Investigations of electronic structures and photocatalytic activities under visible light irradiation of lead molybdate replaced with chromium(VI)

Chromium-replaced PbMoO4, PbMo1-xCrxO4, prepared by an aqueous reflux method, showed a photocatalytic activity for O2 evolution from an aqueous solution containing an electron accepter, such as Ag+ or Fe3+ under visible light irradiation (vis) (λ≥420nm). PbMo0.98Cr0.02O4 (Energy gap: 2.26eV) showed the highest activity for the O2 evolution under vis and UV + vis light irradiation. The activity of PbMo0.98Cr0.02O4 was one of magnitude higher than that of PbMoO4 under UV + vis light irradiation. The crystal structures of PbMo1-xCrxO4 were studied by the Rietveld analysis for powder X-ray diffraction. PbMo1-xCrxO4 had a scheelite-type structure when x was equal to or smaller than 0.2. The energy band structures of PbMo1-xCrxO4 were calculated based on density functional theory using the structural parameters refined by the Rietveld analysis. It was revealed that the top of the valence band of PbMoO4 consisted of O2p and Pb6s orbitals and the accepter level was composed of a Cr3d orbital in the forbidden band below the conduction band consisting of a Mo4d orbital. It was concluded that the visible light response was due to the excitation from the Pb6s + O2p valence band to the Cr3d accepter level. (author)