Synthesis and characterization of novel Cu (II) complexes with 3-substituted-4-amino-5-mercapto-1,2,4-triazole Schiff bases: A new route to CuO nanoparticles

Article abstract of DOI:10.1016/j.molstruc.2015.01.017

Cu (II) complexes, were synthesized with newly derived biologically active 1,2,4-triazole Schiff bases. The Schiff bases were synthesized by condensation of 3-substituted-4-amino-5-mercapto-1,2,4-triazole with dibenzoylmethane. The synthesized compounds were characterized using elemental analysis, magnetic moment, thermal analysis and spectral tools (FT-IR, ¹HNMR, ESR, and UV-Vis spectroscopy). All the synthesized complexes are nonelectrolytes in N,N-dimethylformamide. The synthesized Schiff bases and their Cu (II) complexes have been screened for antibacterial (Escherichia coli & Staphylococcus aureus) and antifungal (Aspergillus flavus & Candida albicans) activity using a modified Bauer-Kirby method. Interestingly, the synthesized Cu (II) complexes were used as precursors for CuO nanoparticles which were characterized using XRD, HR-TEM, FT-IR and UV-Vis spectroscopy. The photocatalytic activity of the prepared CuO nanoparticles was studied by performing the degradation of methylene blue dye under UV illumination in the presence of H₂O₂ and the results showed that the maximum percent of the degradation of methylene blue dye (MB) was found 96.18% after 360 min.

Full text of DOI:10.1016/j.molstruc.2015.01.017

Accepted Manuscript
Synthesis and characterization of novel Cu (II) complexes with 3-substitued-4-
amino-5-mercapto-1,2,4-triazole Schiff bases: A new route to CuO nanoparti-
cles
Hisham M. Aly, Moustafa E. Moustafa, Moustafa Y. Nassar, Ehab A.
Abdelrahman
PII:
S0022-2860(15)00023-X
DOI:
http://dx.doi.org/10.1016/j.molstruc.2015.01.017
MOLSTR 21262
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
27 December 2014
9 January 2015
9 January 2015
Please cite this article as: H.M. Aly, M.E. Moustafa, M.Y. Nassar, E.A. Abdelrahman, Synthesis and characterization
of novel Cu (II) complexes with 3-substitued-4-amino-5-mercapto-1,2,4-triazole Schiff bases: A new route to CuO
nanoparticles, Journal of Molecular Structure (2015), doi: http://dx.doi.org/10.1016/j.molstruc.2015.01.017
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Synthesis and characterization of novel Cu (II) complexes with
3-substitued-4-amino-5-mercapto-1,2,4-triazole Schiff bases: A new
route to CuO nanoparticles
Hisham M. Alya, Moustafa E Moustafa a,*, Moustafa Y. Nassara and Ehab
A. Abdelrahmana
a
Chemistry Dept., Faculty of Science, Benha University, Benha, 13518,
Egypt.
E-mail of the corresponding author*: dr.moustafa1955@yahoo.com
Tel/ Fax: +2013-33222578
Abstract
Cu (II) complexes, were synthesized with newly derived
biologically active 1,2,4-triazole Schiff bases. The Schiff bases were
synthesized by condensation of 3-substituted-4-amino-5-mercapto-1,2,4-
triazole with dibenzoylmethane. The synthesized compounds were
characterized using elemental analysis, magnetic moment, thermal
1
analysis and spectral tools (FT-IR, HNMR, ESR, and UV-Vis
spectroscopy). All the synthesized complexes are nonelectrolytes in
N,N-dimethylformamide. The synthesized Schiff bases and their Cu (II)
complexes have been screened for antibacterial (Escherichia coli &
Staphylococcus aureus) and antifungal (Aspergillus flavus & Candida
albicans) activity using a modified Bauer- Kirby method. Interestingly,
the synthesized Cu (II) complexes were used as precursors for CuO
nanoparticles which were characterized using XRD, HR-TEM, FT-IR and
UV-Vis spectroscopy. The photocatalytic activity of the prepared CuO
nanoparticles was studied by performing the degradation of methylene
blue dye under UV illumination in the presence of H2O2 and the results
showed that the maximum percent of the degradation of methylene blue
dye (MB) was found 96.18% after 360 min.
1

