Photocatalytic degradation of methylene blue with copper(II) oxide synthesized by thermal decomposition of Flubendazole complexes

Article abstract of DOI:10.1016/j.jphotochem.2016.04.022

Novel copper(II) complexes of an anti-parasitic Flubendazole drug (FLU), [Cu(FLU)₂X₂]·zH₂O (X = Cl^- (1), C₂H₃O₂^- (3), and ClO₄^- (4), z = 1-4) and [Cu(NO₃)(FLU)₂(OH₂)]NO₃2H₂O (2) were synthesized and characterized using elemental analysis, TG, IR, EPR, magnetic and conductance measurements. Geometry optimization and natural bond orbital analysis were performed at DFT/B3LYP/6-31G^? level of theory. Electronic transitions were calculated by TD-DFT. Tenorite (CuO) nanoparticles with promising catalytic properties were prepared in air via the controlled thermal decomposition of 1-4. The polymorph and morphology of the prepared nano-tenorite particles were investigated by powder XRD and field emission scanning electron microscope. The catalytic degradation of methylene-blue (MB) dye exposed to the UV radiation in presence of CuO nanoparticles as a catalyst was studied at room temperature in water.

Full text of DOI:10.1016/j.jphotochem.2016.04.022

Accepted Manuscript
Title: Photocatalytic degradation of methylene blue with
copper(II) oxide synthesized by thermal decomposition of
Flubendazole complexes
Author: Ahmed M. Mansour Eslam M. El Bakry Nour T.
Abdel-Ghani
PII:
S1010-6030(16)30102-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2016.04.022
JPC 10215
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
11-2-2016
23-4-2016
30-4-2016
Please cite this article as: Ahmed M.Mansour, Eslam M.El Bakry, Nour T.Abdel-Ghani,
Photocatalytic degradation of methylene blue with copper(II) oxide synthesized by
thermal decomposition of Flubendazole complexes, Journal of Photochemistry and
Photobiology A: Chemistry http://dx.doi.org/10.1016/j.jphotochem.2016.04.022
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Photocatalytic degradation of methylene blue with copper(II) oxide synthesized by
thermal decomposition of Flubendazole complexes
Ahmed M Mansour*, Eslam M El Bakry, Nour T Abdel-Ghani*
Chemistry Department, Faculty of Science, Cairo University, Gamaa Street, Giza 12613, Egypt
* Corresponding author, Tel.: +2 02 01222211253; Fax: +20 2 35728843. E-mail: inorganic_am@yahoo.com;
mansour@sci.cu.edu.eg
Graphical abstract
F
O
Z H2O
C
O
O
MX2
H
N
2
C
O
NH
O
Methanol/water
reflux (12h)
NH
N
Cu
X
N
N
H
F
O
Y
O
MX2 = CuCl2.2H2O, Cu(NO3)2.3H2O, Cu2(CH3COO)4.H2O,
Cu(ClO4)2.6H2O
F
O
N
HN
N
H
C
O
X = Y=Cl, Z = 5 (1)
X = NO3 (2), Y = H2O Z = 2 (2)
X = Y=C2H3O2, Z = 1 (3)
X = Y=ClO4 , Z = 3 (4)
CuO nanoparticles
Thermal decomposition of Flubendazole copper(II) complexes gave Tenorite nanoparticles, which were as
catalyst in the catalytic degradation of methylene-blue dye exposed to UV radiation.
Highlights:



Nano-tenorite were synthesized from thermal decomposition of Flubendazole complexes.
The polymorph and morphology of nano-particles were investigated by XRD and SEM.
Photo-acceleration of the degradation process of methylene blue was reported.
1



