts as an electron sink from which molecular oxygen scavenges the electrons to yield superoxide radical anions (O2-•) first and then •OH radicals, which are known to cause the ultimate self-destruction of the SRB dye.