CHARACTERIZATION OF BENZOIC AND PHENOLIC COMPLEXES AT THE GOETHITE AQUEOUS-SOLUTION INTERFACE USING CYLINDRICAL INTERNAL-REFLECTION FOURIER-TRANSFORM INFRARED-SPECTROSCOPY .2. BONDING STRUCTURES

Bonding structures of benzoic compounds at the goethite (alpha-FeOOH)/water interface were investigated "in situ" using cylindrical internal reflection (CIR) Fourier transform infrared (FTIR) spectroscopy. CIR-FTIR spectra of phthalate (PHTH), p-hydroxybenzoate (PHB), and 2,4-dihydroxybenzoate (2,4DHB) added to goethite suspensions allowed us to identify surface complexes using methodology described in part 1 of this study. The PHTH and PHB/surface iron complexes are mainly formed via a bidentate, binuclear structure involving both oxygens of one carboxylate each bound to one surface iron atom. The 2,4DHB/surface iron complex is formed via a chelation structure involving one carboxylic oxygen and the phenolic oxygen (bidentate, mononuclear). Results obtained from CIR-FTIR studies were consistent with adsorption isotherm data. The type of binding is related to the quantity of species adsorbed due to the numbers of surface sites having a particular coordination possibility.