Enhanced electrochemical removal of dye wastewater by PbO2 anodes using halloysite nanotubes with different surface charge properties

Abstract

• A novel HNTs-CTS-PbO 2 composite anode was prepared. • New anode can effectively improve MB removal efficiency. • Degradation of methylene blue follows the pseudo-first-order reaction kinetics. • Elucidation of the degradation mechanism of methylene blue by modified electrodes. Electrode materials are the core of electrocatalytic oxidation technology. Herein, chitosan (CTS)-modified halloysite nanotubes (HNTs) were used for the first time in the doping modification of PbO 2 electrodes by electrodeposition technique, and novel HNTs-CTS-PbO 2 anodes were prepared and used for the electrochemical removal of the thiazine dye methylene blue (MB). The surface structure information, electrochemical properties and oxidation activity of the materials were systematically investigated, and possible degradation pathways of methylene blue were proposed. The results showed that after doping modification, the coating became flatter and denser, and the crystalline shape and crystalline phase of the PbO 2 electrode did not change, but the grain size was significantly reduced; moreover, the modified electrode had higher oxygen precipitation overpotential, larger reactive surface area and lower charge transfer resistance. Additionally, the decolorization degradation of MB by HNTs-CTS-PbO 2 electrode mainly adopts an indirect degradation mechanism and follows the pseudo-first-order kinetic model, which exhibits higher decolorization degradation rate. Analyzing the mechanism of the electrochemical removal of MB from the modified anode, which mainly involves the breakage of C N bonds under the action of ·OH, followed by demethylation and aromatic ring cleavage to obtain monoaromatic amines, sulfonic acids and phenolic compounds, and finally mineralized into inorganic small molecules such as CO 2 and H 2 O. The above results show that HNTs-CTS-PbO 2 anode is a promising candidate in the field of dye wastewater degradation and provide new insights for the application of HNTs.