Sorption and immersional wetting on clay minerals having modified surface

Nanoplatelets of sodium hectorite showing aspect ratios of ≈20,000 and superior purity

Applying a combination of melt synthesis followed by long-term annealing a fluorohectorite is obtained which is unique with respect to homogeneity, purity, and particle size. Counterintuitively, the hectorite undergoes a disorder-to-order transition upon swelling to the level of the bilayer hydrate. Alkylammonium-exchanged samples show at any chain length only a single basal spacing corroborating a nicely homogeneous layer charge density. Its intracrystalline reactivity improves greatly upon annealing, making it capable to spontaneously and completely disintegrate into single clay lamellae of 1 nm thickness. Realizing exceptional aspect ratios of around 20,000 upon delamination, this synthetic clay will offer unprecedented potential as functional filler in highly transparent nanocomposites with superior gas barrier and mechanical properties.

Removal of organic pollutants in model water and thermal wastewater using clay minerals

Water treatment method was developed for the removal of different anionic dyes such as methyl orange and indigo carmine, and also for thymol applying sodium bentonite and cationic surfactant - hexadecyltrimethylammonium bromide (HTAB) - or polyelectrolytes (polydiallyldimethylammonium chloride, poly-DADMAC and poly-amines). The removal efficiency of these model substrates was examined in model water using UV-Vis spectrophotometry, HPLC and TOC analysis. The clay mineral and HTAB were added in one step to the polluted model water in Jar-test experiments. The influence of the cation exchange capacity (CEC) of the applied clay mineral and the presence of polyaluminium chloride coagulant (BOPAC) were also tested for the water treatment process. The structures of the in situ produced and pre-prepared organoclay composites were compared by XRD analysis. The rapid formation of organoclay adsorbents provided very efficient removal of the dyes (65-90 % in 3-10 mg/L TOC(0) range) with 200 mg/L sodium bentonite dose, however thymol was less efficiently separated. Adsorption efficiencies of the composites were compared at different levels of ion exchange such as at 40, 60 and 100 %. In the case of thymol, the elimination of inorganic carbon from the model water before the TOC analysis resulted in some loss of the analysed volatile compound therefore the HPLC analysis was found to be the most suitable tool for the evaluation of the process. This one-step adsorption method using in situ formed organoclay was better performing than the conventional process in which the montmorillonite-surfactant composite is pre-preapared and subsequently added to the polluted water. The purification performance of this method was also evaluated on raw and artificially polluted thermal wastewater samples containing added thymol.

Interfacial interactions in polymer-layered silicate nanocomposites

Interactions between sodium montmorillonite (Na-MMT) and a variety of probes, some of which are intended to model components of a polyurethane system, have been studied. Particular attention was given to the effect of preadsorbed water on the adsorption behavior of the probes. Flow microcalorimetry (FMC), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), and wide-angle X-ray scattering (WAXS) were used to monitor the adsorption process. The probe set included alcohols, amines, ethers, poly(propylene glycol) monobutyl ethers (PPG), and 4-ethylphenyl isocyanate (4-EPI). FMC revealed that the preadsorbed water molecules on undried Na-MMT hindered the adsorption of alcohol and ether probes, but had little effect on the adsorption of amines. Drying of Na-MMT to less than 0.3% w/w H2O led to an increase in heat of adsorption and generally greater retention of the probes. PPG showed strong interaction with Na-MMT due to multipoint adsorption. With dried Na-MMT, WAXS revealed that PPG of molecular weight (MW) 1000 was partly intercalated into the gallery while lower molecular weight PPG (MW 340) did not intercalate the Na-MMT. DRIFTS spectra of 4-EPI adsorbed on undried Na-MMT revealed urea linkages, indicating formation of N,N'-bis(4-ethylphenyl) urea. In contrast, with dried Na-MMT the 4-EPI formed a urethane linkage with hydroxyl groups present at the edges of the silicate platelets.

