- Email: [email protected]
Electrochemical fabrication and amperometric sensor application of graphene sheets
Superlattices and Microstructures 95 (2016) 56e64
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
Electrochemical fabrication and amperometric sensor application of graphene sheets € lu* Ays¸e Oztürk, Murat Alanyalıog Atatürk University, Sciences Faculty, Department of Chemistry, 25240, Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 April 2016 Accepted 26 April 2016 Available online 27 April 2016
Graphene sheets have been fabricated by applying two-step electrochemical processes in two-electrode cell system containing 0.1 M sodium dodecyl sulfate (SDS). First step is intercalation of SDS into graphite anode electrode and this process has been applied at different intercalation potential values of 1, 3, 5, and 7 V. Second step includes exfoliation of SDS-intercalated graphite electrode in the same medium by acting as cathode. Stable graphene dispersions are obtained after these two electrochemical steps. Characterization of graphene sheets have been carried out using scanning electron microscopy, electron dispersive spectroscopy, fourier transform infrared spectroscopy, UVeVis. absorption spectroscopy, X-ray diffraction, and cyclic voltammetry techniques. Graphene sheets have been modified onto glassy carbon electrode (GCE) by drop-casting of graphene dispersion. Graphene/GCE having a good electrocatalytic activity has been used for amperometric determination of nitrite in both standard laboratory and real samples. The oxidation current density was linearly proportional to the nitrite concentration in a range between 1 and 250 mM. The sensitivity of the sensor was calculated as 0.843 mAmM1 cm2 with a detection limit of 0.24 mM at a signal-to-noise ratio of 3.0. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Graphene Electrochemistry Sodium dodecyl sulfate Amperometric sensor Nitrite
1. Introduction Graphene has been isolated by Novoselov and Geim by scotch-tape method in 2004 [1]. After this exploration, graphene has been focused by the researchers because of its high mobility, unique transport performance, high mechanical stability and high thermal and satisfied electrical conductivity. Electrochemistry is suitable technique for graphene production because it is economic, environmentally friendly, and simple. Upto date, some electrochemical routes have been performed to produce graphene flakes by applying electrochemical intercalation of various compounds e.g. ionic liquids [2e4], poly(sodium-4styrenesulfonate) [5], acetamide-urea-ammonium nitrate melt [6], sodium dodecyl sulfate (SDS) [7e11], sodium dodecyl benzenesulfonate [11,12], cetyltrimethylammonium bromide [13,14], glycine based complex [15], tetrasodium pyrophosphate [16], and NaOH/H2O2 [17]. Nitrite is an important additive and extensively used for fish, meat and cheese products in food technology. Meat is generally not labeled as “cured” without addition of nitrite since it blocks toxins produced by the clostridium botulinum bacteria. Nitrite amount in food products must be under control because its high level causes to toxicity, which have cancer risk for human body. Therefore, quantitative analysis of nitrite in real samples is of great importance. Up to now,
* Corresponding author. lu). E-mail address: [email protected] (M. Alanyalıog http://dx.doi.org/10.1016/j.spmi.2016.04.039 0749-6036/© 2016 Elsevier Ltd. All rights reserved.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
57
electrochemical quantification of nitrite has been applied on modified conductive substrates to decrease electrooxidation potential and increase electroactive surface area. For this purpose, conductive or semiconductive electrodes have been modified with dye polymers [18,19], dye polymer/graphene [20,21] metal nanoparticles/graphene [22,23]. Electrochemical quantification of nitrite has also been initially studied on flexible graphene-based paper electrode by our group [24]. This paper describes the synthesis of graphene sheets including two-step electrochemical processes in two-electrode cell system containing 0.1 M SDS. In the first step, SDS has been intercalated into graphite electrode by serving graphite as anode in the electrochemical cell. We have investigated effect of different intercalation potentials on the quality of produced graphene flakes. Second step includes exfoliation of SDS-intercalated graphite electrode by acting this electrode as cathode. Fabricated graphene sheets have been characterized by scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), fourier transform infrared spectroscopy (FTIR), UVeVis. absorption spectroscopy, X-ray diffraction (XRD), and cyclic voltammetry techniques. Amperometric quantification of nitrite in both laboratory and real samples have been performed by using produced graphene sheets. For this purpose, graphene sheets have been supported onto glassy carbon electrode (GCE) by drop-casting of graphene dispersion. 2. Experimental section 2.1. Materials All the chemicals used in this study were of analytical reagent grade and used without further purification. Milli-Q ultrapure water (conductivity: 5.5 mS$m1) was used all through this study. Phosphate buffer solutions (PBS, 0.1 M) with different pH values were prepared by mixing stock solutions of 0.1 M H3PO4 and KH2PO4, and the pH of the buffer solution was adjusted to desired value by using a pH-meter (Hanna Instruments). The solutions were deaerated by passing dry nitrogen through the electrochemical cell for 15 min prior to each experiment. 2.2. Electrochemical fabrication of graphene sheets Fabrication procedure was presented in Fig. 1. Synthesis procedure includes two step electrochemical processes in 0.1 M SDS (Sigma Aldrich, reagent grade) solution by using two-electrode system. First step is applied for intercalation of SDS into graphite electrode according to following reaction:
i h i h ½Cx þ DS / Cxþ DS þ e To achieve this step, graphite rod (Goodfellow, England, 99.5% purity) is used as anode and Pt-fiol (Sigma Aldrich) served as cathode. Because intercalation conditions effect the quality of graphene sheets, this step is carried out at different intercalation potential values of 1, 3, 5, and 7 V. Second step is performed for exfoliation of SDS-intercalated graphite electrode in the
Fig. 1. Schematic presentation of the electrochemical preparation and amperometric sensor application procedure of graphene sheets.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
58
same medium by serving this electrode as cathode vs Pt-foil anode. After these electrochemical steps are applied, stable graphene/SDS dispersions are obtained as seen in Fig. 1. To supply the exfoliation of possible large graphitic particles to graphene sheets, graphene/SDS dispersion was ultrasonically treated for 1 h. All of the graphene/SDS dispersions are very stable and can be stored at room temperature more than 6 months without precipitation. To remove SDS from graphene dispersions, graphene/SDS dispersions were vacuum-filtered through a polycarbonate membrane (Whatman, Ø ¼ 47 mm, pore size: 0.2 mm) using an ultrafiltration vacuum cell system (EZ-Stream). After washing with plenty of distilled water and air-drying, pure graphene paper was obtained on the membrane with black color. This paper was dispersed into pure-water and 1.0 mg/mL graphene dispersion was prepared for further characterization and amperometric sensor applications. As can be seen in Fig. 1, graphene dispersions prepared at different intercalation potentials reveal different color densities, when compared to transparent 0.1 M SDS solution. It is clear that color of the graphene dispersions darkens by increasing the intercalation potential from 1 to 7 V. It is obvious that intercalation at 1 V is very poor to produce graphene sheets and efficiency is very low. At the intercalation potentials higher than 3 V, color of graphene dispersion shows black color. Concentration for the dispersions were determined by using gravimetry studies and results were presented in Table 1. The graphene amount increases with increasing the intercalation potential. 