Journal of Surface Engineered Materials and Advanced Technology, 2012, 2, 284-291
http://dx.doi.org/10.4236/jsemat.2012.24043 Published Online October 2012 (http://www.SciRP.org/journal/jsemat)
Structural, Surface, Thermal and Catalytic Properties of
Chitosan Supported Cu(II) Mixed Ligand Complex
Materials
R. Antony1, S. Theodore David1*, K. Karuppasamy1, K. Saravanan2, S. Thanikaikarasan1,
S. Balakumar1
1Centre for Scientific and Applied Research, School of Basic Engineering and Sciences, PSN College of Engineering and Technol-
ogy, Tirunelveli, India; 2Discipline of Inorganic Materials and Catalysis, Council of Scientific and Industrial research, Central Salt
and Marine Chemicals Research Institute, Bhavnagar, India.
Received June 9th, 2012; revised July 13th, 2012; accepted July 26th, 2012
ABSTRACT
Schiff base modified chitosan (SC: salicylidenechitosan) has been synthesized by the condensation reaction of chitosan
and salicylaldehyde. From this ligand, three Cu(II) mixed ligand complexes [Cu (SC) (SA)] (1), [Cu (SC) (ST)] (2) and
[Cu (SC) (VA)] (3) (SA: salicyledeneaniline; ST: salicylidenethiourea; VA: o-vanillideneaniline) have been synthesized
successfully. The structure and properties of the complexes have been characterized by spectral and analytical tech-
niques. Their thermal and morphological properties have been also discussed in detail. The crystallinity of the com-
pounds has explored with X-ray diffraction spectroscopy. The catalytic ability of the complexes has been investigated in
the oxidation reaction of cyclohexane into cyclohexanol and cyclohexanone using hydrogen peroxide as oxidant and
their catalytic activity is in the order of complex 1 > 2 < 3.
Keywords: Chitosan; Scanning Electron Microscopy; Active Site; Heterogeneous Catalysts
1. Introduction
Chitosan is a cationic amino polysaccharide, copolymer
of glucosamine and N-acetyl glucosamine, obtained by
the alkaline, partial N-deacetylation of chitin which is the
most important and abundant polysaccharide after cellu-
lose isolated from different natural sources predomi-
nantly marine, such as the shells of crustaceans, squid
pen and krill. It is also found in the exoskeleton of in-
sects and in the cell walls of fungi [1-4]. Chitosan dis-
solves in aqueous solution of organic acids as acetic,
formic, citric; besides inorganic acids, as diluted hydro-
chloric acid resulting in viscous solutions. This biopoly-
mer, due to its unique physiochemical properties and
biological activities has the number of applications rang-
ing from cosmetics, artificial skin, photography, food and
nutrition, ophthalmology and waste water treatment [5,6].
The free amino group available in the chitosan structure
enables a variety of chemical modifications and substitu-
tion processes like carboxylation, acylation, sulfation,
Schiff’s base formation, enzymatic substitution, metal
chelation, cyanoethylation, nitration, phosphorylation,
etc. [7-9]. The reaction of this free amino group with al-
dehydes and ketones resulting in the formation of Schiff
bases which are often reported for the reason that they
offer opportunities for inducing biological activity, ad-
sorption of metal ions and the support of metal complex
catalysts[10-13]. The insertion of functional groups into
the chitosan polymer matrix may improve its capacity of
interaction with metallic ion by complexation. Chitosan
anchored Schiff base complexes have been amongst the
most widely studied coordination compounds in the past
few years, since they are becoming increasingly impor-
tant as biochemical, antimicrobial and catalytic reagents.
There are some reports available with transition metal
complexes obtained from Schiff base modified chitosan
[14,15].
The oxidation of organic compounds with an eco
friendly oxidant, aqueous hydrogen peroxide, is a chal-
lenging goal of catalytic chemistry. In specific, the re-
search on the oxidation of cyclohexane captures special
attention because its oxidized products are of immense
industrial importance, significantly in the manufacture of
adipic acid which is again a raw material of nylon 6, 6’,
detergents, rubber chemicals, pesticides etc [16-18]. Due
to the inherent advantages of heterogeneous catalysis
over homogeneous catalysis, a great deal of efforts has
*Corresponding author.

