Abstract The ability of Fe oxides to adsorb phenol and various substituted phenols from dilute aqueous solution and from the vapor state was investigated, utilizing Fourier transform infrared (FTIR) spectroscopy to evaluate the type of surface complex formed. Adsorption from solution at pH 5.5 was weak (undetectable in the case of the unsubstituted phenol). There was some indication that quantity of adsorption was inversely related to the pKa of the p-substituted phenols, with the most acidic phenols adsorbing the most strongly from solution. The FTIR spectra revealed that adsorption on goethite and amorphous Fe oxide from the vapor state tended to perturb vibrational bands sensitive to the phenolic OH group, an indication of bonding between surface Fe3+ and the phenolic ligand. Depending on level of adsorption, both physically and chemically adsorbed phenols could be detected by FTIR with chemisorption being more in evidence on amorphous Fe oxide. Phenol that was 2,6-methyl-disubstituted failed to interact strongly with the goethite surface, suggesting that steric hindrance from groups adjacent to the phenolic group prevented inner-sphere coordination of the phenols to surface Fe atoms. This steric effect was not evident for low levels of adsorption on amorphous Fe oxide, suggesting an important role of site geometry in limiting chemisorption. The strength of the Fe3+-phenolic coordination bond was correlated to the pKa of the phenol, with more acidic phenols forming weaker CO bonds. The quantity of water present determined whether the phenols adsorbed at barely detectable or much higher levels, suggesting a competition between H2O and phenols for ligand positions of surface Fe.