Influence of cobalt substitution on the crystal structure, band edges and photocatalytic properties of hierarchical Bi2WO6 microspheres

An efficient Bi2WO6 catalyst with Co2+ substitution was synthesized via a facile hydrothermal route, and the materials were characterized by P-XRD, FT-IR, FE-SEM, XPS, DRS, BET and PL techniques. The obtained Co2+ substituted Bi2WO6 materials displayed high photocatalytic activity for organic dye degradation; 97.5% of the dye was photodegraded by 5 mol% of Co2+ substituted Bi2WO6 within 240 min induced by the visible light, which was remarkably better than the degradation of the bare and Co2+ substituted Bi2WO6 (1, 3, 7 and 9% Co2+ concentration). Based on the structural, optical and elemental characterization, it was determined that the substitution of the Co2+ ions in the Bi2WO6 lattice to replace the W6+ ion sites occurred without substantial changes in the crystal structure. The substituent Co2+ played a strategic role, which narrowed the band gap, leading to an enlargement in visible light absorption ability and suppressing the recombination of photogenerated electron–hole pairs credited to the Co2+ inner energy state. Additionally, the photocatalytic mechanism was elucidated by performing the radical trapping experiments, which disclosed that holes (h+) were the main species responsible for the RhB degradation. In addition, the stability of the catalysts was tested by performing recycling experiments. After the four repeating cycles, the degradation efficiency was not dramatically reduced. The results of this study disclosed that Co2+ substitution of W6+ may offer an alternative approach to enhance the Bi2WO6 photocatalytic activity.