Effects of the SrTiO₃ support on visible-light water oxidation with Co₃O₄ nanoparticles

The photocatalytic activity of SrTiO₃ modified with Co₃O₄ nanoparticles for water oxidation under visible light (λ > 480 nm) was investigated with respect to the physicochemical properties of the SrTiO₃ support. SrTiO₃ was synthesized by a polymerized complex method or a hydrothermal method, followed by calcination in air at different temperatures in order to obtain SrTiO₃ particles having different sizes. Co₃O₄ nanoparticles, which provide both visible light absorption and water oxidation centers, were loaded on the as-prepared SrTiO₃ by an impregnation method using Co(NO₃)₂ as the precursor, followed by heating at 423 K in air. Decreasing the SrTiO₃ particle size (that is, improving the crystallinity) enhanced the photocatalytic activity by promoting the formation of Co₃O₄ nanoparticles that provided optimal light absorption and catalytic sites. However, Co₃O₄ aggregation occurred on overly large SrTiO₃ particles, leading to a decrease in activity. This study demonstrates the possibility of tuning the photocatalytic activity of a Co₃O₄-loaded wide-gap semiconductor for visible light water oxidation through the appropriate selection of the support material.