Synthesis and research of electrochemical behavior of magnetic nanocomposites based on Fe3O4

Article abstract of DOI:10.1007/s11172-013-0338-0

The nanocomposites including magnetite nanoparticles, polymer coating and electrochemically active molecules were synthesized and investigated: poly(vinylbenzyl) chloride coating modified by quinoline; coating based on polypyrrole, silica coating modified

Full text of DOI:10.1007/s11172-013-0338-0

Russian Chemical Bulletin, International Edition, Vol. 62, No. 11, pp. 2327—2336, November, 2013
2327
Synthesis and research of electrochemical behavior
of magnetic nanocomposites based on Fe O *
3
4
a,b
N. N. Malysheva, E. V. Verbitsky, I. A. Utepova, Yu. A. Glazyrina,a
a,b
c
a,c
A. N. Kozitsina,
T. S. Mitrofanova, G. L. Rusinov, A. I. Matern,a,b O. N. Chupakhin,
а
a,c
a,b,c
and Kh. Z. Brainina
a,d
aUral Federal University named after the First President of Russia B. N. Eltsyn,
1
9 ul. Mira, 620000 Ekaterinburg, Russian Federation.
Fax: (343) 375 4467. Eꢀmail: a.n.kozitsina@ustu.ru
b
Ural Center of Biopharmaceutical Technologies,
2
8/1 ul. Kirova, 620089 Ekaterinburg, Russian Federation
c
I. Ya. Postovsky Institute of Organic Synthesis Ural Branch of the Russian Academy of Sciences,
2
0 ul. S. Kovalevskoi, 620041 Ekaterinburg, Russian Federation.
Fax: (343) 369 3058. Eꢀmail: rusinov@ios.uran.ru
d
The Ural State University of Economics,
6
2 ul. 8 Marta, 620144 Ekaterinburg, Russian Federation.
Fax: (343) 257 2415. Eꢀmail: baz@usue.ru
The nanocomposites including magnetite nanoparticles, polymer coating and electroꢀ
chemically active molecules were synthesized and investigated: poly(vinylbenzyl) chloride
coating modified by quinoline; coating based on polypyrrole, silica coating modified by ferꢀ
rocene derivative. All samples were investigated by the cyclic voltammetry method.
Key words: magnetite, nanocomposite particles, electrochemically active nanocomposites,
nanoparticles coating, voltammetry.
The sustained interest in nanomaterials is due to the
fact that objects in the 1 to 100 nm size range essentially
differ in physicochemical characteristics from microꢀ
metric size particles, and, as a consequence, nanocomꢀ
posites (NC) created on their basis demonstrate unique
properties.
ticularly, silver nanoparticles on the polymethyl methꢀ
acrylate–polyethyleneimine particles.
1
1
The nanocomposite particles combining the magnetic
core properties and the polymer coating functional charꢀ
1
2—16
acteristics, are of particular interest.
The synthesis
and study of morphology and electrochemical properties
of composite nanoparticles based on Fe O with polyꢀ
The nanocomposites, including those with the elecꢀ
troactive coating, have found wide application in medical
diagnostics and cancer treatment, drug delivery in the huꢀ
man organism, radio electronics, creating various inputꢀ
3
4
1
7
18
styrene and poly(vinylbenzyl chloride) coating, comꢀ
posites based on Y O with polypyrrole coating, and magꢀ
netic nanoparticles coated with the fluorescent labels,
were described.
19
2
3
2
0
1—4
output devices, conducting coatings and various sensors,
electrochemistry.5
The use of polymer nanocomposites based on the Fe O
3
4
The organicꢀinorganic nanocomposite hybrid materiꢀ
als that represent the composite particles with the "coreꢀ
shell" structure are described. A core and shell of the partiꢀ
magnetic nanoparticles as "signal forming labels" seems
rather promising in the developing of immunosensors for
the quick diagnosis of different diseases. The application
of nanocomposites will make it possible to significantly
accelerate the diagnosis of various diseases, in particular
6
cles can be as follows: metal–metal (Pt—Pd) ; metal oxꢀ
7
ide–metal (Fe O —Co) ; metal–polymer (gold—polystyꢀ
3
4
8
9
21,22
rene) ; metal sulfides and tellurides (CdTe—CdS ); polyꢀ
mer–polymer (fluorene derivative copolymer—amorphous
silicon oxide ). The "coreꢀshell"ꢀparticles with the nanoꢀ
"at the bedside".
The aim of the present work is the synthesis and study
of electrochemical properties of the electroactive nanoꢀ
composites based on Fe O nanoparticles with different
1
0
particles immobilized on their surface were obtained, parꢀ
3
4
types of coating, which can further serve as labels in
electrochemical immunoassay for detecting the infecꢀ
tious agent.
*
Dedicated to Academician of the Russian Academy of Sciences
M. P. Egorov on the occasion of his 60th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2327—2336, Novemer, 2013.
066ꢀ5285/13/6211ꢀ2327 © 2013 Springer Science+Business Media, Inc.
1

