Adsorption mechanisms of imazamethabenz-methyl on homoionic montmorillonite

The adsorption of the herbicide imazamethabenz-methyl from water onto Al3+-, Fe3+-, Ca2+-, K+, and Na+-montmorillonite was studied by analytical (HPLC) methods. The adsorption from an organic solvent was also investigated by spectroscopic (IR) and X-ray diffraction measurements. It was observed that, depending on the acidic properties of the exchangeable cations, two different mechanisms may take place. The first one, acting on Fe3+- and Al3+- clays, involves the protonation of the more basic nitrogen atom of imidazolinone ring of the herbicide because of a proton transfer from the acidic metal-bound water, followed by adsorption on the clay surfaces. The second mechanism, taking place on Ca2+-, K+- and Na+-clays, is hydrogen-bond formation between the ester carbonyl group of the herbicide and hydration water metal ions and is not affected by the structure of the isomers.