- Email: [email protected]
Gourd-shaped silver nanoparticle–graphene composite for electrochemical oxidation of glucose
Materials Letters 97 (2013) 133–136
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Gourd-shaped silver nanoparticle–graphene composite for electrochemical oxidation of glucose Jing-He Yang a,b, Ketian Zhang b, Ding Ma b,n a
Department of Catalysis Chemistry and Engineering, School of Chemical Engineering, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, PR China b Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China
a r t i c l e i n f o
abstract
Article history: Received 5 November 2012 Accepted 16 January 2013 Available online 1 February 2013
Graphene nanosheets decorated with gourd-shaped Ag nanoparticles (GAg) were prepared from the precursor silver phosphate–graphene oxide nanocomposite (GOAgPO) by original substrate selfgenerated reduction methods. The material was studied for electrochemical oxidation of glucose in alkaline solution. GAg showed excellent activity at low peak potential. The reason was that the high temperature promoted transformation of GO to graphene, thereby reducing the resistance of the substrate, restructuring from the silver phosphate to gourd-shaped silver and enhancing the interaction between Ag and the substrate. The positive correlation between the scan rates and the anodic currents implied a diffusion-controlled kinetic process even at a high scan rate. & 2013 Elsevier B.V. All rights reserved.
Keywords: Electronic materials Nanocomposites Oxidation Carbon materials
1. Introduction The electrochemical oxidation of glucose has generated much research interest over the years due to its possibility of medical applications such as blood sugar sensors and biological fuel cells [1–4]. The glucose oxidation process, a chemical process that provides energy for organism, is an important process, especially for humans. The level of glucose concentration is very important to the health of humans, so development of electrochemical glucose oxidation technology in medical applications is necessary besides biological fuel. The electrocatalytic activity depends on the nature of the electrode material such as gold [5–7]. To optimize the activity, gold was fabricated into nanoparticles [8] or composite with other metals [9]. However, gold or even platinum is not suitable as electrocatalysts because the chemisorbed intermediates such as CO will poison the electrode surface besides being expensive [6]. Non-noble metals, such as Co [10], Ni [11], Cu [12], are investigated for cheaper and more anti-poisoned replacements, but their overpotentials are much higher with low activity. Silver, as a relatively cheap noble metal and a highly effective electrode material for electro-oxidation of glucose, has been regarded as a prime candidate for electrode material [13–18]. Substrates always play a vital role in the dispersion and stability of the catalysts, especially metallic nanoparticles. Graphene is a huge open p-electron system with a combination of armchair and zigzag edges that are analogous to cis- and trans-polyacetylenes,
n
Corresponding author. Tel./fax: þ 86 10 6275 8603. E-mail address: [email protected] (D. Ma).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.01.071
respectively. Its structure and properties motivated the development of new materials for electronics, batteries, supercapacitors and so on. Its chemical stability and high surface area give a chance as substrate for metallic nanoparticles in heterogeneous catalysis applications [19,20]. Herein, a new facile and distinctive method via silver phosphate– graphene oxide nanocomposite (GOAgPO) as intermediate was developed to synthesize gourd-shaped silver nanoparticle–graphene composite (GAg) catalyst, which showed excellent activity for glucose oxidation at low peak potential with distinct oxidation current in the anodic scan.
