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Reuse of grey water (GW) enables to reduce fresh water consumption, but a treatment is required to prevent potential transmission and propagation of pathogenic organisms. This study presents results on the removal of pathogenic bacteria from GW as well as reduction of turbidity, TSS COD, and BOD by a novel treatment system. Compared to previous studied methods, three new elements are presented in the current treatment of GW: (1) A granulated complex of micelles of the organic cation octadecyltrimethylammonium (ODTMA) with montmorillonite was employed in filtration of GW. This complex was efficient in purifying GW due to its large surface area, positive charge and existence of hydrophobic domains. The granulated complex enabled flow when present exclusively in the filter; (2). A moving bed reactor for decomposition of part of the organic matter in the GW. This pretreatment stage, prior to the micelle-clay filter, was also efficient in removing pathogenic bacteria; (3) A regeneration stage of the micelle-clay filter conducted by passing either dilute solutions of Na-hypochlorite or HCl through the micelle-clay complex, or by heating the complex. Incubation of GW for either two weeks or one day in the pretreatment stage yielded a 10- and 7-fold enhancement in the volume filtered, which did not contain fecal coliforms, i.e., 300 and 210 L for 40 g of complex, respectively. The capacity of purified volume per gram of the complex increased further several-fold (> 23 L/g) for filters filled exclusively with granules. Regeneration of the complex in the filter further enhanced the capacity.

This study aimed at testing the application of nano-composites of micelle–montmorillonite for removal of bacteria and parasites from water. The suitability of these complexes for efficient adsorption of microorganisms was expected on account of their large surface areas, large excess of positive charge, and existence of large hydrophobic domains. Tests included removal from water of bacteria: Gram negative (Escherichia coli K-12), Gram positive (Bacillus megaterium), and a protozoan parasite, Cryptosporidium parvum. Micelles of the organic cations Benzyldimethylhexadecylammonium (BDMHDA), or Octadecyltrimethylammonium complexed with the clay-mineral montmorillonite were shown to reduce by 3–6 orders of magnitude the numbers of microorganisms in water as tested in suspension and by filters (20 cm in length) packed with the complexes mixed with excess sand (100:1, w/w). Respiration tests demonstrated that E. coli K-12 cells adsorbed to micelle (BDMHDA)–montmorillonite complex lost their viability. K...

Shortage of water has resulted in attempts to purify contaminated water. This study demonstrates removal of anionic detergents from synthetic water, well water, and gray water (GW), and the removal of pathogenic microorganisms from GW. The complex of montmorillonite with micelles of the organic cation, octadecyltrimethylammonium, was expected to yield efficient adsorption of anionic detergents and microorganisms on account of its large surface area, positive charge, and existence of large hydrophobic domains. The removal of anionic detergents, total suspended solids, and bacteria was tested by column filters packed with micelle/montmorillonite complexes mixed with excess sand. Efficient removal of anionic detergents was demonstrated for synthetic water (130 and 30 ppm), well water (from 1.35 to below 0.3 ppm) and from two domestic laundries. A model that considers convection, adsorption, and desorption yielded adequate simulations and predictions for the above kinetics of filtration. GW from showers and sinks included several million of fecal coli per 100 mL, indicating health hazard in using the water without proper treatment. The second column of two in series removed all pathogenic bacteria after the passage of 30 L, whereas activated carbon yielded poor removal. The micelle–clay filter can adequately purify such GW for reuse in irrigation and toilet flushing.

Removal of humic acid (HA) from water by octadecyltrimethyl-ammonium (ODTMA) micelle–montmorillonite (MMT) composites and by granulated activated carbon (GAC) was studied in dispersion and by filtration. FTIR measurements emphasized that the ODTMA micelle–clay-mineral composite differs from the ODTMA monomer-clay-mineral one. HA adsorption by GAC in dispersion was moderately reduced from 100% initially to 75% with an increase in HA concentrations. In contrast, the fractions adsorbed by the composite increased monotonically with HA concentrations from very low adsorption up to 80%. This effect was explained by the presence of a small concentration of ODTMA monomers in dispersion, which adsorbed on the negatively charged HA and partially neutralized it, or caused charge reversal, which in turn inhibited HA adsorption by the positively charged composite. This effect was verified by mobility measurements and was found to be more pronounced at low HA concentrations. This trend of increase in HA removal with an increase in HA concentration (3 and 10 ppm) was also observed in filtration (50% and 85% removal, respectively), when employing columns of the composite mixed with sand (to improve flow). Throughout the experiment the removal of high HA concentration (10 ppm) by the composite filter remained ~ 80% whereas, the removal by the GAC filter decreased from an initial 80% removal to a complete recovery of the HA (no removal) after the passage of 20 L (200 pore volumes). Upon applying sand of higher quality in the columns the removal of low HA concentrations was nearly complete by the composite column while the GAC only slightly contributed to its removal (for a passage of 100 L (1000 pore volumes)).

6 pages, 3 tables, 4 figures, 22 references., A new clay-liposome complex was developed for reducing leaching of herbicides and contamination of groundwater. The liposomes were composed of the neutral and Environmental Protection Agency approved phospholipid phosphatidylcholine (PC). Adsorption of PC liposomes on the clay mineral montmorillonite could exceed the cation exchange capacity of the clay, and was well simulated by the Langmuir equation. X-ray diffraction results for 6 mM PC and 1.6 g/L clay (3 day incubation) yielded a basal spacing of 7.49 nm, which was interpreted as the formation of a supported planar bilayer on montmorillonite platelets. Fluorescence methods demonstrated structural changes which reflected adsorption of PC followed by loss of vesicle integrity as measured by the penetration of dithionite into the internal monolayer of fluorescently labeled liposomes, resulting in a decrease in fluorescence intensity to 18% of initial after 4 h. Energy transfer was demonstrated after 1 h from labeled liposomes to montmorillonite labeled by an acceptor. The neutral herbicide alachlor adsorbed on the liposome-clay complex, yielding a formulation of up to 40% active ingredient, and 1.6-fold reduction in herbicide release in comparison to the commercial formulation. Hence, the PC-montmorillonite complex can form a basis for environmentally friendly formulations of herbicides, which would yield reduced leaching., We acknowledge financial support by the Spanish Ministry of Education and Science (Project AGL2005-00164) and Junta de Andalucía (Project P06-FQM-1909).

It is demonstrated that a variety of modified silicate mineral sorbents can be utilized for the removal of organic pollutants from a water suspension or by a filter. Column filters filled with a mixture of quartz sand and organic micelle–montmorillonite (100:1 w/w) or zeolite were constructed. The micelle–clay filter removed 91% of ethylene dibromide (EDB) from an initial solution of 0.2 μg/L and 99.9% of the anionic pollutants sulfosulfuron, imazaquin, sulfentrazone and the neutral bromacil and chlorotoluron from an initial solution of 10 ppm. In contrast a filter filled with activated carbon at the same weight of the organic cation and sand, or without sand removed between 47.6% and 79% of these pollutants. Comparative capacity measurements yielded removal of sulfentrazone (75 ppm initial) at weights corresponding to 18.7% and 5.5% of the weights of the organic cation or activated carbon in the filter, respectively. For the antibiotic trimethoprim the micelle–clay system was not efficient; the clay mineral montmorillonite and the zeolite clinoptilolite yielded respectively 80% and 99.9% removal from its dispersion. A clinoptilolite/sand filter gave 91% removal. We also present varying degrees of efficiencies of removal of isoproturon, benzoic acid, and 1,2 dichlorobenzene by an organo-clay and by silica (controlled pore glass (CPG))-polycation immobilized micelles (SPIM) or without immobilized micelles.

