In this work, bismuth-based oxychloride photocatalysts such as BiOCl, Bi 3 O 4 Cl, Bi 12 O 17 Cl 2 , Bi 24 O 31 Cl 10 and Bi 12 O 15 Cl 6 were prepared by a solvothermal (or hydrothermal) method with the controlled amount between Bi(NO 3 ) 3 ·5H 2 O and NH 4 Cl. The as-prepared photocatalysts were analyzed by X-ray diffraction (XRD) patterns, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance (UV–vis DRS) and photoluminescence (PL) spectra. The photocatalytic activity was evaluated by degrading rhodamine B (RhB) molecules under visible light irradiation. Among those bismuth-based oxychloride photocatalysts, Bi 12 O 15 Cl 6 showed the highest RhB photodegradation activity of 99.85% within 30 min, and its first-order photodegradation rate constant value was 2.30, 5.51, 4.31 and 4.72 folds higher than those of BiOCl, Bi 3 O 4 Cl, Bi 12 O 17 Cl 2 and Bi 24 O 31 Cl 10 , respectively. Bi 12 O 15 Cl 6 had the larger BET specific surface area and pore volume than other samples, which could provide more reactive sites. According to the results of free radical capture experiments, h + played a major role and O 2 - contributed to a lesser extent in the degradation of RhB. Thus, a possible photocatalytic mechanism was proposed. This result showed that the crystal, band structure and morphology of BiOCl, Bi 3 O 4 Cl, Bi 12 O 17 Cl 2 , Bi 12 O 15 Cl 6 and Bi 24 O 31 Cl 10 had a great influence on the photocatalytic performance. This research suggested that the various influencing factors should be studied to better understand the photochemical properties of a photocatalysts. The present work may make some contributions to the field of photocatalysis technology.
Zhiqun Xie,Jiali Zhou,Jinnan Wang,Corvini Philippe François-Xavier,Thomas Wintgens
Novel Fenton-like catalyst γ-Cu-Al 2 O 3 -Bi 12 O 15 Cl 6 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 σ-Cu-ligand with phenolic compounds. On one hand, H 2 O 2 could directly oxidize σ-Cu-ligand to HO-adduct radicals with the generation of OH. Meanwhile, Cu(II) in the σ-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 H 2 O 2 to HO 2 /O 2 − but also enhanced the redox cycle of Cu(II)/Cu(I), which improved the catalytic activity and H 2 O 2 utilization. On the other hand, although the σ-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 Bi 12 O 15 Cl 6 during the calcining process (BiOCl→Bi 12 O 15 Cl 6 ) , which can also increase the generation of OH. Thus, both electron-rich Bi center and OVs could still reduce H 2 O 2 to · OH for organics degradation even without the formation of σ-Cu-ligand. Being attributed to the synergistic effect of σ-Cu-ligand, dual-reaction centre and OVs mentioned above, γ-Cu-Al 2 O 3 -Bi 12 O 15 Cl 6 achieved high catalytic activity for phenolic compounds degradation and utilization efficiency of H 2 O 2 (η). 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, σ-Cu-ligand and OVs of catalyst.
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