Sonochemical preparation and characterization of modified CuO nanocrystalline with bioactive chiral diacids derived from different natural amino acids

Article abstract of DOI:10.1080/15533174.2015.1137047

To improve the dispersion ability of CuO nanoparticles (NPs), their surface was modified by chiral diacids (DAs) containing amino acids. The surface modification process was achieved using ultrasonic irradiation. DA could be absorbed on the surface of CuO

Full text of DOI:10.1080/15533174.2015.1137047

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Sonochemical Preparation and Characterization
of Modified CuO Nano crystalline with Bioactive
Chiral Diacids Derived from Different Natural
Amino acids
Shadpour Mallakpour & Maryam Vahabi
To cite this article: Shadpour Mallakpour & Maryam Vahabi (2016): Sonochemical Preparation
and Characterization of Modified CuO Nano crystalline with Bioactive Chiral Diacids Derived
from Different Natural Amino acids, Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry, DOI: 10.1080/15533174.2015.1137047
To link to this article: http://dx.doi.org/10.1080/15533174.2015.1137047
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Date: 23 April 2016, At: 04:15

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Sonochemical Preparation and Characterization of Modified CuO Nano crystalline with
Bioactive Chiral Diacids Derived from Different Natural Amino acids
SHADPOUR MALLAKPOUR a, b, c, * AND MARYAM VAHABI a
aOrganic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan
University of Technology, Isfahan 84156-83111, Islamic Republic of Iran
bNanotechnology and Advanced Materials Institute, Isfahan University of Technology,
Isfahan 84156-83111, Islamic Republic of Iran
cCenter of excellent in sensor and green chemistry, Department of chemistry, Isfahan
University of Technology, Isfahan 84156-83111, Islamic Republic of Iran
*Corresponding author. E-mail address: mallak@cc.iut.ac.ir, mallak777@yahoo.com;
mallakpour84@alumni.ufl.edu.
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ABSTRACT
To improve the dispersion ability of CuO nanoparticles (NP)s, their surface was modified by
chiral diacids (DA)s containing amino acids. The surface modification process was achieved
using ultrasonic irradiation. DA could be absorbed on the surface of CuO. The carboxyl groups
of DA may interact with surface of CuO NPs and form covalent bond with it. Interactions
between DAs and CuO NPs were investigated by different techniques. The X-ray diffraction
patterns proved that modification process does not change the crystalline phase of CuO. The
results confirmed successful deposition of the organic functional groups on the surface of NPs.
Keywords: bioactive diacids, CuO NPs, surfaces modification, ultrasonic irradiation,
transmission electron microscopy
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Introduction
In recent years, the use of nanoparticles (NP)s have received a lot of attention. Semiconductor
and oxide materials in the nanometric size, due to their high specific surface areas have
photovoltaic, electronic, optical, physical and chemical properties, which are significantly
different from those of the corresponding to their atomic or bulk counterparts.[1-6] In fact,
decreasing from a micrometer to a nanometer size can change electrical conductivity, chemical
reactivity and natural activity and make them, suitable for various applications.[7]
CuO is a p-type semiconductor with a narrow band gap (Eg=1.2 eV) [8] and has a monoclinic
structure. This metal oxide is becoming more common due to excellent properties such as its
nontoxic nature, great temperature superconductivity, spins dynamics, good electrical and optical
properties.[7,9] CuO has broad applications in tools such as superconductors, magnetic storage
media, batteries, solar energy conversion, gas sensing, field emission emitters and other
electronic and optoelectronic devices.[9-13] CuO NPs are added to fluid for improving of viscosity
and increasing the heat conductivity.[11,14,15] Nano crystalline CuO can be used as cheap,
recyclable and stable heterogeneous catalysts in many reactions such as cross-coupling reactions
of organic diselenides with aryl boronic acids [16], N-arylation reaction [17], synthesis of
[18]
polyhydroquinoline
and benzimidazoles.[19] These metal oxide NPs are employed as an
antioxidant, antifouling and antibacterial agent. But, it is interesting to mention that CuO NPs
have a longer shelf lifetime compared to organic antimicrobial agents.[20-23]
Inorganic fillers in nanosizes are mixed with polymer matrixes due to their excellent physical
and chemical properties.[24] CuO NPs simply combined with polymers to improve the thermal
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conductivity, thermal stability and physical properties such as, catalytic and mechanical
properties.[8,18,25,26]
Unfortunately, inorganic oxides particles due to the presence of hydroxyl group (–OH) on
their surface and their high surface energy tend to agglomeration in a polymer matrix and
aqueous solutions.[5,24,27,28] Aggregation causes reduction in effective surface area and weak
dispersion capacity in the organic polymer matrix.[2,3] So, the surface modification of inorganic
NPs is important. Accordingly, in order to avoid the formation of agglomerated NPs and to yield
a perfect dispersion in polymer matrixes, several ways have been suggested. Surface
modification of NPs is usually carried out by different coupling agents or surfactants containing
[26,29-31]
hydroxyl group
or macromolecule.[5,32,33] In our previous work, the surface modification
of TiO2 NPs was reported with bioactive diacids (DA)s containing pyromellitic dianhydride and
different amino acids .The results showed that dispersity of the NPs was improved.[34,35]
In the present work, we have offered a simple and effective method for the surface
modification of nano-copper oxide. In order to achieve biodegradable, biocompatible, nontoxic
and well-dispersed NPs, the surface of CuO was coated with DAs containing various natural
amino acids such as L-alanine, L-phenylalanine, L-methionine, L-valine and L-leucine. The
biodegradability of these DAs have been reported in our previous works.[36,37] The effects of
coupling agents on the properties of NPs were investigated by Fourier transform infrared (FT-IR)
spectra, thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning
electron microscopy (FE-SEM) and transmission electron microscopy (TEM).
