Entrapping pesticides by coagulating smectites

Highly delaminated montmorillonite (from Wyoming) with a high specific surface area when dispersed in water was used as an adsorbent of the hydrophobic herbicide metolachlor. The montmorillonite was coagulated with Na⁺, Ca²⁺, Al³⁺ and benzyl trimethylammonium ions. Ca²⁺ and Al³⁺ screened the surface charges and the adsorption of metolachlor was strongly enhanced by the interaction of metolachlor with the hydrophobic siloxane oxygen atoms and the water molecules of the hydration shell of the interlayer cations. With increasing salt concentration the mechanism changed from a cooperative adsorption process on a heterogeneous surface (S-type isotherm) to adsorption on a homogeneous surface (L-type). Coagulation with Ca²⁺ and Al³⁺ increased the amounts of metolachlor adsorbed from 14–41% (Na⁺) to 57–86% (Ca²⁺) and 67–91% (Al³⁺). The light microscopic images revealed that increasing amounts of metolachlor changed the band-type network into spherical “potato-like” aggregates. The enhanced herbicide adsorption hydrophobized the particles that crowded together to form spherical aggregates. Entrapping the herbicide molecules in clay mineral aggregates—either band-type networks or spherical aggregates—offers a useful tool in creating leaching-resistant herbicide formulations.     

Interactions of pendimethalin with organo-montmorillonite complexes

Pendimethalin (PM) is a dinitroaniline herbicide, highly hydrophobic and with a very low solubility in water. It is used for pre-emergence weed control, is usually applied before sowing, and mechanically incorporated into the soil. We tested sorption of PM on montmorillonite and on two different organo-montmorillonites in a mixed water–chloroform environment, to determine the feasibility of developing an environmentally oriented formulation of the herbicide. FTIR measurements show that the interactions of PM with montmorillonite on which difenzoquat (DZ) or mepiquat (MQ) were previously adsorbed are via the nitro and methyl groups of the herbicide. The pre-adsorbed organocations cause a dehydration of the interlayer space, leading to hydrophobicity of the organoclay. Changes in the electrokinetic surface charge of the organoclay, measured using a particle charge detector, confirm these results. The high affinity to PM and the hydrophobic behavior of the used organoclays were also demonstrated in experiments using a mixed chloroform–water environment. The crude clay mineral stayed in the water phase, whereas DZ- and MQ-montmorillonites concentrated in the PM-chloroform phase. Amounts of PM adsorbed to the organoclays using this method were very high (up to 0.65 mol PM kg⁻¹ compound), which suggests a very efficient technology of preparation of herbicide-clay formulations, compared with techniques used in the past for similar herbicide-organoclay compounds. Plant experiments using the organoclay-herbicide formulation with higher amount of active ingredient (based on DZ-clay) demonstrate efficient herbicidal activity with 30% less active ingredient.     

Carboxylmethylcellulose/bentonite composite gels: Water sorption behavior and controlled release of herbicide

The composite gels were prepared by adding bentonite or its acid‐activated derivative into the carboxylmethylcellulose (CMC) gel, and the resulted products were characterized with infrared spectroscopy. Different from ordinary swellable hydrogels, the CMC/bentonite hydrogel beads shrinked in water. The water sorption of dried gels was limited below 120% of their own weight, and a sorption equilibrium reached quickly within 20–40 min. The water of swollen gels exists mainly in bound status according to the DSC analysis. The release experiments in water were carried out to evaluate the release of herbicide metolachlor from gel formulations. The release mechanism dominated by a Fickian diffusion might be related to the quick and limited swelling of dried gels. Addition of bentonites in CMC gel is beneficial for slowing the release of metolachlor, especially when the acid‐activated bentonite was added. The time taken for 50% of metolachlor to be released, t₅₀ was prolonged to 158 h for the composite gel formulation based on acid‐activated bentonite from the 61.1 h for pure CMC gel formulation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Slow diuron release formulations based on clay–phosphatidylcholine complexes

