Role of O3 in the removal of HCHO using a DC streamer plasma

Formaldehyde is one of the most common volatile organic compounds and indoor contaminant, and one known to cause a variety of health problems. This paper proposes a streamer discharge reactor with negative or positive discharge for formaldehyde removal. The removal of HCHO and the simultaneous production of O3 in a DC streamer plasma were investigated. The performances of the positive and negative discharges were compared. The electrical characteristics such as U-I characteristics, discharge pattern, and power source efficiency were studied, and the reaction results were evaluated by O3 production, HCHO removal, and energy yield. Optical emission spectra were used to characterize the streamer and reactive species produced. A maximum HCHO removal rate of 78% was achieved at a specific energy density of 1700 J l−1. Results suggest that the positive streamer is better at producing O3 and oxidizing HCHO, compared to the negative counterpart. For the positive streamer plasma, the G-values of ozone production and formaldehyde decomposition are 0.59 molecules per 100 eV and 0.035 molecules per 100 eV, respectively. Interestingly, the production of O3 and degradation of HCHO were found to be simultaneous but quasi-individual processes. Both reactions were controlled by the generation of O atoms, however they consumed O atoms independently. The active species of OH, H and O radicals were observed, which had contribution to the degradation of formaldehyde. Finally, the reaction mechanism and most possible reaction pathways for the two processes were discussed.