Experimental
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Materials
Nanosized CuO powder was purchased from Nanosabz Co (Tehran, Iran) with average particle
size of <50 nm. L-alanine, L-phenyl alanine, L-methionine, L-valine, and L-leucine amino acids
were used as obtained without further purification. Trimellitic anhydride was purchased from
Merck Co (Darmstadt, Germany). Other solvent and chemicals were used as obtained without
further purification. Physical properties of CuO NPs are shown in the Table1.
Table 1
Instrumental analysis
The morphology of the CuO NPs was investigated via FE-SEM HITACHI (S-4160) and TEM (a
Philips CM 120 operated, Netherlands). FT-IR spectra were measured with a JASCO
spectrometer 680 spectrophotometer (Tokyo, Japan). The solid sample was mixed with powder
KBr, ground and compressed into a pellet. The thermal properties were characterized by TGA,
on a STA550 (Germany) instrument at 20 ○C/min of heating rate in nitrogen atmosphere from 25
○
to 800 C. The vibrational transition frequencies are reported in wave numbers (cm–1). XRD
patterns were recorded using Bruker, D8 Advance (Germany) diffractometer operating at a
current of 100 mA. Processing of modification carried out by MISONIX ultrasonic liquid
processors, XL-2000 SERIES (USA). The wave of frequency of ultrasound was 2.25× 104 Hz
and power of 100 W.
Synthesis of modifiers
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Bioactive chiral DAs of N-trimellitylimido-L-valine (DA-V), N-trimellitylimido-L-phenylalanine
(DA-Ph), N-trimellitylimido-L-alanine (DA-A), N-trimellitylimido-L-leucine (DA-L) and N-
trimellitylimido-L-methionine (DA-M), (3a-3e) were prepared as described previously (Scheme
1).[38-42]
Sch. 1.
Surface treatment of nano-CuO
The procedure for the preparation of functionalized NPs is described as follows: CuO nano
powder (0.1 g) was added into a mixture of (15 wt%) of DA and 15 ml of methanol. The
resulting colloidal suspension was strongly stirred for 24 h at room temperature and was
irradiated by an ultrasonic radiation for 30 min. After filtration, the precipitated NPs were
washed with methanol to remove unreacted DA and finally, the prepared powder was dried in an
oven at 60 ○C for 24 h. (Scheme 2).
Sch. 2.
Results and discussion
Organophilic property of modified CuO NPs
The pure CuO NPs are hydrophilic, which can be dispersed well in water and highly polar
organic solvents. After modification, the DA-grafted CuO NPs show organophilic property and
have less dispersion ability in the water. On the other hand, modified NPs can be dispersed
successfully in the organic system such as polymer matrix, non-polar and weak polar organic
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solvents such as acetone and chloroform. So, after modification by DA, the surface of CuO NPs
was changed from hydrophilic to organophilic. This is important for the miscibility of the filler
and matrix.
The mechanism of adsorption of DA on the surface of CuO NPs
To prevent the formation of agglomerative NPs and to obtain the uniform distribution of NPs, the
CuO NPs was modified with bioactive DAs as coupling agents to functionalize the surface of
them. No matter what reaction happened, DAs were grafted or anchored on the surface of the
NPs through one or several spots. So, coupling agents generate the steric hindrance between
inorganic NPs which results in better dispersibility of them.
