The Kinetic Mechanisms of Diffuse Nanosecond Pulsed Discharge in the Degradation of Hcho

Abstract

It has been proposed that nanosecond pulsed discharge (NPD) has unique advantages in the degradation of volatile organic compounds (VOCs) with optimized ionization efficiency and prevented thermal instability1, 2 Since the complex kinetics processes of physicochemical and chemical reactions in the plasma system, the kinetics mechanisms for VOCs degradation and the control of by-production are still uncertain. In this work, a diffuse nanosecond pulsed dielectric barrier discharge plasma source is developed for the degradation of HCHO using needles array to plate electrode configuration. The fast exposure images, the time evolution for electrical behavior, and the temporal resolved spectra are used to study the instantaneous characteristics of the discharge and understand the mechanisms of plasma processes. On the assist of instantaneous characteristics, the kinetic mechanisms of physiochemical processes for active species conversion and HCHO degradation are described. It is shown that the metastable nitrogen molecules play the important role in the generation of high energy level state excited particles of $\mathrm{N}_{2}\,(\mathrm{C}^{3}\Pi _{\mathrm{u},}\,\mathrm{C}^{5}\Pi _{\mathrm{u}})$ in the generation of active species of O, H and OH, and in the degradation of HCHO. The oxygen mole fraction has the obvious influences on variety and number density of active species. Corresponding for the mechanisms of HCHO degradation, the radicals OH and H are the dominate particles at low oxygen mole fraction $( <2$%), the atom O becomes the dominate species when the oxygen mole fraction is higher than 5%. And for metastable nitrogen molecules, they still occupy the quotient for about 10%-12% of the HCHO degradation radio when the OMF is 5-21%, although their number densities lower than atom O about 3 orders in magnitude.