- Email: [email protected]
MnWO4 nanocapsules: Synthesis, characterization and its electrochemical sensing property
Journal of Alloys and Compounds 619 (2015) 601–609
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
MnWO4 nanocapsules: Synthesis, characterization and its electrochemical sensing property Selvamani Muthamizh, Ranganathan Suresh, Krishnamoorthy Giribabu, Ramadoss Manigandan, Sivakumar Praveen Kumar, Settu Munusamy, Vengidusamy Narayanan ⇑ Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
a r t i c l e
i n f o
Article history: Received 12 May 2014 Received in revised form 13 August 2014 Accepted 7 September 2014 Available online 16 September 2014 Keywords: MnWO4 Electrochemical detection Quercetin Nanocapsule
a b s t r a c t Manganese tungstate (MnWO4) was synthesized by surfactant free precipitation method. MnWO4 was characterized by using various spectroscopic techniques. The phase, crystalline nature and the morphological analysis were carried out using XRD, scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HR-TEM). Further, FT-IR, Raman, and DRS-UV–Vis spectral analysis were carried out in order to ascertain the optical property and the presence of functional groups. From the analysis, the morphology of the MnWO4 was observed to be in capsules with breadth and thickness were in nm range. The oxidation state of tungsten (W), and manganese (Mn) were investigated using Xray photo electron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR). The synthesized MnWO4 nanocapsules were used to modify glassy carbon electrode (GCE) to detect quercetin. Ó 2014 Published by Elsevier B.V.
1. Introduction In recent years, much research has been focused on the synthesis of nanomaterials in variety of architectures such as nanoparticle, nanorods, nanobars, nanosheets, nanoplatelets and nanotubes, because of their unique physical and optical properties [1–6]. MWO4 (M = divalent transition metal ions) type compounds have much scientific interest in recent times because of their intriguing properties like electrical and electrochemical property, photoluminescence, photocatalyst, energy storage capacity, and humidity sensing ability [7–11]. In particular, MnWO4 has attracted attention because of its wide application in many fields such as electrocatalyst, photocatalyst and battery application. Metal tungstates exists in two different crystal structures namely scheelite and wolframite. Bivalent metal ions with large ionic radius such as Ca2+, Sr2+, Ba2+ and Pb2+ prefer to form scheelite type structures whereas metal ions with smaller ionic radius like Zn2+, Mn2+, Co2+, Ni2+ and Cd2+ tend to crystallize in wolframite type of structure [12–16]. Among this MnWO4 has a monoclinic type structure having space group of P2/C. Several methods have been reported for the synthesis of MnWO4 such as microwave synthesis [17], surfactant assisted complexation–precipitation method [18], hydrothermal synthesis [19], solvothermal route [11] and solid ⇑ Corresponding author. E-mail address: [email protected] (V. Narayanan). http://dx.doi.org/10.1016/j.jallcom.2014.09.049 0925-8388/Ó 2014 Published by Elsevier B.V.
state synthesis [20]. The direct precipitation method has been used for the synthesis of MnWO4 at room temperature [21]. The electrochemical activity of manganese tungstate for energy storage purpose and the detection of hydrogen peroxide, and nitrophenol was reported [10,22]. Flavonoids are important in human diet because of its positive effects on human. Among flavonoids, quercetin is one of the naturally occurring, which is from our daily diet. Quercetin possesses many beneficial effects on human health, including cardiovascular protection, anti-ulcer effects, anti-allergy activity, cataract prevention, antiviral activity, and anti-inflammatory effects, antioxidant, estrogenic activity, and anticancer activity [23]. The beneficial effects of quercetin on human health is due to its polyphenolic nature with radical-scavenging activity and metalchelating properties. Structure of flavonoids consist of 15-carbon skeleton arranged in a C6–C3–C6 configuration, among that two are phenyl rings and one is a heterocyclic ring [24]. The IUPAC name of quercetin is 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy4H-chromen-4-one and the corresponding chemical structure is shown in Fig. 1. Because of all these beneficial effects it has been used in medicine. Though quercetin has beneficial effects as its concentration level increased it may lead to adverse effect such as headache and kidney failure. Hence, it becomes important to determine the levels of quercetin. The determination of quercetin based on modified electrode is very rare. The present work deals with a facile MnWO4 based approach for electrochemical detection of the quercetin. MnWO4 was
602
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
3. Result and discussion 3.1. X-ray diffraction study
Fig. 1. Structure of quercetin.
synthesized chemically by direct precipitation method. The prepared MnWO4 were characterized by XRD, FTIR, DRS-UV, Raman, SEM, HR-TEM, EPR and XPS. The electrochemical determination of quercetin was carried out using cyclic voltammetry (CV) and chronoamperometry (CA). 2. Experimental details 2.1. Materials All the chemicals used in the synthesis such as manganese chloride (MnCl24H2O), hydrated sodium tungstate (Na2WO42H2O) were analytical grade reagents purchased from Qualigens and Merck respectively. All the chemicals were used without further purification. Quercetin was purchased from Sigma Aldrich, double distilled water and ethanol was used as solvent.
XRD pattern of the synthesized MnWO4 was shown in Fig. 2. All the diffraction peaks were indexed to the monoclinic structure of MnWO4 with space group p2/c of JCPDS Card No 01-080-0152. It shows the peaks at 2h:15.5, 18.5, 23.6, 24.1, 30.0, 30.4, 31.1, 36.1, 37.3, 40.3, 40.9, 48.3, 49.3, 51.2, 52.5, and 53.1 corresponds to (0 1 0), (1 0 0), (0 1 1), (1 1 0), (1 1 1), (1 1 1), (0 2 0), (0 2 1), (2 0 0), (0 2 1), (2 0 0), (1 0 2), (1 0 2), (0 2 2), (2 0 0), (1 2 2), (2 0 2), and (2 2 1) planes of monoclinic MnWO4 respectively. The lattice parameters of the MnWO4 are a = 4.815 Å, b = 5.706 Å, c = 4.992 Å, and b = 91.04°. The strong diffraction peaks of synthesized MnWO4 revels that the synthesized sample is high crystalline in nature. No other impurity peaks were detected. 3.2. FT-IR analysis FT-IR spectrum of the synthesized MnWO4 is shown in Fig. 3. A broad band observed at 3436 cm1 is indicative of vibration of O–H bond of the surface hydration. The band at 1637 cm1 corresponds to the H–O–H deformation vibration of surface hydroxyl group. The absorption peaks located at 871 cm1 and 829 cm1 corresponds to symmetric and asymmetric stretching vibration mode of the W–O bond in terminal WO2 group of MnWO4 [25]. The strong band at 706 cm1 is the asymmetrical stretching vibrations of W–O bond in the (W2O4)n chain and 620 cm1 indicates the presence of stretching vibration of Mn–O bond. The band at
2.2. Synthesis of MnWO4 nanocapsules MnWO4 nanocapsules was prepared by direct precipitation method without using any surfactant. The procedure is as follows: 2.474 g of MnCl24H2O (12.5 mmol) and 4.123 g of Na2WO42H2O (12.5 mmol) each were dissolved separately in 25 mL of double distilled water. Then the Mn2+ solution was added dropwise to the WO2 4 solution under magnetic stirring at room temperature. After the addition process manganese tungstate was precipitated which was filtered and washed 3–4 times using distilled water in order to remove the unreacted starting materials. The precipitate was washed with ethanol and allowed to dry in room temperature for two days. The as-synthesized MnWO4 were calcined at 600 °C for 5 h in a muffle furnace. 2.3. Characterization The XRD pattern of the synthesized sample was analyzed by using Rich Siefert 3000 diffractometer with Cu Ka1 radiation (k = 1.5406 Å). FT-IR spectrum was recorded using a Perkin–Elmer FT-IR spectrophotometer. The sample was analyzed using potassium bromide pellet technique in the range 4000–400 cm1. Raman spectrum was recorded using laser Raman microscope, Raman-11 Nano photon Corporation, Japan. DRS UV–Vis absorption spectrum was recorded using Perkin– Elmer lambda 650 spectrophotometer. The morphology of synthesized MnWO4 was analyzed by HITACHI SU6600 scanning electron microscopy (SEM) coupled with EDAX. The shape and average size of nanocapsule was observed by means of FEI, TECHNAI G2, 30 S-twin D905 high resolution transmission electron microscopy (HR-TEM). XPS measurement was performed by Omicron nanotechnology-ESCA-14, Germany. EPR spectrum was recorded using Bruker X-band Electron Paramagnetic Spectrometer, at an operating frequency of 9.4 GHz. All electrochemical measurements were carried out using a CHI 1103A electrochemical workstation with a conventional three electrode cell. A bare GCE (glassy carbon electrode) and MnWO4/ GCE used as the working electrode. A saturated calomel electrode (SCE) and a platinum wire were used as the reference electrode and counter electrode respectively.
