External Surface Of Montmorillonite Research Articles

Methane hydrate formation in clay mineral suspensions containing glycine: Experimental study and molecular dynamics simulation

Understanding the effects of clay minerals and amino acids on methane hydrate (MH) formation is essential for elucidating the occurrence of MH in marine sediments. In this study, kinetic experiments and molecular dynamics simulations of MH formation in montmorillonite and kaolinite systems with the presence of glycine were investigated. The experimental results showed that the addition of 5 wt% montmorillonite and 5 wt% kaolinite inhibited and promoted MH formation, respectively. Adding 1.5 wt% glycine to the montmorillonite suspension shortened the nucleation time and reduced the amount of MH; it also weakened the facilitating effect of the kaolinite suspension. The simulation results showed MH nucleation in the bulk solution due to the hydration properties of Ca2+ on the external surface of montmorillonite. However, the addition of glycine reduced the inhibitory effect of Ca2+ on MH formation due to the electrostatic interaction between the Ca2+ and COO– groups. Adsorbed methane molecules on the kaolinite siloxane surface formed clathrate-like structures. In addition, glycine also abnormally incorporated into the MH structure to inhibit MH nucleation. These findings imply that the clay mineral had a significant effect on the distribution of amino acids, causing the formation of MH in clay mineral suspension to be different from pure water. Therefore, these interactions should be fully considered when studying the occurrence mechanism of natural gas hydrate when clay minerals and amino acids coexist in marine sediments.

Layer Charge Effects on Adsorption and Diffusion of Water and Ions in Interlayers and on External Surfaces of Montmorillonite

Molecular simulations using classical force fields were performed to study the adsorption and diffusion properties of water and ions in the high-charge (Arizona-type) montmorillonite clays with var...

Carbon/montmorillonite hybrids with different activation methods: adsorption of norfloxacin

Within the group of emerging pollutants, antibiotics have raised scientific concern due to, among others, their negative influence on the health of living beings. To investigate the adsorption capacity of the antibiotic norfloxacin (NFX), in this work carbon/montmorillonite hybrid materials (MD) obtained by hydrothermal synthesis using dextrose as carbon source, with acid and thermal activation methods, as well as some precursor materials, were deeply characterized. The characterization results of MD showed the presence of carbon at both the interlayer and external surfaces of montmorillonite (M), with an increase of more than three times in the specific surface area and also in the negative surface electrical charge with respect to M sample. The MD materials assayed were effective (around 40%) to remove NFX from aqueous medium at pH 7, the removal efficiency being within that of the M (75–99%) and hydrothermal carbon (5%) samples. The XRD and zeta potential values of NFX adsorbed products indicated that, while in M sample the interlayer is the preferential adsorbing surface, for the MD material assayed (activated with higher acid concentration) the external surface would be the more active.

Fe3O4 magnetic nanoparticles in the layers of montmorillonite as a valuable heterogeneous nanocatalyst for the one-pot synthesis of indeno[1,2-b]indolone derivatives in aqueous media

In the present work, iron oxide nanoparticles (Fe3O4-NPs) were prepared using a chemical coprecipitation method. At room temperature, Fe3O4-NPs are put in interlamellar space and external surfaces of montmorillonite (MMT) as a supported solid. The MMT@Fe3O4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA) and Fourier transform infrared spectrophotometry (FT-IR). Then, indeno[1,2-b]indolone derivatives were catalyzed by magnetic MMT@Fe3O4-NPs. MMT@Fe3O4-NPs were found to be a recoverable organocatalyst for the effective synthesis of the indeno[1,2-b]indolone derivatives via one-pot multicomponent cyclocondensation of ninhydrin, 1,3-diketo compound and amine derivatives in water. The significant advantages of this method are excellent yield, mild conditions, eco-friendly catalyst, low expense, and not using an environmentally harmful catalyst or solvent.

