Sulfite Activation by Non-Thermal Plasma Coupled with Fe2+ for Ibuprofen Degradation: In-Depth Insight into Activation Energy Barrier and Mechanism

Abstract

This paper underscores the pivotal role of Fe2+ in influencing the degradation of ibuprofen (IBP) within non-thermal plasma (NTP) activated sulfite (S) system. At 200 μM Fe2+ dosage, the rate of IBP degradation can attain 94.8%. In contrast to the absence of Fe2+, there was a 43.1% increase in the rate of IBP degradation. The quenching experiment indicates that SO4·- and ·OH constitute the principal species in the system. This phenomenon predominantly stems from the Fenton-like reaction, expediting the conversion of H2O2 to ·OH. Additionally, the activation of sulfite by the Fe2+ and NTP promotes a concurrent increase in SO4·-. The introduction of Fe2+ results in the detection of a substantial quantity of ·OH and SO4·- in the system, validated through direct detection and electron spin resonance (ESR) signals. According to the density functional theory (DFT), the energy barrier of NTP/Fe2+ activation sulfite is lower than that of NTP system activation. By comparing the specific degradation pathways of NTP/S/Fe2+ and NTP/S systems, it can be concluded that the degradation of pollutants in NTP/S/Fe2+ system mainly depends on the action of active free radicals (·OH and SO4·-), while that in NTP/S system is mainly due to non-free radicals.

Keywords: Sulfite, Plasma, Fe2+, Ibuprofen, Activation energy barrier