Fig. 2. XRD pattern of MnWO4.
2.4. Fabrication of MnWO4/GCE The GCE was modified with MnWO4, before that the working electrode was mechanically polished with 1 lm, 0.3 lm and 0.05 lm alumina pastes for mirror finishing. Then it was subjected to ultrasonication in double distilled water for few minutes in order to clean the surface of GCE. The MnWO4 suspension was prepared by dispersing 5 mg of MnWO4 in 10 mL of ethanol during 20 min of ultrasonic agitation then the GCE was coated with 10 lL of the suspension by drop coating method and dried in air.
Fig. 3. FT-IR spectrum of MnWO4.
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
603
lational levels. A very strong band appeared at the region of 878 cm1 corresponds to the strong symmetric stretching of WO2 group in the MnWO4. The bands at 768, 691 cm1 indicates the presence of weak asymmetric and symmetric stretching vibration mode of W–O–W bond [27]. The peak at 533 cm1 is attributed due to stretching vibration of Mn–O [28]. The band at 394 cm1 indicates the presence of symmetric stretching of W–O–W [29]. The band at 320 cm1 confirms the medium scissoring of both WO2 and W–O–W [30]. A weak band appeared at 290, 253 cm1 indicates the bending mode of [WO6]6 and twisting mode of WO2 group [31,32]. The bands at 160, 123, 87 cm1 were the translational mode of tungsten [33]. 3.4. Optical property of MnWO4
Fig. 4. Raman spectrum of MnWO4.
515 cm1 was observed due to the presence of stretching vibration of Mn–O–Mn bond [26].
3.3. Raman analysis
The optical property of synthesized MnWO4 was analyzed using DRS-UV spectroscopy and the corresponding spectrum is shown in Fig. 5(a). The strong absorption peak at 380 nm are due to the transition between bands of O 2p level and Mn 3d level in MnWO4 and weak band at 563 nm due to the spin-forbidden transition between the eg and t2g orbital of Mn 2p [34]. The observed peaks are similar to reported value of Van Hanh et al. [35]. The band gap value Eg of synthesized MnWO4 was determined by using Tauc’s plot. 1=n
Raman spectrum of synthesized MnWO4 is shown in Fig. 4. The observed bands corresponds to symmetric, asymmetric-stretching, bending, scissoring, twisting and translational modes for the synthesized MnWO4. The bands observed for MnWO4 were 878, 768, 691, 533, 394, 320, 290, 253, 200, 160, 123 and 90 cm1; which are obtained from different modes of absorption of different trans-
ðhtaÞ
¼ Aðht Eg Þ
where h – Planck’s constant, t – frequency of vibration, a – absorption coefficient, Eg – band gap, A – proportional constant. n = 2 (for direct band gap), or n = 1/2 (for indirect band gap). The synthesized MnWO4 showed both direct band gap of 2.67 eV and indirect band gap of 2.5 eV values which is shown in Fig. 5(b and c) [36,37].
Fig. 5. (a) DRS-UV visible spectrum of MnWO4; (b) direct band gap and (c) indirect band gap.
604
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
Fig. 6. (a) SEM images of MnWO4 and (b) EDAX spectrum of MnWO4.
Scheme 1. Formation mechanism of MnWO4 nanocapsule.
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
Fig. 7. HR-TEM images of MnWO4.
Fig. 8. (a) SAED pattern of MnWO4; (b) and (c) fringes pattern of MnWO4.
605
606
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
Fig. 9. (a) XPS survey spectrum of MnWO4 nanocapsule; (b) XPS spectrum of Mn in MnWO4 nanocapsule; (c) XPS spectrum of W in MnWO4 nanocapsule and (d) XPS spectrum of O in MnWO4 nanocapsule.
Table 1 Atomic % of elements present in MnWO4. Element
Mn
W
O
Atomic %
16.1
14.9
69.9
Fig. 11. Cyclic voltammograms of (a) bare GCE and (b) MnWO4/GCE in pH 7 at scan rate of 50 mV s1.
Fig. 10. EPR spectrum of Mn2+ in MnWO4.
3.5. Morphological analysis Fig. 6(a) shows the SEM image of MnWO4. SEM images clearly revels that the synthesized MnWO4 were in capsule like morphology. The corresponding EDAX spectrum (Fig. 6(b)) confirms the
presence of Mn, W, and O as expected and no other impurities were observed. The possible formation mechanism and the pictorial representation are shown in Scheme 1. HR-TEM analysis was further carried out in order to confirm the crystallinity, and morphology of MnWO4. HR-TEM images of MnWO4 nanoparticles are shown in Fig. 7. It can be seen that the MnWO4 nanocapsules are having the width of 177 nm and thickness of 100 nm. Selected area electron diffraction pattern (SAED) (Fig. 8(a)), clearly indicates that the MnWO4 nanocapsule were highly crystalline in nature as observed from XRD analysis. Fringe pattern (Fig. 8(b)) taken on an individual nanocapsule shows the crystalline nature of the
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
607
MnWO4 and the spacing between two adjacent lattice fringes was found to be 0.317 Å, corresponding to the (1 1 1) plane of the monoclinic MnWO4, it is well matched with XRD plane indexing of MnWO4. 3.6. XPS analysis XPS analysis was carried out for the MnWO4 nanocapsules in order to confirm the chemical composition, binding energy and oxidation states of the elements present in MnWO4. Fig. 9(a) shows the survey XPS spectrum of MnWO4. It shows the presence of Mn, W, and O in the synthesized MnWO4.This result is consistent with EDAX analysis. High-resolution XPS spectra of Mn 2p and W 4f of synthesized MnWO4 nanocapsule are discussed below. Fig. 9(b) shows the XPS spectrum of Mn 2p, two peaks are observed that corresponds to Mn 2p3/2 and Mn 2p1/2 at 640.8 eV and 658.0 eV, respectively. It reveals that Mn present in the sample is in +2 oxidation state [38]. XPS spectrum of W 4f was shown in Fig. 9(c). It has two peaks which corresponds to W 4f7/2 and W 4f5/2 at 34.7 and 36.9 eV respectively. The W 4f7/2 and W 4f5/2 spin–orbit doublets was observed to be 2.2 eV, which can be assigned to the oxidation state of W as +6 [39]. The O 1s peak shows a dominant component centered with low binding energy at 530.05 eV, which corresponds to the O2 forming oxide with manganese and tungsten elements (Mn–O–W) as shown in Fig. 9(d). Peak located at 533.2 eV corresponds to water bound at the surface of the samples, peak at 528 eV is due to the presence of O–Mn–O bond in MnWO4 [40,41]. By referring Rauwel et al. atomic % of the elements present in MnWO4 is calculated from the high resolution XPS spectrum (Table 1) and it shows an approximately equal amount of Mn and W elements and O with an error bar the corresponding values are given in Table 1 [42]. 3.6.1. EPR analysis EPR analysis was carried out in order to confirm the oxidation state of Mn ion present in MnWO4. Fig. 10 shows the curve that corresponds to a signal produced due to the presence of ferromagnetic Mn2+ ions. The observed EPR signal was justified by the g factor, that is
g ¼ ht=bH where g is a parameter describing the interaction of the paramagnetic center with the external magnetic field, his the Planck’s constant, t is the microwave frequency, b is the Bohr Magneton and H is the intensity of the resonance magnetic field. The value of g was found to be 2.0028 which is typical of octahedral environment of Mn2+. From both XPS and EPR analysis the oxidation state of Mn present in MnWO4 was found to be Mn2+ [43].
