Green Mediated Synthesis of MgO Nano-Flakes and Its Electro-Chemical Applications

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ScienceDirect Materials Today: Proceedings 5 (2018) 22275–22282

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ICASE_2017

Green Mediated Synthesis of MgO Nano-Flakes and Its ElectroChemical Applications N.B. Arun Kumara, Mahendra. Ba, J Sirajudeeenb, M.R. Anil Kumara, H.P. Nagaswarupaa*, C.R. Ravi Kumara, B. UmeshC a

Research Center, Department of Science, East West Institute of Technology, Bangalore 560 091, India. b Department of Chemistry, Jamal Mohamed College (Autonomus), Tiruchirapalli- 620020, India. c. Department of Humanities, PVP Polytechnic, Dr. AIT Campus, Bangalore 560 056, India.

Abstract MgO nano flakes were synthesized by a green mediated route using Vetiver (Chrysopogonzizanioides) grass as a fuel. The obtained products were characterized by powder X-ray diffraction (PXRD), diffuse reflectance spectroscopy (DRS) Scanning electron microscope (SEM), Travelling Electron Microscope (TEM) and Fourier transform infrared spectroscopy (FTIR). PXRD patterns show singlecubic phase MgO matched with JCPDS card No. 4-829 with the crystallite size was found to be ~ 20-25 nm. SEM result reveals flakes and agglomerated nanoparticles. The optical energy gap was 4.50eV which demonstrates that there is a movement to the higher wavelengths of the absorption edge with reduction of the energy gap when using green fuel for synthesis.The electrochemical properties of MgO havebeen investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements using a modified carbon paste electrode. Further, modified carbon paste electrodeis also found to exhibit higher capacitance and lower charge transfer resistance. These findings suggest that the synthesized electrode possess better electrochemical properties and thus can be recognized as apromising candidate for the battery electrode applications. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility ofInternational Conference on Advances in Science & Engineering ICASE - 2017. Keywords: MgO;PXRD;Cyclic voltammetry; electrochemical impedance spectroscopy.

* Corresponding author. Tel.: +91 9945406900; E-mail address:[email protected]

2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility ofInternational Conference on Advances in Science & Engineering ICASE - 2017.

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1. Introduction MgO is a typical wide energy band gap material attracts researchers because of its glorious stablephysical and chemical properties. MgO finds variety of applications in chemical change, waste matter treatment, additives in refractory, paint, medicament, antifungal and dye decolorization [1].Recently, lot of interest was targeted on the non-rare-earth hosts in an endeavour to cut back the high value of rare-earth for luminescence and photocatalysis. A series of complicated metal oxides, like ZnO, ZrO2, MgO, TiO2, CuOetc were ordinarily used as non-rare-earth host materials [2].Metal oxide nanostructures have attracted special attention in recent years because of their distinctive properties and potential applications in solar cells, photocatalysis, electro-optical devices, sensors, antimicrobial agents, light materials [3]. MgOpossess a sodium chloride structure (fcc) (space group-fm-3m-225) with Mg2+ ions occupy sites of octahedral among the ion closed packed structure. The Mg atoms were corner of the cube and corresponding by 8 equivalent neighbour O atoms. In this lattice, the symmetry of Mg sites within the cubic MgO structure was if possible D2d and Mg site has inversion symmetry. Its nanostructures were expected to possess novel properties superior to their bulk counterparts[4,5]. For the first time we report on preparation of MgO nano particles by a green combustion route using Vetiver plant powderas a fuel under low temperature. In the present work we are looking for electrochemical properties using CV and EIS analysis. 2. Synthesis of MgO nano powder by green route. MgO nano flakes (MNFs) was synthesized by green combustion route using Vetiver plant powderas a fuel. Small cut pieces of Vetiver plant was washed with distilled water and dried in an autoclave, then grinded into a fine powder using pestle and mortar. 1 gram of [Mg(NO3)2 .6H2O] (Sigma Aldrich) and 0.1gram of Vetiver plant powder was taken in a beaker and stirred well using magnetic stirrer for ~ 5-10 min. The mixture was placed in a pre-heated muffle furnace maintained at 400 ± 10 oC. The solution boiled resulting in a transparent gel. The gel then formed white foam, which expanded to fill the vessel. Thereafter, the reaction was initiated in the interior and a flame appeared on the surface of the foam and proceeded rapidly throughout the entire volume, leaving a white powder with an extremely porous structure. The reaction was self-propagating and able to sustain high temperature to form MNFs. The entire process was completed in less than 5 min. 3. Result and Discussion 3.1. PXRD analysis

