# NiO Nanoparticles Synthesis by Chemical Precipitation and Effect of Applied Surfactant on Distribution of Particle Size

Authors: Y. Bahari Molla Mahaleh; S. K. Sadrnezhaad; D.  Hosseini
Journal: Journal of Nanomaterials
 (2008)

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## Abstract

Production of NiO by chemical precipitation is the approach utilized in this work. Materials mainly used in this project are nickel nitrate hex hydrate (as a basic material), sodium hydroxide (as a precipitator material), and the following surfactants (for reduction in particle size). Applied surfactants are in two kinds: polymeric (PVP, PEG) and cationic (CTAB) surfactants, 1.0 gram. Nanopowders properties are identified by TG, FTIR, XRD, SEM, and TEM. The results obtained confirm the presence of nickel oxide nanopowders produced during chemical precipitation.


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## Body

## 1. Introduction

Nanomaterials exhibit
significantly mechanical, electronic, magnetic, thermal, catalytic properties,
and optical properties in comparison with their bulk counterparts, and have
extensively attracted interests [1, 2]. In recent years, there has been an
increasing interest in the synthesis of nanosized crystalline metal oxides
because of their large surface areas, unusual adsorptive properties, surface
defects, and fast diffusivities [3]. NiO nanoparticles may have many
applications such as in the manufacture of electrochromic, films, magnetic
materials, p-type transparent conducting films, gas sensors, catalyst, alkaline
batteries cathode, and solid oxide fuel cells anode [1–10]. Several
methods (mechanical or chemical) have been used and developed for synthesizing
crystalline oxide powders in nanoscale dimensions. In many of them, the main
objective is to reduce the costs of chemical synthesis and to produce materials
for technological applications [11]. The purpose of this work is the synthesis
of NiO nanoparticles by the chemical precipitation process in the presence of
sodium hydroxide, which is
a simple way and low in cost since the starting materials are few and
inexpensive.


## 2. Materials and Method

The reagents used for the synthesis of nanopowders were
prepared from MERC with 99.0% purification. The main
materials were nickel nitrate hex hydrate (Ni(NO3)2⋅6H2O), sodium hydroxide (NaOH), polyvinilpyrolidone
(PVP, MW=65000), polyethylene
glycol (PEG, MW=15000), and cetyl trimethyl ammonium bromide (CTAB).
First, we prepared two separate solutions; one a solution of 8.7 g of nickel
nitrate in 60 mL of deionized water and the other contains a solution of 3.0 g
sodium hydroxide in 150 mL of deionized water. Amount of 1 g of mentioned
surfactants in three different experiments added to latter solution. Next, the former
solution was added dropwise into the later. The mixed solution was stirred by
magnetic stirring apparatus (1000 rpm) at room temperature. The resultant light-green
solution was filtered, and then washed with deionized water and ethanol for 5–10 times and was
dried at 50°C for 24 hours, then calcined at 300°C,
450°C,
and 600°C for 2 hours for three different samples.
The surfactants were removed after the mentioned processes. Main reactions
occur during the experimental procedure can be written briefly  as follows:(1)2NaOH(s)→2Na+(aq)+2OH−(aq),Ni(NO3)2⋅6H2O(s)→Ni2+(aq)+2NO3−(aq)+6H2O(aq),Ni2+(aq)+2OH−(aq)+xH2O(aq)→Ni(OH)2⋅xH2O(s)↓,Ni(OH)2⋅xH2O(s)→50−100Ni(OH)2(s)+xH2O(g)↑,Ni(OH)2(s)→300NiO(s)+H2O(g)↑.