Fig. 12. Cyclic voltammograms of MnWO4/GCE at different pH values vs. scan rate at 50 mV s1. Inset shows the linear plot of anodic potential vs. pH.
3.7.2. pH effect on the detection of quercetin The effect of pH on the oxidation of 0.1 mM quercetin at the MnWO4/GCE was evaluated using cyclic voltammetry in the pH range of 3–10. The obtained cyclic voltammograms were shown in Fig. 12. From Fig. 12, we have observed that as the pH increases the voltammetric peaks become broader with the peak current decreased from 3.9 lA to 2.0 lA. At pH 3, the anodic peak potential was observed at 420 mV, as the pH increases to 10 the peak potential was observed to be 20 mV. When comparing the peak potential at different pH, we observed a gradual decrease up to the pH 7 and beyond pH 7 there is decrement in peak potential along with drastic decrease in peak current. Based on the above observations, pH value for the sensing experiments was fixed at pH 7. Hence, pH 7 was chosen for the subsequent analysis. The anodic potential (Epa) of quercetin decreases linearly (Fig. 12 inset) with a linear regression equation Epa (V) = 0.059 pH + 0.6051 (R2 = 0.9915) close to that given by the Nernst equation, indicating the equal number of electrons and protons involved in the electrooxidation process of quercetin [45]. According to the Nernst equation, Epa = E [(2.303mRT)/(nF)] pH, the ratio of m/n was found to be 1, where m denotes the number of protons intervening in the oxidation process, n denotes the number of electrons transferred, and R, T and F have their usual meanings. The proton transfer number can be calculated when the electron transfer number is known. 3.7.3. Effect of scan rate The effect of scan rate on the electrooxidation of 0.1 mmol quercetin was carried out. The dependency of electrooxidation of
3.7. Electrochemical sensing 3.7.1. Cyclic voltammetry Cyclic voltammetric responses of bare GCE (a) and MnWO4/GCE (b) towards quercetin was investigated in phosphate buffer (Na2HPO4 + NaH2PO4, pH 7) at the scan rate of 50 mV s1 (Fig. 11). From the observed cyclic voltammograms it is clear that at GCE, quercetin is oxidized at 168 mV with the anodic peak current of 3.5 lA and MnWO4/GCE detects the quercetin with higher current response at 4.1 lA with a lower peak potential of 153 mV [44]. From this observation, it can be seen that MnWO4/GCE shows enhanced electrochemical sensing property than the bare GCE. The enhanced electrochemical activity is mainly due to the presence of surface hydroxyl group, smaller crystallite size, and due to the metal ion. Thus the MnWO4/GCE can be utilized for the detection of quercetin at lower potential.
Fig. 13. Cyclic voltammograms of MnWO4/GCE in phosphate buffer (pH 7) at scan rate from 10 to 500 mV s1; Inset shows the log (ipa) vs. log (t) plot.
608
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
quercetin with different scan rates was investigated to study the electrode kinetics for the oxidation of quercetin. From Fig. 13, we observed that as the scan rate increases the peak current of quercetin also increased. To find out the electrode reaction whether diffusion process or surface confined process, a double logarithmic plot was plotted. From (Fig. 13 inset) it is observed that the slope was found to be 0.74 which shows that the electrode reaction is adsorption controlled (surface confined) process. 3.7.4. Number of electron and proton transfer in the electrochemical oxidation of quercetin The number of electrons transferred in the electrochemical oxidation process of quercetin at the MnWO4/GCE can be calculated by using the following equation
ip ¼ nFQ t=4RT where n = number of electron, ip = anodic peak current, R = gas constant, T = temperature (K), F = Faraday constant, Q = charge, t = scan rate. By using the above equation the value of n was found to be 3. The ratio of m/n = 1. Accordingly, the proton transfer number was calculated to be 3. From this, we can conclude that the electrooxidation of quercetin at the MnWO4/GCE involves a three electron and three proton process. The calculated number of electrons and protons involved in the oxidation of quercetin clearly indicates the formation of quinone by the mechanism given in Fig. 14 [46]. 3.7.5. Chronoamperometry Chronoamperometry was carried out to examine linear range and sensitivity of MnWO4/GCE towards 0.1 mM quercetin on successive addition of 50 lL. The obtained result is shown in Fig. 15, a successive addition of quercetin produce a significant increases in quercetin oxidation peak current. The linear range was found
Fig. 15. Chronoamperometric response of MnWO4 for the successive addition 50 lL of 0.1 mM quercetin to 40 mL of pH 7; Inset shows the plot of current vs. concentration of quercetin at an applied potential of 0.17 V.
to be 16.7 106–74.4 106 M and the linear regression equation was Ipa (lA) = 0.003[Q] (lA) + 0.032 (R2 = 0.9915). 4. Conclusion A direct precipitation method was successfully employed to prepare crystalline MnWO4 nanocapsules. The synthesized MnWO4 were analyzed by XRD, FT-IR, DRS-UV, Raman, XPS, SEM and HR-TEM. The synthesized sample was modified on the GCE and used for the detection of quercetin. MnWO4/GCE was sensitive towards quercetin. The electrocatalytic activity towards the detection of quercetin by MnWO4/GCE comparatively higher than bare GCE, there is not only increases in peak current but the corresponding peak potential also decreased. Therefore from the above results MnWO4 has an ability towards the detection of quercetin electrochemically. Acknowledgments One of the authors (S. Muthamizh) wish to thank the UGC-UPEPhase II, University of Madras, for the financial assistance. We acknowledge Central Leather Research Institute (CLRI) for EPR measurement and the National Centre for Nanoscience and Nanotechnology, University of Madras for providing instrumentation facility. References
Fig. 14. Electrooxidation mechanism of quercetin.
