Characterization and dopamine sensing property of V2O5@polyailine nanohybrid

Synthetic Metals 196 (2014) 151–157

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Characterization and dopamine sensing property of V2 O5 @polyailine nanohybrid R. Suresh, K. Giribabu, R. Manigandan, S. Praveen Kumar, S. Munusamy, S. Muthamizh, V. Narayanan ∗ Department of Inorganic Chemistry, University of Madras, Guindy Maraimalai Campus, Chennai 600025, India

a r t i c l e

i n f o

Article history: Received 11 January 2014 Accepted 29 July 2014 Keywords: V2 O5 @PANI Nanohybrid ␤-napthalenesulphonic acid Electrochemical property Dopamine sensor

a b s t r a c t In the present study, V2 O5 @polyaniline (V2 O5 @PANI) nanohybrid was prepared by oxidative polymerization approach in presence of colloidal V2 O5 . X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Visible spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that there is an interaction happened between V2 O5 and PANI. Plausible explanation for the formation of V2 O5 @PANI nanohybrid has been explained. The electrochemical oxidation of DA was examined by cyclic voltammetry (CV) and chronoamperometry (CA). The V2 O5 @PANI modified GC electrode (V2 O5 @PANI/GCE) showed electrocatalytic oxidation of DA in the linear range from 6.6 × 10−6 M to 1.1 × 10−4 M with the detection limit of 3.9 × 10−5 M. The proposed sensor method showed good sensitivity, stability and repeatability. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Nanostructured conducting polymers like polyaniline (PANI), polypyrrole and polythiophene have been extensively investigated as sensors because of their unique electrical, optical and chemical properties. Among them, PANI is frequently used as sensor due to its easy synthesis, stability and good conductivity [1]. However, the problem with PANI is low processing ability, and poor mechanical strength [2]. However, the mechanical strength, thermal stability and characteristics of sensors of PANI could be enhanced by compositing with metal oxide nanoparticles [3–5]. Metal oxide nanoparticles dispersed PANI nanocomposite based sensors have been developed by several research groups. Ram et al. [6] have synthesized PANI/TiO2 ultrathin film for CO gas sensing. Srivastava et al. [7] have developed PANI–TiO2 nanocomposite thin films based resistance sensor devices. Sen et al. [8] have reported PANI/␥Fe2 O3 nanocomposite for sensing of LPG gas at room temperature. Mallikarjuna et al. [9] reported PANI/␥-Fe2 O3 nanocomposites with high dielectric constants by an in situ polymerization method. Somani et al. [10] have reported PANI/V2 O5 nanocomposite with improved conductivity than the pristine V2 O5 . Layered structure V2 O5 is one of the important semiconductors which have great interest because of its potential applications

∗ Corresponding author. Tel.: +91 44 22202793; fax: +91 44 22300488. E-mail addresses: [email protected], [email protected] (V. Narayanan). http://dx.doi.org/10.1016/j.synthmet.2014.07.025 0379-6779/© 2014 Elsevier B.V. All rights reserved.

in catalysis [11], electrochromic devices [12], solar cells [13], lithium-ion batteries [14] and sensors [15]. Particularly, V2 O5 has been proved to be a potential electrode material because of its structure and conductivity. However, the development of sensors using V2 O5 has remained a challenge due to its poor structural stability, low electrical conductivity, and slow electrochemical kinetics [16]. In order to improve the electrochemical performance, V2 O5 could be composited with PANI. Accordingly, we reported the preparation of PANI/V2 O5 nanohybrid by oxidative polymerization approach. The characterization of PANI/V2 O5 nanohybrid was carried out by XRD, Raman, FTIR, UV–Visible spectroscopy, SEM, TEM and CV. Furthermore, a dopamine sensor has been fabricated with GCE immobilized with the as-prepared PANI/V2 O5 nanohybrid. The proposed sensor showed good sensitivity, limit of detection, wide linear range, and acceptable repeatability.

2. Experimental 2.1. Materials used Aniline, potassium persulphate, ␤-napthalenesulphonic acid (␤-NSA) and ammonium metavanadate were purchased from Qualigens and used as received without any further purification. Aniline was distilled under reduced pressure prior to use. Doubly distilled water was used as the solvent.

