Sorption of nitroaromatic compounds to synthesized organoclays

This project quantifies the ability of seven engineered organoclays to sorb TNT and two of its reduction products: 2-amino-4,6-dinitrotoluene (2-A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT). The organoclays used in the TNT sorption studies were synthesized in the laboratory by combining bentonite with benzyltriethylammonium chloride (BTEA) at 50, 75, and 100% of the bentonite's cation exchange capacity and with hexadecyltrimethylammonium bromide (HDTMA) at 25, 50, 75, and 100% of the bentonite's cation exchange capacity. For sorption of 2-A-4,6-DNT and 4-A-2,6-DNT, two organoclays were tested: BTEA at 50% CEC and HDTMA at 75% CEC. Sorption data with HDTMA organoclay and TNT were fit to linear isotherms and demonstrated that the clay's sorptive capacity increased as the amount of total organic carbon exchanged onto the clay increased. Sorption data with BTEA organoclay and TNT were fit to Langmuir isotherms; however, the clay's sorptive capacity increased as the amount of total organic carbon sorbed to the clay's surface was decreased. Sorption behavior for TNT reduction products 2-A-4,6-DNT and 4-A-2,6-DNT to one HDTMA organoclay and one BTEA organoclay demonstrated that HDTMA organoclay at 10.3% total organic carbon was a more effective sorbent than BTEA organoclay at 5.2% total organic carbon.     

Simultaneous sorption of benzene and heavy metals onto two organoclays

An experimental study was performed to determine the feasibility of using hexadecyltrimethylammonium bentonite clay (HDTMA-clay) and benzyltriethylammonium bentonite clay (BTEA-clay) for simultaneous sorption of benzene and one of four heavy metals (Pb, Cd, Zn and Hg). Specifically, the role of competition between benzene and each heavy metal was studied. The sorption of Pb, Cd, and Zn on both BTEA- and HDTMA-clay decreases in the presence of benzene relative to the sorption obtained without benzene present. This indicates that there is competition between Pb, Cd, and Zn and organic compounds during sorption onto both organoclays. On BTEA-clay, Cd, Pb and Zn sorption was reduced by 24, 37, and 51%, respectively. On HDTMA-clay, Cd, Pb, and Zn sorption was reduced by 25, 30, and 57%, respectively. Hg sorption was not affected either by the presence of benzene or by the organoclays used. The sorption of benzene onto BTEA-clay in the presence of Hg, Zn, Pb, and Cd was less than the sorption observed when no heavy metal was present. The presence of Hg resulted in the most significant decrease in sorption, causing a 59% reduction in benzene sorption. The presence of Zn, Pb, and Cd caused a 41, 35, and 31% reduction in benzene sorption, respectively. In general, sorption of benzene onto HDTMA-clay was not affected by the presence of the heavy metals, indicating there are no competitive effects observed with Zn, Cd, and Hg when HDTMA-clay was the sorbent. However, the presence of Pb did cause a 20% reduction in benzene sorption to HDTMA-clay. Both organoclays tested had dual sorptive properties for both heavy metals and an organic contaminant. While the competitive effects were greater for the BTEA clay, both organoclays are capable of simultaneously removing benzene and either Zn, Cd, Hg, or Pb from aqueous solution.     

Characterization and study of sorptive properties of differently prepared organoclays from a Brazilian natural bentonite

Organoclays are used in cleaning natural waters from dissolved hydrocarbons by secondary sorption. Aiming future applications in this field, a Brazilian polycationic bentonite was used to prepare HDTMA organoclays, by using different quaternary ammonium salt loadings and clay content slips, to evaluate how these conditions may affect their sorption properties. The organoclays were characterized by CHN analysis, X-ray diffraction, thermogravimetry, and differential thermal analysis. For secondary sorption tests, to compare with published studies, toluene was used as a reference sorbate. Characterization and sorption results indicate that the Brazilian bentonite organoclays prepared in this study have a potential industrial use in environmental applications.     

Sorption interactions of volatile organic compounds with organoclays under different humidities by using linear solvation energy relationships

