Electrochemical properties of the erbium–chitosan–fluorine–modified PbO2 electrode for the degradation of 2,4-dichlorophenol in aqueous solution

The erbium (Er)–chitosan–fluorine (F) modified PbO2 electrode was prepared by electrodeposition method, and its use for adsorption and electrochemical degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous solution was compared with F–PbO2 and Er–F–PbO2 electrodes in a batch experiment. The electrodes were characterized by scanning electron microscopy, X-ray diffraction and cyclic voltammetry. Degradation of 2,4-DCP depending on Er and chitosan contents was discussed. The results showed that Er2O3 and chitosan were scattered between the prevailing crystal structure of β-PbO2 and thus decreased the internal stress of PbO2 film. Prior to each electrolysis, the modified PbO2 anode was first pre-saturated with 2,4-DCP solution for 360 min to preclude the 2,4-DCP decrease due to adsorption. Among the electrodes examined in our study, the highest adsorption and electrochemical degradation for 2,4-DCP and TOC removals that are due to oxidation and adsorption of the organic products onto the chitosan was observed on Er–chitosan–F–PbO2 electrode. At an applied current density of 5 mA cm−2, the removal percentages of 2,4-DCP and TOC (solution volume: 180 mL, initial 2,4-DCP concentration: 90 mg L−1) were 95% after 120 min and 53% after 360 min, respectively. At Er amount of 10 mM in the precursor coating solution, the degradation and mineralization removal for 2,4-DCP on the Er–F–PbO2 electrode reached a maximum. At chitosan amount of 5 g L−1, the highest TOC removal on the Er–chitosan–F–PbO2 electrode was observed. Intermediates mainly including aliphatic carboxylic acids were examined and a possible degradation pathway for 2,4-DCP in aqueous solution involving dechlorination and hydroxylation reactions was proposed.