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Fig. 1. (a) XRD pattern, (b) Raman spectrum in the region of 1100–1800 cm−1 , (c) FTIR spectrum and (d) DRS UV–Visible spectrum of V2 O5 @PANI nanohybrid.

2.2. Synthesis of nanohybrid The V2 O5 @PANI nanohybrid was synthesized by an oxidative polymerization approach. The mixture of freshly distilled aniline (0.2 mL), appropriate amount of V2 O5 and ␤-NSA (0.26 g) were mixed in 100 mL of double distilled water under constant stirring for 30 min to form an emulsion of aniline–NSA complex containing V2 O5 nanoparticles. Then aqueous solution of potassium persulphate in 20 mL DD water as an oxidant was added drop wise to the above reaction mixture. The above mixture was kept overnight at 0–5 ◦ C to complete the polymerization. The resulting blackish green powder was filtered, washed with distilled water and methanol three times, respectively, and then dried in vacuum for 24 h. V2 O5 nanoparticles were synthesized according to our previous publication [17]. 2.3. Characterizations 2.3.1. Structural characterization XRD measurement was performed using Rich Siefert 3000 diffractometer with monochromatic Cu K˛1 radiation ˚ Raman spectrum was recorded using laser Raman (␭ = 1.5406 A). microscope, Raman-11 Nanophoton Corporation (Japan). FTIR spectrum was recorded using Schimadzu FT-IR 8300 series instrument. The UV-Vis absorption spectrum was recorded using a Perkin-Elmer lambda650 spectrophotometer. HITACHI S600N scanning electron microscopy and FEI TECNAI G2 model T-30 transmission electron microscopy at an accelerating voltage of 250 kV were used to assess the morphology of V2 O5 @PANI nanohybrid.

2.3.2. Electrochemical experiment Electrochemical experiments were performed by CHI 1103A electrochemical instrument with a conventional three-electrode cell. A bare GCE or V2 O5 @PANI/GCE was used as working electrode. A saturated calomel electrode (SCE) and a platinum wire were used as reference electrode and auxiliary electrode, respectively. The modified electrode was treated in the blank 0.1 M H2 SO4 before each measurement by successive cyclic voltammetric sweeps until the steady curve appeared. 2.4. Fabrication of dopamine sensor In order to fabricate dopamine sensor, the GCE was polished with alumina powder. After cleaning in ethanol and doubly distilled water successively, the highly polished GCE was dried at room temperature. The 10 ␮L of homogenous dispersion containing 1 mg of V2 O5 @PANI in 1 mL of ethanol were dropped on the surface of the polished GCE and dried under room temperature. After that, the electrode surface was thoroughly rinsed with doubly distilled water and dried under ambient condition. The obtained electrode was denoted as V2 O5 @PANI/GCE. 3. Results and discussion 3.1. Characterization of V2 O5 @PANI In the diffraction pattern of V2 O5 @PANI (Fig. 1a), there are diffraction peaks at 15.4◦ , 20.2◦ , 21.8◦ , 26.2◦ , 31.1◦ , 34.3◦ , 40.2◦ , 47.6◦ , 51.3◦ , 61.2◦ corresponding to (2 0 0), (0 0 1), (1 0 1), (1 1 0), (3 0 1), (3 1 0), (0 0 2), (6 0 0), (0 2 0), (3 2 1) planes of orthorhombic

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Fig. 2. (a–b) SEM and (c–d) TEM images of V2 O5 @PANI nanohybrid.