Release of organic cations from cationic micelle–clay complexes in slow release herbicide formulations or in column-filters for water purification may pose a problem. In this study we determined the release of octadecyltrimethylammonium (ODTMA) or benzyldimethylhexadecylammonium (BDMHDA) from micelle–clay complexes, and devised a method to retain the released cations by using a column filled with sand/clay mixtures. The adsorption of 5 mM ODTMA or BDMHDA on montmorillonite added at 5 g/l clay was complete. The release was examined at different times and complex concentrations. The percents of release of ODTMA after 24 h were 13.2, 3.8 and 0 for 0.1, 1 and 5 g/L, respectively, whereas for BDMHDA the corresponding values were 31.2, 19.4 and 7.2. Measurements of dissolved organic carbon (DOC) yielded the amount of the released organic cation from micelle–clay complexes in column-filters for water purification after adding a layer (13 cm) of quartz mixed with clay (150:1 w/w ratio) at the bottom of the column. The amount of the released organic cation from columns including the micelle–clay complexes was less (or equal within the experimental error) than the amount released from those including quartz alone or a quartz–clay mixture. Hence, the carbon analysis showed that in the ppm range all the released cations (ODTMA or BDTMA) were retained by the column-filter. The water passing through a 25 cm column filled with quartz mixed with micelle– clay was also passed sequentially through three columns filled with quartz–clay (150:1) and was concentrated 1000-fold. Measurements by GC-MS showed no traces of the organic cations. The conclusion is that the released organic cations from micelle–clay complexes can be completely retained by adding quartz–clay layers. D 2005 Elsevier B.V. All rights reserved.

The adsorption on Na-montmorillonite of the monovalent anion alizarinate and its complexes with micelles of cationic surfactants was investigated. Micelles were prepared from octadecyltrimethylammonium (ODTMA) and benzyldimethylhexadecyl-ammonium (BDMHDA). Alizarinate–micelle complexes are much more efficient for the adsorption of the dye than alizarinate alone, e.g., from 0.05 mM alizarinate solution 12.5 mmol per 100 g clay was adsorbed in the presence of micelles, whereas only 4 mmol per 100 g clay was adsorbed in their absence. However, unlike the adsorption of alizarinate on the clay, where its adsorbed fraction increased with the concentration of the clay, in the presence of micelles, the concentration of the clay should be optimized for achieving maximal adsorption of alizarinate. This effect is due to monomer adsorption on excessive clay sites, which leads to the decomposition of micelles, and consequently, the adsorption of alizarinate is reduced. Visible spectra of alizarinate–micelle complexes in water and adsorbed on montmorillonite were recorded. The absorption band of alizarinate in aqueous solutions at 522 nm was red-shifted in the presence of ODTMA and BDMHDA micelles due to the effect of the micelle microenvironment. Further shifts were observed in the presence of montmorillonite indicating that the alizarinate–micelle complexes were adsorbed on the clay. Significant spectroscopic changes were observed after the adsorption of alizarinate–BDMHDA-micelle complex on the clay indicating that the adsorption leads to changes in the micelle. This observation suggests that the dye may serve as a probe in visible-spectroscopy study of the adsorption of micelles on clay minerals.

The adsorption of difenzoquat (DZ) on montmorillonite was studied at a wide range of concentrations and ionic strengths. Up to difenzoquat loadings of 0.4 mmol/g clay, all the added cation were adsorbed. Maximal adsorbed amounts exceeded slightly the cation exchange capacity (CEC) of the clay (0.8 molc/kg). The adsorbed amounts did not change upon increasing the concentration of NaCl in the medium to 500 mM. An adsorption model that combines electrostatic equations with specific binding in a closed system could adequately predict the adsorbed amounts of DZ, even at high ionic strength. Simultaneous adsorption of the divalent cationic herbicide diquat (DQ) and DZ was also determined and the predictions of the model were adequate for total loadings up to the CEC of the clay. At higher loads the model adequately predicts the DZ adsorbed, but underestimates the amounts of DQ adsorbed. The influence of adsorbed DZ on the hydrophobicity of montmorillonite was tested by using the hydrophobic herbicide pendimethalin (PM). The adsorption isotherm of PM on crude montmorillonite is of the S type, indicating very low adsorption at low added amounts, and increasing affinity after part of the surface is covered with the hydrophobic molecules. Adsorption of PM on montmorillonite saturated with DZ up to 80% of the CEC showed a C behavior, indicating a partition mechanism between the solvent and the adsorbent even at low added amounts. The enhanced hydrophobicity of DZ–montmorillonite was also demonstrated in qualitative experiments in a mixed chloroform–water environment: whereas the crude clay mineral stayed in the water phase, DZ–montmorillonite concentrated in the chloroform phase.

The adsorption–desorption of the herbicide fluridone on Na-montmorillonite and several organo-montmorillonite complexes was studied at a variety of loadings of the organic cation and pH levels. The aim was to find the organo-clay complex, which would be an optimal adsorbent for the hydrophobic fluridone. The organic cations studied were hexadecyltrimethylammonium (HDTMA), benzyltriethylammonium (BTEA), benzyltrimethylammonium (BTMA) and methylene blue (MB) at loadings equal to 25%, 50% and 100% of the cation exchange capacity (CEC) of the clay-mineral. The adsorbed amount of fluridone increased several-fold when montmorillonite was preadsorbed by the organic cation HDTMA up to its CEC and with BTMA at a loading of 5/8 of the CEC. BTEA and MB did not improve the adsorption capacity of the clay for fluridone. The results suggest that interactions between the phenyl rings of the herbicide and that of a small organic cation are geometrically easier to establish than with a larger organic cation. A reduced interaction between the phenyl rings of MB and those of fluridone may account for the low affinity of fluridone adsorption on montmorillonite-MB. In all cases, fluridone adsorption increased with decreasing pH and reached 100% for pH 2.7. Protonation of fluridone molecules with decreasing pH would result in increased adsorption through cation exchange. Thus, by regulating the pH, complete fluridone adsorption can be achieved. Desorption isotherms demonstrate high degree of irreversibility of the adsorption–desorption process and suggest that strong binding mechanisms dominate the fluridone-clay and organo-clay interactions. The results for fluridone adsorption–desorption demonstrate that, for similar molecules, a clay-based slow release formulation can be designed by first lowering the pH.

A new approach was developed for reducing leaching of herbicides and contamination of groundwater. Liposome-clay formulations of the anionic herbicides sulfometuron and sulfosulfuron were designed for slow release by incorporating the herbicide in positively charged vesicles of didodecyldimethylammonium (DDAB), which were adsorbed on the negatively charged clay, montmorillonite. Freeze fracture electron microscopy demonstrated the existence of DDAB vesicles and aggregated structures on external clay surfaces. X-ray diffraction results for DDAB with montmorillonite imply the existence of DDAB bilayers with an oblique orientation to the basal plane within the clay interlayer space at adsorbed amounts beyond the cation exchange capacity of the clay. Adding DDAB with sulfometuron or sulfosulfuron to montmorillonite yielded 95% or 83% adsorption of the herbicide at optimal ratios. Liposome-clay formulations exhibited slow release of the herbicides in water. Analytical measurements in soil columns demonstrated 2-10-fold reduction in leaching of the herbicides from liposome-clay formulations in comparison with commercial formulations. Percents of root growth inhibition of a test plant in the upper soil depths were severalfold higher for the liposome-clay formulations than for the commercial ones. Consequently, liposome-clay formulations of anionic herbicides can solve environmental and economical problems by reducing their leaching., Financial funding by the Spanish Ministry of Science and Technology (Projects REN2000-1540 and AGL2002-00993); The Hebrew University of Jerusalem through a grant from the Wolfson Foundation for Scientific Research, Matching-Bergman; and Grant G-641-106.8/1999 from the German-Israeli Foundation for Research and Development. T. Undabeytia also acknowledges the Spanish government for a Ramón y Cajal research contract.