2.3. Amperometric quantification of nitrite Cyclic voltammetry technique was performed to investigate the electrooxidation behavior of NO 2 on graphene/GCE in 0.1 M PBS (pH 5.0). For this purpose, graphene modified GCE was prepared by drop-casting of graphene dispersion onto GCE, and then drying at room temperature. Before each cyclic voltammetry measurements, the graphene/GCE was placed in 15 mL PBS and the potential scan was cycled between 0 and 1200 mV until a steady cyclic voltammogram was obtained. Amperometry was carried to obtain the calibration curve of the NO 2 sensor. The nitrite content in tap water sample was determined by a conventional amperometric technique according to the standard addition method. Amperometric determination was applied on graphene/GCE under stirring conditions at 750 rpm. After the working electrode reached a steady baseline, the standard nitrite solution was added to electrochemical cell. As a reference work, spectrophotometric method was performed to determine spectrophotometrically the NO 2 content of the real samples [25]. Tap water samples were collected from our laboratory and analyzed without previous treatment. 2.4. Instrumentation In order produce graphene dispersion, two-electrode cell was used with Philip Harris brand AC&DC power supply system. Cyclic voltammetry and amperometry studies were applied with an Epsilon (BASi) potentiostat system connected to a three electrode cell. The SEM analysis and elemental composition determination of the thin films were collected by EDS with a ZEISS system coupled to the SEM instrument. For this purpose, Au(111) surface was used as substrate because it is a reference substrate for morphological studies with an atomically-flat surface structure. Au(111) substrates were prepared in our laboratory based on our previous studies [19,24]. The crystal structure of the samples were collected by powder X-ray diffraction (XRD) using a Rigaku (miniflex) X-ray diffractometer with Cu Ka radiation (l ¼ 1.5405 Å). Fourier transform infrared (FTIR) spectra were collected with a Spectrum One model PerkinElmer spectrophotometer by using a specular reflectance attachment. Optical characterization of the sample dispersions were recorded by using a Shimadzu 3101PC UVeViseNIR spectrophotometer. 3. Results and discussion 3.1. Optical characterization We have performed UVeVis. absorption studies to characterize graphene/SDS dispersions prepared at different intercalation potentials. Fig. 2 demonstrates absorption spectra of graphene dispersions in 0.1 M SDS prepared at 1, 3, 5, and 7 V. For a comparison, absorption spectrum of 0.1 M SDS was also presented in Fig. 2. A maximum for all graphene containing samples was obtained at about 240 nm, corresponding to p / p * transitions of aromatic C]C bonds, and a slight shoulder at about 350 nm, which can be attributed to n / p * transitions of CeO bonds [7]. It is clear from this figure that absorbance of the peaks increases by increasing the intercalation potential due to graphene concentration increases in the suspensions as
Table 1 Gravimetric analysis result of graphene sheets prepared at different intercalation potential values. Intercalation potential (V)
Graphene amount (mg/mL)
1 3 5 7
0.8 4.5 7.0 23.0
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
59
Fig. 2. UVeVis. absorption spectra of 0.1 M SDS solution and graphene dispersions in 0.1 M SDS prepared at different intercalation potentials of 1, 3, 5, and 7 V.
shown in Table 1. Low intensity of shoulder for n / p * transition can be assigned to large amount of reduced form of graphene sheets in the prepared dispersions after applied electrochemical processes. FTIR spectra of graphene sheets were collected by using specular reflectance attachment of the instrument and the results were illustrated in Fig. 3. For comparison, FTIR spectrum of used graphite rod electrode were also presented in Fig. 3. It is clear that all graphene samples (without SDS) show almost similar spectra with graphite rod. The most important difference between graphite rod and graphene samples is the observation of a broad band at around 3000 cm1 and this band is attributed to eOH groups of graphene sheets, which arises due to electrooxidation of graphite rod. This situation proves n/p * transitions in the UVeVis. absorption studies.
3.2. Morphological investigation Morphological studies of the graphene samples were applied on Au(111) substrates and the samples were prepared by drop casting of graphene dispersions onto Au(111) substrate. Fig. 4 demonstrates top-view SEM images of Au(111) substrate
Fig. 3. FTIR specular reflectance spectra of graphite rod and graphene sheets prepared at intercalation potentials of 3, 5, and 7 V.
60
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
Fig. 4. SEM images of graphene sheets on Au(111) substrate prepared at intercalation potentials of 1 (a), 3 (b), 5 (c), and 7 V (d). Graphene sheets were supported on Au(111) substrate by drop casting of graphene dispersions.
coated with graphene sheets prepared at intercalation potentials of 1, 3, 5, and 7 V. Graphene sheets prepared at 1 V shows large, rough, and layered graphitic structures, which may be attributed to poor intercalation of SDS into graphite at 1 V (Fig. 4a). As seen in Fig. 4b, intercalation potential of 3 V reveals a mixed structure of graphene-like wrinkled layers and thick graphitic particles. Fig. 4c shows graphene samples prepared at 5 V and this image clearly exhibit that surface consists of characteristic wrinkled graphene-like flakes. Intercalation potential of 7 V results with small and damaged particles, which is due to high oxidation process. SEM investigation demonstrates that intercalation potential of 5 V is optimum potential value to yield high quality graphene sheets. We have also acquired EDS data for graphene sheets prepared at 7 V (Fig. S1). When the Au atom, which is due to Au(111) substrate subtracted from the spectrum, graphene sample contains 90.29% C, 9.23% O, 0.10% Na, and 0.37% S atoms. Ensafi et al. have prepared graphene oxide (GO) sheets by using modified Hummers method and they determined chemical composition of GO as 61.59% C and 38.41% O by EDS measurement [26]. When compared to GO, graphene sheets include less oxygen atom and this situation is assigned to electrochemical reduction process (second step), which serves for both exfoliation of SDS-intercalated graphite cathode and reduction of oxygen-containing functional groups. Graphene sample involves Na and S atoms with a very little amount and these atoms are due to SDS molecules. This case shows that graphene sheets are still containing SDS molecules even after cleaning with plenty of water for many times.
3.3. XRD Fig. 5 exhibits typical XRD patterns of graphene samples prepared at intercalation potentials of 3, 5, and 7 V on Au(111) substrate and additionally graphite rod. Au(111) substrate does not reflect any diffraction peak between 2q value of 10e30 (JCPDS card no: 04-0784). Graphite rod presents an intensive peak at 2q value of 27.2 with a d-spacing of 0.34 nm and this peak corresponds to (002) diffraction (JCPDS card no: 41-1487). The XRD pattern of graphene sheets reveal peaks at 26.3, 26.4, and 26.5 for intercalation potentials of 3, 5, and 7 V, respectively. This situation shows that electrochemical processes causes increasing of d-space value due to the insertion of SDS and/or oxygen-containing functional groups during intercalation step.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
61
Fig. 5. XRD patterns of graphite rod and graphene sheets on Au(111) substrate prepared at intercalation potentials of 3, 5, and 7 V. Graphene samples were supported on Au(111) substrate by drop casting of graphene dispersions.