Keywords: 1,2,4-triazole; Schiff base complexes; Biological activity;
Nanoparticles; XRD; Photocatalytic degradation.
1. Introduction
Compounds of 1,2,4-triazole and their derivatives constitute an
important class of organic compounds with diverse agricultural, industrial
and biological activities. The synthesis of such compounds has received
a considerable attention in recent years [1- 9]. There are numerous
researches reporting the method of synthesizing 1,2,4-triazole Schiff
bases and their diverse biological activities such as antioxidant, antitumor
and antimicrobial. The results of these previous studies indicated that the
Schiff bases possess mostly moderate to significant activities against
different bacterial and fungal strains, which might be due to azomethine
linkage and/or hetero atoms present in such compounds [10-15].
Moreover, transition metal complexes of triazole Schiff bases have
antibacterial and antifungal activities. It is noteworthy that biological
activities of the majority of the Schiff bases increased upon coordination
with different transition elements. In addition, it was revealed that such
compounds, which were already active, became more active and those
which were not biologically active became very active upon coordination.
The improvement in biological activities upon coordination may be
explained on the basis of Overton’s concept and chelation theory [16-28].
Copper is considered as one of the most important transition metals,
which possess the ability to form biologically active coordination
compounds especially with Schiff bases [29-33]. On the other hand,
using coordination compounds as new precursors to produce nanosized
metal oxides, were regarded as one of the most convenient and practical
routes because it does not only help to avoid special instruments and
complicated processes, but also it provides novel structures and good
purity for the resultant products [34-46]. CuO nanoparticles play an
2

important role among those oxides, because of its vast applications in
different fields such as lithium batteries [47], Pseudo capacitors [48], and
photocatalytic degradation of dyes [49–56]. Although there are several
valid routes for the synthesis of CuO nanostructures such as nanocasting
method, surfactant template approach, and others, those methods are
complicated and/or require long time [49-60]. The numerous methods
developed for the synthesis of CuO nanostructures, using the coordination
compounds as precursors were considered as one of the most convenient
and practical approaches [43-46]. In the present work, new bioactive
triazole Schiff bases were synthesized by reacting 4-amino group of
3-substitued-4-amino-5-mercapto-1,2,4-triazole with dibenzoylmethane.
These newly synthesized triazole Schiff bases were further used to react
with Cu (II) to form their respective Cu (II) complexes with the hope that
the produced complexes would form a novel class of metal based
bioactive compounds and, moreover, may have a tendency to reduce the
resistivity of bacterial/fungal strains. The synthesized triazole Schiff
bases and their Cu (II) complexes were characterized by FT-IR, 1HNMR,
ESR, thermal analysis, molar conductance, magnetic moments, UV-Vis
spectroscopy and elemental analysis data. CuO nanoparticles were
synthesized through the decomposition of the corresponding Cu (II)
complexes, and then their catalytic activities toward methylene blue dye
(MB) have been studied under UV illumination in the presence of H2O2.
The produced CuO nanoparticles were characterized by XRD, HR-TEM,
FT-IR and UV-Vis spectroscopy.
3

2. Experimental
2.1. Materials and reagents
Copper
chloride
(CuCl2.2H2O)
and
dibenzoylmethane
(PhCOCH2COPh) were obtained from Aldrich chemical company.
All reagents were of analytical grade and they were purchased and used
as received without further purification. The thiocarbohydrazide and
3-R-4-amino-5-mercapto-1,2,4-triazoles (R=H, CH3 or C2H5) were
prepared as reported [61- 64].
2.2. Synthesis of precursors
2.2.1. Synthesis of Schiff bases
A methanolic mixtures of 3-R-4-amino-5- mercapto-1,2,4-triazole
(R=H, CH3 or C2H5) and dibenzoylmethane in a 2:1 molar ratio were
refluxed for 5 h in the presence of a few drops of concentrated sulfuric
acid . After that, the reaction mixture was left for some time to attain the
room temperature. The yellow precipitate was filtered off, washed with
cold methanol and ether, re-crystallized from ethanol and dried under
vacuum. The prepared Schiff bases are referred to as HL1, HL2 and HL3
with 65.5, 73.3 and 79.5 % yield in case of R= H, CH3 and C2H5,
respectively.
Anal.Calc. HL1, C19H16N8S2, m.p. (100-104oC), (Mwt = 420.52):
C, 54.27; H, 3.84; N, 26.65; S, 15.25 %. Found: C, 54.25; H, 3.85;
1
N, 26.63; S, 15.24 %. HNMR (DMSO-d6), δ, ppm: 17.06(s, 2H, NH),
7.30-8.20 (m, 10H, Ar-H), 4.80 (s, 2H, CH2 aliphatic), 6.30 (s, 2H, H-
Triazole). IR, ν, Cm-1: 3400 (medium broad, NH-Triazole ring,
stretching), 1625 (medium, C=N, stretching), 1260 (medium, C=S,
stretching), 1575-1400 (multi bands, C=C, aromatic stretching),
785-740 (multi- bands, C-H, out of plan bending of aromatic rings).
Anal.Calc. HL2, C21H20N8S2, m.p. (190-192oC), (Mwt = 448.57):
C, 56.23; H, 4.49; N, 24.98; S, 14.30 %. Found: C, 56.20; H, 4.50;
4

