Carbon Graphite Obtained of Zinc-Carbon Exhausted

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Carbon Graphite Obtained of Zinc-Carbon Exhausted

Transcript Of Carbon Graphite Obtained of Zinc-Carbon Exhausted

Artigo
Carbon Graphite Obtained of Zinc-Carbon Exhausted Batteries Applied as Electrode in Electrochemical Sensors
Santos, C. S.; Pawlak, V. G.; Oliveira, R. D.; Fujiwara, S. T.; Pessôa, C. A.*
Rev. Virtual Quim., 2018, 11 (1), 275-296. Data de publicação na Web: 8 de fevereiro de 2019
http://rvq.sbq.org.br
Carbono Grafite Obtido de Baterias de Zinco-Carbono Exauridas Aplicadas como Eletrodo em Sensores Eletroquímicos
Resumo: Este artigo descreve a construção de um eletrodo de baixo custo e reutilizável, utilizando eletrodo de carbono grafite (CG) obtido de baterias de zinco-carbono exauridas, modificados com micropartículas de ouro. O eletrodo de CG foi modificado pela eletrodeposição potenciostática de micropartículas de ouro e aplicado como sensor eletroquímico para detecção simultânea de dopamina (DA) e ácido úrico (AU). Os efeitos do tempo de deposição, potencial e concentração do precursor tetracloroaurato(III) de hidrogênio (HAuCl4.3H2O) na formação das micropartículas de ouro foram sistematicamente estudados, utilizando microscopia eletrônica de varredura (FEG-SEM), difração de raios X (XRD) e métodos eletroquímicos incluindo voltametria cíclica e cronoamperometria. Os resultados confirmaram que as partículas de ouro possuem boa atividade eletrocatalítica para a detecção eletroquímica simultânea de dopamina e ácido úrico na faixa de 9,9 a 90,0 mol L-1 para DA e na faixa de 0,13 a 0,51 mmol L-1 para AU com limites de detecção de 2,6 μmol L-1 e 58,9 μmol L-1, respectivamente. Esses resultados indicaram que o eletrodo CG reutilizado de baterias exauridas, tem potencial aplicação como sensor eletroquímico, além de benéfico ao meio ambiente e de baixo custo.
Palavras-chave: Eletrodo de grafite de carbono; ouro; eletrodeposição potenciostática; sensor eletroquímico; baterias exauridas.
Abstract
This paper describes the construction of a facile, low cost and reusable electrode using carbon graphite (CG) of zinc-carbon exhausted batteries modified with gold microparticles. CG electrode was modified by potentiostatic electrodeposition of gold microparticles and applied as electrochemical sensor for simultaneous detection of dopamine (DA) and uric acid (UA). The effects of the deposition time, potential and concentration of precursor hydrogen tetrachloroaurate(III) (HAuCl4.3H2O) for the gold microparticles formation were systematically investigated using field emission gun scanning electron microscopy (FEG-SEM), X-ray diffraction (XRD) and electrochemical methods including cyclic voltammetry and chronoamperometry. The results confirmed that gold particles have good electrocatalytic activity for the simultaneous electrochemical detection of dopamine and uric acid in the range from 9.9 to 90.0 mol L-1 for DA and in the range from 0.13 to 0.51 mmol L-1 for UA with detection limits of 2.6 mol L-1 and 58.9 mol L-1, respectively. These results indicated that CG electrodes reused of exhausted batteries have potential application as electrochemical sensors besides advantages such as environmentally friendly and low cost.
Keywords: Carbon graphite electrode; gold; potentiostatic electrodeposition; electrochemical sensor; spent batteries.
* Universidade Estadual de Ponta Grossa, Chemistry Department, Av. General Carlos Cavalcanti 4748, CEP 84030-000, Ponta Grossa-PR, Brazil.
[email protected] DOI: 10.21577/1984-6835.20190020

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Volume 11, Número 1

Janeiro-Fevereiro 2019

Revista Virtual de Química ISSN 1984-6835
Carbon Graphite Obtained of Zinc-Carbon Exhausted Batteries Applied as Electrode in Electrochemical Sensors
Cleverson Siqueira Santos, Valeria Gremisk Pawlak, Rafaela Daiane de Oliveira, Sérgio Toshio Fujiwara, Christiana Andrade Pessôa*
Universidade Estadual de Ponta Grossa, Chemistry Department, Av. General Carlos Cavalcanti 4748, CEP 84030-000, Ponta Grossa-PR, Brazil. * [email protected]
Recebido em 3 de agosto de 2018. Aceito para publicação em 20 de novembro de 2018

