Preparation, physical and chemical studies on metal complexes of Schiff bases as a nucleus key to prepare nanometer oxides have catalytic applications: Nickel (II) complexes derived from 4-aminoantipyrine derivatives

Article abstract of DOI:10.1016/j.molliq.2016.01.097

Three nickel(II) Schiff base complexes derived from 4-amino antipyrine with 2-furaldehyde, 2-thiophene carboxaldehyde and 2-methoxybenzaldehyde has been synthesized and well characterized based on elemental analyses, IR, electronic spectra, molar conducta

Full text of DOI:10.1016/j.molliq.2016.01.097

Journal of Molecular Liquids 216 (2016) 608–614
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Preparation, physical and chemical studies on metal complexes of Schiff
bases as a nucleus key to prepare nanometer oxides have catalytic
applications: Nickel (II) complexes derived from
4-aminoantipyrine derivatives
a
a,c
Samy M. El-Megharbel a,b, , Adel S. Megahed , Moamen S. Refat
⁎
a
Department of Chemistry, Faculty of Science, Taif University, Al-Hawiah, Taif, P.O. Box 888, 21974, Saudi Arabia
Department of Chemistry, Faculty of Science, Zagazig University, Zagazig 44519, Egypt
Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Three nickel(II) Schiff base complexes derived from 4-amino antipyrine with 2-furaldehyde, 2-thiophene
carboxaldehyde and 2-methoxybenzaldehyde has been synthesized and well characterized based on elemental
analyses, IR, electronic spectra, molar conductance, and thermogravimetric analysis. Infrared spectra proved
that three Schiff base chelates are coordinated to the nickel(II) ions as a bidentate fashion with ON and NS for
the (2-furaldehyde and 2-methoxybenzaldehyde) and 2-thiophene carboxaldehyde, respectively. The molar
conductance data reveal that all the Ni(II) chelates are non-electrolytes. The general formula of precursors
nickel(II) complexes is [Ni(Ln)2(Cl)2] with 1:2 (Ni:L) molar ratio. These complexes were used as the primary nu-
cleus to prepare nickel (II) oxide, NiO, nano-particles by thermal degradation in static air. The resulted NiO nano-
particles have been discussed based on X-ray powder diffraction patterns, scanning electron microscopy (SEM),
Energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). All of the obtained
NiO nano-particles are catalytically active in degradation process of hydrogen peroxide
Received 8 January 2016
Accepted 30 January 2016
Available online xxxx
Keywords:
Schiff base
4-amino antipyrine
NiO
Nanometric oxide
IR
Thermal analysis
H2O2
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
antibacterial activity against Escherichia coli, Streptococcus pyogenes,
Staphylococcus aureus, Salmonella typhi and Pseudomonas aeruginosa
The Schiff bases are an important nucleus in the field of coordination
chemistry, that the extensive studies have been conducted on complex-
ation of Schiff bases with different metal ions due to the attractive
physicochemical properties of metal complexes and broad range of
utilization in various areas of science [1–5]. The toxicity report of Schiff
base derived from sulfane thiadizole, 2-thiophene aldehydes and
salicylaldehyde and their some metal complexes against insects
has been tested [6]. The Schiff bases of thiadiazole derivatives with
salicylaldehyde or o-vanillin and their metal complexes have been
insecticidal activities against bollworm [7]. In literature survey, it was
found that the Schiff bases and their complexes have been recorded a
medical importance as well as the essential role in designing medicinal
compounds [8,9].
and antifungal activity against Aspergillus flavus, Aspergillus niger and
Cladosporium were studied [12]. The antibacterial activity of vanillin
and DL-α-aminobutyric acid derived Schiff base complexes of Co(II),
Ni(II), Cu(II) and Zn(II) were much greater than free Schiff bases [13].
The binding properties of DNA with a series of transition metal com-
plexes of 2,6-dibenzoyl 4-methylphenol and diamines derived Schiff
bases having potential NNO-tridentate donors were reported [14–20].
The binding studies of Ni(II) complexes of 5-triethyl ammonium
methyl salicylidene ortho-phenylendiimine ligand, with DNA reflect
that strong interaction occurs between DNA and complexes [21].
