Low-Cost Paper Electrode Fabricated by Direct Writing with Silver

Dec 2, 2016 - A simple, low cost and user-friendly method for the fabrication of paper electrode (PE) using silver nanoparticles capped with octylamin...
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Low Cost Paper Electrode Fabricated by Direct Writing with Silver Nanoparticles Based Ink for Detection of Hydrogen Peroxide in Waste Water Archana Ghosale, Kamlesh Kumar Shrivas, Ravi Shankar, and Vellaichamy Ganesan Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03512 • Publication Date (Web): 02 Dec 2016 Downloaded from http://pubs.acs.org on December 5, 2016

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Low Cost Paper Electrode Fabricated by Direct Writing with Silver Nanoparticles Based Ink for Detection of Hydrogen Peroxide in Waste Water

Archana Ghosale1, Kamlesh Shrivas,1* Ravi Shankar2,3 and Vellaichamy Ganesan4

1

Department of Chemistry, Guru Ghasidas Vishwavidyalaya, Bilaspur, CG-495009, India

2

Nanoscience and Nanoengineering Program, South Dakota School of Mines and Technology, Rapid City, South Dakota-57701, USA

3

Fujifilm Imaging Colorants, Inc. 233 Cherry Lane, New Castle, Delaware-19720, USA

4

Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi, 221005, UP, India

*Corresponding author Email: [email protected] Phone: +91-7752-260488

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ABSTRACT A simple, low cost and user-friendly method for the fabrication of paper electrode (PE) using silver nanoparticles capped with octylamine (AgNPs-OA) is reported for detection of hydrogen peroxide (H2O2) in waste water samples. The PE was prepared by direct writing onto the photo paper using a ball-point pen filled with nano-ink (10 wt% of AgNPs-OA in chloroform). The prepared electrode was sintered at 100oC for 1 hour to make it conductive. The PE/AgNPs-OA was used as a working electrode in cyclic voltammetry (CV) for the detection of H2O2. The PE/AgNPs-OA exhibited a wide linear calibration range from 1.7 µM to 30 mM for the determination of H2O2 with a low limit of detection, 0.5 µM. The good recovery percentage (95.2 to 96.2%) and interference study for determination of H2O2 in waste water samples demonstrated the selectivity of the method from the complex sample matrices. The PE/AgNPsOA electrode is found to be economic, facile and user-friendly for multiple analyses (n=60) of H2O2 in CV compared to other commercially available electrodes and custom made modified electrodes.

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INTRODUCTION Hydrogen peroxide is an oxidizing agent and has broad application in preparation of deodorants, bleaching agents, disinfectants, and also in sewage treatments. It is used as a bleaching agent in paper industry, disinfectants in hospitals and as sterilizers in food industries. The industrial wastes, hospitals and domestic effluents containing H2O2 are main sources for contamination of natural water bodies. The introduction of H2O2 in human system through the drinking water may cause headache, nausea, dizziness and vomiting. Inhalation may cause irritation in nose, throat and lungs. Therefore, the monitoring of H2O2 in waste water samples is important to prevent the entry of this toxic chemical in to the environment.1-3 The analytical techniques such as spectrophotometry,4 infra-red spectroscopy (IR),5 chemiluminescence,6 fluorimetry7 and cyclic voltammetry (CV)8,9 are commonly used for the determination of H2O2 in variety of samples. Spectrophotometry, chemiluminescence and fluorimetry are found to be simple and sensitive techniques. However, these techniques require a chromophore or fluorofore to form a complex with a target analyte which are sometimes not selective for detection of analyte from the sample solution. In CV, the detection of analyte occurs at the surface of electrode through the redox reaction. The detection of H2O2 has primarily been done by immobilization of enzymes on the electrode surface, although the stability of enzyme, storage and reproducibility are the main issues.10 The electrode modification with different nanoparticles (NPs) such as gold (Au),11 silver (Ag)12 and platinum (Pt)13 has drawn attention as alternative of enzyme immobilization on the electrode surface. The use of metal NPs modified electrodes in CV measurements showed better performance, selectivity and sensitivity. The modification and pasting of electrodes or deposition of functionalized materials on the surface of electrodes require tedious, time consuming and complex process. The uniform coating of material on the surface of electrode is challenging and there are chances of breakage and leakage of materials from the surface of electrodes.

