Degradation and mineralization of ciprofloxacin by gas-liquid discharge non-thermal plasma

A typical quinolones antibiotic ciprofloxacin (CIP) in aqueous solution was degraded by a gas-liquid discharge non-thermal plasma system. The discharge plasma power and the emission intensity of the excited reactive species (RS) generated in the gas phase were detected by the oscilloscope and the optical emission spectroscopy. The effects of various parameters on CIP degradation, i.e. input powers, initial concentrations addition of radical scavengers and pH values were investigated. With the increase of discharge power, the degradation efficiency increased but the energy efficiency significantly reduced. The degradation efficiency also reduced under high concentration of initial CIP conditions due to the competitive reactions between the plasma-induced RS with the degradation intermediates of CIP. Different radical scavengers (isopropanol and CCl4) on center dot OH and H center dot were added into the reaction system and the oxidation effects of center dot OH radicals have been proved with high degradation capacity on CIP. Moreover, the long-term degradation effect on CIP in the plasma-treated aqueous solution proved that the long-lived RS (H2O2 and O-3, etc) might play key roles on the stay effect through multiple aqueous reactions leading to production of center dot OH. The degradation intermediates were determined by the method of electrospray ionization (+)-mass spectroscopy, and the possible degradation mechanism were presented.