2. Experimental Reagents: Nafion (5 wt% ethanol solution) was purchased from Alfa Aesar, and diluted to 0.1 wt% with doubly distilled water in use. H3PO4 (85%), sodium hydroxide and AgNO3 were obtained from Beijing Chemical Company. All stock solutions used in this work were prepared with deionized water of resistivity no less than 18.2 MO cm. Synthesis of the materials: Graphene oxide was generated from natural flake graphite according to a modified Hummer’s method [21]. 340 mg AgNO3, 410 mL 85% H3PO4, 1 g sodium dodecyl sulfonate, and 12 g urea were dissolved in 180 ml deionized water. 50 mg graphene oxide was added to the solution and sonicated for 10 min. The solution was then heated for 12 h at 353 K. GOAgPO was separated by filtration and dried in an air oven at 333 K overnight. Following the same process, AgG was obtained by calcining GOAgPO in a tubular furnace under nitrogen
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J.-H. Yang et al. / Materials Letters 97 (2013) 133–136
atmosphere finally. The temperature rose at the rate of 10 K/min till 773 K, and then remained for 2 h. Characterization: Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/max-2400 diffractometer with Cu-Ka radiation. The morphologies of the materials were observed by scanning electron microscopy (SEM, XL30S-FEG, 5 kV). For TEM analysis, samples were dissolved in ethanol under ultrasonic treatment and then put a drop of the solution was placed on a Cu grid. TEM images were taken with a FEI Tecnai G2 T20. UV–visible spectroscopy (Cary Varian 50) with a 1 cm quartz cell was used. XPS spectra were obtained using an Axis Ultra spectrometer (Kratos, UK). A mono Al-Ka (1486.6 eV) X-ray source was used at a power of 225 W (15 kV, 15 mA). To compensate for surface charge effects, binding energies were calibrated using the C1s hydrocarbon peak at 284.8 eV. Raman spectroscopy was obtained using a Horiba HR800 Raman system with three laser lines and a 632.8 nm line from He–Ne laser. Preparation of modified GCE: The glassy carbon electrodes (GCEs, 3 mm diameter, Tianjin Aida, Inc.) were polished with a-Al2O3 powder (40 nm), rinsed twice by deionized water and ethanol, and then dried at room temperature. 5 mg catalyst was
dispersed in 1 ml of 0.1 wt% nafion solution. Then the mixture was dropped on a pre-treated GCE to fabricate a modified GCE. Finally the modified GCEs were dried under infrared light. Electrochemical measurements: Electrochemical experiments were performed on a CHI660D electrochemical workstation (CHI, Shanghai) using a three-electrode setup at 298 K. GCE or modified GCEs acted as working electrodes. A saturated calomel electrode (SCE) was used as reference electrode, and platinum wire as the counter electrode.
1. Results and discussion The hybrid nanomaterial GAg was developed by a two-step facile method (Fig. 1A). Firstly, the exfoliated graphene oxide was decorated with Ag3PO4 NPs in a hydrothermal reactor, and then the silver phosphate–graphene oxide composite materials were calcined at 773 K under N2 atmosphere. Although there was no reducing atmosphere like hydrogen, calash-shaped Ag was obtained but not Ag3PO4. As shown in Fig. 1D, it was still Ag3PO4 obtained after only Ag3PO4 calcification at 773 K. In fact, the XPS
Fig. 1. Scheme of preparation of GOAgPO and GAg (A). SEM images of GOAgPO (B) and GAg (C). XRD patterns of GOAgPO, GAg, GO, GO after hydrothermal treatment (GO-Hydrothermal) and Ag3PO4 calcination at 773 K (AgPO-500) (D). TEM images of GOAgPO (E) and GAg (F).
J.-H. Yang et al. / Materials Letters 97 (2013) 133–136
(Fig. 2A), Raman and UV–vis (Fig. 2B) spectra of GO and GO after the hydrothermal treatment process (GO-Hydrothermal) demonstrated that GO was not reduced to graphene after the hydrothermal treatment process. It has been reported that Ag nanoparticles could be deposited onto graphene by chemical reduction of silver ions by hydroxyl groups of GO accompanied with the conversion of GO to graphene under alkaline conditions as well as heat treatment process [22,23]. We speculated that graphene oxide self-generated reducing agent such as reducing carbon and carbon monoxide was responsible for generation of Ag from Ag3PO4, which could be called substrate self-generated reduction (SSGR). The SEM image of GOAgPO was shown in Fig. 1B; Ag3PO4 NPs had a relatively high degree of dispersion on graphene oxide with particle size around 15 nm because hydroxyl groups and epoxy groups on graphene oxide played a very important role in the dispersion process. As to GAg, there
135
were plenty of dense gourd-shaped Ag particles in the size of about 50 nm (gourd head) and 200 nm (gourd belly) on graphene (Fig. 1C) because the Ag would be aggregated at 77 K calcination. The species of the two materials were determined by XRD (Fig. 1D). Both the silver phosphate and silver had showed relatively pure diffraction peaks. The cyclic voltammograms (CVs) of the GAg modified GCEs are shown in Fig. 2C. In the anodic potential sweep with the absence of glucose, the GAg electrode showed three peaks (A1, A2 and A3) at 0.27, 0.33 and 0.70 V, respectively. In the reverse scan, two cathodic peaks (A4 and A5) appeared at 0.37 and 0.16 V, respectively. As reported, A1 corresponds to the electro-formation of the monolayer of Ag2O and A2 is due to the formation of the multilayer of Ag2O. The third peak A3 is due to formation of AgO from Ag2O or Ag [16]. When glucose was added into the system, one large oxidation current of glucose (G1) appeared at 0.21 V
Fig. 2. C 1s XPS spectra of GO and GO-Hydrothermal (A). UV–vis spectra and Raman spectra (inset) of GO and GO-Hydrothermal (B). CVs of GAg modified composite electrode in the absence (a) and presence (b) of 0.01 M glucose in 0.1 M NaOH solution at 50 mV/s (C). CVs of GAg electrode in 10 mM (a), 15 mM (b), and 20 mM (c) glucose with 0.1 M NaOH solution at 50 mV/s (D).
