Temperature Dependence of Toluene Adsorption on Polyhydroxyaluminum Montmorillonite

Changes in the surface properties and porous structure of montmorillonite resulted from the substitution of polyhydroxyaluminum cations for exchangeable Na⁺ cations are studied. Preliminary thermal treatment in vacuum is found to markedly affect the adsorption behavior of polyhydroxyaluminum montmorillonite with respect to toluene. The transformation of polyhydroxycations in aluminum oxide clusters at temperatures above 600 K somewhat decreases the pore volume of the sorbent and reduces the heat of toluene adsorption.     

Equilibrium adsorption of <Emphasis Type="Italic">n</Emphasis>-hexane and carbon tetrachloride vapors on sodium and polyhydroxyaluminum montmorillonites

Changes in the sorption and energy characteristics of montmorillonite upon the substitution of polyhydroxyaluminum cations for exchange sodium ions are studied. Based on the temperature dependence of the equilibrium parameters of adsorption, it was found that the substitution of polyhydroxyaluminum cations for exchange ions results in an increase of micropore volume and the heat of adsorption. The curves of heats of adsorption for C₆H₁₄ and CCl₄ have extreme characters. The observed maxima are related to the interactions of adsorbate molecules with and between active sites due to their compaction during the filling of micropore volume.     

Heats of adsorption of benzene and toluene vapors on polyhydroxyaluminum montmorillonite

Changes that occur in the surface properties and porous structure of montmorillonite when sodium ions are replaced with polyhydroxyaluminum ions are studied. It is established that thermal evacuation significantly affects the adsorption and energy properties of polyhydroxyaluminum montmorillonite (PHAM). The dependences of the differential isosteric heats of adsorption and desorption on the amount of adsorbed substance are determined from data on a series of isosteres for the sorption of benzene and toluene on dehydrated PHAMs, where the curves of the heats of sorption of C₆H₆ and C₇H₈ are of an extreme character. It is concluded that the occurrence of maxima is determined by the interaction between molecules of adsorbates and active centers (and with one another) due to packing upon the filling of the volumes of slittype micropores.     

Heats of n-hexane and n-heptane vapor adsorption onto polyhydroxyaluminum montmorillonite

The differential isosteric heat of the adsorption of n-hexane and n-heptane vapors on dehydrated polyhydroxyaluminum montmorillonite was determined. Using the temperature dependence of the parameters of the adsorption equilibrium, it was established that substituting sodium ions for polyhydroxyaluminum cations leads to an increase in the volume of micropores and the adsorption heat of hydrocarbons, and the curves of the adsorption heats of C₆H₁₄ and C₇H₁₆ are of an extreme nature. The appearance of the maxima is associated with the interaction between and among the adsorbate molecules and active centers, due to consolidation in the process of filling micropore volumes.     

Peculiarities of Adsorption of Some Polar Substances from Vapor Phase on a Microporous Clay Adsorbent

The adsorption of polar organic substances (methanol, pyridine, and acetonitrile) and water was studied from the vapor phase on microporous adsorbent prepared by the substitution of polyhydroxyaluminum ions for the sodium ions of natural montmorillonite clay. The differential isosteric heats of adsorption of these substances were calculated and analyzed in a wide range of fillings.     

Adsorption of carbon dioxide on montmorillonites of different ion exchange forms

The adsorption isotherms of carbon dioxide are measured at 303, 343, 373, and 400 K and pressure P ranged from 0.1 to 6 MPa for three montmorillonites, i.e., the initial sample in the sodium form and two ion exchanged samples in pyridinium and polyhydroxyaluminum forms. It is shown that the linear character of the isosteres of CO₂ adsorption is retained for polyhydroxyaluminum and sodium montmorillonites, a deviation of the adsorption isosteres from linearity is observed for pyridinium montmorillonite at high temperatures (373–400 K) and high surface fillings. The differential excess entropies of CO₂ adsorbate are calculated for different fillings of montmorillonites. Using various approaches, the adsorption volumes for the systems studied are calculated.     

