Bentonite Interlayer Research Articles

Adsorptive Characteristics of the Siloxane Surfaces of Reduced-Charge Bentonites Saturated with Tetramethylammonium Cation

To elucidate interactions of neutral organic contaminants (NOCs) with siloxane surfaces (often referred to hydrophobic nanosites)found between cations in 2:1 phyllosilicates, adsorption of aliphatic and aromatic compounds onto both internal and external siloxane surfaces oftetramethylammonium-intercalated bentonite with a cation exchange capacity (CEC) of 108 cmol/kg (108TMA) and its reduced-charge bentonite (CEC = 65 cmol/ kg, 65TMA) were investigated. Reduction of the layer charge and saturation of bentonite interlayers with TMA+ modify the interlayer microenvironments, which dramatically promote adsorption of NOCs. Specific mechanisms (i.e., steric restriction and phenyl-effect) control the adsorption of NOCs onto internal siloxane surfaces of TMA+ -bentonites from water. The adsorption sites of 108TMA can not provide sufficient space to accommodate NOCs, hence hindering adsorption. Adsorption mechanism on 65TMA varies with solute-loadings, from polarity-selective at low loadings to aromaticity-preferable at high loadings. Significant contribution of phenyl-effect between adsorbed-solutes to aromatics adsorption on 65TMA is found. Solvent polarity effect on the aggregation of TMA+ -bentonites and aniline adsorption demonstrated that the contribution of external siloxane surfaces to favor adsorption in n-hexane are actually exploited but generally omitted. These observations provide significant insights into distinguishing different uptake mechanisms as well as the potential means for the rational design of better organic sorbents.

Aging mechanism of copper added to bentonite

The extractability, bioavailability and toxicity of metals in soils decline with time owing to aging processes. The processes have important impact on the ecological risk assessment of metals in soils. In this study, a sequential extraction procedure was used to investigate the aging processes of copper added to bentonite and the effects of temperature and pH on the aging processes; X-ray diffraction technique was used to study the changes of basal spacing of bentonite saturated with Cu at different pH. The results from the sequential extraction demonstrated that the proportions of the most labile Cu fractions (viz. water-soluble, NH 4NO 3 extractable and EDTA extractable Cu) to total added Cu decreased with increasing incubation time, whereas the potentially labile fraction extracted by 0.5 mol L − 1 HCl and inert fractions (6 mol L − 1 HCl extractable Cu and residual Cu) exhibited the opposite trend. Also the aging of added Cu was a slow process (more than one year) where the easily extractable Cu species on soil solid surfaces gradually transformed into less extractable Cu forms which possibly diffused into interlayer of bentonite. The aging experimental data were well fitted using a parabolic diffusion equation ( R 2 = 0.690–0.943, p < 0.0001) with apparent diffusion rate coefficients ( D/ r 2) of 6.43–20.0 × 10 − 6 d − 1 and activation energy of diffusion ( E a) of 38.3–56.1 kJ mol − 1 , indicating that micropore diffusion could be the main mechanism of aging processes of Cu added to bentonite. The results of X-ray diffraction showed that the basal spacing of bentonite decreased with increasing pH, which was from 1.51 nm at pH 4.42 and 5.51, 1.37 nm at pH 6.40, to 1.26 nm at pH 7.68. It was proposed that Cu 2+ was dominant diffusive ions at low pH (< 5.5), while CuOH + became dominant at relatively high pH. During long-term aging, copper ions in interlayer of bentonite might diffuse into hexagonal cavities of clay mineral by dehydration.

Modification of bentonite with diphosphonium salts: Synthesis and characterization

Intercalations of diphosphonium salts (bis(triphenylphosphonium methylene) benzene-dichloride (TPhPMB) and bis(tributylphosphonium methylene) benzene-dichloride (TBuPMB)) into bentonite were carried out through the ion-exchange of a purified bentonite with a solution of diphosphonium salt. X-ray diffraction (XRD), 31P MAS NMR, thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were used to assess the effect of product exchange on bentonite surface and the exfoliation phenomenon of bentonite interlayer. Experimental results demonstrated that the purified bentonite has a basal spacing of 13.2 Å while the modified bentonites show a greater basal spacing of about 18 Å and has a good thermal stability (300–400 °C).

