Efficient removal of 2,2′,4,4′-tetrabromodiphenyl ether with a Z-scheme Cu2O-(rGO-TiO2) photocatalyst under sunlight irradiation

Z-scheme Cu2O-(rGO-TiO2) photocatalyst was successfully synthesized via a simple three-step approach for 2,2',4,4'-tretrabromodiphenyl ether (BDE47) reductive removal under simulated solar irradiation. Unlike the traditional heterojunction, the addition of reduced graphene oxide (rGO) enhanced the redox ability of Cu2O-TiO2 by increasing charge transfer. When modifying Cu2O films by adding 1% rGO and coating with 70% TiO2, the resulting Cu2O-(rGO-TiO2) exhibited the best photocatalytic activity for BDE47 removal. The charge transfers of Cu2O-(rGO-TiO2) were proven to follow a Z-scheme pathway through the electron paramagnetic resonance analysis. The degradation pathways of BDE47 were elucidated by identifying intermediate products via gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC). Photo-electrons (e(-)) generated from the conduction band of Cu2O and hydrogen protons (H-0) reduced from H+ in water were the main contributing elements for the removal of BDE47, which response to the ortho and para debromination. Ortho-Br of BDE47 was attacked by e(-) and BDE28 was the dominant debromination product on the first stage. Then e(-) and H-0 attacked ortho-Br and para-Br of BDE28 to form BDE15 and BDE8, respectively. The concentration of BDE8 was higher than that of BDE15, suggesting that H-0 played the most important role on the second debromination stage. An effective Cu2O-(rGO-TiO2)-based Z-scheme system for BDE47 debromination was proposed in this study, which may contribute to the development of novel green technologies. (C) 2020 Elsevier Ltd. All rights reserved.