Slow release formulations of the herbicide diuron were designed to reduce the risk of water pollution resulting from conventional formulations. The new formulations were based on herbicide incorporation in phosphatidylcholine (PC) vesicles that were sorbed on the clay mineral montmorillonite. The active ingredient contents of the formulations reached up to 28% w:w. Thermal analysis revealed that the closely packed arrangement of PC on the clay enhanced diuron sorption by disrupting the interactions among PC molecules. Adsorption experiments using diuron were performed in soils with different physico-chemical properties to evaluate the relationship between the sorption and the mobility of the herbicide. In soil column experiments with sandy soil, the herbicide in PC–clay-based formulations mainly accumulated in the top soil, and there was a one-third reduction in leaching compared to the commercial formulation. The differences in leaching (compared to the commercial formulation) were lower when using loam soil due to its higher sorption of the herbicide and hysteresis effects. In the sandy soil, bioassay experiments showed a higher herbicidal activity in the top-soil layer for the PC–clay formulations than for the commercial formulation. Therefore, PC–clay formulations of this herbicide can be used at lower doses than recommended, thereby reducing the environmental risks associated with the application of diuron formulations.     

Adsorption of difenzoquat on montmorillonite: model calculations and increase in hydrophobicity

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 mol_c/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.     

Improved efficiency of a divalent herbicide in the presence of clay, by addition of monovalent organocations

A severe decrease in efficacy of contact herbicides such as diquat (DQ) is caused by dust accumulated on the weeds. Such inactivation was explained by the adsorption of herbicides on dust particles. As a result of this inactivation, the rates of pesticides needed for efficient pest control are usually larger than the recommended rates, which increases the expenses, and pose a real danger to the environment and to the ecological balance of watersheds. We proposed the hypothesis that the addition of a monovalent organic cation to the herbicide formulation might improve the efficacy by lowering the amount of herbicide that is inactivated by the sorption to clay minerals. This hypothesis was tested on lettuce and pepper plants dusted with clay, using the commercial formulation of diquat (“Reglone”) and adding the monovalent organic cations acriflavin (AF) and mepiquat (MQ). We observed that a clay mineral with a high cation exchange capacity (CEC), such as montmorillonite, reduced the herbicidal activity of DQ more than a lower CEC clay as sepiolite. However, addition of 5–20 mM concentrations of AF or MQ may overcome the influences of a clay dust on the activity of a cationic herbicide. Such addition allowed the obtainment of good herbicidal results with less than 1/3 of the normal used amount of herbicide. The results of our research point out to a mechanism that may lower the needed doses of contact herbicides, due to a competitive adsorption on the clay–dust particles between the pesticide and monovalent organic cations that leaves more herbicide available to act on the weed.     

Sepiolite-based materials for the photo- and thermal-stabilization of pesticides

The present work is related to the use of sepiolite for the stabilization of certain photo or thermolabile herbicides by their adsorption on sepiolite-modified materials that act as organo-inorganic supports of the pesticides. The study demonstrates that formulations based on sepiolite containing a cationic dye (thioflavine-T (TFT)) are very effective in the stabilization of a photolabile herbicide (trifluralin (TF)). A modification of the hydrophilic character of the sepiolite surface by adsorption of cationic surfactants enhances the adsorption on the mineral substrate of non-polar pesticides, such as the herbicides alachlor (ACH) or metolachlor (MCH), thus contributing to the decrease of their losses by volatilization.     

Influence of organoclay and preparation technique on the morphology of polyamide6/polystyrene/organoclay nanocomposites

To have an improved insight about the compatibilization effect of organoclay on immiscible polymers, two different organoclays and preparation techniques were chosen to prepare polyamide6 (PA6)/polystyrene (PS)/organoclay ternary nanocomposites. The morphology analysis based on the results of X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy demonstrated that the type of organoclay and preparation technique had a significant influence on the dispersion and distribution of organoclay in the polymer. It was concluded that blending PS/organoclay nanocomposite synthesized previously via in situ bulk polymerization, with PA6 can realize the full exfoliation of organoclay in the final ternarynanocomposite, while an intercalated structure was achieved by directly blending the three components. The distribution of organoclay could be controlled by tuning the surface property of clay, and hence the interfacial interaction between clay and the polymer matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Organoclays for soil remediation: Adsorption of 2,4-dichlorophenol on organoclay/aquifer material mixtures studied under static and flow conditions

A column material containing organophilic clay particles was developed for soil remediation. 2,4-dichlorophenol adsorption on aquifer material with an effective particle diameter d < 1 mm and various partially modified dioctadecyldimethylammonium–montmorillonite/aquifer material mixtures were studied under static and flow conditions. The 2,4-dichlorophenol adsorption on the aquifer material was negligible. On organoclay/aquifer material mixtures the adsorption capacity increased with increasing organoclay content and the adsorption isotherms could be fitted by the Freundlich equation. In columns filled with organoclay/aquifer material mixtures, the 2,4-dichlorophenol retardation increased with increasing organoclay content up to 1% (w / w). Above 1.5–2.0% (w / w) the permeability of the column material decreased. The HYDRUS_1D model, which solves the convection–dispersion equation for solute transport, was used in a forward and inverse mode to simulate 2,4-dichlorophenol breakthrough in the columns. The simulations revealed that 2,4-dichlorophenol transport exhibited an additional kinetic effect not observed in the batch experiments.     