[1] W. Tong, L. Li, W. Hu, T. Yan, X. Guan, G. Li, J. Phys. Chem. C 114 (2010) 15298– 15305. [2] K.O. Iwua, A. Galeckas, P. Rauwel, A.Y. Kuznetsov, T. Norby, J Solid State Chem. 185 (2012) 245–252. [3] R. Manigandan, K. Giribabu, R. Suresh, L. Vijayalakshmi, A. Stephen, V. Narayanan, Mater. Res. Bull. 48 (2013) 4210–4215. [4] K. Giribabu, R. Suresh, R. Manigandan, E. Thirumal, A. Stephen, V. Narayanan, J. Mater. Sci.: Mater. Electron. 24 (2013) 1888–1894. [5] K. Giribabu, R. Suesh, R. Manigandan, A. Stephen, V. Narayanan, J. Iran. Chem. Soc. 10 (2013) 771–776. [6] Z. Hou, C. Li, J. Yang, H. Lian, P. Yang, R. Chai, Z. Cheng, J. Lin, J. Mater. Chem. 19 (2009) 2737–2746. [7] S. Saranya, S.T. Senthilkumar, K. Vijaya Sankar, R. Kalai Selvan, J. Electroceram. 28 (2012) 220–225. [8] M.A.P. Almeida, L.S. Cavalcante, M. Siu Li, J.A. Varela, E. Longo, J. Inorg. Organomet. Polym. 22 (2012) 264–271. [9] W. Wu, W. Qin, Y. He, Y. Wu, T. Wu, J. Exp. Nanosci. 7 (2012) 390–398. [10] E. Zhang, Z. Xing, J. Wang, Z. Ju, Y. Qian, RSC Adv. 2 (2012) 6748–6751. [11] S.J. Chen, X.T. Chen, Z. Xue, J.H. Zhou, J. Li, J.M. Hong, X.Z. You, J. Mater. Chem. 13 (2003) 1132–1135. [12] H.W. Shim, I.S. Cho, K.S. Hong, A.H. Lim, D.W. Kim, J. Phys. Chem. C 115 (2011) 16228–16233.
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609 [13] L.H. Hoang, N.T.M. Hien, W.S. Choi, Y.S. Lee, K. Taniguchi, T. Arima, S. Yoon, X.B. Chen, I.S. Yang, J. Raman Spectrosc. 41 (2010) 1005–1010. [14] C. Zhang, D. Guo, C. Hu, Y. Chen, H. Liu, H. Zhang, X. Wang, Phys. Rev. B 87 (2013) 035416. [15] Siti Murni M. Zawawi, Rosiyah Yahya, Aziz Hassan, H.N.M. Ekramul Mahmud, Mohammad Noh Daud, Chem. Central J. 7 (2013) 80. [16] P. Parhi, T.N. Karthik, V. Manivannan, J. Alloys Comp. 465 (2008) 380–386. [17] Kisla P.F. Siqueira, A. Dias, J. Nanopart. Res 13 (2011) 5927–5933. [18] S. Lei, K. Tang, Z. Fang, Y. Huang, H. Zheng, Nanotechnology 16 (2005) 2407– 2411. [19] L. Yang, Y. Wang, Y. Wang, X. Wang, L. Wang, G. Han, J. Alloys Comp. 578 (2013) 215–219. [20] W.C. Oh, J.G. Choi, C.Y. Park, C.S. Lim, J. Ceram. Process. Res. 12 (2011) 433– 436. [21] S.M. Pourmortazavi, M.R. Nasrabadi, M.K. Shalamzari, M.M. Zahedi, S.S. Hajimirsadeghi, I. Omrani, Appl. Surf. Sci. 263 (2012) 745–752. [22] L. Pan, L. Li, Y. Chen, J. Sol–Gel Sci. Technol. 66 (2013) 330–336. [23] D. Zielinska, L. Nagels, M.K. Piskuła, Anal. Chim. Acta 617 (2008) 22–31. [24] A.M.O. Brett, M.E. Ghica, Electroanalysis 15 (2003) 1745–1750. [25] W. Tong, L. Li, W. Hu, T. Yan, X. Guan, G. Li, J. Phys. Chem. C. 114 (2010) 15298– 15305. [26] M. Zheng, H. Zhang, X. Gong, R. Xu, Y. Xiao, H. Dong, X. Liu, Y. Liu, Nanoscale Res. Lett. 8 (2013) 166–173. [27] S. Thongtem, S. Wannapop1, T. Thongtem, Trans. Nonferrous Met. Soc. China 19 (2009) 100–104. [28] C. Xiao, J. Chen, B. Liu, X. Chu, L. Wu, S. Yao, Phys. Chem. Chem. Phys. 13 (2011) 1568–1574. [29] L.H. Hoang, N.T.M. Hien, W.S. Choi, Y.S. Lee, K. Taniguchi, T. Arima, S. Yoon, X.B. Chen, I. Yang, J. Raman Spectrosc. 41 (2010) 1005–1010. [30] X.X. Zou, G.D. Li, P.P. Wang, J. Su, J. Zhao, L.J. Zhou, Y.N. Wanga, J.S. Chen, Dalton Trans. 41 (2012) 9773–9780.
609
[31] M. Maczka, M. Ptak, K. Pereira da Silva, P.T.C. Freire, J. Hanuza, J. Phys. Condens. Matter 24 (2012) 345403–345410. [32] J.E. Flores-Mena, J. Dıaz-Reyes, J.A. Balderas-Lopez, Rev. Mex. Fis. 58 (2012) 504–509. [33] Ptaka, M. Maczkaa, K. Hermanowicza, A. Pikula, J. Hanuz, Spectrochim. Acta, Part A 86 (2012) 85–92. [34] A. Nogami, T. Suzuki, T. Katsufuji, J. Phys. Soc. Jpn. 77 (2008) 115001–115003. [35] P.V. Hanh, L.H. Hoang, P.V. Hai, N.V. Minh, X.B. Chen, I.S. Yang, J. Phys. Chem. Solids 74 (2013) 426–430. [36] A.K. Chakraborty, S. Ganguli, M.A. Kebede, J. Cluster Sci. 23 (2012) 437–448. [37] M.A.P. Almeida, L.S. Cavalcante, J.A. Varela, M. Siu Li, E. Longo, Adv. Powder Technol. 23 (2012) 124–128. [38] T.D. Nguyen, D. Mrabet, T.T.D. Vu, C.T. Dinh, T.O. Do, Cryst. Eng. Commun. 13 (2011) 1450–1460. [39] L. Huang, H. Xu, Y. Li, H. Li, X. Cheng, J. Xia, Y. Xu, G. Cai, Dalton Trans. 42 (2013) 8606–8616. [40] L.M. Bertus, C. Faure, A. Danine, C. Labrugere, G. Campet, A. Rougier, A. Duta, Mater. Chem. Phys. 140 (2013) 49–59. [41] X. Xie, W. Liu, L. Zhao, C. Huang, J. Solid State Electrochem. 14 (2010) 1585– 1594. [42] E. Rauwel, A. Galeckas, P. Rauwel, H. Fjellvåg, Adv. Funct. Mater. 22 (2012) 1174–1179. [43] I. Djerdj, G. Garnweitner, D. Arcon, M. Pregelj, Z. Jaglicic, M. Niederberger, J. Mater. Chem. 18 (2008) 5208–5217. [44] R. Sokolova, S. Ramesova, I. Degano, M. Hromadova, M. Ga, J. Zabka, Chem. Commun. 48 (2012) 3433–3435. [45] K. Reddaiah, T. Madhusudana Reddy, P. Raghu, B.E. Kumaraswamy, Anal. Bioanal. Electrochem. 4 (2012) 122–134. [46] B. Pierozynski, D. Zielinska, Croat. Chem. Acta. 83 (2010) 127–133.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
MnWO4 nanocapsules: Synthesis, characterization and its electrochemical sensing property Selvamani Muthamizh, Ranganathan Suresh, Krishnamoorthy Giribabu, Ramadoss Manigandan, Sivakumar Praveen Kumar, Settu Munusamy, Vengidusamy Narayanan ⇑ Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
a r t i c l e
i n f o
Article history: Received 12 May 2014 Received in revised form 13 August 2014 Accepted 7 September 2014 Available online 16 September 2014 Keywords: MnWO4 Electrochemical detection Quercetin Nanocapsule
a b s t r a c t Manganese tungstate (MnWO4) was synthesized by surfactant free precipitation method. MnWO4 was characterized by using various spectroscopic techniques. The phase, crystalline nature and the morphological analysis were carried out using XRD, scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HR-TEM). Further, FT-IR, Raman, and DRS-UV–Vis spectral analysis were carried out in order to ascertain the optical property and the presence of functional groups. From the analysis, the morphology of the MnWO4 was observed to be in capsules with breadth and thickness were in nm range. The oxidation state of tungsten (W), and manganese (Mn) were investigated using Xray photo electron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR). The synthesized MnWO4 nanocapsules were used to modify glassy carbon electrode (GCE) to detect quercetin. Ó 2014 Published by Elsevier B.V.