The interaction of calf-thymus DNA occurs with salicylaldehyde-2-
phenylquinoline-4-carboylhydrazone complexes of Co(II) and Ni(II)
through a binding mode involving groove [22]. The plant growth hor-
mones are also affected by Schiff bases of carboxylic acids and esters
[23]. Some natural food samples are analyzed for the presence of Ni
by using novel tetradentate Schiff base which is utilized as chromogenic
reagents [24]. The Schiff bases which are able to form protective layers
on the surface can be utilized for the preparation of anticorrosive mate-
rials and can therefore, serve as corrosion inhibitors. The commercially
employed corrosion inhibitors include many aldehydes or amines.
Moreover, the presence of C = N functionality in Schiff bases makes
The coordination of Schiff bases toward metals can be enhanced or
minimized their activities [10,11]. The complexes Co(II), Ni(II) and
Cu(II) with a Schiff base of 3-substituted-4-amino-5-mercapto-1,2,4-
triazole and 8-formyl-7-hydroxy-4-methylcoumarin show the potent
⁎
Corresponding author at: Department of Chemistry, Faculty of Science, Taif University,
Al-Hawiah, Taif, P.O. Box 888, 21974, Saudi Arabia.
E-mail address: samyelmegharbel@yahoo.com (S.M. El-Megharbel).
http://dx.doi.org/10.1016/j.molliq.2016.01.097
0167-7322/© 2016 Elsevier B.V. All rights reserved.

S.M. El-Megharbel et al. / Journal of Molecular Liquids 216 (2016) 608–614
609
them more efficient for this purpose [25]. As far as, the use of Schiff
bases as corrosion inhibitors is concerned, chemisorption is the major
interaction [26]. The capability of the inhibitor molecules to make
bonds with the metal surface needs certain electron rich centers
available with the inhibitor molecules. The inhibitors are supposed to
behave as Lewis bases and metal will act as electrophile. In addition to
that, free electrons are available with the oxygen, nitrogen and other
atoms of the protecting compounds which will act as nucleophilic
centers to make bonds with metal. The multiple absorption sites for
the inhibitors assist the inhibitor compounds for making a stable mono-
layer which is due to involvement of the whole benzene ring and its
atoms [27].
The metal oxide nanoparticles explore widely for various scientific
and technological fundamental interests and access to new classes of
functional materials with unprecedented properties and industrial
applications. Nickel(II) oxide has a wide range of applications in
the manufacturing of magnetic materials, alkaline battery cathodes,
dye-sensitized solar cells, semiconductors, solid oxide fuel cells
(SOFC), anti ferromagnetic layers, p-type transparent conducting films,
electrochromic films, heterogeneous catalytic materials and gas sensors
[28–34]. Also, nano crystalline NiO powder shows superparamagnetism
effect; then which can be used for drug delivery and MRI agent [35].
Numerous routes like thermal decomposition [36–38], carbonyl
method, sol–gel technique [39], microwave pyrolysis [40], solvothermal
[41], anodic arc plasma [42], sonochemical [43], precipitation–
calcination [44] and microemulsion [45] have previously been inves-
tigated for the production of nickel oxide nanoparticles.
Fig. 1. Structures of Schiff bases ligands derived from 4-aminoantipyrine.
2.3. Synthesis of Ni(II) Schiff base complexes
Solution of NiCl2.6H2O (1.0 mmol, in 10 mL methanol) is added to
each solution of L1, L2 or L3 Schiff bases (2 mmol, in 20 mL methanol)
under reflux at 60 °C with continuous stirring for 1 h. The olive green
to greenish brown precipitates is resulted after slow evaporation of
methanol solvent at room temperature overnight. The colored solid
complexes are collected by filtration, and dried in a vacuum.
2.4. Synthesis of nickel(II) oxide nano-particles
The known weights of nickel(II) Schiff base complexes are placed
into a porcelain crucible and ignited in an oven at 800 °C for 3 h in air
atmosphere. The final residues are washed with few amounts of ethanol
solvent to discard the organic impurities, then dry the products in drier
at 120 °C for 1 h.