Structural, Surface, Thermal and Catalytic Properties of Chitosan Supported Cu(II) Mixed Ligand Complex Materials 285
been devoted to the development of heterogeneous cata-
lysts. By making the use of the chelating ability of chito-
san with metal ion, researchers have studied a new cata-
lyst with more catalytic activity and reusable features.
Many studies indicate that the copper complexes derived
from chitosan anchored Schiff base acts as good hetero-
geneous catalysts in oxidation reactions [19,20].
Bearing these facts in our mind, herein we report the
synthesis and characterization of the Cu(II) mixed ligand
complexes holding a Schiff base (Figure 1(a)), sali-
cylidenechitosan (SC) derived from chitosan and salicy-
laldehyde. Here, our aim is to establish a comparative
study of the catalytic effectiveness of the complexes in
the oxidation reactions of cyclohexane.
2. Experimental Section
Chitosan powder of medium molecular weight was pur-
chased from Hi media chemical company. The purifica-
tion was carried out by the dissolution of commercial
chitosan powder (approximately 2.5 g) in 1 litre of dilute
0.5 molL–1 acetic acid solution. All other chemicals and
solvents were obtained from Merck and used as received.
All manipulations were completed under aerobic condi-
tions.
2.1. Characterisation Techniques
A Carlo Erba 1108 model elemental analyzer was used to
collect the micro analytical data (C, H and N) and com-
pared with the calculated theoretical values. Copper con-
tent of complexes was estimated gravimetrically as its
oxide [21]. The FT-IR spectra of the complexes were
recorded on a Jasco FT-IR/4100 spectrophotometer with
4 cm–1 resolution in the range of 4000 to 400 cm–1. Elec-
tronic absorption spectral studies were carried out in
DMSO using a Shimadzu UV - 1601 spectrophotometer
in the range of 200 - 800 nm. 1H NMR spectra of SC was
computed on a Bruker Avance 300 FT-NMR spectrome-
ter in 1% HCl/D2O solution. The magnetic susceptibility
values of the complexes were measured on a modified
Hertz SG8-5HJ model Gouy type magnetic balance.
Room temperature molar conductance measurements of
10–3 solutions of the complexes in DMSO were analyzed
with a deep vision model 601 digital direct reading de-
luxe conductivity meter. Thermal properties (from
thermo gravimetric (TG) and differential thermal (DTA)
analyses) were investigated on a Mettler Toledo star sys-
tem in the temperature range of 30˚C - 800˚C with heat-
ing rate of 10˚C min–1 under N2 flow. Surface morphol-
ogy of the synthesized products was studied with the use
of scanning electron microscope of model SEM-JSM
6390 with accelerating voltage of 20 kV at liquid N2
temperature. X-ray powder diffraction determinations
were made using an X-ray diffractometer (XPERT PRO
PANalytical, Netherland) for phase identification. The
patterns were run with CuKα radiation (λ = 0.1545 nm)
with a generator at 40 kV and 30 mA.
2.2. Synthesis of Ligands and Complexes
SC was synthesized according to the following procedure.
Chitosan (10 mmol) was magnetically stirred in ethanol
for 5 hrs and to this pre-treated ethanolic chitosan sus-
pension, salicylaldehyde (10 mmol) was added and the
mixture was refluxed for 24 hrs. After cooling, the yel-
low colour solid was separated by filtration, washed with
ethanol and ether and then dried at 50˚C under vacuum
for 12 hrs.
A mixture of salicylaldehyde (0.1 mol), aniline (0.1
mol) and ethanol was refluxed for the synthesis of sali-
cyledeneaniline (SA). The resultant mixture was cooled,
filtered off washed with hot water and dried in vacuum.
Salicylidenethiourea (ST) from salicylaldehyde and thio-
urea and o-vanillideneaniline (VA) from o-vanillin and
aniline were derived by repeating the similar procedure.
For the preparation of complex 1 (Figure 1(b)), at first
ethanolic solution of SC (0.75 mmol) was stirred for 5
hrs in a flask equipped with a magnetic stirrer. Then, SA
(0.75 mmol) and Cu (CH3COO)2 (0.75 mmol) were
added to this pre-treated SC suspension and it was re-
fluxed for 12 hrs with magnetic stirring. Complex 2 was
synthesized by refluxing the pre-treated SC with ST and
Cu(CH3COO) 2. Complex 3 was synthesized by refluxing
the pre-treated SC with VA and Cu(CH3COO)2. In all the
cases, the final precipitate was filtered off, washed with
ethanol and ether and dried in vacuum.
2.3. Catalytic Oxidation Procedure
The oxidation of cyclohexane was performed in an aero-
bic condition. Typically, 10 mmol 30% hydrogen perox-
ide solution was added to the copper complex (0.05 g) in
10 ml of acetonitrile in a 25 ml flask equipped with a
magnetic stirrer. To this 5 mmol of organic substrate was
Figure 1. Structure of SC (a); and complex 1 (b).

