nitrate amperometric sensor in neutral ph based on pd nanoparticles on epoxy-copper electrodes

Accepted Manuscript

Title: Nitrate amperometric sensor in neutral pH based on Pdnanoparticles on epoxy-copper electrodes

Author: Albert Gutes Carlo Carraro Roya Maboudian

PII: S0013-4686(13)00669-5DOI: http://dx.doi.org/doi:10.1016/j.electacta.2013.03.199Reference: EA 20334

To appear in: Electrochimica Acta

Received date: 31-1-2013Revised date: 27-3-2013Accepted date: 29-3-2013

Please cite this article as: A. Gutes, C. Carraro, R. Maboudian, Nitrate amperometricsensor in neutral pH based on Pd nanoparticles on epoxy-copper electrodes,Electrochimica Acta (2013), http://dx.doi.org/10.1016/j.electacta.2013.03.199

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

http://dx.doi.org/doi:10.1016/j.electacta.2013.03.199

http://dx.doi.org/10.1016/j.electacta.2013.03.199

of 19

Accep

ted

Man

uscr

ipt

Nitrate amperometric sensor in neutral pH based on Pd nanoparticles on epoxy-

copper electrodes

Albert Gutés, Carlo Carraro, Roya Maboudian*

Author for correspondence:

Roya Maboudian

201 Gilman Hall

Department of Chemical and Biomolecular Engineering

University of California

Berkeley, CA, 94720

Tel: +1 510 643 7957

Fax: +1 510 642 4778

Email: [email protected]

Website http://cheme.berkeley.edu/faculty/maboudian/

of 19

Accep

ted

Man

uscr

ipt

1

Nitrate amperometric sensor in neutral pH based on Pd nanoparticles on epoxy-

copper electrodes

Albert Gutés, Carlo Carraro, Roya Maboudian*

Department of Chemical and Biomolecular Engineering, University of California,

Berkeley, CA, 94720, USA

Abstract

Amperometric nitrate sensing at neutral pH using an epoxy-copper electrode

modified with palladium nanoparticles is presented. After epoxy-copper is

hardened and polished, electroless deposition is employed for the deposition of

Pd nanoparticles. Scanning electron microscopy and energy-dispersive X-ray

spectroscopy reveal the morphology and composition of the Cu/Pd surface. The

effect of Pd deposition time towards nitrate electroreduction is investigated,

highlighting the importance of the bimetallic catalyst. The optimized electrode

shows a linear response at pH=7 in the range from 2 to 35 ppm of nitrate. The

simplicity and cost effectiveness of the fabrication process makes this Cu/Pd

electrode a good candidate for distributed nitrate monitoring and determination

in the field.

Keywords Nitrate sensor, electrochemistry, epoxy-copper, palladium

nanoparticles, bimetallic catalyst

1. Introduction

Nitrate ground water pollution has become a growing concern in the last few

decades due to its toxicity at ppm concentration levels [1-2]. Nitrate in

groundwater can be divided into four categories depending on its source: (i)

waste materials, (ii) natural sources, (iii) irrigation in agriculture, and (iv) row

crop agriculture [3-5]. Overuse of nitrogen-based fertilizers and subsequent

leakage of nitrates into waters have caused a tremendous increase and spread

of this water pollutant worldwide [6]. Moreover, NOx increase in the atmosphere

of 19

Accep

ted

Man

uscr

ipt

2

has been traced to overfertilization [7]. For these reasons, nitrate detection and

monitoring is of great importance. Optical UV detection of nitrates at 220 nm

can be employed [8], but is limited to the screening of clear unpolluted water

samples with low organic contents. Other methodologies for nitrate detection

include ion chromatography and the standard cadmium reduction method [9].

The Cd reduction method is a lengthy process and generates cadmium waste

with the associated disposal issues; thus the final cost of analysis is high.