Many of the reported procedures are limited due to specific condi-
tions required, tedious procedure, complex apparatus, low-yield and
high cost. From a practical point of view, it is essential to further inves-
tigate on the development of newer approach for the manufacture of
high-quality low-cost nanoparticles of better optical properties. Tradi-
tional methods do not fully satisfy our needs for mass scale production
of NiO nanoparticles. The thermal decomposition method utilized in
this paper is a two-stage deposition method consisting of a nickel(II)
Schiff base complex that decomposes to nickel oxide. The complexes
can simply be produced by reaction of NiCl2 and three Schiff base
chelates derived from 4-amino antipyrine with 2-furaldehyde,
2-thiophene carboxaldehyde and 2-methoxybenzaldehyde. This
study, then focuses on the morphology and spectral properties of
the nickel oxide nanoparticles. The results show that by different chelates,
the shape of nickel oxide particles have different nanosize structures.
2.5. Instrumentations
The microanalytical analyses of %C, %H and %N percentages were
estimated using a Perkin Elmer CHN 2400 (USA). The molar conduc-
tivities of nickel(II) Schiff base complexes with 1.0 × 10−3 mol/cm3
concentration in dimethylsulfoxide (DMSO) solutions were mea-
sured by Jenway 4010 conductivity meter. The electronic absorption
spectra were recorded in DMSO solvent within 900–200 nm range
using a UV2 Unicam UV/Vis Spectrophotometer fitted with a quartz
cell of 1.0 cm path length. The infrared spectra with KBr disks were
recorded on Bruker FT-IR Spectrophotometer (4000–400 cm−1).
Magnetic moments were calculated using the Magnetic Susceptibili-
ty Balance, Sherwood Scientific, Cambridge Science Park, Cambridge,
England, at Temp 25 °C. The thermal studies TG/DTG–50 H were car-
ried out on a Shimadzu thermo gravimetric analyzer under nitrogen
till 800 °C. Scanning electron microscopy (SEM) images were taken
in Quanta FEG 250 equipment. The X-ray diffraction patterns were
recorded on X ‘Pert PRO PAN-analytical X-ray powder diffraction,
target copper with secondary monochromate. The transmission elec-
tron microscopy images were performed using JEOL JEM-1200 EX II,
Japan at 60–70 kV.
2. Experimental
2.1. Chemicals
All chemicals were purchased and used without further purification.
4-aminoantipyrine, furaldehyde, 2-thiophene carboxaldehyde, 2-
methoxybenzaldehyde, and nickel(II) chloride hexahydrae were re-
ceived from BDH Company, and other chemicals and solvents used
without purification.
2.2. Synthesis of Schiff bases ligands
The Schiff bases (Ln = L1, 2-furaldehyde; L2, 2-thiophene
carboxaldehyde; L3, 2-methoxybenzaldehyde, see Fig. 1) were pre-
pared according to the previous procedures [46–48]. The Schiff
bases were synthesis by mixing 4-aminoantipyrine (10 mmol) with
2-furaldehyde, 2-thiophene carboxaldehyde or 2-methoxybenzaldehyde
(10 mmol) solution that were dissolved in 20 mL of ethanol in the
presence of one drop of glacial acetic acid. The mixtures were refluxed
for 2–3 h. The resulting mixtures were cooled to room temperature
and the obtained precipitates were filtered, washed several times
with distilled water recrystallized from ethanol and dried over anhy-
drous calcium chloride under vacuum.
3. Results and discussion
3.1. Preface
The molecular formulas, color, melting points, yield, elemental anal-
yses (%C, %H, %N, and %Ni elements), magnetic moments, molar conduc-
tance, and electronic spectral data of the resulted Schiff base Ni(II)
complexes have been listed in Table 1. The general formula of Ni(II)
complexes can be presented as [Ni(Ln)2(Cl)2] (where, Ln = L1, L2 or
L3). The respected complexes are olive green to greenish brown color.
These complexes are stable in air and have melting points above

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S.M. El-Megharbel et al. / Journal of Molecular Liquids 216 (2016) 608–614
Table 1
Physical and analytical data of Ni(II) Schiff bases complexes.
Analytical and
physical data
Complexes
[Ni(L1)2(Cl)2]
[Ni(L2)2(Cl)2]
[Ni(L3)2(Cl)2]
Color
Greenish brown
N300
76
Greenish brown
N300
72
Olive green
N300
77
M.p/oC
Yield/%
%C
Calcd.
Found
Calcd.