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013
Kozitsina et al.
Results and Discussion
Scheme 2
1
. Synthesis of nanoparticles and nanocomposites
1
.1. Preparation of magnetite nanoparticles by the coꢀ
precipitation method. The Fe O nanoparticles were obꢀ
3
4
2
3
tained by the coprecipitation method according to the
equation:
Fe2+ + 2 Fe3+ + 8 ОН–
Fe O + 4 Н О.
(1)
3
4
2
The phase composition of synthesized nanoparticles
was verified by electron microscopy method using elecꢀ
tron diffraction. The Fe O structure was confirmed with
3
4
the use of standard crystallographic data. The particle size
distribution maximum corresponds to 10 nm with the narꢀ
row spread of values around this maximum.
1
.2. Preparation of nanocomposites with polymer coatꢀ
ing based on poly(vinylbenzyl chloride) modified by quinoꢀ
line. Nanocomposites with polymer coating based on the
poly(vinylbenzyl chloride) modified by quinoline were obꢀ
tained according to Schemes 1 and 2.
Scheme 1
Scheme 3
Scheme 4
1
.3. Preparation of nanocomposites with electroactive
polymer coating based on polypyrrole. The polymer nanoꢀ
composites (samples 3—9) containing polypyrrole as an
electroactive polymer coating were synthesized by the in
situ polymerization according to Scheme 3.
Reagents and conditions: i. NH , EtOH.
4

Electroactive nanocomposites based on Fe O
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013 2329
3
4
Scheme 5
2. Electronꢀmicroscopic investigations
2
.1. Nanocomposites with polymer coating based on
the poly(vinylbenzyl chloride) modified by quinoline. Nanoꢀ
composites 1 and 2 represent spherical formations with
optically darker magnetite core (the crystalline structure
of the lattice was confirmed by powder Xꢀray diffraction
(
PXRD)). The light halo is a polymer coating, which does
not give the characteristic pattern of the crystall lattice
upon magnification.
The sample 1 nanocomposite particles with the size of
2
0—40 nm are unevenly coated, the coating is present as
separate inclusions from 5 to 20 mn thickness. Apparently
the amount of monomer used for the synthesis of this
sample was insufficient for uniform coating of the nanoꢀ
particles.
The electron micrographs and the particle size distriꢀ
bution of sample 2 are presented in Figure 1. The Figure
shows that the optically lighter areas around the dark cenꢀ
ters of sample 2 are arranged more uniformly than those of
sample 1. The coating thickness is about 7—10 nm. The
particle size distribution maximum accounts for 20 nm
with a narrow spread in the values around this maximum
(see Fig. 1, b).
Reagents and conditions: i. C O Cl /CH Cl , 0 C. ii. (OEt) Siꢀ
2
2
2
2
2
3
(
CH ) NH , DMF, NEt /CH Cl , 0 C.
2 3 2 3 2 2
1
.4. Preparation of nanocomposites with silica coating
modified by ferrocene. Nanocomposites with silica coatꢀ
ing modified by ferrocene were obtained according to
Schemes 4—6.
Thus, the 1 : 10 ratio of components appears to be sufꢀ
ficient to provide the uniform coating of the nanoparticles.
Scheme 6

