Biopolymer protected silver nanoparticles on the support of carbon nanotube as interface for electrocatalytic applications

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Biopolymer protected silver nanoparticles on the support of carbon nanotube as interface for electrocatalytic applications
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  Biopolymer protected silver nanoparticles on the support of carbon nanotube asinterface for electrocatalytic applications M. Satyanarayana, V. Sunil Kumar , and K. Vengatajalabathy Gobi  Citation: AIP Conference Proceedings 1724 , 020097 (2016); doi: 10.1063/1.4945217   View online:   View Table of Contents:   Published by the AIP Publishing   Articles you may be interested in   Enhanced field emission from carbon nanotubes by electroplating of silver nanoparticles J. Vac. Sci. Technol. B 29 , 041003 (2011); 10.1116/1.3610841 Resonance frequency shift of a carbon nanotube with a silver nanoparticle adsorbed at various positions Appl. Phys. Lett. 97 , 133105 (2010); 10.1063/1.3493176 Specific contact resistance at metal/carbon nanotube interfaces Appl. Phys. Lett. 94 , 012109 (2009); 10.1063/1.3067819 Photoacoustic characterization of carbon nanotube array thermal interfaces J. Appl. Phys. 101 , 054313 (2007); 10.1063/1.2510998 Silver-nanoparticle-decorated carbon nanoscaffolds: Application as a sensing platform Appl. Phys. Lett. 89 , 183120 (2006); 10.1063/1.2378431 Reuse of AIP Publishing content is subject to the terms at: IP: On: Tue, 19 Apr 2016 03:27:03  Biopolymer Protected Silver Nanoparticles on the Support of Carbon Nanotube as Interface for Electrocatalytic Applications   M. Satyanarayana, V. Sunil Kumar, K. Vengatajalabathy Gobi*  Department of Chemistry, National Institute of Technology, Warangal - 506004, Telangana, India. *Corresponding author’s e -mail:  Abstract. In this research, silver nanoparticles (SNPs) are prepared on the surface of carbon nanotubes via chitosan, a  biopolymer linkage. Here chitosan act as stabilizing agent for nanoparticles and forms a network on the surface of carbon nanotubes. Synthesized silver nanoparticles-MWCNT hybrid composite is characterized by UV-Visible spectroscopy, XRD analysis, and FESEM with EDS to evaluate the structural and chemical properties of the nanocomposite. The electrocatalytic activity of the fabricated SNP-MWCNT hybrid modified glassy carbon electrode has been evaluated by cyclic voltammetry and electrochemical impedance analysis. The silver nanoparticles are of size ~35 nm and are well distributed on the surface of carbon nanotubes with chitosan linkage. The prepared nanocomposite shows efficient electrocatalytic properties with high active surface area and excellent electron transfer behaviour. Keywords: Silver nanoparticles, Carbon nanotubes, Chitosan, Synthesis, Electrochemical. INTRODUCTION Carbon nanotubes (CNTs) have been recognized as an important material in recent years in various fields due to their unique electrical, mechanical and structural properties. CNTs, especially multiwalled-carbon nanotubes (MWCNTs) have high aspect ratio, nanometer sized dimensions and good electrical conductivity compared with conventional carbon materials. CNTs can easily promote electron transfer between the electroactive species and electrode surface due to its unique long and tubular geometry 1,2 . Their use as electrode modifiers can lead to a decrease of the overpotential, a decrease in the response time, enhanced electrocatalytic activity and an increase in available active surface area in comparison with conventional carbon electrodes. In this research work, we couple silver nanoparticles with MWCNT to enhance the active surface area and the flow of electrons freely across the interface. Silver nanoparticle have demonstrated high catalytic activity for both oxidation and reduction reactions. On the other hand, it is necessary to develop effective methods to synthesize silver nanoparticles which would be free from aggregation. In order to overcome this problem, various schemes have been developed for stabilizing the nanoparticles from aggregation such as polymer coatings, some surfactant stabilizers, and polymer agents capping. Based on the respective advantages of MWNTs and SNPs, the composites containing  both MWNTs and SNPs will bring some special properties and high potential of applications. Chitosan (Chit) is a linear, β -1,4-linked polysaccharide (similar to cellulose) that is obtained by the partial deacetylation of chitin. It possesses many advantages, such as excellent strong film forming ability but with high  permeability towards water and biocompatible, and shows good adhesion and high mechanical strength. Chitosan will act as a very good stabilizing agent for the formation of stable metal nanopaarticles. In chitosan, the amine groups would become responsible to stabilize the SNPs which make nanoparticles stable and preventing from aggregation. By combining all the advantages of CNTs, SNPs and chitosan, we developed a bionanocomposite, chitosan stabilized 2nd International Conference on Emerging Technologies: Micro to Nano 2015 (ETMN-2015) AIP Conf. Proc. 1724, 020097-1–020097-6; doi: 10.1063/1.4945217Published by AIP Publishing. 