Effect of solution pH on the characteristics of pulsed gas-liquid discharges and aqueous reactive species in atmospheric air

Solution pH is a significant parameter that affects the electrical characteristics of gas-liquid discharges and thus potentially produces different plasma chemistries for different plasma-engineered applications. In this study, the discharge characteristics and long-lived aqueous reactive species under different initial pH conditions were investigated. It was found that the discharge contained three phases in one pulse cycle, which occurred at the pulse rising edge, the falling edge, and between the rising and falling edges. The discharge intensity and average power at an initial solution pH of 7.0 are much lower than those obtained at an initial solution pH of 5.0 and 9.0. In contrast, the density ratio of N₂ (C³Π_u, v = 1)/N₂ (C³Π_u, v = 0) is much higher under neutral solution conditions, indicating that the relatively high vibrational energy was obtained in the gas-liquid discharge plasma. Concentrations of aqueous species H₂O₂, NO₂^-, and NO₃^- are higher at the initial pH of 9.0, indicating that different plasma intensities and chemical compositions (H⁺ and OH^-) are involved in their generation and consumption processes. This study provides insights into understanding and controlling the characteristics of the gas-liquid discharge under different solution conditions.