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Thus, gums and adhesives are being used along with the nanocomposites to prevent the rupturing of material from the modified electrode.14,15 The disadvantages of modified electrodes are excluded by the fabrication of the functional materials on different substrates such as plastics, polyvinyl chloride (PVC), polyethylene terephthalate (PET), glass and paper through lithography, chemical vapor deposition, spin coating and printing techniques.16-20 More recently, the direct writing of electrode with nano-ink on paper substrates using a ball pen has been employed.20-22 Moreover it is inexpensive compared to other plastic and polymeric substrates.23 In the present work, nano-ink of silver nanoparticles capped with octylamine (AgNPs-OA) was prepared and applied onto the photo paper for writing electrodes using a ball-point pen. Sintering temperature, sintering time and concentration of nano-ink were optimized for better conductivity of the deposited functional materials on paper substrate. In addition, the effect of pH, electrolyte concentration and scan rate were evaluated using CV for the optimum detection of H2O2. EXPERIMENTAL Reagents and Solution Preparations. Silver nitrate (99.0%), ascorbic acid (99.5%), acetone (99.5%), methanol (99.8%), toluene (99.5%), chloroform (99.0%), dichloromethane (99.5), H2O2 (30.0%), acetic acid (99.6), sodium acetate (99.5%) and potassium chloride (99.5%) were obtained from Himedia (Mumbai, India). Octylamine (98.0%), dopamine hydrochloride (98.0%) and sodium hydroxide (99.0%) were purchased from Sigma-Aldrich (MA, USA). Acetic acid and sodium acetate were used for the preparation of acetate buffer solutions (pH 3.0 to 5.0). Phosphate buffer solutions (PBS) of pH 7.0 and 9.0 were prepared from NaH2PO4 (99.0%) and Na2HPO4 (98.0%) obtained from Merck (Germany). Buffer solution of 11.0 pH was prepared from NaH2PO4 by adjustment with 0.1 M NaOH solution. All other chemicals

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and reagents used in this study were of analytical grade. Photo paper, PET sheet, PVC sheet, glass slides were purchased from local stationary shop. Synthesis of AgNPs-OA. The synthesis of AgNPs-OA in toluene was described by Tobita et al.24 For synthesis, 200 mg of AgNO3 was taken into a round bottom flask containing 10:1 ratio of toluene and octylamine. The solution mixture was stirred for 30 min at room temperature followed by the addition of 70 mg of ascorbic acid. The color of the solution was gradually changed from transparent to yellow and finally grey. The solution mixture was continued to stir for 2 h at room temperature. The synthesis of AgNPs-OA is schematically shown in Fig 1(a). On completion of the reaction, bluish-grey shiny particles were observed. Afterwards, 20 mL of acetone was added into the resulting mixture to precipitate the AgNPs. The supernatant solution was decanted and precipitated AgNPs was washed with acetone for five to eight times till the excess of solvent and OA were removed out. The obtained precipitated product was dried at room temperature. Preparation of AgNPs-OA Nano-Ink and Paper Electrode. An appropriate amount of AgNPs-OA was suspended in different solvents (methanol, toluene, chloroform, and dichloromethane) and stored at 4oC. The prepared nano-ink was filled into empty tube of roller ball pen (length: 10.0 cm, diameter: 0.4 cm and ball-point diameter: 0.1 cm) with the help of microsyringe. Electrode of 7.0 cm × 0.2 cm dimensions with 1.0 cm2 bottom area and ~5.5 µm thickness of film was drawn onto photo paper. The drawn electrode was sintered at 100 oC for 1 h (schematically shown in Fig. 1(b). The prepared electrode was optimized for better performance and applied for the determination of H2O2 using CV, shown in Fig. 1(c). Collection of Waste Water samples for Determination of H2O2. The municipal waste samples from the Bilaspur city (Chhattisgarh, India) were collected in polyethylene bottles during the month of June, 2016. The collected samples were filtered with Whatman filter 42 and stored in refrigerator at 5 oC until the analysis.