Fig. 3. CVs of bare GCE (a), GOAgPO (b) and GAg (c) electrode in 10 mM glucose with 0.1 M NaOH solution at 50 mV/s (A). CVs of glucose electro-oxidation on GAg in 0.1 M NaOH solution containing 0.01 M glucose at different scan rates. Inset: peak current versus the square root of the scan rate (from 5 mV/s to 300 mV/s) (B).
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(near the potential of Ag2O formation) during the anodic scan with excellent activity (peak current density 6.66 A cm 2) and was a small peak G2 appeared at 0.52 V corresponding to further oxidation of glucose by Ag2O on GAg, which suggests that Ag2O was the main active phase for the oxidation of glucose. The oxidation potential of G1 was lower than that of A1, implying that glucose had been oxidized by monolayer Ag2O clusters before the formation of whole monolayer Ag2O on GAg. However, the oxidation peak G3 (0.65 V) following G4 (0.50 V) was observed when the potential scan was reversed, indicating that the oxidation products near 0.52 V can be oxidized further by Ag2O but not AgO because the potential below 0.66 V is not anodic enough to reoxidize Ag2O to AgO [17]. Multilayer Ag2O and metallic silver were produced during the cathodic scan at 0.37 V and 0.1 V, respectively. The presence of glucose increased the reduction potential of Ag2O to Ag by 0.06 V. CVs of various glucose concentrations are shown in Fig. 2D. As the glucose concentration increased, the peak current of glucose oxidation increased, which indicated that GAg was an excellent material for glucose oxidation with high catalytic activity besides being a candidate material for glucose sensor. The CVs of the parent GCE and modified GCEs are depicted in Fig. 3A. The parent GCE shows no significant response for the glucose oxidation while the activity of GAg was more than three times that of GOAgPO, because the high temperature transformed GO to more conductive graphene, generated gourd-shaped silver from silver phosphate and enhanced the interaction between Ag and the substrate. CVs of glucose electro-oxidation on GAg at different scan rates are depicted in Fig. 3B, from which the relation of peak current versus the square root of the scan rate can be drawn (shown in the inset). The linear growth even at high scan rate of the anodic current with the square root of the scan rate indicated that the electro-chemical behavior of GAg for glucose oxidation is a diffusion-controlled process [18–20], which might be explained by the benefit of graphene for the diffusion of reactant molecules from solution to the surface redox sites of GAg.
through original substrate self-generated reduction methods. It was studied for electrochemical oxidation of glucose and showed excellent activity at low peak potential because of the generation of the monolayer Ag2O clusters in situ. The positive correlation between the scan rates and the anodic currents implied a diffusioncontrolled kinetic process even at high scan rate.
