Mn-based material derived from industrial sawdust for the elimination of ciprofloxacin: Loss of antibiotic activity and toxicity via carbocatalysis assisted by ultrasound

A carbonaceous material was prepared from industrial wastes (sawdust), modified with manganese to form SWMn, and tested to activate peroxymonosulfate (PMS) under the influence of ultrasound (US) at frequencies of 40 kHz and 375 kHz. This activation aimed to degrade the relevant antibiotic ciprofloxacin in water. SW-Mn was characterized through spectroscopic, thermal, textural, and electrochemical techniques. The sonocarbocatalytic system (i.e., carbocatalysis using SW-Mn assisted by ultrasound at 40 kHz) synergistically degraded the target pollutant, exhibiting diverse oxidizing properties. A metallic species of SW-Mn underwent oxidation (i.e., =Mn2+ changed to =Mn4+) by PMS action, and at the same time, SW-Mn activated PMS producing singlet oxygen (1O2). Moreover, the low-frequency ultrasound caused particle disaggregation making more available the active sites on SW-Mn and enhancing the elimination of ciprofloxacin. The generated 1O2 attack and oxidation by =Mn4+ species transformed the piperazyl ring of the pollutant, modifying the biological activity of ciprofloxacin. As a result, sonocarbocatalysis reduced both the antimicrobial activity and phytotoxicity caused by the target pollutant. Furthermore, the treatment induced 100% degradation of ciprofloxacin in irrigation crop water, requiring only 5 min of sonocarbocatalysis, even faster than in distilled water, which was associated with enhancing effects by the matrix components. This study demonstrates the suitability of carbonaceous materials derived from sawdust and modified with Mn to act as catalysts to activate PMS and the improvement of the performance of the carbocatalytic process by low-frequency ultrasound waves toward the degradation of ciprofloxacin in water samples.