Fe–Co-SBA assisted by visible light can effectively activate NaHSO₃ or H₂O₂ for enhanced degradation of Orange Ⅱ: Activation of NaHSO₃ versus H₂O₂

Two different visible light (Vis) assisted heterogeneous photocatalytic systems (BS (bisulfite)/Fe–Co-SBA (Fe–Co-Santa Barbara amorphous material)/Vis and H₂O₂ (hydrogen peroxide)/Fe–Co-SBA/Vis) for degrading Orange Ⅱ were investigated. The role of some significant parameters on the degradation of Orange Ⅱ in the two systems were studied separately and compared. The concentration of either BS or H₂O₂ led to a significant effect on the degradation of Orange Ⅱ. In addition, BS/Fe–Co-SBA/Vis system was found to be suitable for a wider pH range of 3–9. However, we found that the initial pH of solution during the reaction had a great influence on the degradation of Orange II in the H₂O₂/Fe–Co-SBA/Vis system. The main free radicals involved in the degradation of Orange II in the BS/Fe–Co-SBA/Vis system were ·OH and SO₄^·- while they were mainly ·OH radicals in the H₂O₂/Fe–Co-SBA/Vis system as determined by electron spin-resonance (ESR) spectroscopy. Photocatalytic dye degradation mechanisms were proposed for both the systems based on the generation of different radicals in each system.