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Abstract  

The mechanochemical solid-state adsorption of the cationic dye crystal violet (CV) by montmorillonite was investigated by XRD and simultaneous DTA-TG. Solid CV was ground with the clay for 5 min and four different varieties of CV mechanochemically treated clay were investigated. X-ray and DTA data were compared with those of CV-montmorillonite obtained from an aqueous suspension. X-ray and DTA studies of a ground mixture and a ground mixture heated at 110°C suggest that the mechanochemical adsorption of organic cations takes place on the external surfaces of the clay. The study of a ground mixture washed with water, and washed with water and acetone reveal that water is essential for the penetration of CV into the interlayer space.

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Journal of Thermal Analysis and Calorimetry
Authors: Z. Yermiyahu, I. Lapides, and S. Yariv

Abstract  

An intense blue organo-clay color pigment was obtained by adding naphthyl-1-ammonium chloride to a Na-montmorillonite aqueous suspension followed by treatment with sodium nitrite. This treatment resulted in the synthesis of the azo dye 4-(1-naphthylazo)-1-naphthylamine adsorbed onto the clay. The pigment was subjected to thermo-XRD-analysis and the diffractograms were curve-fitted. Heating naphthylammonium-montmorillonite at 360°C resulted in the evolution of the amine at temperatures lower than those required for the formation of charcoal and consequently the clay collapsed. On the other hand, heating the pigment at 360°C resulted in the conversion of the adsorbed azo dye into charcoal. The clay did not collapse, thus proving that the azo dye was located inside the interlayer space. Before the thermal treatment a short basal spacing in the pigment compared with that in the ammonium clay (1.28 and 1.35 nm, respectively) indicated stronger surface π interactions between the clayey O-plane and the azo dye than between this plane and naphthylammonium cation. The amount of dye after one aging-day of the synthesis-suspension increased with [NaNO2]/[C10H7NH3] ratio but did not increase with naphthylammonium when the [NaNO2]/[C10H7NH3] ratio remained 1. After 7 and 56 aging days it decreased, indicating that some of the dye decomposed during aging.

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Abstract  

The adsorption of the organic anionic dye Congo red (CR) by montmorillonite saturated with Na+, Cs+, Mg2+, Cu2+, Al3+ and Fe3+ was investigated by XRD of unwashed and washed samples after equilibration at 40% humidity and after heating at 360 and at 420°C. The clay was treated with different amounts of CR, most of which was adsorbed. Clay samples, untreated with CR, after heating showed collapsed interlayer space. Unwashed and washed samples, which contained CR, before heating were characterized by three peaks or shoulders, labeled A (at 0.96-0.99 nm, collapsed interlayers), B (at 1.24-1.36 nm) and C (at 2.10-2.50 nm). Peak B represents adsorbed monolayers of water and dye anions inside the interlayer spaces. Peak C represents interlayer spaces with different orientations of the adsorbed water and organic matter. Diffractograms of samples with small amounts of dye were similar to those without dye showing peak B whereas diffractograms of most samples with high amounts of dye showed an additional peak C. Heated unwashed and washed samples were also characterized by three peaks or shoulders, labeled A' (at 0.96 nm), B' (at 1.10-1.33 nm) and C' (at 1.61-2.10 nm), representing collapsed interlayers, and interlayers with charcoal composed of monolayers or multilayers of carbon. When the samples were heated from 360 to 420°C some of the charcoal monolayers underwent rearrangement to multilayers. In the case of Cu the charcoal decomposed and oxidized. The present results show that most of the adsorbed dye was located inside the interlayer space.

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Summary  

Co- and Ni-montmorillonites adsorb in aqueous suspensions up to 13 mmol alizarinate per 100 g clay, onto the broken-bonds whereas Cu-clay adsorbs up to 25 mmol dye per 100 g clay into the interlayer space. Unloaded Co-, Ni- and Cu-clays and samples loaded with increasing amounts of alizarinate, were gradually heated in air to 360C and analyzed by X-ray diffraction. All diffractograms were curve-fitted. Fitted diffractograms of non-heated samples, showed two peak components labeled C and D, at1.22 and1.32 nm, characterizing tactoids with mono- and non-complete bilayers of water, respectively. After heating at 120C component D decreased or disappeared and two new components A and B appeared at0.99 and1.08 nm, representing collapsed tactoids and tactoids with interlamellar oxy-cations, respectively. At 250C, C and D decreased or disappeared but A and B appeared in all fitted diffractograms. Co- and Ni-clay after heating at 360C did not show C and D. Components A and B proved that these clays collapsed indicating that initially there was no alizarinate in the interlayers. At 360C, C and D persisted in the fitted-diffractograms of Cu-clay, representing tactoids with interlamellar charcoal formed from the partial oxidation of adsorbed dye initially located in the interlayers.