Reversible adsorption deformation of layered adsorbents at high pressures and temperatures

Isotherms of excessive adsorption of N₂ and Ar on three montmorillonite samples (natural sodium (NaMt) and ion-exchange pyridinium (PyMt) and polyhydroxyaluminum (PGAMt)) were measured in the pressure interval from 0.1 to 60 MPa and at temperatures 303, 343, 373, and 400 K. The results of measurements showed the inverse temperature dependence of the measured isotherms of excessive adsorption at elevated pressures and temperatures: for the isotherms at higher temperatures the amounts adsorbed exceed the values measured at lower temperatures. The deformation of montmorillonites with the temperature increase results in an increase in the adsorption volume of the adsorbent.     

Temperature Dependence of the Adsorption of Carbon Tetrachloride on a Microporous Clay Adsorbent

Changes in the surface properties of montmorillonite and its porous structure after the replacement of exchangeable inorganic cations by tetramethylammonium cations were investigated. A thermal pretreatment in a vacuum significantly affects the adsorption properties of tetramethylammonium-montmorillonite with respect to carbon tetrachloride. From a set of sorption isosteres of CCl₄on the dehydrated organomontmorillonite measured over a wide temperature range, dependences of heats of adsorption and desorption on the adsorbed amount of substance were calculated.     

A comparative study of adsorption of vapors of nitrogen-containing compounds on a microporous clay adsorbent

Differential isosteric heats of adsorption of pyridine and acetonitrile vapors on a dehydrated microporous clay adsorbent with intercalated polyhydroxyaluminum cations have been determined. As has been found from the temperature dependence of adsorption, the transformation of these polycations into alumina clusters by the thermal treatment of intercalated clay reduces the micropore volume and the heats of pyridine and acetonitrile adsorption.     

Adsorption of acetonitrile vapor on sodium and polyhydroxyaluminum montmorillonites

The differential isosteric heats of adsorption of acetonitrile vapor on dehydrated sodium and polyhydroxyaluminum montmorillonites are determined. From the temperature dependence of the parameters of adsorption equilibrium, it is established that the substitution of polyhydroxyaluminum ions for Na⁺ ions leads to an increase in the volume of micropores and the heat of adsorption.     

Adsorption of Toluene Vapors on Some Organomontmorillonites

The changes in the surface properties and porous structure of montmorillonite are investigated upon the substitution of tetramethylammonium or pyridinium cations for exchange Na⁺ cations. It is established that preliminary thermal treatment in vacuum substantially affects the adsorption properties of tetramethylammonium and pyridinium montmorillonites in relation to toluene. The dependences of the heats of adsorption and desorption on the amount of adsorbed substance are determined in a wide temperature range using the results of measuring the isosters of toluene adsorption and desorption by dehydrated organomontmorillonites.     

螯合物调控蒙脱石电动电位及其吸附铬离子性能

采用改变pH值、电解质浓度和各种金属离子插层的方法, 调整对蒙脱石胶体的ζ电位, 研究了ζ电位变化与吸附金属铬离子性能的关系, 并用螯合物调控蒙脱石的ζ电位, 探索提高吸附铬离子性能的有效方法. 研究结果表明, 蒙脱石对铬离子的吸附性与ζ电位有关, 随着ζ电位的增大, 吸附量明显增大; 螯合物改性能使蒙脱石ζ电位发生明显变化, 经邻菲罗啉螯合物改性的蒙脱石电性由负变正; 对于离子交换吸附, 蒙脱石吸附前ζ电位的绝对值必须大于吸附后ζ电位的绝对值, 并且吸附前后ζ电位差值越大, 越有利于提高对低浓度铬离子的吸附; 用邻菲罗啉与铬离子的螯合物调控蒙脱石的ζ电位, 能使对铬离子的吸附量增大1倍以上, 因此, 采用螯合物调控蒙脱石ζ电位的方法有利于提高离子交换吸附的效果.     

