Characterization of underwater discharge of microporous air plasma jet and its effect on degradation of liquid-phase formaldehyde

In recent years, research on cold atmospheric plasma has shown good application potential in the field of wastewater treatment. In this study, we designed a micro-porous plasma jet specifically for formaldehyde degradation in wastewater with air as the discharge gas. Electrical diagnosis and optical emission spectroscopy were performed to characterize plasma and identify plasma radicals/species. The mechanism of plasma degradation of formaldehyde was investigated by studying the physicochemical properties of plasma treated solution. The results indicated that the discharge intensity was positively correlated with the voltage. Additionally, the discharge intensity initially increased with the gas flow rate, and then gradually decreased with further increases in the gas flow rate. The spectral intensity was positively correlated with the voltage, and negatively correlated with gas flow. Under the discharge conditions of 8 kV voltage, 1 SLM gas flow, the degradation efficiency was the highest, and the formaldehyde degradation rate after 30 min treatment was 30.2%. Under the synergistic catalysis of plasma/FeSO₄/TiO₂, the degradation rate could reach 51.84%. Our research indicates that the micro-porous air plasma jet has the potential to be a green and efficient way to degrade formaldehyde in wastewater.