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Surface Condensation of Organophosphate Esters on Smectites

Published online by Cambridge University Press:  02 April 2024

U. Mingelgrin  and
F. Tsvetkov
U. Mingelgrin
Affiliation:
Institute of Soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel
F. Tsvetkov
Affiliation:
Institute of Soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel
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Abstract

Parathion and methyl parathion adsorbed at high loads on clays and similar surfaces exhibited properties of a bulk phase, such as a well-defined solubility and a characteristic X-ray powder diffraction (XRD) pattern, different from those of the free substances. The aqueous solubility of parathion condensed at these surfaces was as low as 1.2 μg/ml as compared to 14 μg/ml for free parathion. The BET isotherm described the behavior of the investigated surface condensates even though these condensates were different from the multilayer adsorption for which the BET isotherm was originally developed. The XRD patterns of parathion and methyl parathion adsorbed on Na-bentonite exhibited reflections which were shifted towards higher angles as compared with the XRD patterns of the free compounds. This is in agreement with the lower solubility of the surface condensates. The properties of these condensates were easily controlled by the choice of adsorbent as well as by the choice of conditions under whch they were prepared. The existence of such surface-condensed phases and the manipulation of their properties can be utilized for the slow-release formulation of organophosphate esters which is important, for example, in pesticides application.

Резюме

Резюме

Паратион и метилпаратион, будучи адсорбированы в больших количествах на глинах и сходных поверхностях, образуют самостоятельную фазу, характеризующуюся определенной растворимостью и рентгеноструктурными характеристиками отличными от свойств свободных паратиона и метилпаратиона. Растворимость паратиона сконденсированного на таких поверхностях может достигать 1,2 μг/мл, в то время как растворимость свободного паратиона равна 14 μг/мл. БЭТ-изотерма, выведенная для многослойной адсорбции, описывает поведение исследуемых конденсатов, несмотря на то, что поведение этих конденсатов отличается от многослойной адсорбции. Порошковые диф-фракции рентгеновских лучей адсорбированных на Na-бентоните паратиона и метилпаратиона смещены в сторону больших углов относительно аналогичных диффракций для свободных паратиона и метилпаратиона, что соответствует пониженной растворимости поверхностных конденсатов. Свойствами исследуемых конденсатов легко управлять при помощи выбора адсорбента, а также способами приготовления конденсатов. Существование описанных поверхностных конденсатов и возможность управления их свойствами могут быть использованы для осуществления подачи органофосфорных эфиров способом медленного высвобождения, что, в свою очередь, явится полезным во многих областях, в частности при применении ядохимикатов.

Resümee

Resümee

Parathion und Methylparathion, die in großen Mengen an Tonen und ähnlichen Oberflächen adsorbiert waren, zeigten Eigenschaften einer Gesamtphase, wie z.B. eine gut definierte Löslichkeit und ein charakteristisches Röntgenpulverdiffraktogramm (XRD), die sich von denen der einzelnen freien Substanzen unterscheiden. Die Löslichkeit im Wasser von Parathion, das an diesen Oberflächen kondensiert war, betrug nur 1,2 μg/ml im Vergleich zu 14 μg/ml für das freie Parathion. Das BET-isotherm beschrieb das Verhalten der untersuchten Oberflächenkondensate, obwohl sich diese Kondensate von der Vielschichtadsorption, für die die BET-Isotherme ursprünglich entwickelt wurden, unterschieden. Die XRD-Diagramme von an Na-Bentonit adsorbiertem Parathion und Methylparathion zeigten Reflexe, die im Vergleich zu denen der freien Komponenten nach höheren Winkeln verschoben waren. Dies stimmt mit der geringeren Löslichkeit der Oberflächenkondensate überein. Die Eigenschaften dieser Kondensate konnten leicht gesteuert werden, sowohl durch die Wahl des Adsorbenten als auch durch die Wahl der Bedingungen, bei denen sie hergestellt wurden. Die Existenz solcher an die Oberfläche kondensierter Phasen und die Veränderung ihrer Eigenschaften kann bei der langsamen Abgabe von Organophosphatestern verwendet werden, was z.B. bei der Anwendung in Pestiziden von Bedeutung ist. [U.W.]

Résumé

Résumé

Le parathion et le parathion méthyl adsorbés à charges élevées sur des argiles et des surfaces semblables ont exhibé les propriétés d'une phase de masse, telles qu'une solubilité bien définie et un cliché de diffraction des rayons-X caractéristique, différentes de celles des substances libres. La solubilité aqueuse du parathion condensé à ces surfaces était aussi bas que 1,2 μg/ml, comparé à 14 μg/ml pour le parathion libre. L'isotherme BET a décrit le comportement des condensates de surface investigués, bien que ces condensates étaient différents de l'adsorption multicouche pour laquelle l'isotherme avait été developé à l'origine. Les clichés XRD du parathion et du parathion méthyl adsorbés sur la bentonite-Na ont exhibé des réflections qui étaient deplacées vers des angles plus élevés en comparaison avec les clichés XRD des composés libres. Ceci s'accorde avec la solubilité plus basse des condensates de surface. Les propriétés de ces condensates étaient facilement contrôlables par le choix de l'adsorbant aussi bien que par le choix des conditions sous lesquelles ils étaient préparés. L'existence de telles phases condensées à la surface et la manipulation de leurs propriétés peuvent être utilisées pour la formulation d'estères organophosphates à décharge lente, ce qui est important pour, par exemple, l'application des pesticides. [D.J.]

Keywords

AdsorptionOrganophosphate esterParathionPesticideSmectiteSolubilityX-ray powder diffraction
Type
Research Article
Information
Clays and Clay Minerals , Volume 33 , Issue 1 , February 1985 , pp. 62 - 70
Copyright
Copyright © 1985, The Clay Minerals Society

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