Generation and identification of O in catalysts/peroxymonosulfate systems for water purification.

Catalysts for peroxymonosulfate (PMS) activation are appealing in the purification of organic wastewater. Singlet oxygen (O) is widely recognized as a crucial reactive species for degrading organic contaminants in catalysts/PMS systems due to its adamant resistance to inorganic anions, high selectivity, and broad pH applicability. With the rapid growth of studies on O in catalysts/PMS systems, it becomes necessary to provide a comprehensive review of its current state. This review highlights recent advancements concerning O in catalysts/PMS systems, with a primary focus on generation pathways and identification methods. The generation pathways of O are summarized based on whether (distinguished by the geometric structures of metal species) or not (distinguished by the active sites) the metal element is included in the catalysts. Furthermore, this review thoroughly discusses the influence of metal valence states and metal species with different geometric structures on O generation. Various potential strategies are explored to regulate the generation of O from the perspective of catalyst design. Identification methods of O primarily include electron paramagnetic resonance (EPR), quenching experiments, reaction in DO solution, and chemical probe tests in catalysts/PMS systems. The principles and applications of these methods are presented comprehensively along with their applicability, possible disagreements, and corresponding solutions. Besides, an identifying procedure on the combination of main identification methods is provided to evaluate the role of O in catalysts/PMS systems. Lastly, several perspectives for further studies are proposed to facilitate developments of O in catalysts/PMS systems.