Interactions of the herbicide sulfentrazone with the cationic surfactants octadecyltrimethylammonium (ODTMA), hexadecyltrimethylammonium (HDTMA), and benzyldimethylhexadecylammonium (BDMHDA) have been studied for the design of slow-release formulations based on sulfentrazone adsorbed on a micelle-montmorillonite complex. Adsorbed amounts of sulfentrazone on ODTMA- and BDMHDA-montmorillonite complexes were 99.2-99.8% of that added, and desorption of herbicide in water during 24 h was low. After 10 washings in funnels with soil, only 2.6% of herbicide was released from ODTMA-montmorillonite formulations versus 100% release from the commercial formulation. The strong binding of sulfentrazone to micelles was confirmed by pH and spectroscopic measurements and was explained by the formation of ionic pairs between cationic surfactant and anionic herbicide. The ODTMA-clay and commercial formulations of sulfentrazone yield almost complete and 40% growth inhibition of green foxtail, respectively, at 700 g of active ingredient/ha. Hence, the slow release from micelle-clay formulations of sulfentrazone promotes its biological activity and reduces environmental contamination.

Slow release formulations of the anionic herbicide sulfosulfuron (SFS) were prepared by incorporating it in micelles of an organic cation octadecyltrimethylammonium, which adsorb on the clay-mineral montmorillonite. The fraction of SFS adsorbed on the micelle-clay complex reached 98%, whereas for monomer-clay complexes, its adsorption was insignificant. Fluorescence studies showed surface contact between the micelles and the clay surface. The rate of SFS release from the micelle-clay formulations in aqueous suspensions was slow (

Ground water pollution due to herbicide leaching has become a serious environmental problem. Imazaquin [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-carboxylic acid] is an herbicide used to control broadleaf weeds in legume crops. Imazaquin is negatively charged at the basic pH of calcareous soils and exhibits high leaching potential in soils. Our aim was to design formulations of imazaquin to reduce herbicide leaching. Imazaquin sorption on pillared clay (PC) and crystal violet (CV)-montmorillonite complexes was studied. The CV-montmorillonite complexes become positively charged with adsorption of CV above the cation exchange capacity (CEC) of montmorillonite, and thus can sorb imazaquin. The Langmuir equation provides a good fit to isotherms of imazaquin sorption on PC and CV-montmorillonite complexes, but for charged complexes an equation that combines electrostatics with specific binding was preferred. Maximal imazaquin sorption was 17.3 mmol kg -1 for PC and 22.2 mmol kg -1 for CV-montmorillonite complexes. The extents of imazaquin desorption into water were 21% for PC and 5% for CV-clay complexes. The presence of anions decreased imazaquin sorption on both sorbents in the sequence phosphate > acetate > sulfate. Reduction of imazaquin sorption by the anions and the extent of its desorption in electrolyte solutions were higher for PC than for CV-clay complexes. Leaching of imazaquin from CV-montmorillonite formulations through soil (Rhodoxeralf) columns was two times less than from PC formulations and four times less than that of technical imazaquin. The CV-montmorillonite complexes at a loading above the CEC appear to be suitable for preparation of organo-clay-imazaquin formulations that may reduce herbicide leaching significantly.

The aim of this study was to understand the interactions between alkylammonium cations present as monomers and micelles and a clay mineral, montmorillonite, to develop slow release formulations of anionic herbicides, such as sulfometuron (SFM) whose leaching in soils is an environmental and economic problem. In the proposed formulation the herbicide is incorporated in positively charged micelles of quaternary amine cations, which in turn adsorb on the negatively charged clay. The adsorption of hexadecyltrimethylammonium (HDTMA) and octadecyltrimethylammonium (ODTMA) on montmorillonite was studied above and below their critical micelle concentrations (CMC). At concentrations above the CMC, the loading exceeded the clay's cation exchange capacity (CEC) and indicated higher affinity of the cation with the longer alkyl chain. An adsorption model could adequately simulate adsorption at concentrations below the CMC, and yield fair predictions for the effect of ionic strength. The model indicated that above the CMC adsorbed micelles contributed significantly to the amount of ODTMA adsorbed. Evidence for adsorption of ODTMA micelles on montmorillonite was provided by X-ray diffraction, freeze-fracture electron microscopy, and dialysis bag measurements. SFM was not adsorbed directly on the clay mineral, and adsorbed at low levels, when the organic cation was adsorbed as monomers. In contrast, a large fraction of SFM adsorbed on the clay mineral when incorporated in micelles that adsorbed on the clay.

The current research in herbicide application aims to develop formulations that reduce leaching of the herbicide to deep layers of the soil and to concentrate its biological activity at the top layers. Adsorption of metolachlor on clay minerals, their organic derivatives or pillared forms provides the best possibility to develop slow-release formulations. Metolachlor is a selective pre-emergence herbicide widely used in irrigated crops to control annual weeds. It is adsorbed by bentonites and montmorillonites, but the amount adsorbed strongly depends on the type of bentonite and possible pretreatment reactions. Wyoming bentonites adsorbed considerable amounts of metolachlor but other bentonites did not bind this herbicide. An acid-activated pillared montmorillonite was also an effective adsorbent of metolachlor. Modification of this sample by preadsorbing different amounts of benzyl trimethylammonium ions did not influence the level of herbicide adsorption. The biological efficiency of the formulations was tested with bioassay soil columns. Slow-release formulations could be prepared with raw bentonites and the acid-activated pillared montmorillonite. A formulation, prepared by adsorbing metolachlor from aqueous solution on the acid-activated pillared montmorillonite, showed high herbicide activity at the top 10 cm, and did not diffuse significantly to greater depths. This formulation should allow a better weed control than the commercial formulations.

Adsorption of organic cations on several clay minerals is reviewed with an emphasis on the effect of ionic strength and modeling. The clay exchanged with suitable organic cations forms a basis for ecologically acceptable formulations of herbicides with reduced leaching, ground water contamination and enhanced weed control efficacy. Incomplete neutralization of the clay surface charge by an organic cation may be advantageous in achieving maximal adsorption of hydrophobic herbicides. One conclusion from these studies is that optimization of clay-based herbicide formulations requires a selection of structurally compatible organic cations preadsorbed on the clay at optimal coverage. New experimental results are presented for alachlor formulations, which significantly reduce herbicide leaching under conditions of heavy irrigation. We were able to demonstrate that organo-clay formulations of alachlor and metolachlor can increase crop yields in a 1-year field experiment. The photostabilization of pesticides is reviewed and improved organo-clay formulations of the herbicides trifluralin and norflurazon are described. A pillared clay, nanocomposite micro- and/or meso porous material, was effective in reducing leaching and in conferring photostabilization, without added organic cations.

