Facile synthesis of Ni/NiO nanocomposites via thermal decomposition
Aliakbar Dehno Khalaji
1
(
Department of Chemistry, Faculty of Science, Golestan University, Gorgan, Iran
)
Gholamhossein Grivani
2
(
School of Chemistry, Damghan University, Damghan, P. O. Box 36715-364, Iran
)
Shaghayegh Izadi
3
(
School of Chemistry, Damghan University, Damghan, P. O. Box 36715-364, Iran
)
Mehdi Ebadi
4
(
Department of Chemistry, Islami Azad University, Gorgan Branch, Gorgan, Iran
)
الکلمات المفتاحية: TEM, XRD, Thermal decomposition, Ni/NiO nanocomposites,
ملخص المقالة :
In this work, Ni/NiO nanocomposites have been prepared using simple, environment friendly and low-cost solid-state thermal decomposition method from mixture of nickel acetate tetrahydrate as a Ni precursor, 2-aminophenol and 4-dimethylaminobenzaldehyde at the molar ratio 1:2:2 at 400 and 500C for 3 hours. The Ni/NiO nanocomposites were characterized with Fourier transformed infra-red spectroscopy (FT-IR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-Ray fluorescence (XRF). The XRD and XRF results confirmed that the nanocomposite products contain a mixture of nickel and nickel oxide. The Ni or NiO content vary with the temperature used for the synthesis. Upon increasing the temperature from 400 to 500C, the amount of NiO was found to be increase, due to a complete oxidation of Ni to NiO. The TEM images confiemed that the composites were spherical in shape with a distribution size of about 10-30 nm. In addition, the products display reasonable electrochemical performance.
Facile synthesis of Ni/NiO nanocomposites via thermal decomposition
Abstract
In this work, Ni/NiO nanocomposites have been prepared using simple, environment friendly and low-cost solid-state thermal decomposition method from nickel (II) Schiff base complex at 400 and 500°C for 3 hours. The Ni/NiO nanocomposites were characterized with Fourier transformed infra-red spectroscopy (FT-IR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-Ray fluorescence (XRF). The XRD and XRF results confirmed that the nanocomposite products contain a mixture of nickel and nickel oxide. The Ni or NiO content vary with the temperature used for the synthesis. Upon increasing the temperature from 400 to 500°C, the amount of NiO was found to be increase, due to a complete oxidation of Ni to NiO. The TEM images confirmed that the composites were spherical in shape with a distribution size of about 10-30 nm. In addition, the products display reasonable electrochemical performance.
Keywords: Ni/NiO nanocomposites, Thermal decomposition, XRD, XRD, TEM
1. Introduction
Ni/NiO nanocomposites find interesting properties such as thermal stability [1], magnetic properties [2,3] and applications in lithium ion batteries [4-8], electrocatalysts for hydrogen evolution reaction [9] and electrochemical energy storage [10], as a robust catalyst for the hydrogenation of levulinic acid to γ-valerolactone [11], because of its unique properties. These properties direct correlated to the grain size, morphology and crystalline phases of Ni/NiO nanocomposites [1-21]. It is essential to prepared Ni/NiO nanocomposites with various morphologies and sizes. To the date, several methods [1-21], such as chemical dealloying method [12], thermal annealing of Ni nanowires [13], a combination of chemical anf gaseous reduction [15], citric acid assisted pechini-type method [20], one step solution combustion method [18], hydrothermal assiste polyol process [16], simple sol-gel [17], electrostatic spray deposition (ESD) [7], physical deposition method [8] and calcination of various precursors [5,6,22] have been developed to synthesize nano-sized Ni/NiO nanocompoistes. Mahendraprabhu and Elumalai [17] synthesized Ni/NiO nanocomposites by simple sol-gel process and reported influence of citric acid on the formation of Ni/NiO nanocomposites. The results shows that in lower nanoparticles:citric acid molar ratio (1:1 and 2:1), a mixture of Ni and NiO and in higher molar ratio, single phase of NiO was obtained. Gokul et al [17] prepared Ni/NiO nanocomposites by hydrothermal-assisted polyol process and reported annealing temperature on the magnetic properties of Ni/NiO nanocomposites. The results shows that with increase of annealing temperature the structure of Ni/NiO nanocomposite changed to NiO due to the transformation of Ni to NiO. Farzeneh and Kashanie [19], prepared Ni/NiO nanocomposites from mixture of Ni(CH3COO)2.4H2O, acetylacetone and water under reflux condition, followed by the calcination at 400 °C and stuied the elimination of congo red from aqueous solution. Results shows that the at 497 nm after 30 min, 95% of Congo red has been eliminated. Prabhu et. al [18]., synthesized Ni/NiO nanocomposites synthesized by one step solution combustion method. They reports that the Ni or NiO content in the products vary with the quantity of HNO3 used for the synthesis.