Fig. 6. Cyclic voltammograms of naked GCE and GCE modified with graphene sheets prepared at intercalation potentials of 3, 5, and 7 V in 0.1 M PBS (pH: 5.0) containing 1.0.103 M NaNO2. Scan rate: 50 mV/s.
3.4. Amperometric determination of nitrite Fig. 6 demonstrates the electrochemical oxidation of nitrite in 0.1 M PBS (pH: 5.0) at naked GCE and GCE modified with graphene sheets prepared at intercalation potentials of 3, 5, and 7 V. When potential of the naked GCE is scanned from 0 mV to
62
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
1200 mV, an anodic oxidation wave is observed at 850 mV, with current of 27.4 mA, which is corresponding to the oxidation of NO 2 to NO3 through a two-electron oxidation process [18e24]. The electrooxidation of nitrite is irreversible because no wave is observed by reversing the potential to negative direction. This irreversible electrooxidation peak takes place at 840, 820, and 805 mV, with current values of 34.5, 45.2, and 67.1 on GCE modified with graphene sheets prepared at 3, 7, and 5 V, respectively. Since graphene/GCE prepared at 5 V shows the highest current and the lowest electrooxidation potential, it can be deduced that graphene sheets prepared at 5 V reveals the best electrocatalytic ability for the oxidation of nitrite. A peak pair at about 250/100 mV is also observed on graphene/GCE and this peak pair is also observed in the absence of nitrite, which is assigned to redox behavior of buffer solution. Since the idea is amperometric determination of nitrite, some important parameters, which effect the amperometric determination of nitrite have been optimized by using cyclic voltammetry studies. We have initially tested pH of the nitrite solution for the best amperometric response and the best voltammetric wave is obtained on graphene sheets prepared at 5 V in pH: 5.0 medium as seen in Fig. 7. The amount of graphene on GCE is another important factor and the highest current density and lowest peak potential is obtained in pH: 5.0 (0.1 M PBS) on graphene/GCE prepared by drop casting of 25 mL graphene dispersion prepared at intercalaton potential of 5 V onto GCE (Fig. S2). Therefore, amperometric quantification of nitrite was studied in 0.1 M PBS (pH 5.0) under stirring conditions (750 rpm) on graphene/GCE (prepared by drop casting of 25 mL graphene dispersion fabricated at intercalaton potential of 5 V) at the electrooxidation potential of 805 mV. A current-time transient for the successive addition of NaNO2 into 15 mL 0.1 M PBS (pH: 5.0) is shown in Fig. 8a. It is seen that the anodic current increases suddenly to reach a stable value after addition of nitrite and reaches to almost steady-state current value in less than 3 s, which means the electrocatalytical response is so fast. Fig. 8b demonstrates the calibration curve, which is calculated from Fig. 8a. It is observed that the oxidation current is linearly proportional to the nitrite concentration in the range of 1.0e250 mM. The equation for this calibration curve is obtained as j(mA) ¼ 0.85 þ 0.035 Cnitrite (mM) with a correlation coefficient of 0.9993 (Fig. 8b). The sensitivity of this composite sensor was calculated as 0.843 mAmM1 cm2. The detection limit of the electrode was determined as 0.24 mM at a signal-to-noise ratio of 3.0. The stability of graphene/GCE for amperometric determination of nitrite was assessed by using cyclic voltammetry technique. When the graphene/GCE is used for amperometric detection of nitrite without renewal for 10 times only about 34% loss of the initial current is recorded. If it is used 25 times successively, 58% of the initial amperometric response is obtained (Fig. S3). The storage stability of the sensor was also investigated and 20% decrease of the initial current observed after 15 days (Fig. S4). The interference effect of some ions on the amperometric response of nitrite by using graphene/GCE was evaluated
Fig. 7. Cyclic voltammograms in 0.1 M PBS solutions with different pH values containing 1.0.103 M NaNO2 on GCE modified with graphene sheets prepared at 5 V. Scan rate: 50 mV/s.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
63
Fig. 8. (a) Amperometric response of graphene/GCE at 805 mV upon repetitive additions of NaNO2 to 15 mL of 0.1 M PBS (pH 5.0), (b) Plot of oxidative current density vs nitrite concentration (calibration curve). Electrode surface area: 0.0415 cm2.
Table 2 Determination of NO 2 content in tap water sample (n ¼ 3). Sample
Nitrite amount/mg kg1
Tap water
Amperometry 35.08 ± 1.70
Spectrophotometry 36.50 ± 1.64
2þ 2þ 2þ 2þ 2þ with the addition of 100-fold of various common ions of Co2þ, SO2 into 1.0 mM 4 , Cl , NO3 , Mg , Pb , Zn , Ba , and Ca NO in 0.1 M PBS (pH: 5.0) (Fig. S5). It is clear that the added ions demonstrates very low interference effect (<6.5%) for 2 amperometric detection of nitrite. The practical application of the prepared graphene/GCE was also examined in tap water sample. The concentration of nitrite of the real sample was calculated using standard addition method. In order to compare the results of this method, spectrophotometry [25] was also performed for the determination of nitrite in the same tap water sample. It is determined that the amperometric determination of nitrite by using graphene/GCE is very effective and feasible in the tap water sample (Table 2). The quality of the sensor for amperometric determination of nitrite was compared with that of previously published works (Table 3). The results indicate that the graphene/GCE reveals hopeful results with low detection limit and good sensitivity.