Organoclays are usually used as sorbents to reduce the spread of organic compounds and to remove them at contaminated sites. The sorption equilibrium and the mechanisms of volatile organic compounds (VOCs) on organoclays under different humidities are helpful for developing efficient organoclays and for predicting the fate of VOCs in the environment. In this study, the organoclay was synthesized through exchanging inorganic cations by hexadecyltrimethyl ammonium (HDTMA) into montmorillonite, resulting in 12?% of organic content. The surface area of organoclay was smaller than the unmodified clay due to the incorporation of organic cations into the interlayer. Both adsorption on organoclay surface and partition into the incorporated HDTMA in organoclay played roles on the sorption process. Compared the sorption coefficients in montmorillonite and different modified clays, the incorporated organic cations overcame the inhibition effect of hydrophilic surface of clay on the sorption process of hydrophobic organic compounds from water. The sorption coefficients of VOC vapors on organoclay were further characterized using a linear solvation energy relationship (LSER). The fitted LSER equations were obtained by a multiple regression of the sorption coefficients of 22 probe chemicals against their solvation parameters. The coefficients of the five-parameter LSER equations showed that high HDTMA-content montmorillonite interacts with VOC molecules mainly through dispersion, partly through dipolarity/polarizability and hydrogen-bonds as well as with negative π-/n-electron pair interaction. The interaction analysis by LSERs suggests that the potential predominant factors governing the sorption of VOCs are dispersion interactions under all tested humidity conditions, similar with the lower level modified clay. The derived LSER equations successfully fit the sorption coefficients of VOCs on organoclay under different humidity conditions. It is helpful to design better toxic vapor removal strategy and evaluate the fate of organic contaminants in the environment.     

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.     

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.     

Surface structure of CTMA modified bentonite and their sorptive characteristics towards organic compounds

This work was to examine the correlation between surface structure and sorptive characteristics of cetyltrimethylammonium cations (CTMA⁺) modified bentonite, which will provide novel information for exploring the sorptive mechanisms of organoclays. Various amounts of CTMA⁺ (0.21–1.98 mmol/g) were intercalated into bentonite to prepare a series of organobentonites with different structures. N₂ adsorption–desorption isotherms were plotted for the organobentonites to obtain the surface structure information, and sorption capacities of these organobentonites toward phenol, aniline, nitrobenzene and naphthalene were examined. It was shown that surface areas, pore volumes and surface fractal dimension of the organobentonites decreased with increasing CTMA⁺ loading amount. Sorption capacities of the organobentonites towards the four organic compounds have no evident correlation with their surface structures, and K_oc values of the organic compounds were shown to first increase until the maximum and then decrease as CTMA⁺ loading amount further increased. Combining with the surface structure and sorption capacities of the organobentonites, we proposed that the solute molecules were penetrated into the CTMA⁺ aggregates, and partition rather than adsorption mechanism dominated the sorption processes. The CTMA⁺ aggregates formed optimal partition phases in the intermediate surfactant loading range.     

Modification of the structure of natural bentonite and study on the sorption of Cs+

Natural bentonite clay was treated in order to remove impurities to increase the cation exchange capacity of the montmorillonite and to obtain a more effective radioactive cesium sorption. It was found that the treatment of the clay determines the amount of sorbed cesium. On the other hand it was shown that montmorillonites may retain cesium through several mechanisms which provide strongly retained cations occupying cationic sites into the clay structure or sorbed cesium which may be lost by purification treatments.     

Preparation of organovermiculites using HDTMA: structure and sorptive properties using naphthalene

Three types of organovermiculites with various organic cation (HDTMA) loading were prepared to be used as sorptive material for non-ionic organic compounds. The prepared materials were characterized using XRD and TOC analysis. The experiments evolved the fact that lower loading of HDTMA is more acceptable for sorption of neutral organic molecules from aqueous solutions. One of the possible models of intercalated molecules arrangement in vermiculite spacing was proposed.     

Tefluthrin Sorption to Mineral Particles: Role of Particle Organic Coatings

Abstract

The sorption of tefluthrin was studied on “pure” clay minerals and those that had been coated with aquatic humic substances over a mass percent carbon range of 0.02 to 2.15. Tefluthrin sorption onto humic-coated minerals was significantly greater than on to the clean minerals and increased with increasing quantities of sorbed humic substances. Humic acid, the most aromatic coating, was the strongest sorbent, followed by fulvic acid, hydrophilic macromolecular acid and natural coatings on estuarine suspended particles. This shows the significant impact of humic coatings on the sorptive capacity of mineral particles. The sorption was linear, also consistent with the operation of a partition process. The partition coefficient normalised to organic carbon (K_oc) after deduction of the contribution from the clean mineral, ranged from 120000 to 770000 and was highest for the most aromatic humic acid fraction.     

Very fast sorbent for organic dyes and pollutants

The increasing use of organic compounds endangering the environment encourages search for more efficient sorbents. While crude clay minerals are effective for the adsorption of cations, modified organoclays may adsorb negative and hydrophobic molecules. In this short communication, we present a very fast adsorbing organoclay based on montmorillonite with crystal violet pre-adsorbed up to neutralization of the negative charges. Sorption of erythrosin-B and 2,4,5-trichlorophenol to such organoclay reaches equilibrium in less than a minute, whereas with activated carbon, it took tens of minutes. The pseudo second-order kinetic coefficient for the process was at least two orders of magnitude smaller for the organoclay. Because sorption kinetics is an important factor in water purification, such fast sorbent might have broad environmental applications.     

