Removal of tetracycline antibiotics from aqueous solution by amino-Fe (III) functionalized SBA15

•Amino-Fe (III) functionalized SBA15 was prepared.•The adsorbent had high adsorption efficiency for all three TCs.•The differences in the removal trends may be attributed to their pKa values.•The complexation of Fe (III) and TCs improved the sorption capacity.

The gradual increase of antibiotics in aquatic environments poses a serious threat to human health and ecosystems, and removal technology for antibiotics has attracted great interest in recent years. In this study, to improve the adsorption capacity of mesoporous silica, a new sorbent made by grafting both amino groups and Fe (III) on mesoporous silica SBA15 (named Fe-N,N-SBA15) was prepared and used for the removal of tetracycline antibiotics (TCs) from aqueous solution. The results showed that TCs sorption on Fe-N,N-SBA15 was highly pH-dependent, and the optimal pH was found to be 4.5–5.6 for tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC). The adsorption kinetics fitted the pseudo-second-order model perfectly and the adsorption rate constant followed the order OTC > TC > CTC. The adsorption isotherms study showed the maximum sorption capacity to be 143.31, 96.91 and 69.15 mmol kg−1 for OTC, TC and CTC, respectively. The differences in the removal trends of the three TCs may be attributed to their different pKa values. A thermodynamic study showed that the adsorption of TCs on FeN,N-SBA15 is spontaneous (ΔG < 0) and endothermic (ΔH > 0). FTIR and XPS results showed that the high sorption capacity of antibiotics could be mainly attributed to the complexation of Fe (III) and TCs.

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