Controllable growth on nano-graphite-supported ZrO2–MnOx bimetallic oxides for electrocatalytic antibiotic degradation: mechanism to boost the Mn3+/Mn4+ redox cycle

Abstract

Antibiotic contamination has become one of the most pressing problems in the field of water purification. Using nano-graphite (nano-G) as a carbon carrier, a ZrO₂–MnO_x/nano-G composite electrode with high catalytic activity was prepared by a hot pressing method based on MnO_x/nano-G prepared by a sol–gel method. The results showed that the ZrO₂–MnO_x/nano-G electrode reduces charge transfer resistance while improving surface oxygen desorption ability. MnO_x can catalyze the two-electron reduction of O₂ to produce H₂O₂, which can then be converted to ˙OH and ˙O₂⁻. Thereafter, the results of free radical capture experiments confirmed that ˙O₂⁻ played a significant role in the electrocatalytic degradation of tetracycline hydrochloride (TC) by a ZrO₂–MnO_x/nano-G composite electrode. Furthermore, the abundant hydroxyl groups on the surface of nano-G and ZrO₂ particles can be used as active sites for catalyzing the Mn³⁺/Mn⁴⁺ redox reaction, resulting in the generation of additional free radicals. The high-efficiency electrocatalytic degradation of TC was achieved through the synergistic action of the three. Under optimal reaction conditions, the degradation rate of TC reached 93% after 120 min of electrolysis. ZrO₂–MnO_x/nano-G displayed satisfactory stability following 10 cycles of degradation experiments. Finally, the potential TC degradation pathway was investigated using liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT), and the degradation mechanism was clarified.