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Structural, Thermal and Optical Properties of Nickel Oxide (NiO) Nanoparticles Synthesized by Chemical Precipitation Method Article · August 2016 DOI: 10.4028/www.scientific.net/AMR.1141.65

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Advanced Materials Research ISSN: 1662-8985, Vol. 1141, pp 65-71 doi:10.4028/www.scientific.net/AMR.1141.65 © 2016 Trans Tech Publications, Switzerland

Online: 2016-08-26

Structural, Thermal and Optical Properties of Nickel Oxide (NiO) Nanoparticles Synthesized by Chemical Precipitation Method M. P. Deshpande1a, Kiran N. Patel1, Vivek P. Gujarati1, Kamakshi Patel1, S. H. Chaki1 1

Department of Physics, Sardar Patel University, Vallabh Vidyanagar – 388120, Gujarat, India a

Email:[email protected]

Keywords: NiO nanoparticles, Chemical route, XRD, Raman spectroscopy, PL spectroscopy

Abstract. Nanocrystalline NiO has been prepared successfully by chemical precipitation route using nickel nitrate hexahydrate (Ni(NO3)2 ·6H2O) and sodium hydroxide (NaOH) aqueous solution at a temperature of 60˚C. Their compositional, structural, morphological, thermal and optical properties were studied using energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), ultravioletvisible (UV-Vis) spectroscopy, photoluminescence (PL) spectroscopy and Raman spectroscopy. From XRD pattern we confirmed the face centered cubic (fcc) structure of the synthesized NiO nanoparticles. The selected area electron diffraction (SAED) pattern indicated the same crystalline planes as seen in XRD pattern. TGA indicates good thermal stability of synthesized NiO nanoparticles and the optical absorption spectrum of NiO nanoparticles shows the strong absorption edge at 235nm (4.10eV). PL spectra of NiO nanoparticles shows two wide emission peaks at 420nm (2.95eV) and 440nm (2.82eV) and a strong–broad peak at 460nm (2.70eV) in violet emission band whereas the Raman peak observed at 518cm-1 shows the Ni-O stretching mode of vibration. Introduction. Nanoparticles show novel properties that are significantly different from bulk solid materials. This difference in properties is due to the different effects like small size effect, surface effect, quantum size effect, macroscopic quantum tunnel effect, etc.[1,2]. In the recent years, nanocrystalline transition metal oxides have attracted extensive interest due to their different potential applications. Out of these, nickel oxide (NiO) is an attractive material due to its chemical stability. NiO has a wide intrinsic band gap of ~3.6 eV [3,4]. It shows interesting optical, electrical and magnetic properties. It is a promising candidate for wide range of applications such as smart windows, gas sensors[5], catalysts[6-8], anode material in Li ion batteries and nanoscale optoelectronic devices like elecrochromic display [9,10]. Moreover, nanocrystalline NiO powder shows superparmagnetism effect which can be used for drug delivery and MRI (magnetic resonance imaging) agent [11]. These applications can be enhanced by decreasing the particle size and hence a precise control of the size and distribution in the nanometer region is required. Various techniques have been adopted for the synthesis of NiO nanostructures such as sol-gel, co-precipitation, hydrothermal, solvothermal, anodic arc plasma, sonochemical, pyrolysis by microwave, thermal decomposition, micro-emulsion and chemical precipitation [12,13]. Here in, we report the synthesis of NiO nanoparticles by chemical precipitation route, which can yield high purity products at low cost starting from easily available materials. Synthesized NiO nanoparticles have been characterized by EDAX, XRD, TEM, TGA, UV-visible spectroscopy, PL spectroscopy and Raman spectroscopy. Synthesis of NiO nanoparticles. Materials. All materials used in the experiment were of analytical grade. Nickel nitrate hexahydrate (Ni(NO3)2·6H2O) (99.8%) and sodium hydroxide (NaOH) (99.8%) were used without further purification for the synthesis of NiO nanoparticles.

