New molten-salt synthesis and photocatalytic properties of La2Ti2O7 particles

The (1 1 0)-layered perovskite La2Ti2O7 photocatalyst has been synthesized in high purities and in homogeneous microstructures within a molten Na2SO4/K2SO4 flux in short reaction times of ∼1–10 h. The La2Ti2O7 particle morphologies and sizes were investigated as a function of flux amounts (flux:La2Ti2O7 molar ratios of 1:1, 2:1, 5:1, and 10:1) and reaction times (1, 2, 5, and 10 h). Powder X-ray diffraction confirmed the structure type and high purity, and UV–vis diffuse reflectance measurements yielded optical bandgap sizes of ∼3.75–3.81 eV. Rectangular platelet morphologies are obtained with maximal dimensions of ∼500–5000 nm, but with thicknesses down to <100 nm, and which decrease in size with increasing amounts of flux used in the synthesis. Photocatalytic activities of the La2Ti2O7 products were measured under ultraviolet irradiation in aqueous methanol solutions and yielded rates for hydrogen production from 55 to 140 μmol H2 h−1 g−1, with the maximum photocatalytic rates for the smallest particles, e.g. for 1:1 and 10:1 flux:La2Ti2O7 ratios respectively. The flux-prepared La2Ti2O7 products were also photocatalytically active in pure deionized water, yielding maximal rates for hydrogen formation of 31 μmol H2 h−1 g−1. The observed photocatalytic rates were up to nearly two times greater than that obtained when La2Ti2O7 was prepared by the reported solid-state method, and indicate that the exposed crystallite edges and the (0 1 0) and (0 0 1) crystal faces play a key role in the photocatalysis mechanisms for hydrogen formation.