Our aim was to study the adsorption of the plant regulator mepiquat to montmorillonite and test the suitability of montmorilonite–mepiquat complexes in formulations to reduce leaching of the non-polar herbicide, acetochlor. Adsorption of the monovalent organic cation mepiquat to montmorillonite through a range of ionic strengths was determined and modeled. Mepiquat adsorption reached the cation exchange capacity (CEC) of the montmorillonite. The binding coefficients K=300 M−1 for neutral mepiquat complex formation and K=10 M−1 for positively charged complex formation were employed. Increased NaCl and CsCl electrolyte solution concentrations reduced mepiquat adsorption which was also affected by the inorganic cation binding coefficients. An adsorption model, which includes the electrostatic Gouy–Chapman equations and specific binding in a closed system, effectively simulated of the adsorption isotherms and yielded quantitative predictions for the effect of electrolyte concentration on mepiquat adsorption. Acetochlor adsorption to mepiquat–montmorillonite complexes was about 20% of the amount added, and increasing the mepiquat concentration from 0.5 to 0.8 mmol mepiquat g−1 clay made no difference. Acetochlor desorption from formulations was rather rapid with 38–67% released during 1 day. The rate of acetochlor release was reduced to 8.5% during 1 day after a brief pre-washing of the formulations. Despite the rate reduction in acetochlor release, current formulations are still not satisfactory for reduced acetochlor leaching.

Photostable formulations of the herbicide norflurazon [4-chloro-5-(methylamino)-2-(R,R,R-trifluorom-tolyl)pyridazin-3-(2H)-one] were achieved by adsorbing it on pillared clay or on montmorillonite preadsorbed with the organic cation thioflavin T (TFT). Diffuse reflectance Fourier transform infrared spectra showed the existence of strong interactions between the aromatic moieties of preadsorbed TFT and the herbicide, particularly after irradiation. The photostabilization of norflurazon obtained with TFT-clay was mainly due to energy transfer from the herbicide to the organic cation via ð-ð* interactions. An additional mechanism is the lower production of radicals from the clay when the clay mineral surface is covered with the organic cation. These radicals are responsible for the enhanced photodegradation observed when norflurazon was irradiated in the presence of untreated montmorillonite.

The divalent organic cation, methyl green (MG), undergoes a slow transformation (6 h) to a monovalent cation, carbinol (MGOH(+)) upon dilution of its solution (10 mM), or in a buffer at neutral pH. Adsorption isotherms of MG on montmorillonite were determined by two procedures, both of which yield a final pH of suspensions between 7 to 7.4. When the amounts of MG in suspension were lower than the cation-exchange capacity (CEC) of the clay (0.8 mol(c)/kg clay), no measurable amount of MG remained in solution. The maximal amounts of MGOH(+) adsorbed were larger than those of MG(2+), being 1.15 and 0.75 mol MG/kg clay, respectively, corresponding to 140% of the CEC in the first case. On a charge basis the adsorption of added MG(2+) amounts to 185% of the CEC, which raises the possibility that a certain fraction of MG(2+) transformed into the monovalent form during the incubation period, since other divalent organic cations previously studied only adsorbed up to the CEC (paraquat), or slightly above it (diquat). Adsorption of MG on sepiolite (CEC=0.15 mol(c)/kg) further emphasizes the two patterns of its adsorption. The maximal adsorbed amounts of MG(2+) and MGOH(+) were 0.09 and 0.30 mol/kg clay, respectively. X-ray diffraction measurements gave lower values for the basal spacings for montmorillonite-MG(+) than for MGOH(+), suggesting that MG(2+) binds two clay platelets together, as in the case of other divalent cations. A competition for adsorption between MG and the monovalent organic cation, acriflavin (AF), gave lower adsorbed amounts of AF when competing with MG(+), which is interpreted to be due to the smaller basal spacing in this case, which partially inhibits the entry of AF molecules into the interlammelar space. Spectra of montmorillonite-MG particles in the visible range exhibited significant differences between clay-MG and clay-carbinol. Copyright 2000 Academic Press.

The use of commercially available formulations of metolachlor has resulted in its leaching and migration to water sources. Formulations of metolachlor designed to reduce its leaching in soil have been prepared by adding the herbicide dissolved in an organic solvent or in water to organo-clay complexes. Best formulations were made when the organo-clay complex was formed by adsorbing the monovalent organic cations benzyltrimethylammonium (BTMA) or benzyltriethylammonium (BTEA) onto sodium montmorillonite (Mont) at 0.5 or 0.8 mole kg−1 clay. Adsorption of metolachlor to organo-clays followed the sequence Mont-BTMA 0.5 > Mont-BTMA 0.8 > Mont-BTEA 0.8 > Mont-BTEA 0.5 > Mont. Fourier transform infrared (FTIR) analysis demonstrated the occurrence of shifts of several peaks of adsorbed metolachlor relative to the free herbicide, indicating the existence of strong interactions between metolachlor molecules and the organo-clay surface. Leaching studies employing organo-clay and commercial formulations were carried out under greenhouse and field conditions. Metolachlor applied as organo-clay formulations leached less than the commercial formulation. Organo-clay formulations prepared by adding the herbicide as a water solution showed less leaching in the soil profile than those made by using organic solvent. Under greenhouse conditions, the herbicidal activity of organo-clay formulations was similar to that of the commercial one. Under field conditions, leaching from Mont-BTMA 0.5-metolachlor was less than that from the commercial formulation, demonstrating the environmental and agricultural advantages of the organo-clay formulations of metolachlor. © 1999 Society of Chemical Industry

Abstraet--Sorpti on of several organic and inorganic cations on illite (Clay Minerals Society Source Clay Imt-2) was determined experimentally and results compared to model calculations. The cations studied were crystal violet (CV+), benzyltrimethylammonium (BTMA§ benzyltriethylammonium (BTEA+), Ca 2+, Mg 2+, K +, Na +, Cs +, and Li +. The adsorption-model calculations involved a solution of the electrostatic Gouy-Chapman equations. The model considered specific adsorption and sorption/exclusion in the double-layer region in a closed system. Model calculations considered the simultaneous presence of four to six cations in the system. The adsorption of CV included formation of neutral and charged complexes. The adsorption attained 0.37 mol kg i or 150% of the cation exchange capacity (CEC) of illite in aqueous suspension. The adsorption of BTMA and BTEA did not exceed the CEC and was reduced with an increase in ionic strength. The sorption of CV below the CEC was rather insensitive to the ionic strength because of the large binding coefficients and was only slightly reduced in NaC1, CsC1, or Na2SO4 solutions. When added in amounts exceeding the CEC in high ionic strength, 0.667 M NaNO 3, NaC1, or CsC1 solutions, the adsorbed quantities of CV increased to three times the CEC. At high sulphate concentrations (0.333 M Na2SO4), the adsorption was below the CEC. Model calculations yielded satisfactory simulations for the adsorption, particularly for cations added in amounts approaching or exceeding the CEC. The binding coefficients for formation of neutral complexes followed the sequence: CV > Ca > BTMA > BTEA > Cs > Mg > K > Na > Li. Model calculations also suggested that sites were present which bound exchangeable cations, particularly K +, Na +, and Mg 2+, very tightly.

The use of commercially available formulations of alachlor has resulted in a serious environmental problem due to its leaching and migration to water sources. The objective of this study was to develop organo-clay based formulations that can significantly reduce leaching and improve weed control efficacy. We adsorbed the herbicide to montmorillonite clay particles whose surfaces were modified from hydrophilic to hydrophobic by preadsorbing to the clay an organic cation, such as benzyltrimethylammonium (BTMA) to reduce release of the herbicide into the soil. Alachlor adsorption was determined by gas chromatography. Organo-clay complexes of 0.5 mmol BTMA/g of clay gave larger adsorbed amounts and better formulations of alachlor as compared to BTMA preadsorbed up to the cation exchange capacity (0.8 mmol/g), whereas formulations without organic cations were not effective and gave little adsorption of the herbicide. The use of Fourier transform infrared spectroscopy showed that the optimal formulation also yielded the largest shifts of the stretching vibrations of the phenyl ring. The organo-clay formulations yielded slow release of the herbicide to the environment, maintaining the herbicidal activity in the top soil as measured by a bioassay using green foxtail and wheat as test plants. Laboratory and field experiments showed improved weed control at significantly reduced applied rate when alachlor was applied as organo-clay formulations.