Table 3 Comparison of graphene/GCE with other electrodes for determination of NO 2. Sensor
pH
Applied potential (mV)
Linear region (mM)
Sensitivity (mAmM1 cm2)
Detection limit (mM)
Reference
PTBa/GCE Poly(PyY)b/PGEc Hbd/Au/GACSe/GCE PtNPsf/rGOg/GCE rGO/AgNPsh/poly(PyY) paper Graphene/GCE
3.0 4.0 7.0 7.0 5.0 5.0
1100 (SCE) 930 (Ag/AgCl) 850 (SCE) 750 (SCE) 860 (Ag/AgCl) 805 (Ag/AgCl)
0.1e15.2 1.0e100 0.05e1000 0.25e90 0.1e1000 1.0e250
0.047 6.21 0.15 e 13.5 0.843
0.05 0.5 0.01 0.1 0.012 0.24
[18] [19] [22] [23] [24] This work
a b c d e f g h
Poly(toluidin blue). Poly(pyronin Y). Pencil graphite electrode. Hemoglobin. Graphene with biocompatible chitosan. Pt nanoparticles. Reduced graphene oxide. Ag nanoparticles.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
64
4. Conclusions Graphene sheets were fabricated in a two electrode cell by using two step electrochemical processes including electrochemical intercalation of SDS into graphite anode and exfoliation of SDS-intercalated graphite cathode. UVeVis. absorption, FTIR, and EDS results demonstrated that graphene flakes are partially oxidized and contains very low amount of oxygen atoms. SEM investigations revealed that graphene sheets prepared at intercalation potential of 5 V yielded the best quality graphene, which includes characteristic wrinkled surface structure. When graphene/GCE was used as an electrochemical sensor for determination of nitrite, it presented hopeful results with high stability, long term storage, and repetitive usage. Acknowledgments This work has been supported by Atatürk University (Project No: BAP 2014/59). Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.spmi.2016.04.039. References [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Electric field effect in atomically thin carbon films, Science 306 (2004) 666e669. [2] N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, J. Chen, One-step ionic liquid-assisted electrochemical synthesis of ionic-liquid functionalized graphene sheets directly from graphite, Adv. Funct. Mater. 18 (2008) 1518e1525. [3] A.T. Najafabadi, E. Gyenge, High-yield graphene production by electrochemical exfoliation of graphite: novel ionic liquid (IL)eacetonitrile electrolyte with low IL content, Carbon 71 (2014) 58e69. [4] M.H. Chakrabarti, N.S.A. Manan, N.P. Brandon, R.C. Maher, F.S. Mjalli, I.M. AlNashef, S.A. Hajimolana, M.A. Hashim, M.A. Hussain, D. Nir, One-pot electrochemical gram-scale synthesis of graphene using deep eutectic solvents and acetonitrile, Chem. Eng. J. 274 (2015) 213e223. [5] G. Wang, B. Wang, J. Park, Y. Wang, B. Sun, J. Yao, Highly efficient and large-scale synthesis of graphene by electrolytic exfoliation, Carbon 47 (2009) 3242e3246. [6] V.S. Dilimon, S. Sampath, Electrochemical preparation of few layer-graphene nanosheets via reduction of oriented exfoliated graphene oxide thin films in acetamideeureaeammonium nitrate melt under ambient conditions, Thin Solid Films 519 (2011) 2323e2327. [7] M. Alanyalioglu, J.J. Segura, J. Oro-Sole, N. Casan-Pastor, The synthesis of graphene sheets with controlled thickness and order using surfactant-assisted electrochemical processes, Carbon 50 (2012) 142e152. [8] M. Moradi, J.A. Mohandesi, D.M. Haghshenas, Mechanical properties of the poly(vinyl alcohol) based nanocomposites at low content of surfactant wrapped graphene sheets, Polymer 60 (2015) 207e214. [9] J. Liu, M. Notarianni, G. Will, V.T. Tiong, H. Wang, N. Motta, Electrochemically exfoliated graphene for electrode films: effect of graphene flake thickness on the sheet resistance and capacitive properties, Langmuir 29 (2013) 13307e13314. [10] C.W. Chen, Z.T. Liu, Y.Z. Zhang, J.S. Ye, C.L. Lee, Sonoelectrochemical intercalation and exfoliation for the preparation of defective graphene sheets and their application as nonenzymatic H2O2 sensors and oxygen reduction catalysts, RSC Adv. 5 (2015) 21988e21998. [11] J.M. Munuera, J.I. Paredes, S. Villar-Rodil, M. Ayan-Varela, A. Martínez-Alonso, J.M.D. Tascon, Electrolytic exfoliation of graphite in water with multifunctional electrolytes: en route towards high quality, oxide-free graphene flakes, Nanoscale 8 (2016) 2982e2998. [12] A.A.B. Hamra, H.N. Lim, W.K. Chee, N.M. Huang, Electro-exfoliating graphene from graphite for direct fabrication of supercapacitor, App. Surf. Sci. 360 (2016) 213e223. [13] M.K.P. Kumar, C. Srivatsava, Synthesis of graphene from a used battery electrode, JOM 68 (2016) 374e383. [14] K. Kakaei, K. Hasanpour, Synthesis of graphene oxide nanosheets by electrochemical exfoliation of graphite in cetyltrimethylammonium bromide and its application for oxygen reduction, J. Mater. Chem. A 2 (2014) 15428e15436. [15] K.S. Rao, J. Sentilnathan, H.W. Cho, J.J. Wu, M. Yoshimura, Soft processing of graphene nanosheets by glycine-bisulfate ionic-complex-assisted electrochemical exfoliation of graphite for reduction catalysis, Adv. Funct. Mate. 25 (2015) 298e305. [16] M.K.P. Kumar, M. Nidhi, C. Srivastava, Electrochemical exfoliation of graphite to produce graphene using tetrasodium pyrophosphate, RSC Adv. 5 (2015) 24846e24852. [17] K.S. Rao, J. Senthilnathan, Y.F. Liu, M. Yoshimura, Role of peroxide ions in formation of graphene nanosheets by electrochemical exfoliation of graphite, Sci. Rep. 4 (2014) 4237. [18] C. Yang, J. Xu, S. Hu, Development of a novel nitrite amperometric sensor based on poly(toluidine blue) film electrode, J. Solid State Electrochem. 11 (2007) 514e520. [19] K. Dagci, M. Alanyalioglu, Electrochemical preparation of polymeric films of Pyronin Y and its electrolcatalytic properties for amperometric detection of nitrite, J. Electroanal. Chem. 711 (2013) 17e24. [20] E. Ercarikci, K. Dagci, E. Topcu, M. Alanyalioglu, Electrochemical preparation of poly(methylene blue)/graphene nanocomposite thin films, Mater. Res. Bull. 55 (2014) 95e101. cı, M. Alanyalıog lu, K. Meral, Electrochemical detection of nitrite on poly(pyronin Y)/graphene nanocomposites modified ITO [21] M. Sinoforoglu, K. Dag substrate, Superlattices Microstruct. (2016), http://dx.doi.org/10.1016/j.spmi.2016.04.028. [22] J. Jiang, W. Fan, X. Du, Nitrite electrochemical biosensing based on coupled graphene and gold nanoparticles, Biosens. Bioelectron. 51 (2014) 343e348. [23] B. Yang, D. Bin, H. Wang, M. Zhu, P. Yang, Y. Du, High quality Ptgraphene nanocomposites for efficient electrocatalytic nitrite sensing, Colloids Surf. A 481 (2015) 43e50. [24] K. Dagci, M. Alanyalioglu, Preparation of free-standing and flexible graphene/Ag nanoparticles/poly(pyronin Y) hybrid paper electrode for amperometric determination of nitrite, ACS Appl. Mater. Interfaces 8 (2016) 2713e2722. [25] K.M. Miranda, M.G. Espey, D.A. Wink, A rapid, simple spectrophotometric method for simultaneous detection of nitrate and nitrite, Nitric Oxide 5 (2001) 62e71. [26] A.A. Ensafi, M. Jafari-Asl, B. Rezaei, Graphene/nano-porous silicon and graphene/bimetallic silicon nanostructures (PteM, M: Pd, Ru, Rh), efficient electrocatalysts for the hydrogen evolution reaction, Phys. Chem. Chem. Phys. 17 (2015) 23770e23782.
