Photodegradation of Dye Pollutants Catalyzed by Porous K3PW12O40 under Visible Irradiation

Microporous solid K3PW12O40 is prepared by precipitation of phosphotungstic acid and potassium ion, followed by calcination. Using this material as photocatalyst, a series of dye pollutants, such as rhodamine B, malachite green, rhodamine 6G, fuchsin basic, and methyl violet, were efficiently degraded in the presence of H2O2 under visible light irradiation (λ > 420 nm). The photocatalyst was characterized via SEM, BET surface area, FT-IR, and XRD. The photocatalyst has relative large surface area, and the Keggin structure of phosphotungstic ions is intact during the precipitation and calcination. The degradation kinetics, TOC changes, degradation products, ESR detection of active oxygen species, and the effect of radical scavengers are also investigated to clarify the degradation process and the reaction pathway. The dyes can be facilely bleached and mineralized (ca. 40% of TOC removal for RhB), and the main degradation products of RhB detected, besides CO2, are the small organic acids. They are released from the surface of the catalyst to the bulk solution during the degradation of the dye, which avoids the poisoning of photocatalyst by the intermediates. The formation of active oxygen species such as the O2-•/HO2• and •OH are detected during the degradation of dye, and they are proposed to be responsible for the degradation of dyes. The K3PW12O40 catalyst is very stable and very easily separated from the reaction system for reuse.