Design and test of clay-based formulations of pesticides for solving environmental and economical problems are described. Organoclays were mainly designed to promote the adsorption of neutral and hydrophobic pesticides and slow their release. Adsorption of organic cations modifies the nature of the clay mineral surface, transforming it from hydrophilic to hydrophobic. The modified clay mineral surface can have enhanced affinity for adsorbing neutral organic molecules of hydrophobic characteristics. The adsorption of the hydrophobic herbicides alachlor, metolachlor norflurazon, and acetochlor, which include a phenyl ring, was maximal for montmorillonite preadsorbed by a small cation, for example, phenyl trimethylammonium at a loading corresponding to 5/8 of the cation-exchange capacity (CEC). Loading of the organic cations above the CEC of the clay can promote the adsorption of certain anionic herbicides, such as imazaquin. Reduction of volatilization and photodegradation of herbicides was also achieved by certain organoclay formulations. In certain cases, an organic cation adsorbed on the clay mineral can act as an energy acceptor of the photoexcited molecule of the pesticide, which returns to its ground state before its photodecomposition occurs, thus becoming photostabilized. Clay mineral–micelle and –liposome formulations were introduced for obtaining slow release formulations of certain anionic herbicides, which could not be achieved by organoclay ones. The procedure involves incubation of the clay mineral with organic cations, which are mostly in micelles or liposomes. The complex formed between ODTMA (octadecyl trimethylammonium) and montmorillonite in the presence of excess of micelles is very different from the complex formed in the exclusive presence of ODTMA monomers, as shown by electron microscopy, XRD, and adsorption measurements. Unlike the monomer–clay mineral complex, which was not efficient for the adsorption of anionic organic molecules, such as sulfometuron, the micelle–clay mineral complex was highly efficient. Liposome–clay mineral formulations were prepared by employing the positively charged didodecylammonium and the neutral and EPA approved phosphatidylcholine. Efforts to develop slow release formulations also focused on encapsulation of herbicides in clay mineral polymer nanocomposites. The efficacy of the bypiridil herbicides paraquat (PQ) and diquat (DQ), which are divalent organic cations, used for post-emergence weed control was enhanced by addition to the herbicide formulation of monovalent organic cations which could compete for adsorption to the dust with DQ and PQ, thus making them more available for herbicidal activity.

Removal of Cr(VI) from aqueous solutions under different conditions was investigated using either clay (montmorillonite) or micelle-clay complex, the last obtained by adsorbing critical micelle concentration of octadecyltrimethylammonium ions onto montmorillonite. Batch experiments showed the effects of contact time, adsorbent dosage, and pH on the removal efficiency of Cr(VI) from aqueous solutions. Langmuir adsorption isotherm fitted the experimental data giving significant results. Filtration experiments using columns filled with micelle-clay complex mixed with sand were performed to assess Cr(VI) removal efficiency under continuous flow at different pH values. The micelle-clay complex used in this study was capable of removing Cr(VI) from aqueous solutions without any prior acidification of the sample. Results demonstrated that the removal effectiveness reached nearly 100% when using optimal conditions for both batch and continuous flow techniques.

Adsorption of the divalent organic cations paraquat (PQ) and diquat (DQ) to montmorillonite was studied experimentally and simulated by a model which combines the Gouy–Chapman solution and specific cation binding in a closed system. The model allows for coulombic and noncoulombic interactions as previously considered for monovalent organic cations. The coulombic interactions were expressed in terms of complexes formed between a divalent cation and one or two singly charged surface sites. The noncoulombic interactions also included mixed complexes in which a monovalent organic cation could bind to a complex composed of a divalent organic cation and one or two surface sites, and vice versa, with asymmetric binding coefficients. PQ adsorbed up to the cation exchange capacity (CEC) of the clay, whereas adsorbed amounts of DQ exceeded the CEC by 18%. The binding coefficients determined for PQ and DQ exceed those found for Mg or Ca by several orders of magnitude but are below those previously found for several monovalent organic cations, such as acriflavin (AF) and crystal violet (CV). Unlike the unmodified, or enhanced, adsorption of these monovalent organic cations with an increase in ionic strength, the adsorbed amounts of PQ and DQ decreased with increasing CsCl concentrations. This trend necessitated ignoring noncoulombic interactions when only a divalent organic cation interacted with the clay. The adsorption model could simulate and predict the adsorption of PQ and DQ when added alone or in competition. The model explained qualitatively the larger adsorbed amounts of AF in competition with PQ or DQ but overestimated the amounts of adsorbed AF. We propose that steric restrictions imposed by low basal spacing in montmorillonite interacting with PQ or DQ reduce the amounts of adsorbed AF. This proposal is supported by X-ray diffraction measurements which yield basal spacing values of 1.3 nm when DQ and CV are added at amounts in excess of the CEC, whereas with CV alone the respective values were larger than 1.8 nm.

Complexes between organic cations and clays provide a research tool and have ecological applications. The purpose of this study was to elucidate details of interactions between monovalent organic cationic dyes and montmorillonite. Interactions were studied by x-ray diffraction and ultraviolet and infrared (IR) spectroscopies, IR linear dichroism, and adsorption isotherm measurements with model calculations. The adsorption model combined electrostatic equations with specific binding and considered neutral and positively charged complexes between surface sites and organic cations in a closed system. The model was extended to account for dye aggregation in solution. The adsorption of the dyes to montmorillonite was described by binding coefficients that were at least six orders of magnitude larger than those of inorganic cations such as Na + and Cd ++ . The maximal amounts of crystal violet (CV), methylene blue (MB), and acriflavin adsorbed were 200, 150, and 175%, respectively, of the cation-exchange capacity (CEC) of the clay mineral. The model also simulated the competition between dyes for adsorption sites. The c-spacing of montmorillonite increased by the adsorption of CV. With MB at loadings of up to 40% of the CEC, the spacing was reduced, indicating desorption of water from the interlayer space. We conclude that MB lies preferentially parallel to the clay mineral plates, whereas CV lies at a slight inclination relative to the plates

Methylene blue (MB) and crystal violet (CV) have been found to be adsorbed in amounts greater than the cation exchange capacity (CEC) of clays (Hang & Brindley, 1970; Ghosal & Mukherjee, 1972; Venugopal & Nair, 1974).In previous work (Rytwoet al., 1991), it was shown that CV adsorbs to montmorillonite up to 1·4 mmole dye/g clay. The amount of dye added in those experiments was up to 1·6 mM/g clay. Yet, when the added amount of CV and MB was 3·5 mM/g (Rytwoet al., unpublished), almost 1·6 (200% of the CEC) and 1·2 mM/g clay, respectively, were adsorbed. Margulieset al. (1988), who studied the adsorption of thioflavin T and MB to montmorillonite, showed that these dyes adsorb up to 1·4 and 1·2 mM dye/g clay, which corresponds to 175% and 150% of the CEC, respectively.

