Comparison of two- and three-layer restacked Dion–Jacobson phase niobate nanosheets as catalysts for photochemical hydrogen evolution†

Restacked niobate nanosheets were prepared by exfoliation of the corresponding Dion–Jacobson type layered perovskites (HCa2Nb3O10, HSr2Nb3O10 and HLaNb2O7) with tetra(n-butyl)ammonium hydroxide and subsequent treatment with hydrochloric acid. The nanosheets were characterized by means of X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and diffuse reflectance spectroscopy. With modification by platinum nanoparticles as additional catalysts, these nanosheet materials were tested as photocatalysts for hydrogen evolution from water containing 2-propanol as an electron donor under ultraviolet irradiation (l > 300 nm). The activity of a triple-layered nanosheet (HSr2Nb3O10) was an order of magnitude higher than that of the HLaNb2O7 nanosheet with double perovskite layers, despite their physicochemical similarity. Physicochemical analyses suggested that in triple-layered perovskite nanosheets, photocatalytic activity is influenced by several factors including the conduction band potential and the band-gap energy (the number of available photons), which are derived from the distortion of perovskite blocks consisting of NbO6 octahedra.