MgO Vetiver palnt powder

Intensity (a.u)

(200)

(220)

(111)

30

40 50 2 theta (degrees)

60

70

Fig.1. PXRD patterns of MNF prepared by Vetiver plant powder

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Fig.1.show the PXRD patterns of MNFs synthesized by green combustion route. The powder prepared by solution combustion method show single cubic phase with lattice constant a = 4.212 Å of high purity of MNFs. All the X-ray diffraction peaks of the samples at 2θ, 36.58o (1 1 1), 42.63o(2 0 0), 62 o (2 2 0) were well matched with space group fm-3m (225) and JCPDS card No. 4-829 [5]. The average crystallite size (D) of prepared MNFsis calculated using Scherrer’s formula [7] and was found to be around 22 nm. = [where, K; constant, ; wavelength of X-rays, and ; FWHM]. 3.2. UV - Visible spectroscopy Theprepared MNFssample was analyzed by utilizing UV- visible spectroscopy. The diffused reflectance spectroscopy (DRS) is show in Fig.2. The diffuse reflectance thinks about assumes an essential part in assessing the optical energy gap, as the absorbance or reflectance or transmittance of light is credited to their electronic structures [8].

MgO (Vetiver Palnt powder) Eg=4.4 eV 80

Reflectance (%)

70

fR2

60

50

40 200

300

400

500

600

700

800

Wavelength (nm)

4.0

4.5

5.0

5.5

6.0

Energy gap (eV) Fig.2. DRS Spectraof MNFs (Inset Optical energy gap) prepared by Vetiver plant powder

The Kubelka-Munkfunction F(R) is for the most part connected to change over the diffused reflectance into equivalent absorption coefficient and utilized for examining the powder as given by below equation. The optical energy gap was calculated using Tauc relation as in equation there by giving direct band. The energy gap (4.50 eV)is less (Fig. 2) compared to the literature, may be due to the fuel used during the synthesis. This demonstrates that there is a movement to the higher wavelengths of the absorption edge with the reduction of the energy gap. ( )=

(1 − ) 2

where R is the reflectance, F(R) is Kubelka-Munk function. The optical energy gap was calculatedusing Tauc relation as in equation [6, 7]. F(R)h = A (h –Eg) n

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3.3. FTIR Studies FTIR spectrum of synthesized MNFs by green route wasshow in Fig.3. The absorption peak showing up at 3450 cm-1 of was ascribed to O-H stretching vibrations of adsorbed H2O particle. A higher measure of surface hydroxyl groups over green synthesized MgO.The recurrence band at 1650 cm-1 of green integrated MgO might be identified with amide I groups connected with proteins or vibrations because of -C=C- practical gatherings from heterocyclic mixes.The peak at 2350 cm-1 being credited to extending vibrations of C=O and extendingvibrations of NH2+ and NH3+ in proteins, The retention peak at 1490 and 1076 cm-1belongs to amines and -C-O-C-, for example, alkaloids and flavones. The main peak at ~ 460 cm-1 was because of the characteristic vibrational method of symmetric MgO6 octahedral of MNFs.The top at 890 cm-1 was ascribed to Mg-O-Mg interactions[9, 10]. 50

MgO Vetiver palnt powder 1076

Transmitance(%)

40

890 2350

30

1650

3450

20

1490

10

460

0 4000

3500

3000

2500

2000

1500

1000

absorbence Fig.3. FT-IR spectra of MNFsprepared by Vetiver plant powder

3.4. SEM Analysis

Fig.4. SEM image of MNFs prepared by Vetiver plant powder

500

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SEM was predominantly utilized to contemplate the composition, grain and surface components of powders. Fig.4show the SEM pictures of green routeMNFs having pours and agglomerated morphologies. SEM results revels that the powder was very poly crystalline in nature. Further, it was surely understood that, green burning combination response was impacted by metal–ligand complex development. For the most part, flamingreactions includes freedom of little amount of gas. The pores and voids might be formed due to the more gasses getting away out of the reaction mixture during burning [11]. 3.5. TEM Analysis

