Efficient catalytic degradation of ciprofloxacin in synthetic and real wastewater under aerobic condition using microporous ammonium phosphomolybdate

The fluoroquinolone drug ciprofloxacin (CIP) is increasingly being discovered as a pseudo-persistent pollutant that enters into our drinking water system. In the present work Keggin-type polyoxometalate (POM) ammonium phosphomolybdate (APM) is synthesized and it has been used as an efficient catalyst for ciprofloxacin degradation under aerobic conditions without the help of other chemicals such as hydrogen peroxide, ozone, peroxymonosulfate, etc. Over 92 % of ciprofloxacin is destroyed in the range of pH 3.0 to 6.6, with the maximum degradation percentage achieved at pH 6.6. The microporosity, large surface area, and presence of Mo+6 in the synthesized APM material make it an effective catalyst for CIP destruction in an aqueous medium at room temperature and in a dark environment. The procedure converts the Mo+6 in APM to Mo+5. The dissolved oxygen can oxidize the newly produced Mo+5. Both the radical quenching tests and EPR spectra show that a variety of reactive oxygen species (ROS), including singlet oxygen (1O2) and hydroxyl radical (OH), are produced during these cyclic redox processes. The catalyst is highly stable and can be recycled up to eight times for CIP degradation. Despite of multiple times of recycling, the APM catalyst maintains a high degradation efficiency (>80 %), highlighting its robustness. Strong interference from sulfate (SO4−2) and copper (Cu+2) ions is observed during CIP degradation. CIP is efficiently degraded in the pond water and wastewater. This is the first time APM, an age-old material, is exploited as a catalyst to degrade CIP molecules under aerobic conditions in aqueous medium.