Abstract
This work investigated the interface reactions between water and ionic wind from a positive d.c. corona discharge in nitrogen. The effects of drift ions and active neutral species were investigated on their production of hydrogen peroxide in water. Both positive drift ions and active neutral species were found to produce hydrogen peroxide in water. 1 mol positive drift ions can produce 0.13 mol hydrogen peroxide under atmospheric pressure; a reduced gas pressure increased the production of hydrogen peroxide, with 1 mol ions producing 0.29 mol hydrogen peroxide at 100 torr. The gas pressure has little effect on the production of hydrogen peroxide by active neutral species. The drift positive ions acted as ion anode on water surface, reacting with water to produce hydrogen, oxygen, and hydrogen peroxide. The adsorbed form of OH and O produced at the interface can synergistically work to react with the OH scavengers in water. Both HO2 and H2O2 from the discharge were transported to water to produce the liquid phase hydrogen peroxide.
Highlights
The interactions between water and plasma have been studied for more than two hundred years since the first report by Cavendish’s in 1785
The results prove that the difference in H2O2 production between the water and mesh cathode was mainly caused by the positive drift ions that were filtered by the mesh
The research demonstrated that H2O2 is produced in water under exposure to the ionic wind from d.c. corona discharge in nitrogen
Summary
The interactions between water and plasma have been studied for more than two hundred years since the first report by Cavendish’s in 1785. At the plasma–liquid interface, neutral species such as O, O3, OH, NO, HO2, H2O2, HNO2 and HNO3 from the discharge can be transported to the liquid (Bruggemann et al 2016). Sano investigated the interface reactions between water and corona discharges in N2/O2, and found that the neutral species like oxygen atom was generated in the presence of oxygen, and carried by ionic wind to the water surface, producing aqueous hydroxyl radicals (Sano et al 2002). Energised ions bombard the water surface to excite, ionize or dissociate the water molecules, and produce hydroxyl radicals, which have short lifetime of 2.7 μs at the interface (Attri et al 2015). The kinetic energy of positive ions bombarding the water cathode causes H2O excitation and ionization, and eventually
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