1. Introduction In recent years, much research has been focused on the synthesis of nanomaterials in variety of architectures such as nanoparticle, nanorods, nanobars, nanosheets, nanoplatelets and nanotubes, because of their unique physical and optical properties [1–6]. MWO4 (M = divalent transition metal ions) type compounds have much scientific interest in recent times because of their intriguing properties like electrical and electrochemical property, photoluminescence, photocatalyst, energy storage capacity, and humidity sensing ability [7–11]. In particular, MnWO4 has attracted attention because of its wide application in many fields such as electrocatalyst, photocatalyst and battery application. Metal tungstates exists in two different crystal structures namely scheelite and wolframite. Bivalent metal ions with large ionic radius such as Ca2+, Sr2+, Ba2+ and Pb2+ prefer to form scheelite type structures whereas metal ions with smaller ionic radius like Zn2+, Mn2+, Co2+, Ni2+ and Cd2+ tend to crystallize in wolframite type of structure [12–16]. Among this MnWO4 has a monoclinic type structure having space group of P2/C. Several methods have been reported for the synthesis of MnWO4 such as microwave synthesis [17], surfactant assisted complexation–precipitation method [18], hydrothermal synthesis [19], solvothermal route [11] and solid ⇑ Corresponding author. E-mail address: [email protected] (V. Narayanan). http://dx.doi.org/10.1016/j.jallcom.2014.09.049 0925-8388/Ó 2014 Published by Elsevier B.V.
state synthesis [20]. The direct precipitation method has been used for the synthesis of MnWO4 at room temperature [21]. The electrochemical activity of manganese tungstate for energy storage purpose and the detection of hydrogen peroxide, and nitrophenol was reported [10,22]. Flavonoids are important in human diet because of its positive effects on human. Among flavonoids, quercetin is one of the naturally occurring, which is from our daily diet. Quercetin possesses many beneficial effects on human health, including cardiovascular protection, anti-ulcer effects, anti-allergy activity, cataract prevention, antiviral activity, and anti-inflammatory effects, antioxidant, estrogenic activity, and anticancer activity [23]. The beneficial effects of quercetin on human health is due to its polyphenolic nature with radical-scavenging activity and metalchelating properties. Structure of flavonoids consist of 15-carbon skeleton arranged in a C6–C3–C6 configuration, among that two are phenyl rings and one is a heterocyclic ring [24]. The IUPAC name of quercetin is 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy4H-chromen-4-one and the corresponding chemical structure is shown in Fig. 1. Because of all these beneficial effects it has been used in medicine. Though quercetin has beneficial effects as its concentration level increased it may lead to adverse effect such as headache and kidney failure. Hence, it becomes important to determine the levels of quercetin. The determination of quercetin based on modified electrode is very rare. The present work deals with a facile MnWO4 based approach for electrochemical detection of the quercetin. MnWO4 was
602
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
3. Result and discussion 3.1. X-ray diffraction study
Fig. 1. Structure of quercetin.
synthesized chemically by direct precipitation method. The prepared MnWO4 were characterized by XRD, FTIR, DRS-UV, Raman, SEM, HR-TEM, EPR and XPS. The electrochemical determination of quercetin was carried out using cyclic voltammetry (CV) and chronoamperometry (CA). 2. Experimental details 2.1. Materials All the chemicals used in the synthesis such as manganese chloride (MnCl24H2O), hydrated sodium tungstate (Na2WO42H2O) were analytical grade reagents purchased from Qualigens and Merck respectively. All the chemicals were used without further purification. Quercetin was purchased from Sigma Aldrich, double distilled water and ethanol was used as solvent.
XRD pattern of the synthesized MnWO4 was shown in Fig. 2. All the diffraction peaks were indexed to the monoclinic structure of MnWO4 with space group p2/c of JCPDS Card No 01-080-0152. It shows the peaks at 2h:15.5, 18.5, 23.6, 24.1, 30.0, 30.4, 31.1, 36.1, 37.3, 40.3, 40.9, 48.3, 49.3, 51.2, 52.5, and 53.1 corresponds to (0 1 0), (1 0 0), (0 1 1), (1 1 0), (1 1 1), (1 1 1), (0 2 0), (0 2 1), (2 0 0), (0 2 1), (2 0 0), (1 0 2), (1 0 2), (0 2 2), (2 0 0), (1 2 2), (2 0 2), and (2 2 1) planes of monoclinic MnWO4 respectively. The lattice parameters of the MnWO4 are a = 4.815 Å, b = 5.706 Å, c = 4.992 Å, and b = 91.04°. The strong diffraction peaks of synthesized MnWO4 revels that the synthesized sample is high crystalline in nature. No other impurity peaks were detected. 3.2. FT-IR analysis FT-IR spectrum of the synthesized MnWO4 is shown in Fig. 3. A broad band observed at 3436 cm1 is indicative of vibration of O–H bond of the surface hydration. The band at 1637 cm1 corresponds to the H–O–H deformation vibration of surface hydroxyl group. The absorption peaks located at 871 cm1 and 829 cm1 corresponds to symmetric and asymmetric stretching vibration mode of the W–O bond in terminal WO2 group of MnWO4 [25]. The strong band at 706 cm1 is the asymmetrical stretching vibrations of W–O bond in the (W2O4)n chain and 620 cm1 indicates the presence of stretching vibration of Mn–O bond. The band at
2.2. Synthesis of MnWO4 nanocapsules MnWO4 nanocapsules was prepared by direct precipitation method without using any surfactant. The procedure is as follows: 2.474 g of MnCl24H2O (12.5 mmol) and 4.123 g of Na2WO42H2O (12.5 mmol) each were dissolved separately in 25 mL of double distilled water. Then the Mn2+ solution was added dropwise to the WO2 4 solution under magnetic stirring at room temperature. After the addition process manganese tungstate was precipitated which was filtered and washed 3–4 times using distilled water in order to remove the unreacted starting materials. The precipitate was washed with ethanol and allowed to dry in room temperature for two days. The as-synthesized MnWO4 were calcined at 600 °C for 5 h in a muffle furnace. 2.3. Characterization The XRD pattern of the synthesized sample was analyzed by using Rich Siefert 3000 diffractometer with Cu Ka1 radiation (k = 1.5406 Å). FT-IR spectrum was recorded using a Perkin–Elmer FT-IR spectrophotometer. The sample was analyzed using potassium bromide pellet technique in the range 4000–400 cm1. Raman spectrum was recorded using laser Raman microscope, Raman-11 Nano photon Corporation, Japan. DRS UV–Vis absorption spectrum was recorded using Perkin– Elmer lambda 650 spectrophotometer. The morphology of synthesized MnWO4 was analyzed by HITACHI SU6600 scanning electron microscopy (SEM) coupled with EDAX. The shape and average size of nanocapsule was observed by means of FEI, TECHNAI G2, 30 S-twin D905 high resolution transmission electron microscopy (HR-TEM). XPS measurement was performed by Omicron nanotechnology-ESCA-14, Germany. EPR spectrum was recorded using Bruker X-band Electron Paramagnetic Spectrometer, at an operating frequency of 9.4 GHz. All electrochemical measurements were carried out using a CHI 1103A electrochemical workstation with a conventional three electrode cell. A bare GCE (glassy carbon electrode) and MnWO4/ GCE used as the working electrode. A saturated calomel electrode (SCE) and a platinum wire were used as the reference electrode and counter electrode respectively.
