Degradation of 4-chlorophenol using MnOOH and γ-MnOOH nanomaterials as porous catalyst: Performance, synergistic mechanism, and effect of co-existing anions

Abstract

Transition metal catalysts have been proven to be a highly-potent catalyst for peroxymonosulfate (PMS) activation. The present work aimed to synthesizes the gamma-MnOOH and MnOOH based on the one-pot hydrothermal method as PMS activators for efficient degradation of 4-chlorophenol (4-CP). The effect of operational parameters including solution pH, gamma-MnOOH and MnOOH dose, PMS dose, 4-CP concentration, and also mixture media composition was elaborated. The results showed that the combination of MnOOH and gamma-MnOOH with PMS noticeably creates a synergistic effect (SF) in 4-CP degradation by both PMS/MnOOH and PMS/gamma-MnOOH process, with a SF value of 48.14 and 97.42, respectively. In both systems, the removal of 4-CP decreased in severely alkaline and acidic conditions, while no significant changes were observed in pH 5 to 9. Also, coexisting PO43- significantly reduced the removal efficiency of both systems. In addition, the effect of humic acid (HA) as a classical scavenger was investigated and showed that presence of 4 mg/L HA reduced the removal efficiency of 4-CP in the PMS/MnOOH process from 97.44 to 79.3. The three consecutive use of both catalysts turned out that MnOOH has better stability than gamma-MnOOH with lower Mn ions leaching. More importantly, quenching experiment showed that both non-radical (O-1(2) and O-center dot(2)) and radical ((SO4-)-S-center dot and (OH)-O-center dot) pathways are involved in 4-CP degradation and non-radical pathway was the dominant one in both systems.