Novel synthesis of silver nanoparticles using 2,3,5,6-tetrakis- (morpholinomethyl) hydroquinone as reducing agent

Article abstract of DOI:10.1016/j.saa.2012.03.081

2,3,5,6-Tetrakis-(morpholinomethyl) hydroquinone (TMMH) was used as a reducing agent to synthesize spherical shaped silver nanoparticles in water-ethanol medium without using any stabilizing and capping agents. The reducing agent TMMH is prepared by Mannich-type reaction method and ¹H NMR, ¹³C NMR and FT-IR spectroscopy techniques were used to characterize the compound (TMMH). The nature of bonding, structural and optical properties of the final product were analyzed using different techniques such as UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The interaction between silver and reducing agent was confirmed by using FTIR analysis. The final product obtained showed higher crystallinity with cubic structure and an average crystalline size of about 20 nm. The results revealed that it is possible to synthesize crystalline Ag nanoparticles using organic compound as reducing agent.

Full text of DOI:10.1016/j.saa.2012.03.081

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 305–309
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Novel synthesis of silver nanoparticles using 2,3,5,6-tetrakis-(morpholinomethyl)
hydroquinone as reducing agent
a
a
a
a
a,b,
⇑
P. Manivel , A. Balamurugan , N. Ponpandian , D. Mangalaraj , C. Viswanathan
a
Department of Nanoscience and Technology, Bharathiar University, Coimbatore 641046, Tamilnadu, India
DRDO-BU-Center for Life Science, Physics Division, Bharathiar University, Coimbatore 641046, Tamilnadu, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
2,3,5,6-Tetrakis-(morpholinomethyl) hydroquinone (TMMH) was used as a reducing agent to synthesize
spherical shaped silver nanoparticles in water–ethanol medium without using any stabilizing and
Received 22 January 2012
Received in revised form 19 March 2012
Accepted 25 March 2012
Available online 6 April 2012
1
capping agents. The reducing agent TMMH is prepared by Mannich-type reaction method and H NMR,
13
C NMR and FT-IR spectroscopy techniques were used to characterize the compound (TMMH). The
nature of bonding, structural and optical properties of the final product were analyzed using different
techniques such as UV–Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM)
and Fourier-transform infrared spectroscopy (FTIR). The interaction between silver and reducing agent
was confirmed by using FTIR analysis. The final product obtained showed higher crystallinity with cubic
structure and an average crystalline size of about 20 nm. The results revealed that it is possible to syn-
thesize crystalline Ag nanoparticles using organic compound as reducing agent.
Keywords:
TMMH
Nanoparticles
Reducing agent
FTIR
Organic
Crystalline size
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
The effective method to generate silver nanoparticles in narrow
size distribution of aqueous medium is achieved by the reduction
Nanoparticles are used, due to their potential applications in
various fields like optical device, chemical sensor, bimolecular
sensor and DNA detection [1]. Among various metals, silver nano-
particles are an interesting one because of their size and shape
dependent optical properties which render them very useful for
technical applications [2]. In particular, there is a remarkable inter-
est to produce silver nanoparticles dispersion at large scale [3–4].
Several methods have been reported for the synthesis of silver
nanoparticles, including chemical reduction in aqueous solution
with or without stabilizing agents [5]. Thermal decomposition in
organic solvents [6], chemical and photo reduction in reverse
micelles [7] and microwave assistance [8], are some of the factors
for the formation of silver nanoparticles. Most of the researchers
previously described the stable silver dispersion only at relatively
low concentrations of metal. Hence, they are not suitable for
large-scale production [9]. The simplest, cost effective and the
most commonly used bulk-solution synthetic method for metal
nanoparticles is the chemical reduction of metal salts [10]. In fact,
production of nanoscale metal silver particles with different mor-
phologies and sizes using chemical reduction of silver salts has
been reported [11,12].
method using citrate of sodium [13]. Other reducing agents that
have been used are ascorbic acid, hydrazine hydrate and sodium
dodecyl sulfate. In fact, formation of nanosized silver particles with
different morphologies and sizes using chemical reduction of silver
salts has been reported [12]. A mixture of hydrazine hydrate and
citrate of sodium as a reducing agent in the isolation of silver nano-
particles has been reported by Guzman et al. [14]. Tripathy and Yu
[15] reported the synthesis of
ated silver nanoparticles. The nanoparticles were also obtained
by chemical reduction of AgNO in ethanol, using triethylenetetra-
x-mercaptoundecanoic acid gener-
3
mine as surfactant [16]. In this method control of the size of the
nanoparticles has been achieved by regulating the ratio of metal
chloride to the organic reagent. Recently gold nanoparticles were
obtained by 2,3,5,6-tetrakis-(morpholinomethyl) hydroquinone
as reducing agent [17]. The above approach is well enough to jus-
tify our effort to report a new and effective reducing agent for the
preparation of silver nanoparticles.
In the present work we have made an attempt to synthesize the
silver nanoparticles using TMMH as reducing agent. The as-synthe-
sized compound (TMMH) after purification was used to synthesize
final silver nanoparticles. The secondary hydroxyl groups and
nitrogen of TMMH compound have been used for the reduction
3
of AgNO . This approach is a simple, cost-effective, stable for long
time, reproducible and previously unexploited method. We found
that the size of nanoparticles can be modulated by varying the
⇑
Corresponding author at: Department of Nanoscience and Technology, Bha-
rathiar University, Coimbatore 641046, Tamilnadu, India. Tel.: +91 422 2428422.
E-mail address: viswanathan@buc.edu.in (C. Viswanathan).
1
386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.03.081