Structural, Surface, Thermal and Catalytic Properties of Chitosan Supported Cu(II) Mixed Ligand Complex Materials 286
added. The reaction mixture was stirred at room tem-
perature and 70˚C under atmospheric pressure conditions.
After 8 h, the mixture was filtered, concentrated and col-
lected. A blank experiment for the oxidation of cyclo-
hexane was carried out without the copper complex
keeping the other experimental conditions unaltered. The
collected product samples were analyzed with a Hew-
lett-Packard gas chromatogram (HP 6890) having FID
detector. From the resulting chromatographs, the identi-
fication of the products and the selectivity of the products
also were attained. The reusability of the complexes was
proved with the complex 1 by repeating continuously
five catalytic runs keeping the same catalyst again and
again after successive purification.
N-H stretching band and inter hydrogen bands of the
polysaccharide. The C-H axial stretching band arises at
2878.24 cm–1. The other important observed characteris-
tic bands of chitosan are, bands due to the –NHCOCH3
(acetyl) units (with C = O stretching) at 1651.98 cm–1,
(with N-H bending) at 1580.38 cm–1, (with C-N stretch-
ing coupled with N-H plane deformation) at 1419.07
cm–1 and (symmetrical angular deformation of CH3) at
1375.96 cm–1; C-N amino groups axial deformation at
1322.59 cm–1; C-O-C stretching vibration at 1027.87
cm–1; and the specific bands of the β (1 - 4) glycosidic
bridge at 1149.37 and 895.77 cm–1 [22,23]. In the FT IR
spectrum of SC, there is no evidence for carbonyl
stretching which is a characteristic band of salicylalde-
hyde at around 1720 cm–1, the axial vibration of O-H is
arrived at cm–1, the C-H stretching frequency appears at 2
893.66 cm–1, the significant characteristic β (1 - 4) glyco-
sidic bridge bands Ccur at 1149.37 and 895.77 cm–1 and a
new important band arrived at 1624.73 cm–1 which is a
characteristic stretching frequency of azomethine group
(CH = N) of SC. FT IR spectra of the complexes 1, 2 and
3 (Figures 2(c)-(e), respectively) show the similar spec-
tra like SC with some changes. The C = N stretching
band is shifted to the lower frequency in all the com-
plexes (1602 cm–1 (1), 1613.16 cm–1 (2) and 1596.77
cm–1 (3)) due to the coordination of Cu(II) metal centre
with azomethine nitrogen atom [24]. Figure 2(d) exhib-
its the bands at 773 .02 and 1393.32 cm–1 which are at-
tributed to the coordination of sulfur atom of thiourea
with Cu(II) ion.
3. Results and Discussion
3.1. Degree of Substitution (DS) of SC
The micro analytical data (C, N) obtained from elemental
analysis is used to find out the degree of substitution (DS)
of SC. From Table 1, C/N ratio of chitosan and its Schiff
base ligand, SC are calculated as 5.22 and 11.15, respec-
tively.
The DS of the ligand, SC to-NH2 group on chitosan is
calculated by the Equation (1).