2. Conclusions
[20] [21] [22]
The gourd-shaped Ag nanoparticles graphene nanosheets hybrids were prepared by calcinating the precursor GOAgPO
Acknowledgments We thank the National Natural Science Foundation of China (21176221 and 21173009) for support.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
[23]
Quan H, Park S, Park J. Electrochim Acta 2010;55:2232–6. Newman JD, Turner APF. Biosens Bioelectron 2005;20:2435–9. Wilson GS, Gifford R. Biosens Bioelectron 2005;20 2388-6. Ramanavicius A, Kausaite A, Ramanaviciene A. Biosens Bioelectron 2005;20: 1962–6. Adzic RR, Hsiao MW, Yeager EB. J Electroanal Chem 1989;260 475-11. Vassilyev YB, Khazova OA, Nikolaeva NN. J Electroanal Chem 1985;196 127-18. Larew LA, Johnson DC. J Electroanal Chem 1989;262 167-16. Tominaga M, Shimazoe T, Nagashima M, Taniguchi I. Electrochem Commun 2005;7 189-5. Jin C, Chen Z. Synth Met 2007;157:592–5. Cataldi TRI, Guerrieri A, Casella IG, Desimoni E. Electroanalysis 1995;7: 305–7. Jafarian M, Forouzandeh F, Danaee I, Gobal F, Mahjani MG. J Solid State Electrochem 2009;13:1171–9. Colon LA, Dadoo R, Zare RN. Anal Chem 1993;65 476-16. Chang G, Luo Y, Lu W, Qin X, Asiri AM, Al-Youbi AO, et al. Catal Sci Technol 2012;2:800–7. Zhang Y, Liu S, Wang L, Qin X, Tian J, Lu W, et al. RSC Adv 2012;2 538-538. Zhang Y, Chang G, Liu S, Lu W, Tian J, Sun X. Biosens Bioelectron 2011;28:344–8. Qin X, Lu W, Luo Y, Chang G, Asiri AM, Al-Youbi AO, et al. Analyst 2012;137 939-5. Liu S, Tian J, Wang L, Qin X, Zhang Y, Luo Y, et al. Catal Sci Technol 2012;2:813–5. Lu W, Luo Y, Chang G, Sun X. Biosens Bioelectron 2011;26:4791–7. Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, et al. Science 2004;306 666-4. Geim AK, Novoselov KS. Nat Mater 2007;6:183–9. Hummers WS, Offeman RE. J Am Chem Soc 1958;80 1339–1. Qin X, Luo Y, Lu W, Chang G, Asiri AM, Al-Youbi AO, et al. Electrochim Acta 2012;79 46-46. Tian J, Liu S, Zhang Y, Li H, Wang L, Luo Y, et al. Inorg Chem 2012;51:4742–6.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Gourd-shaped silver nanoparticle–graphene composite for electrochemical oxidation of glucose Jing-He Yang a,b, Ketian Zhang b, Ding Ma b,n a
Department of Catalysis Chemistry and Engineering, School of Chemical Engineering, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, PR China b Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China
a r t i c l e i n f o
abstract
Article history: Received 5 November 2012 Accepted 16 January 2013 Available online 1 February 2013
Graphene nanosheets decorated with gourd-shaped Ag nanoparticles (GAg) were prepared from the precursor silver phosphate–graphene oxide nanocomposite (GOAgPO) by original substrate selfgenerated reduction methods. The material was studied for electrochemical oxidation of glucose in alkaline solution. GAg showed excellent activity at low peak potential. The reason was that the high temperature promoted transformation of GO to graphene, thereby reducing the resistance of the substrate, restructuring from the silver phosphate to gourd-shaped silver and enhancing the interaction between Ag and the substrate. The positive correlation between the scan rates and the anodic currents implied a diffusion-controlled kinetic process even at a high scan rate. & 2013 Elsevier B.V. All rights reserved.