1
N, 24.83; S, 14.27 %. HNMR (DMSO-d6), δ, ppm: 13.40(s, 2H, NH),
7.30-8.20 (m, 10H, Ar-H), 4.80 (s, 2H, CH2 aliphatic), 2.33 (s, 6H, CH3-
Triazole). IR, ν, Cm-1: 3460 (medium broad, NH-Triazole ring,
stretching), 1620 (medium, C=N, stretching), 1265 (medium, C=S,
stretching), 1575-1400 (multi bands, C=C, aromatic stretching),
785-740 (multi- bands, C-H, out of plan bending of aromatic rings).
Anal.Calc. HL3, C23H24N8S2, m.p. (110-112oC), (Mwt = 476.63):
C, 57.96; H, 5.08; N, 23.51; S, 13.46 %. Found: C, 57.73; H, 4.98;
1
N, 23.31; S, 13.29 %. HNMR (DMSO-d6), δ, ppm: 13.40(s, 2H, NH),
7.30-8.20 (m, 10H, Ar-H), 4.80 (s, 2H, CH2 aliphatic), 1.18 (t, 6H, CH3-
Triazole), 2.64 (q, 4H, CH2-Triazole). IR, ν, Cm-1: 3480 (medium broad,
NH-Triazole ring, stretching), 1600 (medium, C=N, stretching),
1260 (medium, C=S, stretching), 1575-1400 (multi-bands, C=C, aromatic
stretching), 785-740 (multi- bands, C-H, out of plan bending of aromatic
rings).
2.2.2. Synthesis of Cu (II) Schiff base complexes
An ethanolic solution of Schiff base (HL1, HL2 or HL3) was
refluxed with an ethanolic solution of CuCl2.2H2O in 1:1 molar ratio on
steam bath for 5 h. Then, to the reaction mixture 2 mmol of sodium
acetate trihydrate was added and reflux was continued for 10 h.
The separated complexes was filtered off, washed thoroughly with water,
ethanol and ether and finally dried in vacuum over fused CaCl2.
Anal.Calc. Cu-HL1, C19H26Cl2Cu2N8O6S2, (Mwt = 724.59):
C, 31.49; H, 3.62; N, 15.46; S, 8.85 %. Found: C, 31.35; H, 3.77;
N, 15.32; S, 8.65 %. IR, ν, Cm-1: 3450 (medium broad, NH-Triazole ring,
stretching), 1600 (medium, C=N, stretching), 1575-1400 (multi bands,
C=C, aromatic stretching), 785-740 (multi bands, C-H, out of plan
bending of aromatic rings), 525 (medium, M-N, stretching).
5

Anal.Calc. Cu-HL2, C21H30Cl2Cu2N8O6S2, (Mwt = 752.64):
C, 33.51; H, 4.02; N, 14.89; S, 8.52 %. Found: C, 33.37; H, 4.11;
N, 14.90; S, 8.54 %. IR, ν, Cm-1: 3450 (medium broad, NH-Triazole ring,
stretching), 1605 (medium, C=N, stretching), 1575-1400 (multi bands,
C=C, aromatic stretching), 785-740 (multi bands, C-H, out of plan
bending of aromatic rings), 522 (medium, M-N, stretching).
Anal.Calc. Cu-HL3, C23H34Cl2Cu2N8O6S2, (Mwt = 780.69):
C, 35.38; H, 4.39; N, 14.35; S, 8.21 %. Found: C, 35.30; H, 4.41;
N, 14.59; S, 8.24 %. IR, ν, Cm-1: 3460 (medium broad, NH-Triazole ring,
stretching), 1597 (medium, C=N, stretching), 1575-1400 (multi bands,
C=C, aromatic stretching), 785-740 (multi bands, C-H, out of plan
bending of aromatic rings), 520 (medium, M-N, stretching).
2.3. Synthesis of nanosized CuO
The as-prepared Cu (II) complexes were thermally decomposed for
o
2 h at 650 C in an open air electric furnace to produce CuO
nanoparticles.
2.4. Physical measurements
FT-IR spectra of Schiff bases, their Cu (II) complexes and Cupper
oxides were recorded on a Nicolet iSio FT-IR spectrophotometer in the
4000–400 cm-1 region in KBr disks. Electronic spectra of the complexes
were recorded in N,N-dimethylformamide (DMF) and nujol oil on
1
Jasco (V-530) UV-Vis spectrophotometer. The HNMR spectra of Schiff
bases were recorded in DMSO on a Bruker 300 MHz spectrometer at
room temperature using TMS as an internal reference. Differential
thermal and thermogravimetric analysis (DTA-TG) of the prepared
Cu (II) complexes, measured from room temperature to 1000oC at
o
a heating rate of 10 C min-1, were obtained using Shimadzu TA-60 WS
thermal analyzer. Elemental analyses for C, H, N, and S were done using
Elementer Vario EL III Carlo Erba 1108 instrument. ESR of Cu (II)
6