It has been reported that the carboxyl group (–COOH) of acids may act as a bridge between
two metal atoms or bond to the metal atom through oxygen as a unidentate chelating and
bidentate chelating. Furthermore, it can be formed covalent bond between –COOH and the –OH
on the surface of CuO, producing ester linkage.[29,34] In addition the strong covalent bond, the
weaker hydrogen bonding between the –OH of CuO and the –COOH is also possible. The
possible interactions of DAs with CuO NPs are shown in Scheme 3.
Sch. 3.
FT-IR analysis
Figure 1 shows typical FT-IR spectra of pure CuO NPs (a), pure DA-V (b) and DA-V-grafted
with CuO NPs (c). In the spectrum of CuO NPs, the appearance of peak at 3452 cm−1 shows the
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existence of OH stretching on the surface of CuO. Characteristic peak at 475 cm-1 is
corresponding to the metal–oxygen (M–O) stretching. In the spectrum of DA (Figure 1b), the
significant peaks are assigned below: The characteristic absorption peak at 1381 cm−1 is due to
the imide heterocyclic ring. The bands corresponding to CH3 and CH2 stretching occurred at
2926 and 2853 cm−1 respectively, and carbonyl stretching band of the carboxylic acid appeared
at 1743 cm−1. In the spectra of modified NPs with DAs (Figures 1c and 2), the presence of peaks
at region of 2837–2920 cm−1 are corresponding to the alkyl groups of the DA chain. These peaks
were not observed in the spectrum of unmodified CuO. Also characteristic peaks of CuO have
been observed in the spectrum of DAs-treated NPs. Decreasing of the carboxylic acid C=O
stretching vibration peaks in comparison with DA (1743 cm−1) and presence of new peaks at
1460 and 1623 cm−1 can be due to interactions of carboxylic ion with the metal ion. These FT-IR
observations illustrated that the carboxyl groups of coupling agents were attached to the surface
of the CuO NPs through the coordination bond. The hydrogen bonding can also be indicated
from the existence of vibration peak of free –COOH at 1715 cm−1. This result indicated the
effective functionalization of CuO NPs with DAs. Nevertheless, the FT-IR results could not
present any quantitative information about the amount of the grafted coupling agents on the CuO
NPs.
Figs. 1 and 2
TGA analysis
To confirm the coordination (chemical) bond and quantitatively estimate the amount of coupling
agent attached on the NPs, TGA was performed. Figure 3 shows the thermal behavior of pure
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CuO (a) and DA-functionalized CuO NPs (b) from 25 to 800 ○C. For untreated NPs, the weight
loss below 500 ○C is perhaps due to desorption of physically adsorbed humidity and dehydration
of chemically hydroxyl groups on the particle’s surface which would be around 5 wt%.[43] For
the modified NPs, The TGA curve of showed weight loss above 300 ○C, which demonstrates the
coordination bond between organic molecules and the surface of the NPs.[44] The weight loss also
indicates the amount of coupling agent grafted on the NPs. For the modified NPs with DA-V, in
○
the temperature range of 25-800 C the weight loss is about 22 wt%, which is corresponding to
the total weight loss. By a simple calculation it would be clear that the amount of incorporation
of coupling agent (DA) on the surface of CuO NPs would be about 17 wt%. Consequently, this
weight loss is owing to thermal decomposition of DA chain. So, these observations indicate that
DA was covalently bound onto the CuO NPs surface. These results are agreement with the FT-IR
results.
Fig. 3
X-ray diffraction analysis
To study the effect of modification process through ultrasonication on the crystalline structure of
CuO NPs, XRD patterns of the particles before and after the modification are presented in Figure
4. Figures 4a-4c shows XRD patterns of the unmodified CuO, DA-V- and DA-L- grafted CuO,
respectively. The diffraction peaks in Figure 4a can be assigned to CuO with a monoclinic
structure.[45] XRD analysis confirms that the crystalline structure of copper oxide NPs remains
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without changed even after surface modification with DA. The crystalline size (D) was
calculated by the Debye–Scherrer formula based on the full width at half-maximum and 2θ. The
calculated average size of nano-CuO is ∼43 nm.
K
D 
 cos
Where k is a constant equal to 0.9, λ is the wavelength of the X-ray source (1.5405A˚), β is the
full width at half maximum of the diffraction peak and θ is the angular position of the peak.
Fig. 4
FE-SEM and TEM analysis of surface modified CuO
In order to realize detail information about the morphology and microstructure of the modified
NPs, FE-SEM images and the size distributions of the modified CuO NPs are shown in Fig. 5.
The FE-SEM images indicate that NPs were homogeneously dispersed and their aggregation
reduced. The size histograms of the modified CuO NPs indicate that the average sizes of the
CuO NPs are about 19-30 nm.The modified CuO NPs with bioactive DAs showed narrower size
distribution. The particle sizes were believed to have reduced owing to growth inhibition via the
surface modifiers.