Found
Calcd.
Found
Calcd.
Found
55.52
55.12
4.37
4.21
12.14
12.09
8.48
8.42
53.06
52.98
4.17
4.10
11.60
11.55
8.10
8.06
59.09
59.00
4.96
4.94
10.88
10.76
7.60
7.54
%H
%N
%Ni
Λ
M/Ω−1·cm2·mol−1
10
16
18
μB/BM
λ/nm
3.20
3.42
3.31
259, 295, 413, 683, 762
262, 295, 362, 539, 753
273, 288, 369, 783
300 °C. All the Schiff base complexes are insoluble in water and ethanol,
but are soluble in DMSO and DMF organic solvents.
(ν1); 3 2g→3T1g (F), (ν2) and 3 2g→3T2g (P), (ν3) transition, respec-
A A
tively (Fig. 2). The 3A2g→3T2g (P), (ν3) transition band is occurring with-
in the 362–413 nm due to organic fraction of the Schiff base complexes.
3.2. Molar conductance
The 3A2g→3T2g (F), (ν1) and 3 2g→3T1g (F), (ν2) transition bands are
A
observed within the 539–783 nm region. The octahedral environment
around Ni(II) ions is further supported by the divide value of ν2/ν1
ratio, which existed in the region 1.1157–1.4527 (see Table 2) [51].
The ligand field parameters like Racah inter-electronic repulsion param-
eter (B), ligand field splitting energy (10 Dq), covalency factor (β) and
ligand field stabilization energy (LFSE) have been calculated. Both
10Dq and B parameters were calculated upon following equations [52];
The molar conductivities were scanned in DMSO solvent with
10−3 mol/cm3 concentration. The low molar conductance values
(10–18 Ω−1·cm2·mol−1) suggest that the Ni(II) Schiff base complexes
are non-electrolytes [49]. The identification test for the chloride ions
inside the coordination sphere was performed using AgNO3 reagent
after decomposition of Ni(II) Schiff base complexes by adding 1 mL of
concentrated HNO3. This result proves that two chlorine atoms are
attached to nickel ion to complete the coordination sphere.
3A2 →3T2 ðFÞ; ðv1Þ ¼ 10Dq
g
g
ꢁ
ꢂ
ꢂ
ꢀ
ꢀ
ꢀ
3A2 →3T1 ðFÞ; ðv2Þ ¼ 7:5B þ 15Dq‐1 225B2 þ 100Dq2−180DqB
1
g
g
2
2
ꢁ
3.3. Electronic spectra
ꢀ
3A2 →3T2 ðPÞ; ðv3Þ ¼ 7:5B þ 15Dq‐1 225B2 þ 100Dq2−180DqB
1
g
g
2
2
UV–vis spectra of the Ln free Schiff base ligands within 200–1100 nm
in DMSO solvent are exhibit two absorption bands at 200–300 nm and
300–400 nm regions. These bands are assigned to π → π* and n → π*
transitions, respectively, for the azomethine, furaldehyde, methoxy,
thiophene and 4-aminoantipyrine moieties. These bands are shifted to
longer wavelength through the status of coordination [50]. The n–π*
transition undergoes a blue shift indicating that the lone pair electrons
of oxygen/sulfur and nitrogen are coordinated to the nickel ion. On
the other hand, the π − π* transition undergoes red shift with an in-
crease in wavelength. The nickel(II) complexes that have an octahedral
geometry exhibit three bands which are assigned to 3A2g→3T2g (F),
The Racah inter-electronic repulsion parameter (B) was also can be
calculated from other following equation [53];
ꢁ
ꢂ
Bcomplex
¼
2v12 þ v22−3v1 v2 =ð15v2−27 v1Þ
The covalency factor was calculated from the following equation;
À
Á
β ¼ Β=Β0 Β0 is the free nickel ion ¼ 1038cm−1
The ligand field stabilization energy (LFSE) is estimated also from
the following equation;
LFSE ¼ 12Dq
Table 2
Ligand field parameters of the Ni(II) Schiff bases complexes.