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Procedure for Detection of H2O2 in CV using PE/AgNPs-OA. The prepared PE/AgNPs-OA was used as a working electrode and conventional Ag/AgCl and platinum electrode (from Metroholm Autolab) were used as reference and counter electrodes, respectively for detection of H2O2. The CV measurement of H2O2 in water/waste water samples was performed in the presence of KCl (0.4 M) and PBS (0.2 M) at scan rate 0.1 V/s. The calibration curve which was prepared by recording the reduction peak current at different concentrations of standard H2O2 was used for determination of H2O2 present in waste water samples. Apparatus for characterization and determination of H2O2. The localized surface plasmon resonance (LSPR) absorption band of AgNPs-OA colloid was measured using UV-VIS Spectrophotometer type-1800 (Shimadzu, Japan). The shape and size of AgNPs-OA were determined by transmission electron microscopy (TEM) at an accelerating voltage of 120 kV. Energy-dispersive X-ray spectroscopy (EDX) connected with SEM was used to determine the composition of prepared AgNPs-OA. The modification of AgNPs with OA and the effect of sintering were confirmed by Fourier transform (FTIR), Type-IRA affinity (Shimadzu, Japan). CV measurements of H2O2 were performed using PGSTAT 101 potentiostat operated by NOVA 8.1 software packages (Metroholm Autolab, Netherland). RESULTS AND DISCUSSION Characterization of AgNPs-OA. The size, morphology and distribution of AgNPs-OA in chloroform solvent were confirmed by TEM measurements. Fig. 2(a) and (b) display the TEM images of AgNPs-OA and the average size of NPs was found to be 15+3 nm. The chemical composition of AgNPs/OA was examined with EDX analysis, shown in Fig. S1. Intense signal peaks were obtained corresponding to silver and carbon atoms due to the presence of capping group on the surface of AgNPs. No significant peak related to oxygen atom was observed in the spectrum illustrating that there was no any oxide formation on the surface of AgNPs.25 The size of AgNPs was primarily estimated by measuring the LSPR absorption band at 410 nm in

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UV-Vis (Fig 2c) confirming the size of AgNPs was in the range of 10-60 nm.20,26 Fig. 2(d) shows the FTIR spectra of AgNPs-OA before and after sintering. The strong peaks are observed at 2376, 1639 and 777 cm-1 corresponding to stretching and bending vibrations of amine capped molecules on the surface of AgNPs. The peaks obtained at 2914 cm-1 attributed to methylene C-H stretching of OA. The decrease in signal intensity after sintering of AgNPsOA showed the removal of some of the OA molecules from the surface of NPs.27 The removal of OA stabilizing molecules from the surface of AgNPs was also confirmed by the optical image of PE/AgNPs-OA before sintering (Fig. 3a) and after sintering (Fig. 3b). Fig. 3(c) shows the SEM image for cross section of photo paper revealing the deposition of AgNPs. Preparation of PE/AgNPs-OA for Detection of H2O2. The selection of substrate material, solvent type and formulation of nano-ink are important paramaters for better performance of the paper based electrode.20,28 In this work, substrates like PET sheet, PVC sheet, glass slides and photo paper were tested for achieving high conductivity of the track after sintering at 100 o

C for 1 h. The conductivity on different substrates were measured using a digital multimeter.

The photo paper exihibited a higher value of conductivity than the other substrates. Shrivas et al. and Fauzia et al. also demonstrated the use of photo paper for electronic and electrochemical applications due to its flexibility, fine pore size, smooth surface and moderate absorption of the solvent within the substrate.20,23 Different organic solvents (chloroform, dichloromethane, methanol and toluene) were tested for the preparation of AgNPs-OA ink and then applied onto photo paper for conductivity measurement. The photo paper which was applied with nano-ink in a chloroform solvent showed better response compared with other solvents due to the moderate surface tension, viscosity, low boiling point and dipole moment of solvent. In addition, chloroform has better interations with paper substrate with moderate pore size (photo-paper) comapred to

PET, PVC or glass substrates. We also optimized the

concentration of nano-ink (2.0, 4.0, 6.0, 8.0, 10.0 and 12%) for obtaining high conductivity of

