The Product Mode And Behavior Of DBD Under Different N₂/O₂ Mixture Ratios And Its Sterilization Application

Dielectric barrier discharge?DBD?,as a technological means for generating large-area non-thermal plasma at atmospheric pressure,had been widely used in ozone synthesis in the early stage.And most scholars were committed to studying the mechanism of ozone generation by DBD,while ignoring the research work on nitrogen oxides generation.With the development of plasma medicine,the role of those nitrogen oxides,especially peroxynitrite?ONOO^-?,in biomedicine has gradually emerged.For example,nitric oxide?NO?not only has antiatherogenic properties,which can be applied for vasodilatation and improvement of microcirculation disorders,but also is beneficial to promoting wound healing.As for nitrogen dioxide?NO₂?,it can be used in the field of medical instrument sterilization with the advantages of less residual disinfectant and sterilization at room temperature.As an inhaled anesthetic gas,N₂O can be used for surgical anesthesia.And ONOO^-plays an important role in cell signal transduction and antimicrobial defense in human body,which is considered to be an environment-friendly antibacterial drug with broad application prospect.However,few studies on regulating mechanism of nitrogen oxides produced by DBD hinder the further development of DBD in the field of biomedicine.Therefore,in this thesis,the product modes and rules of DBD under different applied voltage and gas flow rate conditions are investigated by changing the N₂/O₂ mixture ratio of the working gas.Furthermore,we conduct a study on the problem that whether gaseous ONOO^-exists in the discharge products of DBD.And then the DBD is applied for biological sterilization.Firstly,the discharge products of coaxial DBD driven by an AC power are measured by a Fourier transform infrared spectrometer.It is found that under different N₂/O₂ mixture ratio conditions,the discharge products have three modes:ozone mode,nitrogen oxides mode and transitional mode.The ozone mode tends to appear at lower applied voltage and higher gas flow rate.And the nitrogen oxides mode has a tendency to occur at higher applied voltage and lower gas flow rate.As for the transitional mode,it is observed at the boundary of ozone mode and nitrogen oxides mode.In order to further study the mechanism of mode transition of DBD,the calculation method of energy per area based on ICCD image is introduced in this thesis.Under different product modes of DBD,the energy per area is calculated.And the results show that the value of energy per area in the ozone mode is always lower than that in the nitrogen oxides mode.As for the transitional mode,the energy per area is located in an interval between the ozone mode and the nitrogen oxides mode.Additionally,with the rising of oxygen content in the working gas,the critical energy per area of mode transition tends to increase.Secondly,the variation in the concentration of gaseous product of DBD with applied voltage,gas flow rate and oxygen content is studied.And the product mechanism is explained in combination with the energy per area.In addition,the liquid chromatography-mass spectrometry and fluorescence spectroscopy are used to explore the problem that whether gaseous ONOO^-exists in the chemical products of DBD.And it is found that the discharge can produce gaseous ONOO^-.But the gaseous ONOO^-only exists in the nitrogen oxides mode instead of the ozone mode and the transitional mode.Finally,the gaseous products of DBD are used for the sterilization of Penicillium digitatum.The germination inhibition rate of Penicillium spores under different product modes of DBD is studied.And the sterilization mechanism is explained by the variation rules in the concentration of gaseous product with applied voltage,gas flow rate and oxygen content.The results show that in the ozone mode,lower applied voltage is more beneficial to improving the inhibition effect of DBD products on the germination of Penicillium spores,which is attributed to the existence of O₃.As for the nitrogen oxides mode,lower gas flow rate is more conducive to improving the germination inhibition rate of Penicillium spores,which is ascribed to the existence of NO and ONOO^-.Compared with the ozone mode and the nitrogen oxide mode,the transitional mode has a lower germination inhibition rate of Penicillium spores,and its inhibition effect is considered to be caused by the synergistic effect of various products,such as O₃,NO₂,N₂O and N₂O₅.