Sorption and transformation of phenols on clay surfaces: effect of exchangeable cations

The sorption and transformation of phenol, 2-methylphenol, 3-methylphenol, 2,6-dimethylphenol, 3,5-dimethylphenol, and 2,4,6-trimethylphenol, by homoionic Na-, H-, Ca-, Cu-, Al-, and Fe(III)-montmorillonite from both vapour and aqueous phases were examined by IR spectroscopy. All the phenols were sorbed by the clays but were modified to different degrees depending on the exchangeable cations and on the amount and type of alkyl substitution of the phenols. Sorption of 2,6-dimethylphenol from aqueous solution was irreversible, and the extent of sorption followed the order Fe- > Al- > Cu- > Ca-clay. Both transition and non-transition metal cations were effective in transforming the phenol sorbates and heating the clay/phenol complexes further enhanced transformation. The results are discussed in terms of the nature of the transformation products and the likely role of radical reactions in their formation.