3
06
P. Manivel et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 305–309
amount of TMMH compound in the reaction medium. Even spher-
ical aggregation of Ag nanoparticles could also be obtained with
low and high concentrations of TMMH. To our knowledge there
are no reports on the use of TMMH as a reducing agent in the syn-
thesis of silver nanoparticles using chemical reduction. Hence a
systematic study of synthesis and characterization is undertaken.
obtained on a Nicolet-6700 spectrometer, with samples prepared
as KBr pellets. The absorption spectra were recorded by double-
beam Jasco V-530 UV–Vis spectrometer. X-ray diffraction (XRD)
measurements of the TMMH capped colloidal silver nanoparticles
drop-coated onto glass substrates were done on a PANalytical X’ Pert
Pro MPD instrument operating at a voltage 40 kV and a current of
3
0 mA with Cu Ka radiation (Ni filter). The morphology of Ag nano-
particles was analyzed from ICON Quanta Make II Environmental
Experimental procedure
SEM.
Ultra-pure water was used throughout this study and its resis-
tivity was >18 MO cm. Silver nitrate (AgNO ), hydroquinone, para-
3
Results and discussion
formaldehyde, morpholine, 1,4-dioxane and potassium hydroxide
were of analytical grade and were not further purified before use.
Thin layer chromatography (TLC) analysis was carried out using
silica gel plates.
Spectral analysis of pure compound (TMMH)
Fig. S1 shows 1H NMR spectra of TMMH (see Supplementary
material). A multiplet 16 protons were obtained at d 2.52 due to
Morpholine (18.9 g, 0.2179 mol) and paraformaldehyde (8.18 g,
morpholine in NACH
due to 16 protons of morpholine in OACH
in ArACH AN. A broad singlet at d 10.09 was due to aromatic OH
2
ACH2. A multiplet at d 3.67 was obtained
0
.272 mol) were dissolved in 1,4-dioxane (60 mL) and stirred vigor-
2
ACH and 18 protons
2
ously. The solution was refluxed at 100 °C for 2 h. Then hydroqui-
none (3 g, 0.0272 mol) was added drop wise and the reflux
process was continued for another 24 h at 100 °C. The reaction
was continued until the hydroquinone was bonded to the imines
and confirmed through TLC. Finally, the solution was cooled to
room temperature and filtered, concentrated on a rotary evaporator
to dryness and kept overnight under vacuum. The as-prepared
TMMH mixture was purified using column chromatography and
2
1
groups. This H NMR spectra of the TMMH were quite comparable
with previous reports [17].
Fig. S2 shows 13C NMR spectra of TMMH (see Supplementary
material). A peak at d 149.6 (2C) is due to C
at d 121.4 (4C) is due to C , C , C and C . Three more peaks at d
6.9 (8C), 54.6 (4C) and 52.8 (8C) are due to the presence of
morpholine OACH ACH , ArACH attached C , C , C and C and
morpholine NACH ACH , respectively
Fig. S3 shows FT-IR spectra of TMMH (see Supplementary mate-
1 4
and C AOH and a peak
2
3
5
6
6
2
2
2
2
3
5
6
3
the obtained product was eluted using CHCl :MeOH (95:5) until
2
2
.
the formation of light-yellow powder. The structure of the isolated
TMMH compound was compared with the previously reported
spectral values. The complete reaction mechanism for the forma-
tion of TMMH is shown in Fig. 1.
ꢀ
1
rial). A stretching vibration at 3430 cm is due to the presence of
OAH groups, and two strong vibrational frequencies at 1115 and
ꢀ
1
ꢀ
3
1007 cm
are due to CAC and CAO groups, respectively. The
A series of volume (2.5–10 ml) of a 10 M ethanol solution of
ꢀ
3
stretching CAH bonds are characteristic and they give rise to
TMMH was added into 5 ml of 2 ꢁ 10 M aqueous AgNO
3
solution
ꢀ1
strong bands in the region 2852 cm
.
under vigorous stirring at room temperature. After 1 min the solu-
tion was gradually changed from colorless to pale yellow color.
Then potassium hydroxide was added into the solution to adjust
the pH (pH 8), which makes the solution change from pale yellow
to dark brown colored solution indicating the formation of Ag
nanoparticles.
TMMH capped silver nanoparticles
UV–Vis absorption spectra have been proven to be quite sensi-
tive for the formation of silver colloids because the silver nanopar-
ticles can exhibit an intense absorption peak due to the surface
plasmon (it describes the collective excitation of conduction
1H and 13C NMR spectra were recorded by JEOL 300 MHz spec-
trometer to conform the TMMH structure. FTIR spectra were
Fig. 1. Schematic diagram of the reaction mechanism of TMMH.

