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Few layered graphene by floating catalyst chemical vapour deposition and its extraordinary H2O2 sensing property
Materials Letters 199 (2017) 180–183
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Few layered graphene by floating catalyst chemical vapour deposition and its extraordinary H2O2 sensing property Manishkumar D. Yadav a, Kinshuk Dasgupta b,⇑, Aayushi Kushwaha a, Amit P. Srivastava b, Ashwin W. Patwardhan a,⇑, Dinesh Srivastava b, Jyeshtharaj B. Joshi a,c a b c
Department of Chemical Engineering, Institute of Chemical Technology, Mumbai 400019, India Materials Group, Bhabha Atomic Research Centre, Mumbai 400085, India Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
a r t i c l e
i n f o
Article history: Received 14 February 2017 Received in revised form 29 March 2017 Accepted 17 April 2017 Available online 19 April 2017 Keywords: Graphene Chemical vapour deposition Electron microscopy Sensor Raman spectroscopy
a b s t r a c t Few layered graphene (FLG) was synthesized by substrate-free floating catalyst chemical vapour deposition method for the first time. A sensor prepared from the pristine FLG coated over a glassy carbon electrode without further modification showed high sensitivity towards sensing of H2O2 (355 lA mM1 cm2) with lower detection limit of 0.27 lM and response time of 5 s. Transmission electron microscopy revealed 3–5 layers of graphene sheets with edge defects, which was supported by Raman spectroscopy. X-ray photoelectron spectroscopy confirmed that the defects are due to oxygen present in the FLG in the form of C@O, that played important role in sensing. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Graphene is a two dimensional array of sp2-hybridized carbon atoms, possessing exceptional physical properties and chemical tunability. These properties have attracted attention of many scientists and engineers across the globe in the context of a wide range of applications in energy devices, electrochemical devices, as fillers in composites, sensors [1], etc. Graphene and graphene based materials are widely accepted as a good sensors to monitor small biomolecules, such as hydrogen peroxide (H2O2), uric acid, ascorbic acid, etc [2]. In particular, the detection of the H2O2 molecule is of vital importance, since it plays an essential role as a signaling molecule in regulating various biological signaling transduction processes [3]. Several disorders in the body, such as Parkinson’s, diabetes, cardiovascular, Alzheimer’s and neurodegenerative occurs due to bursting of H2O2 which causes release of several essential signaling proteins affecting the cell proliferation [4]. Hence, an accurate and highly sensitive detection of H2O2 is of practical importance in recent years. To address this issue, various methods have been developed for the rapid and sensitive determination of H2O2 concentration based on different analytical ⇑ Corresponding authors. E-mail addresses: [email protected], [email protected] (K. Dasgupta), [email protected] (A.W. Patwardhan). http://dx.doi.org/10.1016/j.matlet.2017.04.085 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
principles such as chromatography, titrimetry, spectrophotometry, chemiluminescence, fluorescence and electrochemical method [5], etc. Among them, the electrochemical method has been widely used in the detection of H2O2 due to its high sensitivity, rapid response, convenient operation, etc. Graphene based materials are promising electrode materials owing to their unique properties like high surface area, electrical conductivity, excellent chemical stability, etc. Generally, graphene is produced over metallic substrate like, nickel and copper by chemical vapour deposition (CVD). It needs to be transferred and functionalized before using it as sensor. However, we have developed a simple method for synthesis of few-layered graphene (FLG) by floating catalyst chemical vapour deposition (FC-CVD) without using any substrate or support. The pristine FLGs while used to make a sensor exhibited enhanced sensitivity for monitoring the H2O2 concentration in comparison to other enzymatic or non-enzymatic H2O2 sensor reported in the literature. 