The effect of pH on the aqueous reactive species in sodium phosphate buffers induced by surface air discharge

The solution pH is an important parameter for the applications of atmospheric plasmas such as sewage disposal, food processing and biomedicine, mainly because the pH affects both the liquid-phase chemistry and the oxidation potential of the plasma-generated aqueous reactive species. In order to unravel the correlation between the aqueous reactive species and the solution pH, a numerical model was developed in this paper to study the sodium phosphate buffers treated by the surface plasma in atmospheric air, and the initial concentrations of phosphates in the buffers were altered to make the initial pH change from 3.0 to 11.9. After treated by the surface air plasma for 1 min, it was found that the concentrations of aqueous O₃, HNO₂, HNO₃ and NO₃ decreased with an increase in the initial pH, while those of , O^-, , , , ONOO^- and O₂NOO^- anions increased. Additionally, the concentrations of aqueous H₂O₂, HO₃, and NO₂ changed little with the initial pH. The oxidation potentials of O₃, OH, H₂O₂ and HO₂ decreased with the increasing initial pH, but those of ONOOH and ONOO^- peaked at pH ∼ 8. Some phosphorous compounds such as were also produced, which had an undeniable effect on the liquid-phase chemistry of the reactive species at pH 6.0.