Ethanol electrooxidation at carbon paste electrode modified with Pd–ZnO nanoparticles

Accepted Manuscript Title: Ethanol Electrooxidation at Carbon Paste Electrode Modified with Pd–ZnO Nanoparticles Author: E. Tavakolian J. Tashkhourian Z. Razmi H. Kazemi M. Hosseini-Sarvari PII: DOI: Reference:

S0925-4005(16)30155-1 http://dx.doi.org/doi:10.1016/j.snb.2016.02.006 SNB 19665

To appear in:

Sensors and Actuators B

Received date: Revised date: Accepted date:

18-11-2015 26-1-2016 2-2-2016

Please cite this article as: E.Tavakolian, J.Tashkhourian, Z.Razmi, H.Kazemi, M.Hosseini-Sarvari, Ethanol Electrooxidation at Carbon Paste Electrode Modified with PdndashZnO Nanoparticles, Sensors and Actuators B: Chemical http://dx.doi.org/10.1016/j.snb.2016.02.006 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 proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Ethanol Electrooxidation at Carbon Paste Electrode Modified with Pd-ZnO Nanoparticles E. Tavakoliana, J. Tashkhouriana,*, Z. Razmia, H. Kazemib, M. Hosseini-Sarvaria a b

Department of Chemistry, Faculty of Science, Shiraz University, Shiraz, 71454, Iran

Evaluation and Analysis of Materials, Research Institute of Petroleum Industry, Tehran, Iran

*Corresponding author: Department of Chemistry, College of Sciences, Shiraz University, Shiraz, Iran E-mail address: [email protected] (J. Tashkhourian)

Graphical Abstract

Highlights 

The electrocatalytic and analytical performance of palladium-zinc oxide nanoparticles modified carbon paste electrode was investigated.



The electrode was used for determination and oxidation of ethanol in alkaline media.

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

Palladium-zinc oxide nanoparticle is a good candidate for application in ethanol sensor.

Abstract

The electrocatalytic and analytical performance of palladium-zinc oxide nanoparticles modified carbon paste electrode (Pd-ZnO/CPE) for determination and oxidation of ethanol were studied in alkaline media. X-ray diffraction (XRD) and transmission electron microscopy (TEM) was used to characterize Pd-ZnO nanoparticles. The electrochemical characterizations were performed using cyclic voltammetry (CV) and chronoamperometry techniques. The results show that the electrode reveals excellent electrocatalytic characteristics for ethanol oxidation such as high catalytic activity, stability and tolerance toward poisoning effects. Also, the excellent analytical performance for ethanol determination confirms the applicability of this electrode as a nonenzymatic amperometric ethanol sensor. This sensor has the advantages of low detection limit (20.3 µM), two wide linear range (1.99-490.90 mM and 0.491-3.355 M), and good long-term stability (more than 120 days) for ethanol determination. All results showed that palladium-zinc oxide nanoparticle is a good candidate for application in ethanol sensor and ethanol fuel cells.

Keywords: Ethanol, Palladium-Zinc Oxide Nanoparticles, Modified Carbon Paste Electrode

1. Introduction

Direct liquid fuel cells, such as direct alcohol fuel cells (DAFCs), have attracted much attention as one of the most viable candidates to replace batteries as a source of portable power. Among the various liquid fuels, ethanol is less toxic, has higher energy density and is easier to store and handle than methanol. [1, 2]. Among the electrocatalysts for alcohols oxidation, Pd-based catalysts are promising candidate and have comparable or even better electrocatalytic activities than the Pt-based catalysts for alcohol oxidation in alkaline media [3]. So, more efforts have been done for improvement of electrocatalytic performance of Pd-based catalysts. Main strategies to improve the performance of the Pd-based catalysts are: Supporting Pd on materials with large surface areas such carbonaceous material, metal 2

