Ti/β-PbO₂ versus Ti/Pt/β-PbO₂: Influence of the platinum interlayer on the electrodegradation of tetracyclines

ABSTRACT

The behaviors of the electrodes Ti/PbO₂ and Ti/Pt/PbO₂ as anodes in the electro-oxidation of two antibiotics—tetracycline and oxytetracycline—were evaluated at different applied current densities, to evaluate the influence of the Pt interlayer. In the preparation of the electrodes, the electrodeposited β-PbO₂ phase was homogeneous; no Ti or Pt peaks were detected in the diffractograms. The β-PbO₂ surface presented significant roughness when deposited over the Pt interlayer, which also conferred significant conductivity to the material. In the electro-oxidation assays, the COD, TOC and absorbance removals increased with the current density due to an increase in the concentration of hydroxyl radicals, for both electrode materials and antibiotics tested. Slightly better results were obtained with Ti/PbO₂. The primary differences observed in the antibiotics concentration decay consisted of zero-order kinetics at the Ti/Pt/PbO₂ anode and first-order kinetics at the Ti/PbO₂ anode with a higher oxytetracycline concentration decay than the tetracycline concentration decay. A greater amount of total nitrogen was eliminated with the Ti/PbO₂ electrode. At the Ti/Pt/PbO₂ anode, the organic nitrogen primarily transformed into NH₄⁺ and the total nitrogen remained unchanged. The specific energy consumption with the Ti/Pt/PbO₂ anode was significantly lower than the specific energy consumption with the Ti/PbO₂ anode due to the higher electrical conductivity of the Ti/Pt/PbO₂ anode. Both anode materials were also utilized in the electro-oxidation of a leachate sample collected at sanitary landfill and spiked with tetracycline, and the complete elimination of the antibiotic molecule was observed.

KEYWORDS:

• Electro-oxidation
• oxytetracycline
• tetracycline
• Ti/PbO_2; Ti/Pt/PbO₂

Funding

The authors acknowledge Fundação para a Ciência e a Tecnologia, FCT, for the project PEst-OE/CTM/UI0195/2014 of the FibEnTech Research Unit and the BI grants awarded to M.J. Nunes and N. Monteiro.