Ligand field parameters
Complexes
[Ni(L1)2(Cl)2]
[Ni(L2)2(Cl)2]
[Ni(L3)2(Cl)2]
3A2g
3A2g
3A2g
→
→
→
3T2g (F), (ν1)/cm−1
3T1g (F), (ν2)/cm−1
3T2g (P), (ν3)/cm−1
13,123
14,641
24,213
1312.3
1.1157
131
0.126
87.40
45.09
13,280
18,553
27,624
1328.0
1.3971
526
0.507
49.30
45.63
12,771
18,553
27,100
1277.1
1.4527
607
0.585
41.50
43.88
Dq/cm−1
ν2/ν1
B/cm−1
β
βo/%
LFSE/kcal. mol−1
Fig. 2. UV–vis spectra of Ni(II) Schiff bases complexes.

S.M. El-Megharbel et al. / Journal of Molecular Liquids 216 (2016) 608–614
611
The percentage lowering of energy in free gaseous ion (βo) is calcu-
Table 3
Ligand field parameters of the Ni(II) Schiff bases complexes.
lated from the following equation;
Assignments Complexes
βo ¼ 100−ðβ ꢀ 100Þ
L1
Ni-L1
L2
Ni-L2 L3
Ni-L3
ν(C = O)
ν(C = N)
ν(C = C)
νCH; CH3
OCH3
1640
1546
1642
1540
1640 1638 1642
1484 1473 1508
1642
1500
The value of 10 Dq located within 12,771–13,280 cm−1 range and
Racah inter-electronic repulsion parameter (B) has data inside 131–
607 cm−1 region. The B parameter is low in comparison with free
nickel(II) ion (1038 cm−1), this means that nickel(II) complexes have
a covalent character. The LFSE values are located in the range of
43.88–45.63 kcal·mol−1. The covalency factor (β) of resulted com-
plexes has data within 0.126–0.585 range and the percentage lowering
of energy in free gaseous ion (βo) has data inserted within 41.50–87.40%
which they are assigned to the covalency nature of complexes. The
fraction of ν2/ν1 are found in the limit of octahedral geometry
[52–54]. The low values of ν2/ν1 are due to the strong interaction be-
tween 3T1g (P) and 3T1g (F) states.
1600, 1572 1595, 1568 1580 1575 1609, 1593 1604, 1590
3106, 3045 3105, 3041 3045 3045 2933, 2833 2928, 2826
+
the Table 3. In the infrared spectra of the Ni(II) Schiff base complexes,
the presence of the ν(C = O) band at the same place of free Schiff
bases ~1640 cm−1 show that C = O group is uncoordinated to Ni(II)
ion center through oxygen atom. The azomethine, ν(C = N), bands ex-
hibit at 1546, 1484, and 1508 cm−1 for the free L1, L2 and L3 Schiff base
ligands, respectively, are shifted to lower wavenumbers in case of Ni(II)
complexes by 6–9 cm−1. This lower shift of the C = N vibration band is
attributed to the coordination of L1, L2 and L3 toward Ni(II) ion through
nitrogen atom of the azomethine group as a donor center. The bands ap-
pear at ~1300 and 1250 cm−1 in the free ligands may be assigned due to
stretching vibration of C–O or C–S group [55,56] in furaldehyde,
thiopene and methoxy moieties are shifted to lower wavenumber by
10–15 cm−1 in the spectra of Ni(II) complexes. This indicates that the
oxygen or sulfur of C–O or C–S group coordinated to Ni(II) ion in all
complexes. There are new vibration bands within 400–500 cm−1, that
can be assigned to the stretching motions of Ni-O or Ni-N bonds.
Based on this interpretation, Schiff bases coordinated to Ni(II) as a neu-
tral bidentate ligand through the nitrogen and oxygen/sulfur atoms of
azomethine and furaldehyde/thiopene moieties with two chlorine
atoms completed coordination sphere around Ni(II) central ion (see
Fig. 4).
3.4. Magnetic moments
The magnetic moment (μB/BM) data of the [Ni(Ln)2(Cl)2] (where,
Ln = L1, L2 or L3) complexes are inserted in Table 1. The effective mag-
netic moments of respected Ni(II) complexes located within the high
spin octahedral (3.00–3.50 BM). The high spin data are due to the
arise from the spin orbit coupling which causes an orbital contribution
to the quenched 3A2g ground state of Ni(II) ion in an octahedral struc-
ture [51]. Three Ni(II) complexes have magnetic moment values in the
region of 3.20–3.42 BM that are matching with an octahedral geometry.
