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Reactive Species Generation in Water Films Treated by Dielectric Barrier Discharges with Different Gases

This study investigates the generation of reactive species in water films treated by dielectric barrier discharges with various gases. The research explores the plasma's ability to activate liquids for pollutant degradation and biomedical applications.

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Reactive Species Generation in Water Films Treated by Dielectric Barrier Discharges with Different Gases

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  1. Generation of reactive species in water films treated by dielectric barrier discharges with different gases Soheila Mohades1, Amanda M. Lietz1, Vesna V. Kovačević2, Bratislav M. Obradović2, Milorad M. Kuraica2 and Mark J. Kushner1 1University of Michigan, Ann Arbor, MI 48109-2122 USA 2University of Belgrade, 11001 Belgrade, Serbia smohades@umich.edu International Conference on Plasma Medicine June 2018 * Work supported by National Science Foundation and Department of Energy Office of Fusion Energy Science ICPM_2018

  2. University of Michigan Institute for Plasma Science & Engr. AGENDA • Falling Water DBD Reactor • Model Description • Plasma with Multiple Pulses with Different Gases • RONS in Gas and Liquid Phase • Circulating Plasma Activated Water (PAW) • Concluding Remarks ICPM_2018

  3. University of Michigan Institute for Plasma Science & Engr. MOTIVATION • Direct or indirect contact of non-thermal plasma sources are used for plasma activation of liquids with applications in degradation of pollutants in solutions and biomedicine. • Understanding chemical processes in plasma − liquid is important to optimize desired properties of plasma activated liquid. • Gas mixture and configuration such as surface/volume ratio are important factors in RONS production. • Different reactors are being developed water treatment: • Kovalova et al. Bioelectrochemistry 112 (2016) 91-99 • Selma MededovicThagard, MIPSE, University of Michigan, April 4, 2018  • Kovačevićet al. J. Phys. D: Appl. Phys. 50 (2017) 155205 ICPM_2018

  4. University of Michigan Institute for Plasma Science & Engr. FALLING WATER DBD REACTOR • DBD reactor: Two parallel cylindrical glass tubes with bounding electrodes • DBD discharges in the gap in contact with water layer. • Gap 4.3 mm, inner radius 10 mm, outer radius 14.5 mm, water film thickness 0.22 mm. • In experiment PAW was collected in a reservoir and pumped into reactor (recirculated 10 cycles). • In model, we used gas and liquid densities at the end of each cycle as the initial density for the next cycle. • Kovačevićet al. J. Phys. D: Appl. Phys. 50 (2017) 155205 ICPM_2018

  5. University of Michigan Institute for Plasma Science & Engr. DBD OPERATES WITH DIFFERENT GASES • GlobalKin, 0-D • Feed gases: Ar, He, O2, N2, air • Added humid air impurities: 3.5% (N2/O2/H2O=0.8/0.2/2.5) • Liquid: H2O + solvated N2/O2 (~9/5 ppm) • Flow rate: 132 sccm to match gas residence time in the experiment • 87 gas and 92 aqueous species • 2600 total reactions • 21 W, 600 Hz, triangle pulse • 1 cycle: 1,500 pulses (2.5 s), 10 s afterglow • Gas/liquid volume ratio ~ 25 • Plasma activated water (PAW) recirculates through reactor 10 times (here called 10 cycles) 1 cm Dielectrics Water Gas V • Schematic of the reactor ICPM_2018

  6. University of Michigan Institute for Plasma Science & Engr. DESCRIPTION OF GlobalKIN • GlobalKINis a 0-dimensional global model for plasma chemistry, plasma kinetics and surface chemistry. • Complete chemistry can be addressed with rapid computation. • Spatially dependent phenomena are not captured other than by plug flow and diffusion lengths. Boltzmann Equation Solver for Electrons Plasma Chemistry Module Plasma Chemistry Reaction Mechanism Circuit Module DVODE ODE Solver for Rate Equations Surface Chemistry Module Ion Mobility Database Diffusion Option Electron Cross Section Database Gas Flow Option ICPM_2018