978-0-7354-1371-9/$30.00 020097-1  Reuse of AIP Publishing content is subject to the terms at: IP: On: Tue, 19 Apr 2016 03:27:03  silver nanoparticles supported carbon nanotubes for electrochemical applications such as chemical sensors and  biosensors, and biomedical applications. METHODS Functionalization of MWCNTs MWCNTs were functionalized with  –  COOH group by using a method similar to that described by Gouveia-Caridade et al. 3 . MWCNTs (120 mg) were added to 10 mL of 3 M nitric acid solution and stirred for 24 h at 60 o C. The black solid product was filtered and then washed several times with double distilled water until the filtrate solution  became neutral (pH = 7). The obtained solid product was collected in a petri dish and dried in an oven at 80 o C for 24 h. Nitric acid oxidizes CNTs and introduces  –  COOH groups at the ends and at the sidewall defects of the nanotube structure, which increases the electrocalytic activity of CNTs. The functionalized MWCNT was further characterized  by Raman spectroscopy.   Synthesis of SNP-MWCNT Nanocomposite Silver nanoparticles were synthesized by adopting a recipe reported previously 4  with major changes in the presence of carbon nanotubes. Initially 1 wt% of chitosan solution was first prepared by dissolving chitosan powder in 1.0% (v/v) acetic acid solution. Then 5 mg of MWCNTs was added in 10 mL of the above chitosan solution and ultrasonicated until homogeneous black suspension obtained. Then 5 mL of aq. 10 mM AgNO 3  solution was added to the resultant MWCNTs  –  chitosan mixture and stirred for 30 min. Then 2 ml of 10 mM freshly prepared NaBH 4  was added quickly to the above mixture, and immediately a yellowish green colour silver nano particles can be observed in the black suspension whereas yellow colour was observed in the absence of MWCNT. The resulting mixture was kept under stirring for another 90 min. The resulting SNPs were kept in a refrigerator at 4 o C in the dark before use. The chitosan capped SNPs are attached with  –  COOH groups of functionalized MWCNT through amine groups of capped chitosan. Then the SNPs attached MWCNTs are collected by centrifugation of the above mixture and the SNPs which are not attached to MWCNTs and remain in the supernatant are discarded. Finally obtained solid denoted as SNP-MWCNT nanocomposite.   Fabrication of Nanocomposite Electrodes At first, GCE (3 mm diameter) was polished with alumina slurry (down to 0.04 µm), washed thoroughly with double distilled water, sonicated in 1:1 aq. HNO 3, ethanol and double distilled water consecutively and finally dried at room temperature. A solution of chitosan (1 % w/v) was prepared by dissolving 1 g of chitosan powder in 100 mL aq. acetic acid (1 % v/v) solution and sonicated for 30 min. A 3 mg of nanocomposite was added to 1 mL chitosan solution and sonicated for 1 h. Then, 10 µL of the resulting homogeneous suspension of nanocomposite and chitosan mixture was cast on the surface of cleaned GCE and dried for 24  –   30 h at room temperature and the resulting electrodes were denoted as MWCNT-Chit/GCE and SNP-MWCNT-Chit/GCE. Characterization UV-Visible spectra were recorded on Perkin Elmer100 UV-Visible Spectrophotometer of the samples. Powder X- ray diffraction (XRD) patterns of the samples were recorded in 2Ɵ range of 10–  90° on a Brucker AXS D8 diffractometer and Cu was used as the target (k = 1.5406 Å) with a step size of 0.002 o  and a scan speed of 0.5 second  per step. Morphological studies of the samples were carried out on a FEI Quanta 200F scanning electron microscope operating at 15 kV. Elemental composition of the samples were analysed using an energy dispersive X-ray analysis (EDXA) facilitated with the FE-SEM. For the FE-SEM analysis, the samples were smeared on a conducting carbon tape and samples were coated with a thin layer of gold by sputtering method to avoid charging during analysis. Cyclic voltammetry and electrochemical impedance measurements were carried out using Zahner-elektrik workstation (Model IM6e, GmbH, Germany) equipped with Thales 