2. Materials and method High purity ferrocene (Sigma Aldrich), n-hexane (Sigma Aldrich, 95–99%), hydrochloric acid (Merck, 37%), hydrogen peroxide (SD fine chemicals) and Nafion (Duralyst Energy Pvt. Ltd) were used without any further purification. Phosphate buffer solution (0.1 M) was prepared using K2HPO4 and KH2PO4. Argon with high
M.D. Yadav et al. / Materials Letters 199 (2017) 180–183
181
purity grade (99.99%) was purchased from Vadilal Chemicals Ltd. Cyclic voltammetry experiments were carried out using a lAutolab Potentiostat with Metrohm 663 VA stand. Transmission Electron Microscopy (TEM) images were collected using JEM2100 TEM (JEOL Inc.). X-ray Photoelectron Spectroscopy was carried out on XPS- SPECS, Germany and XPS Peak 4.1 software was used to deconvolute O1s peak. Raman spectroscopy was carried out using the Lab Ram HR 800. Indigenous made CVD system having a horizontal quartz tube retort (100 mm ID and 1000 mm long), has been used to synthesize FLGs (Fig. S1). The furnace was heated up to 800 °C with a 100 sccm flow of argon in order to maintain inert atmosphere. Hexane (carbon source) containing dissolved ferrocene (catalyst source) in the ratio 20 mg/ml, was heated to 200 °C in a pre-heater and subsequently driven into the reaction chamber using argon gas (100 sccm) for 30 min. FLGs were formed inside the heating zone and collected after cooling down the furnace and subsequently purified using dilute hydrochloric acid. The synthesized FLGs were used to coat a glassy carbon electrode (GCE) with nafion(Nf) as binder (FLGn-Nf/GCE) and used as sensor. 3. Results and discussion Typically the graphene synthesis rate was 1.4 g/h per g of catalyst with a conversion efficiency of 30 wt% of hexane. In order to investigate the structure of FLG nanosheets, TEM and High Resolution TEM (HRTEM) were performed. Fig. 1 shows presence of numerous ripples depicting wrinkled morphology resembling crumpled silk veil waves. HRTEM micrograph of few-layered graphene (bottom inset of Fig. 1) reveals the graphitic planes (3–5 layers) and defects are indicated by a circle. The SAED pattern (top inset of Fig. 1) depicts the nanocrystalline structure of FLGs. Fig. 2(a) shows the Raman spectrum of the synthesized FLGs. The characteristic 2D or G0 peak at 2705 cm1 is the signature of graphene and it corresponds to the overtone of the D band. The D band (1362 cm1) is relatively intense compared to the G band (1597 cm1), which implies the presence of defects in the synthesized sample. In order to understand the nature of the defects, Xray photoelectron spectroscopy (XPS) was carried out. The pattern (Fig. 2(b)) clearly shows the presence of C1s and O1s peaks, that
Fig. 2. (a) Raman Spectra of FLGs showing characteric peaks (b) XPS pattern of FLGs showing presence of presence of C@O bond.
estimates 10 at.% (13 wt%) oxygen present in FLG. The deconvoluted O1s peak (inset) corresponds to C@O bond (531.6 eV). The C@O species are primarily present at the edges of graphene nanosheets [6,7] and played important role in sensing of H2O2. The oxygen containing groups at the edges of graphene sheet influence its electrochemistry. Chou et al. [8] reported that oxygen con-
Fig. 1. TEM images of FLGs, exhibiting crumpled nanosheets (top inset: SAED pattern of the FLG; bottom inset HRTEM image of FLGs showing layers and defects).