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013
a
Kozitsina et al.
b
%
3
0
5
0
5
0
5
2
2
1
1
1
00 nm
1
0
15 20 25 30 35 40 45 d/nm
Fig. 1. Micrograph (a) and size distribution (b) of nanocomposite particles based on Fe O coated with poly(vinylbenzyl chloride)
3
4
modified by quinoline (sample 2, Jeol JEMꢀ1400 transmission electron microscope (Japan)).
2
.2. Nanocomposites with an electroactive polymer coatꢀ
due to the deficiency of the monomer during the synꢀ
thesis.
ing based on polypyrrole. The Fe O —polypyrrole nanoꢀ
3
4
composites 3–9 of all compositions also represent spheriꢀ
cal formations with optically darker magnetite core (the
crystall structure of the lattice was confirmed by PXRD).
The light halo, which testifies about the polymer coating
and does not give the characteristic pattern of the crystall
lattice upon magnification, is not observed for samples 3
and 9. Probably it is connected with the deficiency of
monomer used for sample 3 synthesis and with the high
dilution of the reaction mixture in the case of the synthesis
of sample 9. Though the polymer coating of 20—30 nm
thickness is present in samples 6 and 7, the nanocomposꢀ
ite particles are aggregated into large agglomerates with an
average size of 400 nm.
The sample 8 micrograph, from which one can see
that the sample particles of the 150—180 nm size have the
uniform coating and low aggregation degree, is presented in
Figure 2, a. Sample 8 is composed of spherical composites,
each consisting of several electronꢀdense magnetite nanoꢀ
particles and semitransparent polypyrrole shell, which has low
electron density. The average coating thickness is 60—80 nm.
The nanocomposite 8 size distribution maximum fulls
on 180 nm with the narrow spread of values around this
maximum (see Fig. 2, b).
Thus, on the basis of the electron microscopy results,
sample 8 with the 1 : 1 ratio of components was chosen for
the further study.
The uneven polymer coating as separate inclusions
is observed in samples 4 and 5. Apparently, it is also
2.3. Nanocomposites with silica coating modified by
ferrocene. Nanocomposites with silica coating are spheriꢀ
a
%
b
3
3
2
2
1
1
5
0
5
0
5
0
5
5
00 nm
1
40
160
180
200
220
240 d/nm
Fig. 2. Micrograph (a) and size distribution (b) of Fe O —polypyrrole composite nanoparticles obtained by polymerization in situ
3
4
(
sample 8, Jeol JEMꢀ1400 transmission electron microscope (Japan)).

