Interface engineering-induced perovskite/spinel LaCoO3/Co3O4 heterostructured nanocomposites for efficient peroxymonosulfate activation to degrade levofloxacin

Conventional perovskite oxides (ABO3) tend to suffer from their inactive surfaces and limited active sites that reduce their catalytic activity and stability, while interface engineering is a facile modulating technique to boost the catalyst's inherent activity by constructing heterogeneous interfaces. In this study, perovskite/spinel LaCoO3/Co3O4 nanocomposites with heterogeneous interfaces were synthesized via sol-gel and in-situ gradient etching methods to activate peroxymonosulfate (PMS) for degrading levofloxacin (LEV). LaCoO3 on the surface was etched into spinel Co3O4, and LaCoO3/Co3O4 nanocomposites with two crystal structures of perovskite and spinel were successfully formed. The surface-modified LaCoO3/Co3O4 exhibited superior catalytic performance with a reaction rate constant more than 2 times that of the original LaCoO3, as well as excellent pH adaptability (3-11) and reusability (more than 6 recyclings) for LEV degradation. Besides, multiple characterization techniques were carried out to find that LaCoO3/Co3O4 possessed a larger specific surface area and richer oxygen vacancies after surface modification, which provided more active sites and accelerated mass transfer rate. The mechanism of reactive oxygen species involved in the reaction system was proposed that LaCoO3/Co3O4 not only reacted with PMS directly to produce SO4•- and •OH but also its surface hydroxyl group helped to form the [≡Co(Ⅲ)OOSO3]+ reactive complex with PMS to produce O2•- and 1O2. In addition, electrochemical experiments demonstrated that the surface electronic structure of LaCoO3/Co3O4 was effectively regulated, exhibiting a faster electron transfer rate and facilitating the redox process. By detecting and identifying degradation intermediates, three degradation pathways for LEV were proposed. Our work provided profound insights into the design of efficient and long-lasting catalysts for advanced oxidation processes.