oxides and combining Pd with other metals such as Ag [2], Ni [4, 5], Pb [6], Sn [7], etc. Transition metal oxides such as CeO2, NiO , Co3O4 , Mn3O4 [8], NiO/MgO [9] , MoOx [10] and TiO2 [11] as supporting materials for Pd significantly improves the electrode performance by enhancing the electrochemical activity. Among the metal oxide nanoparticles, ZnO nanoparticles have been extensively investigated due to their unusual but favorable properties such as high surface area, high catalytic efficiency, non-toxicity, chemical stability and strong adsorption ability [12]. The modification of ZnO with noble metals such as Ag [13], Au [14], Pt [15], and Pd [13, 16] has attracted significant attention. As a noble metal, palladium, whose ionic radius (0.080 nm) is close to that of Zn2+ (0.074 nm), has been widely used in the gas sensors and industry catalysis especially for methanol synthesis [17]. The detection of ethanol concentration is important for medicine, brewing, beverage, traffic safety and etc. Analytical techniques, such as gas/liquid chromatography [18] and mass spectroscopy [19] have been proposed for ethanol determination but they are expensive and not suitable for portable use. Also, application of semiconductor-based ethanol sensors is limited due to some drawbacks such as high working temperature (≥300◦C), complicated fabrication and high cost [20, 21]. In general, the electrochemical ethanol sensors have the highest sensitivity and accuracy among all of the sensors that in which response currents resulted from the ethanol oxidation. There are two types of these sensors: enzymatic sensors and nonenzymatic sensors. Because of loss of enzyme and/or mediator loading and degradation of enzyme activity in critical temperature or solution pH, it is reasonable and practical to develop nonenzymatic sensors for the detection of ethanol. Generally, metal or alloy was usually the basic element for nonenzymatic electrodes [22]. Several nonenzymatic sensors have been reported to detect the ethanol such as Pd [23], NiPd [22], Ni foil [24], Ni/Pt/Ti on an Al2O3 substrate [25], RuO2 modified Ni electrode [24], Pd-Ni/Si NWs [21] and the cobalt nickel oxide electrode [26]. Nonenzymatic ethanol sensors were relatively rare in comparison with the other nonenzymatic sensors In this work, we applied palladium-zinc oxide nanoparticles (Pd-ZnO) used in carbon paste electrode for analytical determination and electrocatalytic oxidation of 3

ethanol in alkaline media. The results show that the Pd-ZnO/CPE provides high electrocatalytic activity and good tolerance toward poisoning species for ethanol oxidation reaction in an alkaline media. Also, this electrode shows excellent analytical performance as a nonanzematic sensor for determination of ethanol. The electrochemical behaviors of this electrode were investigated using cyclic voltammetry (CV) and chronoamperometry.

2. Experimental 2.1 Materials and reagents Potassium hydroxide (KOH, 85%), ethanol (C2H5OH, 99.9%), formic acid, 2propanol, glucose, fructose, formaldehyde, and methanol were obtained from Merck. For determination of ethanol, the stock solution of ethanol (10.0 M) and KOH (2.5 M) were prepared daily in a 100.0-mL flask. Graphite powder (particle size <100.0 μm) and paraffin oil used for constructing electrodes were purchased from Fluka and Merck, respectively. Human serum samples were obtained from Fars Blood Transfusion Organization, Shiraz, Iran.

2.2. Apparatus Electrochemical measurements were carried out with an electrochemical analyzer Autolab PGSTAT 302 N (Metrohm Autolab B.V., Ultrecht and The Netherlands). A conventional three-electrode system was used throughout the experiments at room temperature. The working electrode was Pd-ZnO/CPE and the auxiliary electrode was a platinum wire. Besides, an Ag/AgCl was taken as the reference electrode. Measurements of pH were made with a Denver Instrument Model 780 pH meter equipped with a glass electrode. Transmission electron micrograph (TEM) was taken with Zeiss - EM10C - 80 KV and XRD spectra were obtained by D8ADVANCE type (BRUKER-Germany).

2.3. Synthesis of palladium-zinc oxide nanocomposite The Pd-ZnO catalyst was synthesized as described elsewhere [27]. Briefly, palladium nitrate (0.027 g/mL) and zinc nitrate (0.267 g/mL) solutions were mixed and then an 4

aqueous solution of sodium carbonate (1.0 M) was added to this solution at room temperature to produce a final pH of 8.0. The mixture was aging for 2 h at 70–80°C. The precipitate was then filtered and washed with ethanol and water several times and dried overnight in an oven at 80°C. The product was calcinated at 723 K for 2 h.

2.4. Modified electrode preparation Unmodified carbon paste was prepared by hand mixing of 70% of graphite powder and 30% of paraffin oil thoroughly to form a homogeneous paste. A modified carbon paste electrode was prepared in a similar method, except that the graphite powder, paraffin oil and Pd-ZnO with a ratio of 70:20:10 (%w/w), respectively were mixed thoroughly to form a paste. The resulting pastes were packed firmly into the cavity (3mm diameter) of a Teflon holder. The electric contact was established via a stainless steel rod connected to the paste. A new surface was obtained by smoothing the electrode onto a weighing paper.

