Fenton-like catalytic degradation of tetracycline by magnetic palygorskite nanoparticles prepared from steel pickling waste liquor

Magnetic palygorskite nanoparticles (Pal@Fe₃O₄) were prepared from steel pickling waste liquor and used for Fenton-like catalytic degradation of tetracycline(TC). The results showed that TC can be efficiently removed in a wide pH range of 3–7. The degradation efficiency reached 72.9% within 60 min under neutral conditions. Moreover, since the amount of leached iron ions was <0.03 mg/L after each reaction, the catalytic effectiveness of Pal@Fe₃O₄ hardly changed after five cycles. The microstructure of Pal@Fe₃O₄ was investigated by SEM, TEM and STEM-EDS mapping, which showed that the Fe₃O₄ spherical nanoparticles were supported on the surface of the rod-shaped Pal. Moreover, the saturation magnetization of Pal@Fe₃O₄ was 44.11 emu/g, indicating that the catalyst could be easily separated by magnetic separation technology. Both hydroxyl radicals (•OH) and superoxide radicals (•O₂ ⁻) were proven by electron spin resonance spectroscopy to be the dominant active species responsible for TC degradation. Four degradation products were identified by LC-MS/MS, mainly produced by the attack of the active radicals on the N[sbnd]C bond in the TC molecule.