Mechanism Of Liquid Phase OH Production Induced By Atmospheric Pressure He Plasma Jet

Atmospheric pressure plasma can produce abundant reactive species at nearly room temperature.Studies have shown that these reactive species can cause some unique biological effects,so they have attracted more and more attention in the medical field(such as wound healing,sterilization,cancer treatment,etc.).However,in practical medical applications,the surface of living tissue is often wet or covered with a layer of bodily fluids.Due to the limited penetration of plasma,the plasma often reacts with the liquid first to generate reactive species in the liquid phase,and then these liquid-phase reactive species act on microorganisms or cells to achieve the corresponding medical effects.Among these liquid-phase reactive species,OH and H₂O₂ are the reactive species with significant biological effects.It is of great scientific significance to clarify the formation path and transformation mechanism of OH and H₂O₂ for the later elaboration of plasma biomedical mechanism,so it has attracted the attention of researchers in recent years.Although researchers have done more in-depth work on plasma-initiated liquid phase reactive species,it is still challenging to measure OH and H₂O₂ in both gas and liquid phases.Hitherto,the mechanisms and formation paths of gas-liquid phase transformation of OH and H₂O₂ are not clear.Based on those formation paths,we hope to diagnose these reactive species through appropriate experimental methods and make use of the differences in reactive species formation in the gas-liquid phase.Then we provide some improvement and supplement for the transition path and formation mechanism between the gas and liquid phases of OH and H₂O₂ and provide a specific theoretical and experimental basis for plasma biomedical applications in the future.In this paper,using a pulsed DC power supply,a self-made single electrode dielectric barrier discharge(DBD)plasma jet was used as the experimental device,and the mechanism of plasma-induced OH and H₂O₂ change was studied.1.In order to separate the influence of multiple factors on OH and H₂O₂,the plasma jet liquid system with different structures(plasma directly contacting liquid level and plasma cut-off state)is constructed to study the influence factors of one or some factors:to stop plasma by using grounded tungsten wire conductor to prevent it from being separated from liquid The direct contact of the phase insulates the influence of charged particles on OH and H₂O₂ in the liquid phase.2.The physical characteristics and the changes of gas-phase active particles in the above structures were analyzed using oscilloscopes and emission spectrum OES.The p H change of liquid and the change characteristics of OH free radicals and H₂O₂ of active particles in the liquid phase were studied and analyzed by p H meter,Ta,and H₂O₂ detection box.The results show that different discharge structures do not affect the discharge power of plasma gas-liquid phase system and ensure the comparability of the whole experiment;the relative strength change law of the excited active particle OH in plasma gas phase is clarified:the intensity of OH spectrum of plasma gas-phase cut off by metal is higher than that of other two cases;at the same time,the excited O atom is also obviously enhanced;in plasma,The concentration of OH in the liquid phase is deficient under the cut-off state,but the concentration of H₂O₂ in the liquid phase is significantly higher than that of other two cases.The results show that the hydrogen in liquid is the primary source of OH radicals with a short life in the liquid phase,and a small amount of liquid OH may be formed by gas diffusion.In the liquid phase,H₂O₂ is produced in the gas phase after plasma excitation and then diffuses into the liquid phase,rather than mainly produced by the OH complex in the liquid phase.3.The emission spectrum was used to diagnose the gas phase excited particles of He plasma jet mixed with O₂(0.0%-2.0%)in different volume ratio.The changes of OH free radicals and H₂O₂ in liquid phase induced by different oxygen content he plasma jet was studied by chemical method.The results show that with the increase of oxygen content in the working gas,the liquid OH produced by the regular contact with the liquid phase of plasma does not increase obviously,while the liquid OH caused by plasma in the cut-off structure increases obviously;for the direct contact or the cut-off state,the concentration of H₂O₂ in the liquid phase decreases with the increase of the volume ratio of O₂.The results show that the negative effect of O₂ will reduce the electron density in plasma,which leads to the decrease of OH density in the excited state.The participation of O₂ also causes a large number of O atoms in plasma.These excited O atoms will lead to the reduction of OH in the gas phase,and then the hydrogen dioxide in the gas phase will be reduced,so the H₂O₂ produced in the liquid phase will be reduced.A large number of O atoms will diffuse into the water body,which will consume H₂O₂ to produce HO₂ and produce the liquid OH radicals.In addition,the high activity of HO₂ will continue to react with O atoms to convert into a large number of OH radicals in the liquid phase,which may lead to the rise of liquid OH.4.In brief,the paper studies the elementary particles OH and H₂O₂ in liquid phase under different structure plasma liquid system,expounds the transformation mode and formation mechanism of short-life OH radicals and long-life H₂O₂ in liquid under different conditions,and provides a reasonable explanation,which provides an essential scientific basis for regulating and optimizing the application of cold plasma jet in the biomedical field.