3.08 USB software. All the electrochemical measurements were performed in a conventional electrochemical cell of 20 mL with bare or modified GCE as working electrode, Pt spiral wire as auxiliary electrode and Ag|AgCl (3 N KCl) electrode as reference. All the potentials were 020097-2  Reuse of AIP Publishing content is subject to the terms at: IP: On: Tue, 19 Apr 2016 03:27:03  referred against Ag|AgCl (3 N KCl) electrode throughout the manuscript. The experimental solution was purged with nitrogen gas for 10 min prior the experiment to de-aerate the solution. RESULTS AND DISCUSSION Characterization of SNP-MWCNT Composite The formation of silver nanoparticles could be readily examined by UV  –  visible spectra of the colloidal silver solution. The absorption maxima (λ  max ) of the formed SNP colloidal solution is observed at about 407 nm whereas in the presence of MWCNT λ  max  was 397 nm which indicates that the silver nanoparticles size in the presence of MWCNT is lesser than alone (Fig. 1A). From the λ  max ,   it indicates that the formation of silver nanoparticles is in the ranges of 30  –  35 nm diameters. FIGURE 1 . (A) UV-Visible spectra of AgNO 3  (a), SNP in chitosan matrix (b), SNP in MWCNT-Chit matrix (c). (B) XRD spectra of MWCNT and SNP-MWCNT composite. XRD was used to further confirm the presence of silver in SNP-MWCNT composite. The powder XRD patterns of F-MWCNT and SNP-MWCNT shown in Fig. 1B. XRD pattern of SNP- MWCNT has all Bragg’s reflections due to crystalline silver, which were observed at 38.2, 44.4, 64.6, 77.5 and 81.8 representing (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) planes of face centre cube crystal structures of silver (JCPDS No. 04-0783). The SNP size calculated using Scherrer formula and the average crystalline size found from the calculation is about 36.7 nm. Field emission scanning electron microscope (FESEM) was used to characterize the morphologies of SNP-MWCNT nanocomposite. Figure 2 shows the field emission scanning electron microscope (FESEM) images of the SNP-MWCNT nanocomposite at two different magnifications. Figure 2 clearly illustrates that the SNP were well-distributed along the surface of the MWCNTs and have formed a good network on the MWCNTs, which could  promote a facile electron transfer. As shown in Fig. 2 the SNP-MWCNT film is of porous nature with large surface area, and thus it could enhance the electrodic current of the nanocomposite electrode. The chemical composition of the SNP-MWCNT was determined using EDXA measurements. As shown in Fig. 2C, The EDXA spectra of SNP-MWCNT composite, indicated the presence of C, O, and Ag as the major chemical components with the weight  percentage of 91.29%, 5.11%, and 3.60%, respectively, over the entire region of the prepared sample. 200 300 400 500 600 Absorbance /a. u. Wavelength /nm abc A 102030405060708090  MWCNT SNP - MWCNT  - MWCNT   - Ag 2 2 23 1 12 2 01 1 1 2 0 0  2 0 0 Intensity/ a.u. 2  degree   B 020097-3  Reuse of AIP Publishing content is subject to the terms at: IP: On: Tue, 19 Apr 2016 03:27:03    FIGURE 2 . FESEM images of (A) MWCNT, (B) SNP-MWCNT. (C) EDX analysis of SNP-MWCNT composite. Electrochemical Characterization of SNP-MWCNT Composite Electrode The cyclic voltammetry analysis is a very basic method to analyze electrochemical characteristics of modified electrodes. The electroactive areas of the modified electrodes were estimated by cyclic voltammetry and compared with that of bare GCE. For the purpose, cyclic voltammograms (CVs) of K  3 [Fe(CN) 6 ] were recorded at bare GCE, MWCNT-Chit/GCE and SNP-MWCNT-Chit/GCE electrodes in aq. 2 mM K  3 [Fe(CN) 6 ] + 0.1 M KCl at various scan rates (10 to 150 mV s -1 ). CVs recorded at the scan rate of 100 mV s -1  and the plot of peak currents against the square root of scan rate are shown in Fig. 3. The peak currents observed with the modified electrodes are higher than that observed with bare GCE. The results were analyzed, and the effective surface areas of the modified electrodes were determined by applying the Randles-Sevcik equation and by considering the diffusion coefficient of K  3 [Fe(CN) 6 ] as 6.7×10 -6  cm -2 s -1   5 . The effective surface area of bare GCE is 0.078 cm 2 , which is nearly equal to the geometrical surface area of 3 mm diameter electrode. The electroactive surface areas of MWCNT-Chit/GCE and SNP-MWCNT-Chit/GCE are nearly 4 to 7 times higher than that of bare GCE and are 0.26 and 0.48 cm 2 , respectively. A 5 nm5 nm B C 020097-4  Reuse of AIP Publishing content is subject to the terms at: IP: On: Tue, 19 Apr 2016 03:27:03
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