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
Electrochemical fabrication and amperometric sensor application of graphene sheets € lu* Ays¸e Oztürk, Murat Alanyalıog Atatürk University, Sciences Faculty, Department of Chemistry, 25240, Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 April 2016 Accepted 26 April 2016 Available online 27 April 2016
Graphene sheets have been fabricated by applying two-step electrochemical processes in two-electrode cell system containing 0.1 M sodium dodecyl sulfate (SDS). First step is intercalation of SDS into graphite anode electrode and this process has been applied at different intercalation potential values of 1, 3, 5, and 7 V. Second step includes exfoliation of SDS-intercalated graphite electrode in the same medium by acting as cathode. Stable graphene dispersions are obtained after these two electrochemical steps. Characterization of graphene sheets have been carried out using scanning electron microscopy, electron dispersive spectroscopy, fourier transform infrared spectroscopy, UVeVis. absorption spectroscopy, X-ray diffraction, and cyclic voltammetry techniques. Graphene sheets have been modified onto glassy carbon electrode (GCE) by drop-casting of graphene dispersion. Graphene/GCE having a good electrocatalytic activity has been used for amperometric determination of nitrite in both standard laboratory and real samples. The oxidation current density was linearly proportional to the nitrite concentration in a range between 1 and 250 mM. The sensitivity of the sensor was calculated as 0.843 mAmM1 cm2 with a detection limit of 0.24 mM at a signal-to-noise ratio of 3.0. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Graphene Electrochemistry Sodium dodecyl sulfate Amperometric sensor Nitrite
1. Introduction Graphene has been isolated by Novoselov and Geim by scotch-tape method in 2004 [1]. After this exploration, graphene has been focused by the researchers because of its high mobility, unique transport performance, high mechanical stability and high thermal and satisfied electrical conductivity. Electrochemistry is suitable technique for graphene production because it is economic, environmentally friendly, and simple. Upto date, some electrochemical routes have been performed to produce graphene flakes by applying electrochemical intercalation of various compounds e.g. ionic liquids [2e4], poly(sodium-4styrenesulfonate) [5], acetamide-urea-ammonium nitrate melt [6], sodium dodecyl sulfate (SDS) [7e11], sodium dodecyl benzenesulfonate [11,12], cetyltrimethylammonium bromide [13,14], glycine based complex [15], tetrasodium pyrophosphate [16], and NaOH/H2O2 [17]. Nitrite is an important additive and extensively used for fish, meat and cheese products in food technology. Meat is generally not labeled as “cured” without addition of nitrite since it blocks toxins produced by the clostridium botulinum bacteria. Nitrite amount in food products must be under control because its high level causes to toxicity, which have cancer risk for human body. Therefore, quantitative analysis of nitrite in real samples is of great importance. Up to now,
* Corresponding author. lu). E-mail address: [email protected] (M. Alanyalıog http://dx.doi.org/10.1016/j.spmi.2016.04.039 0749-6036/© 2016 Elsevier Ltd. All rights reserved.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
57
electrochemical quantification of nitrite has been applied on modified conductive substrates to decrease electrooxidation potential and increase electroactive surface area. For this purpose, conductive or semiconductive electrodes have been modified with dye polymers [18,19], dye polymer/graphene [20,21] metal nanoparticles/graphene [22,23]. Electrochemical quantification of nitrite has also been initially studied on flexible graphene-based paper electrode by our group [24]. This paper describes the synthesis of graphene sheets including two-step electrochemical processes in two-electrode cell system containing 0.1 M SDS. In the first step, SDS has been intercalated into graphite electrode by serving graphite as anode in the electrochemical cell. We have investigated effect of different intercalation potentials on the quality of produced graphene flakes. Second step includes exfoliation of SDS-intercalated graphite electrode by acting this electrode as cathode. Fabricated graphene sheets have been characterized by scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), fourier transform infrared spectroscopy (FTIR), UVeVis. absorption spectroscopy, X-ray diffraction (XRD), and cyclic voltammetry techniques. Amperometric quantification of nitrite in both laboratory and real samples have been performed by using produced graphene sheets. For this purpose, graphene sheets have been supported onto glassy carbon electrode (GCE) by drop-casting of graphene dispersion. 2. Experimental section 2.1. Materials All the chemicals used in this study were of analytical reagent grade and used without further purification. Milli-Q ultrapure water (conductivity: 5.5 mS$m1) was used all through this study. Phosphate buffer solutions (PBS, 0.1 M) with different pH values were prepared by mixing stock solutions of 0.1 M H3PO4 and KH2PO4, and the pH of the buffer solution was adjusted to desired value by using a pH-meter (Hanna Instruments). The solutions were deaerated by passing dry nitrogen through the electrochemical cell for 15 min prior to each experiment. 2.2. Electrochemical fabrication of graphene sheets Fabrication procedure was presented in Fig. 1. Synthesis procedure includes two step electrochemical processes in 0.1 M SDS (Sigma Aldrich, reagent grade) solution by using two-electrode system. First step is applied for intercalation of SDS into graphite electrode according to following reaction:
i h i h ½Cx þ DS / Cxþ DS þ e To achieve this step, graphite rod (Goodfellow, England, 99.5% purity) is used as anode and Pt-fiol (Sigma Aldrich) served as cathode. Because intercalation conditions effect the quality of graphene sheets, this step is carried out at different intercalation potential values of 1, 3, 5, and 7 V. Second step is performed for exfoliation of SDS-intercalated graphite electrode in the
Fig. 1. Schematic presentation of the electrochemical preparation and amperometric sensor application procedure of graphene sheets.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
58
same medium by serving this electrode as cathode vs Pt-foil anode. After these electrochemical steps are applied, stable graphene/SDS dispersions are obtained as seen in Fig. 1. To supply the exfoliation of possible large graphitic particles to graphene sheets, graphene/SDS dispersion was ultrasonically treated for 1 h. All of the graphene/SDS dispersions are very stable and can be stored at room temperature more than 6 months without precipitation. To remove SDS from graphene dispersions, graphene/SDS dispersions were vacuum-filtered through a polycarbonate membrane (Whatman, Ø ¼ 47 mm, pore size: 0.2 mm) using an ultrafiltration vacuum cell system (EZ-Stream). After washing with plenty of distilled water and air-drying, pure graphene paper was obtained on the membrane with black color. This paper was dispersed into pure-water and 1.0 mg/mL graphene dispersion was prepared for further characterization and amperometric sensor applications. As can be seen in Fig. 1, graphene dispersions prepared at different intercalation potentials reveal different color densities, when compared to transparent 0.1 M SDS solution. It is clear that color of the graphene dispersions darkens by increasing the intercalation potential from 1 to 7 V. It is obvious that intercalation at 1 V is very poor to produce graphene sheets and efficiency is very low. At the intercalation potentials higher than 3 V, color of graphene dispersion shows black color. Concentration for the dispersions were determined by using gravimetry studies and results were presented in Table 1. The graphene amount increases with increasing the intercalation potential. 