Promoting oxygen vacancies utility for tetracycline degradation via peroxymonosulfate activation by reduced Mg-doped CoO: Kinetics and key role of electron transfer pathway.

Developing cobalt-based catalysts with a high abundance of oxygen vacancies (V) and exceptional V utility efficiency for the prompt removal of stubborn contaminants through peroxymonosulfate (PMS) activation poses a significant challenge. Herein, we reported the synthesis of the reduced Mg-doped CoO nanosheets, i.e. Mg-doped CoO-r, via Mg doping and followed by NaBH reduction, aiming to degrade tetracycline (TC). Various characterization results illustrated that NaBH reduction imparted higher V utility efficiency to Mg-doped CoO-r, along with an ample presence of reduced Co species and an increased surface area, thereby substantially elevating PMS activation capability. Notably, Mg-doped CoO-r achieved more than 97.9% degradation of 20 mg/L TC within 10 min, showing an over 8-fold increase in reaction rate relative to the Mg-doped CoO (k: 0.3285 min vs 0.0399 min). The high removal efficiency of TC was sustained across a broad pH range of 3-11, even in the presence of common anions and humic acid. Radical quenching trials, EPR outcomes, and electrochemical analysis indicated that neither radicals nor O were the primary active species. Instead, electron transfer pathway played a dominant role in TC degradation. The Mg-doped CoO-r displayed excellent recyclability and versatility. Even after the fifth cycle, it maintained an impressive 83.0% removal of TC. Furthermore, it exhibited rapid degradation capabilities for various pollutants, including levofloxacin, pefloxacin, ciprofloxacin, malachite green, and rhodamine B. The TC degradation pathway was proposed based on LC-MS determination of its degradation intermediates. This study showcases an innovative strategy for the rational design of an efficient cobalt-based activator, leveraging electron transfer pathways through PMS activation to degrade antibiotics effectively.