XRD study of intercalation in statically annealed composites of ethylene copolymers and organically modified montmorillonites. 2. One-tailed organoclays

Ethylene copolymers with different polar comonomers, such as vinyl acetate, methyl acrylate, glycidyl methacrylate, and maleic anhydride, were used for the preparation of polymer/clay nanocomposites by statically annealing their mechanical mixtures with different commercial or home-made organically modified montmorillonites containing only one long alkyl tail. The nanostructure of the products was monitored by X-ray diffraction, and the dispersion of the silicate particles within the polymer matrix was qualitatively evaluated through microscopic analyses. The effect of the preparation conditions on the structure and the morphology of the composites was also addressed through the characterization of selected samples with similar composition prepared by melt compounding. In agreement with the findings reported in a previous paper for the composites filled with two-tailed organoclays, intercalation of the copolymer chains within the tighter galleries of the one-tailed clays occurs easily, independent of the application of a mechanical stress. However, the shear-driven break-up of the intercalated clay particles into smaller platelets (exfoliation) seems more hindered. A collapse of the organoclay interlayer spacing was only observed clearly for a commercial one-tailed organoclay – Cloisite^® 30B – whereas the same effect was almost negligible for a home-made organoclay with similar structure.     

Interlayer expansion of dimethyl ditallowylammonium montmorillonite as a function of 2-chloroaniline adsorption

The expansion behaviour of an organically modified montmorillonite during the adsorption of increasing amounts of an organic pollutant: 2-chloroaniline (2-CA). The organophilic montmorillonite, a commercial product, was obtained exchanging the inorganic cation with dimethyl ditallowylammonium ions (DMDTA). 2-CA was added to the organoclay, starting from 193.9 ppm up to 23,531.7 ppm going through twenty-two steps of growing quantities of 2-CA. For each of these twenty-two steps – corresponding to a range of adsorbed 2-CA (C_s) between 0.029 mol/kg (grams of 2-CA per kg of organoclay) and 2.763 mol/kg – the basal spacings were determined.The adsorption isotherm was performed according to ASTM D 4646-87 Standard and, by comparing the experimental C_s data with the corresponding d₀₀₁ values, the basal expansion of the polluted organoclay is characterized by a steep rise for the first steps of adsorption of 2-CA (concentration in water at equilibrium C_w < 0.00373 mol/L), then the d₀₀₁ remains almost constant up to the higher amounts of pollutant adsorbed.The 001 reflections are sharper, their intensity higher, and up to four orders of 00l reflections are observed as the uptake of 2-CA increased. Since in aqueous solution the staking of organoclay platelets is poorly ordered, the observed behaviour may be partially explained by the 2-CA sorbed on the external surface of the clay mineral particles, which brings the silicate layers together.Finally, a tentative interpretation of the adsorption phenomena was carried out by fitting the experimental data according to the most common theoretical models: Freundlich, Langmuir, Dual Mode and Dual Langmuir Model.     

Adsorption and desorption of m-xylene vapor on organically modified montmorillonite

m-Xylene vapor was adsorbed to organically modified montmorillonite (organoclay). Hexadecyltrimethylammonium (HDTMA) was used to modify the surface of the clay. In adsorption experiments, the organoclay, along with the non-modified (washed) clay, was used. m-Xylene was adsorbed from a gaseous phase by using a fixed adsorption bed. The adsorption breakthrough curves and the adsorption isotherms were determined at three different temperatures (24, 34, and 44 °C). The adsorption data were modeled with the BET isotherm equation. It was found that the adsorption isotherms of washed clay exhibited a favorable Type I behavior, which implies that the adsorption capacity is strongly dependent on vapor concentration at low concentration ranges. In regards to the organoclay, isotherms showed a marginally favorable Type II behavior with a reduced adsorption capacity at low concentrations, and exhibited a linear increase at elevated vapor concentrations. The adsorption capacity of both washed clay and organoclay obviously decreased with the temperature. The desorption of m-xylene from the clays was also performed by using pure nitrogen, and the desorption rate constant k was on the order of 10⁻⁵ min⁻¹ for all types of clay.     