V2 O5 observed. Whereas, the broad diffraction peak due to the periodicity parallel to the polymer chains of PANI [18] was not clearly observed at the 2 due to the weak intensity in comparison to the V2 O5 diffraction peak. However, the characteristic peak intensity of V2 O5 in V2 O5 @PANI was significantly suppressed which can be explained by the formation of PANI layer on the V2 O5 nanoparticles [19]. The Raman spectrum of V2 O5 @PANI (Fig. 1b) shows the bands at 1174, 1247, 1330–1350, 1445, 1551, 1592 and 1625 cm−1 . The bands at 1340 and 1551 cm−1 are associated with the polaron (semiquinoid radical cation) during doping process [20]. The strong Raman bands at 1174 and 1625 cm−1 are attributed to C-H in-plane bending and C C stretching in the benzenoid ring respectively. Further, the band observed at 1445 and 1592 cm−1 are inherently assigned to the C N and C C stretching vibration in quinoid rings respectively which are originated from the bipolaron structures [21]. Additionally, the peak at 1247 cm−1 is characteristic of emeraldine state (doped PANI) and related to the bipolaron structure. Furthermore, the high intensity peak at 1340 cm−1 is related to the C N•+ stretching vibration [22]. Hence, it is clear that the synthesized nanohybrids are in the conducting state. Further, the introduction of V2 O5 into the PANI changes the general profile of spectra in 1000–1800 cm−1 region compared with the as-prepared PANI. The FTIR spectrum of V2 O5 @PANI (Fig. 1c) shows symmetric and asymmetric V O vibrational modes at 560 and 822 cm−1 , respectively, while the peak at 1012 cm−1 is assigned to V O stretching vibration. We found that V O vibrational modes are shifted to higher wavenumber upon interaction with PANI. It is reported that, the NH-O V bond promotes a displacement of the vanadium ion position in direction to the VO4 plane [23]. It increases the V O bond length and the interaction between the oxygen of planar base and vanadium ion, increasing the wavenumber corresponding to symmetric and asymmetric V O vibrational modes. From this, it is concluded that the VO5 square pyramid in V2 O5 @PANI is less

distorted than in V2 O5 . The bands positioned above 1000 cm−1 are assigned to the vibrational mode of PANI-NSA. The bands at 3427 and 3237 cm−1 represent N H stretching modes. The bands at 3110 cm−1 can be assigned to aromatic C H stretching mode. The band at about 1568 and 1503 cm−1 indicate the signature of PANI backbone due to the stretching modes of protonated quinoid ring and the benzenoid ring. The band present at 1286 cm−1 can be assigned to the C N stretching mode in a secondary aromatic amine. Two bands at 1178 and 1128 cm−1 correspond to an aromatic C H in-plane bending mode. V2 O5 acts as a counter ion to compensate the positive charge present on the nitrogen atom [24]. Therefore, the results of FTIR spectrum demonstrated that the PANI in V2 O5 @PANI exists in the conducting emeraldine form. Furthermore, the band at 1043 cm−1 is assigned to symmetric S O stretch, and that at 1164 cm−1 to the asymmetric S O stretch [25]. The absorption spectrum (Fig. 1d) of V2 O5 @PANI shows that there are two absorption bands located at ∼381 nm and ∼588 nm. The absorption band ∼381 nm is assigned as ␲–␲* transition and another band at ∼588 nm is associated with the transition of benzenoid rings into quinoid rings [26]. When compared with absorption spectrum of emaraldine state (ES)-PANI, the peak position of quinoid ring transition shifts from 585 nm to 588 nm in the nanohybrid. The reason may be that the nanohybrid of V2 O5 @PANI makes the energy gap of quinoid ring transition narrower and hence transition of electrons becomes easier. The peak corresponds to ␲–␲* transition in PANI shifts, so it can be inferred that there is an interaction happened between V2 O5 and nitrogen atoms on the quinoid ring of PANI. It should be indicating that the peaks due to V2 O5 have merged with PANI peak. 3.2. Formation mechanism of V2 O5 @PANI nanohybrid The SEM and TEM images of V2 O5 @PANI nanohybrids are shown in Fig. 2. It can be found that the agglomerates contain rod-like PANI with irregular V2 O5 particles. The length of the nanorods is

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Scheme 1. Formation mechanism of V2 O5 @PANI nanohybrid.

about several micrometres. The diameter of the nanorod is about 48 nm. The homogenous mixing of the particles reveals the high interaction exists between V2 O5 and PANI. Based on the above discussions, we can conclude the formation of V2 O5 @PANI nanohybrid which can be explained by the following way (Scheme 1): When the ␤-NSA and aniline monomer was added in to the dispersion containing V2 O5 nanoparticles, the aniline monomer get protonated and becomes anilinium cation, which was adsorbed on the negatively charged (due to surface hydroxyl group) V2 O5 nanoparticles due to the strong electrostatic force of attraction. After the addition of potassium persulphate as an oxidant, the polymerization was carried out completely and forms the PANI layer on the nanoparticles and thus we got V2 O5 @PANI nanohybrid [27].

pernigraniline (0.565 V/0.437 V). It is noted that there are no redox peaks attributed to the V2 O5 in the studied conditions, suggesting that these V2 O5 nanoparticles are surrounded by PANI. Also, the broad peaks in the CV suggest strong interaction between the PANI

