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A copper–trimesic acid (Cu–TMA) metal–organic framework incorporated in sPEEK shows restricted methanol crossover in DMFCs.

This paper deals with the textural, microstructural and interfacial properties of Au/TiO(2) nanocomposites, in relation to their photocatalytic activity for splitting of water. TiO(2) samples of two different morphologies were employed for dispersing different cocatalysts, such as: Au, Pt, Ag or Cu, for the sake of comparison. The samples were characterized using powder XRD, XPS, UV-visible, thermoluminescence, SEM, HRTEM and SAED techniques. Compared to other metal/TiO(2) photocatalysts, Au/TiO(2) with an optimum gold loading of 1 wt% was found to exhibit considerably higher activity for visible light induced production of H(2) from splitting water in the presence of methanol. Further, the sol-gel prepared TiO(2) (s.TiO(2)), having spherical grains of 10-15 nm size, displayed better photoactivity than a Degussa P25 catalyst. The electron microscopy investigations on s.TiO(2) revealed significant heterogeneity in grain morphology of individual TiO(2) particles, exposure of the lattice planes, metal dispersion, and the interfacial metal/TiO(2) contacts. The gold particles were found to be in a better dispersed state. O(2) TPD experiments revealed that the gold nanoparticles and Au/TiO(2) interfaces may serve as distinct binding sites for adsorbate molecules. At the same time, our thermoluminescence measurements provide an insight into Au-induced new defect states that may facilitate the semiconductor-to-metal charge transfer transition. In conclusion, the superior photocatalytic activity of Au/TiO(2) may relate to the grain morphology of TiO(2), dispersion of gold particles, and the peculiar architecture of metal/oxide heterojunctions; giving rise in turn to augmented adsorption of reactant molecules and their interaction with the photo-generated e(-)/h(+) pair. The role played by methanol as a sacrificial reagent in photocatalytic splitting of water is discussed.

The application of γ′-Fe4N, a noble-metal-free, low-cost catalyst, in the photosplitting of neat water into stoichiometric amounts of H2 and O2 under visible-light irradiation is reported for the first time. The catalyst showed optical absorption and photoluminescence emission bands in the entire visible region. The photocatalytic water-splitting activity was wavelength-dependent, the quantum efficiency for H2 evolution being ca. 1.7 and 0.7% at excitation wavelengths of 450 and 500 nm, respectively. Addition of electron donor/acceptor sacrificial reagents considerably affected the yield and stoichiometry of H2 and O2. At the same time, the product yield increased in a composition-dependent manner for (γ′-Fe4N) x + (α-Fe2O3)1–x nanocomposites. This activity augmentation is ascribed to the better dispersion of the active component γ′-Fe4N and also to the availability of more active surface sites at Fe4N/Fe2O3 contacts. Moreover, the proximity of the valence band potential of the component photosystems promotes the preferential transfer/entrapment of photoexcited hole carriers. We envisage that the defect/impurity-induced interband-gap energy states may play a vital role in these charge-transfer processes, leading thereby to more effective e––h+ separation and the enhanced rate of the water-splitting reaction. First-principles electronic structure analysis suggests that the extraordinary photocatalytic and optical properties of intermetallic γ′-Fe4N may arise from the particle-size-dependent changes in electronic structure.