Characterization and adsorption properties of tetrabutylammonium montmorillonite (TBAM) clay: Thermodynamic and kinetic calculations

The montmorillonite has been subjected to modification through ion-exchange reaction by tetrabutylammonium bromide (TBAB). The modified sample was studied by X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) methods. The basal spacing of modified montmorillonite was determined as 14.40 A. The IR spectra of modified montmorillonite showed CH vibrations. The characterization of tetrabutylammonium montmorillonite (TBAM) and the adsorption of p-chlorophenol (p-CP) on organomontmorillonite was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit to the pseudo-second-order kinetics. The rate constants were calculated for temperatures ranging between 25.0-35.0 degrees C at constant concentration. The adsorption energy, E, and adsorption capacity, (q(m)), for phenolic compounds adsorbing on organomontmorillonite were estimated using the Dubinin-Radushkevich (D-R) equation. Thermodynamic parameters (delta g(a) = -11.063 and -11.802 kJ/mol, delta h(a) = -30.032 and -30.789 kJ/mol, delta s(a) = -0.0636 and -0.0637 kJ/mol K for 298 and 308 K, respectively) were calculated by a new approximation from the adsorption isotherms of p-CP on organomontmorillonite. These isotherms were modeled according to Freundlich and Dubinin-Radushkevich adsorption isotherms, through which the first-order and second-order coefficients (K(1ads) = 0.0152 and 0.0127 micromol/g min, K(2ads) = 0.0130 and 0.0108 L/min micromol, respectively) were obtained at 298 and 308 K.

The characterization of prepared organomontmorillonite (DEDMAM) and sorption of phenoxyalkanoic acid herbicides from aqueous solution

The montmorillonite has been subjected to modification through ion-exchange reaction by N,N'-didodecyl-N,N'-tetramethylethanediammoniumdiiodide (DEDMAI). The modified sample was studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The basal spacing of modified montmorillonite was determined as 28.72 A. The IR spectra of organomontmorillonite showed changes in C-H vibrations. The characterization of N,N'-didodecyl-N,N'-tetramethylethanediammonium montmorillonite (DEDMAM) and the adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenoxybutyric acid (2,4-DB), 4-chloro-2-methylphenoxyacetic acid (MCPA), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on organomontmorillonite was studied as a function of the solution concentration. The adsorption energy (E) and adsorption capacity (qm) for phenoxyalkanoic acid herbicides adsorbing on organomontmorillonite (DEDMAM) were estimated using the Dubinin-Radushkevic (D-R) equation. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The sorption of the herbicides on DEDMAM increased in order of MCPA<2,4-D<2,4-DB<2,4,5-T.

Swelling behavior of organoclays in styrene and exfoliation in nanocomposites

Organoclays were prepared by cationic exchange of montmorillonite (MMT) with three commercial surfactants: octadecylamine (ODA), hexadecyltrimethylammonium bromide (HTAB), benzalkonium chloride (BAC), and an in-house synthesized surfactant, vinylbenzylalkyldimethylammonium chloride (VDAC). The swelling behaviors of organoclays in styrene were compared by wettability and rheology measurements. VDAC-MMT had the slowest capillary rise rate in styrene. The Washburn equation was found not suitable for the swellable organoclay powders. All organoclay-styrene and organoclay-toluene mixtures demonstrated yield stress. However, VDAC-MMT-styrene and VDAC-MMT-toluene mixtures showed significant higher yield stresses than the other organoclay mixtures. The wettability and rheology measurements indicate that VDAC-MMT bearing a styryl functional group has the strongest interaction with styrene monomer and toluene. In order to further evaluate the extent of swelling and the microstructure, polystyrene (PS)-clay nanocomposites were prepared by in situ polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that ODA and HTAB-MMT led to intercalated PS-clay nanocomposites, while VDAC-MMT formed exfoliated PS-clay nanocomposites.

Aggregation and Decomposition of a Pseudoisocyanine Dye in Dispersions of Layered Silicates