Continuous microwave-assisted extraction, solvent changeover and preconcentration of monophenols in agricultural soils

An automatic extraction, preconcentration and clean-up module for the extraction of phenolic compounds from soils was developed; the separation and quantitation of each phenol is accomplished by GC-MS. The sorption-desorption of thirteen phenols on soils containing variable amounts of organic carbon (0.05-3.4%) and clay minerals (2-43%) at pH 5.7-8.6 was investigated. For this purpose, uncontaminated soils were spiked with 5 or 20 microg of each phenol per g of soil; the soils were then stored at 4 degrees C for at least 3 months prior to analysis in order to simulate analyte-matrix interactions other than material losses and environmental degradation in actual contaminated soils. The organic carbon content in acid and alkaline soils affects the sorption of chlorophenols but not that of alkylphenols. On the other hand, alkylphenols are preferentially sorbed by neutral soils, the process being influenced by the clay mineral content. Based on the results, alkylphenols interact more strongly with agricultural soils than do chlorophenols; also, both types of compound are less strongly sorbed by loamy sand soils owing to their increased sand contents.     

膨润土纳米复合材料的制备、表征及吸附性能研究

用有机螯合剂(CA)和十六烷基三甲基溴化铵(HDTMAB)共同改性膨润土(IMB)，制得一系列膨润土纳米复合材料IMB-HDTMA-CA。X射线衍射(XRD)、热分析(TG-DTA)、红外光谱(FTIR)以及N₂-吸附脱附技术等研究发现，HDTMA⁺和CA已稳定柱撑在膨润土的片层结构中，其层间距增大、比表面积减小而疏水性增强。吸附实验表明，IMB-HDTMA-CA能协同吸附水中有机物对硝基苯酚(PNP)和重金属镉(Cd²⁺)。对水中对硝基苯酚的吸附源于PNP在膨润土层间有机相中分配作用的增加，其吸附容量和膨润土内有机碳含量和层间距大小一致，而与比表面积无关，依次为IMB-HDTMA-TEPA>IMB-HDTMA-TETA>IMB-HDTMA-En>IMB-HDTMA 》IMB；FTIR图谱显示，IMB-HDTMA-CA吸附Cd²⁺后的N-H吸收峰向低频方向移动，其吸附能力和所形成配合物的稳定性一致。     

Sorption study of 25 volatile organic compounds in several Mediterranean soils using headspace-gas chromatography-mass spectrometry

A sorption study of 25 volatile organic compounds (VOCs) in different agricultural soils was carried out by using headspace-gas chromatography-mass spectrometry. The extraction of the VOCs from soil samples was carried out following the EPA method with some differences such as addition of potassium chloride and different instrumental conditions which provide higher sample throughput. In addition, a complementary study on several procedures for soil fortification with VOCs was also assayed, fortification with minimal sample handling was selected in order to minimise evaporation losses of the VOCs. The effect of clay minerals (7.0-69.7%) and organic carbon (0.2-3.5%) contents on acid and alkaline (pH 5.3-8.8) soils were evaluated. Based on the results, all compounds assayed were more sorbed in alkaline soils than acid ones; chlorobenzenes interact more strongly with agricultural soils than do alkylbenzenes. The organic carbon content affects the sorption of 25 VOCs in alkaline soils (the highest sorption was found for the most organic soil), while in acid soils VOC sorption increases as the organic carbon content decreases. The clay mineral fraction plays an important role in the sorption of VOCs in acid soil owing to pi-/n-electron interactions, this effect being more marked for chlorobenzenes.     

Determination of cadmium in Bentonite clay mineral using a carbon paste electrode

Sodium activated Bentonite, a sodium modified Montmorillonite, was submitted to cadmium sorption from nitrate solutions in order to simulate a cadmium polluted clay mineral. The remaining cadmium concentration in solution was analyzed at equilibrium by means of Differential Pulse Polarography (DPP) in order to calculate the cadmium concentration sorbed by the clay. The cadmium distribution between clay mineral and solution was observed for different concentrations, showing a Freundlich sorption profile. The clay mineral, previously submitted to the cadmium sorption procedure, was included in a carbon paste in order to investigate the cadmium content by voltammetric determination. For cadmium detection in Bentonite, a linear response of the carbon paste electrode (CPE) was observed in the 5 · 10^–5– 1.8 · 10^–4 mol/g range with good reproducibility. Received: 23 July 1998 / Revised: 19 November 1998 / Accepted: 26 November 1998     

Determination of cadmium in Bentonite clay mineral using a carbon paste electrode

