Deep mineralization of bisphenol A by catalytic peroxymonosulfate activation with nano CuO/Fe3O4 with strong Cu-Fe interaction

Cu-Fe bimetal oxides yield excellent catalytic activity. However, there are some debates on Cu redox cycle and direction of electron transfer during PMS activation by these Cu-Fe bimetal oxides. In this paper, therefore, CuO/Fe3O4 nanoparticles with strong Cu-Fe interaction were prepared by pyrolysis of copper-hexacyanoferrate(III) at 600 degrees C for 1 h and used to investigate the effect of Cu-Fe interaction on catalytic performance of these Cu-Fe bimetal oxides. The as-prepared CuOFe3O4 as a catalyst presented much stronger reactivity than CuO and Fe3O4 for peroxymonosulfate (PMS) activation and bisphenol A (BPA) degradation. The use of 0.3 g L-1 CuO/Fe3O4 and 0.3 mmol L-1 PMS achieved deep mineralization (> 99%) in 110 min for degradation of 20 mg L-1 BPA at initial pH 6.0. The k value for BPA degradation was 0.32 min(-1) for CuO/Fe3O4, being about 5.3, 3.2 and 2.7 times that for the catalysts of Fe3O4, CuO and the mixture of CuO and Fe3O4, respectively. The synergistic effect between Cu and Fe sites on the surface of CuO/Fe3O4 nanoparticles was attributable to strong Cu-Fe interaction. Characterization by X-ray photoelectron spectra and temperature-programmed reduction with H-2 as a reducing agent showed that the strong Cu-Fe interaction makes Cu species more easily donate electrons to PMS for radicals generation as the main reactive sites and reductive cycle of Fe species easier through accepting electrons from PMS, further promoting Cu catalytic cycle through an electron transfer between Cu and Fe. The clarification of structure activity relationship (SAR) of interaction between bimetal species and their activity for peroxide activation facilitates deep understand of the catalytic mechanism and development of more efficient bimetal based catalysts.