Mechanisms for the photostabilization of pesticides by the use of clays and chromophores are described. The main mechanisms include energy transfer and steric hindrance, whereas the importance of mechanisms such as light scattering and hypsochromic shift is marginal. As an example for energy transfer we describe a procedure where the potent and safe but photolabile insecticide bioresmethrin (BR) is coadsorbed on montmorillonite together with the organic cation methyl green (MG). It is shown that the effective photostabilization of BR occurs by the process of energy transfer, which depends on the matching of energy levels of donor (BR) and acceptor (MG) chromophores, on the distance between them and on their relative orientations. The methods for studying the intermolecular interaction between two coadsorbed organic molecules include Fourier-transform infrared (FTIR) and 13C solid state magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies. Energy transfer processes can also occur from the pesticide to the clay. The presence of transition metal ions in the clay can make it an efficient energy or charge acceptor. Such a mechanism was utilized in the photostabilization of the insecticide tetrahydro-2-(nitromethylene)-2H-1, 3-thiazine (NMH). In the latter case, improved photostabilization was achieved by an addition of the cationic dye acriflavine (AF). Steric hindrance: here the clay introduces a stereochemical factor in preventing or slowing down certain photochemical reactions. An example is the photostabilization of the dinitroaniline herbicide trifluralin (TF). The energy transfer approach was also shown to be effective in the photostabilization of microbial insecticides, such as the Bacillus thuringiensis (B.t.) toxin. Photoprotection was achieved by adsorption of cationic chromophores such as AF, MG and rhodamin B to B.t. © 1993 Wiley-Liss, Inc.

Ahstract--A procedure for the determination of cation exchange capacity (CEC) and the amounts of exchangeable cations adsorbed to montmorillonite is proposed. The method consists of a single incubation of the clay in a suspension containing a low concentration of an organic dye of large binding affinity, followed by analysis of the displaced inorganic cations by inductively-coupled plasma emission spectrometry (ICPES). The CEC is obtained by taking the largest sum of displaced exchangeable cations. Montmorillonite suspensions were incubated with methylene blue (MB) or crystal violet (CV) at dye concentrations below 4 mM, for one, three or fourteen days. For total dye concentrations up to the CEC, all the dye was adsorbed and equivalent amounts of exchangeable cations were released. Both dyes could adsorb to the clay in excess of the CEC. After one day of incubation in the presence of dye concentrations of about 50% in excess of the CEC, the total amounts of cations released were reduced to below the CEC. This reduction was interpreted as due to massive aggregation of the clay particles induced by the dye. With CV the total amounts of cations released after three or fourteen days of incubation increased and became equal to the CEC. The same CEC was found for Na-, Ca- and SWyl crude-montmorillonite, by employing either of the dyes.

8 pages, 5 figures, 1 table, 36 references., Atrazine and alachlor formulations were designed by encapsulating the herbicide molecules into phosphatidylcholine (PC) vesicles, which subsequently were adsorbed on montmorillonite. PC and montmorillonite are classified as substances of minimal toxicological risk by the U.S. EPA. PC enhanced alachlor and atrazine solubilities by 15- and 18-fold, respectively. A 6 mM PC:5 g/L clay ratio was found as optimal for PC adsorption on the clay. Active ingredient contents of the PC-clay formulations ranged up to 8.6% for atrazine and 39.5% for alachlor. Infrared spectroscopy showed hydrophobic interactions of herbicide molecules with the alkyl chains of PC, in addition to hydrophilic interactions with the PC headgroup. Release experiments in a sandy soil showed a slower rate from the PC-clay formulations than the commercial ones. Soil column experiments under moderate irrigation and bioactivity experiments indicate that a reduction in the recommended dose of alachlor and atrazine can be accomplished by using PC-clay formulations., The authors acknowledge financial support by the Spanish Ministry of Education and Science (Project AGL2005-00164) and Junta de Andalucía (Project P06-FQM-1909).

The effect of the ionic strength on adsorption of Cu on Ca-montmorillonite (SAz-1) was studied at concentrations ranging from 31 to 516 µM. An adsorption model was employed in the analysis of the data. When the background electrolyte was NaClO4 the ionic interchange was suppressed at 0.5 M, and Cu adsorption was taking place on edge sites, reaching a plateau at about 24 mmol/kg. A further increase in ionic strength did not make any effect on Cu adsorption, suggesting that the heavy metal was being adsorbed by inner sphere complexes on the edge sites. When the electrolyte used was NaCl the amounts of Cu adsorbed were reduced. The model predicted well the adsorption data by considering adsorption of CuCl+ species. Adsorption-desorption processes of Cu on Ca-montmorillonite in media of 0.01 and 0.1 M NaCl showed hysteresis. Model calculations predict the desorbed amounts fairly well. According to the model the hysteresis is mainly attributed to the heterogeneity of sites for the adsorption of Cu. The hysteresis arising from the planar sites is largely due to reduced competition for adsorption and enhancement in the magnitude of the surface potential. The presence of the cationic pesticide chlordimeform reduces strongly the sorption of the metal on the planar positions unlike the edge sites. However, Cu sorption increases on the clay treated previously with chlordimeform which was due to the opening of the clay platelets after some molecules of the pesticide are adsorbed, facilitating the subsequent penetration of the metal and its adsorption on planar positions. This cooperative adsorption was due to the fact that the loading of the pesticide on the clay was a very small amount of the CEC.

Removal of anionic pollutants (imazaquin, sulfentrazone, sulfosulfuron) and neutral pollutants (alachlor, acetochlor, chlorotoluron, bromacil) from water by micelles preadsorbed on montmorillonite was studied. Micelles of octadecyltrimethylammonium and benzyldimethylhexadecylammonium (BDMHDA) were used. The micelle-clay systems (1% w/w) removed 87-99% of the pollutants from their water solutions containing 1-33 mg/L of herbicide. The nature of the headgroup of the organic cation, which forms the micelles, is critical. Desorption of imazaquin and acetochlor from 0.3% (w/w) suspension of BDMHDA-clay complex after 24 h was around 7% in the range of adsorbed amounts from 0.6 to 15.3 mg/g. These results indicate rather slow rates and small extents of release of pollutants from micelle-clay complexes. Column filters (25 cm) made of a mixture of quartz sand and BDMHDA micelle-clay complex at 100:1 w/w ratio removed at least 99% of above pollutants from initial solutions containing 10 mg/L; 99.5 and 97% of sulfosulfuron and alachlor were removed from their initial solutions containing 200 and 5 microg/L, respectively. These data indicate that micelle-clay complexes are very efficient for water purification from organic contaminants.

Engineering of clay nanocomposite materials by modification of their surfaces can enable the control of retention, transport, and persistence of toxic chemicals in the geosystem. The properties and interactions of clay nanocomposites have been widely studied, but little information exists on their microstructure at a range of scale extending down to atomic dimensions. The pairing of Na-montmorillonite clay with organic cations as well as with the herbicide fluridone, chosen as a model for an organic pollutant, was studied. Three organic cations were selected: hexadecyltrimethylammonium, benzyltrimethylammonium, and benzyltriethylammonium at 0%, 60%, and 100% of cation exchange capacity (CEC) loadings. A detailed microstructural analysis of the organo-clay nanocomposites and of the fluridone nanocomposites was undertaken by high-resolution transmission electron microscopy (HRTEM) and X-ray energy-dispersive spectroscopy (EDS). Morphological observations and chemical analyses were performed simultaneously on the same sample. The combined HRTEM and EDS measurements strongly suggest (a) heterogeneous local intercalation of the organic cations manifested by a range in the measured d001 spacing, implying random expansion of the clay layered structure with increased loading of the organic cations; (b) intercalation within the external layers, which is thoroughly influenced by local defect microstructure and/or edge availability of the montmorillonite nanoparticles as well as by the molecular structure of the intercalating organic cation. Additional intercalation of fluridone molecules did not affect the structure (d001 spacing) of the organo-clay nanocomposites.