2.3. Amperometric quantification of nitrite Cyclic voltammetry technique was performed to investigate the electrooxidation behavior of NO 2 on graphene/GCE in 0.1 M PBS (pH 5.0). For this purpose, graphene modified GCE was prepared by drop-casting of graphene dispersion onto GCE, and then drying at room temperature. Before each cyclic voltammetry measurements, the graphene/GCE was placed in 15 mL PBS and the potential scan was cycled between 0 and 1200 mV until a steady cyclic voltammogram was obtained. Amperometry was carried to obtain the calibration curve of the NO 2 sensor. The nitrite content in tap water sample was determined by a conventional amperometric technique according to the standard addition method. Amperometric determination was applied on graphene/GCE under stirring conditions at 750 rpm. After the working electrode reached a steady baseline, the standard nitrite solution was added to electrochemical cell. As a reference work, spectrophotometric method was performed to determine spectrophotometrically the NO 2 content of the real samples [25]. Tap water samples were collected from our laboratory and analyzed without previous treatment. 2.4. Instrumentation In order produce graphene dispersion, two-electrode cell was used with Philip Harris brand AC&DC power supply system. Cyclic voltammetry and amperometry studies were applied with an Epsilon (BASi) potentiostat system connected to a three electrode cell. The SEM analysis and elemental composition determination of the thin films were collected by EDS with a ZEISS system coupled to the SEM instrument. For this purpose, Au(111) surface was used as substrate because it is a reference substrate for morphological studies with an atomically-flat surface structure. Au(111) substrates were prepared in our laboratory based on our previous studies [19,24]. The crystal structure of the samples were collected by powder X-ray diffraction (XRD) using a Rigaku (miniflex) X-ray diffractometer with Cu Ka radiation (l ¼ 1.5405 Å). Fourier transform infrared (FTIR) spectra were collected with a Spectrum One model PerkinElmer spectrophotometer by using a specular reflectance attachment. Optical characterization of the sample dispersions were recorded by using a Shimadzu 3101PC UVeViseNIR spectrophotometer. 3. Results and discussion 3.1. Optical characterization We have performed UVeVis. absorption studies to characterize graphene/SDS dispersions prepared at different intercalation potentials. Fig. 2 demonstrates absorption spectra of graphene dispersions in 0.1 M SDS prepared at 1, 3, 5, and 7 V. For a comparison, absorption spectrum of 0.1 M SDS was also presented in Fig. 2. A maximum for all graphene containing samples was obtained at about 240 nm, corresponding to p / p * transitions of aromatic C]C bonds, and a slight shoulder at about 350 nm, which can be attributed to n / p * transitions of CeO bonds [7]. It is clear from this figure that absorbance of the peaks increases by increasing the intercalation potential due to graphene concentration increases in the suspensions as
Table 1 Gravimetric analysis result of graphene sheets prepared at different intercalation potential values. Intercalation potential (V)
Graphene amount (mg/mL)
1 3 5 7
0.8 4.5 7.0 23.0
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
59
Fig. 2. UVeVis. absorption spectra of 0.1 M SDS solution and graphene dispersions in 0.1 M SDS prepared at different intercalation potentials of 1, 3, 5, and 7 V.
shown in Table 1. Low intensity of shoulder for n / p * transition can be assigned to large amount of reduced form of graphene sheets in the prepared dispersions after applied electrochemical processes. FTIR spectra of graphene sheets were collected by using specular reflectance attachment of the instrument and the results were illustrated in Fig. 3. For comparison, FTIR spectrum of used graphite rod electrode were also presented in Fig. 3. It is clear that all graphene samples (without SDS) show almost similar spectra with graphite rod. The most important difference between graphite rod and graphene samples is the observation of a broad band at around 3000 cm1 and this band is attributed to eOH groups of graphene sheets, which arises due to electrooxidation of graphite rod. This situation proves n/p * transitions in the UVeVis. absorption studies.
3.2. Morphological investigation Morphological studies of the graphene samples were applied on Au(111) substrates and the samples were prepared by drop casting of graphene dispersions onto Au(111) substrate. Fig. 4 demonstrates top-view SEM images of Au(111) substrate
Fig. 3. FTIR specular reflectance spectra of graphite rod and graphene sheets prepared at intercalation potentials of 3, 5, and 7 V.
60
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
Fig. 4. SEM images of graphene sheets on Au(111) substrate prepared at intercalation potentials of 1 (a), 3 (b), 5 (c), and 7 V (d). Graphene sheets were supported on Au(111) substrate by drop casting of graphene dispersions.
coated with graphene sheets prepared at intercalation potentials of 1, 3, 5, and 7 V. Graphene sheets prepared at 1 V shows large, rough, and layered graphitic structures, which may be attributed to poor intercalation of SDS into graphite at 1 V (Fig. 4a). As seen in Fig. 4b, intercalation potential of 3 V reveals a mixed structure of graphene-like wrinkled layers and thick graphitic particles. Fig. 4c shows graphene samples prepared at 5 V and this image clearly exhibit that surface consists of characteristic wrinkled graphene-like flakes. Intercalation potential of 7 V results with small and damaged particles, which is due to high oxidation process. SEM investigation demonstrates that intercalation potential of 5 V is optimum potential value to yield high quality graphene sheets. We have also acquired EDS data for graphene sheets prepared at 7 V (Fig. S1). When the Au atom, which is due to Au(111) substrate subtracted from the spectrum, graphene sample contains 90.29% C, 9.23% O, 0.10% Na, and 0.37% S atoms. Ensafi et al. have prepared graphene oxide (GO) sheets by using modified Hummers method and they determined chemical composition of GO as 61.59% C and 38.41% O by EDS measurement [26]. When compared to GO, graphene sheets include less oxygen atom and this situation is assigned to electrochemical reduction process (second step), which serves for both exfoliation of SDS-intercalated graphite cathode and reduction of oxygen-containing functional groups. Graphene sample involves Na and S atoms with a very little amount and these atoms are due to SDS molecules. This case shows that graphene sheets are still containing SDS molecules even after cleaning with plenty of water for many times.
3.3. XRD Fig. 5 exhibits typical XRD patterns of graphene samples prepared at intercalation potentials of 3, 5, and 7 V on Au(111) substrate and additionally graphite rod. Au(111) substrate does not reflect any diffraction peak between 2q value of 10e30 (JCPDS card no: 04-0784). Graphite rod presents an intensive peak at 2q value of 27.2 with a d-spacing of 0.34 nm and this peak corresponds to (002) diffraction (JCPDS card no: 41-1487). The XRD pattern of graphene sheets reveal peaks at 26.3, 26.4, and 26.5 for intercalation potentials of 3, 5, and 7 V, respectively. This situation shows that electrochemical processes causes increasing of d-space value due to the insertion of SDS and/or oxygen-containing functional groups during intercalation step.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
61
Fig. 5. XRD patterns of graphite rod and graphene sheets on Au(111) substrate prepared at intercalation potentials of 3, 5, and 7 V. Graphene samples were supported on Au(111) substrate by drop casting of graphene dispersions.
