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

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–MnOx/nano-G composite electrode with high catalytic activity was prepared by a hot pressing method based on MnOx/nano-G prepared by a sol–gel method. The results showed that the ZrO2–MnOx/nano-G electrode reduces charge transfer resistance while improving surface oxygen desorption ability. MnOx 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–MnOx/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–MnOx/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.