A promising method for the detection of nitrate is based on its electroreduction

in the presence of metallic or bimetallic catalyst [10-14]. One of the most

explored bimetallic catalysts with strong electrocatalytic reduction properties

towards nitrate electroreduction is Cu-Pd. Much of the literature on the use of

Cu-Pd or other metallic catalysts has been limited to nitrate electroreduction in

acidic [15-21] and basic [22-27] media but since the majority of ground and

drinking waters are close to neutral pH, the previously developed sensing

materials cannot be directly used without sample pre-treatment. The majority of

studies have focused on the determination of the nitrate electroreduction

mechanism or on the catalytic and selective effect of the Cu-Pd electrode,

showing very high conversion rates to N2. De Vooys et al. presented a

thorough study on the use of Cu-Pd electrodes for the electroreduction of

nitrate, [28] proposing mechanisms in acidic and basic media, noting the

differences as pH values change, as well as the influence of the Cu to Pd ratio

and its effects towards selectivity and activity of the electrode. In addition, a

recent review by Rosca et al. [29] presents an exhaustive compilation of the

various electrocatalytical paths for nitrogen compounds, including nitrate, but

again acidic or basic media were used in all nitrate electroreduction

measurements. A few reports on nitrate detection by electroreduction in neutral

media can be found in the literature [30], but in all cases, the detected nitrate

ranges of concentrations exceed the legislation limits [31]. Here we present a

simple and robust fabrication method for nitrate sensors with a linear response

range of 2 to 35 ppm measured at pH=7.0. To achieve the required sensitivity,

the Pd to Cu ratio had to be carefully optimized which we have achieved via

electroless deposition schemes. To the best of our knowledge, this is the first

time that electrochemical reduction of nitrate at neutral pH has been achieved in

this concentration range.

of 19

Accep

ted

Man

uscr

ipt

3

2. Experimental

2.1 Electrode construction

Figure 1 shows schematically the fabrication of the epoxy-Cu electrodes.

Epoxy-copper (Epoxy Technologies Epotek 430) is prepared as directed by the

manufacturer. PVC tubing of 3 mm inner diameter is cut in 2 cm long pieces. On

one end, a 3 mm in diameter electrical cable is introduced 1 cm into the tubing.

Epoxy-Cu is applied to the other end until filling the remaining 1 cm cavity in the

tube. After hardening, the epoxy-Cu is polished with sandpaper of decreasing

grain size with the final polishing performed with alumina pastes of 1-, 0.3- and

0.05-m size (CHI polishing kit CHI120) until mirror-shine is achieved.

Extensive rinsing with deionized (DI) water (18 MΩ, Barnsted Nanopure Infinity)

is performed prior to drying with nitrogen flow.

Deposition of the Pd nanoparticles is performed, right after polishing, as follows.

The deposition solution consists of 1 mM K2PdCl4 (Aldrich, 99.99% purity) and

20 mM KCl (Aldrich, 99% purity) and is used for all Pd depositions. Excess of

chloride is necessary to stabilize the PdCl42- anion in solution, avoiding its

precipitation as PdCl2. Polished epoxy-Cu electrodes are immersed in the

aforementioned solution for varied time duration, ranging from 10 to 300 s, then

rinsed in DI water and dried in a nitrogen flow. As explained in the results

section, the optimal deposition time towards nitrate reduction corresponds to 2-

min deposition time.

2.2 Characterization instruments

Electrochemical measurements (cyclic voltammetry and coulometry) are

performed using a CH660D potentiostat-galvanostat (CH Instruments, USA). A

standard three-electrode configuration is used with a Ag/AgCl reference

electrode, a Pt wire auxiliary electrode and the modified epoxy-Cu/Pd

nanoparticle working electrode. Scanning electron microscopy (SEM) and

energy-dispersive X-ray (EDX) analyses are obtained using a JEOL JSM 6340F

field emission scanning electron microscope.

of 19

Accep

ted

Man

uscr

ipt

4

2.3 Amperometric detection

All measurements are performed in a 0.1 M phosphate buffer solution (PBS,

Fluka 99.4%) with pH adjusted to 7.0. Potassium nitrate (Fluka 99.8%)standard

solution containing 1000 ppm nitrate in PBS pH = 7.0 is prepared daily. Cyclic

voltammetry is performed between +0.2 and -1.2V at a scan rate of 50 mV/s

without stirring, starting at +0.2V. 10 cycles are performed in order to reach

reproducible voltammograms. The measurements are performed in open glass

beakers without any oxygen scavenging or removal. 3-step voltammetry is

performed by applying potentials (vs. Ag/AgCl) as follows, measuring each 20

ms: +0.2V for 2 s (Cu-Pd cleaning / oxidation step) followed by 2 s at -0.2V (Cu-

