Electrochemical efficient degradation of methylene blue (MB) by two-step electrodeposited Ti/TiO2-NTs/β-PbO2 electrode: Performance, degradation mechanism, and toxicity study of intermediate products

With the advancement of nanotechnology and materials science, anodic electrocatalytic oxidation has been revitalised. In this study, a Ti/TiO₂-NTs/β-PbO₂ electrode with a TiO₂ nanotube interlayer was fabricated using a two-step electrodeposition method for the electrochemical degradation of methylene blue (MB) wastewater. Electrochemical and accelerated lifetime tests demonstrated that the Ti/TiO₂-NTs/β-PbO₂ electrode exhibits superior stability, with a lifespan 2.5 times that of a conventional Ti/PbO₂ electrode. The effects of current density, temperature, initial pH, and Cl^- ion concentration on the electrochemical degradation of MB by Ti/TiO₂-NTs/β-PbO₂ were systematically investigated. Under optimal conditions (current density of 50 mA/cm², temperature of 25 °C, and initial pH of 7), the MB removal rate reached 100 %, and the total organic carbon (TOC) removal rate reached 64.37 %. Based on electron paramagnetic resonance (EPR) and high-performance liquid chromatography-mass spectrometry (HPLC-MS) results, a degradation mechanism for MB was proposed. The Environmental Chemistry and SAR Tool (ECOSAR 2.2) programme was applied to simulate the acute and chronic toxicity of MB degradation intermediates, revealing that some intermediates (TP3, TP5) exhibited higher toxicity than the parent compound. Toxicity of water samples at different degradation times was further evaluated using wheat and Bacillus subtilis. After 60 min of degradation, the wastewater had almost no effect on the growth of wheat or Bacillus subtilis.