Thermo-XRD analysis of the adsorption of Congo-red by montmorillonite saturated with different cations

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.This revised version was published online in November 2005 with corrections to the Cover Date.     

Monoionic montmorillonites treated with Congo-Red

The adsorption of the anionic dye congo-red (CR) by Na-, Cs-, Mg-, Al- and Fe-montmorillonite was studied by simultaneous DTA-TG. Thermal analysis curves of adsorbed CR were compared with those of neat CR. The oxidation of neat CR is completed below 570°C. Thermal analysis curves of adsorbed CR show three regions representing dehydration of the clay, oxidation of the organic dye and dehydroxylation of the clay together with the oxidation of residual organic matter. The oxidation of the dye begins at about 250°C with the transformation of organic H atoms into water and carbon into charcoal. Two types of charcoal are obtained, low-temperature and high-temperature stable charcoal. The former gives rise to an exothermic peak in the second region of the thermal analysis and the latter in the third region. The exchangeable metallic cation determines the ratio between the low-temperature and high-temperature stable charcoal, which is formed. With increasing acidity of the exchangeable metallic cation higher amounts of high-temperature stable charcoal are obtained. It was suggested that aromatic compounds p bonded to the oxygen plane of the clay framework are converted into charcoal, which is burnt at about 550-700°C. With increasing surface acidity of the clay more species of CR are protonated. Only protonated dye species can form p bonds with oxygen plane and are converted to high-temperature stable charcoal during the thermal analysis. The thermal behavior of the dye complex of Cu-montmorillonite is different probably due to the catalytic effect of Cu. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of tributylammonium montmorillonite and laponite

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.     

Visible-spectroscopy study of the adsorption of alizarinate by Al-montmorillonite in aqueous suspensions and in solid state

The adsorption of the monovalent anionic dye alizarinate onto Na- and Al-montmorillonite was carried out by adding the dye into aqueous clay suspensions. Electronic spectra of aqueous suspensions and of air-dried dye-clay complexes were studied. Na-montmorillonite adsorbed only part of the added dye. With total amount of alizarinate up to 5 mmol dye per 100 g clay the adsorption of the dye takes place on the broken bonds, leading to peptization of the clay. Al-montmorillonite adsorbed alizarinate completely up to 10 mmol per 100 g clay. Above this loading there was a partition of the dye between the clay and the supernatant. The maximum adsorption for Na- and Al-clay was 4 and 25 mmol dye per 100 g clay, respectively. Absorption bands in the spectrum of Al-montmorillonite suspensions (488-504 nm) appear at longer wavelengths than in the spectrum of air-dried Al-montmorillonite (415-455 nm). Thermo-X-ray study of these clay-alizarinate complexes suggests that the organic compound was located in the interlayer space in Al-montmorillonite but was not located there in Na-montmorillonite. In Al-montmorillonite alizarinate formed a coordination complex with exchangeable Al(3+). In Na-montmorillonite it formed bonds with Al exposed on the broken-bonds sites.     

X-ray study of the thermal intercalation of alkali halides into kaolinite

Intercalation complexes of kaolinite with a series of alkali halides (NaCl (trace amounts), KCl, RbCl, CsCl, NaBr, KBr, CsBr, Kl, Rbl and Csl) were obtained by a thermal solid state reaction between the kaolinite-dimethylsulfoxide intercalation complex and the appropriate alkali halide. The ground mixtures (11 weight ratio) were pressed into disks that were gradually heated up to 250 °C for different times. X-ray diffractograms of the disks were recorded after each thermal treatment. At the end of the thermal treatment the disks were ground and basal spacings of the powders obtained. As a result of thermal treatment, alkali halide ions diffuse into the interlayers, replacing the intercalated dimethylsulfoxide molecules. Such a replacement may take place only if the thermal diffusion of the penetrating species is faster than the evolution of the intercalated organic molecule. With increasing temperature the intercalated salt diffused outside the interlayer space or underwent a thermal hydrolysis which resulted in the evolution of hydrogen halides from the interlayer space. Consequently, the amounts of intercalation complexes decreased at elevated temperatures.     