Electroactive nanocomposites based on Fe O
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013 2331
3
4
a
b
%
3
2
2
1
1
0
5
0
5
0
5
1
00 nm
1
0
20
30
40
50 d/nm
Fig. 3. Micrograph (a) and size distribution (b) of nanocomposite particles based on Fe O with silica coating modified by ferrocene
3
4
(
sample 10, Jeol JEMꢀ1400 transmission electron microscope (Japan)).
cal formations with the 15—25 nm size with optically darkꢀ
er magnetite core (the crystall structure of the lattice was
confirmed by PXRD). The light halo is the polymer coatꢀ
ing, which does not give the characteristic pattern on the
micrograph upon magnification. The coating thickness is
Scheme 7
5
nm. The electron micrographs of sample 10 are shown
in Fig. 3, a.
The composite nanoparticles 10 distribution maximum
is at 20 nm with the narrow spread of values around this
maximum (see Fig. 3, b).
3
. Electrochemical investigations
Electrochemical investigations were carried out using
a thickꢀfilm graphite working electrode (TGE), which
showed a good advantage in earlier studies of nanoꢀ
particles.2 A graphite epoxide composition used in elecꢀ
trode manufacturing exhibits good adsorption properties
towards the nanocomposite; it is resistant to solvents emꢀ
ployed as supporting electrolytes in the electrochemical
investigations.
4
the quantity of electricity, spent for the quinolinic group
reduction, versus the 1ꢀ(paraꢀvinylbenzyl)quinolinium
–
3
–3
–3
chloride concentration: 2.47•10 , 5.3•10 , 8.87•10
,
–
2
–2
–1
1
.77•10 , 2.47•10 mol L :
3
.1. Nanocomposites with polymer coating based on
Q = 2.5•10–3 C + 0.0001
poly(vinylbenzyl chloride) modified by quinoline
standard deviation Sr = 16.2%; number of measurements
n = 5; confidence interval p = 0.95).
3
.1.1. Electrochemical 1ꢀ(paraꢀvinylbenzyl)quinolinium
chloride. The cyclic voltammogram (CV) of 1ꢀ(paraꢀ
vinylbenzyl)quinolinium chloride solution in acetonitrile
recordered using TGE is shown in Fig. 4, a. The Figure
shows that a clearꢀcut electrochemical signal at 1.4 V poꢀ
tential is present on the cathode curve. The reduction proꢀ
cess of the quinolinic group corresponding to the obtained
signal is given in Scheme 7.
The maximum current value at potential of –1.4 V
served as the analytical signal of quinolinic group reducꢀ
tion (see Fig. 4, а). The calibration plot was obtained for
3.1.2. Electrochemical behavior of nanocomposites with
polymer coating based on poly(vinylbenzyl chloride) modiꢀ
fied by quinoline. Figure 4, b shows CV recordered using
TGE, whose working surface was precoated by a suspenꢀ
sion of the synthesized nanoparticles with polymer coatꢀ
ing based on poly(vinylbenzyl chloride) modified by quinꢀ
oline. On the cathode curve, as in the case of 1ꢀ(paraꢀ
vinylbenzyl)quinolinium chloride, one can easily see the
pronounced electrochemical signal at potential of –1.15 V.
The comparison of CV cathode peaks of 1ꢀ(paraꢀvinylꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013
Kozitsina et al.
benzyl)quinolinium chloride and nanocomposite applied
on the electrode surface allows one to make a conclusion
that the processes are determined by the quinolinic group
reduction process.
I/A
00
a
2
1
00
0
1
2
The maximum current value at potential of –1.15 V
served as the analytical signal of quinolinic group reducꢀ
tion on the nanocomposite surface. The calibration plot
was obtained for the quantity of electricity, spent for the
quinolinic group reduction on the nanocomposite surface
versus its concentration in the initial suspension: 2, 4, 10,
–
100
–200
–
–
300
400
4, 30 g L–1
–500
1
:
Q = 3•10–7 C – 5•10–8
–1.5
–1.0
–0.5
0
0.5
U/V
(
Sr = 15.6%, n = 5, p = 0.95).
I/A
b
1
1
5
During the cyclic scan of electrode potential the maxꢀ
0
5
0
imum current value of quinolinic group reduction abruptꢀ
ly decreases to the background value, which testifies
to fast removal of electroreduction products from the
working electrode surface or to irreversible reduction of
the compound.
–5
–
10
15
20
1
2
3
.2. Nanocomposites with an electroactive polymer
coating based on polypyrrole
–
–
3
.2.1. Electrochemical behavior of polypyrrole. The CV
–
1.0
–0.5
0
0.5
U/V
recorded using TGE with the working surface precoated
by a polypyrrole powder suspension, is presented in Fig. 5, а.
The Figure shows that the electrochemical signal
at potential of 0 V is present in the anode curve, and
those at potentials of –0.4 and 0.35 V – are in the cathode
curve.
Fig. 4. (a) (1) CV of LiClO in MeCN (0.1 M solution); (2) CV of
4
1
ꢀ(paraꢀvinylbenzyl)quinolinium chloride in MeCN solution
–
3
–1
(
concentration 8.84•10 mol L ) recorded using TGE. Scan
–1
rate 100 mV s . (b) (1) — CV of KNO (0.1 M solution); (2) CV
3
of Fe O —1ꢀ(paraꢀvinylbenzyl)quinolinium chloride nanocomꢀ
3
4
posite applied on TGE (initial concentration of nanocomposite
The polypyrrole redꢀox process is well studied25—27 and
in general terms are presented in Scheme 8.
suspension 30 g L ). Scan rate 100 mV s
–1
–1
.
Q = 2.5•10–3 C + 0.0001
Scheme 8
(
Sr = 9.6%, n = 5, p = 0.95).
3.2.2. Electrochemical behavior of nanocomposites. Figꢀ
ure 5, b shows CV recorded using TGE whose working
surface was precoated by a suspension of the synthesized
nanoparticles with polymer coating based on polypyrrole.
In the anode and cathode curves, as in the case of polypyrrole
applied on the TGE working surface, a clearꢀcut electroꢀ
chemical signals are seen at potentials of –0.15, –0.5, and
0
.4 V. The comparison of anode peaks in the CV of polyꢀ
pyrrole and nanocomposite with polypyrrole shell applied
on TGE surface allows one to make a conclusion that the
processes occuring in case of nanocomposite correspond
to the polypyrrole redꢀox process.
The maximum current value at potential of –0.15 V
served as the analytical signal of nanocomposite polypyrꢀ
role shell oxidation process. The calibration plot was obꢀ
tained for the quantity of electricity spent for the nanoꢀ
The maximum current value at potential of 0 V served
as the analytical signal of polypyrrole oxidation. The caliꢀ
bration plot was obtained for the quantity of electricity
spent for the polypyrrole oxidation on the nanocomposite
surface versus its concentration in the initial modifying
–
1
suspension: 0.25, 0.75, 1.5, 3, 7 g L
:

