Abstract--Reaction of hydroxy-A1 oligocations with Ce 3+-and La3+-exchanged montmorillonites, using 1.25, 1.60, or 2.0 mmole A1/g smectite, yielded partially pillared hydroxy-A1 montmorillonite products containing a significant concentration of residual Ce 3+ or La 3+. After heat treatment at 250~ these products showed high surface areas (~340-500 mVg) and high basal X-ray powder diffraction spacings (18.0-18.6 /~). Calcination at 400~176 resulted in lower surface areas of ~200-450 m2/g and basal spacings of 16.3-18.3 A, the values showing a gradual decrease with a decrease in the A1/smectite weight ratio and/ or increase in the heat-treatment temperature. A major modification and improvement in the crosslinking procedure was achieved by fast aging (6-48 hr) of the hydroxy-A1 oligomeric solution at 95 ~ 100~ instead of conventional aging for 2-3 weeks at 25~ Fluorinated NH4+-montmorillonites, containing 0.4 to 2.1 wt. % F, were prepared by reaction ofNH4 § montmorillonite at 600C with 1.0 to 3.0 N aqueous solutions of NH4F. Interaction of the fluorinated montmorillonites with hydroxy-A1 oligocations, using a ratio of 2.0 mmole A1/g smectite, yielded a series of cross'linked fluorinated montmorillonites with basal spacings of 17.9-18.0/~ and surface areas of 180-325 m2/g after heat treatment at 250~ Calcination at 400~176 resulted in lower d(001) (16.6-17.7 /~) and surface-area values (140-300 m2/g). Increase in the fluorine content caused gradual decrease in both values. Transmission electron microscopy of pillared Ce-montmorillonite showed a highly oriented network of well-separated, parallel unit layers with an interlayer distance, Ad(001), of 9-10 A. Calculated lateral (interpillar) distances were in good agreement with the pore-size distributions determined in independent adsorption studies.
Abstract--Interaction of La 3 § and Ce3+-exchanged hectorites with oligomeric hydroxy-A1 cations results in the formation of cross-linked hectorites possessing moderately high surface areas (-220-280 mV~) and high thermal stability. The basal spacings of these products were generally in the range 17.0-18.0 A, the exact d(001) value depending on the age of the hydroxy-A1 oligomeric solution and on the pH of the starting hectorite dispersion. Interaction of Li-or Ce-fluorhectorite with hydroxy-A1 oligocations produced the corresponding cross-linked fluorhectorites, which showed markedly higher basal spacings (18.2-20.0 /~ for air-dried samples), surface areas (-300-380 m2/g), and thermal stability, as compared with those of the cross-linked hectorites. The cross-linking agent applied in the synthesis of the bydroxy-Al hectorite and fluorhectorite products consisted of a solution of hydroxy-A1 oligomers aged for periods of 7 to 27 days. A constant ratio of 2.0 mmole A1/g of smectite was used in all preparations. The high basal spacings and porosity of the newly synthesized products are consistent with a structure similar to that previously proposed for cross-linked hydroxy-A1 montmoriUonite.
A B S T R A C T:The fluorination of montmorillonite by aqueous ammonium bifluoride solution (NH4HF2) has been investigated by chemical, sorptive, porosimetric and electron microscopic methods. Changes in the chemical composition of the montmorillonite during the fluorination were compared both in the crystal surface and in the bulk sample. The accumulation of fluorine was distinctly zonal, being present mainly in the surface layers. The electron microscope studies showed that the 300--400 nm thick macrodomains in the initial montmorillonite were cracked into small microdomains 20-30 nm in thickness, this resulting from disruption in the continuity of the octahedral sheets. These distinct changes in morphology of the montmoriUonite aggregates particularly influenced the porosity and sorptive properties.
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