Sodium activated Bentonite, a sodium modified Montmorillonite, was submitted to cadmium sorption from nitrate solutions in order to simulate a cadmium polluted clay mineral. The remaining cadmium concentration in solution was analyzed at equilibrium by means of Differential Pulse Polarography (DPP) in order to calculate the cadmium concentration sorbed by the clay. The cadmium distribution between clay mineral and solution was observed for different concentrations, showing a Freundlich sorption profile. The clay mineral, previously submitted to the cadmium sorption procedure, was included in a carbon paste in order to investigate the cadmium content by voltammetric determination. For cadmium detection in Bentonite, a linear response of the carbon paste electrode (CPE) was observed in the 5 · 10^–5– 1.8 · 10^–4 mol/g range with good reproducibility. Received: 23 July 1998 / Revised: 19 November 1998 / Accepted: 26 November 1998     

Application of simplified desorption method to study on sorption of americium(III) on bentonite

To elucidate the sorption behavior of americium(III) on bentonite, which is a mixture of montmorillonite clay, quartz and other minerals, simplified desorption experiments were applied to the solid phases collected after the sorption experiments. The sorption–desorption behavior was examined in the final pH range from 2 to 8. The desorption experiments revealed that most of the Am was sorbed on the montmorillonite moiety of the bentonite. The sorption of Am on montmorillonite was divided into two types: one was the “exchangeable” sorption, in which the sorbed Am was desorbed with a 1 M KCl aqueous solution, and the rest was the “unexchangeable” sorption. The exchangeable sorption was ion exchange of mostly Am³⁺. The unexchangeable sorption was the strong sorption of Am hydroxides. An accessory iron mineral, pyrite, might be involved in the Am sorption on bentonite at neutral pH.     

Partially exchanged organophilic bentonites

Using a sodium bentonite (VCNa) as substrate differently exchanged organophilic clays were obtained by reaction with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios (R) from 20 to 120 meq/100 g of clay (VC20–VC120). The sodium bentonite was previously synthesized from a Verde Claro policationic bentonite (VC) from Bravo, Paraiba State, Brazil. From the thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of these clays on calcined mass basis and from TG and DTG curves data of VCNa clay, a method was developed to estimate the mass fraction of the exchanged cation present in each organophilic clay (M _org), as a function of R. When all sodium cations of VCNa are exchanged by HDTMA, the obtained organophilic clay presents a maximum value for M _org. From this value and TG and DTG curves data of VC and VCNa clays, the cation exchange capacity of the original VC bentonite can be estimated.     

Electrochemical sensor for trace determination of cadmium(II) from aqueous solutions: use of hybrid materials precursors to natural clays

A sensitive and efficient electroanalytical method for trace determination of cadmium(II) was developed using hybrid material-modified carbon paste electrodes. The hybrid materials were obtained by modifying the commercial bentonite (BC) and locally collected clay (LC) using the hexadecyltrimethylammonium bromide (HDTMA) as to obtain the organo-modified clay samples (BH and LCH). Moreover, the local clay was pillared with aluminium and modified with the HDTMA (LCAH). The carbon paste electrode was modified with the BC/BCH/LC/LCH/LCAH hybrid materials. Cyclic voltammetric analytical data showed that the modified electrodes were possessed a characteristic reversible behaviour of Cd(II) in aqueous media. Moreover, a significant increase in cathodic or anodic current was obtained using the modified electrodes, BCH, LCH and LCAH. The electroactive surface area of modified electrodes was increased significantly compared to the pristine clay-modified carbon paste electrodes. The response of the modified electrode was not affected significantly varying the pH within the pH region 2.0–10.0. Fairly, a good linearity between the anodic current and concentration of Cd(II) (5.0–40 μg/L) was achieved using the modified electrodes (BCH, LCH and LCAH). The presence of different cations and anions as coexisting ions were studied in order to simulate the real water matrix measurements. Additionally, the real matrix analysis was simulated using the Cd(II) spiked tap water, which showed a good linearity between the concentration of Cd(II) and anodic current.     

Delamination behavior of silicate layers by adsorption of cationic surfactants

Smectite that has reacted for 48 h with hexadecyltrimethylammonium (HDTMA) cations equivalent to 0.01-3.0 times the cation exchange capacity (CEC) converts to HDTMA-smectite. The microstructure of this organoclay is observed using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). When Na cations in the interlayer of clay are exchanged with HDTMA ions, the changes in internal and external surface configuration are augmented by the intercalation of organic surfactants, showing a heterogeneous increase of interlayer spacings. As HDTMA loading increases, the chance of delaminated layers being developed increases locally in the low-charge interlayer regions by the sufficient adsorption of organic surfactants beyond the CEC due to the tendency of alkyl chain interaction.