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Fluorescence Spectroscopy for Quantifying OH Radicals Produced by Electrical Discharge Plasmas
Stephanie Hernandez1,2 and Selma Mededovic Thagard3
1ASSETs to Server Humanity REU Program, Clarkson University2Washington and Lee University, Department of Physics & Engineering
3Clarkson University, Department of Chemical and Biomolecular Engineering
Symposium on Undergraduate Research Experiences (SURE), July 30, 2015This project was supported in part by the National Science Foundation under Grant No. EEC-
1359256.
Gas Discharge Plasma
2
Plasma:A “soup” of electrons, ions, radicals and neutral molecules in an ionized gas which can be produced by electrical discharge in a liquid or gas.
Motivation and Objectives
Motivation:Plasma can be used for drinking and waste water treatment. As an Advanced Oxidation Process (AOP), its efficiency is proportional to the rate of ·OH radical production.
Objective: Development of a new method for quantifying ·OH radicals based on
fluorescence spectroscopy that uses sodium salicylate as a reagent. Comparison of ·OH radical production rates in three different plasma
reactors: liquid discharge, gas discharge, and gas discharge with bubbling.
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Fluorescence: The radiation emitted by certain substances when excited by a wavelength of light. The excitation and emission occur at different wavelengths.
Fluorescence Spectroscopy
Advantages: Sensitive Quantitative Quick Safe
Fluorescence Spectrophotometer
Ocean Optics Cuvettes
4
·OH scavenger - good selectivity Very soluble in water Affordable compared to other fluorescent probes High quantum efficiency Linear response over a wide spectral region
Sodium Salicylate (NaSCL)
5
Experimental: Plasma Reactor
Experimental ParametersVolume 100mLvoltage 20 kVRepetition Frequency 52 HzSalicylate 3.5mg/L or 10 mg/LArgon Flow Rate 440 mL/min
Liquid Discharge Plasma Gas Discharge Plasma Gas Discharge Plasma with Bubbling
Experimental ParametersVolume 1500mLvoltage 20.6 kVRepetition Frequency 52 HzSalicylate 3.5mg/L or 10 mg/LArgon Flow Rate 605 mL/min
Experimental ParametersVolume 1500mLvoltage 20.6 kVRepetition Frequency 52 HzSalicylate 3.5mg/L or 10 mg/LArgon Flow Rate 605 mL/min
Methods & Data Collection Prepare a calibration curve. Run 3.5 mg/L and 10 mg/L
Solutions of NaSCL in plasma reactors.
Collect 3 mL samples every 10 min for fluorescence spectroscopy analysis.
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Experimental: Analytical Method
Salicylate Emission Spectra
Inte
nsity
(a.u
) 10min20min30min40min
0min
Wavelength (nm)
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Results: Fluorescence
0 5 10 15 20 25 30 35 40 45 500
100
200
300
400
500
600
700
800
Fluorescence Quenching of NaSCL in Liquid Discharge
Plasma Reactor
10mg/L NaSCL3.5 mg/L NaSCL
Time (min)
Inte
nsity
(a.u
)
0 5 10 15 20 25 30 35 40 450
100
200
300
400
500
600
700
800
Fluorescence Quenching of NaSCL in Gas Discharge
Plasma Reactor
3.5 mg/L Gas Discharge3.5 mg/L Gas Discharge with Bubbling 10 mg/L Gas DIscharge
Time (min)
Inte
nsity
(a.u
)
8
Data Presentation/FindingsResults: Hydrogen Peroxide 2 2OH OH H OOH salycilate products
15 20 25 30 35 40 450.0
0.5
1.0
1.5
2.0
2.5
3.03.5
4.0
Hydrogen Peroxide Concentra-tion vs Time
0 mg/L NaSCL
3.5 mg/L Liquid Discharge
10mg/L Liquid Discharge
Time (min)C
once
ntra
tion
(mM
)0 10 20 30 40 50
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Hydrogen Peroxide Concentration vs Time
0 mg/L NaSCL Gas Discharge
3.5 mg/L Gas Discharge
3.5 mg/L Gas Discharge with Bubbling
10 mg/L Gas Discharge
Time (min)
Con
cent
ratio
n (m
M)
9
OH
Cathode
Direction of e- movement Plasma interior
Interface
Bulk liquid
Anode
Direction of e- movement
e-aq
Small surfactant (PFBA)
Polar head
Nonpolar tail
Non-surfactant (Salicylate)
Large surfactant (PFOA, PFOS, Gemfibrozil)
Nonpolar tail
Polar head
OH
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Fluorescence spectroscopy appears to be a good technique for relative comparison of OH radicals produced by electrical discharge plasmas.
Salicylate is not hydrophobic enough (i.e., it does not lower the surface tension of the solution) so its concentration at the plasma-liquid interface is not high enough. Not all ·OH radicals can be scavenged.
Because salicylate is hydrophilic, not a significant difference between the three plasma reactors was observed.
Data Presentation/FindingsConclusions
11
References
1. M.F. Al-Kuhaili, “A study of the Fluorescent Properties of spin-coated Sodium Salicylate Films,” Journal of Luminescence, vol. 117, iss.2, pp. 209-216, 2006.
2. Rahmi and H. Itagaki “Application of 2,5 Dihydroxybenzoic Acid as a fluorescent probe to the Clarification of Microevniorment in Hydrogels of Biopolymers,” Journal of Photopolymer Science and Technology vol. 24, no.5, pp.517-521,
2011.3. M. Karima, H.Leeb, Y. Kimb, H. Baeb, S. Lee “Analysis of salicylic acid based on the fluorescence enhancement of the
As(III)–salicylic acid system” vol. 576, iss 1, pp. 136-139, 2006.S. Kanazawa, T. Furuki, T. Nakaji, R. Ichiki, “Application of Chemical dosimetry to hydroxyl radical measurement during
underwater discharge.,” Journal of Physics: Conference Series, 2013.5. A. Gomes, E. Fernandes, J. Lima “Fluorescent Probes used for detection of reactive oxygen species,” Journal of
Biochemical and biophysical methods 2005 6. S. Kanazawa, T. Furuki, T. Nakaji, S. Akamine, R. Ichiki “Measurement of OH Radicals in Aqueous Solution Produced by
Atmospheric LF Plasma Jet,” 2005.7.R. Joshi, S.Mededovic Thagard, “Streamer-Like Electrical Discharges in Water: Part II Environmental Applications,” 2013.
References
12
Data Presentation/FindingsAcknowledgments
MentorsSelma Mededovic Thagard
Special thanks to Gunnar Stratton
Joshua FranclemontFei Dai
Xiangru Fan