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Synthesis method. To synthesize nickel oxide nanoparticles, in a typical experiment, 20 ml of 0.25M aqueous solution of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and 100 ml of 0.5M aqueous solution of sodium hydroxide (NaOH) were prepared in distilled water separately. Then the beaker containing NaOH solution was heated at the temperature of about 60°C. The Ni(NO3)2·6H2O solution was added drop wise to the above heated solution under high speed stirring for 2 hours. The resulting light green solution was seen at this condition and was left for 2 hours. The resulting light green precipitate was filtered by whatman filter paper and washed twice with deionized water and ethanol to remove the unreacted salts, and dried in a hot air oven at 80˚C for 3 hours. The dried material (Ni(OH)2) was powdered with mortar and pestle. This dried powder obtained was calcined at 400°C for 4 hours, which resulted in a black powder. The calcined powder was again slightly crushed with mortar and pestle to obtain pure NiO nanoparticles. The reactions that occur during experimental procedure can be written briefly as follows which is also reported in [14]. Ni(NO3)2·6H2O(s) → Ni+2(aq) +2NO-3(aq) + 6H2O(aq) 2NaOH(s) → 2Na+(aq) +2OH-(aq) Ni+2(aq) + 2OH-(aq) + xH2O(aq) → Ni(OH)2·xH2O(s)↓

Ni(OH)2·xH2O(s) Ni(OH)2(s)

˚

˚

> Ni(OH)2(s) + xH2O(g)↑

> NiO(s) + H2O(g)↑

Results and discussion. EDAX analysis. The composition of grown NiO nanoparticles was determined using the spectra obtained by energy dispersive analysis of X-rays (EDAX). The weight percentage and atomic percentage of nickel oxide nanoparticles are shown in table 1.This reveals that synthesized nanoparticles are non-stoichiometric, meaning that Ni:O ratio deviates from 1:1. In nickel oxide this nonstoichiometry is accompanied by color change, with the stoichiometrically correct NiO being green and non-stoichiometric NiO being black [12]. Table 1. EDAX results of NiO nanoparticles

Elements

Weight % (calculated)

Weight % (observed)

Atomic % (calculated)

Atomic % (observed)

Ni

78.58

62.27

49.99

31.03

O

21.42

37.73

49.99

68.97

XRD analysis. The X-ray diffraction pattern of Ni(OH)2 and NiO were recorded on Philips Xpert MPD X-ray diffractometer with CuKα radiation (λ=1.5418 Å). The X-ray diffractograms of Ni(OH)2 and NiO nanoparticles are shown in figure 1 and figure 2 respectively. Main crystallographic planes in the XRD pattern are (001), (100), (101), (110) and (111) for Ni(OH)2 which confirms the hexagonal structure of the dried powder (JCPDS NO. 01-1047). The diffractogram of NiO nanoparticles is indexed based on cubic system shown in figure 2 and the peaks appearing at 2θ = 37.38°, 43.42°, 63.02°, 75.53° and 79.54° are indexed as (111), (200), (220), (311) and (222) respectively and represents pure bunsenite face centered cubic (FCC) crystalline structure of nickel oxide. All these diffraction peaks, not only in peak position but also in their relative intensity are matched with the standard spectrum (JCPDS NO. 04-0835). The lattice parameter of NiO nanoparticles calculated from XRD data is 4.17Å, which is in good agreement with the reported data [15-17].The average crystallite size of NiO nanoparticles is calculated by Xray diffraction line broadening using Scherrer’s formula [17,13]: t =k λ/β2θcosθ

(1)

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where t represents grain size, k=0.9 is Scherrer’s constant related to the spherical shape, λ represents wavelength of X-ray (Cu Kα, 1.5418Å), θ is the diffraction angle of the peak, β2θ represents full width at half maximum of the peak (in radian). The crystallite size calculated for different 2θ angles varies between 15nm to 21nm approximately.

Fig.1. X-ray diffractogram of dried powder of (Ni(OH)2

Fig.2. X-ray diffractogram of NiO crystallites

TEM analysis. Figure 3 shows the TEM image of NiO nanoparticles. TEM analysis provides the information on the size and morphology of NiO nanoparticles and their state of agglomeration. It can be seen from figure 3 that NiO nanoparticles aggregate into secondary particles because of their extremely small dimensions and high surface energy. The synthesized NiO nanoparticles are in nanorange as seen from TEM images and particle size ranging between 14nm to 15nm [18-20].