Keywords: Electronic materials Nanocomposites Oxidation Carbon materials
1. Introduction The electrochemical oxidation of glucose has generated much research interest over the years due to its possibility of medical applications such as blood sugar sensors and biological fuel cells [1–4]. The glucose oxidation process, a chemical process that provides energy for organism, is an important process, especially for humans. The level of glucose concentration is very important to the health of humans, so development of electrochemical glucose oxidation technology in medical applications is necessary besides biological fuel. The electrocatalytic activity depends on the nature of the electrode material such as gold [5–7]. To optimize the activity, gold was fabricated into nanoparticles [8] or composite with other metals [9]. However, gold or even platinum is not suitable as electrocatalysts because the chemisorbed intermediates such as CO will poison the electrode surface besides being expensive [6]. Non-noble metals, such as Co [10], Ni [11], Cu [12], are investigated for cheaper and more anti-poisoned replacements, but their overpotentials are much higher with low activity. Silver, as a relatively cheap noble metal and a highly effective electrode material for electro-oxidation of glucose, has been regarded as a prime candidate for electrode material [13–18]. Substrates always play a vital role in the dispersion and stability of the catalysts, especially metallic nanoparticles. Graphene is a huge open p-electron system with a combination of armchair and zigzag edges that are analogous to cis- and trans-polyacetylenes,
n
Corresponding author. Tel./fax: þ 86 10 6275 8603. E-mail address: [email protected] (D. Ma).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.01.071
respectively. Its structure and properties motivated the development of new materials for electronics, batteries, supercapacitors and so on. Its chemical stability and high surface area give a chance as substrate for metallic nanoparticles in heterogeneous catalysis applications [19,20]. Herein, a new facile and distinctive method via silver phosphate– graphene oxide nanocomposite (GOAgPO) as intermediate was developed to synthesize gourd-shaped silver nanoparticle–graphene composite (GAg) catalyst, which showed excellent activity for glucose oxidation at low peak potential with distinct oxidation current in the anodic scan.
2. Experimental Reagents: Nafion (5 wt% ethanol solution) was purchased from Alfa Aesar, and diluted to 0.1 wt% with doubly distilled water in use. H3PO4 (85%), sodium hydroxide and AgNO3 were obtained from Beijing Chemical Company. All stock solutions used in this work were prepared with deionized water of resistivity no less than 18.2 MO cm. Synthesis of the materials: Graphene oxide was generated from natural flake graphite according to a modified Hummer’s method [21]. 340 mg AgNO3, 410 mL 85% H3PO4, 1 g sodium dodecyl sulfonate, and 12 g urea were dissolved in 180 ml deionized water. 50 mg graphene oxide was added to the solution and sonicated for 10 min. The solution was then heated for 12 h at 353 K. GOAgPO was separated by filtration and dried in an air oven at 333 K overnight. Following the same process, AgG was obtained by calcining GOAgPO in a tubular furnace under nitrogen
134
J.-H. Yang et al. / Materials Letters 97 (2013) 133–136
atmosphere finally. The temperature rose at the rate of 10 K/min till 773 K, and then remained for 2 h. Characterization: Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/max-2400 diffractometer with Cu-Ka radiation. The morphologies of the materials were observed by scanning electron microscopy (SEM, XL30S-FEG, 5 kV). For TEM analysis, samples were dissolved in ethanol under ultrasonic treatment and then put a drop of the solution was placed on a Cu grid. TEM images were taken with a FEI Tecnai G2 T20. UV–visible spectroscopy (Cary Varian 50) with a 1 cm quartz cell was used. XPS spectra were obtained using an Axis Ultra spectrometer (Kratos, UK). A mono Al-Ka (1486.6 eV) X-ray source was used at a power of 225 W (15 kV, 15 mA). To compensate for surface charge effects, binding energies were calibrated using the C1s hydrocarbon peak at 284.8 eV. Raman spectroscopy was obtained using a Horiba HR800 Raman system with three laser lines and a 632.8 nm line from He–Ne laser. Preparation of modified GCE: The glassy carbon electrodes (GCEs, 3 mm diameter, Tianjin Aida, Inc.) were polished with a-Al2O3 powder (40 nm), rinsed twice by deionized water and ethanol, and then dried at room temperature. 5 mg catalyst was
dispersed in 1 ml of 0.1 wt% nafion solution. Then the mixture was dropped on a pre-treated GCE to fabricate a modified GCE. Finally the modified GCEs were dried under infrared light. Electrochemical measurements: Electrochemical experiments were performed on a CHI660D electrochemical workstation (CHI, Shanghai) using a three-electrode setup at 298 K. GCE or modified GCEs acted as working electrodes. A saturated calomel electrode (SCE) was used as reference electrode, and platinum wire as the counter electrode.