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M.D. Yadav et al. / Materials Letters 199 (2017) 180–183
taining groups at the edges of graphene enhances the electron transfer rate. In addition, the oxygen containing groups influence the adsorption/desorption of molecules, which takes place before and after the electrochemical reaction and can be used as anchoring sites for a range of sensing applications [9–11]. The high intensity of D peak in the Raman spectra could be explained by the presence of these defects. Therefore, the TEM, Raman spectroscopy and XPS data were complementary to each other. The thermal stability of the FLG was investigated by thermogravimetric (TG) analysis in dry air, which in turn describes the quality of the product. The details can be found in the Supplementary information. The electrocatalytic activity of the FLG modified electrode (FLGn-Nf/GCE) was investigated. Fig. 3(a) shows the cyclic voltammogram (CV) of the FLGn-Nf/GCE electrode recorded at different scan rates (50–1000 mV/s). The redox current shows linear behaviour with the square root of the scan rate (inset in Fig. 3a), depicting it as a diffusion-controlled electron-transfer process. Amperometric studies were carried out in order to evaluate the
electrocatalytic performance of the modified electrode. During the amperometric measurements the electrode potential was held at 0.39 V (from CV curves) and the N2 saturated PBS (pH 7.4) was constantly stirred. The response of the plain buffer solution was subtracted from the response obtained in the presence of H2O2. Fig. 3(b) shows the calibration curve of the response of the FLG sheet modified electrode. It depicts that the electrode has a wide linear response to H2O2 ranging from 0.5 to 3 mM with a sensitivity of 355 lA mM1 cm2 at 25 °C. The response time (defined as the time needed for the sensor to reach 90% of the final signal for a given concentration of analyte) is less than 5 s. The linear regression equation is I(lA) = 24.91 * C H2 O2 (mM) + 1.8 (R2 = 0.981) where I is the current and the C H2 O2 is the H2O2 concentration. To determine the effect of temperature on H2O2 sensing, a temperature range of 25–50 °C was chosen. Details about the effect of temperature on sensing have been explained in Supporting information. Hydrogen peroxide gets adsorbed on the surface and edges of graphene. After adsorption hydrogen peroxide gets
Fig. 3. (a) Cyclic voltammetry (CV) studies of the FLGn-Nf/GCE electrode as a function of scan rate (50–1000 mV/s). Inset: Redox peak current of FLGn-Nf/GCE electrode as a function of the square root of scan rate. (b) Calibration plot of different concentration of H2O2 vs. response current into a continuously stirred N2 saturated pH 7.4 PBS solution at 25 °C. Applied potential 0.39 V.
M.D. Yadav et al. / Materials Letters 199 (2017) 180–183 Table 1 Comparison of analytical parameters of several modified electrodes for H2O2 determination. Electrode
Detection Limit (lM)
Sensitivity (at 25 °C) (lA mM1 cm2)
References
Ag NWsgraphene* FeTSPc-GRNafiony GSnano/CS# FLGn-Nf/GCE
1
12.27
[13]
0.08
36.93
[14]
2.6 0.27
18.78 355
[15] Present work
* Ag NWs-graphene nanowires: Silver nanowires-graphene hybrid. FeTSPc-GR-Nafion: iron-tetrasulfophthalocyanine-graphene-Nafion screen printed electrode. # GSnano/CS: Graphene-Silica-Chitosan modified glassy carbon electrode. y
reduced to water molecule. This electron transfer is converted into the electronic signals and recorded in the potentiostat (details in Supporting information). The sensing performance of the FLGnNF/GCE for H2O2 is summarized in Table 1 along with those reported in the literature. High sensitivity of FLGs can be attributed to the van der Waals interaction between the analyte and the sensor. It has been reported in literature that defective graphene exhibit enhanced sensitivity in comparison to highly ordered graphene as diffusion of atomic oxygen is much faster in case of defective graphene in comparison to ordered graphene due to lower energy barrier [12]. In present case, we can see that defect band as shown in Fig. 2(a) is very prominent, depicting presence of defects in the FLGs giving rise to high sensitivity when used as a sensor. 4. Conclusions In summary, synthesis of few-layered graphene nanosheets using hexane and ferrocene at 800 °C, by one-step FC-CVD without using any substrate or support was developed. Due to presence of edge defects, the graphene nanosheet modified electrode exhibited excellent catalytic activity to hydrogen peroxide. The sensor displayed excellent sensitivity at 355 lA mM1 cm2 with response time less than 5 s at 25 °C. The properties could be correlated to the structure as revealed in microscopy and spectroscopy. As a future perspective, we believe that the graphene nanosheet synthesized by FC-CVD could be a promising electrode material for the fabrication of on-site, compact electrochemical sensor without any need of amplification techniques. Acknowledgements MDY gratefully acknowledges the financial support from the J. C. Bose PhD Fellowship-Department of Science and Technology (DST), Government of India.