complexes was recorded on Varian E-9 spectrophotometer.
Molar conductivity measurements of the complexes were recorded on an
YSI conductivity bridge with a cell having cell constant 1. X-ray powder
diffraction (XRD) of the as-prepared cupper oxides were recorded on
a 18 kW diffractometer (Bruker; model D8 Advance) with
monochromated Cu Kα radiation (λ) 1.54178 Å. The HR-TEM images
were taken on a transmission electron microscope (JEOL; model
1200 EX) at an accelerator voltage of 220 kV. The molar magnetic
susceptibility; χM of the synthesized Cu (II) complexes was measured
using Gouy balance at room temperature. The sample was packed in
a Gouy tube of known mass. Mercury (II) tetrathiocyanatocobaltate
[Hg {Co (SCN) }] was used for the calibration of the Gouy tube.
4
The obtained values were corrected for diamagnetism using Pascal's
constants.
2.4.1. Biological activity
Antimicrobial activities of Schiff bases, their Cu (II) complexes
and as-prepared CuO nanoparticles were determined using a modified
Bauer- Kirby method [65]. Briefly, 100 μL of the pathogenic
bacteria/fungi were grown in 10 mL of fresh media until they reached
a count of 108 cells/mL for bacteria or 105 cells/mL for fungi [66].
100 μL microbial suspensions were spread onto agar plates corresponding
to the both pathogens in which they were maintained. Isolated colonies of
each organism were selected and tested for susceptibility by disc
diffusion method. A filter paper disc impregnated with the tested
chemical was placed on agar. Plates with fungi (Aspergillus flavus and
o
Candida albicans) were incubated at 25-27 C for 24-48 h. whereas,
plates with gram negative bacteria (Escherichia coli)/ gram positive
bacteria (Staphylococcus aureus) were incubated at 35-37 oC for 24-48 h.
The diameter of the inhibition zone was measured in millimeters.
7

2.4.2. Photocatalytic activity measurements
The Photocatalytic degradation of methylene blue dye (MB)
solution is performed using CuO sample prepared using Cu (II)-HL3.
For a typical photocatalytic experiment, 100 mg of the prepared
photocatalyst is added to 50 mL of 10 mg/L aqueous dye solution.
The solution in which the prepared photocatalysts are dispersed is first
kept in the dark for 2 h to allow the system to reach an adsorption
desorption equilibrium. Afterwards, 2 mL of 0.2 M H2O2 solution was
added and UV light (at 365 nm) irradiation of the solution is started.
The degradation was investigated in a Pyrex beaker under the UV
illumination using a 250 W xenon arc lamp (Thoshiba, SHLS-002)
(λ = 365 nm). After recovering the catalyst by centrifugation, the light
absorption of clear solution is measured at 664 nm (λmax for MB) at a set
time using a UV–Vis spectrophotometer.
3. Results and Discussion
3.1. Synthesis and characterization of HL1, HL2 and HL3 Schiff
bases.
New triazole Schiff bases were synthesized by the reaction of
3-R-4-amino-5-mercapto-1,2,4-triazole (R=H, CH3 or C2H5) with
dibenzoylmethane in 2:1 ratio as shown in Scheme 1. Characterization of
the synthesized Schiff bases was carried out by m.p, FT-IR, 1HNMR and
elemental analysis. The C, H, N and S % obtained from elemental
analysis are in excellent agreement with the proposed molecular
formulas.
3.1.1. FT-IR spectra of HL1, HL2 and HL3 Schiff bases
In the FT-IR spectra of the synthesized Schiff bases (Fig. 1),
a medium intensity broad band observed in the range of 3500-3100 cm-1
is attributed to NH stretching of the triazole ring whereas, a medium to
high intensity band observed in the range of 1625-1600 cm-1 is attributed
8

