Comparison of three different zeolites to activate peroxymonosulfate for the degradation of the pharmaceutical ciprofloxacin in water

Abstract

Zeolites are typically used as adsorbents for the removal of organic pollutants from water but recently are gaining attention as catalysts for the activation of persulfates toward contaminants degradation. In this work, the capability of a zeolite Y (FAU-type) and two zeolites beta (BEA-type) to activate peroxymonosulfate (PMS) toward the degradation of one representative pollutant of a pharmaceutical nature (i.e., ciprofloxacin) was tested and compared. Initially, the characterization of the considered zeolites was carried out, evidencing that they had different Si/Al, surface area, and basicity. Then, the main degradation pathway involved in the target pollutant degradation was determined and the activating ability of three zeolites was compared. It was found that among the three tested materials, zeolite Y had the highest activating capability toward PMS for ciprofloxacin degradation (showing ~ 90% degradation after 10 min of treatment). The synergy (S) of the systems followed the order: zeolites beta/PMS (S, 0.5–1.4) < zeolite Y/PMS (S, 3.9), revealing that the Si/Al ratio has a determinant role in the zeolite/peroxymonosulfate combination, being convenient lower values of such a ratio. In the most adequate combination (i.e., zeolite Y/PMS), the pharmaceutical was attacked by singlet oxygen (coming from the PMS activation by the zeolite via basic sites), which modified ciprofloxacin on its piperazyl ring, producing two intermediates. Theoretical analyses based on the structure suggested that the two intermediates have low toxicity against mammals. Additionally, experimental tests showed that the zeolite Y/PMS process led to a resultant solution without antimicrobial activity against S. aureus. Finally, it can be mentioned that ZY/PMS was used to deal with ciprofloxacin in synthetic hospital wastewater, achieving ~ 40% pollutant elimination after 60 min of treatment.