Intercalation Compounds between Ethyl 2-oxocyclopentanecarboxylate and Saponite

The retention of ethyl 2-oxocyclopentanecarboxylate by a saponite has been studied. Intercalation compounds were prepared by two different methods: 1) in repose at room temperature and 2) heating at 60 °C under reflux. Contact times between 2 and 12 days were considered for each method. The intercalation compounds obtained were characterized by X-ray diffraction, infrared spectroscopy, chemical analyses and thermal analyses. This characterization indicates that the organic compound is retained both in the interlayer region and at the edge of the clay particles. The amount retained outside of the interlayer space is eliminated by careful washing with benzene and cyclohexane. The results obtained when using acid-activated saponite -obtained by treatment of the clay with dilute HCl solutions- in the intercalation experiments were similar to those obtained when using non-activated saponite.     

Thermoanalytical studies on montmorillonite-pirimicarb complexes

The thermal decomposition of the interlayer complexes of homoionic samples of montmorillonite with the carbamate insecticide pirimicarb (2-dimethylamino-5, 6-dimethyl pyrimidin 4-yl-dimethyl carbamate) was studied using TG and DSC techniques. The decomposition of the organic compound was followed by IR spectroscopy and X-ray diffraction. It was observed that the thermal decomposition of pirimicarb is catalyzed by adsorption by the clay. Both the catalytic capacity of the clay and the values of the decomposition enthalpies depend on the characteristics of the interlayer cation of the montmorillonite.     

Thermal study of naphthylammonium- and naphthylazonaphthylammonium-montmorillonite

The blue organo-clay color pigment (OCCP) naphthylazonaphthylammonium-montmorillonite was synthesized from the white naphthylammonium-montmorillonite by treating with NaNO₂, the azo colorant being located in the interlayer space. The following effects on the basal spacing of naphthylazonaphthylammonium-and naphthylammonium-clay were investigated: (1) the amount of naphthylammonium loading the clay, (2) the amount of NaNO₂ used for the staining, (3) aging of the preparation suspension and (4) thermal treatment. Samples were heated at 120, 180, 240, 300 and 360°C and diffracted by X-ray. During aging, some of the dye decomposed. Samples, after one day aging, were investigated by DTA. During the dehydration stage both organo-clays gradually decomposed, the naphthylammonium-clay at 120°C and the OCCP at 180°C. That fraction of organic matter, which did not escape, was air-oxidized at above 200°C and charcoal was obtained. The appearance and size of the DTA exothermic peaks depended on the amount of organic matter, which did not escape and this depended on the total amount of organic matter in the DTA cell. DTA proved that naphthylammonium reacted with NaNO₂ to form OCCP.     

Thermal analyis of hexadecyltrimethylammonium–montmorillonites

Na-montmorillonite (Na-MONT) was loaded with hexadecyltrimethylammonium cations (HDTMA) by replacing 41 and 90% of the exchangeable Na with HDTMA, labeled OC-41 and OC-90, respectively. Na-MONT, OC-41, and OC-90 were heated in air up to 900 °C. Unheated and thermally treated organoclays heated at 150, 250, 360, and 420 °C are used in our laboratory as sorbents of different hazardous organic compounds from waste water. In order to get a better knowledge about the composition and nature of the thermally treated organoclays Na-MONT and the two organo-clays were studied by thermogravimetry (TG) in air and under nitrogen. Carbon and hydrogen contents in each of the thermal treated sample were determined and their infrared spectra were recorded. The present results showed that at 150 °C both organoclays lost water but not intercalated HDTMA cations. At 250 °C, many HDTMA cations persisted in OC-41, but in OC-90 significant part of the cations were air-oxidized into H₂O and CO₂ and the residual carbon formed charcoal. After heating both samples at 360 °C charcoal was present in both organo clays. This charcoal persisted at 420 °C but was gradually oxidized by air with further rise in temperature. TG runs under nitrogen showed stepwise degradation corresponding to interlayer water desorption followed by decomposition of the organic compound, volatilization of small fragments and condensation of non-volatile fragments into quasi-charcoal. After dehydroxylation of the clay the last stages of organic matter pyrolysis and volatilization occurred.     