The Amounts of Water Adsorbed to the Surface of Clay Minerals at the Plastic Limit

Abstract The paper presents results of a study on the amount of water associated with the solid phase of the clay water system at the plastic limit. Two model monomineral clays, namely kaolinite, and montmorillonite, were used in the study. The latter was obtained by gravitational sedimentation of Na-bentonite (Wyoming). The calculated mean number of water molecule layers on the external surface of montmorillonite was 14.4, and water in interlayer spaces constituted 0.3 of the water mass at the plastic limit. The number of water layers on the external surface of kaolinite particles was 63, which was related to the higher density of the surface electrical charge of kaolinite compared to that of montmorillonite. The calculations were made on the basis of the external surface area of clays and the basal spacing at the plastic limit measured by an X-ray diffraction test. The external surface area of clays was estimated by measuring sorption at a relative humidity p/p 0 = 0.5.

Immobilization of self-assembled pre-dispersed nano-TiO2 onto montmorillonite and its photocatalytic activity

The immobilization of pre-dispersed TiO2 colloids onto the external surface of the clay mineral montmorillonite (Mt) was accomplished and regulated via a self-assembly method employing the cationic surfactant cetyltrimethylammonium bromide (CTAB). The role of CTAB in the synthesis process was investigated by preparing a series of TiO2-CTAB-Mt composites (TCM) with various CTAB doses. The results indicated that a uniform and continuous TiO2 film was deposited on the external surface of montmorillonite in the composite synthesized with 0.1wt.% of CTAB, and the TCM nano-composites showed much higher values for specific surface area, average pore size and pore volume than the raw montmorillonite clay. Then, the formed TCM materials were applied in photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous solution. The degradation efficiency reached as high as 94.7%. Based on the degradation intermediates benezoquinone, fumaric acid and oxalic acid identified by LC–MS analysis, a mechanism for the photocatalytic oxidation of 2,4-DCP on TiO2/Mt nano-composites is proposed.

Size‐Controlled Synthesis of Fe3O4 Magnetic Nanoparticles in the Layers of Montmorillonite

Iron oxide nanoparticles (Fe3O4‐NPs) were synthesized using chemical coprecipitation method. Fe3O4‐NPs are located in interlamellar space and external surfaces of montmorillonite (MMT) as a solid supported at room temperature. The size of magnetite nanoparticles could be controlled by varying the amount of NaOH as reducing agent in the medium. The interlamellar space changed from 1.24 nm to 2.85 nm and average diameter of Fe3O4 nanoparticles was from 12.88 nm to 8.24 nm. The synthesized nanoparticles were characterized using some instruments such as transmission electron microscopy, powder X‐ray diffraction, energy dispersive X‐ray spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and Fourier transform infrared spectroscopy.

A highly efficient heterogeneous catalyst of Ru/MMT: Preparation, characterization, and evaluation of catalytic effect

This study focuses on the evaluation of the catalyst activity and reutilization in the catalyzed hydrolysis of sodium borohydride (NaBH4). To date, few studies on reutilization are available in literature. In the present study, a facile method was used to obtain a highly efficient catalyst, Ru nanoparticles deposited on external surface of montmorillonite (Ru/MMT). Catalytic activity and reutilization were evaluated by analyzing the H2 generation rate from an alkaline NaBH4 solution. The catalytic activity of the as-prepared Ru/MMT was determined as a function of the catalyst amount, NaBH4 concentration, and temperature. By using the as-prepared Ru/MMT catalyst with a concentration of 1wt% NaBH4, an average hydrogen generation rate as high as 28,500±500mLmin−1g(Ru)−1 is achieved at 25°C. The kinetic study demonstrates that the hydrolysis reaction is first-order in terms of the catalyst concentration and zero-order in terms of the substrate concentration. The apparent activation energy of NaBH4 hydrolysis is 54.7±1kJ/mol, which is lower than most Ru-based catalysts reported in literatures. However, the catalytic activity of the reused catalyst dramatically decreased, with only 49% of the initial H2 generation rate remaining after 10 runs. The degradation mechanism of the Ru/MMT catalyst during cycling was investigated and discussed in detail. Before and after 10 reutilizations, the textural properties of the catalysts were characterized based on the nitrogen adsorption–desorption isotherms (obtained using Brunauer–Emmett–Teller analysis), the surface morphology (obtained using field-emission scanning electron microscopy, and transmission electron microscopy), and on the surface composition (obtained using energy-dispersive X-ray spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy). The deterioration of the reused catalyst seemed to be caused by the aggregation and partial fall-off of the Ru nanoparticles deposited on the MMT external surface.