3. Results and discussion 3.1. Characterization of ZnO and Pd/ZnO nanoparticles X-ray diffraction patterns of ZnO and Pd/ZnO nanoparticles are presented in Fig. 1. As shown in this Figure, all the XRD peaks are indexed by a hexagonal Wurtzite phase of ZnO (JCPDS card no. 36-1451). The absence of characteristic impurity peaks such as Zn(OH)2 and unhydrolyzed Zn(II)-acetate indicate a high-quality ZnO nanoparticles. The XRD patterns of Pd/ZnO exhibits one additional broad peak appear at a Bragg’s angle of 41.2 ̊originated from the diffraction of (111) planes that agree well with the face-centered cubic (fcc) morphology of palladium (JCPDS Card File No. 05-0681) that confirms the formation of palladium nanoparticles on ZnO surface. Also, the crystallite size of nanoparticles of Pd and ZnO estimated from Scherrer’s formula are about 5 and 22 nm respectively [28].The morphology of the Pd/ZnO particles were characterized by TEM images (Fig. 2). As shown in low magnification TEM image (Fig. 2A), the Pd/ZnO nanoparticle were undefined (shapeless) nanoparticles with average particle size of 26 nm. The average size of Pd

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nanoparticles on the surface of ZnO which was obtained from higher magnification TEM (Fig. 2B) image was found lower than 6 nm. Figure 1 Figure 2 3.2. Preliminary study Fig. 3 shows the cyclic voltammograms of modified electrode before (a) and after (b) reduction step (100 seconds in -1.0 V). As shown in Fig. 1a, there is no significant response to ethanol oxidation on the electrode surface before applied potential step. However, after applied potential step, the current was specifically increased. This is due to the fact that partially oxidized Pd on the ZnO surface reduced to Pd nanoparticles. So, this optimum time and potential were used before each analysis. Figure 3 3.3. Electrocatalytic studies of ethanol oxidation at Pd-ZnO/CPE Fig. 4 shows the cyclic voltammograms (CVs) of 1.0 M KOH solution at different electrodes containing Pd or Pd/ZnO-nanoparticles. As shown in this Figure, a pair of two redox peak was observed which are attributed to the oxidation of Pd (0.1 V) and reduction of PdOx (between -0.3 to -0.4 for Pd/CPE and -0.4 to -0.5 for ZnO-Pd/CPE), respectively [18]. Moreover, the current of Pd-ZnO /CPE is much larger than that at the Pd/CPE, which is due to the larger surface area provided by Pd nanoparticles that supported on ZnO nanoparticles. This is very favorable for application of ZnO nanomaterials as support for catalysts [27,29].The electrochemical active surface area (ECSA) was determined using the charge associated with the surface oxide reduction peak by assuming formation of a monolayer of PdO on Pd [30]. The ECSAs of Pd/CPE and Pd-ZnO/CPE are 1.41 cm2 and 7.8 cm2, respectively. It is evident that the ECSA of the Pd is largely improved (3 times) when Pd formed on the surface of ZnO nanoparticles as compared to Pd alone. This confirms the aggregation of Pd-NPs on the surface of ZnO nanoparticles is prevented and Pd nanoparticles were formed at a small size. Figure 4 The cyclic voltammograms (CVs) of 1.0 M methanol, ethanol, and 2-propanol in 1.0 M KOH solution on Pd-ZnO modified carbon paste electrode were shown in Fig. 5. 6

The scan rate was 50 mV s-1 in the potential range of – 0.8 to 0.5 V. As shown in this Figure, Pd-ZnO/CPE showed the highest forward current density for ethanol electrooxidation compared to other alcohols with the same molar concentration. Therefore, ethanol was chosen as the best alcohol for further studies. Figure 5 Electrooxidation activity of Pd/CPE and Pd-ZnO/CPE toward ethanol was investigated in a solution containing 1.0 M KOH and 1.0 M C2H5OH (Fig. 6). As shown, the peak current for Pd-ZnO/CPE is obviously better than when pure Pd is present. This may be due to the larger surface area of Pd nanoparticles on the ZnO nanoparticles as compared to Pd alone that can be due to separation and decreasing in size of Pd nanoparticles on the surface of ZnO nanoparticles. Figure 6 The onset potential (Eonset ) and ratio of the forward peak current to the backward peak current (If /Ib) are two important parameters to characterize the activity of ethanol electrooxidation on an electrocatalyst [31]. From the CV curves (Fig. 6), it is obvious that the onset potentials for the oxidation of ethanol on the Pd-ZnO/CPE are more negative than that observed on the Pd/CPE electrode, indicating an enhancement in the kinetics of the ethanol oxidation reaction and better catalytical activity. Also, The If/Ib value of Pd-ZnO/CPE electrode is 3.9, which is much larger than that of Pd/CPE electrode (1.4). This indicates that Pd-ZnO/CPE has better poisoning-tolerant behavior and catalytic efficiency. This value is higher than the most previously reported values for Pd-based electrocatalysts for ethanol oxidation reaction in the alkaline media. These results indicate that the presence of ZnO has improved the electrocatalytic activity of the Pd nanoparticles toward ethanol electrooxidation.