3.3. Electrochemical property The cyclic voltammograms of V2 O5 @PANI recorded in 0.1 M H2 SO4 with different scan rates is shown in Fig. 3. It shows three anodic and three cathodic peaks corresponding to PANI [28]. The first redox peak is due to transition of (A) leucoemeraldine/(A1 ) leucoemeraldine radical cation (0.067 V/−0.065 V), the second one is the (B) emeraldine radical cation/(B1 ) emeraldine (0.306 V/0.163 V) and the third redox peak is the (C) pernigraniline radical cation/(C1 )

Fig. 3. Cyclic voltammogram of V2 O5 @PANI/GCE in 0.1 M H2 SO4 at the scan rate of (a) 100, (b) 150, (c) 200, (d) 250, (e) 300, (f) 350, (g) 400, (h) 450 and (i) 500 mVs−1 .

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Fig. 4. Cyclic voltammogram of V2 O5 @PANI/GCE and bare GCE in absence (a) and presence (b) of 0.1 mM UA at the scan rate of 50 mVs−1 .

and V2 O5 nanoparticles. When the scan rate was increased from 30 to 500 mV s−1 , cathodic and anodic peak potentials increases linearly with the scan rate, indicating that the electrode process is a surface-controlled process. 3.4. Dopamine sensing property 3.4.1. Cyclic voltammetry Electrochemical property of V2 O5 @PANI/GCE in the absence (Fig. 4a) and presence of 0.1 × 10−4 M DA were investigated by CV. Well-defined redox peaks have been observed for V2 O5 @PANI/GCE. It indicates that the modified electrode is electroactive in the selected potential range. Fig. 4b displays the cyclic voltammograms of 1 × 10−4 M DA at bare and V2 O5 @PANI/GCE. At bare GCE, a relatively small oxidation (0.86 V) and reduction (0.08 V) peak with the peak current of 12.43 ␮A and −6.94 ␮A were observed (Fig. 4b). After immobilized with V2 O5 @PANI nanohybrid, the oxidation and reduction peak were observed at 0.82 V and 0.12 V respectively. The redox potentials of DA at V2 O5 @PANI/GCE are lowered (40 mV) than the bare GCE. The observed redox peaks are due to the oxidation of dopamine into dopaminequinone. In addition, the oxidation peak current increases drastically to 18.09 ␮A than the bare GCE (12.43 ␮A). The electrochemical experiments show that V2 O5 @PANI nanohybrid can enhances the electron transfer rate and lower the overpotential of DA. Hence, V2 O5 @PANI nanohybrid acts as an effective electron promoter for electrocatalytic oxidation of DA. This enhanced dopamine sensing property was mainly attributed to (i) the larger electroactive sites of the modifying layer due to the nanometre size of nanohybrid. (ii) Synergistic effect between V2 O5 nanoparticles and electroactive PANI. According to the observed results and previous reports [29,30], the possible electrochemical redox mechanism of DA at V2 O5 @PANI/GCE is shown in Scheme 2. After the exposure of DA, the DA molecule can interacts with nitrogen site of PANI. The adsorbed DA undergoes oxidation by two paths. In path-I, the electrons transfer from DA to electrode by conversion of PE salt to PE base [31] whereas in path-II, the electrons transfer from DA to electrode through PANI chain by electron hopping mechanism [32]. 3.4.2. Effect of scan rate Fig. 5 shows the influence of scan rate on the electrochemical response of 1 × 10−4 M DA at V2 O5 @PANI/GCE. From Fig. 5, it can be seen that the oxidation peak current moved positively and the reduction peak current moved negatively with increasing scan rate from 30 to 500 mVs−1 . Inset in Fig. 5 shows both the oxidation and