Interlayer expansion of dimethyl ditallowylammonium montmorillonite as a function of 2-chloroaniline adsorption

The expansion behaviour of an organically modified montmorillonite during the adsorption of increasing amounts of an organic pollutant: 2-chloroaniline (2-CA). The organophilic montmorillonite, a commercial product, was obtained exchanging the inorganic cation with dimethyl ditallowylammonium ions (DMDTA). 2-CA was added to the organoclay, starting from 193.9 ppm up to 23,531.7 ppm going through twenty-two steps of growing quantities of 2-CA. For each of these twenty-two steps – corresponding to a range of adsorbed 2-CA (C_s) between 0.029 mol/kg (grams of 2-CA per kg of organoclay) and 2.763 mol/kg – the basal spacings were determined.The adsorption isotherm was performed according to ASTM D 4646-87 Standard and, by comparing the experimental C_s data with the corresponding d₀₀₁ values, the basal expansion of the polluted organoclay is characterized by a steep rise for the first steps of adsorption of 2-CA (concentration in water at equilibrium C_w < 0.00373 mol/L), then the d₀₀₁ remains almost constant up to the higher amounts of pollutant adsorbed.The 001 reflections are sharper, their intensity higher, and up to four orders of 00l reflections are observed as the uptake of 2-CA increased. Since in aqueous solution the staking of organoclay platelets is poorly ordered, the observed behaviour may be partially explained by the 2-CA sorbed on the external surface of the clay mineral particles, which brings the silicate layers together.Finally, a tentative interpretation of the adsorption phenomena was carried out by fitting the experimental data according to the most common theoretical models: Freundlich, Langmuir, Dual Mode and Dual Langmuir Model.     

Fe-pillared clay mineral-based formulations of imazaquin for reduced leaching in soil

Slow release formulations of the herbicide imazaquin (2-(4-isopropyl-4-methyl-5-oxo-4,5-dihydro-1H-imidazol-2-yl)quinoline-3-carboxylic acid) were prepared by its adsorption on Fe-pillared clay minerals (Fe PILCs). Fe PILCs were synthesized by the reaction of Na⁺-montmorillonite (SWy-2) with base-hydrolyzed solutions of Fe and Al. The Fe/(Fe + Al) ratios used were 0, 0.05, 0.15 and 0.50. Fe PILCs showed basal spacing values of 5.2 and 1.8 nm which were due to iron clusters between delaminated clay layers, and intercalated aluminum polyoxocations, respectively. As iron content increased, the pillaring process yielded PILC with lower microporosity and larger mesoporosity. The affinity of imazaquin on Fe PILCs was very high relative to Al PILC, as revealed in its higher herbicide adsorption values and lower desorption percents. Competitive adsorption of anions such as sulfate, phosphate and chloride provided evidence of formation of inner sphere complexes of imazaquin on Fe PILCs. Slow release formulations were prepared by enhanced adsorption of the herbicide from imazaquin–cyclodextrin (CD) complexes in solution. CDs were able to enhance up to 8.5-fold the solubility of imazaquin, by the formation of inclusion complexes where the quinolinic moiety of the herbicide was partially trapped within the CD cavity. Release of the herbicide in sandy soil was about 1/2-fold lower from Fe PILC formulations relative to the commercial formulation.     

Facile Hydrothermal Synthesis of Hierarchical Sodium P Zeolite as a Nonphosphate Detergent Builder

This study reports the preparation of hierarchical NaP zeolite with the aim of obtaining a non-phosphate detergent builder as an alternative for environmental remediation from eutrophication phenomenon. Hierarchically structured NaP zeolite was easily synthesized hydrothermally and under different syntheses conditions. Samples were characterized using several standard techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and N₂ adsorption–desorption analysis. Three powder detergents were prepared by mixing main components such as linear alkylbenzene sulfonate, sodium sulfate, sodium silicate, and sodium carbonate as well as different amounts of as-synthesized zeolite and sodium tripolyphosphate in the detergent formulation as potential detergency builders. Some different detergency tests as pH value, water insolubility, foam height, moisture content, alcohol insolubility, and surface tension measurement were carried out for all synthetic detergent samples and two commercial ones. The results demonstrated that the high cleaning performance of the powders was obtained as using eco-friendly zeolite builders in comparison with phosphate-based commercial and synthetic detergent samples.     