183
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.04. 085. References [1] Y. Zhang, L. Zhang, C. Zhou, Review of chemical vapor deposition of graphene and related applications, Acc. Chem. Res. 46 (10) (2013) 2329–2339. [2] Y. Shao, J. Wang, H. Wu, J. Liu, I.A. Aksay, Y. Lin, Graphene based electrochemical sensors and biosensors: a review, Electroanalysis 22 (10) (2010) 1027–1036. [3] J. Bai, C. Sun, X. Jiang, Carbon dots-decorated multiwalled carbon nanotubes nanocomposites as a high-performance electrochemical sensor for detection of H2O2 in living cells, Anal. Bioanal. Chem. (2016) 1–10. [4] S.N. Baker, G.A. Baker, Luminescent carbon nanodots: emergent nanolights, Angew. Chem. Int. Ed. 49 (38) (2010) 6726–6744. [5] J. Bai, C. Sun, X. Jiang, Carbon dots-decorated multiwalled carbon nanotubes nanocomposites as a high-performance electrochemical sensor for detection of H2O2 in living cells, Anal. Bioanal. Chem. 408 (17) (2016) 4705–4714. [6] Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Graphene and graphene oxide: synthesis, properties, and applications, Adv. Mater. 22 (35) (2010) 3906–3924. [7] A. Lerf, H. He, M. Forster, J. Klinowski, Structure of graphite oxide revisited, J. Phys. Chem. B 102 (23) (1998) 4477–4482. [8] A. Chou, T. Böcking, N.K. Singh, J.J. Gooding, Demonstration of the importance of oxygenated species at the ends of carbon nanotubes for their favourable electrochemical properties, Chem. Commun. 7 (2005) 842–844. [9] A.T. Masheter, L. Xiao, G.G. Wildgoose, A. Crossley, J.H. Jones, R.G. Compton, Voltammetric and X-ray photoelectron spectroscopic fingerprinting of carboxylic acid groups on the surface of carbon nanotubes via derivatisation with arylnitro labels, J. Mater. Chem. 17 (33) (2007) 3515–3524. [10] A.F. Holloway, G.G. Wildgoose, R.G. Compton, L. Shao, M.L. Green, The influence of edge-plane defects and oxygen-containing surface groups on the voltammetry of acid-treated, annealed and ‘‘super-annealed” multiwalled carbon nanotubes, J. Solid State Electrochem. 12 (10) (2008) 1337. [11] C.A. Thorogood, G.G. Wildgoose, A. Crossley, R.M. Jacobs, J.H. Jones, R.G. Compton, Differentiating between ortho- and para-quinone surface groups on graphite, glassy carbon, and carbon nanotubes using organic and inorganic voltammetric and X-ray photoelectron spectroscopy labels, Chem. Mater. 19 (20) (2007) 4964–4974. [12] F. Mehmood, R. Pachter, W. Lu, J.J. Boeckl, Adsorption and diffusion of oxygen on single-layer graphene with topological defects, J. Phys. Chem. C 117 (20) (2013) 10366–10374. [13] M. Zhang, Z. Wang, Nanostructured silver nanowires-graphene hybrids for enhanced electrochemical detection of hydrogen peroxide, Appl. Phys. Lett. 102 (21) (2013) 213104. [14] M. Zhu, N. Li, J. Ye, Sensitive and selective sensing of hydrogen peroxide with iron-tetrasulfophthalocyanine-graphene-nafion modified screen-printed electrode, Electroanalysis 24 (5) (2012) 1212–1219. [15] Y. Huang, S.F.Y. Li, Electrocatalytic performance of silica nanoparticles on graphene oxide sheets for hydrogen peroxide sensing, J. Electroanal. Chem. 690 (2013) 8–12.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Few layered graphene by floating catalyst chemical vapour deposition and its extraordinary H2O2 sensing property Manishkumar D. Yadav a, Kinshuk Dasgupta b,⇑, Aayushi Kushwaha a, Amit P. Srivastava b, Ashwin W. Patwardhan a,⇑, Dinesh Srivastava b, Jyeshtharaj B. Joshi a,c a b c
