Photocatalytic activity of G-TiO2@Fe3O4 with persulfate for degradation of alizarin red S under visible light.

A composite photocatalyst combined with TiO2, graphite (G) and Fe3O4 was prepared by co-precipitation method. Then the G-TiO2@Fe3O4 was employed with persulfate (PS) to degrade alizarin red S (ARS) under visible light. The removal rate of ARS reached 100% after 60 min irradiation. The degradation rate constant of G-TiO2@Fe3O4/PS exhibited 20.8, 9.0 and 3.1 times than that of TiO2, G-TiO2 and G-TiO2@Fe3O4, respectively. The effects of photocatalyst dosage, mass ratios of graphite and Fe3O4 to TiO2, PS dosage, initial pH and ARS concentration on the degradation efficiency were investigated. The optimal removal efficiency of ARS was obtained when G-TiO2@Fe3O4 dosage was 0.25 g/L, G: TiO2 = 0.005, Fe3O4: TiO2 = 0.8, PS concentration was 6 mmol/L, initial pH = 3, and initial concentration of ARS was 100 mg/L. The SO4·- was demonstrated more important than O2- and·OH in the degradation of ARS. The intermediates and possible degradation pathways of ARS were discussed. Reuse and stability of G-TiO2@Fe3O4 were also tested, and 88.3% photocatalytic activity was maintained after five cycles. Therefore, the proposed G-TiO2@Fe3O4/PS not only had excellent photocatalytic activity, but also showed superior stability and reusability.