reduction peak currents were linearly related to the square root of scan rate in the range from 30 to 500 mV s−1 . It suggests that the V2 O5 @PANI layer has good electrochemical activity and fast electron transfer. It also suggests that the electrode reaction corresponds to adsorption-controlled process. The linear regression equation for anodic and cathodic process were Ia (␮A) = 2.0341 1/2 (mVs−1 )1/2 + 1.6468 (R2 = 0.9990) and Ic (␮A) = −1.2503 ␯1/2 (mVs−1 )1/2 −2.3996 (R2 = 0.9972) respectively. 3.4.3. Linear range, detection limits and limit of quantification Chronoamperometry (CA) with high sensitivity was used to evaluate the analytical performance of the dopamine sensor (Fig. 6). 0.2 mL of 1 × 10−4 M DA was added to 30 mL of 0.1 M H2 SO4 solution successively under constant magnetic stirring. As DA is added to the stirred H2 SO4 solution, well-defined steady state current responses are obtained at the applied potential of 0.8 V, and the catalytic current increases stepwise with successive additions of DA. It must be indicated that the current obviously increases when the concentration of DA is low (12 ␮M). The corresponding calibration plot shown in Fig. 6b indicates that the DA sensor based on V2 O5 @PANI nanohybrid exhibits a linear range from 6.6 × 10−6 M to 1.1 × 10−4 M with a linear regression equation of I (␮A) = 0.015 CDA (␮M) + 0.3632 (R2 = 0.9834), and a sensitivity of 0.015 ␮A ␮M−1 . The limit of detection (LOD) and limit

Fig. 5. Cyclic voltammogram of V2 O5 @PANI/GCE at the scan rate of (a) 30, (b) 50, (c) 70, (d) 100, (e) 150, (f) 200, (g) 250, (h) 300, (i) 350, (j) 400, (k) 450 and (l) 500 mVs−1 . Inset figure: Plot of square root of scan rate versus anodic and cathodic peak current.

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Scheme 2. Possible electrochemical oxidation of DA at V2 O5 @PANI/GCE.

of quantification (LOQ) were calculated from (i) and (ii), respectively. LOD =

 3s  b

(i)

LOQ =

 10s  b

(ii)

where, s is the standard deviation and b is the slope of the calibration curve. The calculated LOD and LOQ are 3.9 × 10−5 M

Fig. 6. (a) Chronoamperometric responses of V2 O5 @PANI/GCE for the successive additions of 0.2 mL of 1 × 10−4 M DA to 30 mL of 0.1 M H2 SO4 . (b) Plot of current versus concentration of DA. Applied potential is 0.8 V.

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and 1.3 × 10−4 M respectively. The sensitivity and LOD of the present sensor is better or comparable with graphene/carbon fibre microelectrode [33], Cobalt-5-nitrosalophen/tetraoctylammonium bromide/carbon paste electrode [34], 2,4,6-Triphenylpyrylium ion zeolite Y/carbon paste electrode [35], and Calix[4]arene crown-4 ether/GCE [36]. 3.4.4. Repeatability and stability In order to investigate the repeatability of the present sensor, 5 repetitive measurements were examined in 1.0 × 10−4 M DA solutions using CV. The five prepared V2 O5 @PANI/GCE in the same protocol were measured successively. The results show a relative standard deviation (RSD) of 3.21%, which indicated that the V2 O5 @PANI/GCE has an excellent repeatability. The stability of the V2 O5 @PANI/GCE for the sensing of 1.0 × 10−4 M DA was examined. The oxidation potential for DA was unchanged and the oxidation peak current decreased about 4.5% of its initial oxidation peak current after the 4 weeks. These results prove that the V2 O5 @PANI/GCE shows a good stability. 4. Conclusion A new dopamine sensor has been successfully fabricated by using GCE coated with V2 O5 @PANI nanohybrid synthesized by an oxidative polymerization method. Formation of V2 O5 @PANI nanohybrid has been confirmed by various techniques. The electrochemical experiments indicate that V2 O5 @PANI nanohybrid significantly improves the electrochemical sensing DA compared with the bare GCE. The electrocatalytic currents increase linearly with the DA concentrations in the ranges of 6.6 × 10−6 M to 1.1 × 10−4 M by CA, with the sensitivity of 0.015 ␮A ␮M−1 . With the excellent features such as wide linear dynamic range, acceptable sensitivity and limit of detection mentioned above, the present sensor provides a new strategy for determination of DA in real samples. Acknowledgements One of the authors (RS) acknowledges the CSIR, New Delhi, India for the financial assistance in the form of Senior Research Fellowship. We acknowledge the FE-SEM, HR-TEM, and Raman facility provided by the National Centre for Nanoscience and Nanotechnology, University of Madras. References [1] P.R. Somani, R. Marimuthu, U.P. Mulik, S.R. Mulik, S.R. Sainkar, D.P. Amalnerkar, High piezoresistivity and its origin in conducting polyaniline/TiO2 composites, Synth. Met. 106 (1999) 45–52. [2] M. Matsuguchi, A. Okamoto, Y. Sakai, Effect of humidity on NH3 gas sensitivity of polyaniline blend films, Sens. Actuators B 94 (2003) 46–52. [3] F.Y. Chuang, S.M. Yang, Titanium oxide/polyaniline core-shell nanocomposites, Synth. Met. 152 (2005) 361–364. [4] A.Z. Sadek, W. Wlodarski, K. Shin, R.B. Kaner, K. Kalantar-zadeh, A layered surface acoustic wave gas sensor based on a polyaniline/In2 O3 nanofibre composite, Nanotechnology 17 (2006) 4488–4492. [5] C.G. Wu, Y.C. Liu, S.S. Hsu, Assembly of conducting polymer/metal oxide multilayer in one step, Synth. Met. 102 (1–3) (1999) 1268–1269. [6] M.K. Ram, O. Yavuz, V. Lahsangah, M. Aldissi, CO gas sensing from ultrathin nano-composite conducting polymer film, Sens. Actuators B 106 (2005) 750–757. [7] S. Srivastava, S. Kumar, V.N. Singh, M. Singh, Y.K. Vijay, Synthesis and characterization of TiO2 doped polyaniline composites for hydrogen gas sensing, Int. J. Hydrogen Energy 36 (2011) 6343–6355. [8] T. Sen, N.G. Shimpi, S. Mishra, R. Sharma, Polyaniline/␥-Fe2 O3 nanocomposite for room temperature LPG sensing, Sens. Actuators B 190 (2014) 120–126.

