Degradation of Acid Orange 7 using magnetic AgBr under visible light: The roles of oxidizing species

AgBr was creatively immobilized on a magnetic substrate (SiO2-coated Fe3O4 nanoparticle, SFN) to achieve magnetic separation after visible light-driven photocatalytic oxidation (PCO). The resulted Ag/AgBr/SFN was characterized by TEM, vibrating sample magnetometer and other techniques. It is found that the average diameter of the Ag/AgBr/SFN particle is less than 20 nm. The typical superparamagnetic behavior of Ag/AgBr/SFN implies that the catalyst can be magnetically separated. The physicochemical features of the used Ag/AgBr/SFN after visible light irradiation were not dramatically changed by X-ray diffraction, UV-Vis diffuse reflectance spectra and Fourier transform-infrared analysis. SiO2 interlayer was proven to slightly increase the degradation efficiency for an azo dye Acid Orange 7. UV-Vis spectra and HPLC analysis indicated that the dye was oxidized and decomposed. The photoactivity of Ag/AgBr/SFN was partly maintained after successive PCO under visible light. In order to evaluate the roles of e(-)-h(+) pairs and reactive oxygen species, the quenching effect was examined by employing Ag/AgBr/SFN and commercial TiO2 (P-25) under visible light (lambda > 400 nm) and UV-A irradiation, respectively. Active h(+) and the resulting (OH)-O-center dot played the major roles for degradation. The effect of active h(+) and (OH)-O-center dot were proven to be highly dependent on the concentration of photocatalysts. The effect of (OH)-O-center dot was more obvious for P-25, while that of active h(+) was more predominant for Ag/AgBr/SFN. (C) 2009 Elsevier Ltd. All rights reserved.