Degradation of p-nitrophenol through microwave-assisted heterogeneous activation of peroxymonosulfate by manganese ferrite

P-nitrophenol (PNP) is considered as a priority pollutant due to its toxicity, non-biodegradation and high persistence in the environment. In this work, microwave (MW) acted as an assistant to enhance the degradation efficiency of PNP in MnFe2O4 activated peroxymonosulfate (PMS) catalytic oxidation. The magnetic MnFe2O4 particles were prepared using the co-precipitation method. The performance of PMS/MnFe2O4/MW is evaluated by the degradation efficiencies of PNP under varied conditions. The results showed that the degradation efficiency of PNP was greatly increased by the use of microwave radiation. 97.2% of PNP was degraded in 2 min using PMS/MnFe2O4/MW. The PNP degradation increased with higher PMS concentration, MnFe2O4 dosages and microwave output, while a slight decrease in PNP degradation was observed when the PMS concentration exceeded 2.5 mM. PNP degradation showed no dependence on initial pH, indicating that PMS/MnFe2O4/MW can be conducted at a wide range of pH value. Moreover, MnFe2O4 remained high catalytic activity after five runs. The mechanism of catalytic degradation was investigated by scavenging test and XPS measurement. Using methanol and tertbutanol as radical scavengers, the dominant radicals of the catalytic oxidation in the PNP degradation were identified as sulfate radicals rather than hydroxyl radicals. XPS measurement showed that both Mn(II)/Mn(III) and Fe(III)/Fe(II) were involved in the activation of PMS in this system. Additionally, the mechanism of microwave activation in PMS/MnFe2O4/MW system is also discussed. The enhancement of electron transfer and the increasing of reactants collision numbers are two potential mechanisms for the non-thermal effect of microwave activation. (C) 2015 Elsevier B.V. All rights reserved.