Enhancement of Photocatalytic Water Oxidation by the Morphological Control of LaTiO2N and Cobalt Oxide Catalysts

Controlled morphological and structural variations of LaTiO 2 N and CoO x nanoparticles loaded as a cocatalyst increased the photocatalytic O 2 evolution. Four different LaTiO 2 N samples were prepared from two varied La 2 Ti 2 O 7 precursors by thermal ammonolysis with and without flux. The most effective transformation from La 2 Ti 2 O 7 into LaTiO 2 N in terms of crystallinity and nitrogen contents was obtained in the following two cases: flux-assisted ammonolysis of La 2 Ti 2 O 7 characterized by a comparatively small particle size and a large surface area and ammonolysis without flux of highly crystalline La 2 Ti 2 O 7 . In both cases, high activity for O 2 evolution under visible-light illumination (λ ≥ 420 nm) (∼50 μmol h –1 ) was obtained. Loading LaTiO 2 N with CoO x enhanced the photocatalytic activity for O 2 evolution, although the effect of CoO x depended on the morphologies of LaTiO 2 N as a support. The promotional effect was most pronounced for LaTiO 2 N with a skeletal morphology, because such LaTiO 2 N contain most unsaturated bonds that act as nucleation centers that in turn generate small and highly dispersed CoO x nanoparticles.