Mesoporosity in Photocatalytically Active Oxynitride Single Crystals

Abstract

Mesoporosity in photocatalytically active oxynitride single crystals and single-crystalline zones has been investigated by transmission electron microscopy techniques including nanobeam diffraction, electron energy loss spectroscopy, electron tomography, and high-resolution imaging. Several particle morphologies of the perovskite-related oxynitride LaTiO2N were synthesized by solid-state and polymer complex synthesis of the La2Ti2O7 precursor followed by thermal ammonolysis. A detailed analysis of pore sizes, pore shapes, and lattice defects and the local analysis of oxidation states allowed correlation between morphology, synthesis procedures, chemical and crystal defects, and photocatalytic activity. A pore formation mechanism via lattice condensation is proposed, which is simultaneously linked to lattice defect formation processes. On the basis of mechanistic understanding of the transformation from oxide to oxynitride, mesoporosity, and hence the photocatalytic or photoelectrochemical properties of the material, can be tuned.