Fig. 2. XRD pattern of MnWO4.
2.4. Fabrication of MnWO4/GCE The GCE was modified with MnWO4, before that the working electrode was mechanically polished with 1 lm, 0.3 lm and 0.05 lm alumina pastes for mirror finishing. Then it was subjected to ultrasonication in double distilled water for few minutes in order to clean the surface of GCE. The MnWO4 suspension was prepared by dispersing 5 mg of MnWO4 in 10 mL of ethanol during 20 min of ultrasonic agitation then the GCE was coated with 10 lL of the suspension by drop coating method and dried in air.
Fig. 3. FT-IR spectrum of MnWO4.
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
603
lational levels. A very strong band appeared at the region of 878 cm1 corresponds to the strong symmetric stretching of WO2 group in the MnWO4. The bands at 768, 691 cm1 indicates the presence of weak asymmetric and symmetric stretching vibration mode of W–O–W bond [27]. The peak at 533 cm1 is attributed due to stretching vibration of Mn–O [28]. The band at 394 cm1 indicates the presence of symmetric stretching of W–O–W [29]. The band at 320 cm1 confirms the medium scissoring of both WO2 and W–O–W [30]. A weak band appeared at 290, 253 cm1 indicates the bending mode of [WO6]6 and twisting mode of WO2 group [31,32]. The bands at 160, 123, 87 cm1 were the translational mode of tungsten [33]. 3.4. Optical property of MnWO4
Fig. 4. Raman spectrum of MnWO4.
515 cm1 was observed due to the presence of stretching vibration of Mn–O–Mn bond [26].
3.3. Raman analysis
The optical property of synthesized MnWO4 was analyzed using DRS-UV spectroscopy and the corresponding spectrum is shown in Fig. 5(a). The strong absorption peak at 380 nm are due to the transition between bands of O 2p level and Mn 3d level in MnWO4 and weak band at 563 nm due to the spin-forbidden transition between the eg and t2g orbital of Mn 2p [34]. The observed peaks are similar to reported value of Van Hanh et al. [35]. The band gap value Eg of synthesized MnWO4 was determined by using Tauc’s plot. 1=n
Raman spectrum of synthesized MnWO4 is shown in Fig. 4. The observed bands corresponds to symmetric, asymmetric-stretching, bending, scissoring, twisting and translational modes for the synthesized MnWO4. The bands observed for MnWO4 were 878, 768, 691, 533, 394, 320, 290, 253, 200, 160, 123 and 90 cm1; which are obtained from different modes of absorption of different trans-
ðhtaÞ
¼ Aðht Eg Þ
where h – Planck’s constant, t – frequency of vibration, a – absorption coefficient, Eg – band gap, A – proportional constant. n = 2 (for direct band gap), or n = 1/2 (for indirect band gap). The synthesized MnWO4 showed both direct band gap of 2.67 eV and indirect band gap of 2.5 eV values which is shown in Fig. 5(b and c) [36,37].
Fig. 5. (a) DRS-UV visible spectrum of MnWO4; (b) direct band gap and (c) indirect band gap.
604
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
Fig. 6. (a) SEM images of MnWO4 and (b) EDAX spectrum of MnWO4.
Scheme 1. Formation mechanism of MnWO4 nanocapsule.
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
Fig. 7. HR-TEM images of MnWO4.
Fig. 8. (a) SAED pattern of MnWO4; (b) and (c) fringes pattern of MnWO4.
605
606
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
Fig. 9. (a) XPS survey spectrum of MnWO4 nanocapsule; (b) XPS spectrum of Mn in MnWO4 nanocapsule; (c) XPS spectrum of W in MnWO4 nanocapsule and (d) XPS spectrum of O in MnWO4 nanocapsule.
Table 1 Atomic % of elements present in MnWO4. Element
Mn
W
O
Atomic %
16.1
14.9
69.9
Fig. 11. Cyclic voltammograms of (a) bare GCE and (b) MnWO4/GCE in pH 7 at scan rate of 50 mV s1.
Fig. 10. EPR spectrum of Mn2+ in MnWO4.
3.5. Morphological analysis Fig. 6(a) shows the SEM image of MnWO4. SEM images clearly revels that the synthesized MnWO4 were in capsule like morphology. The corresponding EDAX spectrum (Fig. 6(b)) confirms the
presence of Mn, W, and O as expected and no other impurities were observed. The possible formation mechanism and the pictorial representation are shown in Scheme 1. HR-TEM analysis was further carried out in order to confirm the crystallinity, and morphology of MnWO4. HR-TEM images of MnWO4 nanoparticles are shown in Fig. 7. It can be seen that the MnWO4 nanocapsules are having the width of 177 nm and thickness of 100 nm. Selected area electron diffraction pattern (SAED) (Fig. 8(a)), clearly indicates that the MnWO4 nanocapsule were highly crystalline in nature as observed from XRD analysis. Fringe pattern (Fig. 8(b)) taken on an individual nanocapsule shows the crystalline nature of the
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
607
MnWO4 and the spacing between two adjacent lattice fringes was found to be 0.317 Å, corresponding to the (1 1 1) plane of the monoclinic MnWO4, it is well matched with XRD plane indexing of MnWO4. 3.6. XPS analysis XPS analysis was carried out for the MnWO4 nanocapsules in order to confirm the chemical composition, binding energy and oxidation states of the elements present in MnWO4. Fig. 9(a) shows the survey XPS spectrum of MnWO4. It shows the presence of Mn, W, and O in the synthesized MnWO4.This result is consistent with EDAX analysis. High-resolution XPS spectra of Mn 2p and W 4f of synthesized MnWO4 nanocapsule are discussed below. Fig. 9(b) shows the XPS spectrum of Mn 2p, two peaks are observed that corresponds to Mn 2p3/2 and Mn 2p1/2 at 640.8 eV and 658.0 eV, respectively. It reveals that Mn present in the sample is in +2 oxidation state [38]. XPS spectrum of W 4f was shown in Fig. 9(c). It has two peaks which corresponds to W 4f7/2 and W 4f5/2 at 34.7 and 36.9 eV respectively. The W 4f7/2 and W 4f5/2 spin–orbit doublets was observed to be 2.2 eV, which can be assigned to the oxidation state of W as +6 [39]. The O 1s peak shows a dominant component centered with low binding energy at 530.05 eV, which corresponds to the O2 forming oxide with manganese and tungsten elements (Mn–O–W) as shown in Fig. 9(d). Peak located at 533.2 eV corresponds to water bound at the surface of the samples, peak at 528 eV is due to the presence of O–Mn–O bond in MnWO4 [40,41]. By referring Rauwel et al. atomic % of the elements present in MnWO4 is calculated from the high resolution XPS spectrum (Table 1) and it shows an approximately equal amount of Mn and W elements and O with an error bar the corresponding values are given in Table 1 [42]. 3.6.1. EPR analysis EPR analysis was carried out in order to confirm the oxidation state of Mn ion present in MnWO4. Fig. 10 shows the curve that corresponds to a signal produced due to the presence of ferromagnetic Mn2+ ions. The observed EPR signal was justified by the g factor, that is
g ¼ ht=bH where g is a parameter describing the interaction of the paramagnetic center with the external magnetic field, his the Planck’s constant, t is the microwave frequency, b is the Bohr Magneton and H is the intensity of the resonance magnetic field. The value of g was found to be 2.0028 which is typical of octahedral environment of Mn2+. From both XPS and EPR analysis the oxidation state of Mn present in MnWO4 was found to be Mn2+ [43].