It

has been previously proposed [32] that, the concentration of hydroxyl groups on the Pd catalyst surface (as adsorbed OH−) has a crucial role on its catalytic performance toward the ethanol electrooxidation. The adsorbed OH− plays an important role in the removal of dissociated intermediate to release active sites for further ethanol electrooxidation process. Hence, the improvement of OH− adsorption leads to a faster ethanol oxidation. As previously reported, the metal oxide causes an increase in adsorption ability of the hydroxyl ion onto the catalyst surface. Also, the use of a 7

metal oxide activates water, which can oxidize the adsorbed carbonaceous intermediate species and thereby liberate the active sites of the surface [2,8, 33].

3.4. Chronoamperometric studies In order to evaluate the activity, stability and the poisoning of the Pd-ZnO/CPE and Pd/CPE, chronoamperometric tests were performed at a fixed potential of −0.1 V in a 1.0 M KOH solution containing 1.0 M ethanol. As shown in Fig.7 it can be seen that all of the chronoamperometric curves decrease sharply in the initial times. This decrease commonly arises from the contributions of double-layer charging and the establishment of the diffusion layer. As is shown in this figure, the current density on Pd-ZnO/CPE was considerably higher than that on Pd/CPE. Also, the current density on Pd-ZnO/CPE was constant and not decays with time but, because of intermediate poisoning, the current density of Pd/CPE was significantly decayed during the chronoamperometric test. All these results confirmed that the Pd-ZnO/CPE had better catalytic activity, stability and anti-poisoning effect than Pd/CPE toward the oxidation of ethanol in an alkaline media. As discussed above (section 3.3), CV results shown the current value and anti –poisoning effect (the ratio of the forward peak current to the backward peak current (If /Ib)) of Pd-ZnO/CPE were much higher than of Pd/CPE. These results agree very well with result of chronoamperometric test that the current value on Pd-ZnO/CPE was much higher and constant and not decays with time (anti – poisoning effect) than of Pd/CPE Figure 7 3.5. Amperometric determination of ethanol in alkaline media As stated before, Pd-ZnO modified carbon paste electrode has a good surface area. In addition, unlike Pd disk electrodes which need complicated procedures for regenerating their working surfaces, a new surface of the electrode can be obtained easily by polishing the carbon paste electrodes onto a smooth paper. Therefore, for further investigation of the applicability of this electrode, this nanocomposite electrode was used as a nonenzymatic amperometric ethanol sensor. Fig. 8A displays the amperometric response of Pd-ZnO carbon paste electrode toward the successive increase in ethanol concentrations at an operating potential of 8

0.25 V. The complete calibration curve for this amperometric sensor is shown in Fig. 8A. As it was shown in Fig. 8B this sensor exhibited two wide linear ranges of response to ethanol, in the concentration range of 1.99-490.90 mM and 0.491-3.355 M with correlation coefficients of R1 = 0.9995 and R2 = 0.9952, respectively. The limit of detection was 20.3 µM. Figure 8 These results indicate that the Pd-ZnO carbon paste electrode has a much wider linear range for ethanol determination than most of the other sensors reported previously (Table 1). The results show that the obtained linear range for this work is a good performance of electrode compared to previously reported works. Also, in some of these electrodes, different compositions of metals and other materials were used with hard and time consuming methods. The good stability and wide linear range of this electrode can be attributed to three aspects: Firstly, the well-dispersed and small sized of Pd nanoparticle on ZnO nanoparticles not only increase electrochemical active sites and active surface area but also increase electrolyte contact area which can promote linear range and sensitivity. Secondly: the use of a metal oxide increase adsorbed OH− and activates water, which can oxidize the adsorbed poisoning intermediate species and complete oxidation reaction which cause improve linear range, tolerance to the poisoning species, catalytic activity and stability of the Pd-ZnO/CPE electrode. Thirdly, the annulling step in synthesis method causes effective anchoring Pd nanoparticle to ZnO nanoparticle. This can lead to the improved stability. Table 1

