Adsorption of picloram on clays nontronite, illite and kaolinite: equilibrium and herbicide-clays surface complexes

Abstract

The picloram (PCM) adsorption on nontronite, illite and kaolinite was studied at pH 3, 5 and 7. The adsorption isotherms had well-fitted to Langmuir and Freundlich models equations. The interactions of PCM with the clay mineral surfaces exhibited an anionic profile adsorption, with a decrease in adsorption when the pH increases. The PCM adsorption capacity increases in the following order: kaolinite < illite < nontronite. The X-ray diffraction (XRD) analysis of PCM-clay samples revealed that the picloram molecule does not enter into the clays basal space. The interaction of PCM with clays surface sites through nitrogen of the pyridine ring was confirmed by X-ray photoelectron spectroscopy (XPS). Due to the anionic form of PCM, the adsorption onto the external and edges surface sites of the clay minerals was proposed.

Keywords:

• Adsorption
• picloram
• herbicide
• clays
• XPS
• surface complexes

Additional information

Funding

The authors acknowledge the Universidad de Buenos Aires (UBA) and Ministerio de Ciencia y Tecnología, Agencia Nacional de Promoción Científica y Tecnológica, Fondo para la Investigación Científica y Tecnológica (MINCyT-ANPCyT-FONCyT) for financial support through out UBACyT and PICT grants. Authors are also thankful to Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET). J.L.M.-B. acknowledges CONICET fellowship. R.M.T.S and J.L.M.-B. are members of CONICET. The authors also are grateful to Michel I. Genet for his assistance with XPS interpretation.