Electronic structures were assigned by the aid of TD-DFT calculations.
Hybridization, electronic arrangements and M-L interactions were discussed.
Abstract
Novel copper(II) complexes of an anti-parasitic Flubendazole drug (FLU), [Cu(FLU)2X2]·yH2O (X = Cl-
-
-
(1), C2H3O2 (3), and ClO4 (4), y = 1-4) and [Cu(NO3)(FLU)2(OH2)]∙NO3∙2H2O (2) were synthesized and
characterized using elemental analysis, TG, IR, EPR, magnetic and conductance measurements. Geometry
optimization and natural bond orbital analysis were performed at DFT/B3LYP/6-31G* level of theory.
Electronic transitions were calculated by TD-DFT. Tenorite (CuO) nanoparticles with promising catalytic
properties were prepared in air via the controlled thermal decomposition of 1-4. The polymorph and
morphology of the prepared nano-tenorite particles were investigated by powder XRD and field emission
scanning electron microscope. The catalytic degradation of methylene-blue dye exposed to UV radiation
and in presence of CuO nanoparticles as a catalyst was studied at room temperature in water.
Key Words: Flubendazole; TD-DFT; Methylene-blue, Tenorite nanoparticles
Flubendazole (Scheme 1) is an anti-parasitic agent used for the treatment of various human and
animal helminthoses [1, 2].Recent reports suggested that FLU found an application in cancer treatment
[3]. Its mode of action involves the destruction of cytoplasmic microtubules in the intestinal or absorptive
cells of the parasite [4].Inhibition of glucose uptake and depletion of glycogen stores follow lead to death
of the parasite [5].Several analytical techniques such as fluorescence spectroscopy [6], liquid
chromatography [7], and polarography [8] were applied for determination of FLU in its pharmaceutical
preparations. To the best of knowledge, the coordination behavior of FLU towards different metal ions has
not been previously discussed in the literature.
2

Here, synthesis, spectroscopic and thermal characterization of Cu(II) complexes of FLU drug are
reported both experimentally (see the supporting information for details) and theoretically [9, 10] and
are correlated. Theoretical calculations were carried out by Gaussian 03 [11] suite of programs. In
addition, a simple and nontoxic method for preparation of CuO nanoparticles based upon the thermal
decomposition of the synthesized Cu (II) complexes has been explored. The morphology has been
characterized by different physical methods such as XRD and FE-SEM. Finally, the degradation of MB by
the catalytic performance of CuO nanoparticles has been investigated with the aid of the ultraviolet
radiation.
-
-
The binary complexes [Cu(FLU)2X2]·yH2O (X = Cl- (1), y = 4; C2H3O2 (3), y = 1; X = ClO4 (4), y = 3)
and[Cu(NO3)(FLU)2(OH2)]∙NO3∙2H2O (2) were prepared (see the supporting information for details).
Elemental analysis (supporting information) data are in agreement with those calculated for the
suggested structures. Lower conductance values were reported for 1, 3 and 4 (in DMF) compared with the
reported values [12], while the higher one (100.10 ohm-1 cm2 mole-1) of2 suggests its ionic nature. IR
bands observed at 3308, 1736, 1646 and 1595 cm-1 are assigned to ν(NHcarb), ν(C=Ocarb), ν(C=Obenzoyl) and
ν(C=N), respectively. In complexes, the shift of ν(NHcarb) and ν(C=Obenzoyl) to higher values, 3374-3429 and
1636-1644 cm-1, indicates that these groups remain intact. The ν(C=Ocarb) moves to lower wave numbers,
which suggests its involvement in the chelation. As the effect of H-bond on the pyridine-type N is replaced
by the complex formation, the position of ν(C=N) in IR spectra of FLU and its complexes is the same [13,
-
14]. The new bands at 1301, 1388 and at 1347 cm-1 in 2 are due to ν3(NO3)modes of NO3 group [15],
while those at 1352 and 1573 cm-1 (∆ν = 221 cm-1)are taken as evidence for the monodentate mode of the
acetate group [16].
The TG curve of 1 (Fig. S1a†) shows two decomposition stepsat 192 and 690 ºC due loss of hydrated
4H2O+Cl and pyrolysis of two FLU molecules with overall mass amounts to 86.91% (calcd. 87.57%) and
CuO+2C as a residue [17]. For 2 (Fig. S1b†), four decomposition stages at 54, 186, 465 and 834 ºC are
observed. Two hydrated water molecules are desorbed in the first step. The elimination of coordinated
H2O + 2 NO3 + 2FLU takes place in the next stages and results in formation of Cu+CuO as a final residue,
3