Synthesis and thermo-XRD-analysis of the organo-clay color pigment

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.     

Thermal decomposition of long-chain fatty acids and its derivative in the presence of montmorillonite

In sedimentary environments or clay-rich rocks, clay minerals are usually combined with organic matter; however, little research has focused on the effects of combinations of organic matter and clay minerals on the thermal degradation of organics and on subsequent hydrocarbon generation. In this study, the long-chain fatty acid octadecanoic acid (OA) and its derivative octadecy trimethyl ammonium bromide (OTAB) were selected as model organics. The organics were prepared for clay–organic associations with Na-based montmorillonite (Mt(Na)). The thermal decomposition behaviors of these associations were studied via thermogravimetric (TG/DTG) analysis. In the presence of Mt(Na), OA decomposed at 275.2 °C, decomposing sooner than pure OA. The thermal decomposition behavior of OTAB is nearly consistent with that of pure OTAB, but for interlayer OTAB, the decomposition temperature increased to higher than 300 °C. The results indicate that Mt(Na) plays a dual role in the thermal decomposition of fatty acid. Mt(Na) may accelerate the thermal decomposition of OA, and inherent solid acidity levels may be the key factor. In addition, the interlayer structure of Mt(Na) can increase the thermal stability of OA and OTAB. The above results further demonstrate that the thermal decomposition behavior of a given organic material may also depend on its structure and composition. In the presence of Mt(Na), organics with amino and amine structures are more stable than those with carboxyl groups.

     

Thermo-XRD-analysis and peptization study of the adsorption of alizarinate by Co-, Ni-, and Cu-montmorillonite

The adsorption of the monovalent anionic dye alizarinate onto Co-, Ni- and Cu-montmorillonite was carried out by adding the dye into aqueous clay suspensions. During the loading of the clay suspension by alizarinate, only some of the added organic anion is adsorbed by the clay forming d-coordination chelate complexes on the clay surface. Maximum adsorption of Co-, Ni- and Cu-clay were 13, 13 and 25 mmol dye per 100 g clay. Since the capacity of the clay for these transition metal cations is 38 mmol per 100 g clay, these saturations indicate that only part of the transition metal cations form positively charged d-coordination chelate complexes with metal:ligand ratio of 1. The complex cations can be located inside the interlayer spaces or on the broken bonds surfaces. Thermo-XRD-analysis and peptization studies of the solids and the clay water systems respectively were used here to identify the sorption sites. The Co and Ni complexes were obtained on the broken bonds surfaces whereas the Cu complexes were obtained in the interlayer space. Co²⁺, Ni²⁺ and Cu²⁺ were extracted from the clay into suspensions containing excess alizarinate.     

Investigation of the formation of nickel and cobalt nanoparticles upon thermal decomposition of Ni,Al-and Co,Al-layered double hydroxides pillared with complexes [Ni(edta)]<Superscript>2−</Superscript> and [Co(edta)]<Superscript>2−</Superscript>

Double layered hydroxides [M_0.7Al(OH)_3.6] [M(edta)]_0.4·nH₂O (M,Al-M(edta), M = Ni, Co) containing nickel or cobalt edta complexes in the interlayer space were obtained for the first time. Vacuum thermal decomposition of these compounds results in the formation of metal nanoparticles dispersed in an amorphous matrix. Thermal decomposition products were studied by powder X-ray diffraction and ferromagnetic resonance technique. The scheme of structural rearrangements occurring during heating was derived from the data obtained. According to this scheme, below 200°C the interlayer and absorbed water escapes, and at 200–325°C metal-hydroxide layers undergo dehydration. At higher temperatures organic fragment of the complex suffers destruction to yield metal. It is shown that thermal decomposition of Ni, Al-Ni(edta) at 325–340°C gives isotropic nickel nanoparticles, while at higher temperatures the metal consists of a mixture of isotropic and anisotropic particles. Isotropic particles of β-Co formed at 350°C and above are of size 3–4 nm, no anisotropic particles being observed.     