mo aCN CN
DS n

 (1)
where

mCN is the C/N ratio of modified chitosan,
SC,

CNo is the C/N ratio of original chitosan and
“a” and “n” are the number of nitrogen and carbon in-
troduced after Schiff base modification, respectively. The
DS calculated for chitosan is 0.46.
Electronic spectral studies of the transition metal com-
plexes are generally used to confirm their geometry
around the central metal ion. The nature of geometry
around this central transition metal ion is further sup-
ported and confirmed by the magnetic susceptibility and
molar conductance studies which also help to prove the
stoichiometry and formation of the complexes.
3.2. Structural Properties
FT IR spectra of chitosan and SC are shown in Figures
2(a) and 2(b), respectively. The IR spectrum of chitosan
exhibits strong peak at 3359 cm–1 which can be assigned
to the axial vibration of O-H. It is superimposed to the
UV-Vis spectra of SC, complex 1, 2 and 3 are given in
Figures 3(a)-(d), respectively. The UV-Vis spectrum of
Table 1. Physical characterization, micro analytical data (C, H and N) of the complexes.
Elemental and metal analysis data
Calculated (%) Found (%)
Compound
C H N Cu C H N Cu
Molar
conductivity (λm,)
(Ω–1cm2mol–1)
Magnetic
susceptibility (µeff)
(BM)
Chitosan 44.72 6.88 8.69 44.35 6.518.49
SC 58.86 5.70 5.28 58.12 5.444.93
Complex 1 59.59 4.62 5.35 12.13 59.08 4.305.0812.01 11 1.70
Complex 2 49.75 4.17 8.29 12.53 49.37 3.988.1612.14 15 1.93
Complex 3 58.53 4.73 5.06 11.47 58.05 4.464.8710.98 17 1.72

Structural, Surface, Thermal and Catalytic Properties of Chitosan Supported Cu(II) Mixed Ligand Complex Materials 287
Figure 2. FT-IR spectra of chitosan (a); SC (b); complex 1
(c); complex 2 (d); and complex 3 (e).
Figure 3. UV-Vis. Spectra SC (a); complex 1 (b); complex 2
(c); and complex 3 (d).
free SC shows strong absorption bands at the range 235 -
255 nm which could be assigned to π - π* and n - π* tran-
sitions in the aromatic ring or azomethine (–C = N) [25].
These absorption bands differ in intensities and in the
UV-Vis spectra of the complexes 1, 2 and 3. More than
this, the slight shift in the wavelength is also noted.
These changes may be due to the coordination of azo-
methine nitrogen and phenolic oxygen of SC to the Cu(II)
ion. In addition, all the complexes exhibit a new band
arising from their characteritic d-d transition which ex-
plains the nature of the geometry of the complexes. This
characteristic band appeared at 540 - 560 nm for the
complexes, 1 and 3. It corresponds to the 2B1g →2A1g
transition and makes a confirmation to assign the tetra
coordinated (N2O2) square planar geometry for these two
complexes, 1 and 3 [26]. But for the complex 2, this sig-
nificant band appeared at the higher wavelength range
(735 - 755 nm) for the complex 2. It clearly supports the
penta coordinated (N2O2S) square pyramidal geometry to
the complex 2.
Table 1 also shows the magnetic moment and molar
conductance values of complexes. The magnetic moment
values measured at room temperature for the complexes
1, 2 and 3 are 1.70, 1.93 and 1.72 BM, respectively.
These values consent with the spin only magnetic mo-
ment of S = 1/2, d9 Cu(II) system and also support the
square planar geometry to the complexes 1 and 3 and
square pyramidal geometry to complex 2. The molar
conductance values of 10–3 M solution of complexes are
in the range of 11 - 17 ohm–1cm2mol–1. These values as-
sign the very expected non-electrolyte nature to all the
studied complexes.
1H NMR spectroscopy is a powerful technique used to
investigate the proton environment of organic molecule.
In 1H NMR spectral study, the chemical shifts observed
for SC are: 2.4 ppm (acetyl proton of chitosan), 3.9 ppm
(C2 proton), and 4.2 - 4.77 ppm (C3, C4, C5 and C6 pro-
tons). The chemical shift at 9.8 ppm (azomethine proton)
confirms the formation of Schiff base SC. It is further
confirmed by the multiplets between 6.7 - 8.1 ppm (aro-
matic protons).
3.3. Thermal Properties
TG-DTA study is used to explain thermal stability and
mode of decomposition of SC and complexes. The TG
curves of SC and complexes show two mass loss stages.
The first one might be due to the elimination of physi-
cally adsorbed water molecules. And the second one with
endothermic decomposition could be the decomposition
of polymer matrix. The thermal stability of the ligand,
SC is greater than that of its complexes which may be
due to the change in stacking order of ligand, SC after
the complex formation with Cu(II).

