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 (center dot OH) and superoxide radicals (center dot O-2(-)) 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-C bond in the TC molecule.