157

[9] N.N. Mallikarjuna, S.K. Manohar, P.V. Kulkarni, A. Venkataraman, T.M. Aminabhavi, Novel high dielectric constant nanocomposites of polyaniline dispersed with ␥-Fe2 O3 nanoparticles, J. Appl. Polym. Sci. 97 (2005) 1868–1874. [10] P.R. Somani, R. Marimuthu, A.B. Mandale, Synthesis, characterization and charge transport mechanism in conducting polyaniline/V2 O5 composites, Polymer 42 (2001) 2991–3001. [11] V.I. Parvulescu, S. Boghosian, V. Parvulescu, S.M. Jung, P. Grange, Selective catalytic reduction of NO with NH3 over mesoporous V2 O5 –TiO2 –SiO2 catalysts, J. Catal. 217 (2003) 172–185. [12] C. Imawan, H. Steffes, F. Solzbacher, F. Obermeier, Structural and gas-sensing properties of V2 O5 –MoO3 thin films for H2 detection, Sens. Actuators B 77 (2001) 346–351. [13] S. Passerini, A.L. Tipton, W.H. Smyrl, Spin coated V2 O5 XRG as optically passive electrode in laminated electrochromic devices, Sol. Energy Mater. Sol. Cells 39 (1995) 167–177. [14] Y. Wang, G. Cao, Synthesis and enhanced intercalation properties of nanostructured vanadium oxides, Chem. Mater. 18 (2006) 2787–2804. [15] S. Zhuiykov, W. Wlodarski, Y. Li, Nanocrystalline V2 O5 –TiO2 thin-films for oxygen sensing prepared by sol–gel process, Sens. Actuators B 77 (2001) 484–490. [16] J. Livage, Vanadium pentoxide gels, Chem. Mater. 3 (1991) 578–593. [17] R. Suresh, K. Giribabu, L. Vijayalakshmi, A. Stephen, V. Narayanan, Visible light photocatalytic property of Zn doped V2 O5 nanoparticles, AIP Conf. Proc. 1447 (2012) 351–352. [18] R. Murugesan, E. Subramanian, Charge dynamics in conducting polyaniline–metal oxalate composites, Bull. Mater. Sci. 26 (2003) 529–535. [19] Y. Li, Y. Yu, L. Wu, J. Zhi, Processable polyaniline/titania nanocomposites with good photocatalytic and conductivity properties prepared via peroxo-titanium complex catalyzed emulsion polymerization approach, App. Surf. Sci. 273 (2013) 135–143. [20] A.G. Macdiarmid, J.C. Chiang, A.F. Richter, A.J. Epstein, Polyaniline: a new concept in conducting polymers, Syn. Met. 18 (1987) 285–290. [21] A. Kellenberger, E. Dmitrieva, L. Dunsch, The stabilization of charged states at phenazine-like units in polyaniline under p-doping: an in situ ATR-FTIR spectroelectrochemical study, Phys. Chem. Chem. Phys. 13 (2011) 3411–3420. [22] Z. Ping, In situ FTIR-attenuated total reflection spectroscopic investigations on the base–acid transitions of polyaniline. Base–acid transition in the emeraldine form of polyaniline, J. Chem. Soc., Faraday Trans. 