Surface restructuring of red mud to produce FeOx(OH)y sites and mesopores for the efficient complexation/adsorption of β-lactam antibiotics

Abstract

In this work, iron oxide in the red mud (RM) waste was restructured to produce mesopores with surface [FeOx(OH)y] sites for the efficient complexation/adsorption of β-lactam antibiotics. Red mud composed mainly by hematite was restructured by an acid/ base process followed by a thermal treatment at 150–450 °C (MRM150, MRM200, MRM300, and MRM450) and fully characterized by Mössbauer, XRD, FTIR, BET, SEM, CHN, and thermogravimetric analyses. The characterization data showed a highly dispersed Fe3+ oxyhydroxy phase, which was thermally dehydrated to a mesoporous α-Fe2O3 with surface areas in the range of 141–206 m2 g−1 . These materials showed high efficiencies (21–29 mg g−1 ) for the adsorption of β-lactam antibiotics, amoxicillin, cephalexin, and ceftriaxone, and the data was better fitted by the Langmuir model isotherm (R2 = 0.9993) with monolayer adsorption capacity of ca. 39 mg g−1 for amoxicillin. Experiments such as competitive adsorption in the presence of phosphate and H2O2 decomposition suggested that the β-lactamic antibiotics might be interacting with surface [FeOx(OH)y] species by a complexation process. Moreover, the OH/Fe ratio, BET surface area and porosity indicated that this complexation is occurring especially on [FeOx(OH)y]surf sites contained in the mesopore space.