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fabricated material on the paper substarte and we found 10% nano-ink displayed the better result. Further, we optimized the sintering temperature and sintering time for better conductivity of the functionalized material on the photo paper. The sintering processes is done to get the particles close enough to weld together without burning off organic ligands from the surface of NPs. In addition, the ligands on metal NPs are not covalently bonded instead they are weakly adsorbed on the surface. The sintering of small particles into a continuous film or metallic network, which is important to achieve desired conductivity from the fabricated pattern using conductive inks.29 For this, 1.0 cm length of straight line was drawn on photo paper with the AgNPs-OA ink using a ball pen. The prepared conductive line was sintered at different temperatures (25, 60, 80, 100, 120 and 140 oC) for 60 min and the conductivity was measured by the multimeter.20 The results are given in Fig. 4(a) and Table S1. The maximum conductivity of the fabricated material on the paper was acquired when the sintering temperature was 100oC. The sintering time from 10 to 80 min was investigated by sintering the drawn paper electrode at 100 oC for different time intervals, shown in Fig. 4(b) and Table S2. The sintering time of 60 min (1 h) was found the most suitable for maximum conducitivity of the prepared material on the paper substrate. The excess sintering temperature (>100 oC) and sinterting time (>1 h) might cause the removal of carbonaceous material which resulted the decrease in conductivity of fabricated material.20 Therefore, the better performance of paper based electrode with nano-ink was acquired by sintering the material at 100 oC for 1 h. Detection of H2O2 Using PE/AgNPs-OA. In recent years, AgNPs have been used as electrocatalyst for electrochemical detection of H2O2 in variety of samples.11,30-33 This encouraged us to prepare a paper electrode for the determination of H2O2 through the reduction reaction in CV. We performed a different set of experiments to confirm the reduction of H2O2

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on the surface of AgNPs-OA which was fabricated on the photo paper substrate. Fig. 5(a) shows the CV of bare glassy carbon electrode (GCE) and PE/AgNPs-OA when used as working electrode for detection of H2O2 in presence KCl (0.4 M) and 0.2 M PBS (pH 7.0). It can be seen that no peak was obtained at GCE, while PE/AgNPs-OA showed a clear reduction peak current for detection of H2O2. These results showed the catalytic reduction of H2O2 with AgNPs-OA. Fig. 5(b) displays the reduction current when PE/AgNPs-OA was used as a working electrode in the presence and absence of H2O2. The peak current observed around 0.54 V indicate the electrocatalytic activity of PE/AgNPs-OA towards the H2O2 reduction. The catalytic mechanism proposed for the reduction of H2O2 on the surface of PE/AgNPs-OA29, 31 is shown in equations 1 and 2. Ag0 + H2O2 → Ag0-H2O2

(1)

Ag0-H2O2+ 2e- +2H+ →Ag0 + 2 H2O

(2)

In the first step (1), Ag0 interacts with H2O2 to form a complex, Ag0-H2O2. In the next step (2), Ag0-H2O2 is electrochemically reduced to give Ag0 and H2O which can be seen as a reduction peak at -0.54 V. This makes the catalytic cycle. Therefore, a high catalytic current was observed on PE/AgNPs-OA electrode. The electrochemical reduction of H2O2 was diffusion controlled which was verified by performing CV measurements of H2O2 (25 mM) at different scan rates from 0.01 to 0.1 V/s. The reduction peak current was increased linearly with square root of scan rate with a correlation coefficient of 0.991 (Fig. 6(a) and 6(b)). This concludes that the reduction occurs on PE/AgNPs-OA is a diffusion controlled process.30 Optimisation of pH and Supporting Electrolyte for Detection of H2O2. The pH of the sample solution is very important because it defines the state in which the reactant molecules exist in the solution. CV meaurements were performed at different pH (3.0, 5.0, 7.0, 9.0 and 11.0) for detection of H2O2 using PE/AgNPs-OA as a working electrode in the presence of KCl (0.4 M) at the scan rate of 0.1 V/s. The results are shown in the supporting information Fig. 9 ACS Paragon Plus Environment