6 pages, 5 tables, 2 figures, 26 references. The authors acknowledge Dr. Justo for help in the XRD section., Clay-vesicle systems exhibit a potential for environmental applications, such as herbicide formulations for reduced leaching. Clay-vesicle interactions were addressed by combining adsorption and XRD measurements with fluorescence studies for didodecyldimethylammonium bromide (DDAB), dioctadecyldimethylammonium bromide (DDOB), and montmorillonite. XRD and adsorption data indicated that the adsorbing vesicles were transformed after 3 days into paraffinic and bilayer structures. Fluorescence studies revealed that adsorption was almost complete within 5 min for a loading below the cation exchange capacity (CEC). Aggregation and sedimentation of clay-surfactant particles occurred within several minutes. Fluorescent measurements of supernatants indicated decomposition of vesicles at a high clay/surfactant ratio due to rapidly adsorbing cationic monomers. The kinetics of energy transfer between vesicles labeled by NBD-PE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)) and montmorillonite labeled by rhodamine-B follows that of aggregation of surfactant-clay particles and structural changes of the vesicles at times of minutes to hours. Experiments following the reduction of NBD fluorescence by addition of dithionite indicate faster permeabilization of DDOB than DDAB vesicles, which was confirmed by leakage experiments. The faster permeabilization of DDOB vesicles in the presence of clay was correlated with their inferior suitability for the preparation of clay-based formulations of anionic herbicides for slow release., Financial support of the Spanish Ministry of Science and Technology under projects AGL2002-00993 and REN2000-1540 and Junta de Andalucia (PAI RNM166) is acknowledged herewith. Dr. Undabeytia is also grateful to the Spanish Government for a Ramon y Cajal research contract.

7 pages, 3 figures, 5 tables, 34 references., The effect of the ionic strength on adsorption of Cu on Ca-montmorillonite (SAz-1) was studied at concentrations ranging from 31 to 516 BM. An adsorption model was employed in the analysis of the data. When the background electrolyte was NaClO4 the ionic interchange was suppressed at 0.5 M, and Cu adsorption was taking place on edge sites, reaching a plateau at about 24 mmol/kg. A further increase in ionic strength did not make any effect on Cu adsorption, suggesting that the heavy metal was being adsorbed by inner sphere complexes on the edge sites. A binding coefficient for Cu2+ on the edge sites K= 2x104 M-1 was determined indicating very high affinity of Cu2+ for these sites. When the electrolyte used was NaCl the amounts of Cu adsorbed were reduced. The model predicted well the adsorption data by considering adsorption of CuCl+ species. Adsorption-desorption processes of Cu on Ca-montmorillonite in media of 0.01 and 0.1 M NaCl showed hysteresis. Model calculations predict the desorbed amounts fairly well. According to the model the hysteresis is mainly attributed to the heterogeneity of sites for the adsorption of Cu. The hysteresis arising from the planar sites is largely due to reduced competition for adsorption and enhancement in the magnitude of the surface potential., Dr. Undabeytia acknowledges the European Community (Contract N. FAIR-BM- 970892) for a postdoctoral fellowship at the Seagram Centre and the Spanish Government for a research contract (ref. AMB98-0888) at the Institute of Natural Resources and Agrobiology.

This study aimed to design ecologically acceptable formulations of acetochlor by adsorbing it on montmorillonite exchanged by a small organic cation, phenyltrimethylammonium (PTMA). Adsorption of acetochlor on the clay mineral exchanged with different organic cations and its release from these complexes were determined by GC and modeled by Langmuir equation. Interactions between acetochlor molecules and the exchanged organic cation on the clay surface were studied by Fourier transform infrared spectroscopy. Leaching of acetochlor in soil was determined by a bioassay using a column technique and Setaria viridis as a test plant. The adsorbed amounts of acetochlor on montmorillonite exchanged by PTMA at a loading of 0.5 mmol/g of clay were higher than at a loading up to the cation-exchange capacity, i.e., 0.8 mmol/g, and were higher than obtained by using a clay mineral exchanged by other organic cations. Preloading montmorillonite by PTMA at 0.5 mmol/g yielded maximal shifts of the infrared peaks of the herbicide. The above formulation of acetochlor yielded slow release in water and showed improved weed control in field and greenhouse experiments in comparison with the commercial formulation. The PTMA-clay formulation of acetochlor maintained herbicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching and persistence under field conditions. The application of this formulation can minimize the risk to groundwater and can reduce the applied rates.

The study aimed to reduce leaching of the hydrophobic herbicide norflurazon (4-chloro-5-methylamino-2-(alpha,alpha,alpha)-trifluoro-m-tolylpyridazin-3-(2H)-one)by adsorbing it on clays or organoclays. The surface of the clay mineral montmorillonite was modified from hydrophilic to hydrophobic by preadsorbing it with organic cations, of which thioflavin-T (TFT) at a loading corresponding to 5/8 of the cation-exchange capacity of the clay mineral yielded the highest affinity of adsorption of norflurazon. Pillared clay (PC): used without organic cations exhibited enhanced affinity for norflurazon adsorption, much higher than that of montmorillonite or sepiolite. Fourier transform infrared (FTIR) results showed interactions between aromatic moieties of preadsorbed TFT and the herbicide. Stronger interaction of the herbicide with a clay mineral or organo-day corresponded to its slower release. Formulations prepared on the basis of montmorillonite-TFT and PC were more effective in reducing herbicide leaching in soil columns in; comparison to the commercial formulation, whereas the herbicidal efficiencies were comparable.

This study aimed to design formulations of hydrophobic herbicides, alachlor and metolachlor, by adsorbing them on the clay mineral montmorillonite preadsorbed by the small organic cation phenyltrimethylammonium (PTMA). An adsorption model that considers electrostatics and specific binding and the possibility of cation adsorption above the cation exchange capacity (CEC) could explain and yield predictions for PTMA adsorption in the presence of NaCl concentrations from 0 to 500 mM. Adsorption of alachlor and metolachlor from aqueous solution on a clay mineral preadsorbed by PTMA was determined by GC and modeled by Langmuir equation. Herbicide interactions with the organoclay were studied by Fourier transform infrared spectroscopy. Leaching of herbicides was determined by a bioassay using a column technique and Setaria viridis as a test plant. The adsorbed amounts of alachlor and metolachlor on montmorillonite preadsorbed by PTMA at a loading of 0. 5 mol/kg (Mont-PTMA0.5) were higher than at a loading up to the CEC, that is, 0.8 mol/kg, and were higher than those obtained by using several other organic cations. Herbicide formulations based on Mont-PTMA0.5 yielded the largest shifts of the infrared peaks of the herbicides. These formulations based on Mont-PTMA0.5 gave slower release and showed improved weed control in comparison with formulations based on other organoclays. These formulations maintained herbicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching.

This study aimed to optimize organo-clay formulations for reduction of leaching of the herbicides alachlor, metolachlor, and norflurazon, which include a phenyl ring in the structure. The adsorbed amounts of herbicides increased severalfold when montmorillonite was preadsorbed by an organic cation; benzyltrimethylammonium (BTMA) was more effective than benzyltriethylammonium (BTEA). Fourier transform infrared studies indicated interactions between alachlor molecules and adsorbed BTMA. The adsorption affinity of the herbicides increased with BTEA loading up to the cation exchange capacity (CEC) of montmorillonite but reached a maximum at a BTMA loading of 5/8 of the CEC. The enhanced adsorbed amounts of herbicides are mainly due to interactions between the phenyl rings of herbicide molecules and organic cations, which are favored with the smaller cation, BTMA.BTMApreadsorbed on the clay up to the CEC forms a fraction (14-18%) of charged dimers so that less phenyl rings are available for interacting with herbicide molecules. This effect is small for preloading by BTEA, so that the amounts adsorbed increase with the degree of preloading. Thus, optimization of claybased herbicide formulations requires a selection of structurally compatible organic cations preadsorbed on the clay at optimal coverage.

