Stable metal–organic framework fixing within zeolite beads for effectively static and continuous flow degradation of tetracycline by peroxymonosulfate activation

Abstract

Heterogeneous peroxymonosulfate (PMS) based advanced oxidation process has been proven as a promising method for tetracycline removal from water. Among the heterogeneous catalysts, Co based metal–organic framework (ZIF-67) is a good candidate to activate PMS in the aforementioned advanced oxidation system. However, their high metal ion leaching and fine powder form limit their practical application. Herein, zeolite bead-supported ZIF-67 was prepared through the Co ion-exchange and organic ligand reaction, which is simple, cost-efficient and recyclable. The obtained zeolite@ZIF-67 composites were employed for PMS activation to degrade tetracycline in the water. The uniform ZIF-67 loading could provide abundant catalytic sites and the results demonstrated that 93.7% of tetracycline (50 mg/L) could be removed in 60 min with high recycling stability. Intriguingly, due to the strong metal-support interaction, the Co ion leaching from the composite beads during the degradation reaction was much lower compared to pure ZIF-67 particles. In addition, zeolite@ZIF-67 composites with the microsphere form could be easily packed into the bed column to effectively remove tetracycline in a continuous flow process. The degradable mechanism and degradation pathway were comprehensively investigated by quenching experiments, electron paramagnetic resonance spectra, X-ray photoelectron spectroscopy and liquid chromatography-mass spectroscopy. Overall, our work provides a novel PMS heterogeneous catalyst based on macroscopic supported MOF composites for efficient tetracycline removal.