January 2003
Materials Letters 57 (2003) 1045 – 1050
www.elsevier.com/locate/matlet
Electrodeposition of hybrid organic–inorganic films
containing iron oxide
I. Zhitomirsky *, M. Niewczas, A. Petric
Department of Materials Science and Engineering, McMaster University, 1280 Main Street West Hamilton, ON, Canada L8S 4L7
Received 13 May 2002; accepted 15 May 2002
Abstract
A novel method has been developed for the preparation of hybrid organic – inorganic films containing iron oxide. The
method is based on cathodic electrodeposition of iron oxide nanoparticles in situ in a polyelectrolyte matrix. Prepared films
were studied using thermogravimetric analysis and magnetic measurements. By manipulation of deposition conditions, the
amount of the deposited material, deposit composition and magnetic properties could be varied. Magnetic measurements
revealed that the nanocomposite films are superparamagnetic.
D 2002 Elsevier Science B.V. All rights reserved.
Keywords: Electrodeposition; Iron oxide; Poly(diallyldimethylammonium chloride); Film; Hybrid; Organoceramic; Superparamagnetism
1. Introduction
The development of nanostructured organic –inorganic hybrid materials presents new challenges and
opportunities for future technologies [1– 6]. The nanocomposites combine the advantageous properties of
organic and inorganic components. Nanostructured
magnetic materials are now being extensively studied
for high-capacity magnetic storage media, integrated
circuits, color imaging, magnetic refrigerators and
biomedical applications. Below a critical size, nanocrystalline magnetic particles may be single domain
and show the unique phenomenon of superparamagnetism [7,8]. A critical obstacle in assembling and
maintaining a nanoscale magnetic material is its
tendency to aggregate. To overcome this, nanopar-
*
Corresponding author. Fax: +1-905-528-9295.
E-mail address: zhitom@mcmaster.ca (I. Zhitomirsky).
ticles of magnetic materials were isolated in a polymer
matrix and advanced hybrid materials were developed
[7– 14].
Novel applications of superparamagnetic materials
are inevitably related to the development of advanced
techniques for deposition of thin films. Cathodic
electrolytic deposition of thin films is a new technique
in ceramic processing. The feasibility of electrodeposition of various thin film materials from aqueous
solutions has recently been demonstrated. Review
papers describing materials science aspects, mechanisms, kinetics of deposition and applications of
electrolytic films are now available [15 – 17]. This
method brings new opportunities in electrosynthesis
of nanostructured thin films and powders from aqueous solutions of metal salts [18 – 21]. The important
discovery was the feasibility of electrochemical intercalation of water-soluble polyelectrolytes into cathodic deposits prepared by electrolytic deposition [22].
We have begun to use charged polymers for prepara-
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 9 2 2 - 9
1046
I. Zhitomirsky et al. / Materials Letters 57 (2003) 1045–1050
tion of organoceramic films [23 – 25]. More recent
explorations have illustrated the importance of this
method for various applications [26,27]. Electrolytic
deposition produces nanoparticles from solutions of
metals salts in electrode reactions and provides their
deposition. In this work by using cationic polyelectrolytes for electrodeposition, magnetic nanoparticles
were created in situ in a polymer matrix. The process
of electrodeposition and the properties of hybrid iron
oxide-poly(diallyldimethylammonium chloride) films
are presented in this report.
2. Experimental procedures
Ferric chloride hexahydrate (FeCl36H2O), ferrous
chloride tetrahydrate (FeCl24H2O) and poly(diallyldimethylammonium chloride) (PDDA) from Aldrich
were used to formulate two stock solutions for electrodeposition. Stock solution 1 contained 3.3 mM FeCl3,
1.65 mM FeCl2 and 1 g/l PDDA. Stock solution 2
contained 3.3 mM FeCl3, 1.65 mM FeCl2 and 0.5 g/l
PDDA. Deionized water was de-aerated prior to solution preparation using 93% Ar – 7% H2 gas. The gas
flow was maintained through the solutions during
deposition and through the chamber for film drying.
