Effect of different dimethylphenols on the interactions with Ni2+-exchanged montmorillonite

The influence of different steric and electronic properties of 2,4-; 2,5-; and 3,5- dimethylphenols (2,4-; 2,5-; and 3,5- DMP, respectively) on Ni²⁺-montmorillonite (Ni²⁺-MMT) (I) were studied. The results of X-ray diffraction show that the observed changes of the basal spacing were due to the intercalation of phenol derivatives into the interlayer space of montmorillonite. The existence of one peak at ~1,633 cm^?1 in the IR spectra of sample Ni²⁺-MMT + 2,4-DMP (II) and Ni²⁺-MMT + 2,5-DMP (III) and shift of this peaks to higher frequency indicate that 2,4-DMP and 2,5-DMP exist in the interlayer space of Ni²⁺-MMT in the protonated form. The two bands at ~1,622 and 1,597 cm^?1 in the sample Ni²⁺-MMT + 3,5-DMP (IV) indicate that 3,5-DMP may be also directly coordinated to Ni²⁺ cations. The different interactions of phenol derivatives in the silicate interlayers will be connected with different position of methyl groups on the phenol ring.     

Co(II)-exchanged montmorillonite with ethylenediamine,trimethyl- and tetramethyl-ethylenediamine and their thermal decomposition

The influence of different steric properties of ethylenediamine (EDA), trimethylenediamine (TrMeEDA) and tetraethylenediamine (TeMeEDA) on the type of interactions with Co(II)-exchanged montmorillonite and thermal decomposition of these materials were studied. The results of X-ray diffraction (XRD), thermogravimetry (TG), derivative thermogravimetry (DTG) and spectral analysis shows that the studied ethylenediamines are intercalated into the interlayer space of montmorillonite. Thermal decomposition at 20–500 °C of studied samples with EDA proceeds in three steps (the release of chemosorbed amines, coordinated EDA and dehydroxylation) while the sample with TrMeEDA and TeMeEDA in five steps (also release the protonated forms). The effect of different steric properties of individual diamines is evident.     

Thermal, spectral, and diffraction properties of Co-exchanged montmorillonite with 2-, 3-, and 4-hydroxyphenol

The influence of the 2-, 3-, and 4-OH phenols on the type of interaction with Co-exchanged montmorillonite and thermal properties of these materials were studied. The results of XRD, IR, and thermal (TG, DTG) analysis show that organic species are intercalated into the interlayer space of montmorillonite. Thermal decomposition in the temperature interval 20?C700?°C of studied samples with 2- and 3-hydroxyphenol proceeds in three steps (the release of adsorbed H₂O molecules, combustion/desorption of protonated hydroxy phenols and dehydroxylation), while the sample with 4-hydroxyphenol decompose in four steps (the new peak at ~222?°C corresponds to directly coordinated organic species). The effect of different position of the hydroxyl groups on the phenol ring on the thermal decomposition is evident.     

Ni-exchanged montmorillonite with methyl-, dimethyl- and trimethylamine and their thermal properties

The influence of different steric properties of methylamine (MA), dimethylamine (DIMA) and trimethylamine (TRMA) on the type of interactions with Ni-exchanged montmorillonite and thermal properties of these materials were studied. The results of diffraction, spectral (IR) and thermal (TG, DTG) analysis show that MA, DIMA and TRMA are intercalated into the interlayer space of montmorillonite. Thermal decomposition in the temperature interval 20–450°C of studied samples with MA and DIMA proceeds in three steps (the release of chemisorbed amines, coordinated amines and alkylammonium cations) while the sample with TRMA decompose only in two steps (the peak corresponds to the release of coordinated TRMA is absent). The effect of different steric properties of individual amines is evident.     

Interactions of different heterocyclic compounds with monoionic forms of montmorillonite

Interactions of 3-R-and 2-R pyridine (R=CH₃, Cl, NH₂) with Ni(II)-exchanged montmorillonite have been studied. Thermal and X-ray analyses indicate that pyridine derivatives are intercalated into the interlayer spaces of montmorillonite. Infrared spectral data shown that the Lewis and/or Brönsted type of interactions of pyridine derivatives is connected with different steric and inductive effects of the substituents (R) on the pyridine ring. The alkylpyridines increase the electron density on the donor nitrogen atom and support the coordination to the central atom. The halogen substituents have a negative inductive effect (–I), so that those ligands show a lower basicity and weaker σ-bonding properties than pyridine and also the lower possibility of the coordination.     