Cetylpyridinium Aggregates at the Montmorillonite− and Muscovite−Water Interfaces: A Monte Carlo Study of Surface Charge Effect

Monte Carlo simulations of the interface between the external surface of montmorillonite and aqueous cetylpyridinium chloride (CPCl) solution at ambient conditions are reported and compared with the preceding simulation study of muscovite. Simulation results reveal that a segregation of inorganic ions into the regions near the montmorillonite-water and bilayer-water interfaces leads to a nearly complete displacement of water molecules from the intermediate region of the bilayer aggregate. Such segregation does not occur for muscovite because of a considerably higher surface concentration of inorganic cations compensating its mineral charge. The presence of hydrated inorganic ions in the interfacial region containing the aliphatic part of the bilayer aggregate on muscovite leads to a more compact aggregate structure in agreement with a previously experimentally observed effect of added electrolyte. It also results in a lateral segregation of hydrophilic and hydrophobic clusters in this region in agreement with earlier experimental observations of striped surfactant structures on the muscovite surface. A configuration of the surfactant adsorption complex is found to strongly depend on the water content at the mineral-aggregate interface and suggested to be controlled by the types of inorganic counter- and co-ions present there. A transformation between characteristic configurations of the surfactant adsorption complexes is proposed as an explanation for previous experimental observations of the slow secondary surfactant adsorption.

Preparation and characterization of novel organo-clay minerals for Hg(II) ions adsorption from aqueous solution

Novel organo-clay minerals for adsorption of Hg(II) ions were prepared. The clay minerals were grafted with 2-(3-(2-aminoethylthio)propylthio)ethanamine (AEPE). AEPE-montmorillonite and AEPE-hectorite were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), CHN element analysis (EA) and surface area analysis. The XRD patterns indicated that the chelating agents (AEPE) were mainly grafted on the external surface of montmorillonite while AEPE was grafted on both the external and interlayer surfaces of hectorite. The results from IR, TGA and EA showed a difference in chemical composition of the unmodified and modified clay minerals. The results confirmed that montmorillonite and hectorite were modified with the desired organic groups. The extent of ligand loading depended on the nature of the clay mineral. The AEPE-modified clay minerals were good chelating materials for Hg(II) ions, compared to the unmodified clay minerals. The adsorption capacity for Hg(II) of AEPE-montmorillonite and AEPE-hectorite was 46.1 and 54.7 mg g − 1 , respectively, for solution containing 140 mg L − 1 Hg(II) ions (pH 4).

Diffusion mechanism of sodium ions in compacted montmorillonite under different NaCl concentration

Compacted bentonite, the major mineral being montmorillonite, is a candidate buffer material for geological disposal of high-level radioactive waste. The diffusion behavior of radionuclides in the compacted montmorillonite is an important issue to be clarified for the safety assessment of geological disposal. In this study, one-dimensional, non-steady diffusion experiments using 22Na at different diffusion temperatures and the measurement of the basal spacings by XRD were conducted for Na-montmorillonite saturated with NaCl solutions of different concentrations. Some basal spacings of the montmorillonite were found to decrease from 1.88 to 1.56 nm as the NaCl concentration increased from 0 to 0.1 M. The apparent self-diffusion coefficients at 298 K obtained in this study slightly increased as the NaCl concentration increased from 0 to 0.5 M, while the activation energies, calculated from the temperature dependences of the diffusion coefficients, were found to be 14, 22, and 17 kJ mol −1 at NaCl concentrations of 0, 0.1, and 0.5 M, respectively. These NaCl concentration dependences of the diffusion coefficients and their activation energies can be explained by assuming three independent diffusion processes (diffusion in pore water, on external surface of montmorillonite, and in interlayer of montmorillonite).

