Pillaring of synthetic hectorite by mixed [Al_13-xFe_x] Pillars

Abstract

The pillaring of a Laponite by alumina pillars, iron pillars and mixed AI-Fe pillars was obtained by a simple in situ method starting from A1CI3 and/or FeCI 3 solutions with different molar ratio Fe/(Fe + AI), and from NaOH solution added simultaneously to the clay suspension. The All 3 pillars were evidenced by XRD and NMR spectra. The density and the charge of these pillars were calculated from the chemical analysis. The Fe pillars (in samples with Fe content >26%) are larger than A113 pillars and slowly reducible by hydrogen temperature programmed reduction (H2TPR), but we do not have any information on their structure. There is also an excess of non-pillar Fe retained by the pillared clays probably as oxyhydroxides. The isomorphic substitution in the mixed (A1-Fe)a3 pillars (in samples with an Fe content >26%) was evidenced by H2TPR results compared to the chemical analyses and by the interpretation of the 27A1 peaks in the NMR spectra.

Effect of Ultrasound on the Structural and Textural Properties of Al–Fe Pillared Clays in a Concentrated Medium

“…Intercalation with Al and Fe solutions has been reported in detail by several authors [17][18][19][20][21][22]. Pálinkó et al analyzed the nature of the Al-Fe mixed species generated in pillared clays, by FTIR and Mössbauer spectroscopy, as well as the pillaring agent, and concluded that there is no tetrahedral or octahedral isomorphous substitution of Fe in the Keggin structure of Al 13 .…”

“…The calcined natural bentonite evidences three reduction peaks at around 478, 567 and 691°C. The signal at 478°C corresponds to the reduction of a-Fe 2 O 3 to the Fe 3 O 4 surface iron oxide; the signal at 567°C is associated with the reduction of Fe 3 O 4 to FeO, and the signal at 691°C is related to the reduction of FeO to Fe metal [36,37].…”

Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce and La

“…One way to achieve this goal is to introduce mixed-oxide pillars. These materials have been used in isomerization and dehydrogenation reactions: A1-Ga (Viera Coelho and Poncelet, 1991), A1-Zr (Occelli, 1986), A1-Fe (Oades, 1984;Lee et al, 1989;Bergaya et al, 1993), and A1-Cr (Lee et al, 1989). Another possible method to obtain pillared clays with mixed-oxide pillars is to use transition-metal ions by impregnation (Gil and Montes, 1997), with the pillared clay acting as a substrate.…”

“…Pillared clays have been prepared also by cation exchange, either before or after initial pillaring of the clay (Suzuki et al, 1988;Carrado et al, 1986). In other cases, pillared clays were prepared by first combining the transition-metal ion with the pillaring agent and the resulting species subsequently used to pillar the clay (Occelli, 1986;Viera Coelho and Poncelet, 1991;Lee et al, 1989;Bergaya et al, 1993;Fetter et al, 1995;Cafiizares et al, 1999).…”

Redox Treatment of an Fe/Al Pillared Montmorillonite. A Mössbauer Study

“…(Vaughan and Lussier, 1980;Occelli, 1983;Bergaya et al, 1991) has stimulated research not only for the synthesis of new PILCs, but also for their extensive microscopic characterization. A wide spectrum of analytical techniques, e.g., magic-angle spinning NMR (Plee et al, 1985;Tillak et aL, 1986), EPR (Harsh and Doner, 1984;Braddell et aL, 1987), neutron scattering (Pinnavaia et al, 1984), NMR and HzTPR (Bergaya et al, 1993) and M6ssbauer spectroscopy (Gangas et aL, 1985;Lee Woo et al, 1989;Petridis et al, 1989), has been used for unravelling the structure and the properties of these novel materials. However, in spite of the substantial advance made up to now in the synthesis and characterization of PILCs, the elucidation of additional aspects of the pillared structure (e.g., the diameter of the pillars) is of cardinal importance for understanding the role of their morphology in physicochemical processes occurring in the interlayer space, as well as developing applications,…”