3.5. Infrared spectra
The infrared spectroscopic tool is an essential technique to identify
the functional groups of any synthetic organic molecules. Fig. 3 is repre-
sented to the infrared spectra of the three Ni(II) Schiff base complexes
and nickel(II) oxide residual product which prepared at the 800 °C for
3 h by thermal decomposition method for the three Ni(II) Schiff base
complexes. In Table 3, All free Schiff bases ligands L1, L2 and L3 have
two peaks at 1640–1642 and 1484–1546 cm−1 due to the stretching vi-
brations of C = O and C = N bonds, respectively. The presence of C = N
band is assigned to the synthesis of Schiff base ligand based on the
condensation reactions between 4-aminoantipyrine and three types of
aldehydes 2-furaldehyde (L1), 2-thiophene carboxaldehyde (L2) and
2-methoxybenzaldehyde (L3). The bands existed at 1580–1609 cm−1
were assigned to stretching, vibration bands of C = C for the aromatic
moieties [55]. The bands at 3100–3045 cm−1 were referred to the –
CH3 group of 4-aminoantipyrine, meanwhile, the two bands at 2933
and 2833 cm−1 in the manner of L3 were attributed to C-H stretching
vibration of –OCH3 group. The main FT-IR vibration bands are listed in
The FT-IR spectrum of NiO nanoparticles resulted from the thermal
decomposition of the three Ni(II) Schiff base complexes at 800 °C for
3 h is shown in Fig. 5. The band at 466 cm−1 in the spectrum is assigned
to Ni–O stretching which agreement with standard data [57].
3.6. Thermal analysis
Fig. 6 refers to the decomposition process with the calcination tem-
peratures of the three nickel(II) Schiff base complexes as a nucleus key
to prepare nanometer nickel oxide. The Ni-L2 and Ni-L3 complexes are
completely decomposed at ~600 °C, but, Ni-L1 complex decompose at
~700 °C to gave NiO. So, it's better to select Ni-L2 and Ni-L3 as a prefer-
able precursors for the preparation of NiO nanoparticles. The thermal
degradation of Ni(II)-Ln (n = L1, L2 or L3) complexes were occurred
at three overlapping steps, that attributed to decompose and loss of
two ligands and two chlorine atoms. The residual product is agreement
with NiO molecule (Fig. 5). The percentage found for the residuals after
decomposition are 10.15, 10.78 and 9.41% giving an actual total weight
losses of 89.85, 89.22 and 90.59% in agreements with our calculated
total weight loss values of 89.21, 89.69 and 90.33%.
3.7. XRD, EDX, SEM and TEM morphological studies
Fig. 7 shows XRD and EDX spectra of NiO obtained from the thermal
decomposition of Ni-L2 complex at 600 °C. The chemical composition of
the NiO was determined using energy-dispersive X-ray diffraction
(EDX), this spectrum of NiO (Fig. 7) has two essential peaks of nickel
and oxygen elements only. The chemical analysis resulted by EDX for
the residual molecule shows a homogenous distribution of each nickel
metal ion. XRD patterns of the NiO is depicted in Fig. 7. Inspecting
of these patterns, we notice that the system is well crystalline. The def-
inite diffraction data like angle (2θ°), interplanar spacing (d value,
Angstrom), and relative intensity (%) have been calculated. The values
Fig. 3. FT-IR spectra of Ni(II) Schiff bases complexes.

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S.M. El-Megharbel et al. / Journal of Molecular Liquids 216 (2016) 608–614
Fig. 6. TG diagrams of Ni(II) Schiff bases complexes.
Deby-Scherrer formula D = 0.94λ/βCosθ [58]. Where D is the particle
size of the crystal gain, λ is the x-ray wavelength (1.5406 Ǻ), θ is the
Bragg diffraction angle and β is the integral peak width. The particle
size was estimated according to the highest value of intensity compared
with the other peaks, This data gave an impression that the particle size
of NiO exhibit within nano scale range at 18, 15 and 20 nm for Ni-L1, Ni-
L2 and Ni-L3 complexes as a primary nucleus for preparation of NiO. The
main diffraction patterns of NiO well indexed to pure cubic phase [57].