to C=N stretching. The absorption at about 1260 cm-1 can be assigned to
C=S stretching. Various absorption bands observed in the range of
1575-1400 cm-1 are assigned to C=C aromatic stretching vibrations
whereas, bands observed in the range of 785-740 cm-1 are assigned to
C-H out of plane bending of aromatic rings [ 67-69].
3.1.2.1HNMR spectra of HL1, HL2 and HL3 Schiff bases
The 1HNMR spectra (in d6-DMSO) of the synthesized Schiff bases
have signals at about : 13.40 (s, 2H, NH) (HL2 and HL3), 17.06(s, 2H,
NH) (HL1), 7.30-8.20 (m, 10H, Ar-H), 4.80 (s, 2H, CH2 aliphatic),
6.30 (s, 2H, H-Triazole- HL1), 2.33 (s, 6H, CH3-Triazole- HL2),
1.18 (t, 6H, CH3-Triazole- HL3) and 2.64 (q, 4H, CH2-Triazole-HL3)
[70]. The existence of NH on the triazole ring also was proved through its
disappearance in 1HNMR (d6-DMSO-D2O).
3.2. Synthesis and characterization of Cu (II) Schiff base complexes
Solid Cu (II) Schiff base complexes were synthesized by allowing
the synthesized Schiff bases to react with CuCl2.2H2O in 1:1 ratio.
All the synthesized Cu (II) complexes are stable at room temperature,
nonhygroscopic and soluble in DMF and DMSO. The synthesized
Cu (II) complexes were characterized using elemental analysis, molar
conductivity, FT-IR, magnetic moment, ESR, DTG analysis, and UV-Vis
spectroscopy. The elemental analyses of Cu (II) complexes are in
excellent agreement with the proposed molecular formulas. The structure
of the Cu (II) complexes are shown in scheme 1.The molar conductivity
-3
measurements at 10
nonelectrolytes.
M in DMF indicate that these complexes are
3.2.1. FT-IR spectra of Cu (II) Schiff base complexes
In the FT-IR spectra of the synthesized Schiff bases, a medium
intensity broad band observed in the range of 3500-3400 cm-1 is
attributed to NH stretching of the triazole ring. This band was observed in
9

all the complexes (Fig. 1) in the range of 3450-3460 cm-1, confirming that
NH is not involved in coordination. A medium to high intensity band in
the range of 1625-1600 cm-1 is attributed to C=N stretching which shifts
lower by 20-25 cm-1 to 1602-1580 cm-1 after coordination. This supports
Schiff base coordination to Cu (II) through the nitrogen atom of C=N
group. This is further supported by the appearance of a medium intensity
band in the range of 525-520 cm-1 which assigned to Cu-N stretching
[71]. The characteristic absorption at about 1260 cm-1 for C=S group
disappeared after coordination and this confirming that; sulfur atom is
involved in coordination.
3.2.2. Electronic spectra of Cu (II) Schiff base complexes
In octahedral crystal field, the ground state electronic distribution
6
3
2
of Cu2+ is t2g eg which yields Eg term whereas, the excited electronic
5
4
2
state is t2g eg which corresponds to T2g term. Thus only one single
2
2
electron transition, i.e., Eg → T2g, is expected in an octahedral crystal
field. Octahedral coordination is distorted either by elongation or
2
compression leading to tetragonal symmetry. Normally, the ground Eg
state is split due to Jahn-Teller effect and hence lowering of symmetry is
2
2
expected for Cu (II) ion. Thus, Eg state splits into B1g (dx2-y2) and
2
2A1g (dz2) in tetragonal symmetry whereas, the excited term T2g also
2
2
splits into B2g (dxy) and Eg (dxz, dyz). Electronic spectra of Cu (II)
complexes exhibit broad bands in the range of 14598 - 14947cm-1 with
a shoulder on the low energy side at the range of 11587 - 11820cm-1,
which can be assigned respectively to 2B1g→2Eg and 2B1g→2A1g transition
in a tetragonally distorted octahedral configuration as shown in
Table (1) [71].
10

3.2.3. Magnetic studies and Conductivity measurements of
Cu (II) Schiff base complexes
The magnetic measurements for Cu (II)-HL1, Cu (II)-HL2, and
Cu (II)-HL3 complexes are 1.76, 1.82 and 1.86 B.M., respectively, which
regarded slightly higher than the spin only value 1.73 B.M. expected for
one unpaired electron [71] whereas the molar conductivity values,
24, 24 and 28 Ω-1 cm2 mol-1., respectively, indicates the non-electrolyte
nature of such complexes [71].
3.2.4. ESR of Cu (II) Schiff bases complexes
Electron Spin Resonance (ESR) is a branch of spectroscopy in
which radiation of microwave frequency is absorbed by molecules
possessing electrons with unpaired spins [72]. This method is an essential
tool for the analysis of the structure of molecular systems or ions
containing unpaired electrons, which have spin-degenerate ground states
in the absence of magnetic field. In the study of solid state materials,
ESR method is employed to understand the symmetry of surroundings of
the paramagnetic ion and the nature of its bonding to the nearest
neighboring ligands. When a paramagnetic substance is placed in a steady
magnetic field (H), the unpaired electron in the outer shell tends to align
with the field. So the two fold spin degeneracy is removed. Thus the two
energy levels, E1/2 and E-1/2 are separated by gβH, where g is
spectroscopic splitting factor and is called gyro magnetic ratio which was
divided into two types (g11 (in z-direction) and g┴(in x or y-direction))
and β is the Bohr magneton. Since there is a finite probability for
a transition between these two energy levels, a change in the energy state
can be stimulated by an external radio frequency. When microwave
frequency (υ) is applied perpendicular to the direction of the field,
resonance absorption will occur between the two split spin levels.
11