Effect of the aggregation state of montmorillonite clays of types SAz-1 and SWy-1 on the adsorption of the monovalent organic cation chlordimeform was studied. The shapes of the adsorption isotherms were related to the degree of dispersion of the clay, changing from S- to L-type by decreasing clay concentration. Unlike monovalent organic cations denoted dyes, chlordimeform adsorption did not exceed the cationic exchange capacity of the clay (CEC). At larger Ca2+/Na+ charge ratio (≃0.5), chlordimeform exhibited low apparent affinity for adsorbing to the SAz-1 clay, due to steric inhibition of its penetration between closely opposed clay platelets. The apparent affinity increased dramatically at smaller Ca2+/Na+ charge ratios (

6 pages, 1 figure, 5 tables., Adsorption-desorption of Cd to Ca montmorillonite (SAz-1) was studied at concentrations ranging from 44.5 to 266.8 IzM. An adsorption model was employed in the analysis of the data. The procedure consists of solving the electrostatic Gouy-Chapman equations and calculating adsorbed amounts of the cations as the sum of the cations residing in the double-layer region, and the cations chemically bound to the surface, in a closed system. The model also accounts explicitly for cation complexation in solution. The model yields good predictions for the adsorbed amounts of Cd, Ca and Mg, by employing binding coefficients from previous studies for the divalent cations and for Na, K and CdCI +. The model calculations also yield good predictions for the apparent hysteresis observed in the adsorbed amounts of Cd after each of 3 cycles of desorption. The apparent hysteresis is explained by the reduction in the total concentrations of Ca and Mg in desorption cycles, and the corresponding increase in the magnitude of the surface potential. Our estimates indicate that adsorption of Cd is mostly to planar, rather than edge sites of the clay mineral., This work was mostly supported by funds from the Spanish Government, Research Project AMB95-0904. T. Undabeytia acknowledges the Spanish Government for a postdoctoral fellowship (ref. PF96 33975424) at the Seagram Center.

The adsorption on montmorillonite of two monovalent organic cations, methylene blue (MB) and thioflavin T (TFT), was studied in four different situations: (1) separate adsorption of MB or TFT; (2) competitive adsorption of TFT and Cs; (3) competitive adsorption of the two organic cations from their equimolar solutions; and (4) adsorption of TFT on a clay whose cation-exchange capacity (CEC) had been previously saturated with MB. MB and TFF adsorbed to as much as 120% and 140% of the CEC, respectively. Cs did not appear to compete with TFT for the adsorption sites of the clay. TFT molecules adsorbed more strongly than those of MB and displaced them from the clay surface. A model was developed to evaluate the strength of the clay-organic cation interactions. The specific binding of the cations to the negatively charged surface, determined by solving the electrostatic equations, appears to account for adsorption exceeding the CEC and formation of positively charged complexes, which are due to non-coulombic interactions between the organic ligands. The charge reversal predicted by the model beyond the CEC of the clay was confirmed by microelec- trophoretic experiments. Particles in a sample of montmorillonite loaded with 50 meq TFT/100 g clay moved to the positive electrode, whereas in samples containing the two dyes, MB and TFT, coadsorbed at a total concentration of 100-120 meq/100 g clay, the particles moved to the negative electrode. Binding coefficients describing the formation of neutral and charged complexes of TFT and the clay were larger than those for MB and the clay, thereby explaining the preferential adsorption of TFT observed exper- imentally. The binding coefficients for the formation of neutral complexes of either MB and TFT and the clay were more than six orders of magnitude larger than those previously reported for inorganic

The purpose of this study is to elucidate details of the interactions between the divalent cationic herbicides diquat (DQ) and paraquat (PQ) and montmorillonite. Interactions were studied by ultraviolet absorption (UV) and linear dichroism infrared (LDIR) spectroscopies, x-ray diffraction, and adsorption isotherm measurements. For added herbicide amounts below the cation-exchange capacity (CEC) of the clay, adsorption was almost complete. At saturation, the adsorption of DQ was 125% of the CEC, whereas PQ adsorbed up to the CEC. In competitive adsorption experiments, when total cationic charges exceeded the CEC, monovalent organic cations were preferentially adsorbed to the clay at the expense of the divalent cations, in accord witb the expected larger exclusion of divalent cations from positively charged surfaces. Adsorption of the divalent herbicides reduced the basal spacing of the clay from 1.45 nm to 1.30 nm. This result implies the desorption of interlayer water and can be explained in terms of the flat orientation of the adsorbed PQ cation and the compact size and keying of the DQ cation into the ditrigonal cavity of the basal surface of the clay. This explanation is also supported by LDIR results. For adsorption up to the CEC, the main UV absorption bands of the herbicides around 300 nm were red shifted. The absorption spectrum of DQ adsorbed beyond the CEC suggests that some of the molecules were attached to the clay via weaker interactions, similar to the mechanisms found for monovalent organic cations. In view of the low basal spacing of the clay, the observed red shift cannot be due to the existence of DQ or PQ dimers.

The adsorption of the monovalent organic cations benzyltrimethylammonium (BTMA) and benzyltriethylammonium (BTEA) to montmorillonite was studied as a function of their concentrations and ionic strength. At low ionic strength the adsorbed amounts of BTMA and BTEA reached values of the cation exchange capacity (CEC) of the clay. An increase in the ionic strength resulted in reduction in the adsorbed amounts of the organic cations, unlike the pattern observed previously with organic monovalent cationic dyes. The reduction in adsorbed amounts of BTMA and BTEA depended on the inorganic cations according to the sequence Cs + > Na + > Li +, which follows the sequence of binding coefficients of these inorganic cations added. The type of the anion (that is, C1 , C104-, SO4 z ) had no effect on the adsorbed amounts. An adsorption model which considers the electrostatic Gouy~Chapman equations, specific binding and closeness of the system could adequately simulate the adsorbed amounts of BTMA and BTEA and yield predictions for the effect of the ionic strength and concentration of electrolytes. The binding coefficient employed was K = 5000 M ~ for the formation of neutral complexes of BTMA and BTEA. This value is larger than those found for the inorganic cations but is several orders of magnitude below those found for the monovalent dyes. The binding coefficients for the formation of charged complexes of BTMA and BTEA were 20 and 5 M ~, respectively. The basal spacing of the clay did not change significantly with the adsorbed amounts of both BTMA and BTEA up to the CEC.

The exchange reactions of Na, Ca and Mg on montmorillonite are revisited employing recently developed analytical and theoretical approaches. The fractional adsorption of the cations has been deter- mined by displacing them from the adsorbed state in one step, using a low concentration of an organic cation of large binding affinity. The analysis of displaced and solution cations employed inductively coupled plasma emission spectrometry. An adsorption model was employed in the analysis of the data. The procedure consists of solving the electrostatic Gouy-Chapman equations and calculating adsorbed amounts of the cations as the sum of the cations residing in the double layer region, and the cations chemically bound to the surface, in a closed system. The model also accounts explicitly for cation complexation in solution. Thus the calculations also considered the adsorption of CaC1 + and MgCI +, which eliminated the apparent increase of the cation exchange capacity (CEC) with divalent cation con- centration. The model could explain and yield predictions for our measured adsorbed amounts as well as previously published data, in the binary and ternary systems of Ca/Mg/Na, provided that the fraction of surface sites occupied by calcium did not exceed 0.4. For a larger coverage of surface sites by calcium, a fit of the experimental data required an order of magnitude increase in the binding coefficients of the divalent cations in the binary system Ca/Na and in the ternary system Ca/Mg/Na.