A Nuclear Magnetic Resonance (NMR) and Fourier-Transform Infrared (FTIR) Study of Glycine Speciation on a Cd-Rich Montmorillonite

AbstractAs a consequence of treatments with glycine solutions, glycine molecules enter the interlayer of both Ca- and Cd-rich montmorillonite. Measurements of d value suggest that at low glycine concentration (0.01 and 0.1 M glycine solutions) a “flat” arrangement of the glycine molecules occurs in the interlayer. In contrast, intercalation of more than one monolayer of glycine molecules occurs for the montmorillonite treated with a higher concentration of glycine (1 M glycine solution).Interlayer complexation of glycine occurs only for the Cd-rich form of montmorillonite, whereas no complexation is observed for Ca-rich montmorillonite. Both nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) results suggest that the adsorbed glycine, which fully protonates in the interlayer of montmorillonite to give the GlyH2− species, interacts with the interlayer Cd2+ to form the CdGlyx complex mainly through the carboxylate group. The interlayer cadmium, present as both Cd2+ and CdCl−, is complexed by the ligand glycine. In contrast, the cadmium adsorbed on the external surfaces of montmorillonite does not interact with the ligand. Complexation of CdCl+ only occurs for large amounts of adsorption of glycine (e.g., for samples treated with 1 M glycine solution).

Deamination of aspartic acid by aspartase—Ca-montmorillonite complex

Aspartase was adsorbed by Ca-montmorillonite at an initial pH of 7.0 and 25°C; the equilibrium adsorption isotherm was of L (Langmuir) type with a maximum adsorption of 0.22 mg aspartase protein/mg clay. The d 001 spacing of the aspartase—Ca-montmorillonite complex was 26.5 Å when 0.20 mg aspartase protein was adsorbed per mg clay, indicating the intercalation of the aspartase in the clay structure. After washing, the amount of aspartase protein remaining immobilized on the clay surfaces was 0.0073 mg/mg clay. The activity of free and immobilized aspartase in the deamination of aspartic acid was studied in unbuffered systems at pH of 7.0 to avoid the effect of the buffer on the surface reactivity of montmorillonite. During the first 2 h of the reaction no ammonium was released from aspartic acid in the presence of aspartase—Ca-montmorillonite complex, probably because there was insufficient time for the expansion and swelling of the mineral and/or the diffusion of the aspartase molecules to the interlayer edges and external surfaces of montmorillonite or the infusion of the substrate (aspartic acid). After 3 days, the specific activity of the aspartase immobilized on Ca-montmorillonite was slightly higher than that of free aspartase in homogenous solution. This was evidently due to the preservation of the activity of the adsorbed aspartase, the contribution of the catalytic power of the montmorillonite to the deamination of aspartic acid, and the complementary effects of the enzymatic and abiotic catalysis. The purification treatment of the montmorillonite did not show a significant effect on either the adsorption or the activity of the immobilized aspartase.

Reduction of copper acetate hydroxide hydrate interlayers in montmorillonite by a polyol process. A new approach in the preparation of metal-supported catalysts

Copper metal clusters of 4–5 A have been intercalated in the interlayers of montmorillonite by in situ reduction of bulky copper acetate hydroxide species with ethylene glycol (polyol process) at 195 °C. Various amounts of CuII as copper acetate hydroxide hydrate in excess of ion-exchange capacity were introduced into the interlayers by titrating copper acetate solution with sodium hydroxide in the presence of montmorillonite. The exchange of fully developed copper acetate hydroxide hydrate interlayers in the montmorillonite gave a basal spacing of 19.6 A. The reduced samples exhibited a basal spacing of 14.4 A indicating the presence of 4.8 A copper metal clusters after subtracting the thickness of the silicate layer (9.6 A). Further evidence for formation of copper metal clusters in the interlayers was obtained from transmission electron microscopy (TEM) and UV-VIS-NIR spectroscopy. Both water sorption isotherms and nitrogen B.E.T. surface-area measurements indicated the porous nature of Cu metal intercalated phases similar to pillared clays. During the process of reduction, large amounts of copper metal particles were expelled from the interlayers which grew to ca. 0.1-0.5 µm on the external surfaces of montmorillonite.

Preparation of metal supported montmorillonite catalyst: A new approach

A new approach for the preparation of metal supported montmorillonite catalyst is reported here for the first time. The polyol process in which ethylene glycol is used as reducing agent was employed for the preparation of uniformly distributed copper metal particles on and within the montmorillonite matrix. A hydroxy copper acetate intercalated form of montmorillonite was refluxed at 195 °C with liquid ethylene glycol for 6 h. The reduction of copper acetate to copper metal was apparent from the red color of the reduced product. An X-ray powder diffraction pattern showed the deposition of copper metal on the external surface of montmorillonite and scanning electron micrographs exhibited uniformly distributed spherical copper metal particles of about 0.5 μm size. This process may also be extended for the preparation of other fine metal particles supported on montmorillonite catalysts.

