Plasma-water interface reactions caused by positive corona and glow discharges

Student thesis: Doctoral Thesis

Abstract

Plasma in and in contact with water has drawn extensive attention in the field of advanced oxidation processes, due to its advantages of producing various reactive species such as O, OH, HO2, H2O2 and O3 in water. Plasma-water interface reactions are one of the core challenges in this field since it involves multiple physical and chemical processes leading to complex mechanism of mass/energy transfer and reactive species production at interface. Exploration of the plasma-water interface reactions would promote the wide application of plasma in environmental remediation and plasma medicine.The objective of this research is to investigate the interface reactions between water cathode and positive plasma produced by two types of gas discharges: corona discharge producing low energy drift positive ions and glow discharge producing energetic positive ions. A nine-needle electrode was developed to initiate d.c. corona discharge in nitrogen and oxygen. The experiments with a mesh cathode above water and a water cathode were conducted to explore the effects of ions and reactive neutral species. Glow discharge was generated between a single-needle anode and water cathode in nitrogen, oxygen and helium. The electrical characteristics of the discharges have been studied. The treated solutions have been investigated, including hydrogen peroxide (H2O2) production, pH and conductivity change. The effects of gas flow rate, gas pressure and hydroxyl radical (OH) scavengers on H2O2 production were studied.In corona discharges, the contribution of positive ions and reactive neutral species to H2O2 production has been quantified. An analytical model that describes interface processes has been developed. The drift positive ions accumulated on water surface acted as ion-anode, on which the adsorbed hydroxyl radical (•OH) and oxygen radical (•O) were formed. The H2O2 production under both nitrogen corona discharge and oxygen corona discharge was proved not from the OH dimerization.In glow discharge, the amount of hydrogen peroxide (H2O2) produced by each positive ion has been proved higher than that in corona discharge, which is thought caused by the large kinetic energy of positive ions. In nitrogen and helium glow discharge, the majority of H2O2 production was found to be from OH dimerization. Oxygen glow discharge did not produce OH in water. The effects of ions’ kinetic energy and potential energy on the interface reactions were discussed.
Date of Award17 Dec 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorTao Wang (Supervisor) & Scott MacGregor (Supervisor)

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