3.6. Repeatability, reproducibility and stability of the Pd-ZnO modified carbon paste electrode The repeatability and reproducibility of this sensor were examined by cyclic voltammetry in 1.0 M KOH with 1.0 M ethanol. Satisfactory results (RSDs) were obtained for repeatability (3.84%), run-to-run reproducibility (4.16%) and reproducibility (4.67%) for Pd-ZnO modified carbon paste electrode. In addition, renewal of the newly fabricated nanocomposite electrode surface by simply rubbing the electrode surface against a smooth paper significantly improves the repeatability 9

and reproducibility. The fabricated nanocomposite electrode has long term stability (more than 120 days) under ambient conditions and showed less than 0.1 percent decrease in current density, and also the new electrode surfaces could be simply obtained by polishing the electrode. The activity and stability of Pd-ZnO/CPE electrocatalysts are also related to the stability of the oxides in alkaline solutions.

3.7. Interference study The influence of various substances on the determination of ethanol (20 mM) was studied. The results are presented in Table 2. Most of the two or three valances metals such as Pd2+, Ca2+, Cd2+, Mg2+, Mn2+, Al3+ and Zn2+ are precipitated in alkaline medium. However, methanol, formaldehyde, glucose and fructose can interfere in the determination of ethanol. In this situation, due to high stability, Pd-ZnO modified carbon paste electrode can be used as an amperometric detector in separation techniques. Table 2 3.8. Real sample analysis The applicability of the fabricated Pd-ZnO modified carbon paste electrode in real sample analysis was investigated. Standard addition method was used for the analysis of the prepared samples. The results are presented in Table 3. For a real sample, the amount of spiked ethanol in human blood serum was determined after 8 minutes. In this case, very satisfactory recoveries and RSDs were obtained which clearly indicate the applicability and reliability of the proposed nanocomposite electrode for the determination of ethanol. Table 3

4. Conclusion In this study, the characteristic of Pd-ZnO/CPE catalyst was investigated by XRD, TEM, CV and chronoamperometry. The result indicated that the particle size of Pd crystal was decreased by the addition of ZnO into the catalyst. Although adding ZnO remarkably enhances the anti-poison ability of Pd-ZnO/CPE catalyst, the reaction 10

mechanism does not change, and the OHads is the active species. Ease of electrode fabrication, cleaning and activating the electrode surface, high electrocatalytic activity, increased the degree of the active area and surface roughness, antipoisoning effect, good signal to noise ratio and low weight is among the advantageous features of this electrode for ethanol detection. The investigation of the performance of this nanocomposite electrode in human blood serum as a real sample clearly indicates the reliability of the proposed nanocomposite electrodes for ethanol determination.The excellent analytical performance confirms the applicability of this fabricated nanocomposite electrode for ethanol detection and as a nonenzymatic amperometric ethanol sensor. The fabricated nanocomposite electrode has long term stability (more than 120 days) under ambient conditions and showed less than 0.1 percent decrease in current density.

Acknowledgment We gratefully acknowledge the support of this work by Shiraz University Research Council.

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Authors Biographies Ebrahim Tavakolian received his M.Sc.

degree in

analytical chemistry from Shiraz

University, Shiraz, Iran in 2015. His field of interest is synthesis and application of metallic nanoparticles in electrochemical analysis. Javad Tashkhourian received his M.Sc. and Ph.D. degrees in analytical chemistry from

Shiraz University in 1999 and 2004, respectively. He was a member of chemistry department of Persian Gulf University (2004–2010). He joined the chemistry department of Shiraz University in 2010 where he is now an Assistant Professor. His research is focused on design and construction of chemical sensors (optical and electrochemical) and synthesis and applications of nanomaterials in electrochemical analysis. Zahra Razmi received her M.S. from Yazd University and Ph.D. (2012) in organic chemistry from Shiraz University, I. R. Iran. Her research interests is the preparation and characterization of nano Pd doped ZnO and its application in organic transformations, especially C-C crosscoupling reactions.

H. Kazemi received his Ph.D. degree in analytical chemistry from Shiraz University in 2013. He is currently an Assistant Professor of analytical chemistry with the Evaluation and Analysis of Materials, Research Institute of Petroleum Industry, Tehran, Iran. His current research interests include electroanalytical chemistry and separation. Mona Hosseini-Sarvari received her M.S. (1999) and Ph.D. (2003) in organic chemistry from Shiraz University, I. R. Iran. In 2003 straightaway she joined the faculty of the Shiraz University as assistant professor. She is currently a full professor of organic chemistry. Her research interests include the preparation and characterization of nano metal oxides and metal doped metal oxides as well as their application in organic reactions, especially under solvent-free conditions. She has published over than 80 ISI papers and 2 books (in Persian) and one book chapter.