Recently, we usued the variouse Ni(II) Schiff base complexes as new precursor for preparation of NiO nanoparticles by solid state thermal decomposition as simple, low cost and environmentally friendly [23,24]. Here in, we used nickel (II) Schiff base complex (Scheme 1) and report the synthesis of Ni/NiO nanocomposites using thermal decomposition method at 400 and 500 °C. The preoduct characterized with FT-IR, XRD, SEM, TEM and XRF. In addition, electrochemical properties of prepared nanocomposites were investigated.
Scheme 1. Chemical structure of nickel(II) Schiff base complex
2. Materials and Methods
2.1. Materials and measurements
All materials were commercially available and used as received without further purifications. Fourier transform infrared (FT-IR) spectra were recorded as a KBr disk on a FT-IR Perkin–Elmer spectrophotometer. X-ray powder diffraction (XRD) pattern of the complex was recorded on a Bruker AXS diffractometer D8 ADVANCE with Cu-Kα radiation with nickel beta filter in the range 2θ = 10o–80o. The transmission electron microscopy (TEM) images were obtained from a JEOL JEM 1400 transmission electron microscope with an accelerating voltage of 120 kV. The X-ray fluorescence (XRF) was carried out using a Skyray Instrument EDX3600H. Electrical energy saving properties of the synthesized nickel (II) Schiff base complexes were characterized by cyclic voltammetry (CV) and Galvanostatic charge/discharge techniques. While, three compartment electrodes were used: Pt sheet (1 × 1 cm2) as a counter, the fixed synthesized nickel (II) Schiff base complexes (2 mg) on the copper plate (1 × 1 cm2) as a working and Ag/AgCl as reference electrodes were used in the 0.5 M Na2SO4 medium. Cyclic voltammetry was done in the potential rang of 0.1- (-0.7) V vs. Ag/AgCl at the variety scan rates (10-100 mV s-1), while the charge/ discharge were performed at -5 - +5 and -4 - +4 mV using potantiostat/galvanostat (Autolab 302N).
2.2. Preparation of nickel(II) Schiff base complex
The nickel(II) Schiff base complex was synthesized in methanol described elsewhere [25]. To a solution of 4-dimethylaminobenzaldehyde (4 mmol) in CH3OH (10 mL) was added, with continuous stirring, a solution of 2-aminophenol (4 mmol) in the 15 mL of CH3OH. The mixture was stirred at room temperature for about 45 min to give a clear orange solution. Then, to this solution we added a solution of nickel acetate tetrahydrate (2 mmol) in methanol (15 mL). The resulting mixture was heated with stirring to evaporate the solvents to get precipitate of dark red nickel(II) Schiff base complex. The precipitate washed with cold ethanol, and dried at room temperature for several days. Yield: 65%. Anal. Calcd. for C30H30N4O2Ni: C.; 67.07 (66.95), H.; 5.59 (5.64), N.; 10.43 (10.39). FT-IR (KBr, cm-1): 2877-3031 (C-H aromatic and aliphatic), 1586 (-C=N-), 1451 – 1557 (-C=C- aromatic).
2.3. Preparation of Ni/NiO nanocomposites
For preparation of Ni/NiO nanocomposites, 0.5 gr of nickel(II) Schiff base complex is loaded into a crucible and then placed in the electrical furnace and heated, at a rate of 10ºC/min in air, follow by a calcination at 400 and 500ºC for 3 h. Nanoparticles of Ni/NiO nanocomposites are produced, washed with ethanol and dried at room temperature. FT-IR (KBr, cm-1): 458 (Ni-O) for Ni/NiO product at 400ºC and 462 (Ni-O) for Ni/NiO product at 500ºC.
2.4. Electrochemical study
Ni/NiO particles (S400 and S500) were obtained by calcination of the synthesized nickel (II) Schiff base complexes at 400 and 500 ºC, respectively. Electrical energy saving properties of S400 and S500 were characterized by cyclic voltammetry (CV) and Galvanostatic charge/discharge techniques. While, three compartment electrodes were used: Pt sheet (1 × 1 cm2) as a counter, the fixed Ni/NiO particles (S400 and S500) (2 mg) on the copper plate (1 × 1 cm2) as a working and Ag/AgCl as reference electrodes were used in the 0.5 M Na2SO4 medium. Cyclic voltammetry was done in the potential range of 0.1- (-0.7) V vs. Ag/AgCl at the variety scan rates (10-100 mV s-1), while the charge/ discharge were performed at -5 - +5 and -4 - +4 mV using potentiostat/galvanostat (Autolab 302N). It have to be mentioned that the Ni/NiO particles were fixed on the Copper plates using Silver conductive paste (Sigma-Aldrich)
3. Results and Discussion
3.1. FT-IR spectra
The FT-IR spectra of the Ni(II) Schiff base complex and Ni/NiO nanocomposites are shown in Figs. 1 and 2, respectively. In the FT-IR spectra of complex, the peak at about 3000 cm-1 assigned to C-H aliphatin and aromatic and the peaks at 1586 cm-1 assigned to iminic group (C=N). The peak at about 458 cm-1 for Ni/NiO obtained from 400 °C and at about 461 cm-1 for Ni/NiO obtained from 500 °C assigned to the Ni-O stretching vibration mode [22,23], while the two peaks appear 1610 and 3421 cm-1 for Ni/NiO obtained from 400 °C and 1637 and 3448 cm-1 for Ni/NiO obtained from 500 °C could be assigned to O-H stretching and binding vibration of H2O molecules adsorbed on the surface of Ni/NiO, respectively [22,23].
