Evaluation of diclofenac degradation effect in "active" and "non-active" anodes: A new consideration about mineralization inclination.

This work investigates the electrochemical oxidation (EO) of diclofenac (DCF) in water with Ti/TiO, Ti/Ru-Ir, Ti/Sb-SnO and Ti/PbO electrodes. Scanning electron microscope and X-ray diffraction results suggest that Ti/TiO has porous stacked surface morphology and Ti/Sb-SnO possesses the smallest grain size. Linear sweep voltammetry test results indicate that PbO has the highest oxygen evolution potential, while Ti/TiO and Ti/Ru-Ir show better oxygen evolution activity. DCF degradation results reveal that PbO possessed the highest DCF removal (R = 99.2%) and chemical oxygen demand (COD) removal (R = 97.0%), the fastest COD degradation rate (k = 0.0275 min, R = 0.964), the lowest specific energy consumption (EC = 1.81 kWhg DCF, EC = 6.90 kWhg TOC). The toxicity variation of DCF during EO process on PbO is rise first and then to fall. Considering the differences of the four electrodes in residual, conversion and mineralization aspects, mineralization selectivity (MS) was proposed to estimate the mineralization inclination of electrodes during EO process, and PbO displays the strongest mineralization inclination (MS = 0.594). In addition, the possible degradation pathway of DCF on PbO electrode indicates a composite behavior of conversion and mineralization. All of them above indicate the promising application potential of PbO in lower concentration pharmaceuticals and personal care products wastewater treatment. Moreover, MS could be employed as a supplementary index to assess the different inclinations of this composite behavior on various electrodes used for electrochemical treatment of organics in later studies.