INFRARED SPECTROSCOPY OF PICLORAM INTERACTIONS WITH AI(III)-, Fe(III)-, AND Cu(II)-SATURATED AND HYDROUS OXIDE-COATED MONTMORILLONITE

Abstract--Thin clay films prepared from aqueous uspensions ofthe potassium or sodium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) with AI-, Fe-, or Cu-saturated montmorillonite or with montmoril-lonite coated with hydrous oxides of AI, Fe, or Cu were examined inan air-dry condition by infrared (IR) techniques toelucidate possible modes of interaction between picloram and the mineral surfaces. Deuter-ation was used to confirm band assignments of picloram and its salts prior to interaction with montmoril-lonite. Picloram interactions with AI- and Fe-saturated montmorillonite and with montmorillonite coated with hydrous oxides of A1 and Fe were concentration dependent. At high picloram concentrations simi-larities with the IR spectrum of potassium picloram indicated that much of the picloram was present in the salt form. As the concentration f picloram was reduced below that equivalent to 1 meq/g clay, the IR spectrum indicated the presence of the monomeric acid on the mineral surface. The spectrum of picloram on montmorillonite with a coating of copper hydrous oxide was similar to that of a Cu-picloram complex indicating coordination type bonding. The spectrum of picloram with Cu-saturated montmorillonite did not correspond to any of the other spectra of picloram examined. The interaction of picloram with montmo-rillonite coated with a hydrous oxide coating of Cu and with Cu-saturated montmorillonite w re indepen-dent of picloram concentration in the range 2.20-0.44 meq/g clay. Key Words--Adsorption, Hydrous oxides, Infrared spectroscopy, Montmorillonite, Picloram