The electrochemical cell for deposition included a
cathodic substrate centered between two parallel platinum counterelectrodes. The films were deposited on Pt
foil cathodes (50500.1 mm) at a current density of
10 mA/cm2. The Pt substrates were weighed before and
after deposition experiments followed by drying at
room temperature for 48 h. After drying, the electrolytic deposits were scraped from the Pt electrodes for
thermogravimetric (TG) analysis and magnetic measurements. The thermoanalyzer (Netzsch STH-409) was
operated in air between room temperature and 1200 jC
at a heating rate of 5 jC/min.
Magnetic properties were studied using a Quantum
Design PPMS-9 system. DC magnetization studies
were performed using the extraction magnetometer
option. Magnetization hysteresis loops were measured
in the field range up to 10 kOe at temperatures ranging
from 2 to 298 K. The external magnetic field was
changed in the sweep mode at the sweep rate of 10 Oe/
min. The temperature dependence of the magnetization
was studied by both zero-field- (ZFC) and field-cooled
(FC) procedures. The sample was cooled down to 1.9 K
in the zero external field (ZFC) and then magnetization
was measured during heating to 298 K under the
applied field of 200 Oe. The sample was subsequently
cooled back to 1.9 K under an applied field of 200 Oe
(FC) and the measurements of magnetization were
carried out during heating to 298 K.
3. Results and discussion
In the cathodic electrodeposition method, the high
pH of the cathodic region brings about formation of
colloidal particles, which precipitate on the electrode.
Reduction of water is the cathodic reaction that
generates OH:
2H2 O þ 2e ! H2 þ 2OH :
ð1Þ
In previous work [22], it was suggested that
intercalation of PDDA into electrolytic deposits is
achieved via heterocoagulation of oppositely charged
PDDA and colloidal particles of oxides or hydroxides
formed near the cathode.
Electrodeposition from stock solutions 1 and 2
resulted in the formation of cathodic deposits (deposits 1 and 2, respectively). Deposit weight increased
linearly with deposition time as shown in Fig. 1.
Fig. 1. Deposit weight vs. deposition time for deposits 1.
I. Zhitomirsky et al. / Materials Letters 57 (2003) 1045–1050
Results of thermodynamic modeling [28,29] indicate that iron species precipitate as Fe3O4 under basic
conditions at a molar ratio of Fe2+:Fe3+=1:2 under a
nonoxidizing environment:
Fe2þ þ 2Fe3þ þ 8OH ! Fe3 O4 þ 4H2 O:
ð2Þ
Cathodic electrolytic deposition is similar to the
wet chemical method of ceramic powders processing
that utilizes an electrogenerated base instead of alkali.
Therefore, it could be suggested that iron species in
our experiments precipitate as Fe3O4. However, when
precipitation of iron oxide is performed in a polymer
matrix, we cannot exclude the possibility of formation
of other phases [29]. Indeed, the formation of Fe2O3
was observed in Refs. [8,14].
Fe2O3 can exist in a thermodynamically stable aFe2O3 form and a metastable g-Fe2O3 form. a-Fe2O3
(hematite) is antiferromagnetic. Both Fe3O4 (magnetite) and g-Fe2O3 (maghemite) are ferrimagnetics with
the spinel structure. The use of these ferrimagnetic
materials with high Curie points allowed formation of
advanced hybrid materials, which exhibited room
temperature superparamagnetism when particle size
was lower than 10 –20 nm [7 –10,14]. Some difficulties were reported [13,14] in distinguishing between
nanostructured magnetite and maghemite in composite materials using X-ray diffraction. The difficulties
are related to peak broadening of the two nanostructured phases having relatively close lattice constants.