1. Results and discussion The hybrid nanomaterial GAg was developed by a two-step facile method (Fig. 1A). Firstly, the exfoliated graphene oxide was decorated with Ag3PO4 NPs in a hydrothermal reactor, and then the silver phosphate–graphene oxide composite materials were calcined at 773 K under N2 atmosphere. Although there was no reducing atmosphere like hydrogen, calash-shaped Ag was obtained but not Ag3PO4. As shown in Fig. 1D, it was still Ag3PO4 obtained after only Ag3PO4 calcification at 773 K. In fact, the XPS
Fig. 1. Scheme of preparation of GOAgPO and GAg (A). SEM images of GOAgPO (B) and GAg (C). XRD patterns of GOAgPO, GAg, GO, GO after hydrothermal treatment (GO-Hydrothermal) and Ag3PO4 calcination at 773 K (AgPO-500) (D). TEM images of GOAgPO (E) and GAg (F).
J.-H. Yang et al. / Materials Letters 97 (2013) 133–136
(Fig. 2A), Raman and UV–vis (Fig. 2B) spectra of GO and GO after the hydrothermal treatment process (GO-Hydrothermal) demonstrated that GO was not reduced to graphene after the hydrothermal treatment process. It has been reported that Ag nanoparticles could be deposited onto graphene by chemical reduction of silver ions by hydroxyl groups of GO accompanied with the conversion of GO to graphene under alkaline conditions as well as heat treatment process [22,23]. We speculated that graphene oxide self-generated reducing agent such as reducing carbon and carbon monoxide was responsible for generation of Ag from Ag3PO4, which could be called substrate self-generated reduction (SSGR). The SEM image of GOAgPO was shown in Fig. 1B; Ag3PO4 NPs had a relatively high degree of dispersion on graphene oxide with particle size around 15 nm because hydroxyl groups and epoxy groups on graphene oxide played a very important role in the dispersion process. As to GAg, there
135
were plenty of dense gourd-shaped Ag particles in the size of about 50 nm (gourd head) and 200 nm (gourd belly) on graphene (Fig. 1C) because the Ag would be aggregated at 77 K calcination. The species of the two materials were determined by XRD (Fig. 1D). Both the silver phosphate and silver had showed relatively pure diffraction peaks. The cyclic voltammograms (CVs) of the GAg modified GCEs are shown in Fig. 2C. In the anodic potential sweep with the absence of glucose, the GAg electrode showed three peaks (A1, A2 and A3) at 0.27, 0.33 and 0.70 V, respectively. In the reverse scan, two cathodic peaks (A4 and A5) appeared at 0.37 and 0.16 V, respectively. As reported, A1 corresponds to the electro-formation of the monolayer of Ag2O and A2 is due to the formation of the multilayer of Ag2O. The third peak A3 is due to formation of AgO from Ag2O or Ag [16]. When glucose was added into the system, one large oxidation current of glucose (G1) appeared at 0.21 V
Fig. 2. C 1s XPS spectra of GO and GO-Hydrothermal (A). UV–vis spectra and Raman spectra (inset) of GO and GO-Hydrothermal (B). CVs of GAg modified composite electrode in the absence (a) and presence (b) of 0.01 M glucose in 0.1 M NaOH solution at 50 mV/s (C). CVs of GAg electrode in 10 mM (a), 15 mM (b), and 20 mM (c) glucose with 0.1 M NaOH solution at 50 mV/s (D).
Fig. 3. CVs of bare GCE (a), GOAgPO (b) and GAg (c) electrode in 10 mM glucose with 0.1 M NaOH solution at 50 mV/s (A). CVs of glucose electro-oxidation on GAg in 0.1 M NaOH solution containing 0.01 M glucose at different scan rates. Inset: peak current versus the square root of the scan rate (from 5 mV/s to 300 mV/s) (B).