Fig. 12. Cyclic voltammograms of MnWO4/GCE at different pH values vs. scan rate at 50 mV s1. Inset shows the linear plot of anodic potential vs. pH.
3.7.2. pH effect on the detection of quercetin The effect of pH on the oxidation of 0.1 mM quercetin at the MnWO4/GCE was evaluated using cyclic voltammetry in the pH range of 3–10. The obtained cyclic voltammograms were shown in Fig. 12. From Fig. 12, we have observed that as the pH increases the voltammetric peaks become broader with the peak current decreased from 3.9 lA to 2.0 lA. At pH 3, the anodic peak potential was observed at 420 mV, as the pH increases to 10 the peak potential was observed to be 20 mV. When comparing the peak potential at different pH, we observed a gradual decrease up to the pH 7 and beyond pH 7 there is decrement in peak potential along with drastic decrease in peak current. Based on the above observations, pH value for the sensing experiments was fixed at pH 7. Hence, pH 7 was chosen for the subsequent analysis. The anodic potential (Epa) of quercetin decreases linearly (Fig. 12 inset) with a linear regression equation Epa (V) = 0.059 pH + 0.6051 (R2 = 0.9915) close to that given by the Nernst equation, indicating the equal number of electrons and protons involved in the electrooxidation process of quercetin [45]. According to the Nernst equation, Epa = E [(2.303mRT)/(nF)] pH, the ratio of m/n was found to be 1, where m denotes the number of protons intervening in the oxidation process, n denotes the number of electrons transferred, and R, T and F have their usual meanings. The proton transfer number can be calculated when the electron transfer number is known. 3.7.3. Effect of scan rate The effect of scan rate on the electrooxidation of 0.1 mmol quercetin was carried out. The dependency of electrooxidation of
3.7. Electrochemical sensing 3.7.1. Cyclic voltammetry Cyclic voltammetric responses of bare GCE (a) and MnWO4/GCE (b) towards quercetin was investigated in phosphate buffer (Na2HPO4 + NaH2PO4, pH 7) at the scan rate of 50 mV s1 (Fig. 11). From the observed cyclic voltammograms it is clear that at GCE, quercetin is oxidized at 168 mV with the anodic peak current of 3.5 lA and MnWO4/GCE detects the quercetin with higher current response at 4.1 lA with a lower peak potential of 153 mV [44]. From this observation, it can be seen that MnWO4/GCE shows enhanced electrochemical sensing property than the bare GCE. The enhanced electrochemical activity is mainly due to the presence of surface hydroxyl group, smaller crystallite size, and due to the metal ion. Thus the MnWO4/GCE can be utilized for the detection of quercetin at lower potential.
Fig. 13. Cyclic voltammograms of MnWO4/GCE in phosphate buffer (pH 7) at scan rate from 10 to 500 mV s1; Inset shows the log (ipa) vs. log (t) plot.
608
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609
quercetin with different scan rates was investigated to study the electrode kinetics for the oxidation of quercetin. From Fig. 13, we observed that as the scan rate increases the peak current of quercetin also increased. To find out the electrode reaction whether diffusion process or surface confined process, a double logarithmic plot was plotted. From (Fig. 13 inset) it is observed that the slope was found to be 0.74 which shows that the electrode reaction is adsorption controlled (surface confined) process. 3.7.4. Number of electron and proton transfer in the electrochemical oxidation of quercetin The number of electrons transferred in the electrochemical oxidation process of quercetin at the MnWO4/GCE can be calculated by using the following equation
ip ¼ nFQ t=4RT where n = number of electron, ip = anodic peak current, R = gas constant, T = temperature (K), F = Faraday constant, Q = charge, t = scan rate. By using the above equation the value of n was found to be 3. The ratio of m/n = 1. Accordingly, the proton transfer number was calculated to be 3. From this, we can conclude that the electrooxidation of quercetin at the MnWO4/GCE involves a three electron and three proton process. The calculated number of electrons and protons involved in the oxidation of quercetin clearly indicates the formation of quinone by the mechanism given in Fig. 14 [46]. 3.7.5. Chronoamperometry Chronoamperometry was carried out to examine linear range and sensitivity of MnWO4/GCE towards 0.1 mM quercetin on successive addition of 50 lL. The obtained result is shown in Fig. 15, a successive addition of quercetin produce a significant increases in quercetin oxidation peak current. The linear range was found
Fig. 15. Chronoamperometric response of MnWO4 for the successive addition 50 lL of 0.1 mM quercetin to 40 mL of pH 7; Inset shows the plot of current vs. concentration of quercetin at an applied potential of 0.17 V.
to be 16.7 106–74.4 106 M and the linear regression equation was Ipa (lA) = 0.003[Q] (lA) + 0.032 (R2 = 0.9915). 4. Conclusion A direct precipitation method was successfully employed to prepare crystalline MnWO4 nanocapsules. The synthesized MnWO4 were analyzed by XRD, FT-IR, DRS-UV, Raman, XPS, SEM and HR-TEM. The synthesized sample was modified on the GCE and used for the detection of quercetin. MnWO4/GCE was sensitive towards quercetin. The electrocatalytic activity towards the detection of quercetin by MnWO4/GCE comparatively higher than bare GCE, there is not only increases in peak current but the corresponding peak potential also decreased. Therefore from the above results MnWO4 has an ability towards the detection of quercetin electrochemically. Acknowledgments One of the authors (S. Muthamizh) wish to thank the UGC-UPEPhase II, University of Madras, for the financial assistance. We acknowledge Central Leather Research Institute (CLRI) for EPR measurement and the National Centre for Nanoscience and Nanotechnology, University of Madras for providing instrumentation facility. References
Fig. 14. Electrooxidation mechanism of quercetin.