P. Manivel et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 305–309
307
electrons in a metal) excitation [13]. Formation and stability of
silver nanoparticles in aqueous colloidal solution are confirmed
by UV–Vis spectral analysis. Fig. 2 shows the UV–Vis spectra of
TMMH capped silver nanoparticles formation at constant volume
of AgNO
c) 7.5 mL and (d) 10 mL] in water ethanol medium. It is worth-
while mentioning that AgNO can be completely reduced to form
3
with different volume of TMMH [(a) 2.5 mL, (b) 5 mL,
(
3
silver nanoparticles, which is confirmed by the observation that
there is no further change in UV–Vis spectrum after TMMH is
introduced into silver solution. Our result showed that there are
two strong absorption bands appeared upon varying the volume
of TMMH in the reaction medium. In the presence of TMMH, it
exhibited well resolved absorption bands at 420 nm (curves b
and d of Fig. 2). Also the UV absorption intensity increased with in-
crease in the volume of TMMH in the solution phase.
The XRD technique was used to determine the crystal structure
of silver nanoparticles. Fig. 3 shows the XRD pattern of TMMH
capped silver nanoparticles. In order to study the crystallinity of
silver nanoparticles, the colloidal solution was drop coated onto
a glass substrate to obtain a film and dried at ambient temperature.
The entire reflection of well defined peaks, which were obtained
from XRD, confirms the formation of silver nanoparticles to face-
centered cubic structure (Fig. 3(a) 1:1 volume ratio and (b) 2:1 vol-
ume ratio). Face center cubic structure was revealed with 2h values
of 38, 44, 64, 77 and 81 corresponding to the (111), (200), (220),
Fig. 3. XRD pattern of TMMH capped silver nanoparticles (TMMH:AgNO
volume ratio (b) 2:1 volume ratio.
3
): (a) 1:1
control the background effect. In order to measure the instrumen-
tal contribution to line broadening, the diffraction pattern was
recorded for the sample with standard silicon (Si). The instrumen-
tal correction of line broadening, (bhkl) [20] corresponding to each
diffraction peak of silver nanoparticles was estimated using the
equation
(
8
311) and (222) crystalline planes, respectively (JCPDS PDF No.
9-3722). Thus XRD pattern clearly demonstrated that the nano-
2
2
1=2
particles formed by chemical reduction of Ag+ ions, were crystal-
line in nature. The reflections were observed at lower angles
compared to the standard which might be due to a slight increase
in lattice parameters of nano-phased silver. Also, the broadening of
the diffraction peaks was observed due to the effect of nano-sized
particles. The background observed was high, which could be from
glass substrate used for data collection and also because of the
presence of organic moieties in TMMH and ethanol that were used
for nanoparticle synthesis. As indicated in Fig. 3, the highly intense
diffraction peak was located at 2h = 37.96°. So, we can conclude
that (111) lattice plane is the preferred orientation for these silver
nanoparticles, attributable to its lower surface free energy com-
pared to other planes [18]. In addition, high atom density facets
such as (111) are used for their high antiviral activity [19].
We obtained the average crystal size by Williamson–Hall
b
hkl ¼ ½ðbhklÞ measured ꢀ ðbÞ measuredꢂ
ð1Þ
Williamson and Hall proposed a method of deconvoluting size
and strain broadening by looking at the peak width as a function
of diffracting angle 2h and obtained a mathematical expression
[
21] as
ꢀ
ꢁ
Kk
D cos h
bhkl
¼
þ ð4
e
tan hÞ
ð2Þ
m
or by rearranging
ꢀ
ꢁ
Kk
bhkl cos h ¼
þ ð4
e
sin hÞ
ð3Þ
D
v
where bhkl is instrumental corrected integral breadth of the reflec-
tion (in radians) located at 2h, k is the shape factor (0.9 for spherical
(
W–H) plot. Before estimation the instrument was corrected to
v
shape), D is the volume weighted crystallite size, and h is the angle
of reflection (in degrees). A plot is drawn for 4 sinh along the X-axis
and bhkl cosh along the Y-axis for prepared Ag nanoparticles and is
shown in Fig. 4. For the entire W–H model, the plot is drawn only
for the preferred orientation peaks of Ag with the face-centered
cubic phase. The lattice planes corresponding to those preferred
peaks are (111), (200), (220), (311) and (222). The crystallite size
is intercept of the linear fit made to the plot. The as-estimated value
of the crystallite size is 19 nm for (TMMH:AgNO
Fig. 4(a)) and 16 nm for 2:1 volume ratio (Fig. 4(b)) prepared
sample.
3
) 1:1 volume ratio
(
The morphology and size of the prepared silver nanoparticle
were investigated using scanning electron microscopy. Fig. 5(a
and b) shows surface morphology and particle size distribution
of silver nanoparticles synthesized from 1:1 volume ratio of TMMH
3
with AgNO . All the nanoparticles are nearly in spherical shape and
the average diameter was 42.4 ± 5 nm (150 nanoparticles were
measured for averaging). Fig. 5(c and d) shows representative sil-
ver nanoparticles synthesized using 2:1 volume ratio of TMMH
with AgNO3. Also, it has been confirmed that all the silver nanopar-
ticles are in spherical shape. The average diameter was 26 ± 4.2 nm
(
160 nanoparticles were measured for averaging). The size of the
Fig. 2. UV–Vis spectra of silver nanoparticles synthesized using 5 mL AgNO
(
3
2 ꢁ 10ꢀ3 M) with different volume of TMMH (a) 2.5 mL, (b) 5 mL, (c) 7.5 mL and (d)
silver nanoparticles was found to be decreased with an increase
in TMMH reducing agent. The self-assembled nanoparticles can
1
0 mL.

