Peroxymonosulfate decomposition by homogeneous and heterogeneous Co: Kinetics and application for the degradation of acetaminophen.

Peroxymonosulfate (PMS) decomposition, hydroxyl radical (•OH) generation, and acetaminophen (ACT) degradation by the Co/PMS system using homogeneous (dissolved cobalt) and heterogeneous (suspended Co3O4) cobalt were assessed. For the homogeneous process, >99% PMS decomposition was observed and 10 mmol/L of •OH generation was produced using 5 mmol/L of PMS and different dissolved cobalt concentrations after 30 min. A dissolved cobalt concentration of 0.2 mmol/L was used to achieve >99% ACT degradation using the homogeneous process. For the heterogeneous process, 60% PMS decomposition and negligible •OH generation were observed for 5 mmol/L of the initial PMS concentration using 0.1 and 0.2 g/L of Co3O4. Degradation of ACT greater than 80% was achieved for all experimental runs using 5 mmol/L of the initial PMS concentration independently of the initial Co3O4 load used. For the heterogeneous process, the best experimental conditions for ACT degradation were found to be 3 mmol/L of PMS and 0.2 g/L of Co3O4, for which >99% ACT degradation was achieved after 10 min. Because negligible •OH was produced by the Co3O4/PMS process, a second-order kinetic model was proposed for sulfur-based free radical production to allow fair comparison between homogeneous and heterogeneous processes. Using the kinetic data and the reaction by-products identified, a mechanistic pathway for ACT degradation is suggested.