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

Abstract

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 TiO 2 particles (Degussa P25 titania) by photocatalytic deposition from a hexachloroplatinic acid solution. The various TiO 2 /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 TiO 2 /Pt specimens is 3-fold faster than that occurring on TiO 2 alone under visible light irradiation and under otherwise identical conditions. That is, the TiO 2 /Pt system exhibited greater catalytic activity than P25 TiO 2 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 H 2 O 2 formed, chemical oxygen demand (COD Cr ), 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 (O 2 -• ) first and then • OH radicals, which are known to cause the ultimate self-destruction of the SRB dye.