The optical properties of reaction systems composed from a pseudoisocyanine (PIC) solution and dispersed layered silicates were studied using visible spectroscopy. Two series of reduced-charge montmorillonites were used as the silicate materials. Each series consisted of eight samples with different layer charges, which were prepared from one parent material. Observed trends were verified with another series of dioctahedral and trioctahedral smectites of different layer charges, structure, and origin. The layer charge density of the silicates significantly affected the aggregation of PIC cations. In addition to the formation of J-aggregates, dye spectral bleaching was also observed. Silicates with very low charge densities induced neither significant aggregation nor spectral bleaching of the dye. The highest levels of PIC J-aggregate formation were found in dispersions of the layered silicates with a medium surface charge. However, reversible spectral bleaching was also observed in some cases. PIC dye cations probably change their conformations during the adsorption process, due to the tension resulting from the large size of the cations and the relatively high charge density at the silicate surface. The bleached dye recovers, at least partially, with the rearrangement and redistribution of the dye cations over the time. In contrast, the presence of silicates with very high charge densities (synthetic taeniolite and fluorohectorite) led to the very fast and irreversible decomposition of the PIC. Perhaps, the tension in adsorbed dye cations, induced by the high charge density at the silicate surface, resulted in significant destabilization and a decomposition reaction of the chromophore.

Stabilization of chloro-organics using organophilic bentonite in a cement-blast furnace slag matrix

The application of cement-based stabilisation/solidification treatment to organic-containing wastes is made difficult by the adverse effect of organics on cement hydration. The use of organophilic clays as pre-solidification adsorbents of the organic compounds can reduce this problem because of the high adsorption power of these clays and their compatibility with the cementitious matrix. This work presents an investigation of the effect on hydration kinetics, physico-mechanical properties and leaching behaviour of cement-based solidified waste forms containing 2-chlorophenol and 1-chloronapthalene adsorbed on organophilic bentonites. These were prepared by cation exchange with benzyldimethyloctadecylammonium chloride and trimethyloctadecylammonium chloride. The binder was a 30% pozzolanic cement, 70% granulated blast furnace slag mixture. Several binder-to-bentonite ratios and different concentrations of the organics on the bentonite were used. Kinetics of hydration were studied by measurement of chemically bound water and by means of thermal and calorimetric analyses. Microstructure and other physico-mechanical properties of the solidified forms were studied by means of mercury intrusion porosimetry, scanning electron microscopy and unconfined compressive strength measurement. Leaching was checked by two different leaching tests: one dynamic, on monolithic samples, and the other static, on powdered samples. This study indicates that the incorporation of the organic-loaded bentonite in the binder matrix causes modifications in the hardened samples by altering cement hydration. The effects of the two organic contaminants are differentiated.

Sorptive Characteristics of Acridine-Surfactant-Phyllosilicate Systems

The effects of the presence of a cationic surfactant on the sorption of two typical nitrogen heterocyclic compounds (NHCs) on swelling and nonswelling phyllosilicates were investigated. The addition of a cationic surfactant to a NHC-phyllosilicate system can either solubilize the sorbed NHC molecules or immobilize the suspended NHC molecules, depending upon the concentration and sequence of the surfactant added. The presence of surfactant molecules on the clay mineral surfaces promoted sorption of more neutral NHC molecules due to hydrophobic effect, and this resulted in a considerable increase in sorption at high pH conditions. Both surfactant and NHC molecules were sorbed not only on the external surfaces of the phyllosilicates but also on the interlayer spaces of swelling-type clay minerals, and the resulting change in basal spacings indicates the competition between the two groups of molecules in the interlayer space. Copyright 2000 Academic Press.

Cadmium Ion Adsorption Controls the Growth of CdS Nanoparticles on Layered Montmorillonite and Calumit Surfaces

Adsorption isotherms have been determined for the intercalation of cadmium ions (Cd2+) into layered hydrophobized montmorillonite (HDP-M) and calumit (DBS-C) sheets dispersed in ethanol (1)-cyclohexane (2) mixtures. The amount of Cd2+ adsorbed depended strongly on the composition of the binary liquid; at an ethanol mole fraction of 0.05 (x1 = 0.05), 95% of the added Cd2+ is located in the ethanolic nanoreactor at the HDP-M (or DBS-C) surface. CdS nanoparticles have been generated in situ in ethanolic nanoreactors at the HDP-M and DBS-C surfaces. Absorption spectrophotometric measurements provided information on the number of CdS nanoparticles formed and on their absorption edges, bandgaps, and mean diameters. Good correlations have been obtained between the adsorption isotherms and the size (and the amount) of the CdS formed. X-ray diffractometry established that CdS nanoparticles stretched the HDP-M and DBS-C lamellas unevenly upon intercalation. Copyright 1999 Academic Press.