Fig. 6. Cyclic voltammograms of naked GCE and GCE modified with graphene sheets prepared at intercalation potentials of 3, 5, and 7 V in 0.1 M PBS (pH: 5.0) containing 1.0.103 M NaNO2. Scan rate: 50 mV/s.
3.4. Amperometric determination of nitrite Fig. 6 demonstrates the electrochemical oxidation of nitrite in 0.1 M PBS (pH: 5.0) at naked GCE and GCE modified with graphene sheets prepared at intercalation potentials of 3, 5, and 7 V. When potential of the naked GCE is scanned from 0 mV to
62
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
1200 mV, an anodic oxidation wave is observed at 850 mV, with current of 27.4 mA, which is corresponding to the oxidation of NO 2 to NO3 through a two-electron oxidation process [18e24]. The electrooxidation of nitrite is irreversible because no wave is observed by reversing the potential to negative direction. This irreversible electrooxidation peak takes place at 840, 820, and 805 mV, with current values of 34.5, 45.2, and 67.1 on GCE modified with graphene sheets prepared at 3, 7, and 5 V, respectively. Since graphene/GCE prepared at 5 V shows the highest current and the lowest electrooxidation potential, it can be deduced that graphene sheets prepared at 5 V reveals the best electrocatalytic ability for the oxidation of nitrite. A peak pair at about 250/100 mV is also observed on graphene/GCE and this peak pair is also observed in the absence of nitrite, which is assigned to redox behavior of buffer solution. Since the idea is amperometric determination of nitrite, some important parameters, which effect the amperometric determination of nitrite have been optimized by using cyclic voltammetry studies. We have initially tested pH of the nitrite solution for the best amperometric response and the best voltammetric wave is obtained on graphene sheets prepared at 5 V in pH: 5.0 medium as seen in Fig. 7. The amount of graphene on GCE is another important factor and the highest current density and lowest peak potential is obtained in pH: 5.0 (0.1 M PBS) on graphene/GCE prepared by drop casting of 25 mL graphene dispersion prepared at intercalaton potential of 5 V onto GCE (Fig. S2). Therefore, amperometric quantification of nitrite was studied in 0.1 M PBS (pH 5.0) under stirring conditions (750 rpm) on graphene/GCE (prepared by drop casting of 25 mL graphene dispersion fabricated at intercalaton potential of 5 V) at the electrooxidation potential of 805 mV. A current-time transient for the successive addition of NaNO2 into 15 mL 0.1 M PBS (pH: 5.0) is shown in Fig. 8a. It is seen that the anodic current increases suddenly to reach a stable value after addition of nitrite and reaches to almost steady-state current value in less than 3 s, which means the electrocatalytical response is so fast. Fig. 8b demonstrates the calibration curve, which is calculated from Fig. 8a. It is observed that the oxidation current is linearly proportional to the nitrite concentration in the range of 1.0e250 mM. The equation for this calibration curve is obtained as j(mA) ¼ 0.85 þ 0.035 Cnitrite (mM) with a correlation coefficient of 0.9993 (Fig. 8b). The sensitivity of this composite sensor was calculated as 0.843 mAmM1 cm2. The detection limit of the electrode was determined as 0.24 mM at a signal-to-noise ratio of 3.0. The stability of graphene/GCE for amperometric determination of nitrite was assessed by using cyclic voltammetry technique. When the graphene/GCE is used for amperometric detection of nitrite without renewal for 10 times only about 34% loss of the initial current is recorded. If it is used 25 times successively, 58% of the initial amperometric response is obtained (Fig. S3). The storage stability of the sensor was also investigated and 20% decrease of the initial current observed after 15 days (Fig. S4). The interference effect of some ions on the amperometric response of nitrite by using graphene/GCE was evaluated
Fig. 7. Cyclic voltammograms in 0.1 M PBS solutions with different pH values containing 1.0.103 M NaNO2 on GCE modified with graphene sheets prepared at 5 V. Scan rate: 50 mV/s.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
63
Fig. 8. (a) Amperometric response of graphene/GCE at 805 mV upon repetitive additions of NaNO2 to 15 mL of 0.1 M PBS (pH 5.0), (b) Plot of oxidative current density vs nitrite concentration (calibration curve). Electrode surface area: 0.0415 cm2.
Table 2 Determination of NO 2 content in tap water sample (n ¼ 3). Sample
Nitrite amount/mg kg1
Tap water
Amperometry 35.08 ± 1.70
Spectrophotometry 36.50 ± 1.64
2þ 2þ 2þ 2þ 2þ with the addition of 100-fold of various common ions of Co2þ, SO2 into 1.0 mM 4 , Cl , NO3 , Mg , Pb , Zn , Ba , and Ca NO in 0.1 M PBS (pH: 5.0) (Fig. S5). It is clear that the added ions demonstrates very low interference effect (<6.5%) for 2 amperometric detection of nitrite. The practical application of the prepared graphene/GCE was also examined in tap water sample. The concentration of nitrite of the real sample was calculated using standard addition method. In order to compare the results of this method, spectrophotometry [25] was also performed for the determination of nitrite in the same tap water sample. It is determined that the amperometric determination of nitrite by using graphene/GCE is very effective and feasible in the tap water sample (Table 2). The quality of the sensor for amperometric determination of nitrite was compared with that of previously published works (Table 3). The results indicate that the graphene/GCE reveals hopeful results with low detection limit and good sensitivity.
Table 3 Comparison of graphene/GCE with other electrodes for determination of NO 2. Sensor
pH
Applied potential (mV)
Linear region (mM)
Sensitivity (mAmM1 cm2)
Detection limit (mM)
Reference
PTBa/GCE Poly(PyY)b/PGEc Hbd/Au/GACSe/GCE PtNPsf/rGOg/GCE rGO/AgNPsh/poly(PyY) paper Graphene/GCE
3.0 4.0 7.0 7.0 5.0 5.0
1100 (SCE) 930 (Ag/AgCl) 850 (SCE) 750 (SCE) 860 (Ag/AgCl) 805 (Ag/AgCl)
0.1e15.2 1.0e100 0.05e1000 0.25e90 0.1e1000 1.0e250
0.047 6.21 0.15 e 13.5 0.843
0.05 0.5 0.01 0.1 0.012 0.24
[18] [19] [22] [23] [24] This work
a b c d e f g h
Poly(toluidin blue). Poly(pyronin Y). Pencil graphite electrode. Hemoglobin. Graphene with biocompatible chitosan. Pt nanoparticles. Reduced graphene oxide. Ag nanoparticles.
