In this work, [FeOx(OH)(y)]/Al2O3 composites with different Fe oxyhydroxy contents, i.e. 10, 20 and 50 wt% treated at 150, 200, 300 and 450 degrees C were investigated as adsorbents of beta-lactamic antibiotics, i.e. cephalexin, ceftriaxone and especially amoxicillin, from aqueous solutions. The obtained results showed that the nature of the surface Fe3+ species play a fundamental role on the adsorption process. The most efficient adsorption was obtained for the sample 150Fe50A (50% [FeOx(OH)(y)] supported in Al2O3 treated at 150 degrees C) whereas the thermal treatment at higher temperatures caused a strong decrease on the adsorption capacity. Mossbauer, XRD, FTIR, Raman, TG-MS, SEM, CHN and BET of the composite 150Fe50A suggested an approximate composition of FeO0.65(OH)(1.7) whereas at 450 degrees C strong dehydroxylation process takes place to form FeO1.4(OH)(0.21). These results combined with competitive adsorption using amoxicillin mixed with phosphate or H2O2 suggest that the antibiotic molecules adsorb by complexation on surface sites likely based on FeOx(OH)(y) by the replacement of the labile OH ligands. (C) 2016 Elsevier B.V. All rights reserved.