Novel Fenton-like catalyst γ-Cu-Al2O3-Bi12O15Cl6 with electron-poor Cu centre and electron-rich Bi centre for enhancement of phenolic compounds degradation and H2O2 utilization: The synergistic effects of σ-Cu-ligand, dual-reaction centres and oxygen vacancies

Novel Fenton-like catalyst gamma-Cu-Al2O3-Bi12O15Cl6 with electron-poor Cu centre and electron-rich Bi centre was synthesized for selective degradation of phenolic compounds. Different from electron-rich Cu centre catalysts, the electron-poor Cu centre, which was induced by high electronegativity of Bi, could facilitate the formation of sigma-Cu-ligand with phenolic compounds. On one hand, H2O2 could directly oxidize sigma-Cu-ligand to HO-adduct radicals with the generation of (OH)-O-center dot. Meanwhile, Cu(II) in the sigma-Cu(II) complexes could be reduced to Cu(I) by oxidization of the HO-adduct radicals to hydroxylation products. Such reaction not only prevented Cu(II) from oxidizing H2O2 to HO2 center dot/O-2(center dot) - but also enhanced the redox cycle of Cu(II)/Cu(I), which improved the catalytic activity and H2O2 utilization. On the other hand, although the sigma-Cu-ligand was gradually decreased with the decrease of phenolic compounds, dual-reaction centre played the dominant role in catalytic reaction. In addition, large amounts of oxygen vacancies (OVs) are formed in Bi12O15Cl6 during the calcining process (BiOCl -> Bi12O15Cl6), which can also increase the generation of OH. Thus, both electron-rich Bi center and OVs could still reduce H2O2 to center dot OH for organics degradation even without the formation of sigma-Cu-ligand. Being attributed to the synergistic effect of sigma-Cu-ligand, dual-reaction centre and OVs mentioned above, gamma-Cu-Al2O3-Bi12O15Cl6 achieved high catalytic activity for phenolic compounds degradation and utilization efficiency of H2O2 (eta). In addition, various analytic methods (XPS, TPR, FT-IR, Raman, EPR and solid-state EPR) were used to prove the synergistic effect of the electron-poor/rich centre, sigma-Cu-ligand and OVs of catalyst.