Enhanced activation of persulfate by FeS2/HNTs microspheres with nanochannels for rapid tetracycline degradation

Tetracycline (TC), as a widely used antibiotic, poses severe threats to ecosystems and human health. In this study, the FeS 2 /halloysite nanotubes (FeS 2 /HNTs) microspheres as heterogeneous catalysts were used for sulfate radical-based advanced oxidation processes (SR-AOPs) to degrade TC. By assembling HNTs into the interior of FeS 2 microspheres, the diffusion of TC and persulfate (PS) to the active sites inside the FeS 2 microspheres was enhanced, thereby improving the degradation ability of the catalyst for TC. Within 90 min, the FeS 2 /HNTs + PS system achieved 85.13% removal efficiency of TC, over 30% higher than that of the FeS 2  + HNTs + PS system. Moreover, the FeS 2 /HNTs + PS system not only exhibited excellent degradation efficiency at a low catalyst dosage (0.05 g/L), but also demonstrated robust adaptability to TC concentrations of 10–60 mg/L and pH values of 3–9. The reactive oxygen species (ROS) in the system include · S O 4 − $·\mathrm{S}{\mathrm{O}}_4^{-}$ , ·OH, · O 2 − $·{\mathrm{O}}_2^{-}$ , and 1 O 2 , among which · S O 4 − $·\mathrm{S}{\mathrm{O}}_4^{-}$ and · O 2 − $·{\mathrm{O}}_2^{-}$ played a dominant role. Liquid chromatography-mass spectrometry identified 21 possible degradation intermediates. TC was mainly converted into small-molecule organics through pathways such as demethylation and ring opening. Furthermore, with the extension of degradation time, the mutagenicity and developmental toxicity of the intermediates decreased.