Adsorption of Thiophene Vapor on Sodium and Polyhydroxoaluminum Montmorillonites

Changes in the surface properties and pore structure of montmorillonite in substitution of inorganic exchange cations by polyhydroxoaluminum cations were studied by measuring the adsorption of thiophene vapor.     

Adsorption of oleic acid and triolein onto various minerals and surface treated minerals

A systematic investigation of the adsorption of oleic acid was under-taken with various minerals and surface treated minerals, viz., kaolinite, treated kaolinites, montmorillonites, talcs, gibbsites, calcites and a treated calcite. Adsorption onto kaolinite, two of the treated kaolinites (amine and MgSiO₃ treated), talcs and gibbsites was well correlated by the Langmuir model, while adsorption on the treated calcite was well correlated by the Freundlich model. Adsorption on a cationic polymer-treated kaolinite was explained in terms of a cooperative mechanism. Adsorption onto montmorillonites was explained in terms of a penetrative mechanism involving exchangeable cations.Oleic acid adsorption was compared with triolein adsorption on one of the montmorillonites, two adsorbents produced by the surface treatment of this montmorillonite, and one of the talcs. The triolein adsorption of the montmorillonite was considerably less than its oleic acid adsorption, and was explained in terms of a cooperative mechanism. Triolein adsorption of the treated montmorillonites, and the talc was well correlated by the Langmuir model. Larger amounts of triolein were taken up by the treated montmorillonites than by the untreated montmorillonite. The triolein adsorption of the talc was greater than its oleic acid adsorption.     

Theoretical study of the atrazine pesticide interaction with pyrophyllite and Ca2+‐montmorillonite clay surfaces

Atrazine, a pesticide belonging to the s‐triazine family, is one of the most employed pesticides. Due to its negative impact on the environment, it has been forbidden within the European Union since 2004 but remains abundant in soils. For these reasons, its behavior in soils and water at the atomic scale is of great interest. In this article, we have investigated, using DFT, the adsorption of atrazine onto two different clay surfaces: a pyrophyllite clay and an Mg‐substituted clay named montmorillonite, with Ca²⁺ compensating cations on its surface. The calculations show that the atrazine molecule is physisorbed on the pyrophyllite surface, evidencing the necessity to use dispersion‐corrected computational methods. The adsorption energies of atrazine on montmorillonite are two to three times larger than on pyrophyllite, depending on the adsorption pattern. The computed adsorption energy is of about −30 kcal mol⁻¹ for the two most stable montmorillonite‐atrazine studied isomers. For these complexes, the large adsorption energy is related to the strong interaction between the chlorine atom of the atrazine molecule and one of the Ca²⁺ compensating cations of the clay surface. The structural modifications induced by the adsorption are localized: for the surface, close to substitutions and particularly below the Ca²⁺ cations; in the molecule, around the chlorine atom when Ca²⁺ interacts strongly with this basic site in a monodentate mode. This study shows the important role of the alkaline earth cations on the adsorption of atrazine on clays, suggesting that the atrazine pesticide retention will be significant in Ca²⁺‐montmorillonite clays. © 2016 Wiley Periodicals, Inc.     

蒙脱石-有机化合物的相互作用

综述了蒙脱石与有机物的相互作用，包括蒙脱石对有机化合物的分配吸附现象及原理；蒙脱石与有机阳离子的离子交换反应；蒙脱石与芳香性化合物的三种吸附的相互作用形式以及这种反应在环境保护方面的应用。     

Colloid chemistry of clay minerals: the coagulation of montmorillonite dispersions

