Layered metal oxide photocatalysts for hydrogen evolution

Full text: Layered metal oxides have been studied for photocatalytic hydrogen evolution by water splitting. Two classes of oxides are under investigation, namely the honeycomb layered structure (Na₃Co₂SbO₆, Na₃Cu₂SbO₆, Na₃Ni₂SbO₆ and Na₃Zn₂SbO₆) and layered perovskite material (KLaTiO₄, KCa₂Nb₃O₁₀ and K_2:5Bi_2:5Ti₄O₁₃). Polycrystalline samples were prepared using standard solid-state synthesis method that involved mixing stoichiometric quantities of the appropriate metal oxides/carbonates and heating the mixtures in air. The crystal structures, and sample purity, was determined using X-ray powder diffraction. The structures have been refined by the Rietveld method using synchrotron X-ray diffraction data. The band gap of each sample was determined by diffuse reflectance spectroscopy, with the bandgap ranging from 2.08 eV for Na₃Co₂SbO₆ to 4.69 eV for Na₃Zn₂SbO₆. Hydrogen evolution was tested by illuminating a suspension of powder sample in water. Evolved gases were identified and quantified using gas chromatography. (author)