Structural, Surface, Thermal and Catalytic Properties of Chitosan Supported Cu(II) Mixed Ligand Complex Materials 288
3.4. Surface Morphology
Scanning electron microscopy is a fundamental tool to
predict surface morphology and particle sizes of materi-
als. The morphology and the distribution of particle sizes
of the compounds are explained as illustrated in Figure 4.
Figure 4(a) exhibits smooth and regular surface mor-
phology with particle sizes of greater than 10 μm. Schiff
base, SC reveals irregular surface with small particle
sizes of less than 10 μm as shown in Figure 4(b). These
surface morphology changes accompanied with decrease
in particle sizes for SC could be obtained from the
chemical modification of chitosan [6,27,28]. The de-
crease in the particle sizes after the formation of SC re-
sulting from the Schiff base modification could enhance
adsorption capacity of the metal ions through complex
formation [28,29]. However, the interaction between
chitosan and salicylaldehyde surmounts the reduction of
particle sizes by reducing the number of free amino
groups available on the surface of the chitosan [28].
Figure 4(c) describes completely different surface mor-
phology accompanied with pores and roughness for the
complex1. The particle sizes of complex 1 are signifi-
cantly less than that of both chitosan and SC. The ap-
pearance of pores on surface of complex 1 proves that
the imprinting of the copper ions on SC could leave their
footprints which increase the number of pores in the sur-
face. This behavior may be attributed to the coordination
of copper ion to the active sites of the ligand [30]. The
pores and roughness emerged on surface of these chito-
san supported complexes can able to act as active sites in
heterogeneous catalytic reactions.
3.5. Crystalline Properties
A significant intermolecular hydrogen bond leads to the
crystalline character of chitosan that distinguishes it from
most other carbohydrate polymers [31]. It is evidenced
from the diffraction pattern of chitosan (Figure 5(a))
which exhibits its characteristic peak at 2θ = 20˚ in ac-
cordance with the previous reports [12,13,32,33]. The
XRD pattern of the Schiff base, SC (Figure 5(b)) shows
two peaks at 2θ = 14˚ and 20.1˚. The peak at 20.1˚ is
slightly wider than that of the free chitosan which sug-
gests the decrease in crystallinity after the grafting of
salicylaldehyde in the backbone of chitosan structure.
This notable characteristic peak is much wider than that
of the ligand (SC) and chitosan. Figures 5(c)-(e) are
XRD patterns of all the complexes which show the non
existence of the characteristic peaks for pure copper. This
observation concludes that the basic structure of the chi-
tosan was not disturbed in the whole process of the com-
plex preparation.
Moreover, the crystallinity of all the analyzed com-
pounds was calculated as following the previous reports
(a)
(b)
(c)
Figure 4. Scanning electron microscopes of chitosan (a); SC
(b); and complex 1 (c).
[33,34]. The crystallinity of the compounds can be re-
lated on the basis of the parameter, crystalline index. The
crystalline index is calculated as follows using Equation
(2):

110
110
% 100
amII
CrystallineIndex
I

 (2)
where I110 is the maximum intensity at ~20˚ and Iam is the
intensity of amorphous diffracion at 16˚. Table 2 explicates t