Fig.3. TEM Image of NiO nanoparticles

Fig.4. SAED Pattern of NiO nanoparticles

Figure 4 shows the corresponding selected area electron diffraction (SAED) pattern, which is indexed on the basis of f.c.c. system (Fm3m space group). The SAED pattern consist of five diffraction rings which represents (111), (200), (220), (311) and (222) planes respectively. Small particles cause the widening of diffraction rings that made up of many diffraction spots, which indicates that the NiO nanoparticles are polycrystalline in nature. The SAED pattern also shows that NiO nanoparticles are face centered cubic (FCC) which also supports the X-ray diffraction results [20]. The d-spacing corresponding to each ring can be calculated from the formula of camera constant: λL = Rd

(2)

where λ is wavelength of electron beam, L is distance between specimen and photographic film, R is radius of ring and d is inter-planar spacing. The average lattice parameter calculated from ring pattern is 4.17 Å. These results are in good agreement with the XRD results.

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TGA analysis. Previously, researchers [12,13] reported the thermal decomposition results of the precursor (Ni(OH)2). They have observed that weight loss of the precursor occurred from 50˚C to 350˚C which represents that precursor decomposed completely at 350˚C to become nickel oxide. They have observed two distinct intervals of weight loss in the TGA curve, accompanied by two peaks of weight loss rate in the DTG curve.

Fig.5. TGA/DTA/DTG Curves of NiO nanoparticles Fig.6. Plot of ln(ln(1/y)) Vs 1/T (K-1) NiO nanoparticles

The first peak located around 100˚C (373K) might be attributed to the thermal dehydration of Ni(OH)2 and evaporation of physically adsorbed impurities. The second peak near 300˚C (573K) may be related to the decomposition of nickel carbonate. Based on the results of TGA, they have chosen a temperature of 400°C to form NiO from the complete decomposition of Ni(OH)2. Therefore looking to the above results we report the thermal decomposition result of NiO nanoparticles obtained after calcinations at 400˚C (673K) for 4 hours. Figure 5 shows the TGA, DTA and DTG curves for NiO nanoparticles. It can be observed from TGA curve that weight loss from ambient temperature to 900K of nearly 13% is seen. This low amount of weight loss indicates good stability of NiO nanoparticles. The weight loss determined from TGA curve is used to calculate the activation energy by plotting a curve for ln(ln(1/y)) versus 1/T (K-1) as shown in Figure 6 by Broido relation. The value of activation energy so obtained is 1.48eV. Moreover, TGA curve shows two small distinct intervals in the region of weight loss which is supported by two peaks of weight loss rate in the DTG curve as well as two small kinks in the DTA curve. The first peak and second peak located around 375K and 550K might be attributed to the evaporation of physically adsorbed impurities. UV-Vis studies. The UV-Visible absorption spectrum of NiO nanoparticles is shown in figure 7. The wavelength of absorption maximum depends on the particle size which decreases with decreasing particle size. It can be seen that the strongest absorption edge of NiO nanoparticles appears at around 235 nm, which is fairly blue shifted from the absorption edge of bulk NiO which is at around 340nm. This is because of quantum confinement effect. We determined the energy band gap of NiO nanoparticles using well known Tauc relation [21] (αhν)n = A (hν–Eg)

(3)

where α is absorption coefficient, hν is photon energy, A is absorbance, Eg is optical band gap, n is the number characterizing the nature of the transition process; n = 2 for the direct transition and n = 1/2 for indirect transition. Hence, the optical band gap for the absorption edge can be obtained by extrapolating the linear portion of the (αhν)2 Vs hν curve to the energy axis as shown in figure 8. The band gap energy calculated from this plot comes out to be 4.10eV. This value is much higher than band gap of bulk NiO which is 3.65eV. Therefore, it is confirmed that the synthesized NiO particles are in nanoscale. Further, relatively higher value of band gap energy of smaller size NiO agrees well with the concept that band gap increases with decreasing particle size [13].


