MgO/Co3O4 composite activated peroxymonosulfate for levofloxacin degradation: Role of surface hydroxyl and oxygen vacancies

Abstract

Heterogeneous activation of peroxymonosulfate (PMS) by transition metal oxides has drawn more and more attention in the past decades, while the loss of M−OH on the catalyst surface has been a primary rate-limiting factor for PMS activation. Here, the MgO/Co3O4 composite with hydroxyl groups and oxygen vacancies (Ov) were obtained by modifying Co3O4 with alkaline earth metal oxide MgO, and used for activating PMS to remove levofloxacin (LEV). LEV removal rate constant (kapp) in the MgO/Co3O4-PMS system was 0.9077 min−1. It is above 124 and 101 times that of the (MgO + Co3O4)-PMS mixed mechanically system (0.0073 min−1) and the sum of MgO-PMS (0.0025 min−1) and Co3O4-PMS (0.0064 min−1) systems. The MgO/Co3O4-PMSsystem achieved effective LEV removal in a wide range of pH from 3.00 to 10.00, as well as excellent reusability and universality. Effects of various factors, such as reaction temperature, anions, and organic matter on the removal of LEV were explored. The activation energy of MgO/Co3O4 for LEV degradation was 27.50 kJ mol−1. X-ray photoelectron spectroscopy and electrochemical characterization revealed that MgO incorporation enhanced surface hydroxyl level and electronic transfer ability of Co3O4. The existence of Ov was confirmed by electron paramagnetic resonance characterization. Ov can accelerate the Co2+/Co3+ cycle to enhance PMS activation. Radical quenching tests and EPR trials proved the combined action of radicals (•OH, SO4•–) and non-radical (1O2) pathways for the efficient oxidative decomposition of LEV. The likely mechanism of PMS activation by the MgO/Co3O4 and LEV degradation pathways were discussed.