## 3. Results and Discussion

Figure1 shows the TG curve
of NiO precursor. It can be seen that the thermal decomposition of the
molecule can be divided to four separated regions. The first one is related to
the evaporation of the absorbed water between 50∘C and 100∘C,
at which most of
the water will be vanished. In the second region, the residue water will be
evaporated by a temperate rate. We have a significant weight loss in the third
region because of calcination of structural water. The structural water, which
has band structure with nickel
and oxygen atoms inside the molecule, will be eliminated before 300∘C. This event may lead to pure
NiO particles. In the last region, the molecule will be stable and the weight
of molecule is nearly constant without any other of weight loss.Figure 1
Thermograph of the NiO precursor.The IR spectrum
of the precursor (Figure2(a)) exhibits absorption peaks. The broad absorption
band centered at 3438 cm−1 is attributed to the band O–H stretching
vibrations, and the band at 1649 cm−1 is attributed to bending mode (H–O–H). The band at
1383 cm−1 is primarily due to the banding vibration of ionic CO32−.
The three bands appearing around 1061, 830, 700 cm−1 confirm the
presence of C–O in the precursor, and it vanishes after calcination (in Figure 2(b)).
The strong band at 423 cm−1 corresponds to the banding
vibration of NiO. The band at 3445 cm−1 and the band in 1383 cm−1 in Figure 2(b) are due to the fact that the calcined
powder tends to physically absorb water and carbonate ion.The FT-IR spectra. (a) Precursor and
(b) calcined powder.
(a)(b)The XRD pattern of precursor
and final product (after calcination) are shown in Figure3. Comparing to XRD standard table the
diffraction peaks in Figure 3, a (precursor) is in agreement with the
diffraction peaks of Ni(OH)2⋅H2O which is consistent with predicted reactions.
Main crystallographic planes in precursor XRD pattern (Figure 3(a)) are (001),
(100), (101), (102), (110), and (111). In XRD-calcined product pattern (Figure
3(b)), crystallographic planes such as (111), (200), (220), and (311) are
appeared, which indicates NiO particles crystallization and elimination of the
former phase (nickel hydroxide). First peak in each case of Figure 3 is referring to instrumental
error based on the fact that our instrument made this error for all samples. It
may be concluded
that the product is nickel oxide without any disturbing component. By
increasing calcination temperature (Figures 3(c) and 3(d)), it will result in
sharper diffraction peaks, which means that bigger particle size may be
generated from higher calcination temperatures. So calcination in low
temperatures (near 300∘C) is better than that in high temperatures. Figure 4 shows the SEM
images of the product synthesized. It is clear that in all cases (Figures 4(a),
4(b), and 4(c)), NiO nanoparticles were successfully prepared. For comparing
the effect of surfactant on particle size distribution, however, the particle
size was identified by measuring 100 particles in each case. Figure 5 shows the
results of such identification. The ranges of particle sizes vary
between 25 nm and 65 nm. In the case of PVP, the
maximum size of particles is less than 55 nm, and thus it results in small size
particle (Figure 4(a)). Most of the particles in PEG sample have the same and uniform size
(35–45 nm), and most
of particles (near 80%) have less than 45 nm size (Figure 4(b)). It seems that
CTAB has a weaker effect on the reduction in particle size rather than PVP or
PEG because the majority of particles (near 70%) have a larger size than 45 nm
(Figure 4(c)).XRD patterns. (a) Precursor and calcined powder at (b)
300, (c) 450, and (d)600°C.
(a)(b)(c)(d)The SEM image of NiO nanoparticles. (a) PVP, (b)
PEG, and (c) CTAB.
(a)(b)(c)Figure 5
Distribution of particle sizes.Figure6 is a TEM image of the NiO nanoparticles with PEG surfactant.
It can be seen that the uniform NiO nanoparticles had narrow size distribution and
sphere shapes with weak agglomeration. Most of the particle sizes are less than
45 nm, which confirms the SEM results.Figure 6
TEM image of
the NiO nanoparticles (PEG 1 g).


## 4. Conclusion

NiO nanopowder was
successfully prepared by chemical precipitation method, using nickel nitrate
hex hydrate and sodium hydroxide as raw materials. The majority of obtained NiO
nanopowders had an
average particle size less than 50 nm in all cases. It sounds that PEG and PVP are more useful surfactants
than CTAB for reduction in size of particles, exhibitation narrow size
distribution, and weak agglomeration.



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*Source: 470595-2009-03-12.xml*