Fig.5. a) TEM image of MNFs prepared by Vetiver plant powder b) SAED

TEM studies revels the crystalline size of the MNFs.TEM picture and SAED patterns investigation of MNFs prepared by Vetiver plant powderwere show in Fig.5 (a-b). The picture demonstrated that the particles were spherical, very scattered and crystallite size was estimatedto be 20-25 nm. The SAED design gives the polycrystalline way of the nanopowders were identified by some bright spots and rings.The "d" spacing was calculated around 0.265 nm for the plane (200), which is near that of 0.269 nm for (200) plane of MgO [12]. 3.6. Cyclic voltammetric analysis Fig. 6 show the cyclic voltammogram of MNFs electrodein 6 M KOH electrolyte at various scan rates at the potential window of -0.8 to +1 V vs. Ag/AgCl.For MNFs electrode, one anodic oxidation peak and one cathodic reduction peak were noticed on the CV curves. The polarized current is low before the appearance of electrochemicalreaction because there are not free electrons in the electrolyte.The presence of polarized current indicates the occurrenceof redox reaction. Normally, the average of the anodic and cathodic peak potentials(Erev) can be taken as an estimate of the reversible potential for MNFs electrode, and the potential difference (ΔEa,c)between the anodic (Ea) and cathodic (Ec) peak potentials is a measureof the reversibility of the redox reaction [13, 14]. At a scan rateof 50 mV s-1, the values of Erev and ΔEa,c for the present sample is found to be 0.402 V and 0.161 V respectively.Fig. 7 show cyclic voltammogram of MNFs electrode (at a scanrate of 50 mV s-1) of MNFs electrode for 20 cycles. It can beseen that the positions of the oxidation and reduction peak of bothelectrodes did not change with increasing number of cycles. Therefore,it can be inferred that MgO electrode possess stablecycle and the structural changes did not occur during charge/dischargeprocess for 20 cycles [15].

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Fig. 6.Cyclic voltammograms of the MNFs electrode at various scan rates.

Fig. 8represents the electrochemical impedance spectra of MgO electrode at steady state, at an applied DC potential of500 mV, electrode was fully charged and oxygen evolution wascommencing on the electrode. This charge transfer reaction [16] would be expected to give rise to a semicircle in the impedanceplane; however, in Fig. 8, only the first part of the semicircle isobserved due to its large diameter. The presence of a Warburg line indicated that theelectrode reaction process was diffusion controlled. Experimental data was analyzed by fitting equivalent circuit shown in Fig. 9 Parameters R1, R2 and Q1 are ohmic resistance, charge-transfer resistance and constant phase element (CPE) respectively, it displays that R1 is in series with parallel connection of Q1 and R2. The impedance of constant phase element (ZCPE) is given by ZCPE= 1/Y (jω)n, where u is angular frequency in rad s-1, Y and n are variable factors of CPE [16].Equivalent circuit parameters for MgO electrode is tabulated in the Table 1.

20 cycles at 50 mV/s 0.00004

Potential (V)

0.00002

0.00000

-0.00002

-0.00004 0.8

0.6

0.4

0.2

0.0

Current (A)

-0.2

-0.4

-0.6

Fig. 7.Cyclic voltammograms of the MNFs electrode at a scan rate of 50 mV s-1for 20 cycles.

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-3000 -2500

Z" (ohm)

-2000 -1500 -1000 -500 0 0

2000

4000

Z' (ohm)

6000

8000

Fig. 8.Electrochemical impedance spectra of MNFs electrode

Fig. 9.Proposed equivalent circuit for MNFs electrode. Table 1 Equivalent circuit parameters for MNFselectrode.

Electrode

R1 (Ω)

R2 (Ω)

MgO

0.9843

1682

4. Conclusions For the first time cubic MNFsparticles were synthesized successfully by green combustion technique using Vetiver plant powder as a fuel. The crystallite size was in nano range and the same was confirmed by TEM results. The structural, morphological, electrochemical properties are sensitively dependent on the oxygen vacancies of MNFs. The reversibility of the MgO electrode is found to higher side it was confirmed by CV analysis. Further, modified MNF electrode is also found to exhibit higher lower charge transfer resistance. These findingssuggest that