Investigation of structure and thermal stability of surfactant-modified Al-pillared montmorillonite

For combining the properties of organoclays and pillared clays, inorganic–organic clays have attracted much attention in recent years. In this study, Al Keggin cation pillared montmorillonites (Al-Mts) were first prepared and parts of Al-Mts were calcined at different temperatures (C-Al-Mts). The inorganic–organic montmorillonites were synthesized by intercalating Al-Mts and C-Al-Mts with the cationic surfactant, hexadecyltrimethyl ammonium bromide (HDTMAB). The products were characterized by X-ray diffraction, X-ray fluorescence, and simultaneous thermogravimetric analysis. For HDTMAB-modified uncalcined Al Keggin cation pillared montmorillonites (H-Al-Mts), the basal spacing increased with the increment of surfactant loading level, but the Al content of H-Al-Mts decreased simultaneously, indicating that the intercalated surfactant replaced some Al Keggin cations in the interlayer space. However, in the case of C-Al-Mts, the interlayer spaces could not be further expanded after surfactant modification, implying that the neighboring montmorillonite layers were “locked” by the aluminum pillars which were formed by dehydroxylation of Al Keggin cation pillars during thermal treatment. The thermal stability of HDTMAB-modified C-Al-Mts (H-C-Al-Mts) was much better than that of H-Al-Mts. The major mass loss of H-C-Al-Mts occurred at ca. 410 °C, corresponding to decomposition of intercalated surfactant cations. In contrast, H-Al-Mts displayed two mass loss temperatures at ca. 270 and 410 °C, corresponding to the evaporation of surfactant molecules and the decomposition of surfactant cations in the interlayer space, respectively.     

Organic Pillared Clays

Commonly used organophilic clays are modified by alkylammonium cations which hold apart the aluminosilicate layers permanently. The cations fill the interlayer space and are contemplated as flexible pillars, resulting from the mobility of the alkyl chains. Therefore, the interlayer distance varies depending on the layer charge and on the alkyl chain length. Contrary to these cations, rigid pillaring cations guarantee a constant interlayer distance without occupying the interlayer by themselves and show special adsorption properties such as hydrophilic behavior contrary to the generally hydrophobic ones. Smectites were modified by flexible organic cations, e.g., dimethyldioctadecylammonium, and by rigid ones, e.g., tetraphenylphosphonium. Their adsorption properties are compared. Our investigations showed improved adsorption properties for rigid organic cations on smectites using 2-chlorophenol as pollutant. Best adsorption results are achieved using pillaring cations in combination with low charged smectites, especially at low pollutant concentrations. The properties of organic modified smectites are discussed by a pollution intercalation model. The intercalation process of an organic pollutant into an organic modified smectite is expressed by a two-step Born-Haber cycle process: (i) the formation of an adsorbing position by layer expansion and (ii) the occupation of the adsorbing position by the pollutant. The first step of the formation of the adsorbing position is an endothermal transition state which lowers the total intercalation energy and therefore worsens the adsorption behavior. Thus, an already expanded organophilic smectite will show improved adsorption behavior. The formed adsorbing position state on organic modified smectites is comparable to the pillared state of inorganic pillared clays. Copyright 2001 Academic Press.     

Simultaneous DTA-TG Study of Montmorillonite Mechanochemically Treated with Crystal-violet

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.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mild pre-heating of organic cation-exchanged clays enhances their interactions with nitrobenzene in aqueous environment

Aqueous sorption kinetics and equilibrium isotherms of nitrobenzene were studied on two series of sorbents that were prepared by (i) replacing inorganic exchangeable cations in Wyoming bentonite with tetraethylammonium (TEA) and benzyltrimethylammonium (BTMA) and (ii) heating synthesized complexes in air at different temperatures (between 150 and 420°C). The aim of this work was to examine recently observed enhancement of aqueous sorption of a probe organic sorbate on organoclays after mild thermal pre-treatment of sorbents. Thermal pre-treatment of TEA- and BTMA-clays at 150°C results in the maximal enhancement of nitrobenzene–sorbent interactions as compared with treatment of original bentonite and its exchange complexes formed with long-chain quaternary ammonium (n-hexadecyltrimethylammonium, HDTMA). Based on C, N content data and FTIR spectra of TEA- and BTMA-clay complexes, no indications of decomposition of organic matter were found in organoclays heated at 250°C (and below this temperature). Suppressed hydration of pre-heated sorbents resulting in a lessening of water–organic sorbate competition for sorption sites is considered to be responsible for thermally induced enhancement of nitrobenzene–sorbent interactions. In the HDTMA-based organoclays, the long-chain aliphatic groups of the quaternary ammonium can additionally interact with clay surface thus competing with organic sorbate–sorbent surface interactions and, in this way, mitigating the enhancement of nitrobenzene sorption on thermally treated sorbents.     

