New Series of Solid-Solution Semiconductors (AgNbO₃)_1−x(SrTiO₃)_x with Modulated Band Structure and Enhanced Visible-Light Photocatalytic Activity

A novel series of solid-solution semiconductors (AgNbO₃)_1−x(SrTiO₃)_x (0 ≤ x ≤ 1) have been developed as highly visible-light-active photocatalysts for efficient O₂ evolution and decomposition of organic pollutants. Rietveld refinement reveals that the perovskite-type solid solutions (AgNbO₃)_1−x(SrTiO₃)_x are crystallized in an orthorhombic system (0 ≤ x < 0.9) or a cubic system (0.9 ≤ x ≤ 1). In the mixed valent perovskites (AgNbO₃)_1−x(SrTiO₃)_x, the hybridization behaviors between the Ag 4d and O 2p orbitals and between the Nb 4d and Ti 3d orbitals play a crucial role in tuning the energy band structure (band gap, band edge, and bandwidth, etc.) and, thus, in tailoring the photophysical and photocatalytic properties. As a result of competition between the absorption ability to visible-light and the reductive/oxidative abilities, the highest visible-light activities for both O₂ evolution and decomposition of gaseous 2-propanol (IPA) are realized over (AgNbO₃)_0.75(SrTiO₃)_0.25. In addition, very fine Ag particles are precipitated on the catalyst surface to construct a nanocomposite structure of Ag/(AgNbO₃)_1−x(SrTiO₃)_x, of which the photocatalytic activities are further improved significantly.