Adsorption Of Diquat Research Articles

Adsorption of diquat, paraquat and methyl green on sepiolite: experimental results and model calculations

Adsorption of the divalent organic cations paraquat (PQ), diquat (DQ) and methyl green (MG) on sepiolite was determined experimentally and investigated with an adsorption model. The largest amounts of DQ, PQ and MG adsorbed were between 100% and 140% of the cation exchange capacity (CEC) of sepiolite. In previous experiments with monovalent organic cations (dyes), the largest amounts of dyes adsorbed were about 400% of the CEC of sepiolite. Consequently, it was proposed that most of this adsorption was to neutral sites of the clay. The large differences between the adsorption of these divalent organic cations and the monovalent dyes may indicate that there is almost no interaction between DQ, PQ and MG and the neutral sites of sepiolite. This assumption was confirmed by infrared (IR) spectroscopy measurements, that did not show changes in the peaks arising from the vibrations of external SiOH groups of the clay when the divalent organic cations were added. Adsorption results were compared with calculations of an adsorption model that combines the Gouy–Chapman solution and specific binding in a closed system. The model considers cation adsorption on neutral sites of the clay, in addition to adsorption to mono- or divalent negatively charged sites, forming neutral or charged complexes. The model could adequately simulate the adsorption of the divalent organic cations DQ and PQ when added alone, and could yield good fit for the competitive adsorption experiment between the monovalent dye methylene blue and DQ. In competitive adsorption experiments, when total cationic charges exceeded the CEC, monovalent organic cations were preferentially adsorbed on the clay at the expense of the divalent cations.

Removal of diquat and deisopropylatrazine from water by montmorillonite-(Ce or Zr) phosphate crosslinked compounds

The adsorption of diquat (1,1′-ethylene-2,2′-dipyridilium dibromide) and one intermediate compound of the degradation of atrazine in water, deisopropylatrazine, on two montmorillonite-(Ce or Zr) phosphate crosslinked compounds from aqueous solution under conditions of varied temperature (288 K and 308 K) has been studied. The experimental adsorption isotherms obtained for diquat on both adsorbents may be classified as H-type of the Giles classification which suggests that diquat molecules are strongly adsorbed on the samples. For the deisopropylatrazine, L-type isotherms were obtained for both montmorillonite-(Ce or Zr) phosphate compounds, which suggests a moderate affinity of this metabolite by the active sites of the adsorbents. The increase of temperature from 288 K to 308 K does not clearly affect the adsorption process of diquat on both adsorbents whereas the deisopropylatrazine adsorption decreases slightly as temperature increases possibly due to a mainly physical process. Fourier transform infrared (FTIR) spectroscopic studies reveal that at the pH generated by the adsorbents, the cationic herbicide interacts to a greater extent with the negative charged surface of the adsorbents than deisopropylatrazine. For both model compounds, the ceriummontmorillonite adsorbent shows the higher capacity of adsorption compared with zirconiummontmorillonite adsorbent.

Adsorption and Interactions of Diquat and Paraquat with Montmorillonite

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.

A mathematical model of diffusion under saturated conditions to assess the pollution potential of herbicides to aquatic systems

Abstract The physicochemical dynamics of a pesticide-sediment-water system were studied utilizing a one-dimensional numerical model of diffusion under saturated conditions, with nonlinear Freundlich/Langmuir adsorption-desorption. Specifically, the model was formulated to assess the pollution potential of pesticides to aquatic systems, based upon their ability to migrate within the aquatic environment. Initial physical and chemical characterization of eight freshwater sediments, and adsorption studies using two chemically dissimilar herbicides—bromacil and diquat—revealed insightful positive relationships between adsorption coefficients and sediment properties. Bromacil showed a high positive correlation between the Freundlich sorption partition coefficient and the organic carbon content. Diquat adsorption, as characterized by a Langmuir-type adsorption, showed a high positive correlation between the Langmuir affinity constant and the surface area, while the Langmuir adsorption maxima correlated highly with the cation exchange capacity of sediments treated for the removal of organic matter. Apparent heats of adsorption for bromacil at 5° and 25°C were low, indicating a predominantly physical type of adsorption. Temperature change was found to have little or no effect upon the adsorption of diquat over the range of observed temperatures, 5° and 25°C. Rates of adsorption for both bromacil and diquat were very rapid, especially on sediments with small organic matter fractions. In general, diquat took slightly longer than bromacil to attain equilibrium. The slower adsorption rate of diquat on high-organic-matter sediments confirms previous findings indicating a possible redistribution of diquat from adsorption sites on the organic fraction to adsorption sites on the clay surface. Varying the initial solution concentration of either bromacil or diquat did not significantly affect the reaction rates. Desorption studies for bromacil and diquat showed that for each sediment, a unique linear relationship existed between the adsorbate concentration at which desorption began and the slope of the desorption isotherm.

ChemInform Abstract: ADSORPTION OF CATIONIC PESTICIDES (DIQUAT AND PARAQUAT) FROM AQUEOUS SOLUTION BY ACTIVATED CARBON

Abstract Adsorption of diquat and paraquat cationic pesticides from aqueous solution studied on three different activated carbons varying in N2-BET surface area from 660 m2/g to 1280 m2/g suggests that the rate limiting step for removal of these pesticides in agitated non-flow systems is one of intraparticle transport of the solute in the pores and capillaries of the adsorbent. The sorption rates for both adsorbates may be characterized by diffusion coefficients, D, calculated in the usual manner assuming the flux of diffusion to be proportional to the concentration gradient. The resultant values for D vary fairly inversely proportionately with the N2-BET surface area of an activated carbon for an individual adsorbate. Adsorption capacities on active carbon of diquat and paraquat from water vary from ~18 to 36% and ~6 to 14% respectively by weight of active carbon, depending upon the surface area of the carbon. These values are fairly attractive, especially for diquat, from a practical point of view of removing trace quantities of these pesticides. Thermodynamic studies indicate that the rate of removal of these pesticides by active carbon is an endothermic process which is in agreement with a suggested intraparticle transport rate control mechanism; however, the equilibrium position is governed by an exothermic reaction, as is expected for adsorption. Competitive adsorption studies of diquat and paraquat when present as an equimolar mixture, which should indicate the relative affinity of the surface available for each of the two adsorbates, suggest that different sites on the active carbon surface probably adsorb both adsorbates in a different manner.