1. Introduction
2. Materials and Methods
2.1. Reagents and apparatus 2.2. Characterization of CG electrode 2.3. Electrochemical measurements 2.4. CG electrode modification with gold 2.5. Electrochemical detection of DA and UA
3. Results
3.1. Characterizations of CG 3.2. Gold electrodeposition on CG 3.3. The influence of the electrodeposition potential on morphology 3.4. Effect of precursor concentration 3.5. Effect of electrodeposition time 3.6. Electrochemical detection of Dopamine and Uric Acid 3.7. Simultaneous Electrochemical detection of DA and UA at CG/Au
4. Conclusion

1. Introduction
Due to the increased production of portable electronic equipment, the use of batteries has expanded, mainly the use of non-rechargeable (zinc/carbon) batteries, because of their low cost. However, the useful life of these batteries is small, therefore, it is

necessary to constantly replace them.1 The zinc/carbon batteries are constituted of zinc coating as anode and carbon graphite (CG) as cathode. Nowadays, some processes have been developed to recycle the metals of these batteries,2,3 however the reuse of CG electrodes present in these batteries is also of great importance. Carbonaceous materials can be applied in the development of the electrochemical sensors due to its

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electrochemical properties, besides its low

cost, good mechanical rigidity and

environmentally friendly. Additionally, CG

electrodes can be easily modified with

different species in order to improve their

electrocatalytical

properties.4,5

The

conductive properties of CG electrode can

been enhanced by modifying it with

nanoparticles or metallic microstructures,

such as: Pt, Ni and Au,6-9 which leads to a wide

variety of applications, such as electrode

materials for supercapacitors,10 fuel cells,11

and

electrochemical

sensors.12

Microstructures of noble metals, especially

gold, have received great interest due to their

large electroactive area and electrocatalytic

activities.8,13,14 Compared with other methods

of obtaining gold nano/microstructures, the

potentiostatic electrodeposition technique is

often utilized, because it enables the control

of the size and morphology of

electrodeposited structures by adjusting the

deposition conditions, such as precursor

concentration, applied potential and

electrodeposition time.15 Recently, several

works have reported the modification of

glassy carbon electrodes,11,12 and carbon

graphite,8,9,16 with gold nano/microstructures

, due to physicochemical properties such as

good electrical conductivity, large surface area

and biocompatibility which have been applied

as electrochemical sensors in the detection of

glucose, ibuprofen, nitrate, azathioprine and

dopamine.16-19 Dopamine (DA) is a

neurotransmitter present in the mammalian

central nervous system and assists the

neurophysiological control of attention,

perception, motivation, and emotion.

Changes in the concentration of dopamine on

the dopaminergic system may cause several

neurobehavioral disorders, such as

Parkinson's disease, schizophrenia and

depression.20 However, the electrochemical

detection of DA in biological fluids is

hampered due to the presence of interfering,

such as uric acid (UA) due to the overlap of the

potential peaks.19 Therefore, this study

consists in the use of carbon graphite

electrodes obtained from spent batteries as a

current collector modified with gold

microstructures, as an electrochemical sensor

for the simultaneous detection of dopamine and uric acid.
2. Materials and Methods
2.1. Reagents and apparatus
Dopamine, uric acid, HAuCl4.3H2O, Na2HPO4, NaH2PO4, NaCl, KCl were purchased from Sigma-Aldrich. Phosphate buffered solution (PBS) were prepared with 0.1 mol L-1 NaH2PO4, 0.1 mol L-1 Na2HPO4, and 0.1 mol L-1 NaCl, and the pH was adjusted to 7.0 by adding NaOH. All reagents were of analytical grade and were used as received without further purification. The zinc-carbon batteries of 1.5 V were collected in batteries disposal sites.
2.2. Characterization of CG electrode
The morphology of the surface CG was analyzed using scanning electron microscopy (SEM) MIRA-TESCAN. Images were recorded with an accelerating voltage of 20 kV. The structure of the CG was analyzed using Raman and FTIR spectroscopy. The spectrometers used were BRUKER Senterra at 632.8 nm, in the range from 100 to 2500 cm-1 and SHIMADZU FTIR-8400 in the range from 500 to 3500 cm-1, respectively. The XRD measurements were obtained with a diffractometer Rigaku, modelo IV, Cu Kα (K = 1.54 Å). The XRD patterns were collected in continuous-scanning mode with interval from 10 to 80°.
2.3. Electrochemical measurements
The CG electrodes (0.4 cm diameter) were removed of zinc–carbon spent batteries and were cleaned using the