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S2(a). Only, the reduction peak was obtained when the pH of solution was 7.0. This is due to the favorable reduction process acquired by the analyte molecule at the surface of PE/AgNPsOA.34 The concentration of supporting electrolyte (KCl) is also important for acquiring an optimum current density in CV measurement. Different concentrations of KCl (0.1, 0.2, 0.3, 0.4 and 0.5 M) were tested for the detection of H2O2 at pH 7.0 and at a scan rate of 0.1 V/s. The results are shown in Fig. S2(b). The optimum reduction current was obtained when the concentration of KCl was 0.4 M. Similar results are reported elsewhere in the literature.30 Analytical Evaluation for Determination of H2O2 Using Paper Electrode in CV. Linear range, limit of detection (LOD) and precision are the most important analytical parameters that should be evaluated for a newly developed method. Linear range was estimated by CV measurement of different concentrations of H2O2 from 1.7 µM to 30 mM using paper based electrode at the optimized conditions. The calibration curve was plotted between different concentrations of H2O2 against the reduction peak current. Good linearity was obtained for the determination of H2O2 in the range 1.7 µM-30 mM with correlation of coefficient (r2) of 0.993. The results are shown in Fig. 7(a) and 7(b). The LOD was calculated (0.5 µM) based on the three times of the standard deviation of the blank solution. Precision (reproducibility) of the method was expressed as a relative standard deviation (RSD which was estimated by performing five analyses of 25 mM of H2O2 at the optimized conditions using PE/AgNPs-OA (Fig. S3(a) to S3(f)). The RSD of the reduction potential and reduction current was +2.0% and +1.3%, respectively showing the better precision of the method (Table S3). Stability of the Paper Electrode for Determination of H2O2. The stability and reusability of the paper electrode were tested for determination of H2O2 in CV at the optimized conditions. The stability and reusability of the prepared electrode was checked by keeping the electrode in H2O2 solution (25 mM) and measuring 60 CV cycles. The reproducibility of the paper electrode showed a better RSD value of +1.9% (for 60 analyses) for the detection of H2O2,

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shown in supplementary information Fig. S4. In addition, the prepared electrode was also checked after 60 days and we found the same CV response as the first day of analysis. These results demonstrate the good stability and reusability of the paper based electrode for number of analyses and for number of days. Interference studies of the Paper Electrode for Determination of H2O2. Further, the common metal ions (Fe3+, Fe2+, Cr3+ and Cu2+) and anions (SO42-, Cl-, NO3- and NO2-) that might present in waste water samples were investigated at the optimized conditions. For this, metal ions and anions of 100 mgL-1 were spiked in to solution containing H2O2 solution and CV was recorded at scan rate 0.1 V/s. No interference peaks were observed in the regular curve of H2O2. This concluded that the common metal ions and anions existed in water sample did not interfere for the determination of H2O2 using PE/AgNPs-OA in CV measurement. In addition, the selectivity of the paper electrode was checked for detection of H2O2 at 10 fold high concentrations of ascorbic acid (AA) and dopamine (DA). No additional peaks for AA and DA were observed in the CV curve revealed that the addition of AA and DA did not affect the determination of H2O2 in water sample solution. Therefore, the paper based electrode showed a better selectivity for the detection of target analyte from sample solution in the presence of common entities. Application of Paper Based Electrode for Determination of H2O2 in Waste Water Samples. The practical applicability of the paper based electrode was checked by determining H2O2 in waste water samples under the optimized conditions. No peak for the reduction of H2O2 was observed in the waste water sample when the paper based electrode was used as a working electrode in CV measurement. Therefore, the samples were spiked with three different concentrations of H2O2 (0.63, 1.2 and 5 mM) and recovery percentage of target analyte was calculated using the calibration curve. The recovery percentage was calculated by concentration ratio of H2O2 added to found in water sample. The good recovery percentage