Photosensitive poly(amic acid)/organoclay nanocomposites

A project was carried out aimed at reducing the coefficient of thermal expansion (CTE) of photosensitive polyimide formulations (photoresists) through the incorporation of small amounts of an organoclay. The organoclay was formed by a cation exchange reaction between a NA⁺-montmorillonite clay and an ammonium salt of dodecylamine. Two polyimide precursors, a poly(amic ester) (PAE) and a poly(amic acid) (PAA), were used in this study. The PAE was prepared by direct polymerization of 2,2′-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane and bis(n-butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. The polymer had an inherent viscosity of 0.23 dL/g. The PAA copolymer was prepared by polymerization of pyromellitic dianhydride, oxydiphthalic anhydride and oxydianiline. The polymer had an inherent viscosity of 1.00 dL/g. Two photosensitive resin/clay formulations were prepared from these two PI precursors using 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy)-benzophenone as the photosensitizer and 3 wt% organoclay. The films obtained from the PAA formulation were transparent and tough, while the films prepared from the PAE formulation were opaque and brittle. Both X-ray diffraction and transmission electron microscope analyses showed that, although the organoclay was not dispersed well in the PAE matrix, it was dispersed in the PAA matrix on a nanometer scale. The clay particles remained well dispersed after the PAA film was thermally imidized. The CTE of the polyimide film obtained was 23% lower than that of a similar film that did not contain the organoclay. The temperature at which the polyimide underwent a 5% weight loss when subjected to TGA in nitrogen was also increased by 13%. The photosensitive PAA/clay nanocomposite showed a sensitivity of 301 mJ/cm² and a contrast of 1.66 when a 0.2 wt% tetramethylammonium hydroxide developer was used. A line/space pattern with a resolution of 10 μm was obtained from this formulation.     

Preparation and evaluation of novel mixed micelles as nanocarriers for intravenous delivery of propofol

Novel mixed polymeric micelles formed from biocompatible polymers, poly(ethylene glycol)-poly(lactide) (mPEG-PLA) and polyoxyethylene-660-12-hydroxy stearate (Solutol HS15), were fabricated and used as a nanocarrier for solubilizing poorly soluble anesthetic drug propofol. The solubilization of propofol by the mixed micelles was more efficient than those made of mPEG-PLA alone. Micelles with the optimized composition of mPEG-PLA/Solutol HS15/propofol = 10/1/5 by weight had particle size of about 101 nm with narrow distribution (polydispersity index of about 0.12). Stability analysis of the mixed micelles in bovine serum albumin (BSA) solution indicated that the diblock copolymer mPEG efficiently protected the BSA adsorption on the mixed micelles because the hydrophobic groups of the copolymer were efficiently screened by mPEG, and propofol-loaded mixed micelles were stable upon storage for at least 6 months. The content of free propofol in the aqueous phase for mixed micelles was lower by 74% than that for the commercial lipid emulsion. No significant differences in times to unconsciousness and recovery of righting reflex were observed between mixed micelles and commercial lipid formulation. The pharmacological effect may serve as pharmaceutical nanocarriers with improved solubilization capacity for poorly soluble drugs.     

Adsorption of nitrobenzene and orthochlorophenol on dimethyl ditallowyl montmorillonite: A microstructural and thermodynamic study

The adsorption of two different organic aromatic pollutants (nitrobenzene and orthochlorophenol) onto a commercial organoclay (dimethyl ditallowyl ammonium montmorillonite) was investigated. Adsorption was investigated over a wide range of concentrations, corresponding to 0.0016–0.24 mol/L for nitrobenzene and 0.002–0.29 mol/L for orthochlorophenol. The uptake of nitrobenzene and orthochlorophenol by the organobentonite was demonstrated to determined different processes: in the former case a partition process seemed to be favoured, while in the latter a combination of partition and adsorption onto specific sites appeared to be more reasonable.     

毛细管气相色谱法同时测定异丙甲草胺和莠去津

采用毛细管气相色谱法,在R tx-1701(30 m×0.32 mm×0.25μm)毛细管柱上以三唑酮为内标,氢火焰离子化检测器(FID)检测对异丙甲草胺和莠去津混剂,标准偏差分别为0.23%、0.20%,变异系数分别为0.919%、0.995%,线性相关系数分别为0.9987、0.9992,平均回收率为:99.7%、99.6%。     

Fluridone adsorption–desorption on organo-clays

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.