Pd regeneration step) and a final measuring step at -1V for 3 s. All the 3-step

measurements are performed without stirring. The average of the final 10-

recorded currents is used as analytical data. The first two steps (cleaning and

regeneration) are found to be crucial in order to avoid surface poisoning

reported previously for nitrate electroreduction [21,30] and are selected by

direct observation on the obtained cyclic voltammograms, where maximum

currents are achieved on the positive scan at around -0.1 V due to Cu/Pd

oxidation and maximum currents are achieved on the negative scan at around -

0.2 V during Cu/Pd reduction.

3. Results and discussion

3.1 Characterization of the epoxy-Cu/Pd nanoparticle substrate

Figure 2 shows the SEM image of the polished epoxy-copper prior to palladium

nanoparticles deposition (a) and after 2 min of palladium deposition (b). As can

be observed, the electrode surface morphology changes substantially upon Pd

deposition, with the formation of Pd nanostructures and films. Figure 2c shows

the EDX spectrum of the same sample as in Figure 2b. The spectrum confirms

the Pd deposition, with Pd/Cu ratio of 1:4.6. The Al signal is attributed to the

presence of Al in the epoxy-Cu formulation as-received.

of 19

Accep

ted

Man

uscr

ipt

5

3.2 Catalytic reduction of nitrate by cyclic voltammetry

Figure 3a shows the typical cyclic voltammograms of the bare Cu electrode in a

0.1M PBS solution at pH=7.0 and in the presence of 20 ppm of nitrate. Figure

3b shows the response obtained with the epoxy-Cu/Pd electrode (2 min of

palladium deposition) in the same PBS and nitrate dissolutions. Scan rate is 50

mV/s in both cases. As can be observed, a reduction tail is obtained in the

negative scan starting at -0.8V, corresponding to nitrate reduction on the Cu/Pd

surface. In order to minimize possible interferences of hydrogen evolution, a

less extreme potential of -1V is selected for the third step in the nitrate detection

described next.

3.3 Three-step nitrate amperometric sensing

To characterize fully the electrodes’ responses, three-step voltammetry

measurements without solution stirring are performed, following a similar

protocol as described in the literature [32] as described in section 2.3. Figure 4a

shows the typical current responses obtained for the three-step voltammetry on

the bare epoxy-Cu electrode while figure 4b shows the same response using an

epoxy-Cu electrode after a 2 min Pd deposition time. In both cases PBS pH=7.0

baseline (black line) and after nitrate is added to a final concentration of 20 ppm

(red dashed line) is shown. It can be observed that no significant difference is

obtained when no Pd is present on the surface of the electrode (Figure 4a)

while an increase in the current is obtained when the Cu/Pd electrode is used

(Figure 4b). The current differences in the first two steps when using the Cu/Pd

electrode are due to the liberation and regeneration of adsorbed nitrogenated

compounds on the electrode surface that otherwise would cause its poisoning

as reported earlier [21,30].

The currents recorded during the last second of the three-step voltammetry

measurements are averaged and used as experimental data and plotted

against the different nitrate concentrations in the electrochemical cell obtained

by nitrate addition. Stirring of the solution is performed after each addition at

600 rpm for 5 s in order to homogenize the nitrate concentration in the

electrochemical cell. Before each three-step measurement, the stirring is

of 19

Accep

ted

Man

uscr

ipt

6

stopped. Figure 5a shows the responses obtained from the electrodes with

various Pd deposition times. As can be observed, nitrate reduction sensitivity

increases with the amount of deposited Pd showing an optimal response at a

deposition time of 120 s. After this Pd deposition time, the response signal

decreases.

The observed behavior may be understood by the analysis put forth by Gao and

Li [33] for PdCu bimetallic catalyst for nitrate reduction. Namely, for nitrate

reduction, both Cu and Pd must be available during the electron transfer

process. The need for Pd in the catalyst mixture is demonstrated in Figure 4a,

where an electrode with no deposited Pd is used and signal remained

unchanged in the presence of nitrate. The need of copper is demonstrated by

using an epoxy-silver electrode instead of an epoxy-copper electrode with a 2-

min Pd deposition following the same procedures as before [32].

Figure 5b shows the calibration plot obtained when using this electrode. As can

be observed, the data obtained in the absence of Cu in the catalyst only

presents noise. We conjecture that for Pd deposition times longer than 2 min,

Cu starts being covered by Pd to such an extent that it is no longer available to

nitrate in solution. Figure 6 shows the calibration curve for the optimal 2 min Pd

deposition time electrode on a log-log plot. The linear range for nitrate reduction

at pH=7.0 is 2 to 35 ppm, with excellent linear correlation. The achieved

detection range is well in the legislation limits of 10 ppm [31]. Reproducible

response of the electrodes is obtained over periods of months. This is attributed

to the regenerative nature of the 3-step measurements described in section

2.3.Table 1 compares the performance of the here presented Cu-Pd electrode

to those reported previously. The table clearly shows that the Cu-Pd electrode

provides an excellent response towards nitrate reduction when compared to

previous reports in the literature with the added novelty of sensing in neutral pH.