3.2. XRD patterns
XRD patterns of Ni/NiO nanocoposites (Fig. 3) show five obvious diffraction peaks located at about 37, 43, 63, 75 and 80° and agree with hexagonal structure of NiO [4-7] with lattice constant a = b = 2.955, c = 7.223 Å and space group R-3m. Furthermore, two diffraction peaks located at about 44 and 52° and agree with cubic structure of Ni [4-7] with lattice constant a = b = c = 3.528 Å and space group Fm3m. The intensity of the characteristic peaks of the Ni phase decrease considerably as the temperature increases from 400 to 500°C, due to the oxidation of Ni to NiO [13,16]. The crystallite size was calculated using Debye-Scherrer formula and was found to 24.6 and 24.1 nm, based on the NiO(012) plane and 24.5 nm, based on the Ni(111) plane, with an increase in decomposition temperature from 400 to 500 °C [13,16]. Results suggests that the crystallinity of the Ni cubic structure was slightly greater than that of NiO hexagonal structure. The increasing of the decomposition temperature has no appreciable effect on the crystallite size of the prepared Ni/NiO nanocomposites.
Figure 1. FT-IR spectra of the Schiff base ligand and its Ni(II) complex.
Figure 2. FT-IR spectra of the prepared Ni/NiO nanocomposites at a) 400 °C and b) 500 °C.
3.3. TEM images
The TEM images of Ni/NiO nanocomposites prepared at 400 and 500 °C, are depicted in Fig. 4. Comparison between the TEM images confirmed that there is no difference between the morphology of the products. Relative 
fraction of metallic Ni was recorded by XRF and was found to be 19 and 7%, for Ni/NiO nanoparticles prepared at 400 and 500 °C, respectively. These results indicate that the products should be composite of metallic nickel and nickel oxide [13,16].
Figure 3. XRD patterns of the prepared Ni/NiO nanocomposites at a) 400 °C and b) 500 °C.
Figure 4. TEM images of Ni/NiO nanocomposites prepared at 400 (left) an at 500 °C (right).
3.4. Electrochemical Studies
The electrochemical behavior of the Fixed Ni/NiO particles (S400 and S500) on the copper plates were evaluated using Cyclic Voltammetry technique as shown in Figures 5a and c, respectively. It was found that the curve areas were increased due to the enhancing of scan rates. It means that linearly, the curve area of voltammograms was a function of scan rate (v). The linear relationship between curves area and scan rates (0.5 V) was illustrated in Figs. 4b and d. It was demonstrated that the electrochemical behavior of the fixed Ni/NiO particles on the copper plates for S400 and S500 were different.
The synthesized Ni/NiO particles at 500 °C (S500) has shown the linear behavior, while the synthesized Ni/NiO particles at 400 °C (S400) was deviated from linear behavior by the scan rates increasing. Noteworthy, it can be seen that the potential position of peaks was same (S500), whereas, the potential position of peaks were shifted in the synthesized S400 with increasing scan rates as shown in Fig. 5a and c, respectively. From these results (both linearity and the potentials shift), it can be concluded that the electrochemical behavior of S500 is diffusion-controlled while the mentioned behavior was partially diffusion-controlled for S400.
Figure 4. a) Cyclic voltammograms of prepared electrodes as S500 at different scan rates (10–100 mV s-1). b) Linear relationship between voltammogram areas vs scan rate for S500. c) Cyclic voltammograms of prepared electrodes as S500 at different scan rates (10–100 mV s-1). d) relationship between voltammogram areas vs scan rate for S400.
The kinetic and diffusion–controlled of the electrochemical behavior of process have been explained by Ebadi et al. [24]. The specific capacitance of activated materials is in depended on scan rate and anodic or cathodic currents. It can be calculated by equation (C= i/ v.w). Where i is the average cathodic or anodic current (A), v is the scan rate (V s-1) and w is the mass of activated material (g).
As displayed in Figs. 5a and b, CV results were verified by galvanostat charge/discharge test. The prepared electrodes (S400 and S500) have shown the reasonable load and unload charge behavior for both applied currents (±5 and ±4 mV) in the 0.5 M Na2SO4. In both case, it was found that the loading time were faster than unloading time for S500 while, it was not changed for S400.
Figure 5. a) Charge-discharge curves of (a) S500 (b) S400 at ±5 and ±4 mV current.
4. Conclusion
The Ni/NiO nanocomposites with various mass ratio between Ni and NiO have been prepared and characterized. XRD and XRF results reveal that the amount of metallic Ni was found to decrease due to oxidation to NiO upon increasing the temperature from 400 to 500 °C. Also, SEM results show that upon increasing the temperature increases the agglomeration of nanoparticles. The synthesized nanocomposites at the different tempratures have shown the different electrochemical behavior as S500 was diffusion-controlled and S400 was not entirely diffusion-controlled.
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