Pd-Ti-MCM-48 cubic mesoporous materials for solar simulated hydrogen evolution

摘要

A facile synthetic method (in as little as four hours) for simultaneously loading high amounts of titania (Si/Ti = 3) and Pd~0 co-catalyst (0.1 wt.% per gram of total catalyst) in cubic mesoporous MCM-48 material was developed at room temperature. The solar simulated photocatalytic hydrogen evolution from photocatalysts containing Pd~0 and TiO_2 nanoclusters in periodic cubic MCM-48 and aperiodic mesoporous silica was compared. The results indicate that the periodicity of the mesoporous silica support, the oxidation state of Pd, the location and dispersion of Pd~0 have a significant impact on the photocatalytic activity. Periodic cubic MCM-48 mesoporous silica containing Pd~0 in close contact with titania exhibit superior hydrogen evolution rates compared to Pd~0-TiO_2 containing aperiodic mesoporous silica. The highly ordered and open three-dimensional mesoporous cubic MCM-48 support has high surface area and facilitate good dispersion and close contact of titania and Pd~0. At very low loadings of 0.1 wt.% of Pd, hydrogen yield was found to be 560 μ mol h~(-1), which is among the highest reported in the literature for Pd~0 containing TiO_2 based materials under solar simulated conditions. The results suggest that the pore architecture of the support is also an important parameter that governs the photocatalytic activity. In addition, the Pd~0-mesoporous materials in general possess higher activity than Pd~(2+) containing mesoporous materials. The photocatalysts were extensively characterized by a variety of techniques such as powder X-ray diffraction (XRD), nitrogen sorption analysis, transmission and scanning electron microscopic studies, photoluminescence, diffuse reflectance spectroscopy (DRS), CO Chemisorption, and X-ray photoelectron spec-troscopy (XPS).