[1] W. Tong, L. Li, W. Hu, T. Yan, X. Guan, G. Li, J. Phys. Chem. C 114 (2010) 15298– 15305. [2] K.O. Iwua, A. Galeckas, P. Rauwel, A.Y. Kuznetsov, T. Norby, J Solid State Chem. 185 (2012) 245–252. [3] R. Manigandan, K. Giribabu, R. Suresh, L. Vijayalakshmi, A. Stephen, V. Narayanan, Mater. Res. Bull. 48 (2013) 4210–4215. [4] K. Giribabu, R. Suresh, R. Manigandan, E. Thirumal, A. Stephen, V. Narayanan, J. Mater. Sci.: Mater. Electron. 24 (2013) 1888–1894. [5] K. Giribabu, R. Suesh, R. Manigandan, A. Stephen, V. Narayanan, J. Iran. Chem. Soc. 10 (2013) 771–776. [6] Z. Hou, C. Li, J. Yang, H. Lian, P. Yang, R. Chai, Z. Cheng, J. Lin, J. Mater. Chem. 19 (2009) 2737–2746. [7] S. Saranya, S.T. Senthilkumar, K. Vijaya Sankar, R. Kalai Selvan, J. Electroceram. 28 (2012) 220–225. [8] M.A.P. Almeida, L.S. Cavalcante, M. Siu Li, J.A. Varela, E. Longo, J. Inorg. Organomet. Polym. 22 (2012) 264–271. [9] W. Wu, W. Qin, Y. He, Y. Wu, T. Wu, J. Exp. Nanosci. 7 (2012) 390–398. [10] E. Zhang, Z. Xing, J. Wang, Z. Ju, Y. Qian, RSC Adv. 2 (2012) 6748–6751. [11] S.J. Chen, X.T. Chen, Z. Xue, J.H. Zhou, J. Li, J.M. Hong, X.Z. You, J. Mater. Chem. 13 (2003) 1132–1135. [12] H.W. Shim, I.S. Cho, K.S. Hong, A.H. Lim, D.W. Kim, J. Phys. Chem. C 115 (2011) 16228–16233.
S. Muthamizh et al. / Journal of Alloys and Compounds 619 (2015) 601–609 [13] L.H. Hoang, N.T.M. Hien, W.S. Choi, Y.S. Lee, K. Taniguchi, T. Arima, S. Yoon, X.B. Chen, I.S. Yang, J. Raman Spectrosc. 41 (2010) 1005–1010. [14] C. Zhang, D. Guo, C. Hu, Y. Chen, H. Liu, H. Zhang, X. Wang, Phys. Rev. B 87 (2013) 035416. [15] Siti Murni M. Zawawi, Rosiyah Yahya, Aziz Hassan, H.N.M. Ekramul Mahmud, Mohammad Noh Daud, Chem. Central J. 7 (2013) 80. [16] P. Parhi, T.N. Karthik, V. Manivannan, J. Alloys Comp. 465 (2008) 380–386. [17] Kisla P.F. Siqueira, A. Dias, J. Nanopart. Res 13 (2011) 5927–5933. [18] S. Lei, K. Tang, Z. Fang, Y. Huang, H. Zheng, Nanotechnology 16 (2005) 2407– 2411. [19] L. Yang, Y. Wang, Y. Wang, X. Wang, L. Wang, G. Han, J. Alloys Comp. 578 (2013) 215–219. [20] W.C. Oh, J.G. Choi, C.Y. Park, C.S. Lim, J. Ceram. Process. Res. 12 (2011) 433– 436. [21] S.M. Pourmortazavi, M.R. Nasrabadi, M.K. Shalamzari, M.M. Zahedi, S.S. Hajimirsadeghi, I. Omrani, Appl. Surf. Sci. 263 (2012) 745–752. [22] L. Pan, L. Li, Y. Chen, J. Sol–Gel Sci. Technol. 66 (2013) 330–336. [23] D. Zielinska, L. Nagels, M.K. Piskuła, Anal. Chim. Acta 617 (2008) 22–31. [24] A.M.O. Brett, M.E. Ghica, Electroanalysis 15 (2003) 1745–1750. [25] W. Tong, L. Li, W. Hu, T. Yan, X. Guan, G. Li, J. Phys. Chem. C. 114 (2010) 15298– 15305. [26] M. Zheng, H. Zhang, X. Gong, R. Xu, Y. Xiao, H. Dong, X. Liu, Y. Liu, Nanoscale Res. Lett. 8 (2013) 166–173. [27] S. Thongtem, S. Wannapop1, T. Thongtem, Trans. Nonferrous Met. Soc. China 19 (2009) 100–104. [28] C. Xiao, J. Chen, B. Liu, X. Chu, L. Wu, S. Yao, Phys. Chem. Chem. Phys. 13 (2011) 1568–1574. [29] L.H. Hoang, N.T.M. Hien, W.S. Choi, Y.S. Lee, K. Taniguchi, T. Arima, S. Yoon, X.B. Chen, I. Yang, J. Raman Spectrosc. 41 (2010) 1005–1010. [30] X.X. Zou, G.D. Li, P.P. Wang, J. Su, J. Zhao, L.J. Zhou, Y.N. Wanga, J.S. Chen, Dalton Trans. 41 (2012) 9773–9780.
609
[31] M. Maczka, M. Ptak, K. Pereira da Silva, P.T.C. Freire, J. Hanuza, J. Phys. Condens. Matter 24 (2012) 345403–345410. [32] J.E. Flores-Mena, J. Dıaz-Reyes, J.A. Balderas-Lopez, Rev. Mex. Fis. 58 (2012) 504–509. [33] Ptaka, M. Maczkaa, K. Hermanowicza, A. Pikula, J. Hanuz, Spectrochim. Acta, Part A 86 (2012) 85–92. [34] A. Nogami, T. Suzuki, T. Katsufuji, J. Phys. Soc. Jpn. 77 (2008) 115001–115003. [35] P.V. Hanh, L.H. Hoang, P.V. Hai, N.V. Minh, X.B. Chen, I.S. Yang, J. Phys. Chem. Solids 74 (2013) 426–430. [36] A.K. Chakraborty, S. Ganguli, M.A. Kebede, J. Cluster Sci. 23 (2012) 437–448. [37] M.A.P. Almeida, L.S. Cavalcante, J.A. Varela, M. Siu Li, E. Longo, Adv. Powder Technol. 23 (2012) 124–128. [38] T.D. Nguyen, D. Mrabet, T.T.D. Vu, C.T. Dinh, T.O. Do, Cryst. Eng. Commun. 13 (2011) 1450–1460. [39] L. Huang, H. Xu, Y. Li, H. Li, X. Cheng, J. Xia, Y. Xu, G. Cai, Dalton Trans. 42 (2013) 8606–8616. [40] L.M. Bertus, C. Faure, A. Danine, C. Labrugere, G. Campet, A. Rougier, A. Duta, Mater. Chem. Phys. 140 (2013) 49–59. [41] X. Xie, W. Liu, L. Zhao, C. Huang, J. Solid State Electrochem. 14 (2010) 1585– 1594. [42] E. Rauwel, A. Galeckas, P. Rauwel, H. Fjellvåg, Adv. Funct. Mater. 22 (2012) 1174–1179. [43] I. Djerdj, G. Garnweitner, D. Arcon, M. Pregelj, Z. Jaglicic, M. Niederberger, J. Mater. Chem. 18 (2008) 5208–5217. [44] R. Sokolova, S. Ramesova, I. Degano, M. Hromadova, M. Ga, J. Zabka, Chem. Commun. 48 (2012) 3433–3435. [45] K. Reddaiah, T. Madhusudana Reddy, P. Raghu, B.E. Kumaraswamy, Anal. Bioanal. Electrochem. 4 (2012) 122–134. [46] B. Pierozynski, D. Zielinska, Croat. Chem. Acta. 83 (2010) 127–133.