7.86% (calcd. 8.24%). Incomplete degradation was observed in case of the acetato complex 3(Fig. S1c†),
with overall mass loss amounts to 77.76% (calcd. 88.92%), assuming the formation of CuO+C as a residue
at 1000 ºC. Complex 4 (Fig. S1d†) is thermally decomposed via five steps (49, 251, 335, 505 and 955 ºC).
The 1st step is responsible for desorption of three hydrated water molecules. The following stages give up
a residue of CuO+C, 10.45% (calcd. 9.71%) through loss of two FLU and two perchlorate groups.
The observed effective magnetic moment (µeff) values, were found to be (1.80-2.06) µB (298 K) for the
complexes (1-4). These values are expected for non-interacting Cu(II) ions (S=½; t62ge3 ), and in the
g
acceptable range for copper complexes (1.60-2.2 μB) [18]. Room temperature powdered ESR spectra of 1-
4were recorded at X-band frequency, Fig. S2†. The chloride complex 1shows a slightly rhombic spectrum,
with three g values, g1 = 2.003, g2 = 2.188, g3 = 2.282. The parameter R{R = (g2 – g1)/(g3 –g2) for rhombic
systems} is found to be 1.968, i.e. R˃1, which is characteristic for Cu(II) trigonal bipyramidal complexes
[19]. The spectrum of 2 displays an isotropic signal with gave=2.131. The ESR spectra of 3 and 4 are axial
with two well-defined g∥ = 1.780, 2.073 and g⊥ = 2.078, 2.189, respectively and g⊥˃ g∥˃ ge (2.0023)
2
suggesting that dz orbital is the most populated ground state. Therefore the stereochemistry around the
metal centre is proposed to be compressed trigonal bipyramidal with D3h symmetry [20].
The fully optimized geometries of complexes (1-4) and the numbering of atoms are shown in Fig. 1.
The atomic coordinates are presented in Table S1. Complexes (1-4) adopt distorted trigonal-bipyramidal
geometry. The basal plane is defined by carbamate oxygen atom [Cu-O(34)=2.306 Å (1); 2.174 Å (2);
2.326 Å (3); 2.142 Å (4)] and two chlorine atoms [Cu-Cl(66)=2.413 Å and Cu-Cl(67)=2.267 Å] (1), two
acetate groups [Cu-O(44)=1.915 Å and Cu-O(45)=1.946 Å] (3) or two perchlorate groups [Cu-O(44)=2.164
Å and Cu-O(45)=1.963 Å] (4). In case of 2, three oxygen atoms; monodentate nitrate ligand [Cu-O(44) =
1.955 Å], water [Cu-O(45) = 2.137 Å] and carbamate group [Cu-O(34) = 2.174 Å], constitute the basal
plane of the metal center. In each complex, the axial positions are occupied by two pyridine-type nitrogen
atoms [Cu-N(10) = 1.997Å (1), 1.973Å (2), 2.059 Å (3), 1.967 Å (4); and Cu-N(15) = 2.032 Å (1), 1.977Å
(2), 2.085Å (3), 2.009 Å (4)]. The N(10)-Cu-N(15) angle somewhat deviate from the linearity and is equal
168.8, 172.4 and 171.2ºfor 1, 2 and 4, respectively. This deviation leads to formation of an irregular
4