92 (1996) 3063–3067. [23] D.C. Trivedi, in: H.S. Nalva (Ed.), Handbook of Organic Conductive Molecules and Polymers, Wiley, New York, 1997, p. 537. [24] J.M. Savariault, D. Lafargue, J.L. Parise, J. Galy, Intercalation chemistry in layered transition metal oxide structures: pyridine vanadium pentoxide, J. Solid Sate Chem. 97 (1992) 169–178. [25] M. Trchova, J. Stejskal, Polyaniline: the infrared spectroscopy of conducting polymer nanotubes (IUPAC Technical Report), Pure Appl. Chem. 83 (2011) 1803–1817. [26] L.C. Mendes, A.P.S. Falco, M.S. Pinho, P.O. Marques, Sulfonated polyaniline: influence of sulfonation routes on its thermal and structural characteristics, Mat. Res. 14 (2011) 466–471. [27] N. Asima, S. Radimana, M.A. Bin Yarmo, Preparation and characterization of core–shell polyaniline/V2 O5 nanocomposite via microemulsion method, Mat. Lett. 62 (2008) 1044–1047. [28] E.I. Iwuoha, S.E. Mavundla, V.S. Somerset, L.F. Petrik, M.J. Klink, M. Sekota, P. Bakers, Electrochemical and spectroscopic properties of fly ash–polyaniline matrix nanorod composites, Microchim. Acta 155 (2006) 453–458. [29] S.R. Ali, Y. Ma, R.R. Parajuli, Y. Balogun, W.Y.C. Lai, H. He, A nonoxidative sensor based on a self-doped polyaniline/carbon nanotube composite for sensitive and selective detection of the neurotransmitter dopamine, Anal. Chem. 79 (2007) 2583–2587. [30] S. Sharath Shankar, B.E. Kumara Swamy, B.N. Chandrashekar, K.J. Gururaj, Sodium do-decyl benzene sulfate modified carbon paste electrode as an electrochemical sensor for the simultaneous analysis of dopamine, ascorbic acid and uric acid: a voltammetric study, J. Mol. Liq. 177 (2013) 32–39. [31] R. Suresh, R. Prabu, A. Vijayaraj, K. Giribabu, R. Manigandan, A. Stephen, V. Narayanan, Poly(anthranilic acid) microspheres: synthesis, characterization and their electrocatalytic properties, Bull. Korean Chem. Soc. 33 (2012) 1919–1924. [32] S. Nasirian, H.M. Moghaddam, Hydrogen gas sensing based on polyaniline/anatase titania nanocomposite, Int. J. Hydrogen Energy (2013), http://dx.doi.org/10.1016/j.ijhydene.2013.09.152. [33] M.F. Zhu, C.Q. Zeng, J.S. Ye, Graphene-modified carbon fiber microelectrode for the detection of dopamine in mice hippocampus tissue, Electroanalysis 23 (2011) 907–914. [34] S. Shahrokhian, H.R. Zare-Mehrjardi, Cobalt salophen-modified carbon-paste electrode incorporating a cationic surfactant for simultaneous voltammetric detection of ascorbic acid and dopamine, Sens. Actuators B 121 (2007) 530–537. [35] A. Domenech, H. Garca, M.T. Domenech-Carbo, M.S. Galletero, 2,4,6Triphenylpyrylium ion encapsulated into zeolite Y as a selective electrode for the electrochemical determination of dopamine in the presence of ascorbic acid, Anal. Chem. 74 (2002) 562–569. [36] G.S. Lai, H.L. Zhang, C.M. Jin, Electrocatalysis and voltammetric determination of dopamine at a calix[4]arene crown-4 ether modified glassy carbon electrode, Electroanalysis 19 (2007) 496–501.