Adsorption of cationic pesticides (diquat and paraquat) from aqueous solution by activated carbon

Adsorption of diquat and paraquat cationic pesticides from aqueous solution studied on three different activated carbons varying in N 2-BET surface area from 660 m 2/g to 1280 m 2/g suggests that the rate limiting step for removal of these pesticides in agitated non-flow systems is one of intraparticle transport of the solute in the pores and capillaries of the adsorbent. The sorption rates for both adsorbates may be characterized by diffusion coefficients, D, calculated in the usual manner assuming the flux of diffusion to be proportional to the concentration gradient. The resultant values for D vary fairly inversely proportionately with the N 2-BET surface area of an activated carbon for an individual adsorbate. Adsorption capacities on active carbon of diquat and paraquat from water vary from ~18 to 36% and ~6 to 14% respectively by weight of active carbon, depending upon the surface area of the carbon. These values are fairly attractive, especially for diquat, from a practical point of view of removing trace quantities of these pesticides. Thermodynamic studies indicate that the rate of removal of these pesticides by active carbon is an endothermic process which is in agreement with a suggested intraparticle transport rate control mechanism; however, the equilibrium position is governed by an exothermic reaction, as is expected for adsorption. Competitive adsorption studies of diquat and paraquat when present as an equimolar mixture, which should indicate the relative affinity of the surface available for each of the two adsorbates, suggest that different sites on the active carbon surface probably adsorb both adsorbates in a different manner.

Mechanism of adsorption of diquat and paraquat on montmorillonite surface

Mechanism of adsorption of diquat and paraquat on montmorillonite surface

Effect of light environment on the activity and behaviour of diquat and paraquat in plants

AbstractThe importance of controlling the light environment of experiments involving diquat and paraquat is shown in experiments where activity is markedly dependent on the light quality and intensity before treatment and on the time of day of treatment.Activity and uptake are not directly related since treatments after low light intensities give increased activity associated with reduced uptake; following afternoon treatments, reduced activity is associated with increased uptake. Uptake increased when plants were darkened after treatment but the increase was not directly related to its duration, because after a time, uptake decreased. Three possible explanations for this decrease are considered: diquat exudation from the leaves, downward movement into the roots, and the adsorption of diquat in plant tissue. Evidence did not support exudation from leaves or downward movement into the roots.

Adsorption and Desorption of Diquat, Paraquat, and Prometone by Montmorillonitic and Kaolinitic Clay Minerals

AbstractThe adsorption of diquat, paraquat, and prometone by montmorillonite and kaolinite clays and their desorption using several extracting solutions has been investigated. Diquat and paraquat were adsorbed by the clay minerals to approximately the cation‐exchange capacity of the clays. Approximately 80% of each of the herbicides was displaced from kaolinite clay with Ba2+ ions. A total of 5% of each of the compounds was removed from montmorillonite using 1M BaCl2 solutions. The two herbicides were found to exchange for one another on both clay minerals in a one‐for‐one manner. Paraquat was preferentially adsorbed over diquat by both clays in competitive ion studies and was also found to be more difficult of the two herbicides to displace.Prometone which was adsorbed by the montmorillonite clay was more readily desorbed with deionized water than with 1M BaCl2. Small amounts of prometone which were adsorbed by the kaolinite clay were also readily desorbed by deionized water.

Adsorption and Desorption of Diquat, Paraquat, Prometone, and 2,4‐D by Charcoal and Exchange Resins

AbstractThe adsorption of diquat, paraquat, prometone, and 2,4‐D by charcoal and cation‐ and anion‐exchange resins and their desorption with water and 1M NaCl solutions has been investigated. Prometone and 2,4‐D were adsorbed by charcoal in much greater amounts than were diquat and paraquat, but all of the compounds were readily desorbed with deionized water following normal Freundlich isotherms. Diquat and paraquat were adsorbed by the cation exchange resins (H and Na forms) and both herbicides were readily desorbed by Na+ ions but not with deionized water. Diquat was preferentially adsorbed over paraquat by the cation‐exchange resins and diquat was also more effective in displacing paraquat from the resins. Prometone was adsorbed in small amounts by the cation resin in the Na form and the anion resin in the Cl form and was readily desorbed with deionized water. Prometone was adsorbed by the cation resin in the H form in amounts which were similar to those for diquat and paraquat. None of the prometone adsorbed by the H‐resin was desorbed by equilibrating with water. Prometone desorbed from the H‐resin with 1M NaCl solutions was identified as hydroxypropazine.

The uptake and adsorption of diquat and paraquat by tomato, sugar beet and cocksfoot

SUMMARYExperiments on leaves of tomato, sugar beet and cocksfoot show that uptake of diquat and paraquat, although rapid in the light, is increased by darkness and therefore takes place through the cuticle and not through stomata. Darkness for as little as 4 hr. increased uptake almost twofold.Diquat and paraquat are rapidly and strongly adsorbed both to leaf tissue and to extraneous matter on the leaf surface.Uptake in the field is so rapid that rain immediately after treatment has little adverse effect.