structure. According to NBO analysis, the electronic arrangement of Cu(II) in complex 1 is
1.954
1.759
1.891
[Ar]4s0.393d9.184p0.485p0.01. The occupancies of Cu 3d are: 푑푥푦
3, the electronic configurations of Cu atom in
푑
푥푧
푑
푑
1.608푑푧 1.973. For 2, and
푥 −푦
2
2
2
푦푧
2
and
3
are [Ar]4s0.323d9.144p0.36and
[Ar]4s0.353d9.154p0.355p0.01 , respectively. For complex 4, the electronic arrangement of Cu is
[Ar]4s0.313d9.144p0.375p0.01, distributed as 18 core electrons, 9.825 valence electrons (on 4s, 3d, and 4p
atomic orbitals) and 0.012 Rydberg electrons (mainly on 5p orbital). The second order interaction energy
(E2) values [21, 22], for 1, are 0.46, 0.09, 0.10, 0.29 and 0.18 Kcal mol-1 for LP(1)N10→RY*(5)Cu,
LP(1)O34→RY*(4)Cu, LP(1)Cl67→RY*(2)Cu, LP(1)N15→RY*(5)Cu and LP(1)Cl66→RY*(2)Cu, respectively.
Similar values are observed for the complexes (2-4), as tabulated in Table S2.
The UV-vis. absorption spectra of (1-4) exhibit the highest energy band at 317-323 nm corresponding
to the internal ligand transitions. Both 1 and 4display MLCT band at 22727 and 26667 cm-1, respectively.
The spectra of complexes 1-4 show broad absorption bands with a maximum in the visible range (11111-
13245 cm-1) assigned to 2E'→ 2A1'transitions in trigonal bipyrimidal complexes [23].In order to
understand the transitions occurring in the studied complexes, TD-DFT calculations were performed [24].
The spectrum of 1 shows five transitions at 441, 420, 399, 386 and 306 nm, which are mainly assigned to
H→L, H-1→L, H-2→L, H-3→L and to H→L+1/L+2(H: HOMO and L: LUMO). The TD-DFT spectrum of
2exhibits three main bands at 471, 431 and 300 nm with oscillator strengths of 0.0007, 0.0005 and
0.6552, corresponding to H/H-1→L, H-2/H-4→L and H→L+1/L+2 transitions. Four transitions at 413, 366,
355 and 304 nm are observed in the calculated spectrum of complex 3 owing to ß-spin H to ß-spin L+1, H-
2/H-1/H→L and H-1→L/L+1 transitions. The absorption bands at 549, 518, 487 and 302 nm, in complex
4, are allocated for H→L, H-1→L, H-3/H-2→L and H→L+1/L+2, in that order.
CuO nanoparticles were prepared by heating complexes (1-4) in an electric furnace (700 ºC) under
the ambient air condition before cooling to room temperature. Their XRD diffraction peaks are in
agreement with the reported JCPDS card no. 04-015-5866, characteristic for CuO tenorite nanoparticles,
as shown in Fig.S3†. Samples 1 and 4 are contaminated with CuCl (nantokite) (JCPDS card no. 04-007-
3881). CuO nanoparticles are almost spherical, as shown in the FE-SEM images, (Fig. 2). The influence of
5