The electrochemical nitrate detection scheme presented here should not be

influenced by many ions that are usually present in natural waters (such as

HCO3-, SO4

2- Ca2+, and Mg2+) since none of these cations or anions can be

either reduced or oxidized in the potential range of our measurements. The

possibility of nitrite interference was studied using the optimal 2 min Pd

electrode by adding 1000 ppm NaNO2 (Fluka 99.8%) to 25 ml PBS buffer as

performed for nitrate measurements, with no response observed over the

of 19

Accep

ted

Man

uscr

ipt

7

examined range of ?? to 50 ppm. Previous studies on the electroreduction of

nitrite by copper complexes [34] suggest that nitrite reduction follows a different

reaction pathway than nitrate reduction that might not be possible in the

presence of Pd.

4. Conclusions

In conclusion a facile fabrication method for a new electrochemical nitrate

sensor based on epoxy Cu and electrolessly deposited Pd is presented. The

main advantage of the presented electrode is the possibility of nitrate

determination in the legislation-relevant range at neutral pH. Nitrate response is

achieved by a three-step amperometry consisting of a surface cleaning and

regeneration followed by a nitrate electroreduction. Stable current is used as

analytical signal for the calibration of the electrodes. Optimization of the amount

of deposited Pd has been performed and a final condition of 1mM Pd

dissolution with a 2-min deposition time is found to provide the highest

sensitivity towards nitrate reduction. The linear range provided by the here

presented electrode is 2-35 ppm, a suitable range for its use in the detection of

nitrates in drinking water and crop soils among others. The simplicity of the

fabrication process, the low cost of the starting components, the high rate of

precursor utilization expected in the electroless deposition and the possibility of

using inexpensive counter electrodes, such as graphite, open potential for mass

production of the described sensor.

Acknowledgements

The authors are grateful to Mr. Peter Lobaccaro for his help with SEM and EDX

imaging. This work was supported by National Science Foundation under

Grant# EEC-0832819 (Center of Integrated Nanomechanical Systems).

References

[1] E.H. Burden, Toxicology of nitrates and nitrites with particular reference to

potability of water supplies, Analyst 102 (1961) 429.

of 19

Accep

ted

Man

uscr

ipt

8

[2] M.H. Ward, T.M. deKok, P. Levallois, J. Brender, G. Gulis, B.T. Nolan, J.

Van Derslice, Workgroup report: Drinking-water nitrate and health-recent

findings and research needs, Environ. Health Perspect. 113 (2005) 1607.

[3] L.W. Canter, Nitrates in Groundwater, CRC Press, Boca Raton, FL, 1996.

[4] B.A. Stewart, F.G. Viets, G.L. Hutchins, Agricultures effect on nitrate

pollution of groundwater, J. Soil Water Conserv. 23 (1968) 13.

[5] M.N. Almasri, J.J. Kaluarachchi, Assessment and management of long-term

nitrate pollution of ground water in agriculture-dominated watersheds, J. Hydrol.

295 (2004) 225.

[6] J.M. Beman, K.R. Arrigo, P.A. Matson, Agricultural runoff fuels large

phytoplankton blooms in vulnerable areas of the ocean, Nature 434 (2005) 211.

[7] S. Park, P. Croteau, K.A. Boering, D.M. Etheridge, D. Ferretti, P.J. Fraser,

K.R. Kim, P.B. Krummel, R.L. Langenfelds, T.D. van Ommen, L.P. Steele, C.M.

Trudinger, Trends and seasonal cycles in the isotopic composition of nitrous

oxide since 1940, Nature Geosci. 5 (2012) 261.

[8] T. Kamiura, M. Tanaka, Determination of nitrate in suspended particulate

matter by high-performance liquid-chromatography with UV detection, Anal.

Chim. Acta 110 (1979) 117.

[9] APHA. Standard methods for the examination of water and wastewater. 18th

ed. American Public Health Association, Washington, DC, 1992.

[10] K. Fajerwerg, V. Ynam, B. Chaudret, V. Garçon, D. Thouron, M. Comtat,

An original nitrate sensor based on silver nanoparticles electrodeposited on a

gold electrode, Electrochem. Comm. 12 (2010) 1439.