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J.-H. Yang et al. / Materials Letters 97 (2013) 133–136
(near the potential of Ag2O formation) during the anodic scan with excellent activity (peak current density 6.66 A cm 2) and was a small peak G2 appeared at 0.52 V corresponding to further oxidation of glucose by Ag2O on GAg, which suggests that Ag2O was the main active phase for the oxidation of glucose. The oxidation potential of G1 was lower than that of A1, implying that glucose had been oxidized by monolayer Ag2O clusters before the formation of whole monolayer Ag2O on GAg. However, the oxidation peak G3 (0.65 V) following G4 (0.50 V) was observed when the potential scan was reversed, indicating that the oxidation products near 0.52 V can be oxidized further by Ag2O but not AgO because the potential below 0.66 V is not anodic enough to reoxidize Ag2O to AgO [17]. Multilayer Ag2O and metallic silver were produced during the cathodic scan at 0.37 V and 0.1 V, respectively. The presence of glucose increased the reduction potential of Ag2O to Ag by 0.06 V. CVs of various glucose concentrations are shown in Fig. 2D. As the glucose concentration increased, the peak current of glucose oxidation increased, which indicated that GAg was an excellent material for glucose oxidation with high catalytic activity besides being a candidate material for glucose sensor. The CVs of the parent GCE and modified GCEs are depicted in Fig. 3A. The parent GCE shows no significant response for the glucose oxidation while the activity of GAg was more than three times that of GOAgPO, because the high temperature transformed GO to more conductive graphene, generated gourd-shaped silver from silver phosphate and enhanced the interaction between Ag and the substrate. CVs of glucose electro-oxidation on GAg at different scan rates are depicted in Fig. 3B, from which the relation of peak current versus the square root of the scan rate can be drawn (shown in the inset). The linear growth even at high scan rate of the anodic current with the square root of the scan rate indicated that the electro-chemical behavior of GAg for glucose oxidation is a diffusion-controlled process [18–20], which might be explained by the benefit of graphene for the diffusion of reactant molecules from solution to the surface redox sites of GAg.
through original substrate self-generated reduction methods. It was studied for electrochemical oxidation of glucose and showed excellent activity at low peak potential because of the generation of the monolayer Ag2O clusters in situ. The positive correlation between the scan rates and the anodic currents implied a diffusioncontrolled kinetic process even at high scan rate.
2. Conclusions
[20] [21] [22]
The gourd-shaped Ag nanoparticles graphene nanosheets hybrids were prepared by calcinating the precursor GOAgPO
Acknowledgments We thank the National Natural Science Foundation of China (21176221 and 21173009) for support.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
[23]
Quan H, Park S, Park J. Electrochim Acta 2010;55:2232–6. Newman JD, Turner APF. Biosens Bioelectron 2005;20:2435–9. Wilson GS, Gifford R. Biosens Bioelectron 2005;20 2388-6. Ramanavicius A, Kausaite A, Ramanaviciene A. Biosens Bioelectron 2005;20: 1962–6. Adzic RR, Hsiao MW, Yeager EB. J Electroanal Chem 1989;260 475-11. Vassilyev YB, Khazova OA, Nikolaeva NN. J Electroanal Chem 1985;196 127-18. Larew LA, Johnson DC. J Electroanal Chem 1989;262 167-16. Tominaga M, Shimazoe T, Nagashima M, Taniguchi I. Electrochem Commun 2005;7 189-5. Jin C, Chen Z. Synth Met 2007;157:592–5. Cataldi TRI, Guerrieri A, Casella IG, Desimoni E. Electroanalysis 1995;7: 305–7. Jafarian M, Forouzandeh F, Danaee I, Gobal F, Mahjani MG. J Solid State Electrochem 2009;13:1171–9. Colon LA, Dadoo R, Zare RN. Anal Chem 1993;65 476-16. Chang G, Luo Y, Lu W, Qin X, Asiri AM, Al-Youbi AO, et al. Catal Sci Technol 2012;2:800–7. Zhang Y, Liu S, Wang L, Qin X, Tian J, Lu W, et al. RSC Adv 2012;2 538-538. Zhang Y, Chang G, Liu S, Lu W, Tian J, Sun X. Biosens Bioelectron 2011;28:344–8. Qin X, Lu W, Luo Y, Chang G, Asiri AM, Al-Youbi AO, et al. Analyst 2012;137 939-5. Liu S, Tian J, Wang L, Qin X, Zhang Y, Luo Y, et al. Catal Sci Technol 2012;2:813–5. Lu W, Luo Y, Chang G, Sun X. Biosens Bioelectron 2011;26:4791–7. Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, et al. Science 2004;306 666-4. Geim AK, Novoselov KS. Nat Mater 2007;6:183–9. Hummers WS, Offeman RE. J Am Chem Soc 1958;80 1339–1. Qin X, Luo Y, Lu W, Chang G, Asiri AM, Al-Youbi AO, et al. Electrochim Acta 2012;79 46-46. Tian J, Liu S, Zhang Y, Li H, Wang L, Luo Y, et al. Inorg Chem 2012;51:4742–6.