Morphological design of LaTiO2N particles by topotactic growth mechanisms for photocatalytic applications

Abstract

Solar water-splitting using particle photocatalysts is a promising approach to sustainably produce hydrogen. LaTiO₂N is an auspicious visible light absorbing photocatalyst regarding the oxygen evolution reaction. In this work, the topotactic growth mechanism of LaTiO₂N particles is investigated by varying the precursor material and the synthesis conditions during thermal ammonolysis. Their influence is discussed in regard to structure, composition, morphology, optical, and functional properties. Using the conventional, layered perovskite oxide, La₂Ti₂O₇, as precursor resulted in brick-shaped porous LaTiO₂N particles with a high degree of crystallinity and a high surface area. When adding flux, the increased mobility during thermal ammonolysis leads to larger morphology changes resulting in non-porous, perforated particles with skeletal features. In a novel, alternative approach, LaTiO₂N is prepared via the topotactic conversion of a double-layered Sillén-Aurivillius type oxyhalide material, La_2·1Bi_2·9Ti₂O₁₁Cl. The facile formation of LaTiO₂N results in a perforated porous structure exhibiting skeletal features whilst maintaining a high surface area due to the presence of pores. By alternating the morphology of the material in this matter the oxygen evolution under one sun illumination is improved by around 10% or 30% depending on whether thermal ammonolysis of La₂Ti₂O₇ is performed with or without flux, respectively.