Visible photocatalytic degradation of Rhodamine B using Fe(III)-substituted phosphotungstic heteropolyanion

The paper reported for the first time the photodegradation of Rhodamine B (RhB) under visible light irradiation using the Keggin-type Fe(III)-substituted phosphotungstic heteropolyanion PW11O39 Fe(III)(H2O)(4-)(PM I Fe) as a photocatalyst in a neutral aqueous solution. A visible photocatalysis mechanism differing from that of the dye photosensitization was proposed. Influences of various factors such as the initial RhB concentration, the PW11Fe concentration and the solution pH on the rate of RhB degradation as well as the stability of the catalyst were also examined. The interaction between RhB and PW11Fe was discussed in accordance with the visible absorption and fluorescence emission spectra in detail. It was found that 100% of RhB degradation was reached at 80 min under visible light irradiation in the presence of 25 mu mol L-1 PW11Fe for the 10 mu mol L-1 RhB solution. A total organic carbon (TOC) removal of 35% at 120 min was achieved. The visible photocatalytic degradation of RhB followed a pseudo-first-order kinetic regime. The apparent rate constants were estimated to be 6.23 x 10(-2), 3.16 x 10(-2) and 1.24 x 10(-2) min(-1) at the RhB concentrations of 10,20 and 50 mu mol L-1, respectively. Complexation between RhB and PW11Fe occurred readily at a low solution pH, which resulted in a low rate of RhB degradation. (C) 2012 Elsevier B.V. All rights reserved.