Scallop shell coated Fe₂O₃ nanocomposite as an eco-friendly adsorbent for tetracycline removal

The present study focused on the usability of scallop shell coated Fe₂O₃ nanoparticles as an eco-friendly new absorbent in the treatment of tetracycline (TC). The process performance in terms of TC removal was investigated at different operating conditions, i.e. at solution pH of 3–11, Fe₂O₃-scallop dosage of 0.4–2.4 g L⁻¹, initial TC content of 20–120 mg L⁻¹ and temperature of 25–55°C. Solution pH of 7 yielded the highest TC removal efficiency (99%). At this pH value, almost complete TC removal was achieved at a Fe₂O₃-scallop shell nanocomposite dose of 1.6 g L⁻¹ and 25°C. The responsible TC removal mechanism is suggested as the non-electrical π–π dispersion interaction between the bulk π system on the absorbent surface and TC molecules bearing both benzene rings and double bonds at this solution pH. TC removal efficiency appreciably enhanced up to the Fe₂O₃-scallop dosage of 1.6 g L⁻¹ being an optimum. Adsorption rate was found to be fast at lower initial TC concentrations than 40 mg L⁻¹. The effect of temperature on TC removal efficiency was insignificant. Adsorption followed the pseudo-second-order kinetic model. Experimental data perfectly fitted by the Langmuir equation. The maximum adsorption capacity was calculated as 49.26 mg g⁻¹. Thermodynamic analysis demonstrated that adsorption process was spontaneous process and endothermic. The results obtained from the present study proved the excellent performance of scallop shell coated Fe₂O₃ nanoparticles as an eco-friendly adsorbent in TC treatment.