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Abstract  

Montmorillonite and Laponite loaded with different amounts of tributylammonium cations (TBAH+), up to 40 and 30 mmol, respectively, per 100 g clay, were studied by thermo-XRD-analysis. TBAH-smectites heated at 300 and 420°C exhibited basal spacings of 1.30 and 1.24 nm, attributed to smectite tactoids with low- and high-temperature-stable monolayer charcoals, respectively in the interlayers. DTA-EGA and TG of the TBAH-smectites showed four stages of mass loss labeled A, B, C and D. Stage A below 250°C, accompanied by an endothermic DTA peak, resulted from the dehydration of the clay. Mass loss stages B, C and D, at 250–380, 380–605°C and above 605°C, respectively, accompanied by exothermic DTA peaks, were due to three oxidation steps of the organic matter. In mass loss stage B (first oxidation step) mainly organic hydrogen was oxidized to H2O whereas carbon and nitrogen formed low- and high-temperature-stable charcoals. In stages C and D (second and third oxidation steps) low- and high-temperature- stable charcoals were oxidized, respectively. Dehydroxylation of the smectites occurred together with the second and third oxidation steps. Thermal mass loss at each step was calculated from the TG curves showing that in montmorillonite the percentage of high-temperature-stable charcoal from total charcoal decreased with higher TBAH+ loadings of the clay whereas in Laponite this percentage increased with higher loadings of the clay.

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Abstract  

Montmorillonite (M) saturated with H+,Li+,Na+,K+,Rb+,Cs+,NH4 +,Mg2+,Ca2+,Sr2+,Ba2+,Mn2+,Co2+,Cu2+,Al3+ and Fe3+ were dry-ground with urea (U) in mass ratios U/M between 0.1 and 2.0 in an agate mortar and diffracted by X-ray. Extensive swellings occurred with H-, Li-, Na-, di-and trivalent cation-clays, suggesting the formation of urea-montmorillonite intercalation complexes. Mechanochemically treated samples were heated at different temperatures up to 375°C. The rise in temperature was accompanied by a decrease in the basal spacing. There was a correlation between the results of the thermo-XRD-analysis and the fine structures of the urea-montmorillonite complexes described in the literature. Five stages in the basal spacing vs. temperature curves were identified. In the first stage (at 150°C) the decrease was due to dehydration. In the second stage (175°C) this dehydration was accompanied by some thermal intercalation of excess urea. The other stages (at 225, 325 and 375°C) were associated with the degradation of urea and the condensation of the degraded species to polymeric products. At 375°C Li-, Na-, K-NH4-, Mh-, Co- and Cu-montmorillonite collapsed, indicating that urea was evolved. The other urea-clay complexes did not collapse due to intercalated polymers formed by the degradation products of urea.

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Abstract  

In the present research we studied the effect of the solvent used, whether it was polar water or a non-polar organic solvent (n-hexane or n-hexadecane), on the basal-spacing and bulk structure of the sorbate-sorbent complexes obtained by the secondary adsorption of nitrobenzene and m-nitrophenol by two types of organo-montmorillonites. X-ray measured basal spacings before and after thermal treatments up to 360°C. The organo-clays were synthesized, with 41 and 90% replacement of the exchangeable Na+ by hexadecyltrimethylammonium (HDTMA), with mono-and bilayers of HDTMA cations in the interlayer space, labelled OC-41 and OC-90, respectively. After heating at 360°C both organo-clays showed spacing at 1.25–1.28 nm, due to the presence of interlayer-charcoal, indicating that in the preheated organo-clays the HDTMA was located in the interlayer. The thermo-XRD-analysis of Na-clay complexes showed that from organic solvents both sorbates were adsorbed on the external surface but from water they were intercalated. m-Nitrophenol complexes of both organo-clays obtained in aqueous suspensions contain water molecules. Spacings of nitrobenzene complexes of OC-41 and OC-90 and those of nitrophenol complexes of OC-41 showed that the adsorbed molecules were imbedded in cavities in the HDTMA layers. Adsorption of m-nitrophenol by OC-90 from water and n-hexane resulted in an increase of basal spacing (0.21 and 0.29 nm, respectively) suggesting the existence of a layer of nitrophenol molecules sandwiched between two parallel HDTMA layers.

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Abstract  

Solid state intercalation of alkali halides into kaolinite takes place by heating pressed disks of dimethylsulfoxide (DMSO)-kaolinite complex ground in different alkali halides. This reaction involves diffusion of the DMSO outside the interlayer space and the alkali halide into the interlayer space. IR and Raman spectroscopy reveal two types of intercalation complexes: (i) almost non-hydrous, obtained during thermal treatment of the DMSO complex; and (ii) hydrated, obtained by regrinding the disk in air. The strength of the hydrogen bonds between intercalated water or halide anions and the inner surface hydroxyls decreases in the order Cl>Br>I. Chlorides penetrate the ditrigonal holes and form hydrogen bonds with the inner OH groups.

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