The resonance condition is given by, hυ = gβH, where h is Planck’s
constant. ESR results give rise to a new parameter, G which is defined as:
(1)
The ESR spectrum of the prepared Cu (II) complexes shows
g11 ˃ g┴ ˃ ge (2.0023) as shown in Fig. 2 and Table 2. This indicates that
tetragonal elongation distortion is predominant and hence, the unpaired
electron is localized in the dx2-y2 orbital. The G parameter observed for
these complexes is less than 4 indicating exchange interaction in the solid
complexes, consistent with distorted octahedral configuration [72].
The optical absorption and ESR data in tetragonal elongation distortion
are related as follows,
(2)
Where,
λ
is the spin-orbit coupling constant for free
Cu (II) ion = - 830 cm-1. The calculated ∆E values are summarized in
Table 2.
Further, if A11, g11 and g┴ values are known, α2 (covalency parameter) can
be estimated using the equation
α2 = (AII/0.036) + (g II-2.0023) + 3/7 (g┴ - 2.0023) + 0.04
(3)
3.2.5. Thermogravimetric and Differential Thermal analysis of
Cu (II) Schiff base complexes
TG and DTG curves (Fig. 2) for Cu-HL3 Schiff base complex
showed two decomposition steps. The first exothermic step in the
12

temperature range 24 - 315oC can be attributed to the loss of six
coordinated water molecules and Cl2 with a weight loss of 22.86 %
(calc. 23.00%) whereas, the second exothermic step in the temperature
range 315-522oC can be attributed to the loss of organic moiety with
a weight loss of 60.00% (calc. 60.87%). Above 522 oC,
Cu (II) complexes were decomposed to their respective oxide (CuO).
The theoretical percent of cupper was 16.27% (calc. 17.14%) [71].
3.3. Synthesis and characterization of CuO nanoparticles
o
Solid Cu (II) complexes were ignited at 650 C to produce the
corresponding copper oxide (CuO), which were characterized using
XRD, HR-TEM, FT-IR and optical properties. By this fast and simple
method, CuO nanoparticles can be produced without expensive and toxic
solvents or complicated equipment.
3.3.1. XRD and HR-TEM of CuO
The crystalline structures of CuO samples were characterized using
XRD as shown in Fig. 3. All these diffraction peaks, including not only
the peak positions but also their relative intensities, can be perfectly
indexed into the monoclinic phase of CuO with cell constants:
a = 4.678 Å, b = 3.431 Å and c = 5.136 Å (space group C2/c, JCPDS card
80-0076); these data are in agreement with the ones published by
Z. S. Chickneyan. [73]. No characteristic peaks of other impurity phases
have been detected, indicating that the final product is of high purity.
The average crystal size was estimated using the Debye–Scherrer formula
[74, 75]:
D=0.9λ/βcosƟB
Where, λ, β, ƟB are the X-ray wavelength, the full width at half maximum
(FWHM) of the diffraction peak and the Bragg diffraction angle,
respectively. The estimated crystal size of CuO samples, prepared using
Cu (II) complexes of HL1, HL2 and HL3, using XRD data was found
13

