| Plasma jets are rich in ROS and RNS,which is assumed to have great effect on many applications,such as sterilization,tooth whitening,blood coagulation.The hydroxyl radical(·OH),an environmental-friendly radical with strong oxidation,can decompose the organic chemicals into CO2 and H2 O.It can also kill all kinds of bacteria,fungi.So,improving the · OH production has a great significance in plasma applications.In order to improve the production of it,an air-water ring-needle plasma jet was designed and fabricated.Adding some water,the properties,mechanisms and its applications of this air-water plasma jet were studied.First of all,the air-water ring-needle plasma jet driven by DC power was generated.The influences of current,water ratio and gas flow rate on jet length,temperature and ROS production were studied.With the increase of water ratio,the length of plasma plume is shorter obviously,at the same time the temperature rises.Besides,the higher water ratio results in higher ·OH production and lower O production.This DC plasma jet was used in inactivation experiment of P.digitatum suspension.It can be found that the air-water plasma jet had a significant effect on sterilization.When the water ratio is 100%,the sterilization rateis 93%,which is much higher than that in the case of 0% water ratio.Then,because the temperature of DC air-water plasma jet is higher,the PDC power was employed to excite this jet.The results show that the temperature of PDC plasma is lower.The addition of water results in an increase of ·OH production with two kinds of power supplies.Inversely,the O production show a declining tendency with higher water ratio.Combined with temperature and ROS production,the PDC plasma with 100% water ratio is the best.It achieves lower temperature and more abundant production of ·OH and O,compared with DC power with 0% water ratio.At last,the temporal resolved optical emission spectroscopy measurement were presented.Besides,the head-on and side-on ICCD photographs were also taken.From the PDC discharge current waveform,it can be found that there are two pulses: the first one is steep-sided pulse lasts rapidly for 1?s;the second one is slower for about 40-45?s.The changing rule of O content is almost the same as the law of the current.The ·OH content just has one pulse.When the current reaches its first peak value,the ·OH content is not the highest.The ICCD photographs show that the air plasma propagation depends on the gas flow.The applied voltage and gas flow rate have little influence on the discharge area.Only high water ratio has a significant effect on it.With the increase of water ratio,the discharge area is much larger.In the discharge zone,the light emission at 100% water ratio is obviously stronger,compared with 0% water ratio;whereas in the plume zone,the light emission of the former is much weaker and the length is shorter.And the initial propagation velocity at higher water ratio is a little slower.All in all,the PDC air-water plasma jet has the advantage of lower temperature and higher ROS production,which has a wider prospect in the field of medical applications.In order to understand and control this air-water plasma jet better,the mechanisms of plasma propagation are also studied.Those studies provide some fundamental knowledge about non-noble gas plasma jets,and provide theoretical support for its applications. |
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