Degradation of aqueous methylparaben by non-thermal plasma combined with ZnFe2O4-rGO nanocomposites: Performance, multi-catalytic mechanism, influencing factors and degradation pathways

Non-thermal plasma (NTP) combined with zinc ferrite-reduced graphene oxide (ZnFe2O4-rGO) nanocomposites were used for the degradation of aqueous methylparaben (MeP). ZnFe2O4-rGO nanocomposites were prepared using the hydrothermal method, with the structure and photoelectric properties of nanocomposites then characterized. The effects of discharge power, initial MeP concentration, initial pH, and air flow rate on MeP degradation efficiency were investigated, and the multi-catalytic mechanism and MeP degradation pathways were established. Results showed that ZnFe2O4-rGO nanocomposites with a 10%:90% mass ratio of GO:ZnFe2O4 had an optimal catalytic effect. The MeP degradation efficiency of NTP combined with ZnFe2O4-rGO (10 wt%), was approximately 25% higher than that of NTP alone. Conditions favorable for MeP degradation included higher discharge power, lower MeP concentration, neutral pH value, and higher air flow rate. The degradation of MeP by NTP combined with ZnFe2O4-rGO nanocomposites followed pseudo-first-order kinetics. O-2(center dot-), center dot OH, H2O2, and O-3 were found to play important roles in the MeP degradation, as part of the multi-catalytic mechanism of NTP combined with ZnFe2O4-rGO nanocomposites. MeP degradation pathways were proposed based on the degradation intermediates detected by gas chromatography mass spectrometry, including demethylation, hydroxylation, carboxylation, ring-opening, and mineralization reactions. The prepared ZnFe2O4-rGO nanocomposites provide an approach for improved contaminant degradation efficiency, with reduced energy consumption in the NTP process. (C) 2021 Elsevier Ltd. All rights reserved.