Structural, Surface, Thermal and Catalytic Properties of Chitosan Supported Cu(II) Mixed Ligand Complex Materials 289
Table 2. 2θ values, d spacing and crystalline index of the complexes.
Crystalline index
Compound 2 Theta (degree)
(d spacer value( nm)) % Error (±)
Chitosan 20 (0.444) 47.31 2.3655
SC 14 (0.639) 20.1 (0.441) 42.19 2.1095
Complex 1 13.4 (0.662) 18.4 (0.482) 19.3 (0.460) 39.07 1.9535
Complex 2 - 14 (0.648) 20.3 (0.437) 41.70 2.0850
Complex 3 - 14.1 (0.637) 20 (0.436) 31.17 1.5585
important point in the oxidation of cyclohexane is the
reduction of Cu(II) to Cu(I) of the complexes. This re-
duction of Cu(II) facilitates the ligand around the metal
ion.
3.7. Catalytic Reusability
The reusability of the catalyst is the very important one
in the field of heterogeneous catalysis. To check the re-
usability of the complexes, complex 1 was selected. This
complex 1 was investigated by separating through filtra-
tion after the first catalytic reaction was completed. This
filtered catalyst was recovered by washing with solvent
and dried under vacuum, then used in the second run by
following the same reaction conditions. The catalytic run
was repeated five times with the further addition of sub-
strates in sufficient amount under the same reaction con-
ditions. The nature and yield of the final products were
comparable to that of the original one. The reusability of
the catalyst, complex 1 was illustrated in Figure 6 for the
five repeated cycles. It shows that catalytic efficacy did
diminish significantly after fourth repeated run. The rea-
son might be the poor chemical resistance and mechani-
cal strength of chitosan bio polymeric backbone [35]
which provides the heterogeneity to the complex.
Figure 5. XRD patterns of chitosan (a); SC (b); complex 1
(c); complex 2 (d); and complex 3 (e).
2θ, d-space and calculated crystal index values for all
compounds. The variation of crystalline index for the
different compounds may be due to the formation of
Schiff base/grafting of salicylaldehyde, spacial hindrance,
hydrophobic force and π-π stacking.
3.6. Catalytic Ability
The catalytic oxidation of alkanes with 30% H2O2 as
oxidant under mild aerobic conditions is significantly a
fascinating reaction, because the direct functionalisation
of inactivated –C-H bonds in saturated hydrocarbons
usually requires drastic reaction conditions such as high
temperature and pressure. Table 3 explains the conver-
sion percentage of cyclohexane at room temperature and
70˚C. There is no product obtained at room temperature
conditions which may be due to the non decomposing
nature of H2O2 at room temperature. The results also ex-
plore that there is no evidence for the product without the
catalyst and also without H2O2 even at 70˚C. According
to the products obtained from the GC analyses, the first
and slow step might be the formation of cyclohexanol
and the second step may be the oxidation of cyclohexa-
nol to cyclohexanone.
4. Conclusion
Three new different Cu (II) mixed ligand complexes
have synthesized and characterized. They were found to
be air stable. Tetra coordinated square planar geometry
were allotted to complexes 1 and 3 and penta coordinated
square pyramidal geometry was assigned to complex 3
by the spectral evidences. Thermal stability of the com-
plexes was found to be less than that of their Schiff base
ligand, SC due to the change in stacking order. SEM im-
ages of the complexes displayed rough surface with some
pores (active sites) compared to chitosan and its Schiff
base, SC. This surface morphology changes with pores
formation added the positive effects in catalytic reactions.
The crystalline property of the compounds was explored
by X-ray diffraction studies. The crystallinity of the ana-
lysed compounds was in the following order: chitosan >
Complex 1 is the most efficient catalyst with the %
conversion of cyclohexane. The highest selectivity of the
desired products was reached with complex 1. Very

Structural, Surface, Thermal and Catalytic Properties of Chitosan Supported Cu(II) Mixed Ligand Complex Materials 290
Table 3. Conversion percentage of cyclohexane and selecti-
vity of the products.
Conversion (%) Selectivity (%)
Conditions C1 C2 C3(C1/C2/C 3)
A
B
C
D 34 22 27Cyclohexanol (77/42/61)
Cyclohexanone (23/58/39)
A: Without catalyst at room temperature and 70˚C; B: Without H2O2 at
room temperature and 70˚C; C: With catalyst and H2O2 at room temperature;
D: With catalyst and H2O2 at 70˚C; C1: complex 1; C2: complex 2; C3:
complex 3.
Figure 6. Catalytic reusability of complex 1.
SC > complex 2 > complex 1 > complex 3. Cyclohexane
was oxidized into cyclohexanol and cyclohexanone by
the complexes and complex 1 showed highest catalytic
activity than other two complexes. Currently, we are
analysing the effect of irradiation on the surface, struc-
ture and catalytic ability of these reported complexes.
5. Acknowledgements
The authors gratefully acknowledge the Department of
Atomic Energy-Board of Research in Nuclear Sciences
(DAE-BRNS), Mumbai, India for providing financial
support to carry out this research work. The authors also
thank the management of PSN College of Engineering
and Technology, Tirunelveli-627 152, India for provid-
ing essential research facilities. XRD analysis facility
provided by Department of Physics, Alagappa University,
Karaikudi-630 003, India is gratefully acknowledged.
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