35.60, 34.47 and 28.28 nm, respectively. Whereas, particle size was
supported using HR-TEM (cubic, sphere and irregular shaped aggregates
with average particle size of 26.75, 33.45 and 27.15 nm, respectively) as
shown in Fig. 3. Diffraction patterns obtained from both of HR-TEM
and XRD showed exactly the same d- spacing values (1.26 to 2.54Å) as
shown in Fig. 3. This indicates the crystalline nature of the synthesized
oxides.
3.3.2. FT-IR of CuO
The FT-IR spectra (Fig. 4) showed several significant absorption
peaks. The broad absorption bands in the range of 519- 592 cm−1 is
assigned to Cu–O stretching vibration mode while, the broad absorption
band centered at 3440 cm−1 is attributable to the band O–H stretching
vibrations and the weak band near 1634 cm−1 is assigned to H–O–H
bending vibrations mode were also presented due to the adsorption of
water in air when FT-IR sample disks were prepared in an open air [76].
3.3.3. Optical properties of CuO
UV–Vis absorption spectra were carried out in order to
characterize the optical absorbance properties of the prepared CuO
nanoparticles, as presented in Fig. 4. The band gap (Eg) can be calculated
using the following equation:
(αhυ) n = K (hυ - Eg)
Where, α is the absorption coefficient, K is a constant, Eg is the band gap
and n equals either 1/2 for an indirect allowed transition or 2 for a direct
allowed transition. For the prepared CuO nanoparticles, (αhυ) 2 is plotted
versus hυ, as shown in Fig. 4. The extrapolation of each graph to
2
(αhυ) = 0 yields the optical direct band gaps (Eg) which were found
0.96, 1.00 and 0.98 eV for CuO nanoparticles prepared using Cu (II)
complexes of HL1, HL2 and HL3, respectively. These values reveal that
14

the as-prepared CuO nanoparticles products are semiconductors and are
in a good agreement with the reported data [77].
4. Biological activities
All the synthesized Schiff bases (HL1, HL2 and HL3), their
Cu (II) complexes and as-prepared CuO nanoparticles were screened in
vitro for their biological activities using bacteria ( Escherichia coli
& Staphylococcus aureus) and fungi (Aspergillus flavus &
Candida albicans). Ampicillin (antibacterial agent) and Amphotericin B
(antifungal agent) served as positive controls for antimicrobial activity
and filter disc impregnated with 10 μL of solvent (DMSO) was used as
negative control. During incubation time, the tested chemical diffuses
from the disc into the agar; only around the disc. When the organism is
susceptible to the chemical, it will not grow in an area around the disc.
This area of no growth, known as "zone of inhibition", was measured
and tabulated in Table 3. All tested compounds showed moderate activity
against both pathogenic bacteria strains and poor antifungal activity.
All Cu (II) complexes and CuO nanoparticles showed no activity on both
of A. flavus and C. albicans fungi.
5. Photocatalytic Activity of CuO nanoparticles
The methylene blue dye degradation over the as-prepared CuO,
prepared using Cu (II) - HL3, under UV illumination in the presence of
H2O2 was studied to investigate the photocatalytic activity via photo
Fenton reaction [49-56]. However, it is worthy to mention that CuO
product prepared using Cu (II)-HL3 has specifically been chosen, in
order to exploit high surface area of this product because it has the lowest
crystallite size (28.28 nm). The UV– Vis spectra of the decomposed MB
dye at different reaction times (from 0 to 8 h) under UV illumination in
the presence of H2O2 were depicted in Fig 5(A and B). Fig 5(A and B)
shows that the dye exhibits an absorption peak at 664 nm and the
15

absorption intensity of the dye solution gradually decreases with the
increase of exposed time, indicating a decrease in the MB dye
concentration which consequently means the effective photodegradation
of the dye using CuO catalyst under UV illumination in the presence of
H2O2.This study revealed that almost 96.18% of the MB dye decomposed
under UV illumination in the presence of H2O2 within 6 h which is
considered a very high percent compared with others in literature [49-65].
Several experiments were carried out to degrade MB dye solution in the
presence or absence of UV light and with or without oxidant or catalyst
but the results showed that the photolysis of the dye was negligible
(~ 5-10 %) (Figures omitted for brevity). Photodegradation reaction
mechanism in the presence of UV only, (Catalyst + UV) and (UV+
Catalyst+ H2O2) has been clarified in Scheme 2. After absorbing UV-
-.
light only, the excited MB reduces O2 to O2
Which in turn reacts with
,
.
a proton (from the autoprotolysis of the solvent water) to produce OOH .
In total, the cationic dye radical is degraded to carbon dioxide, water and
mineral acids via intermediate. They also explained OOH. and OH. ,
which are necessary for the complete degradation of the dye [49, 52].
Photocatalytic degradation of MB dye in the presence of (Catalyst+ UV)
usually includes the separation of electron hole pairs and the subsequent
reduction–oxidation reactions under UV-light irradiation, electrons and
holes are generated on the surface of CuO. The electrons scavenged by
the adsorbed molecular oxygen species, and the holes trapped by water or
adsorbed MB molecules. Then MB dye is degraded directly by
-.
.
.
photogenerated oxidants [49, 52] such as O2 , OOH and OH . Adding
H2O2 in the presence of catalyst and UV increases the photodegradation
rate of MB dye because the direct decomposition of H2O2 under UV light
.
produces OH , which directly oxidize MB dye as shown in scheme 2.
16