Efficient removal and mechanisms of water soluble aromatic contaminants by a reduced-charge bentonite modified with benzyltrimethylammonium cation

A novel strategy utilizing the phenyls interaction and the hydrophobic affinity of available siloxane surface in the interlayer of bentonite was proposed to improve the sorption capabilities of organobentonites for water soluble aromatic contaminants. A unique organobentonite (65BTMA) was synthesized by intercalating benzyltrimethylammonium cation (BTMA +) into the interlayer of a reduced-charge bentonite with cation exchange capacity (CEC) of 65 cmol kg −1. Phenol, aniline and toluene were used as model compounds of water soluble aromatic contaminants. Their respective removal efficiencies by 65BTMA were achieved at 83.3%, 89.2% and 97.3% at the initial concentration of 20 mg l −1. To reveal the sorption mechanism, sorption characteristics of aromatic contaminants to 65BTMA were compared with that of aliphatic contaminants in similar molecular size. And various organobentonites were prepared by combining TMA + (tetramethylammonium), BTMA +, HTMA + (heptyltrimethylammonium) and CTMA + (cetyltrimethylammonium) with two bentonites (CEC = 108 and 65 cmol kg −1). To 65BTMA, sorption magnitudes of aromatic contaminants were much greater than that of aliphatic compounds with similar size; and dramatically higher than those to other organobentonites at low pollutant concentrations. These observations revealed that the strong phenyls interactions contributed significantly to sorb the aqueous soluble aromatic contaminants to 65BTMA (>90%), and which favored to design uniquely powerful sorbents.

Adsorption of Protein from Model Wine Solution by Different Bentonites

The adsorption of protein from model wine was investigated under different temperatures, pH values, contact times, and concentrations of ethanol, by certain bentonites. The results showed that ethanol molecules could broaden the protein molecules' channel to the interlayer of bentonite, and the maximum protein adsorption amount occurred under an ethanol concentration of 12% (by volume) and a pH value of 3.56. The increased single point Brunauer-Emmitt-Teller (BET) surface area (S BET) and adsorption pore volume ( V Ads) suggested a larger amount of active adsorption sites of the bentonite surface and a wider protein channel from the surface to the inner adsorption sites of bentonite, respectively. At the same time, higher methylene blue test (MBT) and swelling index (Sw) indicated that it was easy for the entrance of water and the absorbance of protein. Higher temperature was found favorable to eliminate more proteins and it took about 20 to 40min to arrive at the maximum adsorption.

Amino acid interaction with and adsorption on clays: FT-IR and Mössbauer spectroscopy and X-ray diffractometry investigations.

In the present paper, the adsorption of amino acids (Ala, Met, Gln, Cys, Asp, Lys, His) on clays (bentonite, kaolinite) was studied at different pH (3.00, 6.00, 8.00). The amino acids were dissolved in seawater, which contains the major elements. There were two main findings in this study. First, amino acids with a charged R group (Asp, Lys, His) and Cys were adsorbed on clays more than Ala, Met and Gln (uncharged R groups). However, 74% of the amino acids in the proteins of modern organisms have uncharged R groups. These results raise some questions about the role of minerals in providing a prebiotic concentration mechanism for amino acids. Several mechanisms are also discussed that could produce peptide with a greater proportion of amino acids with uncharged R groups. Second, Cys could play an important role in prebiotic chemistry besides participating in the structure of peptides/proteins. The FT-IR spectra showed that the adsorption of amino acids on the clays occurs through the amine group. However, the Cys/clay interaction occurs through the sulfhydryl and amine groups. X-ray diffractometry showed that pH affects the bentonite interlayer, and at pH 3.00 the expansion of Cys/bentonite was greater than that of the samples of ethylene glycol/bentonite saturated with Mg. The Mössbauer spectrum for the sample with absorbed Cys showed a large increase ( approximately 20%) in ferrous ions. This means that Cys was able to partially reduce iron present in bentonite. This result is similar to that which occurs with aconitase where the ferric ions are reduced to Fe 2.5.