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Caption of Figures Figure 1. XRD pattern of ZnO, and Pd -ZnO nanoparticles. Figure 2. TEM images of, Pd -ZnO (a), higher magnification of Pd -ZnO (b). Figure 3. CVs of Pd -ZnO /CPE (a) before, and (b) after an applied potential step in 1.0 M ethanol+1.0 M KOH at scan rate of 50 mV s-1. Figure 4. CVs for (a) ZnO/CPE, (b) Pd/CPE, and (c) Pd -ZnO/CPE in 1.0 M KOH at the scan rate of 50 mV s-1. Figure 5. CVs of Pd -ZnO/CPE in (a) 1.0 M 2-propanol+1.0 M KOH, (b) 1.0 M methanol+1.0 M KOH, and (c) 1.0 M ethanol+1.0 M KOH at scan rate of 50 mV s-1 Figure 6. CVs of Pd/CPE, and Pd -ZnO/CPE in 1.0 M KOH containing 1.0 M ethanol at scan rate of 50 mV S-1 Figure 7 Chronoamperometric results of the Pd/CPE and Pd -ZnO/CPE Pd/CPE solution at a working potential of −0.1 V. Figure 8 Amperometric responses for increasing ethanol concentrations at PdZnO/CPE in 1.0 M KOH for (a) whole range with complete calibration curve and (b) two calibration ranges.

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Intensity

2/degree

Figure 1

18

Figure 2

19

Figure 3

20

Figure 4

21

Figure 5

22

Figure 6

23

Figure 7

24

A

B

Figure 8

25

Table 1. A comparison of basic parameters for amperometric ethanol sensors Working electrode

Linear range

Detection limit

Reference

RuO2 modified Ni electrode

2.17–21.70 mM

-

[24]

Ni/Pt/Ti on Al2O3 substrate

82.95–

-

[25]

2.0–252.0 µM

1.7 µM

[34]

up to 1.5 mM

13 µM

[35]

up to 0.7 mM

29.7 µM

[36]

Pd-Ni/SiNWs electrode

0.0–20.4 mM

10 µM

[21]

CNT-Ni nanocomposites on

50–600 µM

-

[37]

25 to 200 µM

5.0 µM

[38]

NiCFP electrode

0.0–87.5 mM

0.25 mM

[39]

Pd/Ni/Si-MCP

0–60 mM

16.8 µM

[40]

Foam Ni electrode

0.87–30.40 mM

0.174 mM

[41]

Pd -ZnO/CPE

1.99 mM -3.35 M

20.3 µM

497.72 µM Poly(thionine)–CNF/AOD biocomposite on GCE PVA/MWCNT/ADH modified GCE PNR/AOD on carbon film electrodes

Si substrate ADH/IL-graphene/chitosanmodified electrode

This work

CNF: carbon nanofiber; AOD: alcohol oxidase; GCE: glassy carbon electrode; PVA: poly(vinyl alcohol); MWCNT: multiwall carbon nanotube; ADH: Alcohol dehydrogenase; PNR: Poly(neutral red); SiNWs: silicon nanowires; CNT: carbon nanotubes; IL: ionic liquid; NiCFP: nickel nanoparticle-loaded carbon fiber paste; MCP: microchannel-plate.

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Table 2. Results of interference study for the determination of 20.0 mM ethanol. Species

Maximum tolerable concentration ratio

Li+, Na+, K+, NO3-, SO4-2, PO4-3, CO3-2, C2O4-2,

1000

FFormic acid

20

2-Propanol

5

Glucose, fructose

1

Formaldehyde, methanol

1

Pd2+, Ca2+, Cd2+, Mg2+, Mn2+, Al3+, Zn2+

Precipitated in alkaline medium

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Table 3. Applicability of Pd -ZnO/CPE electrode for ethanol determination in a human blood serum sample.

Human blood

Added (mM)

Found (mM) (RSD %) *

Recovery (%)

-

-

-

34.0

36.0 (4.8)

105.8

68.0

71.0 (3.6)

104.4

102.0

101.0 (4.9)

99.0

153.0

148.0 (2.8)

96.7

204.0

206.0 (3.2)

101.0

serum

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