Photophysical and photocatalytic properties of Li2M(WO4)2 (M = Co and Ni)

Li2M(WO4)2 (M = Co and Ni) were synthesized by a conventional solid-state reaction method and characterized by powder x-ray diffraction, Brunauer-Emmet-Teller (BET) measurement, ultraviolet-visible (UV-vis) diffuse reflectance spectra, Raman spectroscopy, and photocatalytic evaluation measurements. Photocatalytic water splitting results showed that Li2M(WO4)2 (M = Co and Ni) exhibited abilities for H2 evolution with Pt cocatalyst from an aqueous methanol solution and for O2 evolution from an aqueous AgNO3 solution under UV light irradiation. Theoretical calculation, absorbance analysis, and photocatalytic H2 evolution experiment revealed that the position of W 5d level shifted to the negative side with respect to the reduced potential of H+/H2. The photocatalytic H2 evolution over Li2M(WO4)2 is discussed from the view of crystal and electronic structure point.