The NiO nanoparticles obtained from the three Schiff base primary nu-
cleus have the same crystal structure and have a narrow scale with par-
ticle size ~18 nm. From this result, we can conclude that the difference
in aldehyde molecule (2-furaldehyde, 2-thiophene carboxaldehyde and
2-methoxybenzaldehyde) don't have any massive change in the particle
size, but we decided in the future to explain the effect of different
amines in the crystal structure and particle size of the residual oxides.
Fig. 8 shows the surface morphology of NiO nanoparticles prepared
from Ni-L2 and Ni-L3 complexes which calcinated at 600 °C based on
SEM and TEM images. These images show the size of pores to be quite
different with different precursors. SEM images show small to medium
particles which tendency to agglomerates formation with different
shapes. The TEM image (Fig. 8) refers to nanoparticles size of NiO with
a patchy fashion. The nanosized of NiO molecule was calculated from
TEM that has ~18 nm which agrees with XRD data.
Fig. 4. Speculated structures of Ni(II) complexes.
of 2θ°, d value (the volume average of the crystal dimension normal to
diffracting plane), full width at half maximum (FWHM) of prominent
intensity peak, relative intensity (%) and particle size of NiO were
estimated. The maximum diffraction patterns of NiO exhibited at 2θ°
(Intensity) = 43(100%). The crystallite size could be estimated from
the XRD patterns by applying FWHM of the characteristic peaks using
3.8. Catalytic activity
Hydrogen peroxide is an oxidizing agent and its play an important
role in the industrial applications such as bleach in the textile, paper
pulp and in treatment of waste water [59]. The catalytic activities of
oxides and mixed oxides on the decomposition of H2O2 have been stud-
ied in literature [60,61]. These studies reveal that mixed oxide catalyst
is more active in the decomposition reaction of hydrogen peroxide
[62,63]. These catalysts have a great attention of the chemist due to
their application as low-cost fuel cells, their stability and highly activity
[64]. The catalytic activity of this catalyst depends on the preparative
methods viz. combustion method, oxalate route, co-precipitation meth-
od, solid solution precursor wet chemical method, sol–gel method, mi-
crowave synthesis, oxidation method, spray dry etc. [65,66]. Out of
these methods, thermal decomposition method is important because a
catalyst is prepared within a short time, simple technique. This paper
aimed to study the H2O2 decomposition on NiO nanoparticles at room
temperature with different weights of NiO in solid phase.
Different weights (10, 20, 30, 40 and 50 mg) from the NiO nanopar-
ticles catalyst which resulted from thermal decomposition of Ni-L2
complex at 600 °C were shaken with 15 mL of H2O2 (0.2 N) in a volu-
metric flask for 45 min at room temperature in order to determine the
decomposition rate of H2O2 and escalation of oxygen gas. The reaction
mixtures were acidified by adding 15 mL of 0.5 N sulfuric acid and
Fig. 5. FT-IR spectrum of NiO nanoparticles resulted from thermal decomposition of Ni(II)
Schiff base complexes at 800 °C.

S.M. El-Megharbel et al. / Journal of Molecular Liquids 216 (2016) 608–614
613
Fig. 7. XRD and EDX of NiO resulted from the thermal decomposition of Ni-L2 Schiff base complex precursor at 600 °C.
start the titration process using 0.02 N of potassium permanganate re-
agent [67]. The decomposition of H2O2 can be used as a simple paradigm
to recognize about the catalytic activity of NiO nanoparticles with
different weights. The effect of variable weights and their relationship
to the exposed surface area on the decomposition of H2O2 at constant
room temperature and concentration of H2O2 was performed
Fig. 8. SEM images of (A and B) and TEM images of (C and D) for Ni-L2 and Ni-L3 complexes, respectively, after ignited at 600 °C.

614
S.M. El-Megharbel et al. / Journal of Molecular Liquids 216 (2016) 608–614
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Variable weights (mg)
Decomposition percentages of H2O2 (%)
10
20
30
40
50
Blank test
51
63
71
79
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29
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−
NiO þ HO−2 → ½NiO :::::::HO2ꢁ
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−
½NiO :::::::HO2ꢁ þ H2O2 → NiO þ H2O þ OH− þ O2
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