Water sorption on Ca-saturated clays: II. Internal and external surfaces of montmorillonite

AbstractWater-sorption isotherms and interlamellar spacings were measured for Ca montmorillonite (from Redhill. UK) over the relative pressure range 1 >P/P0> 0. By taking account of the change in interlamellar volume with relative pressure, it is shown that internal and external surfaces can be calculated by a modifiedt-plot analysis. The results also show that sorption on the external surfaces of the montmorillonite is quantitatively similar to that on reference oxide surfaces. Desorption-sorption hysteresis occurred and was apparently caused by an ageing process in which the interlamellar volume increased at the expense of the external surfaces.

Adsorption of Aldicarb By Clays and Soil Organo‐Clay Complexes

AbstractAdsorption experiments conducted with S‐methyl‐14C‐aldicarb resulted in what appeared to be negative adsorption (exclusion) of the toxicant on Ca− and Al− saturated montmorillonite clays. Calculated exclusion volumes indicated that aldicarb did not penetrate the interlamellar region. Aldicarb was excluded from at least the first 16 layers of water on external surfaces of montmorillonite. Positive adsorption occured with Ca− and Al− saturated illite and kaolinite clays. Equilihration of aldicarb solutions with one acid and two calcareous Vertisols, and with the organo‐clay complexes isolated from these Vertisols, produced negative adsorption isotherms for the acid and positive adsorption isotherm for calcareous adsorbents.

Interactions Between Montmorillonite and a Soil Humic Compound

Interactions between montmorillonite and fulvic acid* extracted from a Podzol soil were investigated by X-ray and chemical methods.Adsorption of fulvic acid by montmorillonite strongly depended on the pH of the system and the amount of added fulvic acid. 40 mg of Na-montmorillonite (<0.2 µ) adsorbed 31 mg of fulvic acid at pH 2.5, but only 15.8 mg of fulvic acid at pH 6.0 from 100 mg of fulvic acid added. D-spacings of the organo-clay complexes were 17.6 Å and 10.5 Å, respectively, under the condition of 1% relative humidity. The steepest decrease in spacing occurred between pH 4 and 5 when the ionization of the functional groups in the fulvic acid increased rapidly. At pH <4, relatively few of these groups had ionized, so that the fulvic acid behaved like a neutral molecule that could penetrate the interlamellar spaces of montmorillonite.Fulvic acid gave a diffuse X-ray pattern typical of non-crystalline substances. The pattern consisted of a broad maximum at about 4.0 Å, accompanied by a few minor humps. Radial-distribution analysis of the diffuse pattern suggested that the structure of fulvic acid was basically similar to that of carbon black. Since analytical data indicated that one molecular weight of fulvic acid (M · Wn=670) contained aromatic rings, possibly an aliphatic chain or an alicyclic ring between aromatic rings, and functional groups such as COOH, OH, CH3, and C=O, the spacing of 4.0 Å may correspond to the distance between sheets of rings and chains. On the basis of this, the expansion of montmorillonite at pH 2.5 (17.6−9.6=8.0. Å) was considered to be equivalent to a double layer of fulvic acid. On the other hand, the molecular volume of fulvic acid as estimated from its molecular weight and density was 690 Å3. The resulting cross-sectional area of 172.5 Å2 conformed to those of various models of plane molecules. The net amount of interlamellar-adsorbed fulvic acid was possibly of the order of 15 ∼18 mg/40 mg clay. Provided that the surface area of montmorillonite was 500 m2/g, the fulvic acid adsorbed in the interlamellar spaces was approximately one molecule per 172.5 Å2.In the presence of various metal cations, similar interaction between montmorillonite and fulvic acid took place. X-ray data suggested that the complexes contained up to three layers of fulvic acid. Adsorption of higher amounts of fulvic acid could be explained by the formation of metallo-organic complexes on the external surface of montmorillonite.