Characterization and thermal properties of Ni-exchanged montmorillonite with benzimidazole

Thermal analysis (TG, DTG), powder diffraction analysis (XRD) and infrared (IR) spectra were used to study of composition and release of benzimidazole from Ni(II)-exchanged montmorillonite under heating. Diffraction analysis indicated that benzimidazole molecules are intercalated into the interlayer space of montmorillonite. IR spectra and the analytical characteristics have shown that different type of interactions of benzimidazole is connected with different reaction conditions (acid or neutral solution). The release of benzimidazole from Ni(II)-montmorillonite under heating from studied samples proceeds in three distinct steps. The first step can be assigned to the release of water molecules while the last (third) one corresponds to the lattice dehydroxylation. The second step can be assigned to release of chemically bonded benzimidazole.     

Interlayer expansion and mechanisms of anion sorption of Na-montmorillonite modified by cetylpyridinium chloride: a Monte Carlo study

To study the change of interlayer structure of a Wyoming-type Na-montmorillonite as a result of the replacement of interlayer Na+ ions by cetylpyridinium (CP+) ions, a series of NPT Monte Carlo simulations of the clay mineral with different contents of CP+, Na+, Cl- ions and water in its interlayer space is carried out. In agreement with conclusions from experimental studies, the simulations show that the CP+ ions form monomolecular, bimolecular, and pseudotrimolecular layers with increasing interlayer contents. Calculated potential energies reveal that clay-organic interactions are stronger than organic-organic interactions in CP+-modified montmorillonite, which is in conformity with observations of earlier thermogravimetric experiments. The simulation results indicate that the pseudotrimolecular arrangement of CP+ ions is a prerequisite for the experimentally observed interlayer sorption of inorganic anions. Furthermore, in the interlayer space with a pseudotrimolecular layer, chloride ions favor the formation of pairs with inorganic rather than organic cations. On the basis of these findings and available experimental data, we propose that the interlayer sorption of inorganic anions from the pore space of an organically modified montmorillonite may occur not only in pairs with organic cations, as suggested earlier, but also in pairs with inorganic cations, which represents a so-far unconsidered and maybe more important mechanism of anion sorption on clay minerals.     

Rapid analysis of the nitrification inhibitor 3,4-dimethylpyrazole phosphate in soil using LC-MS/MS

Nitrate from the biological nitrification of ammonium fertilisers causes environmental damage via groundwater contamination and nitrous oxide emission. To limit nitrate formation, nitrification inhibitors (NIs) are used in conjunction with ammonium-based fertilisers in agricultural land management. The NI 3,4-dimethyl-1H-pyrazole phosphate (DMPP), with an active constituent 3,4-dimethyl-1H-pyrazole (3,4-DMP), is commercially available and its effectiveness and behaviour in soils have been studied. However, only one method for the analysis of 3,4-DMP in soil has been reported and relies on extensive sample preparation to remove matrix interferences prior to HPLC analysis. A new method was developed to allow monitoring of 3,4-DMP residues in soil after appliaction, which utilises the greater selectivity and sensitivity of LC-MS/MS. A 3,4-DMP limit of quantitation of 0.5 ng/g was achieved, which is 10 times more sensitive than the published method, and was achieved using 10,000 times less 3,4-DMP injected on-column, with an injection volume 100 times smaller. Four internal standards were evaluated to improve the accuracy of the extraction method. The isotope-substituted structural isomer 3,5-dimethyl pyrazole-¹⁵N₂ provided the best and most consistent recoveries over the 300-fold concentration range tested. The new method was employed to investigate the persistence and mobility of 3,4-DMP in an agricultural soil. 3,4-DMP had a half-life of 5 days in the top 0.5 cm of soil at normal and double recommended application rates, while half-lives in the 2.5 cm soil profile were 28 and 21 days, respectively. 3,4-DMP mobility in the clay loam soil tested was low, with only 15–25% of applied 3,4-DMP detected below the top 0.5 cm, suggesting the loss of 3,4-DMP was either due to volatilisation or degradation, rather than leaching into the soil profile.     

Thermal properties of different transition metal forms of montmorillonite intercalated with mono-, di-, and triethanolammonium compounds

In the present study, different transition metal forms of montmorillonite have been intercalated with mono-, di-, and triethanolammonium cations via d coordination mechanism to investigate their thermal behavior, structural characteristics, surface properties, and elemental composition using TG, XRD, BET, and CHNS techniques. Thermogravimetric analysis showed two thermal transition steps for transition metal-exchanged montmorillonites, which attributed to desorption of the physically adsorbed water and hydrated water, and dehydroxylation of the structural water; whereas for ammonium-montmorillonite complexes, the TG curves showed three thermal transition steps which attributed to desorption of the adsorbed water and dehydration, decomposition of the ammonium cations in the interlayer space of montmorillonite, and the dehydroxylation of the structural water. The thermal analysis of ammonium-montmorillonites affirmed that the molar mass of amine compounds used affects both desorption temperature (position) and the amount of the adsorbed water (intensity). XRD results revealed that the molar mass of amine used has linear relation with the basal spacings of the corresponding ammonium-montmorillonites, indicating structural changes. BET results showed that the molar mass of amines has an inverse effect on the surface area of the studied samples. CHNS analysis for the studied samples quantitatively confirmed the intercalation of ammonium cations into the interlayer space of montmorillonite.     