Department of Chemical Engineering, Institute of Chemical Technology, Mumbai 400019, India Materials Group, Bhabha Atomic Research Centre, Mumbai 400085, India Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
a r t i c l e
i n f o
Article history: Received 14 February 2017 Received in revised form 29 March 2017 Accepted 17 April 2017 Available online 19 April 2017 Keywords: Graphene Chemical vapour deposition Electron microscopy Sensor Raman spectroscopy
a b s t r a c t Few layered graphene (FLG) was synthesized by substrate-free floating catalyst chemical vapour deposition method for the first time. A sensor prepared from the pristine FLG coated over a glassy carbon electrode without further modification showed high sensitivity towards sensing of H2O2 (355 lA mM1 cm2) with lower detection limit of 0.27 lM and response time of 5 s. Transmission electron microscopy revealed 3–5 layers of graphene sheets with edge defects, which was supported by Raman spectroscopy. X-ray photoelectron spectroscopy confirmed that the defects are due to oxygen present in the FLG in the form of C@O, that played important role in sensing. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Graphene is a two dimensional array of sp2-hybridized carbon atoms, possessing exceptional physical properties and chemical tunability. These properties have attracted attention of many scientists and engineers across the globe in the context of a wide range of applications in energy devices, electrochemical devices, as fillers in composites, sensors [1], etc. Graphene and graphene based materials are widely accepted as a good sensors to monitor small biomolecules, such as hydrogen peroxide (H2O2), uric acid, ascorbic acid, etc [2]. In particular, the detection of the H2O2 molecule is of vital importance, since it plays an essential role as a signaling molecule in regulating various biological signaling transduction processes [3]. Several disorders in the body, such as Parkinson’s, diabetes, cardiovascular, Alzheimer’s and neurodegenerative occurs due to bursting of H2O2 which causes release of several essential signaling proteins affecting the cell proliferation [4]. Hence, an accurate and highly sensitive detection of H2O2 is of practical importance in recent years. To address this issue, various methods have been developed for the rapid and sensitive determination of H2O2 concentration based on different analytical ⇑ Corresponding authors. E-mail addresses: [email protected], [email protected] (K. Dasgupta), [email protected] (A.W. Patwardhan). http://dx.doi.org/10.1016/j.matlet.2017.04.085 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
principles such as chromatography, titrimetry, spectrophotometry, chemiluminescence, fluorescence and electrochemical method [5], etc. Among them, the electrochemical method has been widely used in the detection of H2O2 due to its high sensitivity, rapid response, convenient operation, etc. Graphene based materials are promising electrode materials owing to their unique properties like high surface area, electrical conductivity, excellent chemical stability, etc. Generally, graphene is produced over metallic substrate like, nickel and copper by chemical vapour deposition (CVD). It needs to be transferred and functionalized before using it as sensor. However, we have developed a simple method for synthesis of few-layered graphene (FLG) by floating catalyst chemical vapour deposition (FC-CVD) without using any substrate or support. The pristine FLGs while used to make a sensor exhibited enhanced sensitivity for monitoring the H2O2 concentration in comparison to other enzymatic or non-enzymatic H2O2 sensor reported in the literature. 2. Materials and method High purity ferrocene (Sigma Aldrich), n-hexane (Sigma Aldrich, 95–99%), hydrochloric acid (Merck, 37%), hydrogen peroxide (SD fine chemicals) and Nafion (Duralyst Energy Pvt. Ltd) were used without any further purification. Phosphate buffer solution (0.1 M) was prepared using K2HPO4 and KH2PO4. Argon with high