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following procedures a) mechanical polishing of the electrode surface with sandpaper (grit 1300); b) washing with chloroform, isopropyl alcohol and finally with distilled water. After, the surface of CG was isolated using epoxy resin. In Fig S1 is showed the image of the electrode after being removed from the battery. The residues of batteries were stored for further treatment, because the Zn and Mn can be recovered and recycled for manufacturing of new batteries and they can also be used in the synthesis of ferrites.21,22 The CG electrode was used as working electrode. For all electrochemical measurements a conventional three electrode compartment with an

electrochemical cell with volume of 10.0 mL was employed using a Pt wire (1.0 cm2 geometric area) as auxiliary electrode and Ag|AgCl in 3.0 mol L-1 KCl as reference electrode. The cyclic voltammetry measurements were performed in presence of 5.0 mmol L-1 [Fe(CN)6]3-/4- in 0.1 mol L-1 PBS, pH 7.0, in the potential range from -0.2 to 0.7 V and scan rate of 50.0 mV s-1.
The electroactive area of the modified and unmodified electrode was determined by Randles-Sevcik equation (Eq. 1) using cyclic voltammetric method in presence of the 5.0 mmol L-1 K3Fe(CN)6 in KCl 0.5 mol L1.

𝐼pa = 𝑘. 𝑛3⁄2. 𝐴. 𝐷1⁄2. 𝐶. 1⁄2

Eq. 1

In this equation, Ipa is the peak current, k is a constant of 2.69 x 105 C mol-1, n is the number of electrons, A is the electrode area (cm2), C is the concentration of K3Fe(CN)6 in mol cm-3, D is the diffusion coefficient (7.6 x 10-6 cm2 s-1) of K3Fe(CN)6 and ν is the scan rate in V s-1.23,24 Electrochemical impedance spectroscopy (EIS) measurements were carried out performed in presence of 5.0 mmol L-1 [Fe(CN)6]3-/4-, in 0.1 mol L-1 PBS (pH 7.0), applying a sine wave with amplitude of 10 mV on the open-circuit potential (OCP) in the frequency range of 10 kHz to 0.1 Hz. Electrochemical experiments were performed using a PGSTAT100 Autolab electrochemical system and GPES/FRA softwares. To obtain the charge transfer resistance (RCT) values from the EIS results, the Randles equivalent circuit was applied using Zview software.
2.4. CG electrode modification with gold
Direct electrodeposition of the gold microstructures in the CG electrode

surface was carried out via potentiostatic method. The variables involved in the electrodeposition process, such as the deposition time, deposition potential and the concentration of precursor solution were investigated. The influence of the applied potential was evaluated from -0.6 at +0.6 V. After determining the optimal potential, the concentration of precursor (HAuCl4.3H2O) solution was investigated in the range from 1.0 mmol to 100.0 mmol L1 in Na2HPO4 0.1 mol L-1. Finally, the electrodeposition time was evaluated in the range from 200 to 1200 s. These optimizations were evaluated in presence of the probe molecule [Fe(CN)6]3-/4-. The modified electrodes were characterized by scanning electron microscopy (FEG-SEM) using a MIRA-TESCAN equipment with accelerating voltages of 20 kV and with different magnifications. The images were analyzed using ImageJ software for average diameter measurements of the electrodeposited gold particles. The X-ray diffractograms were obtained as described in item 2.1.
The CG/Au electrode obtained under the optimal electrodeposition conditions

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was selected to investigate the catalytic properties for electrochemical detection of the DA and UA.
2.5. Electrochemical detection of DA and UA

was from 134.0 to 517.0 mol L-1, with a fixed DA concentration of 90.0 mol L-1. All experiments were performed at room temperature (296.15 K).
3. Results

The simultaneous determination of DA and UA was evaluated using square wave voltammetry (SWV) with the following optimized conditions: f = 40 Hz, a = 70 mV and ΔEs = 1.0 mV, in a potential range from 0.0 to 0.75 V. For the analytical curve, the concentration of DA ranged from 9.9 to 90.0 mol L-1 keeping the concentration of UA fixed in 100.0 mol L-1. For the UA analytical curve, the concentration range

3.1. Characterizations of CG
Firstly, the CG obtained from spent batteries was characterized. As presented in Fig. 1, the SEM images show the surface of the CG before and after polishing process.

(a)

(b)

2µm

2µm

Figure 1. SEM images of CG surface (a) before and (b) after the polishing process

Comparing the images of CG surface, it is verified that the roughness of the surface significantly reduced and a homogeneous pattern was obtained after polishing. The homogeneity of the surface is important to ensure the reproducibility of subsequent modification. Therefore, before use, the electrodes were submitted to the procedure of cleaning and polishing. The results of elementary composition of

the CG electrodes obtained with SEM-EDS are showed in the Table 1.
The result of this analysis showed that 99.75 % of the atomic composition of the CG electrodes is carbon. However, the possible influence of low percentages of impurities in the voltammetric profile of the GC electrode was evaluated by voltammetric studies.