Figure 6a shows TEM image of pure CuO NPs and Figures 6b and 6c show TEM
micrographs of the modified CuO NPs with DA-V. It is obvious that the pure CuO NPs are
spherical with average particle size of 30-50 nm and the agglomerated NPs can be seen in this
image (Figure 6a). Figure 6b and 6c displayed that the shape and size of particles were changed
after modification. The agglomerated and spherical-like NPs can be altered to a nanorod-like
shape with 30-50 nm in diameter. There is a possibility about this phenomenon, after absorption
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of DA on the surfaces of CuO NPs, hydrogen bonding between NPs increased their connection
and therefore spherical shape of CuO NPs changed to a rod-like form.[10] Figure 6 shows TEM
micrographs of polymer nanocomposite (NC) containing modified CuO with N-trimellitylimido-
L-valine (DA-V) (Figure 6d-6f). Unusual and fairly rod-like shape of CuO NPs can also be
observed in Figure 6.[46]
Figs. 5 and 6
Conclusions
In this paper, CuO NPs were sonically dispersed in methanol solution containing bioactive DAs.
These DAs were selected as modifier due to properties such as their nontoxic nature, optically
active and environmentally friendly properties. The surface of the NPs was changed from
hydrophilic to organophilic in some extent after modification. The results of FT-IR and TGA
analyses indicated the presence of DAs onto the surface of NPs. TEM images showed changes in
the morphology of the CuO NPs after modification. FE-SEM micrographs represented good
dispersity of CuO NPs. XRD analysis indicated that there is no change in the crystalline structure
of NPs after modification. Therefore, it was an effective method to decrease the agglomeration of
CuO NPs.
Acknowledgments
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The authors would like to acknowledge the help and support of the Research Affairs Division of
Isfahan University of Technology (IUT), Isfahan. We also gratefully acknowledge National Elite
Foundation (NEF), Iran Nanotechnology Initiative Council (INIC), and Center of Excellency in
Sensors and Green Chemistry Research (IUT) for financial assistance to carry out this work.
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Table 1
Physical properties of CuO NPs
Property
Purity
CuO NPs
99%
Particle size (nm)
Specific surface area(m2g-1)
Appearance
<50
>80
Black powder
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O
O
O
O
O
NH2
CH3COOH
18 h Reflux
*
HO
HO
+
H
R
1a-1e
2
O
O
O
HO
N
O
*
OH
H
R
3a-3e
R:
,
,
,
,
CH2
H2C
S
CH2
CH2
CH
CH
CH3
H3C
CH3
H3C
CH3
CH3
e
c
a
d
b
Sch. 1. Synthesis of optically active diacids (3a–3e)
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HO
O
H
O
O
N
O
O
CuO
HO
HO
HO
*
OH
OH
H
R
OH
2) 30 min
Ultrasonic irradiation
1) Methanol
24 h stirring
HO
O
OH
CuO
O
H
OH
O
O
O
N
O
C
u
H
O
H
O
N
O
O
OH
O
*
O
O
*
OH
R
H
R
H
Sch. 2. Surface modification of CuO NPs
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(a)
(b)
(c)
Cu
O
O
Cu
O
O
C
Cu
C
O
C
O
Cu
O
Unidentate chelating
Bidentate Chelating
Bridge
(e)
(d)
O
H
Cu
O
Cu
O
O
R
R
Ester Linkage
H-Bonding
Sch. 3. The possible interactions of DAs with CuO NPs: (a) unidentate chelating, (b) bidentate
chelating, (c) bridging between a carboxylate ion and metal atoms, (d) ester linkage and (e) H-
bonding
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Fig. 1. FT-IR spectra of pure CuO NPs (a),
pure DA-V (b) and DA-V-grafted CuO (c).
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Fig. 2. FT-IR spectra of DA-V-grafted CuO (a), DA-Ph-grafted CuO (b), DA-A-grafted CuO (c),
DA-L-grafted CuO (d) and DA-M-grafted CuO (e )
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Fig. 3. TGA curve of pure CuO NPs (a) DA-V-grafted CuO(b) under nitrogen atmosphere at
heating rate of 20 ○C/min
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Fig. 4. XRD curves of pure CuO NPs (a), DA-V-grafted CuO (b) and DA-L-grafted CuO (c)
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Fig. 5. FE-SEM photographs and particle size distribution histogram of DA-A-grafted CuO (a),
DA-M-grafted CuO (b), DA-L-grafted CuO (c), DA-Ph-grafted CuO (d) and DA-V-grafted CuO
(e)
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Fig. 6. TEM micrographs of pure CuO (a), modified CuO with DA-V (b, c) and PAI/CuO NC
containing 4 wt% CuO NPs (d-f).
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