Photophysical and photocatalytic properties of a new series of visible-light-driven photocatalysts M3V2O8 (M = Mg, Ni, Zn)

A new series of visible-light-driven photocatalysts M3V2O8 (M = Mg, Ni, Zn) was synthesized by theconventional solid-state reaction method. The crystal structure and photophysical properties were characterized by powder X-ray diffraction and UV-vis diffuse reflectance spectroscopy, respectively. Photocatalytic properties were evaluated by O-2 evolution from an aqueous AgNO3 solution under visible light irradiation. The results showed that the three compounds of M3V2O8 (M = Mg, Ni, Zn) were all crystallized in an orthorhombic system with the space group Abam. However, the substitution of M2+ cations with different electronic states imposed significant effects on their photophysical and photocatalytic properties. Zn3V2O8 showed a higher activity than Mg3V2O8, while Ni3V2O8 showed almost no activity. Theoretically calculated energy band structures and density of states (DOS) by the plane-wave-density function theory (DFT) revealed that the different photophysical and photocatalytic properties of M3V1O8 (M = Mg, Ni, Zn) could be ascribed to their different electronic structures. The Zn 3d and O 2p orbitals were hybridized to construct the valence band of Zn3V2O8, favoring the mobility of photoexcited holes in the valence band and thus promoting the O-2 evolution activity. In contrast, no such hybridization effect occurs in Mg3V2O8 as the Mg 2p orbitals are not involved in the valence band. The split Ni 3d orbitals inserted between the O 2p and the V 3d orbitals in Ni3V2O8 are not suitable for O-2 evolution.