Pillaring of Layered Perovskites, K1−xLaxCa2−xNb3O10, with Nanosized Fe2O3 Particles

✍ Scribed by Yang-Su Han; Shin-Hei Choi; Jae-Up Jang; Dong-Kuk Kim

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 445 KB
• Volume: 160
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9271

✦ Synopsis

Nanosized Fe 2 O 3 clusters are pillared in the interlayer spaces of layered perovskites, H 1؊x La x Ca 2؊x Nb 3 O 10 (04x40.75) by a guest-exchange reaction using the trinuclear acetato-hydroxo iron cation, [Fe 3 (OCOCH 3 ) 7 OH ' 2H 2 O] ؉ . The interlayer spaces of niobate layers are pre-expanded with n-butylammonium cations (n-C 4 H 9 NH ؉ 3 ), which are subsequently replaced by bulky iron pillaring species to form Fe(III) complex intercalated layer niobates. Upon heating at 3803C, the interlayered acetato-hydroxo iron complexes are converted into Fe 2 O 3 nanoclusters with a thickness of ca. 3.5 A > irrespective of the interlayer charge density (x). The band-gap energy of the Fe 2 O 3 pillars (E g &2.25 eV) is slightly larger than that of bulk Fe 2 O 3 (E g &2.20 eV) but is smaller than that expected for such a smallsized semiconductor, which can be assigned to the pancakeshaped Fe 2 O 3 pillars of 3.5 A > in height with comparatively large lateral dimension. X-ray absorption spectroscopic measurements at the Fe K-edge are carried out in order to obtain structural information on the Fe 2 O 3 pillars stabilized between the niobate layers. XANES analysis reveals that the interlayer FeO 6 octahedra have coordination environments similar to that of bulk -Fe 2 O 3 , but noncentrosymmetric distortion of interlayered FeO 6 is enhanced due to the asymmetric electric potential exerted by the negatively charged niobate layers. Scanning electron microscopic observation and nitrogen adsorption+desorption isotherm measurement suggest that the pillared derivatives are nanoporous materials with the highest BET speci5c surface area of ca. 116 m 2 /g.