Magnetic properties of nanoparticles could be different from the properties of corresponding bulk materials. It is known that decrease in particle size below 20
nm results in a significant decrease of the saturation
magnetization of g-Fe2O3 [30]. In contrast, antiferromagnetic material may acquire a net moment when
particle size is sufficiently low. However, magnetization of hybrid material based on a-Fe2O3 [11,13]
was found to be low compared to that of composites
based on g-Fe2O3 or Fe3O4.
Electrolytic deposition was proven to be an important technique for synthesis of nanostructured thin
films [17 – 21]. In the current work, electrosynthesis
of iron oxide was performed in situ in a polymer
matrix. The polymer matrix is necessary to prevent
oxide particle agglomeration caused by Van der Waals
forces and magnetostatic interparticle interactions.
1047
Organic molecules exert an influence on the size of
the oxide particles [7– 14,28]. We utilized TG analysis
and magnetic measurements to study the composition
and properties of the prepared films.
Fig. 2 compares the results of TG analysis of
deposits 1 and 2. The TG curves indicate that the
weight loss occurs in several steps. The total weight
loss in the temperature range up to 1200 jC was found
to be 75.4 and 58.1 wt.% for deposits 1 and 2,
respectively. We suggest that observed weight loss is
mainly attributed to burning out of an organic phase.
It is important to note that magnetite might be
oxidized during heating in air in the TG experiments
[29]. However, our TG data indicate that the amount
of an inorganic phase in deposits 2 is larger than that
in the deposits 1. Indeed, sample weight at 1200 jC
was found to be 24.6% and 41.9% of the initial
sample weight for deposits 1 and 2, respectively.
Therefore, higher concentration of PDDA in stock
solution 1 compared to stock solution 2 resulted in
higher concentration of an organic phase and lower
concentration of an inorganic phase in deposits 1
compared to deposits 2. Similar results were reported
in our previous investigations of other hybrid materials [23,26]. It was demonstrated that the amount of
organic phase in deposits increases with increasing
PDDA concentration in solutions [23,26]. Charged
PDDA particles exert a shielding effect preventing
electrosynthesis of oxide or hydroxide particles [23],
Fig. 2. TG data for (a) deposits 1 and (b) deposits 2.
1048
I. Zhitomirsky et al. / Materials Letters 57 (2003) 1045–1050
ence of magnetization was observed at room temperature and at lower temperatures (Fig. 4a,b). For both
deposits 1 and 2, the magnetization increased with
decreasing temperature (Fig. 3a,b and 4a,b). Higher
magnetization was observed for deposits 2 compared
to deposits 1 at the same temperatures (Fig. 3a,b vs.
Fig. 4a,b). The difference is related to higher amount
Fig. 3. Magnetization vs. applied field for deposits 1 at (a) 298, (b)
20 and (c) 5 K.
thus reducing the amount of inorganic phase in the
hybrid materials.
Room temperature magnetic measurements showed
that dependence of magnetization vs. magnetic field
for deposits 1 is nearly linear (Fig. 3a). However, at
low temperatures, the isothermal magnetization as a
function of applied field is essentially nonlinear as
shown in Fig. 3b. For deposits 2, nonlinear depend-
Fig. 4. Magnetization vs. applied field for deposits 2 at (a) 298, (b)
20 and (c) 5 K.
I. Zhitomirsky et al. / Materials Letters 57 (2003) 1045–1050
of iron oxide in deposits 2 compared to deposits 1.
Magnetization curves recorded in the range 20 –298 K
showed zero remanence and zero coercivity. These
data are consistent with superparamagnetic behavior of
the nanoparticles. As expected, the saturation magnetization of hybrid films was found to be lower compared to that of bulk magnetite and maghemite.
However, the magnetization of hybrid films was comparable to the magnetization of bulk composite materials prepared by other methods [7,9,13]. Magnetic
hysteresis loops were observed at 5 K in prepared
deposits as shown in Figs. 3c and 4c. Similar hysteresis
loops were reported for other hybrid materials below
the blocking temperature [7,9].
