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Tetracyclines (TCs) constitute a group of antibiotics that are commonly used to treat bacterial diseases, in veterinary medicine and as an additive in animal feed. This broad application has led to their accumulation in food products and the environment because sewage treatment plants cannot completely remove them. Therefore, the aim of this study was to synthesize graphene oxide (GO) and evaluate its TC adsorption properties in aqueous media. The effects of pH (between 2.5 and 11) and Ca2+ concentration (between 0 and 1 M) were thoroughly investigated. Structural, textural, and electrokinetic properties of the prepared GO were determined by N2 adsorption/desorption, XRD, TEM, UV–vis, FTIR, XPS, thermogravimetry and electrophoretic mobility measurements. TC adsorption on GO is an interplay between the two main roles played by Ca2+: competitor or bridging cation. At low pH, there is cation exchange, and Ca2+ behaves as a competitor of the positively charged TC species, decreasing adsorption as calcium concentration increases. At high, the formation of Ca bridges between the surface and TC (GO-Ca2+-TC) is favored, increasing the adsorption of the antibiotic by increasing calcium concentration. Different combinations of Ca2+ and pH effects are important to improve the use of GO either as a pH-dependent and reversible TC adsorbent for decontamination or as pH-independent adsorbent for TC quantification with electrochemical sensors. [ABSTRACT FROM AUTHOR]

Abstract: The remotion of the antibiotic minocycline (MC) on mesoporous silica (SiO2) and on the binary system iron(III) oxide–SiO2 (Fe-SiO2) has been studied in batch experiments by performing adsorption isotherms/kinetics under different conditions of pH, KCl concentration and temperature. The adsorption of MC on the studied materials is strongly dependent on pH, increasing as pH decreases. The incorporation of a low concentration of iron (1.03wt.%, mainly as amorphous Fe2O3) on the SiO2 matrix not only increases the adsorption capacity but also changes the adsorption mechanism. The adsorption of MC on SiO2 strongly decreases as KCl concentration increases but it is not significantly affected by varying the temperature. This is attributed to electrostatic attractions and H-bond formations between dimethylamino, amide, carbonylic and phenolic groups of the antibiotic and the functional groups of silica particles. The adsorption of MC on Fe-SiO2, on the contrary, strongly increases as temperature increases but remains invariable by varying the KCl concentration. This suggests that the formation of inner-sphere complexes between the functional groups of the antibiotic and the active sites of Fe2O3 plays a key role on the adsorption mechanism. The analysis of adsorption thermodynamic parameters is also reported and discussed. The synthesized materials can act as excellent adsorbents for environmental and engineering processes. [Copyright &y& Elsevier]