M.D. Yadav et al. / Materials Letters 199 (2017) 180–183
181
purity grade (99.99%) was purchased from Vadilal Chemicals Ltd. Cyclic voltammetry experiments were carried out using a lAutolab Potentiostat with Metrohm 663 VA stand. Transmission Electron Microscopy (TEM) images were collected using JEM2100 TEM (JEOL Inc.). X-ray Photoelectron Spectroscopy was carried out on XPS- SPECS, Germany and XPS Peak 4.1 software was used to deconvolute O1s peak. Raman spectroscopy was carried out using the Lab Ram HR 800. Indigenous made CVD system having a horizontal quartz tube retort (100 mm ID and 1000 mm long), has been used to synthesize FLGs (Fig. S1). The furnace was heated up to 800 °C with a 100 sccm flow of argon in order to maintain inert atmosphere. Hexane (carbon source) containing dissolved ferrocene (catalyst source) in the ratio 20 mg/ml, was heated to 200 °C in a pre-heater and subsequently driven into the reaction chamber using argon gas (100 sccm) for 30 min. FLGs were formed inside the heating zone and collected after cooling down the furnace and subsequently purified using dilute hydrochloric acid. The synthesized FLGs were used to coat a glassy carbon electrode (GCE) with nafion(Nf) as binder (FLGn-Nf/GCE) and used as sensor. 3. Results and discussion Typically the graphene synthesis rate was 1.4 g/h per g of catalyst with a conversion efficiency of 30 wt% of hexane. In order to investigate the structure of FLG nanosheets, TEM and High Resolution TEM (HRTEM) were performed. Fig. 1 shows presence of numerous ripples depicting wrinkled morphology resembling crumpled silk veil waves. HRTEM micrograph of few-layered graphene (bottom inset of Fig. 1) reveals the graphitic planes (3–5 layers) and defects are indicated by a circle. The SAED pattern (top inset of Fig. 1) depicts the nanocrystalline structure of FLGs. Fig. 2(a) shows the Raman spectrum of the synthesized FLGs. The characteristic 2D or G0 peak at 2705 cm1 is the signature of graphene and it corresponds to the overtone of the D band. The D band (1362 cm1) is relatively intense compared to the G band (1597 cm1), which implies the presence of defects in the synthesized sample. In order to understand the nature of the defects, Xray photoelectron spectroscopy (XPS) was carried out. The pattern (Fig. 2(b)) clearly shows the presence of C1s and O1s peaks, that
Fig. 2. (a) Raman Spectra of FLGs showing characteric peaks (b) XPS pattern of FLGs showing presence of presence of C@O bond.
estimates 10 at.% (13 wt%) oxygen present in FLG. The deconvoluted O1s peak (inset) corresponds to C@O bond (531.6 eV). The C@O species are primarily present at the edges of graphene nanosheets [6,7] and played important role in sensing of H2O2. The oxygen containing groups at the edges of graphene sheet influence its electrochemistry. Chou et al. [8] reported that oxygen con-
Fig. 1. TEM images of FLGs, exhibiting crumpled nanosheets (top inset: SAED pattern of the FLG; bottom inset HRTEM image of FLGs showing layers and defects).