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(95.2 to 96.2%) for the determination of H2O2 in waste water using paper based electrode demonstrated the selectivity for the detection of target analyte from complex sample matrices (Table 1). Comparison of the PE/AgNPs-OA for Determination of H2O2 with Other Reported Methods. The potentiality of paper electrode was examined by comparing the linear range, LOD, stability and reproducibility with other reported electrochemical methods for the determination of H2O2. The detailed comparison (Table 2) showed that the paper based electrode, PE/AgNPs-OA exhibits wide linear calibration range, high sensitivity and low LOD compared to GCE/Ag-PVA, GCE/Au, Au/cysteamine-HRP, GCE/Ag-PVP, Fluorine-doped tin oxide/AgNPs/ZnO (FTO/AgNPs/ZnO) and GCE/AgNPs/Collagen methods.10,28,29,34,36,37 However, the GCE/Hb-Ag method exhibited a higher sensitivity for detection of H2O2, though the precision of this method was found less than present method.35 In addition, PE/AgNPs-OA can be used for number of analyses (more than 60) with stability of 60 days or more with high precision. CONCLUSIONS In summary, the fabricated PE/AgNPs-OA was successfully used as a working electrode in CV measurement for the detection of H2O2 in municipal waste water samples. The sensitivity obtained with PE/AgNPs-OA was found to be higher than modified GCE and other electrodes for determination of H2O2 in variety of samples. It is also found that the presence of other entities such as ascorbic acid and dopamine did not interfere in the determination of H2O2. Therefore, PE/AgNPs-OA exhibits good selectivity, low detection limit, wide linear calibration range with high reproducibility.

ACKNOWLEDGEMENT We would like to thank the Department of Science Technology, New Delhi for awarding Kamlesh Shrivas a fast track project (No.SB/FT/CS-128/2012).

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(a)

(c)

(b)

Fig. 1. Schematic diagram for the preparation of (a) AgNPs-OA nano-ink, (b) Direct-writing of paper based electrode (PE/AgNPs-OA) and (c) Electrochemical measurements of H2O2 by CV using PE/AgNPs-OA as a working electrode

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(a)

(b)

50 nm

10 nm

(c)

(d)

Fig. 2. (a) TEM images of AgNPs-OA, (b) Enlraged view of AgNPs-OA, (c) UV-Vis spectrum of AgNPs-OA, (d) FTIR spectra of AgNPs-OA before and after the sintering at 110oC for 1 h

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(a)

(b)

(c)

Fig. 3. (a) Optical image of PE/AgNPs-OA before sintering, (b) after sintering and (c) SEM image for cross section of photo paper showing the deposition of AgNPs

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Fig. 4. (a) Effect of sintering temperature (25, 60, 80, 100, 120, 140 and 160 oC) on the conductivity of PE/AgNPs-OA at sintering time of 60 min. (b) Effect of different sintering time (0, 5, 10, 15, 30, 60, 90 and 120 min) on the conductivity of PE/AgNPs-OA at constant sintering temperature of 100 oC

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(a)

(b)

Fig. 5. CV of (a) bare GCE and paper based AgNPs-OA electrode when used as working electrodes for detection of 25 mM H2O2 in the presence of 0.2 M PBS (pH 7.0) and 0.4 M KCl as supporting electrolyte at 0.1 V/s scan rate; (b) Paper based AgNPs/OA electrode when used as a working electrode in absence and presence of 25 mM H2O2 in 0.2 M PBS (pH 7.0) and 0.2 M KCl as a supporting electrolyte at 0.1 V/s scan rate.

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(a)

(b)

Fig. 6. (a) CV measurement of 25 mM H2O2 in the presence of 0.2 M PBS buffer (pH 7.0) and 0.4 M KCl as a supporting electrolyte at different scan rates from 0.01 to 0.1 V/s; (b) Plot showing the relationship between scan rate and current

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(a)

(b)

Fig. 7. (a) CV measurement of different concentrations of H2O2 using PE/AgNPs-OA as a working electrode in presence of 0.2 M PBS buffer (pH 7.0) and 0.4 M KCl as supporting electrolyte at 0.1 V/s scan rate; (b) Calibration curve for the determination of H2O2 from 1.7 µM to 30 mM with correlation coefficient of 0.993

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Table 1. Determination of recovery % of H2O2 in municipal waste water using PE/AgNPs-OA at the optimized conditions Amount of H2O2

Amount of H2O2

Recovery, %

added, (mM)

Found, (mM)

0.63

0.60

95.2

1.25

1.20

96.0

5.00

4.81

96.2

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Table 2 : Comparison of modified electrodes with PE/AgNPs-OA electrode for determination of H2O2 Technique

LOD, 10-6 M

Linear Range, M

GCE/Au-Sol

CV

2.0

7x10-6-7.8x10-3

-

-

10

GCE/Ag-PVP

CV

1.2

4x10-3 – 0.5