Visible Light Assisted Heterogeneous Catalysis. Decomposition of Peroxomonosulfate over Doped and Undoped WO3 Dispersions in Aqueous Medium

Abstract

Aqueous suspension of RuO2-loaded WO3 powder on illumination with light of λ≥410 nm was found to decompose peroxomonosulfate (PMS, HSO5−) efficiently. The rate and other kinetic parameters indicated that the decomposition process followed Langmuir kinetics; at low concentrations of HSO5− (0.54–2.06×10−3 mol dm−3) the reaction obeyed a first-order kinetics and at higher concentrations, ([HSO5−]>3.00×10−3 mol dm−3) the rate became independent of [HSO5−]. The effects of pH and the molar percentage of the dopant on the rates were also investigated. Small amount of doping by RuO2 (2.5 molar percentage) was found to increase the photocatalytic decomposition of HSO5− whereas the higher amount of doping decreased the rate. Added 2-propanol to the system was found to increase the rate of decomposition of peroxomonosulfate. The proposed mechanism of the decomposition of PMS involves the reactions of the photogenerated valence band holes and the conduction band electrons of WO3, by radiation of wavelength ≥410 nm, in presence and absence of 2-propanol. The rate constants and quantum yields have also been evaluated. The photocatalytic decomposition of peroxomonosulfate is one of the few examples of a unimolecular reaction catalyzed by both the photogenerated holes (hvb+) and electrons (ecb−).