YMgGa as a hydrogen storage compound

The hydrogen absorption and desorption properties of the recently found ternary phase YMgGa have been studied. This compound absorbs 2.2 wt% hydrogen during the first cycle, but only 1.1 wt% can be stored reversibly for the following cycles under the applied pressure and temperature conditions. Hydrogen absorption and desorption properties were investigated by measuring the thermal desorption spectra and the pressure-composition isotherms while the crystal structure was determined using X-ray diffraction (XRD). The compound absorbs hydrogen at pressures above 0.2 MPa and 250 °C by decomposing into YH₃ and MgGa. This reaction is reversed when heating the hydride in a He atmosphere; hydrogen is released and the YMgGa phase is partially recovered together with YGa₂ and YH₂. The reformation of YMgGa occurs at temperatures below 450 °C on the expenses of hydrogen desorption from YH₂. This is not expected under these temperature conditions as YH₂ normally does not desorb hydrogen below 800 °C.     

Thermal analysis of tetraethylammonium and benzyltrimethylammonium montmorillonites

Na-montmorillonite was loaded with tetraethylammonium cations (TEA) or with benzyltrimethylammonium cations (BTMA) by replacing 77 and 81% of the exchangeable Na with TEA or BTMA, labeled TEA-MONT and BTMA-MONT, respectively. TEA- and BTMA-MONT were heated in air up to 900?°C. Thermally treated organoclays are used in our laboratory as sorbents of organic compounds from water. The two organoclays were studied by TG and DTG in air and under nitrogen. Carbon content in each of the heated sample was determined. They were diffracted by X-ray, and fitting calculations of d(001) peaks were performed on each diffractogram. TG and thermo-C analysis showed that at 150 and 250?°C both organoclays lost water but not intercalated ammonium cations. DTG peak of the first oxidation step of the organic cation with the formation of low-temperature stable charcoal (LTSC) appeared at 364 and 313?°C for TEA- and BTMA-MONT, respectively. The charcoal was gradually oxidized by air with further rise in temperature. DTG peak of the second oxidation step with the formation of high-temperature stable charcoal (HTSC) appeared at 397 and 380?°C for TEA- and BTMA-MONT, respectively. DTG peak of the final oxidation step of the organic matter appeared at 694 and 705?°C for TEA- and BTMA-MONT, respectively, after the dehydroxylation of the clay. Thermo-XRD analysis detected TEA-MONT tactoids with spacing 1.40 and 1.46?nm up to 300?°C. At 300 and 360?°C, LTSC-MONT tactoids were detected with spacing of 1.29?nm. At higher temperatures, HTSC-MONT-?? and -?? tactoids were detected with spacings of 1.28 and 1.13?nm, respectively. BTMA-MONT tactoids with spacings 1.46 and 1.53?nm were detected up to 250?°C. At 300 and 360?°C, LTSC-MONT tactoids were detected with a spacing of 1.38?nm. At higher temperatures, HTSC-MONT-?? and -?? tactoids were detected with spacings of 1.28 and 1.17?nm, respectively. At 650?°C, both clays were collapsed. HTSC-??-MONT differs from HTSC-??-MONT by having carbon atoms keying into the ditrigonal holes of the clay-O-planes. At 900?°C, the clay fraction is amorphous. Trace amounts of spinel and cristobalite are obtained from thermal recrystallization of amorphous meta-MONT.     

Secondary adsorption of nitrobenzene and m-nitrophenol by hexadecyltrimethylammonium-montmorillonite thermo-XRD-analysis

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.