It is noteworthy that the advantage of using nanosized CuO in the
degradation of MB dye over other copper salts is that they are insoluble
in water, nonpoisonous, highly surface area and reusability performance
[49-56].
6. Conclusion
The Cu (II) complexes were synthesized by the reaction of the
newly prepared 3-R-1,2,4-triazole Schiff bases (R=H, CH3 or C2H5) with
CuCl2.2H2O in 1:1 molar ratio in the presence of sodium acetate
trihydrate at reflux temperature. The synthesized Cu (II) complexes were
characterized using elemental analysis, molar conductivity, FT-IR,
magnetic moment, ESR, DTG analysis, and UV-Vis spectroscopy.
CuO nanoparticles were synthesized via thermal decomposition of newly
prepared Cu (II) triazole Schiff base complexes, as solid precursors.
The as-prepared CuO nanoparticles were characterized using XRD,
HR-TEM, FT-IR and optical properties. By this fast and simple method,
CuO nanoparticles can be produced without expensive and toxic solvents
or complicated equipment. The crystal size was found 35.60, 34.47 and
28.28 nm whereas, the optical enegy gap was found 0.96, 1.00 and 0.98
eV for CuO nanoparticles prepared using Cu (II) complexes of HL1,
HL2 and HL3, respectively. The as-prepared CuO using HL3 (Lowest
particle size = 28.28 nm) was studied for the photocatalytic degradation
of methylene blue dye (MB) under UV illumination in the presence of
H2O2 and the results revealed that almost 96.18% of the MB dye was
decomposed within 6 h. All Schiff bases, their Cu (II) complexes and
CuO nanoparticles showed moderate activity against both pathogenic
bacteria strains (Escherichia coli & Staphylococcus aureus) and poor
antifungal activity (Aspergillus flavus &Candida albicans).
17

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Figure captions:
Fig. 1 FT-IR of Schiff bases (HL1, HL2 and HL3) and their Cu (II)
complexes.
Fig. 2 (A) ESR of Cu-HL1 (B) ESR of Cu-HL2 (C) ESR of Cu-HL3
(D) DTG of Cu-HL3.
Fig. 3 XRD and HR-TEM of CuO prepared using Cu (II) complex of (A)
HL1 (B) HL2 (C) HL3.
Fig. 4 (A) FT-IR of CuO prepared using HL1, HL2and HL3 (B) optical
energy gap of CuO prepared using HL1 (C) optical energy gap of CuO
prepared using HL2 (D) optical energy gap of CuO prepared using HL3.
Fig. 5 (A) photocatalytic degradation of MB dye using CuO prepared
using HL3 (B) % degradation versus time.
Table captions:
Table (1): Electronic absorption spectral data of the synthesized Cu (II)
complexes
Table (2): ESR spectral parameters of the synthesized Cu (II) complexes
Table (3): The antimicrobial activity (in vitro) of synthesized Schiff
bases, their Cu (II) complexes and their copper oxides
23

24

25

26

Scheme 1: Synthesis of 3-R-4-amino-5-mercapto-1,2,4-triazole Schiff
bases (HL1, HL2 and HL3) and their Cu (II) complexes.
27

28

Table (1)
Complex
Nujol mull
CT band
d→d
bands
DMF
28169
28328
28011
Nujol
mull
DMF Assignmen
t
2
26891
30328
25954
11820
14947
11820
14598
11587
14619
11120 B1g→ 2A1g
Cu-HL1
15421 2B1g→ 2Eg
11786 B1g→ 2A1g
2
Cu-HL2
Cu-HL3
13985 2B1g→ 2Eg
11976 B1g→ 2A1g
2
14867 2B1g→ 2Eg
Table (2)
Compound
α2
∆E
g11
g┴
G
∆
∆
II
┴
2.23
2.20
2.45
2.06
2.06
2.13
3.80
3.30
3.46
0.83
0.89
0.89
28869
33200
14755
27666
27666
12769
Cu-HL1
Cu-HL2
Cu-HL3
Table (3)
Compound
E. coli (G-)
Bacteria
Fungi
S. aureus(G+)
A. flavus
C. albicans
9
10
10
11
0.0
9
0.0
9
9
0.0
0.0
0.0
0.0
0.0
10
9
0.0
0.0
0.0
0.0
HL1
HL2
HL3
12
11
0.0
0.0
0.0
10
Cu-HL1
Cu-HL2
Cu-HL3
CuO from
HL1
0.0
11
10
10
11
11
0.0
0.0
0.0
0.0
CuO from
HL2
CuO from
HL3
29