  7. University of Michigan Institute for Plasma Science & Engr. GlobalKINLIQUID MODULE • Liquid is treated as separate "zone" with its own reaction mechanism. • Transport from gas to liquid is through an interfacial surface. • From gas plasma’s perspective, interface is analogous to a reactive surface, with a sticking coefficient and a return flux. • All charged species diffusing to liquid surface solvate. • Neutrals diffusion is restricted by h - Henry’s law constant • Water evaporates into gas phase. • "Sticking" gas phase species enter liquid. • Sticking coefficient, S, based on Henry’s law limited transport into liquid ICPM_2018

  8. University of Michigan Institute for Plasma Science & Engr. GlobalKINLIQUID MODULE Charged and Excited Species RNS ROS M* M+ e M- O3 O H2O2 H HO2 N NOx NxOy HNOx O2 H O2 O3 O H2 H HO2 N N2 OH eaq O2-, OH-, O3- H2O+ HO2 NOx OH H NOx NxOy M- OH OH, HO2 H3O+ H, OH, HO2 O3- OH H2O2 H3O+ H, H2 H3O+ O2- ONOOH HO2NO2 HNO2 HNO3 H3O+ H3O+ ,OH- H2O HO2- O3 ONOO- O2NO2- NO2- NO3- = slow decay = equilibrium = reaction with H2O ICPM_2018

  9. University of Michigan Institute for Plasma Science & Engr. PLASMA PROPERTIES Power (W/cm-3) • 1 atm, Argon with saturated water vapor. • 40 ns triangle pulse with peak power density at 1340 W/cm-3 • Te and ne are from the first pulse • ne peak is at maximum power ICPM_2018

  10. University of Michigan Institute for Plasma Science & Engr. Te AND ne IN DIFFERENT GASES • Te and ne are higher in He than other gases. • Highest ne in He then in Ar and lowest in N2. • ne quenches quickly in O2 due to its high electronegativity. ICPM_2018

  11. University of Michigan Institute for Plasma Science & Engr. GAS RONS, ARGON PLASMA, 1st CYCLE Density (cm-3) • “Cycle” refers to one trip of PAW through reactor. • RONS produced due to air impurities. • H2O2quickly saturates and its highest density is in Ar plasma due to higher OH and HO2 : • OH + OH + M  H2O2 + M H + H2O2  HO2 + H2 • Relatively high H and NO3- yields highest HNO3 in Ar. ICPM_2018

  12. University of Michigan Institute for Plasma Science & Engr. LIQUID RONS, ARGON, 1st CYCLE Density (cm-3) • H2O2aq and NO-3aq saturate during pulses and remain stable in afterglow • Highest H2O2aq in Ar plasma due to high H2O2(g) or OHaq. • Highest H3O+aq and lowest pH in Arplasma. Positive ion from gas quickly charge exchange with water forming H2O+aq and then H3O+aq. ICPM_2018

  13. University of Michigan Institute for Plasma Science & Engr. GAS RONS, HELIUM PALSMA, 1st CYCLE Density (cm-3) • He after Ar has the highest efficiency in OH and H2O2production which significantly drops during after glow. • H2 and H are higher in He: • H + H + M  H2 + M • Higher NO and HNOx in He and Ar plasma due to higher OH: • NO + OH + M  HNO2 + M • NO2+ OH + M  HNO3 + M ICPM_2018

  14. University of Michigan Institute for Plasma Science & Engr. LIQUID RONS, HELIUM, 1st CYCLE Density (cm-3) • RNS aqueous density and trends of decay in He and Ar are similar. • High H2aq in He helps dissociation of H2O2aqinto Haqand OHaqand a slight drop in it density during after glow. • Drop in O3aq can be due to drop in O3(g) and diffusing out of liquid which is prominent in thin film configuration (low Vl/Vg) and low Henry’s law species. ICPM_2018

  15. University of Michigan Institute for Plasma Science & Engr. GAS RONS, OXYGEN PLASMA,1st CYCLE Density (cm-3) • Largest O3 production in air and O2 plasmas due to high Oxygen: • O + O2 + M  O3 + M • NO is lowest in O2 plasma due to low N density, as NO is precursor of many RNS reactions lower density of NO2- and NO2: • O2+ N  NO + O • However, N2O is high which depends on O density on N2 proximity ICPM_2018