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the modified MNFby green synthesis method electrode possess improved electrochemical properties and thus can be recognized as a promisingcandidate for the battery electrode applications. References [1] J. Yu, X. Yu, Hydrothermal Synthesis and Photocatalytic Activity of Zinc Oxide Hollow Spheres, Environ. Sci. Technol. 42 (2008) 4902– 4907. [2] C. Jin, H. Kim, S. Park, C. Lee, Synthesis of biaxial MgO/Mg–Sn–O nanowire heterostructures and their structural and luminescence properties, J. Alloys Compd. 541 (2012) 163–167. [3] Q. Yang, J. Sha, L.Wang, J.Wang, D. Yang, MgO nanostructures synthesized by thermal evaporation, Mater. Sci. Eng., C 26 (2006) 1097– 1101. [4] X. Yi, W. Wenzhong, Q. Yitai, Y. Li, C. Zhiwen, Deposition and microstructural characterizationof MgO thin films by a spray pyrolysis method, Surf. Coat. Technol. 82(1996) 291–293. [5] M.R. Anil Kumar, H.P. Nagaswarupa, K.S. Anantharaju, K. Gurushantha, C. Pratapkumar, S.C. Prashantha, H. Nagabhushana, S.C. Sharma, Y.S. Vidya, B. DarukaPrasad, C.S. VivekBabu,Banyan latex: a facile fuel for the multifunctional properties of MgO nanoparticles prepared via auto ignited combustion route,Mater. Res. Express 2 (2015) 095004. [6] M.R. Anilkumar, H.P. Nagaswarupa, K.S. Anantharaju, K. Gurushantha, C. Pratapkumar, S.C. Prashantha, T.R. ShashiShekhar, H. Nagabhushana, S.C. Sharma, Y.S. Vidyaand Daruka Prasad,Green engineered ZnO nanopowders by banyan tree and E-tirucalli plant latex: auto ignited route, photoluminescent and photocatalytic properties, Mater. Res. Express 2 (2015) 035011. [7] L. Kumari,W.Z. Li, C.H. Vannoy, R.M. Leblanc, D.Z.Wang, Synthesis, Characterization and Optical Properties of Mg(OH)2 Micro/Nanostructure and Its Conversion to MgO, Ceram. Int. 35 (2009) 3355–3364. [8] Paresh Chandra Ray,Size and Shape Dependent Second Order Nonlinear Optical Properties of Nanomaterials and Their Application in Biological and Chemical Sensing, Chem. Rev., 110 (2010) 5332–5365. [9] M.R. Anilkumar, H.P. Nagaswarupa, H. Nagabhushana, S.C. Sharma, Y.S. Vidya, K.S. Anantharaju, S.C. Prashantha, C. Shivakumara, K. Gurushantha,Bio-inspired route for the synthesis of spherical shaped Mgo:Fe3+ nanoparticles: structural, photoluminescence and photo catalytic investigation.,SpectrochimicaActa Part A: Molecular and Biomolecular Spectroscopy149 (2015) 703-713. [10] C R Ravi Kumar, M S Santosh, H P Nagaswarupa, S C Prashantha, S Yallappaand M R Anil Kumar, Synthesis and characterization of βNi(OH)2 embedded with MgOand ZnO nanoparticles as nanohybrids for energy storage devices, Mater. Res. Express4 (2017) 065503. [11] J. Huang, Q. Li, D. Sun, Y. Lu, Y. Su, X. yang, H. Wang, Y. Wang, W. Shao, N. He, J. Hong, C. Chen, Biosynthesis of silver and gold nanoparticles by novel sundried Cinnamomum camphora leaf, Nanotechnol. 18 (2007) 105104-105104. [12] M.R. Anilkumar, H.P. Nagaswarupa, H. Nagabhushana, S.C. Sharma, Y.S. Vidya, K.S. Anantharaju, S.C. Prashantha, C. Shivakumara, K. Gurushantha,Bio-inspired route for the synthesis of spherical shaped Mgo:Fe3+ nanoparticles: structural, photoluminescence and photo catalytic investigation.,SpectrochimicaActa Part A: Molecular and Biomolecular Spectroscopy149 (2015) 703-713. [13] C.R. Ravikumar, M.S. Santosh, H.P. Nagaswarupa, S.C. Prashantha, S. Yallappa, M.R. Anil Kumar. Mater. Res. Express 4 (2017) 065503. [14] C.R. Ravikumar, M.R. Anil Kumar, H.P. Nagaswarupa, S.C. Prashantha, Aarti S. Bhatt, M.S. Santosh, Denis Kuznetsov, Journal of Alloys and Compounds 736 (2018) 332-339. [15] B. Shruthi, V. BheemaRaju, B.J. Madhu, SpectrochimicaActa Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 683–689. [16] B.Shruthi, B.J.Madhu, V. BheemaRaju, S.Vynatheya, B.VeenaDevi,G.V.Jayashree, C.R. Ravikumar, Journal of Science: Advanced Materials and Devices 2 (2017) 93-98.