Pillaring of Ruddlesden–Popper perovskite tantalates, H₂ATa₂O₇(A = Sr or La_2/3), with n-alkylamines and oxidenanoparticles

Abstract

The Ruddlesden–Popper-type layered perovskite tantalates, H2ATa2O7 (A = Sr or La2/3), 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 H2La2/3Ta2O7 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.