The Formation Pathways And The Quantification Of Aqueous Hydrogen Peroxide In The DC Plasma-liquid Systems

When discharge plasma is in contact with a liquid,various physical and chemical processes take place at the plasma-liquid interface via the plasma-liquid interactions,making the plasma-liquid system an interdisciplinary field involving plasma science,chemistry and physics.These processes ultimately induce changes in the bulk liquid on which a number of emerging technologies and applications are based,such as the nanomaterial synthesis,the plasma-based water treatment,plasma medicine,and plasma agriculture.The liquid changes usually involve the participation of short-and long-lived reactive species generated by the plasma-liquid interactions.In order to improve the applications of the plasma-liquid system,it is of great importance to figure out the formation pathways of reactive species in the liquid as well as to quantify these species,since which can provide a guide for controlling the generation of the reactive species.H2O2 is the most common long-lived reactive species and important in liquid chemistry of the plasma-liquid system.The formation pathways and quantification of aqueous hydrogen peroxide in the DC plasma-liquid systems are investigated in this paper.Using an aqueous solution of NaCl as cathode,we explored the atmospheric pressure Ar discharge plasma generated above the solution surface.The formation pathways of aqueous hydrogen peroxide(H2O2aq)in this system were investigated.Dimethyl sulfoxide was used as a scavenger of hydroxyl(OH)radicals to investigate the contribution of dissolved OH radicals to the H2O2aq.The results indicate that the H2O2aq is mainly formed by the combination of the dissolved OH radicals at the plasmaaffected thin liquid layer,while the H2O2 formed in the gas phase and the H2O2aq formation inside water by the plasma-induced ultraviolet radiation have no contribution.Using an aqueous solution of titanium sulfate[Ti(SO4)2&H2SO4],we investigated the H2O2 concentrations for liquid cathode and liquid anode at several discharge currents.The results indicate that the transformation efficiency of OHg?H2O2aq in the liquid cathode case is much larger than that in the liquid anode case,and initial H2O2 yield is proportional to the discharge current.