Solar simulated hydrogen evolution using cobalt oxide nanoclusters deposited on titanium dioxide mesoporous materials prepared by evaporation induced self-assembly process

Abstract

Cobalt containing TiO2 mesoporous materials were prepared by Evaporation-Induced Self-Assembly (EISA) process. The resulting mesoporous materials were characterized using powder X-ray diffraction (XRD), nitrogen physisorption, Raman spectroscopy, diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). The photocatalytic activities of the mesoporous materials were investigated for hydrogen production under solar simulated conditions. The non-modified TiO2 sample produced only 4 μmole H2/g catalyst after 4 h of irradiation. In contrast, the Co containing mesoporous materials produced significantly higher amounts of hydrogen under identical conditions. The highest solar hydrogen evolution (634 μmole H2/g catalyst after 4 h of irradiation) was from the Co-TiO2-0.5 material. The physico-chemical characterization results indicate that the Co2+ ions are dispersed as oxide species on the surface of the mesoporous titania. These cobalt surface species act as trap sites preventing recombination of the charge carriers as shown by PL measurements. The addition of Co2+ ions to the synthesis mixture prevents the formation of anatase-to-rutile which favorably permits more solar hydrogen production.