Glyphosate adsorption on montmorillonite: An experimental and theoretical study of surface complexes

George A. Khoury, Todd C. Gehris, Lorena Tribe, Rosa M. Torres Sánchez, Maria dos Santos Afonso

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79 Scopus citations


In this study we perform X-ray diffraction and XPS analysis to study the adsorption of the herbicide glyphosate on montmorillonite. Structures of the surface complexes are proposed based on the XPS and XRD patterns and explored using molecular modeling techniques. Adsorption isotherms showed multistep profiles at all pHs studied, indicating the adsorption on aluminol and/or silanol groups of the external surface and in the interlayer space. PMG intercalation was indicated by the XRD patterns. The increase of the basal spacing as a function of the number of water molecules in the calculations indicated the appropriateness of the theoretical model to simulate macroscopic behaviors of the water/clay mineral interactions. Final conformations of the system determined by molecular mechanics indicated that the charged amino moiety was attracted by the negative surfaces of the interlayer space in absence or presence of water molecules, with marked pH dependence. Negative values of the estimated adsorption energies at all pH values studied suggested that glyphosate molecules were adsorbed via the amino moiety or through monodentate or bidentate complexes formed between the phosphonate moiety and the internal surfaces of the clay mineral, explaining the basal spacing changes at high concentrations of PMG.

Original languageEnglish (US)
Pages (from-to)167-175
Number of pages9
JournalApplied Clay Science
Issue number2
StatePublished - Oct 2010

All Science Journal Classification (ASJC) codes

  • Water Science and Technology
  • Geochemistry and Petrology
  • Geology
  • Soil Science


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