Fig.7. UV-Visible absorption spectra NiO nanoparticles

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Fig.8. Plot of (αhν)2 Vs hν for NiO nanoparticles

PL studies. Room temperature photoluminescence emission spectrum of NiO nanoparticles calcined at 400°C, is shown in figure 9. NiO nanoparticles exhibited two wide emission peaks in the range 400nm to 450nm and a strong - broad peak at 460nm with an excited wavelength of 280nm (4.43eV). The origin of photoluminescence peaks is attributed to electronic transitions involving 3d8 electrons of the Ni+2 ions [12].

Fig.9. Room temperature PL spectra of NiO nanoparticles

Fig.10. Room temperature Raman spectra of NiO nanoparticles

A strong and broad peak in PL spectrum corresponds to the direct recombination between electrons in the conduction band and holes in the valence band. As stronger the PL intensity of NiO nanoparticles, higher the recombination rate of photoinduced electron-hole pair. The deeply trapped holes are more or less localized at deep traps, exhibit a lower oxidizing potential and prefer to react with physically adsorbed substances. Heat treatment may result in a slight deviation from NiO stoichiometry and the cation vacancy or interstitial oxygen trapping in the NiO lattice leads to two wide emission peaks at 420nm(2.95eV) and 440nm(2.82eV) and a strong - broad peak at 460nm(2.70eV) in violet emission band and confirmed presence of such defects in NiO lattice. Nickel vacancies can be produced due to the charge transfer between Ni+2 and Ni+3 [22]. As seen from figure 9 that excitonic, PL emission band at 460nm results from the surface oxygen vacancies of NiO nanoparticles. Raman studies. Room temperature Raman spectra of NiO nanoparticles was obtained with the help of Raman spectrometer using argon laser (488nm, 5mW cw power) as excitation source, is shown in figure 10. The Raman spectrum exhibited a strong-broad peak at 518cm-1 due to the Ni-O stretching mode of vibration (1LO mode) and another peak at 1058cm-1 due to two phonon (2LO mode). The absence of magnon peak in the Raman spectrum at 1500cm-1 reveals the antiferromagnetic to superparamagnetic transition of NiO nanoparticles [22,23].

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Conclusions. NiO nanoparticles have been successfully synthesized by chemical precipitation method using nickel nitrate hexahydrate (Ni(NO3)2 ·6H2O) and sodium hydroxide (NaOH). XRD and TEM results confirm that NiO nanoparticles are crystalline in nature and belongs to the face centered cubic phase. TGA results indicate good thermal stability of synthesized NiO nanoparticles. The UV-Visible absorption spectra shows the strongest absorption edge of NiO nanoparticles appears at around 235 nm, which is blue shifted from the absorption edge of bulk NiO which is at around 340nm. PL spectrum of NiO nanoparticles shows two wide emission peaks at 420nm(2.95eV) and 440nm(2.82eV) and a strong-broad peak at 460nm(2.70eV) in violet emission band with an excited wavelength of 280nm (4.43eV) whereas Raman spectrum shows absence of magnon peak at 1500cm-1 indicating superparamagnetic behavior of NiO nanoparticles. Acknowledgement. We acknowledge Department of Science and Technology (DST), Technology Bhawan, New Mehrauli Road, New Delhi-110016 for giving INSPIRE Fellowship to the Research student Kiran N. Patel (IF150775). We are grateful to Dr. Vasant G. Sathe, UGC-DAE (CSR), Indore for helping in obtaining Raman spectra. We also acknowledge SICART, V. V. Nagar for assisting us in EDAX, XRD, TEM and UV-VIS spectrophotometer characterization of our sample. References. [1] H. Gleiter, Prog. Mater. Sci. 33 (1989) 223-315. [2] R. Sessoli, D. Gatteschi, A. Caneschi, M. A. Novak, 365 (1993) 141-143. [3] N. Dharmaraj, P. Prabu, S. Nagarajan, C.H. Kim, J.H. Park, H.Y. Kim, Materials Science and Engineering B. 128 (2006) 111-114. [4] C. Feldman, H.O. Jungk, Angew Chem. Int.Ed. 40 (2001) 359-362. [5] M. Matsumiya, F. Qiu, et al., Thin Solid Films. 419 (1-2) (2002) 213-217. [6] Y. Wang, J. Zhu, Thermochim. Acta. 437 (1-2) (2005) 106-109. [7] Y. Ichiyanagi, N. Wakabayashi, Physica B. 329-333(Part 2) (2003) 862-863. [8] V. Biju, M. Abdul Khadar, Mater. Sci. Eng. A. 304-306 (2001) 814-817. [9] F. Li, H. Chen, C. Wang, K. Hu, J. Elec-troanal. Chem. 531(1) (2002) 53-60. [10] Y. Nuli, S. Zhao, Q. Qin, J. Power Sources. 114(1) (2003) 113-120. [11] J.T. Richardson, D.I. Yiagas, B. Turk, K. Forster, M.V. Twigg, J. Appl Phys. 70 (1991) 69776982. [12] P. A. Sheena, K.P. Priyanka, N. Aloysius Sabu, Boby Sabu, Thomas Varghese, Nanosystems: physics, chemistry, mathematics, 5 (3) (2014) 441-449. [13] M. Mohammadijoo, Z. NaderiKhorshidi, S.K. Sadrnezhaadb and V. Mazinanic, Nanoscience and Nanotechnology: An International Journal 4(1) (2014) 6-9. [14] Y. Bahari Molla Mahaleh, S. K. Sadrnezhaad, and D. Hosseini. Journal of Nanomaterials Volume (2008), Article ID, :10.1155/2008/47059. [15] S. V. Ganachari, R. Bhat, R. Deshpande and A. Venkataraman, Recent Research in Science and Technology. 4(4) (2012) 50-53. [16] N. Dharmaraj, P. Prabu, S. Nagarajan, C. H. Kimb, J.H. Park, H. Y. Kimb,Materials Science and Engineering B 128 (2006) 111–114.