the type of the coordinated anion has been reflected in the size of the nanoparticles. The diameter of some
nanoparticles is less than300 nm (1), 200 nm (2), 250 nm (3) and 225 nm (4). Therefore, the thermal
decomposition of the nitrato complex 2 gives rise to the smallest copper oxide nanoparticles. The sizes of
the current nanoparticles are comparable to those of reported copper oxide nanoparticles prepared under
the thermal decomposition conditions [25].
To evaluate the catalytic performance of the synthesized CuO nanoparticles, the absorption spectra of
the illuminated MB samples at various time intervals were monitored. The degradation process of MB was
initiated by addition of H2O2 solution to the MB solution and immediately turning on the ultraviolet
irradiation (see the supporting information for details). For comparison, the MB degradation experiment
was also done without CuO nanoparticles, but in presence of H2O2 and illumination with UV light. Fig. 3a
shows the time-dependent absorption electronic spectra of MB as a function of the illumination time at
365 nm in presence of H2O2/CuO nanoparticles (sample no. 2). Similar spectra for samples no. 1, 3 and 4,
and for the blank sample are given in Fig. S4†. In other words, control experiment indicated that the
degradation of MB hardly proceeds in absence of CuO nanoparticles.
The degradation efficiency [R = 100 × ((At-A0)/A0)] of methylene blue (MB) was determined, where A0
and At are the initial absorbance and that obtained after the illumination time (t). The addition of CuO
nanoparticles to the MB+H2O2+UV system degraded about 99% (1), 90% (2), 83 % (3) and 42 % (4) of MB
exposed to the UV light (365 nm), while 29% of MB is degraded in the absence of CuO nanoparticles,
within about 150 min. The obtained results are comparable to the previously published data used CuO
nanostructures as a catalyst [26]. The photo-catalytic degradation of MB was found to be first order
reaction [ln(Ct/C0)=kt]. Its ln(Ct/C0) plot versus time, shows a linear relationship with the illumination
time (Fig. 3b), where slope is the rate constant (k). The calculated rate constants for the photo-catalytic
reactions are 2.26×10-2 (1), 1.47×10-2 (2), 1.22×10-2 min-1 (3) and 4.92×10-3 min-1 (4) while it is only
about 2.05×10-3 min-1 (MB+UV+H2O2) for blank sample. The t1/2 value was found to be 31 (1), 47 (2), 57
(3) and 141 min (4) compared with 5.6 hours for (MB+UV+H2O2) blank sample .It is worthy to mention
6

that almost no degradation of MB was observed in dark, which reveals that the mechanism of the reaction
is photo-degradation rather than adsorption [27].
In summary, synthesis and structural study of new trigonal-bipyramidal Cu(II) complexes of FLU drug
have been developed. FLU is a neutral bidentate ligand coordinated to Cu(II) via the pyridine-type N of
benzimidazole ring and C=O of the carbamate group. Thermal decomposition of the studied complexes
proved to be a simple and nontoxic method for preparation of tenorite nanoparticles. The prepared CuO
nanoparticles exhibited good photo-catalytic activity in the degradation process of an industrial pollutant
methylene-blue by means of Fenton-like reagent.
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8

F
O
Z H2O
C
O
C
O
MX2
H
N
2
O
NH
O
Methanol/water
reflux (12h)
NH
N
Cu
X
N
N
H
F
O
Y
O
MX2 = CuCl2.2H2O, Cu(NO3)2.3H2O, Cu2(CH3COO)4.H2O,
Cu(ClO4)2.6H2O
F
O
N
HN
N
H
C
O
X = Y=Cl, Z = 5 (1)
X = NO3 (2), Y = H2O Z = 2 (2)
X = Y=C2H3O2, Z = 1 (3)
X = Y=ClO4 , Z = 3 (4)
Scheme 1: Synthesis of Flubendazole-Copper(II) complexes 1-4.
a)
b)
c)
d)
Fig. 1: Local minimum structures of complexes a) 1, b) 2, c) 3, and d) 4 obtained at the
DFT/B3LYP level of theory.
a)
b)
c)
d)
Fig. 2: FE-SEM images of CuO nanoparticles obtained from thermal decomposition of a) 1, b) 2, c) 3
and d) 4.

2
1.8
1.6
1.4
1.2
1
0
-1
-2
-3
-4
-5
MB
MB + H2O2
Zero time
30 min
60 min
90 min
0.8
0.6
0.4
0.2
0
120 min
150 min
180 min
200 min
H2O2+UV
1
2
3
4
0
50
100
150
200
Time (min.)
530
550
570
590
610
630
650
670
690
710
Wavelength (nm)
a)
b)
Fig. 3: a) Time-dependent UV-vis. absorption spectra for the photocatalytic degradation of MB with
CuO (2) [10 mL dye (14 mg L-1), 0.1 mL H2O2 (35%), 10 mg CuO, λ = 365 nm], b) Linear plots of
ln(Ct/C0) vs. time for the decolorization of MB under different conditions.