Zero remanence and zero coercivity are observed
in the superparamagnetic state for very small particles
because thermal fluctuations can prevent the existence
of a stable magnetization. Below the blocking temperature, magnetic particles become magnetically frozen
[31], and as a result, remanence and coercivity appear
on the plot of magnetization as a function of applied
field.
Low field magnetization measurements in ZFC and
FC modes are important for the characterization of
superparamagnetic materials [9,28,31]. Results of the
ZFC and FC magnetization measurements are shown
in Fig. 5. The ZFC magnetization measurements show
a peak at Tmax=25 K indicative of a characteristic
blocking temperature for superparamagnetic particles.
It is important to note that the Tmax for superpara-
Fig. 5. Temperature dependence of the magnetization at for zerofield- (ZFC) and field-cooled (FC) deposits 2.
1049
magnetic material depends on the strength of the
magnetic field and particle size distribution [9,32].
Above the blocking temperature, all the nanoparticles are at the superparamagnetic state. As a result, at
temperatures higher than Tmax, the ZFC and FC curves
are superimposed. Similar behavior was observed in
other materials [28,31,33]. A separation of the ZFC
and FC curves was observed at lower temperatures.
This observation is consistent with the behavior of
ultrafine magnetic particles below the blocking temperature [9].
Obtained experimental data indicate that superparamagnetic films based on iron oxide and PDDA could
be produced by electrodeposition. However, more
comprehensive investigations of magnetic properties
coupled with results of electron microscopy, Mössbauer spectroscopy and other methods are necessary for
characterization of the hybrid films. We cannot exclude the possibility that some weight loss in our TG
experiments could also be related to the liberation of
adsorbed water. Moreover, as mentioned in our previous papers, some hybrid materials cannot be considered as a simple mixture of organic and inorganic
phases. It is in this regard that in our method the
hybrid material is formed as a result of the interaction and heterocoagulation of polymer molecules
and oxide particles formed at the electrode surface
[23,26]. Work in progress deals with characterization
of the composition and properties of the prepared
films.
One of the important possibilities provided by
electrodeposition is the ability of agglomerate-free
processing of nanostructured materials. It is important
to note that this method has important advantages
compared to other techniques, which enable synthesis
of oxide particles in situ in a polymer matrix. Electrodeposition not only produces hybrid materials but also
provides film deposition. In this method, the electrogenerated base is used instead of alkali, thus reducing
risk of film contamination. The composition, microstructure and morphology of the films could be
tailored by variation of bath composition and mass
transport conditions for organic and inorganic components. There is no need to reiterate advantages of
electrodeposition for formation of uniform films on
substrates of complex shape and selected areas of the
substrates [15,17]. Experimental results of this work
open new opportunities in the formation of hybrid thin
1050
I. Zhitomirsky et al. / Materials Letters 57 (2003) 1045–1050
film materials with valuable magnetic properties. Our
preliminary results indicate that other polyelectrolytes
could also be used for electrodeposition of such films.
4. Conclusions
We have demonstrated a new method of fabrication
of superparamagnetic films. This method has the
advantage of permitting nanostructured iron oxides
to be synthesized in situ in a polymer matrix on an
electrode to form hybrid organic– inorganic films. The
amount of the deposited material, film composition
and properties could be varied with variation of
deposition time and polymer concentration in the
solutions. The method opens new opportunities in
the development of hybrid nanostructured magnetic
materials.
References
[1] J.H. Fendler, Chem. Mater. 13 (2001) 3196.
[2] T. Ito, Y. Okayama, S. Shiratori, Thin Solid Films 393 (2001)
138.
[3] D.B. Mitzi, Chem. Mater. 13 (2001) 3283.
[4] F. Caruso, Adv. Mater. 13 (2001) 11.
[5] P.G. Lacroix, Chem. Mater. 13 (2001) 3495.