The transition between stable colloidal dispersions and coagulated or flocculated systems is a decisive process in practical applications of million of tons of bentonites (containing the clay mineral montmorillonite). Dispersion into the colloidal state requires the transformation of the original bentonite into the sodium form, for instance by soda activation. Therefore, we review here the coagulation of sodium montmorillonite dispersions by inorganic and organic cations and the influence of compounds of practical interest such as phosphates, cationic and anionic surfactants, alcohols, betaine-like molecules and polymers like polyphosphates, tannates, polyethylene oxides with cationic and anionic end groups, and carboxy methylcellulose. Typical properties of the sodium montmorillonite dispersions are the very low critical coagulation concentrations, the specific adsorption of counterions on the clay mineral surface, and the dependence of the c_K values on the montmorillonite content in the dispersion. In most cases coagulation occurs between the negative edges and the negative face. The phosphates Na₂HPO₄, NaH₂PO₄ and Na₄P₂O₇ increase the edge charge density and change the type of coagulation from edge (−)/face (−) to face (−)/face (−) with distinctly higher c_K values. Polyanions like polyphosphate and tannate stabilize in the same way. Carboxy methylcellulose causes steric stabilization. Montmorillonite particles with adsorbed betaine-like molecules provide an example of lyosphere stabilization.     

Development of Composite Adsorbents of Carbon and Intercalated Clay for N2and O2Adsorption: A Preliminary Study

Composite adsorbents of carbon and alumina intercalated montmorillonite were prepared and characterized by adsorption of N₂and O₂at various temperatures. The effects of pyrolysis, temperature, heating rate, subsequent degassing, and doping of cations and anions were investigated. The adsorption capacities of the composite adsorbents developed at higher temperatures (0 and −79°C) are found to be larger than those of normal alumina pillared clays. The experimental results showed that the framework of these adsorbents is made of alumina particles and clay sheets while the pyrolyzed carbon distributes in the space of interlayers and interpillars. The pores between the carbon particles, clay sheets, and alumina pillars are very narrow with very strong adsorption forces, leading to enhanced adsorption capacities at 0 and −79°C. The composite adsorbents exhibit features similar to those of carbonaceous adsorbents. Their pore structures, adsorption capacities, and selectivities to oxygen can be tailored by a controlled degassing procedure. Meanwhile, ions can be doped into the adsorbents to modify their adsorption properties, as usually observed for oxide adsorbents like zeolite and pillared clays. Such flexibility in pore structure tailoring is a potential advantage of the composite adsorbents developed for their adsorption and separation applications.     

Adsorption of gases on layered silicates at high pressures

Equilibrium adsorption of nitrogen, carbon dioxide, and argon was examined on the sodium and pyridinium forms of montmorillonite and on the hydrogen form of bentonite. The measurements were carried out at 303, 343, 373, and 400 K over pressure ranges of 0.1–90 MPa (Ar and N₂) and 0.1–6 MPa (CO₂). The amount of nitrogen vapor adsorbed was determined at 77 K and pressures from 0 to 0.1 MPa. The porous structure parameters of the studied samples were determined using adsorption isotherms of nitrogen, argon, and carbon dioxide vapors. At elevated temperatures and pressures >10 MPa, Ar and N₂ adsorption processes on the Na-form of montmorillonite and Ar adsorption on bentonite are activated, since the amounts of the gases adsorbed and adsorption volumes increase with temperature. No activated adsorption is observed for carbon dioxide adsorption on these adsorbents. A comparison of the excess adsorption isotherms of gases on the Py-form of montmorillonite and H-form of bentonite shows that adsorption in micropores predominates for the Py-form of montmorillonite, whereas for the Na-form of bentonite and H-form of bentonite adsorption occurs mainly in meso- and macropores.     

Preparation and characterization of microporous SiO2-ZrO2 pillared montmorillonite

SiO₂-ZrO₂ pillared montmorillonite (SZM) was prepared by the reaction of Na-montmorillonite with colloidal silica-zirconia particles which were prepared by depositing zirconium hydroxy cations on silica particles. By pillaring with the colloidal particles, the basal spacing of montmorillonite was expanded to ca. 45 Å and the calcined SZM samples showed large specific surface areas up to 320 m²/g at 400 °C. In spite of large interlayer separation, adsorption results indicated the presence of micropores generated between the colloidal particles. The microporous structure was maintained at least up to 600 °C and exhibited specific shape selectivity for the adsorption of large organic molecules, especially between toluene and mesitylene. According to the temperature-programmed-desorption (TPD) spectra of ammonia, the calcined SZM showed weakly acidic sites.