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P. Manivel et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 305–309
3
Fig. 4. W–H plot of silver nanoparticles (TMMH:AgNO ): (a) 1:1volume ratio, (b)
2
:1 volume ratio.
be regulated smoothly and the growth can be controlled by the
critical TMMH/AgNO volume ratio.
3
Fig. 6. FT-IR spectra of silver nanoparticles (a) 1:1 volume ratio TMMH with Ag and
b) 2:1 volume ratio TMMH with Ag.
The interaction of Ag nanoparticles with TMMH compound was
confirmed by FT-IR spectra (Fig. 6). The strong vibration band (pure
TMMH) was corresponding to the stretching of CAC bond assigned
(
3
of AOH bond. After the reduction with AgNO , the shift in the peak
ꢀ
1
ꢀ1
at 1115 cm , CAO bond assigned at 1007 cm , CAH stretching
at 3430 toward lower frequency which is attributed to the binding
of AOH group with nanoparticles is shown in Fig. 6(a and b). Also,
the AOH peak suppresses in the presence of nanoparticles, which
ꢀ1
assigned at 2852 cm , respectively. While the intense broad peak
observed at 3430 cm was corresponding to stretching vibration
ꢀ1
Fig. 5. SEM image of Ag nanoparticles; (a) 1:1 volume ratio and (b) corresponding size distribution histogram, (c) 2:1 volume ratio and (d) corresponding size distribution
histogram.

P. Manivel et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 305–309
309
+
indicates that Ag ions are reduced with the hydroxyl groups of
TMMH. Similarly, the stretching vibrations of CAH, CAO and CAC
bonds are slightly shifted with low intense. In conventional liquid
phase preparation of TMMH capped silver nanoparticle, the inter-
action between the two components appeared clearly either as
changes in the wave number or changes in the intensity of some
absorption peaks of TMMH [22].
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We have successfully prepared 2,3,5,6-tetrakis-(morpholinom-
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.03.081.