Solar photoelectrocatalytic degradation of ciprofloxacin at a FTO/BiVO₄/MnO₂ anode: Kinetics, intermediate products and degradation pathway studies

The removal of pharmaceuticals from contaminated water has remained a major challenge in recent times. This present work reports the solar photoelectrocatalytic removal of ciprofloxacin using n-n heterojunction BiVO₄/MnO₂ prepared by electrodeposition on a FTO glass as anode. The semiconductor photoanodes were characterised with XRD, SEM, EDS, diffusive reflectance UV-vis, voltammetry, impedance spectroscopy and chronoamperometry. The calculated charge carrier density of BiVO₄/MnO₂ from Mott-Schottky plot as well as its photocurrent response were greater than those of pristine BiVO₄ and MnO₂ revealing that the band alignment between the two semiconductors resulted in inhibition of rapid recombination of electron - hole pairs. A degradation efficiency of 76 % was achieved in the photoelectrocatalytic oxidation of ciprofloxacin using a bias potential of 1.5 V within 2 h with holes and hydroxyl radicals playing predominant roles. The highest degradation efficiency obtained with photoelectrocatalytic oxidation was due to synergistic effect of both electrochemical and photocatalytic degradation. The degradation of ciprofloxacin on the electrode proceeded through the rapid oxidation of piperazine ring of ciprofloxacin within a short time as indicated by chromatographic analysis of the degradation products. The electrode has excellent stability and reusability suggesting its suitability as photoanode for the photoelectrocatalytic oxidation of pharmaceuticals in wastewater.