€ A. Oztürk, M. Alanyalıoglu / Superlattices and Microstructures 95 (2016) 56e64
64
4. Conclusions Graphene sheets were fabricated in a two electrode cell by using two step electrochemical processes including electrochemical intercalation of SDS into graphite anode and exfoliation of SDS-intercalated graphite cathode. UVeVis. absorption, FTIR, and EDS results demonstrated that graphene flakes are partially oxidized and contains very low amount of oxygen atoms. SEM investigations revealed that graphene sheets prepared at intercalation potential of 5 V yielded the best quality graphene, which includes characteristic wrinkled surface structure. When graphene/GCE was used as an electrochemical sensor for determination of nitrite, it presented hopeful results with high stability, long term storage, and repetitive usage. Acknowledgments This work has been supported by Atatürk University (Project No: BAP 2014/59). Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.spmi.2016.04.039. References [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Electric field effect in atomically thin carbon films, Science 306 (2004) 666e669. [2] N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, J. Chen, One-step ionic liquid-assisted electrochemical synthesis of ionic-liquid functionalized graphene sheets directly from graphite, Adv. Funct. Mater. 18 (2008) 1518e1525. [3] A.T. Najafabadi, E. Gyenge, High-yield graphene production by electrochemical exfoliation of graphite: novel ionic liquid (IL)eacetonitrile electrolyte with low IL content, Carbon 71 (2014) 58e69. [4] M.H. Chakrabarti, N.S.A. Manan, N.P. Brandon, R.C. Maher, F.S. Mjalli, I.M. AlNashef, S.A. Hajimolana, M.A. Hashim, M.A. Hussain, D. Nir, One-pot electrochemical gram-scale synthesis of graphene using deep eutectic solvents and acetonitrile, Chem. Eng. J. 274 (2015) 213e223. [5] G. Wang, B. Wang, J. Park, Y. Wang, B. Sun, J. Yao, Highly efficient and large-scale synthesis of graphene by electrolytic exfoliation, Carbon 47 (2009) 3242e3246. [6] V.S. Dilimon, S. Sampath, Electrochemical preparation of few layer-graphene nanosheets via reduction of oriented exfoliated graphene oxide thin films in acetamideeureaeammonium nitrate melt under ambient conditions, Thin Solid Films 519 (2011) 2323e2327. [7] M. Alanyalioglu, J.J. Segura, J. Oro-Sole, N. Casan-Pastor, The synthesis of graphene sheets with controlled thickness and order using surfactant-assisted electrochemical processes, Carbon 50 (2012) 142e152. [8] M. Moradi, J.A. Mohandesi, D.M. Haghshenas, Mechanical properties of the poly(vinyl alcohol) based nanocomposites at low content of surfactant wrapped graphene sheets, Polymer 60 (2015) 207e214. [9] J. Liu, M. Notarianni, G. Will, V.T. Tiong, H. Wang, N. Motta, Electrochemically exfoliated graphene for electrode films: effect of graphene flake thickness on the sheet resistance and capacitive properties, Langmuir 29 (2013) 13307e13314. [10] C.W. Chen, Z.T. Liu, Y.Z. Zhang, J.S. Ye, C.L. Lee, Sonoelectrochemical intercalation and exfoliation for the preparation of defective graphene sheets and their application as nonenzymatic H2O2 sensors and oxygen reduction catalysts, RSC Adv. 5 (2015) 21988e21998. [11] J.M. Munuera, J.I. Paredes, S. Villar-Rodil, M. Ayan-Varela, A. Martínez-Alonso, J.M.D. Tascon, Electrolytic exfoliation of graphite in water with multifunctional electrolytes: en route towards high quality, oxide-free graphene flakes, Nanoscale 8 (2016) 2982e2998. [12] A.A.B. Hamra, H.N. Lim, W.K. Chee, N.M. Huang, Electro-exfoliating graphene from graphite for direct fabrication of supercapacitor, App. Surf. Sci. 360 (2016) 213e223. [13] M.K.P. Kumar, C. Srivatsava, Synthesis of graphene from a used battery electrode, JOM 68 (2016) 374e383. [14] K. Kakaei, K. Hasanpour, Synthesis of graphene oxide nanosheets by electrochemical exfoliation of graphite in cetyltrimethylammonium bromide and its application for oxygen reduction, J. Mater. Chem. A 2 (2014) 15428e15436. [15] K.S. Rao, J. Sentilnathan, H.W. Cho, J.J. Wu, M. Yoshimura, Soft processing of graphene nanosheets by glycine-bisulfate ionic-complex-assisted electrochemical exfoliation of graphite for reduction catalysis, Adv. Funct. Mate. 25 (2015) 298e305. [16] M.K.P. Kumar, M. Nidhi, C. Srivastava, Electrochemical exfoliation of graphite to produce graphene using tetrasodium pyrophosphate, RSC Adv. 5 (2015) 24846e24852. [17] K.S. Rao, J. Senthilnathan, Y.F. Liu, M. Yoshimura, Role of peroxide ions in formation of graphene nanosheets by electrochemical exfoliation of graphite, Sci. Rep. 4 (2014) 4237. [18] C. Yang, J. Xu, S. Hu, Development of a novel nitrite amperometric sensor based on poly(toluidine blue) film electrode, J. Solid State Electrochem. 11 (2007) 514e520. [19] K. Dagci, M. Alanyalioglu, Electrochemical preparation of polymeric films of Pyronin Y and its electrolcatalytic properties for amperometric detection of nitrite, J. Electroanal. Chem. 711 (2013) 17e24. [20] E. Ercarikci, K. Dagci, E. Topcu, M. Alanyalioglu, Electrochemical preparation of poly(methylene blue)/graphene nanocomposite thin films, Mater. Res. Bull. 55 (2014) 95e101. cı, M. Alanyalıog lu, K. Meral, Electrochemical detection of nitrite on poly(pyronin Y)/graphene nanocomposites modified ITO [21] M. Sinoforoglu, K. Dag substrate, Superlattices Microstruct. (2016), http://dx.doi.org/10.1016/j.spmi.2016.04.028. [22] J. Jiang, W. Fan, X. Du, Nitrite electrochemical biosensing based on coupled graphene and gold nanoparticles, Biosens. Bioelectron. 51 (2014) 343e348. [23] B. Yang, D. Bin, H. Wang, M. Zhu, P. Yang, Y. Du, High quality Ptgraphene nanocomposites for efficient electrocatalytic nitrite sensing, Colloids Surf. A 481 (2015) 43e50. [24] K. Dagci, M. Alanyalioglu, Preparation of free-standing and flexible graphene/Ag nanoparticles/poly(pyronin Y) hybrid paper electrode for amperometric determination of nitrite, ACS Appl. Mater. Interfaces 8 (2016) 2713e2722. [25] K.M. Miranda, M.G. Espey, D.A. Wink, A rapid, simple spectrophotometric method for simultaneous detection of nitrate and nitrite, Nitric Oxide 5 (2001) 62e71. [26] A.A. Ensafi, M. Jafari-Asl, B. Rezaei, Graphene/nano-porous silicon and graphene/bimetallic silicon nanostructures (PteM, M: Pd, Ru, Rh), efficient electrocatalysts for the hydrogen evolution reaction, Phys. Chem. Chem. Phys. 17 (2015) 23770e23782.