Degradation Of Pyraclostrobin In Water By Nanosecond Pulsed Gas-Liquid Discharge Plasma At Atmospheric Pressure

With the development of agricultural society,the problem of pesticide residues in the environment caused by the excessive use of pesticides has become increasingly prominent.Atmospheric pressure gas-liquid discharge plasma has been applied in pollutant control because of its advantages:low energy consumption,abundant active particles,simple operation,fast and efficient degradation of pollutants,and no secondary pollution.Firstly,a self-designed array of pin-wire structure discharge reactor was used to obtain a uniformly dispersed gas-liquid discharge,and the plasma characteristics were diagnosed.Secondly,an array of pin-wire structure discharge reactor was optimized to obtain mixed gas-liquid discharge at the same time as bubble discharge at the liquid level and gas phase discharge at the liquid level.The generation of active particles was controlled by changing experimental parameters.Finally,the mixed discharge generated by an array of the needle-needle reactor was applied to remove pyraclostrobin,a typical pollutant in water.The main research contents are as follows:（1）Characteristics diagnosis of atmospheric nanosecond pulsed gas-liquid discharge plasma.An array of the needle-wire reactor obtained the gas-liquid discharge plasma with uniform dispersion.The discharge image,voltage and current waveform,gas-phase active species,gas temperature,solution p H value,and liquid-phase active species were studied.The study found that The active substances in the discharge process mainly include N₂（C³Π_u→B³Π_g）,N₂⁺（B²∑_u⁺→X²∑_g⁺）,OH（A²∑→X²Π）,and O（3p¹P→3s⁵S）.T Using Specair software for plasma N₂（C³Π_u→B³Π_g）to carry on the fitting when pulse peak voltage of 24k V,plasma resonance rotational temperature of 360 K,the dynamic temperature of 3250 K.With the increase of pulse peak voltage and discharge time,the p H value of solution decreased gradually,while the contents of active species（OH,H₂O₂,NO₃^-,NO₂^-）in liquid phase increased.（2）Generation and regulation of active species of atmospheric nanosecond pulsed,mixed gas-liquid discharge plasmas.The mixed discharge of bubble discharge under the liquid and gas phase discharge on the liquid surface is obtained through the improvement of the array pin-wire structure discharge reactor.The plasma generation and the transformation of discharge mode are studied by analyzing the plasma discharge photos and voltage and current waveform.Usingline of the stark broadening method calculated the plasma electron density;The effects of peak pulse voltage and oxygen ratio on the generation of active species were investigated.It is found that when the peak pulse voltage is greater than 24 k V,the discharge mode changes from streamer discharge to spark discharge.When the peak pulse voltage is 24 k V,the plasma’s rotational temperature and vibration temperature are 450 K and 3200 K,respectively.The plasma electron density is 7.14×10¹⁷ cm^-3.With the increase of peak pulse voltage and discharge time,the content of plasma active species increases,and with the rise of oxygen content,N₂（C³Π_u→B³Π_g）,N₂⁺（B²∑_u⁺→X²∑_g）⁺,and OH（A²∑→X²Π）content decreased,while O（3p¹P→3s⁵S）.（3）Removal of pyraclostrobin from water by atmospheric nanosecond pulsed mixed gas-liquid discharge plasma.The needle-needle structure discharge reactor array was used to remove pyraclostrobin residue in water.It was found that the removal rate of pyraclostrobin increased with the increase of pulse peak voltage.When the pulse peak voltage was 28 k V,and the initial concentration was 20 mg/L,the pyraclostrobin was wholly degraded after 10 min of discharge treatment.By measuring the liquid phase active particles in deionized water and pollutant solution and adding the liquid phase active particle catcher,the influence of OH and H₂O₂ produced in the discharge process on the degradation was studied.OH played a crucial role in the degradation process.HPLC-MS/MS was used to analyze the degraded intermediates,and the possible degradation paths were deduced by combining the molecular structure,mass spectrum information,and related literature reports.The Gibbs free energy of each intermediate was calculated by density functional theory to verify the derivation of the degradation paths.