Further Studies of the Anaerobic Corrosion of Steel in Bentonite

ABSTRACTIn the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters with cast iron inserts will be surrounded by bentonite buffer and mounted in perforated carbon steel support structures in boreholes within the bedrock. The groundwater will be reducing, leading to anaerobic corrosion of the ferrous material. It is important to understand both the effect of bentonite on the corrosion behaviour of the steel and the effect of the corrosion products on the performance of the bentonite. Previous work on the corrosion of steel in bentonite was extended to investigate a wider range of conditions, including the possible effects of alkaline plumes released from concrete support structures and the effect of chloride concentration and temperature on the corrosion rate of steel in bentonite. Corrosion rates were measured by collecting hydrogen produced by the anaerobic corrosion of iron. In addition, a range of analytical techniques was applied to study the composition and morphology of the corrosion products and the distribution and chemical state of the iron released into the bentonite. Comparison was also made between corrosion in compacted bentonite and artificial bentonite porewater. In the presence of bentonite, the corrosion product layer was relatively thin compared to fully aqueous conditions, probably because the ferrous ions released by corrosion exchanged with the bentonite interlayer or attached to the surface of the bentonite grains, rather than forming a separate iron oxide phase.

Enhanced Photodegradation of 2,4,6-Trichlorophenol over Palladium Phthalocyaninesulfonate Modified Organobentonite

This article explores a supported photocatalyst of palladium(II) phthalocyaninesulfonate (PdPcS) onto organoclay for removal of 2,4,6-trichlorophenol (TCP) from water under visible light (lambda > or = 450 nm) irradiation. The composite clay was not only a good sorbent for uptake of TCP from water, but it also exhibited notable activity for TCP oxidation via singlet molecular oxygen, generated in situ from PdPcS photosensitization. Complete dechlorination of TCP could be achieved after TCP was totally oxidized. The initial rate of TCP degradation was observed to increase with the initial amount of TCP sorption, the kinetics following well the Langmuir-Hinshelwood equation. The resulting rate constant of TCP oxidation was found to increase with the alkyl chain length of the intercalated surfactant from dodecyltrimethylammonium to cetyltrimethylammonium and to octadecyltrimethylammonium. Such the trend in photoactivity was in agreement with the catalyst capacity for TCP sorption from aqueous medium. The result showed that enrichment of toxic TCP on the catalyst was indeed an efficient way for enhancement of the photosensitized degradation of target pollutant. However, PdPcS loading led to a notable decrease in TCP sorption, because of partial blocking of the sorptive sites. The optimal loading of PdPcS was about 1.0 wt %. The catalyst was characterized by nitrogen adsorption, X-ray diffraction, visible diffuse reflectance spectroscopy, and TCP sorption, which revealed that the incorporated PdPcS, mainly in the form of photoactive monomer, coexisted with the intercalated surfactant in the bentonite interlayers. Seven repeated experiments demonstrated that the composite clay was relatively stable and could be repeatedly used for sorption and degradation of TCP pollutant via molecular oxygen and visible light.

Adsorption of p-Nitrophenol onto PDMDAAC-Modified Bentonites

A novel organobentonite was prepared by modifying bentonite with poly(dimethyldiallylammonium chloride) (PDMDAAC), a harmless and cost-effective type of polycation. Zeta potential and X-ray diffraction measurements suggest that PDMDAAC was intercalated into the bentonite interlayer space. PDMDAAC—bentonite has been found to be effective for the removal of p-nitrophenol with a removal rate of 81.4% being achieved. The adsorption process was pH-dependent and was slightly decreased by the Ca2+ and Mg2+ ions co-existing in the solution. A dual-phase adsorption mechanism was suggested for the process. The adsorbents obtained from the regeneration of PDMDAAC—bentonite still exhibit good adsorption capacities.

Commercial development of coal-bed methane in Russia : Puchkov, L. A. and Slastunov, S. V. Gazovaya Promyshlennost, 2002, (3), 57–59. (In Russian)

In this study, we report to prepare six modified inorganic mineral materials, including bentonite, attapulgite, montmorillonite, kaolinite and diatomite, in a novel semidry-method. Compared with traditional wet-method, this semidry-method requires fewer procedures and, thus, consumes shorter reaction time and less energy. In addition, the modified materials were found to have larger surfactant concentrations, which could result in higher removal efficiency to organic contaminants. Among these six materials, the modified bentonite (organobentonite) performed the best adsorption efficiency to 2,4-dichlorophenol (2,4-D) from aqueous solution and the removal efficiency reached 97.0%. Among four surfactants, hexadecyltrimethylammonium (HDTMA), a cationic and long hydrophobic tail surfactant, was found to be the most efficient modifier. Compared with raw bentonite, the removal efficiency of 2,4-D by HDTMA-modified bentonite (HDTMA-Bent) was enhanced up to more than 40%. The characterizations of raw bentonite and HDTMA-Bent indicated that there were smaller but more separated lamella in the HDTMA-Bent and the basal spacing could be enlarged by 128% as HDTMA inserting into the interlayers of bentonite. After being modified by HDTMA, the Zeta-potential of bentonite was transformed from negative to positive, and this variation of Zeta-potential was also consistent with the change of 2,4-D removal efficiency.