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Table 1. Elemental composition of CG electrode obtained with SEM-EDS

Element

% atomic

Carbon

99.75 ± 0.12

Iron

0.08 ± 0.04

Sulphur

0.14 ± 0.04

Calcium

0.03 ± 0.02

Graphitic materials are constituted by a

series of layers of carbon atoms, which

form a hexagonal network of graphene

layers. These layers can be stacked in the

ABAB sequence leading to the hexagonal

structure or in the ABCABC arrangement

characteristic

of

rhombohedral

structures.25 Highly ordered graphite structures show hexagonal structure but even high quality samples can contain a fraction of the rhombohedral phase.26 Therefore, X-ray diffraction (XRD) technique was used (Fig. 2) to investigate the structure of the CG electrodes.

Figure 2. XRD patterns of carbon graphite electrodes

According to the literature,25,26 the peaks in 26.5◦, 54.4° and 77.2° are due to (0 0 2),(0 0 4) and (1 1 0) reflections related to hexagonal structure. However, the peak in 43.8° is due to (1 0 1) which correspond to the rhombohedral structures. This phase normally coexists with common hexagonal phase.23 From XRD pattern and using Bragg equation,27,28 the interlayer spacing was determined as 3.4 Å.

According to the literature, the spacing between two perfectly oriented graphitic layers is 3.3 Å.26
The Raman and FTIR spectroscopy were employed to investigate the presence of possible functional groups and defects in the structure of the CG electrodes. The results are showed in the Fig. 3.

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Figure 3. (a) FTIR (b) Raman spectra of carbon graphite electrodes

The FTIR band at 3245 cm-1 can be attributed to -OH stretching. The bands at 2905 and 2847 cm-1 are due to vibrational stretching of the C-H group with hybridization sp3 and sp2.4,29,30 The bands observed in 1690 and 1413 cm-1 can be attributed to stretching of the C=C and ester groups, respectively.31 These results indicate the presence of functional groups and defects in the structure of CG electrode. The Raman spectra of the CG electrodes revealed two bands at 1337 and 1573 cm-1 attributed to the D and G bands, respectively.32-34 The G band is related to the aromatic carbon stretching in the plane,27 and D band reflects the presence of disorders or defects in the graphitic structure, such as the presence of functional groups and carbon with sp3 hybridization.34
The intensity ratio of G and D bands (ID/IG) has been used to evaluate the degree of disorder in carbon graphite.35 Analyzing the intensities of D and G bands, it was possible to estimate the ratio between them and the value found was 0.84. According to the literature,35,36 the ID/IG estimated for carbon nanotubes is 0.81. After oxidative treatment

the ratio between these bands increased to 1.01, indicating the functionalization and the presence of defects in the structure. Therefore, analyzing the spectra and the ratio between the intensities of the bands D and G, it is evident the presence of defects and heteroatoms in the structure of the CG electrodes.

The reproducibility of five CG

electrodes

was

evaluated

electrochemically by cyclic voltammetry

technique in the presence of the probe

[Fe(CN)6]3-/4- (Fig. S1). The results showed

that the CG electrodes exhibited potential

anodic peak constant Epa = 0.34 ± 0.06 V

and Ipa = 0.70 ± 0.06 mA.cm-2. Therefore,

the electrodes showed a good

reproducibility with a small relative

standard deviation.

3.2. Gold electrodeposition on CG

The potential of the reduction of [AuCl4]- on the surface of the CG electrode was evaluated by cyclic voltammetry and the voltammetric profile is shown in Fig. 4.

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Figure 4. Cyclic voltammograms recorded during gold electroreduction at a CG electrode in a 0.1 mol L-1 Na2HPO4 deaerated solution containing HAuCl4 10.0 mmol L-1: first (solid line) and second (dashed line) consecutive scans,  = 50 mV s-1