Redox polymerization of acrylamide to high molecular weights: effect of the mineral clay montmorillonite

Polymerization of acrylamide with the redox couple Fe(III)/thiourea in the presence of the mineral clay montmorillonite has been investigated. Polyacrylamide is obtained in good yield having molecular weight (ca. 0.7–2.5 × 10⁶) approximately one order of magnitude higher than without clay. Apparently, the locus of polymerization is the interlayer space of the clay.     

Racemic 3,5‐di­chloro‐2‐{[(1‐phenyl­ethyl)­imino]­methyl}phenol

The title compound, (RS)‐3,5‐di­chloro‐2‐{[(1‐phenyl­ethyl)­imino]­methyl}phenol, C₁₅H₁₃Cl₂NO, was synthesized from racemic 1‐phenyl­ethyl­amine and 3,5‐di­chloro­salicyl­aldehyde. The π‐conjugate system around the imine group is essentially planar in the phenol–imine tautomer. Intramolecular O⋯N hydrogen‐bond and intermolecular C—H⋯π interactions are present in the crystal structure.     

Effect of surfactant agent upon the structure of montmorillonite

The modification of sodium montmorillonite (MMT) through the incorporation of amphiphilic octadecylammonium cations in various concentrations (10–200% CEC) into the clay’s interlayer spaces has been studied. High resolution thermogravimetric analysis shows that the thermal decomposition of modified montmorillonite occurs in three steps. The first step of mass loss is related to dehydration of adsorbed water and water hydrating metal cations such as Na⁺. The second step of mass loss is attributed to the decomposition of surfactant. The third step is due to the loss of OH units during the dehydroxylation of the montmorillonite. The conformation of the surfactant cations in the confined space of the silicate galleries is investigated by X-ray diffraction analysis. These analyses are very important for any attempt to incorporate the organomodified MMT particles into different media for various applications such as polymer nanocomposite preparation.     

Novel copolymers of styrene. 10. halogen ring-disubstituted butyl 2-cyano-3-phenyl-2-propenoates

Novel trisubstituted ethylenes, halogen ring-disubstituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCH?C(CN)CO₂C₄H₉ (where R is 2,5-diBr, 3,5-diBr, 2,3-diCl, 2,4-diCl, 2,5-diCl, 2,6-diCl, 3,4-diCl, 3,5-diCl) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-disubstituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (2–5% wt.), which then decomposed in the 500–800°C range.     

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.     

Molecular dynamics simulation of TCDD adsorption on organo-montmorillonite

In this work, molecular dynamics simulation was applied to investigate the adsorption of Tetrachlorodibenzo-p-Dioxin (TCDD) on tetramethylammonium (TMA) and tetrapropylammonium (TPA) modified montmorillonite, with the aim of providing novel information for understanding the adsorptive characteristics of organo-montmorillonite toward organic contaminants. The simulation results showed that on both outer surface and interlayer space of TPA modified montmorillonite (TPA-mont), TCDD was adsorbed between the TPA cations with the molecular edge facing siloxane surface. Similar result was observed for the adsorption on the outer surface of TMA modified montmorillonite (TMA-mont). These results indicated that TCDD had stronger interaction with organic cation than with siloxane surface. While in the interlayer space of TMA-mont, TCDD showed a coplanar orientation with the siloxane surfaces, which could be ascribed to the limited gallery height within TMA-mont interlayer. Comparing with TMA-mont, TPA-mont had larger adsorption energy toward TCDD but smaller interlayer space to accommodate TCDD. Our results indicated that molecular dynamics simulation can be a powerful tool in characterizing the adsorptive characteristics of organoclays and provided additional proof that for the organo-montmorillonite synthesized with small organic cations, the available interlayer space rather than the attractive force plays the dominant role for their adsorption capacity toward HOCs.     