182
M.D. Yadav et al. / Materials Letters 199 (2017) 180–183
taining groups at the edges of graphene enhances the electron transfer rate. In addition, the oxygen containing groups influence the adsorption/desorption of molecules, which takes place before and after the electrochemical reaction and can be used as anchoring sites for a range of sensing applications [9–11]. The high intensity of D peak in the Raman spectra could be explained by the presence of these defects. Therefore, the TEM, Raman spectroscopy and XPS data were complementary to each other. The thermal stability of the FLG was investigated by thermogravimetric (TG) analysis in dry air, which in turn describes the quality of the product. The details can be found in the Supplementary information. The electrocatalytic activity of the FLG modified electrode (FLGn-Nf/GCE) was investigated. Fig. 3(a) shows the cyclic voltammogram (CV) of the FLGn-Nf/GCE electrode recorded at different scan rates (50–1000 mV/s). The redox current shows linear behaviour with the square root of the scan rate (inset in Fig. 3a), depicting it as a diffusion-controlled electron-transfer process. Amperometric studies were carried out in order to evaluate the
electrocatalytic performance of the modified electrode. During the amperometric measurements the electrode potential was held at 0.39 V (from CV curves) and the N2 saturated PBS (pH 7.4) was constantly stirred. The response of the plain buffer solution was subtracted from the response obtained in the presence of H2O2. Fig. 3(b) shows the calibration curve of the response of the FLG sheet modified electrode. It depicts that the electrode has a wide linear response to H2O2 ranging from 0.5 to 3 mM with a sensitivity of 355 lA mM1 cm2 at 25 °C. The response time (defined as the time needed for the sensor to reach 90% of the final signal for a given concentration of analyte) is less than 5 s. The linear regression equation is I(lA) = 24.91 * C H2 O2 (mM) + 1.8 (R2 = 0.981) where I is the current and the C H2 O2 is the H2O2 concentration. To determine the effect of temperature on H2O2 sensing, a temperature range of 25–50 °C was chosen. Details about the effect of temperature on sensing have been explained in Supporting information. Hydrogen peroxide gets adsorbed on the surface and edges of graphene. After adsorption hydrogen peroxide gets
Fig. 3. (a) Cyclic voltammetry (CV) studies of the FLGn-Nf/GCE electrode as a function of scan rate (50–1000 mV/s). Inset: Redox peak current of FLGn-Nf/GCE electrode as a function of the square root of scan rate. (b) Calibration plot of different concentration of H2O2 vs. response current into a continuously stirred N2 saturated pH 7.4 PBS solution at 25 °C. Applied potential 0.39 V.
M.D. Yadav et al. / Materials Letters 199 (2017) 180–183 Table 1 Comparison of analytical parameters of several modified electrodes for H2O2 determination. Electrode
Detection Limit (lM)
Sensitivity (at 25 °C) (lA mM1 cm2)
References
Ag NWsgraphene* FeTSPc-GRNafiony GSnano/CS# FLGn-Nf/GCE
1
12.27
[13]
0.08
36.93
[14]
2.6 0.27
18.78 355
[15] Present work
* Ag NWs-graphene nanowires: Silver nanowires-graphene hybrid. FeTSPc-GR-Nafion: iron-tetrasulfophthalocyanine-graphene-Nafion screen printed electrode. # GSnano/CS: Graphene-Silica-Chitosan modified glassy carbon electrode. y
reduced to water molecule. This electron transfer is converted into the electronic signals and recorded in the potentiostat (details in Supporting information). The sensing performance of the FLGnNF/GCE for H2O2 is summarized in Table 1 along with those reported in the literature. High sensitivity of FLGs can be attributed to the van der Waals interaction between the analyte and the sensor. It has been reported in literature that defective graphene exhibit enhanced sensitivity in comparison to highly ordered graphene as diffusion of atomic oxygen is much faster in case of defective graphene in comparison to ordered graphene due to lower energy barrier [12]. In present case, we can see that defect band as shown in Fig. 2(a) is very prominent, depicting presence of defects in the FLGs giving rise to high sensitivity when used as a sensor. 4. Conclusions In summary, synthesis of few-layered graphene nanosheets using hexane and ferrocene at 800 °C, by one-step FC-CVD without using any substrate or support was developed. Due to presence of edge defects, the graphene nanosheet modified electrode exhibited excellent catalytic activity to hydrogen peroxide. The sensor displayed excellent sensitivity at 355 lA mM1 cm2 with response time less than 5 s at 25 °C. The properties could be correlated to the structure as revealed in microscopy and spectroscopy. As a future perspective, we believe that the graphene nanosheet synthesized by FC-CVD could be a promising electrode material for the fabrication of on-site, compact electrochemical sensor without any need of amplification techniques. Acknowledgements MDY gratefully acknowledges the financial support from the J. C. Bose PhD Fellowship-Department of Science and Technology (DST), Government of India.
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