Exclusion of the main role of oxygen vacancy in Cu-Mn-O/N-doped carbon catalysts for activating peroxymonosulfate to degrade p-nitrophenol (PNP) and reducing PNP in water by NaBH4

Abstract

Heterogeneous catalysts based on transition metal oxides are promising for activating peroxymonosulfate (PMS) for the degradation of organic pollutants and oxygen vacancy (VO) is often considered to be important in controlling catalytic performances. Herein, Cu-Mn-O/N-doped carbon catalysts were designed by changing the atomic ratio of Cu: Mn from 5:95 to 33.3:66.7, 50:50, and 95:5, resulting in the formation of VO or copper vacancy (VCu). Unexpectedly, all these catalysts showed excellent catalytic behavior toward the oxidation of p-nitrophenol (PNP) by PMS, indicating that VO is not the main factor in determining the catalytic performance, and the synergistic effect between Cu and Mn species was suggested to be the main factor. The impact of initial pH, catalyst dosage, PMS concentration, the concentration of PNP, and inorganic anions on the removal of PNP were explored. Electron paramagnetic resonance (EPR) tests and radical scavenging experiments revealed that both radicals and non-radicals were involved in the degradation of PNP and single oxygen (1O2) was the main reactive species. The intermediates were detected by using liquid chromatography mass spectrometry (LC-MS) in the degradation process, and a possible degradation mechanism was proposed. The developed catalysts also exhibited outstanding catalytic activities toward reduction reaction of PNP to P-aminophenol (PAP) by NaBH4. These results exclude the consideration of designing high-performance Cu-Mn-O oxide catalysts with oxygen vacancies.