Pillaring of Ruddlesden–Popper perovskite tantalates, H2ATa2O7 (A = Sr or La2/3), with n-alkylamines and oxidenanoparticles

Abstract

The Ruddlesden–Popper-type layered perovskite tantalates, H₂ATa₂O₇ (A = Sr or La_2/3), were pillared with n-alkylamines and oxide nanoparticles for the first time. H₂SrTa₂O₇ can accommodate n-alkylamines (carbon numbers = 4, 8, 12, 16) to form intercalation compounds. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains, indicating the formation of a bilayer of the n-alkylamines. Porous metal oxides were synthesized by pillaring the n-octylamine intercalated H₂ATa₂O₇ perovskites with Fe₂O₃ or Fe–Si mixed oxide (FeSi). These materials were well characterized by XRD, TEM, N₂ adsorption, and Fe K-edge XAFS (XANES and EXAFS). FeSi pillared H₂SrTa₂O₇ and H₂La_2/3Ta₂O₇ have a high surface area (52 and 130 m² g⁻¹) and microporosity. Fe₂O₃ pillared H₂SrTa₂O₇ has a macroporous structure with a relatively low surface area (14 m² g⁻¹). XAFS analysis reveals that the Fe species in FeSi pillared perovskites are tetrahedral Fe³⁺ species incorporated in a silica matrix or highly dispersed on silica particles, while those in the Fe₂O₃ pillared one are α-Fe₂O₃ nanoparticles. The acidic property is tested by temperature programmed desorption (TPD) of ammonia, and the result shows that pillaring increases the number of acid sites in perovskites.