Improved Photocatalytic Activity of WO3 through Clustered Fe2O3 for Organic Degradation in the Presence of H2O2

Abstract

Photocatalytic degradation of organic substrates over WO(3) in an aerated aqueous suspension is very slow due to the difficulty of O(2) reduction by the conduction band electron on WO(3). In this work, we report on H(2)O(2) as an electron scavenger significantly accelerating the photodegradation of phenol and azo-dye X3B in water under UV or visible light. More importantly, an iron-containing WO(3) (FeW) synthesized through thermal decomposition of a ferrotungstenic acid displayed a much higher activity than pure WO(3) (HW) prepared in parallel. As the sintering temperature increased, both FeW and HW showed an exponential increase in activity. The maximum rate constant of phenol degradation obtained with FeW at 400 °C was about 2 times larger than that with HW at 600 °C. Sample characterization with electron paramagnetic resonance (EPR) spectroscopy and other techniques revealed that ferric species (0.3 wt % Fe(2)O(3)) were mainly present as clusters on the oxide surface at 120 °C and then they diffused toward the lattice sites of WO(3) at high temperature, which was detrimental to the photocatalytic reaction. 5,5-Dimethyl-1-pyrroline N-oxide spin-trapping EPR showed that the production of hydroxyl radicals was greatly enhanced upon the addition of H(2)O(2), the trend of which among different catalysts was the same as that of the rate of phenol degradation. The catalysts after excitation at 350 nm displayed a blue emission centered at 469 nm, the intensity of which varied with the catalyst activity nearly as expected. A possible mechanism for the improved photoactivity of WO(3) is proposed involving the electron transfer from WO(3) to Fe(2)O(3) and the reaction of the reduced oxide with H(2)O(2) to generate hydroxyl radicals.