Adsorption of the Organic Fraction of a Tannery Sludge by Means of Organophilic Bentonite

Two different organophilic bentonites obtained by cationic exchange with benzyldimethyloctadecylammonium chloride and trimethyloctadecylammonium chloride have been used to adsorb the organic fraction of a tannery sludge. The exchange process was carried out to different extents to obtain bentonite samples with different organophilicities and different interlayer spacings. Before adsorption, the organic matter was extracted by contacting the sludge with a Ca(OH)2 saturated solution. The adsorption capacity was found to increase with the amount of ammonium salt exchanged for both bentonites, but the one exchanged with benzyldimethyloctadecylammonium chloride proved to be more active: up to about 80% TOC could be removed from the contacting solution. The adsorption of the organic matter caused a further increase of the bentonite interlayer spacing. In both cases, the adsorption isotherms were found to be of cooperative type, due to weak adsorbent-adsorbate interactions at low loading followed by increasing adsorbate-adsorbate interactions at increasing loading. The results may be applied to tannery sludge stabilization by cementitious systems.

Electrical conductivity of modified bentonites and FT-IR spectroscopic investigations of some aromatic molecules adsorbed by bentonites

Abstract Electrical conductivity of natural and ion-exchanged Anatolian bentonites (Ag–, Cu–) and of different organic molecules (benzidine–, pyrazine– and 1,4-diamino benzene–) adsorbed by bentonites were investigated. Dc and ac measurement techniques were applied to ribbon and sandwich type samples. Measurements were made under standard pressure, humidity and room temperature. It was observed that conductivity of ion exchanged Ag–, Cu–bentonite and benzidine–bentonite complexes has increased. In addition, FT-IR spectrometry was used to assign complex pattern and composition in clay–organic molecule complexes. Spectroscopic investigations suggest that organic molecules intercalate the interlayers of bentonite with a monolayer arrangement.

Fourier transform Raman and fourier transform ir spectroscopic investigation of pyrazine adsorbed by sepiolite and bentonite from anatolia

AbstractThe adsorption of pyrazine by two different Anatolian sepiolites and by natural and ion‐exchanged (Fe, Co, Cu and Sn) bentonites was investigated by vibrational spectroscopy. The spectroscopic results indicate that the pyrazine molecules adsorbed on sepiolite and bentonites are coordinated to either surface hydroxyls by H‐bonding interaction (in the case of sepiolite) or to exchangeable cations (in the case of bentonites) through both nitrogen lone pairs as bidentate ligands. X‐ray diffraction patterns of the clays were also recorded and the basal spacings of pyrazine‐treated natural and ion‐exchanged bentonites were found to be around 14.7 Å. The results suggest that pyrazine molecules intercalate the interlayers of bentonite with a monolayer arrangement.

Formation of Polymeric Species in the Interlayer of Bentonite

AbstractInfrared spectroscopic, X-ray powder diffraction, diffuse reflectance, and electron-spin resonance examination of homoionic bentonite from Sardinia treated with diazomethane indicates that poly-methylene was formed in the interlayer position. Polymerization can be attributed to the acidic properties of the residual water in the interlamellar space, depending on the nature of the exchanged ion. The presence of an interlayer polymer causes the clay to assume strong hydrophobic properties.

Inhibition of ribonuclease activity by bentonite.

The inhibition of ribonuclease activity by bentonite and the adsorption of the protein molecule within the clay matrix were assessed by enzyme and X-ray diffraction analysis, respectively.Pretreatment of bentonite with EDTA, potassium, barium, and barium–EDTA caused varying expansion of the d(001) spacing of the clay. The d(001) variation was sensitive to pH.Inhibition of the enzyme activity generally followed the pattern of expansion of the d(001) spacing of the clay, but failed when the interlayers of bentonite expanded beyond their maximum capability.Vermiculite, which is a clay having a higher cation exchange capacity than bentonite, did not expand from the normal state after similar treatment nor did it inhibit ribonuclease activity.When the secondary and tertiary structures of the protein molecule were disrupted, the denatured protein still entered the interlayers of bentonite, but caused a greater expansion of the d(001) spacing than the native ribonuclease.