[11] F. Gauthard, F. Epron, J. Barbier, Palladium and platinum-based catalysts

in the catalytic reduction of nitrate in water: effect of copper, silver, or gold

addition, J. Catal. 220 (2003) 182.

[12] G.E. Dima, A.C.A. de Vooys, M.T.M. Koper, Electrocatalytic reduction of

nitrate at low concentration on coinage and transition-metal electrodes in acid

solutions, J. Electranal. Chem. 554-555 (2003) 15.

[13] L.A. Estudillo-Wong, E.M. Arce-Estrada, N. Alonso-Vante, A. Manzo-

Robledo, Electro-reduction of nitrate species on Pt-based nanoparticles:

Surface area effects, Catal. Today 166 (2011) 201.

[14] M. J. Moorcroft, J. Davis, R. G. Compton, Detection and determination of

nitrate and nitrite: a review, Talanta 54 (2001) 785.

of 19

Accep

ted

Man

uscr

ipt

9

[15] N. G. Carpenter, D. Pletcher, Amperometric method for the determination

of nitrate in water, Anal. Chim. Acta 317 (1995) 287.

[16] A. G. Fogg, S. P. Scullion, T. E. Edmonds, Assessment of online nitration

reactions as a means of determining nitrate by reverse flow-injection with

reductive amperometric detection at a glassy-carbon electrode, Analyst 114

(1989) 579.

[17] A. G. Fogg, S. P. Scullion, T. E. Edmonds, B. J. Birch, Direct reductive

amperometric determination of nitrate at a copper electrode formed insitu in a

capillary-fill sensor device, Analyst 116 (1991) 573.

[18] M. J. Moorcroft, L. Nei, J. Davis, R. G. Compton, Enhanced electrochemical

detection of nitrite and nitrate at a Cu-30Ni alloy electrode, Analytical Letters 33

(2000) 3127.

[19] Z. Zhao, X. Cai, Determination of trace nitrite by catalytic polarography in

ferrous iron thiocyanate medium, J. Electroanal. Chem. 252 (1988) 361.

[20] J. Davis, M. J. Moorcroft, S. J. Wilkins, R. G. Compton, M. F. Cardosi,

Electrochemical detection of nitrate and nitrite at a copper modified electrode,

Analyst 125 (2000) 737.

[21] A. O. Solak, P. Gulser, E. Gokmese, F. Gokmese, A new differential pulse

voltammetric method for the determination of nitrate at a copper plated glassy

carbon electrode, Mikrochim. Acta 134 (2000) 77.

[22] S. Cattarin, Electrochemical reduction of nitrogen oxyanions in 1-M sodium-

hyrdoxide solutions at silver, copper and CuInSe2 electrodes, J. Appl.

Electrochem. 22 (1992) 1077.

[23] H.L. Li, J.Q. Chambers, D.T. Hobbs, Electroreduction of nitrate ions in

concentrated sodium-hydroxide solutions at lead, zinc, nickel and

phtalocyaninie-modified electrodes, J. Appl. Electrochem. 18 (1988) 454.

[24] J.O. Bockris, J. Kim, Electrochemical reductions of Hg(II), ruthenium-

nitrosyl complex, chromate, and nitrate in a strong alkaline solution, J.

Electrochem. Soc. 143 (1996) 3801.

[25] J.D. Genders, D. Hartsough, D.T. Hobbs, Electrochemical reduction of

nitrates and nitrites in alkaline nuclear waste solutions, J. Appl. Electrochem. 26

(1996) 1.

of 19

Accep

ted

Man

uscr

ipt

10

[26] M. Fedurco, P. Kedzierzawski, J. Augustynski, Effect of multivalent cations

upon reduction of nitrate ions at the Ag electrode, J. Electrochem. Soc. 146

(1999) 2569.

[27] R. Tenne, K. Patel, K. Hashimoto, A. Fujishima, Efficient electrochemical

reduction of nitrate to ammonia using conductive diamond film electrodes, J.

Electroanal. Chem. 347 (1993) 409.

[28] A.C.A. de Vooys, R.A. van Santen, J.A.R. van Veen, Electrocatalytic

reduction of NO3- on palladium/copper electrodes, J. Mol. Catal. A: Chem. 154

(2000) 203.

[29] V. Rosca, M. Duca, M.T. de Groot, M.T.M. Koper, Nitrogen Cycle

Electrocatalysis, Chem. Rev. 109 (2009) 2209.