The first scan exhibits the reduction of Au(III) to Au(0) with a cathodic peak at 0.50 V. This peak is assigned the deposition of gold onto the CG electrode surface. On the backward scan, a current crossover occurred at 0.62 V, which is an indicate of nucleation process. However, this behavior was not observed in the following scans, due to the growth of Au nanoparticles on the nuclei formed during the first scan.13,17
It is observed in the first and fifth scans (dashed lines), the reduction peak of Au (III) was shifted from 0.50 to 0.69 V. This displacement in the potential of Au deposition occurred due to fact that thermodynamically the growth of new particles on previously formed particles is easier than the nucleation of new particles on CG electrode, therefore the energy necessary for deposition of gold on gold is lower than on CG.17,37 For this reason, the voltammetric peak tends to shift in the direction to the standard reduction

potential of the AuCl4-/Au redox pair, which is 0.99 V vs the standard hydrogen electrode (SHE).38
The deposition of gold may be performed using a cyclic voltammetry technique. However, the potentiostatic method allows varying the potential and deposition time, thereby controlling the size and morphology of the electrodeposited particles.
3.3. The influence of the electrodeposition potential
Among the parameters involved in the electrodeposition technique, the applied potential is an important parameter for the control of the morphologies of gold microstructures. Therefore, the influence of the applied potential was evaluated and the results of these characterizations are showed in the Fig. 5.

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(a)

(b)

2µm

2µm

(c)

(d)

2µm

2µm

Figure 5. SEM images of Au particles electrodeposited in 0.1 mol L-1 Na2HPO4 solution containing 10.0 mmol L-1 HAuCl4 for 700 s at potentials of (a) E = +0.6 V, (b) E = +0.3 V, (c)
E = -0.3 V, and (d) E = -0.6 V. The scale bars for all images is 2 m

Under a potential of deposition of +0.6 V (Fig. 5a), the image reveals gold microstructures dispersed with flower-like shapes with diameter of approximately 1.8 m, however their distribution of microstructures on the electrode surface is not homogeneous. Similar results were reported by Guo et al.39 studied the influence of the electrodeposition potential in the morphology of the gold structures. The microstructures obtained at potentials of 0.5 and 0.7 V exhibited flower-like structures with average diameter of 2 m. When the applied potential was +0.3 V (Fig. 5b), it was verified a homogenous coating by gold particles with spherical shapes. These particles showed an average diameter of

420 nm. Decreasing the electrodeposition potential for -0.3 V resulted in some dendrite-like gold microstructures on the surface (Fig. 5c), and when applying -0.6 V it was observed particles with morphology of rods as shown in Fig. 5d. In this potential of -0.6 V, it was observed air bubbles on the surface of the CG electrode hindering the growth of the Au microstructures. Moreover, the gold particles easily detached from the surface of CG electrode. Similar results were reported by Shu et al.14 which reported the study of electrodeposition of gold microstructures on glassy carbon electrode using different potentials. It was observed that at potentials of -0.5 and -0.7 V, a large amount of air bubbles on the surface of the GC electrode were formed, preventing the

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growth of gold structures on the surface of the substrate.
The change in the morphology of particles due to the change of overpotential is related to the process of nucleation and grain growth.13,40 The process of nucleation/growth

for gold particles can be described according to the model proposed by Scharifker and Hills.41 According to this model, the mechanism can be instantaneous or progressive, which are described by the following equations:

(𝑖⁄𝑖max)p2ro = 1.2254(𝑡max⁄𝑡){1 − exp⁡[−2.336(𝑡⁄𝑡max)2]}2 Eq. 2 (𝑖⁄𝑖max)i2nst = 1.9542(𝑡max⁄𝑡){1 − exp⁡[−1.2564(𝑡⁄𝑡max)2]}2 Eq. 3

The mechanism of gold nucleation on

CG electrodes was investigated by

potentiostatic transient measurements

obtained at different potentials in the

range +0.6 at -0.6 V (Fig. S 2). Comparing

the experimental data with theoretical

curves given by Eqs. (2) and (3) it is verified

that there is a transition between the

progressive

and

instantaneous

mechanisms due to applied potential. For

the deposition in potentials of -0.6 and -0.3

V, the nucleation resembles more to

instantaneous growth than progressive. In

potentials positive (+0.3 and +0.6 V) the

profile of the experimental curves can be

described by the progressive mechanism. These results are in agreement with data reported in the literature which report that high overpotentials favors instantaneous nucleation and low potential favors progressive nucleation.13,42
The electrochemical behavior of CG modified electrodes with gold microstructures obtained with different applied potentials were investigated by cyclic voltammetry, in presence of [Fe(CN)6]3-/4-. The results are shown in Fig. 6.

Figure 6. Cyclic voltammograms obtained for the CG electrodes modified with microstructures of gold obtained with different electrodeposition potentials, ([HAuCl4] 10.0 mmol L-1 and electrodeposition time of 700 s) in presence of [Fe(CN)6]3-/4- 5.0 mmol L-1 in 0.1 mol L-1 KCl,  = 50 mV s-1

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PresenceBatteriesFigSurfaceQuim