Thermogravimetric analysis of different molar mass ammonium cations intercalated different cationic forms of montmorillonite

Different cationic forms of montmorillonite, mainly K-, Na-, Ca- and Mg-montmorillonites were intercalated in this study via ion exchange process with mono-, di-, and triethanolammonium cations. The developed samples were characterized by TG, XRD, and CHNS techniques. Thermogravimetric study of ammonium-montmorillonites shows three thermal transition steps, which are attributable to the volatilization of the physically adsorbed water and dehydration, followed by the decomposition of the intercalated ammonium cations and dehydroxylation of the structural water of the modified clay, respectively, while untreated and cationic forms of montmorillonite showed only two decomposition steps. The type of ammonium cation has affected both desorption temperature (Position) and the amount of the adsorbed water (intensity). XRD results show a stepwise change in the crystallographic spacings of montmorillonite with the molar mass of ammonium cation, reflecting a change in the structure of the clay. CHNS data confirm the intercalation of ammonium cations into the interlayer space of montmorillonite and corroborate the effect of the molar mass of ammonium cation on the amount adsorbed by the clay.     

Chloride ion migration in natural bentonite

The disposal of nuclear wastes in geological formations demands the construction of engineering barriers. Bentonite clay rock is frequently used both as natural and engineering barrier. The natural bentonite rock in its original form is considered as compacted bentonite if the density is higher than 1.2 g/cm³. In this paper, the risk of the extrapolation of the laboratory experiments to field conditions and the high differences of the natural samples are emphasized: as much as 52 % standard deviation was obtained in the migration coefficients characterizing bentonite samples collected from the same site with a very small extent of sampling. Moreover, the bulk densities (1.18–1.87 g/cm³) and montmorillonite content are also rather different (45–71 m/m %).The contradictions of the effects of the swelling clay mineral (montmorillonite) content and the bulk density of bentonite are illustrated: it is shown that the migration rate of chloride anion is determined by the ratio of the different water types (interlayer water of montmorillonite to free pore water of bentonite, including the electric double layer water). The apparent migration coefficients of bentonite clay and concrete (natural and artificial engineering barrier) are compared.     

Thermal properties of Co-, Ni- and Cu-exchanged montmorillonite with 3-hydroxypyridine

Thermal analysis (TG, DTG), powder diffraction analysis (RTG) and infrared absorption spectra (IR spectra) were used to study of release of 3-hydroxypyridine (3-OHpy) from Co-, Ni- and Cu-exchanged montmorillonite (Co-MMT, Ni-MMT, Cu-MMT). It was found that release of 3-OHpy under heating from Co- and Ni-MMT proceeds in three distinct steps while from Cu-MMT in four steps. The first step can be assigned to the release of physically sorbed 3-OHpy while the last one corresponds to the lattice dehydroxylation. The second step (Co-, Ni-MMT) and/or second and third steps (Cu-MMT) can be assigned to release of chemically bonded 3-OHpy. This investigation shows that studied exchanged montmorillonites predominantly exhibit Lewis acid character. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of Novolac/Layered Silicate Nanocomposites by Reaction Exfoliation Using Acid‐Modified Montmorillonite

Novolac/layered silicate nanocomposites were synthesized by condensation polymerization of phenol and formaldehyde catalyzed by H‐montmorillonite (H‐MMT). Exfoliation of the clay was investigated by X‐ray diffraction and transmission electron microscopy (TEM). It turned out that the intra‐gallery condensation of phenol and formaldehyde played a predominant role in the exfoliation of MMT. Exfoliated clay plates with interlayer spacings of 10–30 nm were dispersed in the matrix uniformly as shown by the TEM micrograph.     

Catalytic activation of layered silicates for the synthesis of nanocomposite materials based on ultra-high molecular weight polyethylene

The effects of the structure of organomodified montmorillonite and the conditions of its catalytic activation by titanium and vanadium chlorides on the synthesis of nanocomposite materials based on ultra-high molecular weight polyethylene with an exfoliated structure by an in situ polymerization method were studied. It was shown that, with the use of organomodified montmorillonite with the interplanar spacing d₀₀₁ = 1.6–1.8 nm, in which the alkyl radicals of a modifier are arranged in parallel to the basal silicate surfaces, the catalyst is adsorbed only on the external surface of particle, and it does not penetrate into the interlayer space (in this case, the exfoliation of a filler does not occur). With the use of montmorillonite samples with d₀₀₁ > 2 nm with the packing of a modifier as paraffin-like mono- or bilayers, the catalyst is predominantly intercalated into the interlayer space of the layer silicate. As a result, in the course of polymerization, polyethylene is formed in the interlayer space of particles to facilitate the exfoliation of the filler in separate nanolayers. Conditions for the supporting of a catalyst onto organomodified montmorillonite, which prevent the transfer of the catalyst into solvent and the formation of a free polymer on the synthesis of nanocomposites under the conditions of suspension polymerization in n-heptane, were determined. The intercalation of a catalyst into the interlayer space of the particles of layered silicates and the exfoliation of filler particles in the course of the synthesis of composites were confirmed by X-ray diffraction analysis.