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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