Synergistic generation of N₂O₅ by needle-ring electrode and gliding arc discharge air plasmas for enhanced bacterial inactivation

In recent years, non-thermal plasma has been widely used in the field of sterilization. This study aims to enhance the plasma’s bactericidal efficacy by increasing N₂O₅ production in the plasma effluent. In this study, a novel hybrid plasma system [combining needle-ring electrode (NRE) air plasma with gliding arc discharge (GAD) air plasma] was developed. The voltage-current waveforms and optical emission spectroscopy results were used to characterize the fundamental discharge properties of both air plasmas. Fourier-transform infrared spectroscopy results confirmed three distinct product profiles: the NRE air plasma primarily generated O₃ with trace N₂O₅, while the GAD air plasma predominantly produced NO and NO₂. Remarkably, the hybrid system presented a substantial increase in N₂O₅ yield through synergistic interactions of the products of the two air plasma sources. Then, water treatment experiments demonstrated that the hybrid system induced drastic physicochemical changes in liquid, including significantly reduced pH (≈2), high ORP (≈500 mV), and elevated NO₃⁻ concentration (>5 mM), outperforming individual treatments. Finally, the results of plate count assay demonstrated that the bactericidal efficiency of the hybrid system surpassed that of individual air plasma treatments. This work proposes an innovative strategy for plasma-based disinfection utilizing reactive oxygen and nitrogen species, with potential applications in medical sterilization and water treatment.