[6] F. Leroux, J.-P. Besse, Chem. Mater. 13 (2001) 3507.
[7] R.F. Ziolo, E.P. Giannelis, B.A. Weinstein, M.P. O’Horo, B.N.
Ganguly, V. Mehrotra, M.W. Russell, D.R. Huffman, Science
257 (1992) 219.
[8] M. Kryszewski, J.K. Jeszka, Synth. Met. 94 (1998) 99.
[9] B.H. Sohn, R.E. Cohen, G.C. Papaefthymiou, J. Magn. Magn.
Mater. 182 (1998) 216.
[10] M. Wan, W. Zhou, J. Li, Synth. Met. 78 (1996) 27.
[11] T. Yogo, T. Nakamura, K. Kikuta, W. Sakamoto, S. Hirano, J.
Mater. Res. 11 (1996) 475.
[12] J.L. Dormann, F. D’Orazio, F. Lucari, E. Tronc, P. Prené, J.P.
Jolivet, D. Fiorani, R. Cherkaoui, M. Noguès, Phys. Rev. B 53
(1996) 14291.
[13] T. Yogo, T. Nakamura, W. Sakamoto, S. Hirano, J. Mater. Res.
14 (1999) 2855.
[14] D.Yu. Godovsky, A.V. Varfolomeev, G.D. Efremova, V.M.
Cherepanov, G.A. Kapustin, A.V. Volkov, M.A. Moskvina,
Adv. Mater. Opt. Electron. 9 (1999) 87.
[15] I. Zhitomirsky, L. Gal-Or, Electrochemical coatings, in: N.B.
Dahotre, T.S. Sudarshan (Eds.), Intermetallic and Ceramic
Coatings, Marcel Dekker, New York, 1999, pp. 83 – 145, Chapter 3.
[16] G.H.A. Therese, P.V. Kamath, Chem. Mater. 12 (2000) 1195.
[17] I. Zhitomirsky, Bull. Am. Ceram. Soc. 79 (2000) 57.
[18] I. Zhitomirsky, L. Gal-Or, J. Mater. Sci. 33 (1998) 699.
[19] Y. Zhou, R.J. Phillips, J.A. Switzer, J. Am. Ceram. Soc. 78
(1995) 981.
[20] I. Zhitomirsky, Nanostruct. Mater. 8 (1997) 521.
[21] R. Chaim, Nanostruct. Mater. 1 (1992) 479.
[22] I. Zhitomirsky, A. Petric, Mater. Lett. 42 (2000) 273.
[23] I. Zhitomirsky, A. Petric, Mater. Lett. 46 (2000) 1.
[24] I. Zhitomirsky, A. Petric, Mater. Sci. Eng., B 78 (2000) 125.
[25] I. Zhitomirsky, A. Petric, Ceram. Int. 27 (2001) 149.
[26] I. Zhitomirsky, A. Petric, Bull. Am. Ceram. Soc. 80 (2001) 41.
[27] I. Zhitomirsky, A. Petric, JOM, Miner., Met. Mater. Soc. J. 53
(2001) 48.
[28] D.K. Kim, Y. Zhang, W. Voit, K.V. Rao, M. Muhammed, J.
Magn. Magn. Mater. 225 (2001) 30.
[29] R.M. Cornell, U. Schwertmann, The Iron Oxides, VCH, Weinheim, 1996.
[30] A.J. Koch, J.J. Becker, J. Appl. Phys. 39 (1968) 1261.
[31] B.H. Sohn, R.E. Cohen, Chem. Mater. 9 (1997) 264.
[32] R.W. Chantrell, M. El-Hilo, K. O’Grady, IEEE Trans. Magn.
27 (1991) 3570.
[33] J. Mira, J.A. López-Pérez, J. Rivas, M.A. López-Quintela, R.
Caciuffo, D. Rinaldi, D. Fiorani, IEEE Trans. Magn. 33 (1997)
3724.