[30] O. Ghodbane, M. Sarrazin, L. Roue, D. Belanger, Electrochemical

reduction of nitrate on pyrolytic graphite-supported Cu and Pd-Cu

electrocatalysts, J. Electrochem. Soc. 155 (2008) F117.

[31] http://water.epa.gov/drink/contaminants/basicinformation/nitrate.cfm,

consulted on October 31st 2012.

[32] A. Gutes, C. Carraro, R. Maboudian, Nonenzymatic glucose sensing based

on deposited palladium nanoparticles on epoxy-silver electrodes, Electrochim.

Acta 56 (2011) 5855.

[33] W. Gao, F. Li, Catalytic Hydrogenation of Nitrate Ions over Pd-Cu/ZSM-5

Catalyst, Advanced Materials Research 197-198 (2011) 967.

[34] J.G. Woollard-Shore, J.P. Holland, M.W. Jones, J.R. Dilworth, Nitrite

reduction by copper complexes, Dalton Trans. 39, (2010) 1576.

of 19

Accep

ted

Man

uscr

ipt

11

Table 1.

Comparison of analytical performance of some electrochemical nitrate sensors

Electrode material Solution nitrate concentration (M) Ref.

AgNP on Au Synthetic seawater 10-5 – 10-2 [10]

Polycrystalline metal 0.5M H2SO4 or

HClO4

0.1 [12]

Cu/graphite and Pd–

Cu/graphite

1M NaCl 1 [30]

Pt-based NP 0.5M NaOH 0.001 – 1 [13]

Vitreous carbon 0.1 M Na2SO4 at

pH = 2.9

10-4 - 10-3 [15]

Glassy carbon Concentrated

H2SO4

5 ·10-4 – 5 ·10-3 [16]

Electrodeposited Cu 0.5 - 2M H2SO4 10-4 - 10-3 [17]

Epoxy-Cu-Pd-NP PBS buffer pH=7.0 3.2·10-5 – 5.6·10-4 This work

of 19

Accep

ted

Man

uscr

ipt

12

Figure Captions:

Figure 1: Top: electrode construction diagram. A 3mm inner diameter PVC tube

(a) is cut into 2cm long pieces. Half of the tube is filled with a 3mm electrical

cable (b) and the rest is filled with epoxy-Cu and hardened (c). After hardening,

the electrode surface is polished with sandpaper and alumina slurry until a

mirror-shine surface is obtained (d). Bottom: picture of the unmodified Cu-epoxy

electrode (left) and after the 2 min Pd deposition (right).

Figure 2: SEM images of (a) polished epoxy Cu and (b) after a 2 min Pd

deposition; (c) EDX spectrum of pristine epoxy-Cu and (d) EDX spectrum of

sample shown in (b).

Figure 3: (a) Cyclic voltammograms for the bare Cu electrode in PBS (black

line) and in a PBS solution containing 20 ppm nitrate (red dashed line). (b)

Cyclic voltammograms obtained at pH=7.0 on the epoxy-Cu/Pd electrode (2 min

Pd deposition) in a 0.1M PBS solution (black line) and in a PBS solution

containing 20 ppm nitrate (red dashed line). Scan rate 50 mV/s. Scans started

at +0.2V

Figure 4: (a) Three-step voltammetry on the epoxy-Cu in PBS pH=7.0 baseline

(black line) and in the presence of 20 ppm nitrate (red dashed line). (b) Same

measurements as in (a) when Pd has been deposited on the epoxy-Cu

electrode surface for 2 min. Blue dashed line shows the applied voltage along

the 7 second measurement.

Figure 5: (a) calibration responses for the studied set of Pd deposition times.

Plotted currents correspond to the average of the currents recorded during the

last second in the three-step measurements after nitrate additions. (b)

Calibration response of an epoxy-Ag/Pd electrode with Pd deposited for 2 min.

Figure 6: Linear response of the optimal 2 min Pd deposition in the range of 2 -

35 ppm of nitrate.

of 19

Accep

ted

Man

uscr

ipt

13

Figure 1

of 19

Accep

ted

Man

uscr

ipt

14

Figure 2

of 19

Accep

ted

Man

uscr

ipt

15

Figure 3

of 19

Accep

ted

Man

uscr

ipt

16

Figure 4

of 19

Accep

ted

Man

uscr

ipt

17

Figure 5

of 19

Accep

ted

Man

uscr

ipt

18

Figure 6

nitrate amperometric sensor in neutral ph based on pd nanoparticles on epoxy-copper electrodes

Documents