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Structural, Thermal and Optical Properties of Nickel Oxide (NiO) Nanoparticles Synthesized by Chemical Precipitation Method 10.4028/www.scientific.net/AMR.1141.65 DOI References [1] H. Gleiter, Prog. Mater. Sci. 33 (1989) 223-315. 10.1016/0079-6425(89)90001-7 [2] R. Sessoli, D. Gatteschi, A. Caneschi, M. A. Novak, 365 (1993) 141-143. 10.1038/365141a0 [3] N. Dharmaraj, P. Prabu, S. Nagarajan, C.H. Kim, J.H. Park, H.Y. Kim, Materials Science and Engineering B. 128 (2006) 111-114. 10.1016/j.mseb.2005.11.021 [4] C. Feldman, H.O. Jungk, Angew Chem. Int. Ed. 40 (2001) 359-362. 10.1002/1521-3773(20010119)40:23.0.co;2-b [5] M. Matsumiya, F. Qiu, et al., Thin Solid Films. 419 (1-2) (2002) 213-217. 10.1016/s0040-6090(02)00762-9 [7] Y. Ichiyanagi, N. Wakabayashi, Physica B. 329-333(Part 2) (2003) 862-863. 10.1016/s0921-4526(02)02578-4 [8] V. Biju, M. Abdul Khadar, Mater. Sci. Eng. A. 304-306 (2001) 814-817. 10.1016/s0921-5093(00)01581-1 [10] Y. Nuli, S. Zhao, Q. Qin, J. Power Sources. 114(1) (2003) 113-120. 10.1016/s0378-7753(02)00531-1 [11] J.T. Richardson, D.I. Yiagas, B. Turk, K. Forster, M.V. Twigg, J. Appl Phys. 70 (1991) 6977- 6982. 10.1063/1.349826 [17] R. Hada, A. Rani, V. Devra and S. S. Amritphale, International Research Journal of Pure &Applied Chemistry. 3(2) (2013) 111-117. 10.15373/2249555x/apr2013/16 [18] V.S. Reddy Channu, Rudolf Holze, B. Rambabu, Colloids and Surfaces A: Physicochem. Eng. Aspects 414 (2012) 204-208. 10.1016/j.colsurfa.2012.08.023 [20] H. Qiao, Z. Wei, H. Yang, L. Zhu and X. Yan, Journal of Nanomaterials. Volume (2009), Article ID 795928, doi: 10. 1155/2009/795928. 10.1155/2009/795928 [21] B.S. Rema Devi, R. Raveendran and A.V. Vaidyan, Pramana-J. Phys., 68 (2007), 679-687. 10.1007/s12043-007-0068-7

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