Novel process of NO removal from simulated flue gas using a Fe/Gr periodically reversing electro-activated peroxymonosulfate system

Nitric oxide (NO) emissions seriously threaten the atmospheric ecology and cause air quality degradation, and the acid rain type has gradually changed from sulfuric acid to nitric acid in some areas of China. To this end, an efficient, facile, innovative strategy of NO removal from simulated flue gas using Fe/Gr periodically reversing electro-activated peroxymonosulfate (PMS) system is proposed for the first time. Encouragingly, we find that the graphite (Gr) electrode has the similar electrochemical property to those of the boron-doped diamond (BDD) and platinum (Pt) electrodes, converting SO42- to sulfate radicals (SO4 center dot-), and provide direct spectroscopy evidence for the theory that the electron e(-) can activate PMS to generate SO4 center dot- and hydroxyl radicals ((OH)-O-center dot) via the electron paramagnetic resonance (ESR) tests. In addition to the two free radicals mentioned above the singlet oxygen (O-1(2)) is detected synchronously in the electrical-activated PMS system. And the signal intensity of the radicals detected increases with increasing current intensity correspondingly. Addition of excess methanol has a greater effect on the NO removal than tert-butanol and sodium azide, demonstrating that SO4 center dot- dominates the NO removal. Furthermore, the results show PMS concentration, current intensity, pH, in-situ generated Fe2+ and O-2 concentration have the distinct effect on the NO removal. Compared with different electro-activation systems of Fe/Fe and Gr/Gr and BDD/Gr, Fe/Gr achieves the optimum NO removal effect. Finally, the reaction mechanism is proposed: direct electrode oxidation, non-radical oxidation, and radical oxidation are combined to remove NO in the electro-activated PMS reaction system.