  16. University of Michigan Institute for Plasma Science & Engr. LIQUID RONS, OXYGEN,1st CYCLE Density (cm-3) • O3aq saturates quickly and is ~2-log higher in O2 and air plasma • O3aq drops quickly during afterglow by diffusion out, consumed by NO-2, or decomposition to HO2 radical (Equ. slide 18). • Primary source of ONOOH is NO2 and OH and as OH density drops slower in air and O2, ONOOH decay is slower. ICPM_2018

  17. University of Michigan Institute for Plasma Science & Engr. GAS RONS, AIR PLASMA,1st CYCLE Density (cm-3) • O3 is the dominant ROS in air • Largest production of NO2 and N2O due to high O and N density and lowest in H2 production. • NO quickly reacts with O in each pulse yields to high NO2: • NO + O + M  NO2 + M • NOxthen reacts with OH to form HNOxwhich is relatively high in air. ICPM_2018

  18. University of Michigan Institute for Plasma Science & Engr. LIQUID RONS, AIR,1st CYCLE Density (cm-3) • O2-aq , OH-aq, and HO2aq density grows during afterglow in air and O2 plasma via chain reactions: • 2O3 + H2O O2 + HO2·+ OH· • O2-aq quickly charge exchanges with O3aq. Higher O3-aq in air and O2 increases produces OH during after glow: • O3-aq+ H3O+aq O2aq+ H2Oaq+ OHaq ICPM_2018

  19. University of Michigan Institute for Plasma Science & Engr. GAS RONS, NITROGEN PLASMA,1st CYCLE Density (cm-3) • N2 is less efficient in RNS production than air (0.2% vs. 20% O2) • NO2 is the most stable RNS in after glow • Least efficient gas in ROS production. ICPM_2018

  20. University of Michigan Institute for Plasma Science & Engr. LIQUID RONS, NITROGEN,1st CYCLE Density (cm-3) • Decay of HNOxaq is faster in O2 and N2 plasma while it is relatively stable in Ar and He • Thermal decays of HNO4aq in O2, N2 and air results in growth in HO2 : • HNO4aq HO2aq + NO2aq • NO2aq is consumed to produce HNO2aq and HNO3aq ICPM_2018

  21. RECIRCULATION OF PAW University of Michigan Institute for Plasma Science & Engr. Number of cycles Number of cycles • Density of RONSaq at the end of each cycle (2.5 s plasma + 10 s afterglow). • H2O2aq increases with recirculation and max production rate is in Ar plasma in agreement with experimental results. • Recirculation slightly grows OHaqin Ar and drops in N2 and air which correlates to OHgas phase density. ICPM_2018

  22. University of Michigan Institute for Plasma Science & Engr. RONS IN LIQUID WITH RECIRCULATION Number of cycles Number of cycles • O3aqaccumulation is independent of recirculation to some extend with the highest production rate in He which is similar to the experiment results. • Significant accumulation of NO-3aq with all gases. HNO3 is a main source of plasma acidification and is more stable in its conjugate ion form, NO3-. Lowest pH in experiment was measured in Air (pH=2.5). ICPM_2018

  23. University of Michigan Institute for Plasma Science & Engr. SUMMARY • In solution aqueous densities after 10th cycle. • Arplasma is the most efficient in generating H2O2aqwhich agrees with experiments. • O2 is the most efficient gas in O3aq and OHaq production which also agrees with experiments. • Our results indicate most efficient NO3−aqand HO2aqproduction is in Ar. • HNO3(g) which is stable and accumulates with pulsing is higher in Ar. ICPM_2018

  24. University of Michigan Institute for Plasma Science & Engr. CONCLUDING REMARKS • With constant applied power for all gases He produces highest ne and Teand supports the highest O2−aq. • Ar plasma is the most efficient in generating H2O2due to high OH(g) density. He is second most efficient. • Highest solvated O3aq in both gas and liquid phase is O2 plasma followed by air plasma. Lowest O3aq density in Ar. • High HNOxaq in air and Ar is due to high NO and NO2 in gas phase which are source of NO2-aq and NO3- aq in liquid. • Circulation can enhance H2O2aq and NO-3aq density with highest rate in Ar and N2. ICPM_2018

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