Electroactive nanocomposites based on Fe O
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013 2333
3
4
I/A
a
tials of 0.45 and 0.75 V are present in the cathode and
anode curves, respectively.
600
500
400
200
100
0
2
The ferrocene group redꢀox process corresponding to
2
8
the obtained signals was studied earlier and in general
terms was presented in Scheme 9.
1
Scheme 9
–
–
–
–
100
200
300
400
–
0.75 –0.50–0.25
0
0.25 0.50 0.75
U/V
I/A
b
The maximum current value at potential of 0.75 V served
as the analytical signal of ferrocene group oxidation (see
Fig. 6, а). The calibration plot was obtained for the quanꢀ
tity of electricity spent for the ferrocene group oxidaꢀ
4
3
2
1
00
00
00
00
0
2
1
I/A
00
a
1
2
1
8
6
4
2
0
–
100
0
0
0
0
–
0.75 –0.5 –0.25
0
0.25 0.5 0.75 U/V
Fig. 5. (a) (1) CV of KNO (0.1 M solution); (2) CV of polypyrꢀ
3
role applied on TGE (initial concentration of nanocomposite
–20
–40
–60
suspension 1.5 g L–1). Scan rate 100 mV s . (b) (1) CV of KNO3
–1
(
0.1 М solution); (2) CV of Fe O — polypyrrole nanocomposite
3 4
applied on TGE (initial concentration of nanocomposite susꢀ
pension 0.75 g L–1). Scan rate 100 mV s
–1
.
–
0.2
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 U/V
I/A
b
composite polypyrrole shell oxidation, versus its concenꢀ
0
0
0
0
0
.7
.6
.5
.4
.3
–
1
tration in the initial suspension: 0.25; 0.75; 1.5; 3; 6 g L
:
Q = 3•10–7 C – 5•10–8
2
1
(
Sr = 10.2%, n = 5, p = 0.95).
During the cyclic scan of electrode potential the curꢀ
rent of polypyrrole oxidation practically does not change,
which indicates that the electrooxidation products are not
removed from the electrode surface.
0.2
0
.1
0
3
.3. Nanocomposites with silica coating modified
by ferrocene
0
.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 U/V
Fig. 6. (a) (1) CV of LiClO in MeCN (0.1 M solution); (2) CV of
4
[
(
3ꢀ(ferrocenoylamide)propyl]triethoxysilane in MeCN solution
3
.3.1. Electrochemical behavior of [3ꢀ(ferrocenoylꢀ
–
4
–1
concentration 7.25•10 mol L ), recorded using TGE. Scan
amide)propyl]triethoxysilane. The CV of [3ꢀ(ferrocenoylꢀ
amide)propyl]triethoxysilane chloride in acetonitrile reꢀ
corded using TGE is presented in Fig. 6, а. The Figure
shows that the clearꢀcut electrochemical signals at potenꢀ
–1
rate 100 mV s . (b) (1) CV of KNO (0.1 M aqueous solution);
(
(initial concentration of nanocomposite suspension 10 g L ).
Scan rate 100 mV s–
3
2) CV of Fe O — ferrocene modified silica applied on TGE
3 4
–
1
1
.

2334
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013
Kozitsina et al.
tion versus the [3ꢀ(ferrocenoylamino)propyl]triethoxyꢀ
obtain clearꢀcut reproducible analytical signal; 3) provide
higher sensitivity of measurements as indicated by the
smaller regression equation slope of the quantity of elecꢀ
tricity dependence on the content of nanocomposite parꢀ
ticles in the initial suspension.
–
4
–4
–4
silane concentration: 1.84•10 ; 3.66•10 ; 5.46•10
7
;
.25•10– ; 2.3•10 mol L ):
4
–3
–1
Q = 0.0219 C + 3•10–7
The combination of characteristics (magnetic properꢀ
ties, size, electroactivity, stability) of obtained nanocomꢀ
posite particles will allow one to employ them in the future
as a "signal forming label" in the electrochemical immuꢀ
noassay method.
(
Sr = 10%, n = 5, p = 0.95).
3
.3.2. Electrochemical behavior of nanocomposites with
silica coating modified by ferrocene. Figure 6, b shows CV
recorded using TGE, whose working surface was precoatꢀ
ed by a suspension of the synthesized nanoparticles with
silica coating modified by ferrocene.
Experimental
In the anode curve, as in the case of [3ꢀ(ferrocenylꢀ
amide)propyl]triethoxysilane, one can easily see the proꢀ
nounced electrochemical response at potential of 0.55 V.
The comparison of anode peaks in the CV of [3ꢀ(ferroꢀ
cenylamide)propyl]triethoxysilane and nanocomposite
applied on the electrode surface allows one to make
a conclusion that the processes occuring in the case of
using nanocomposite correspond to the ferrocene group
oxidation process.
Reagents. Iron(III) chloride hexahydrate (FeCl •6H O),
3
2
iron(II) chloride tetrahydrate (FeCl •4H O), oleic acid, paraꢀ
2
2
vinylbenzyl chloride, styrene, 1,4ꢀdivinylbenzene, quinoline,
pyrrole, sodium persulfate, sodium thiosulfate, sodium dodecyl
sulfate, tetraethoxysilane, aminopropyltriethoxysilane were comꢀ
mercial chemicals (SigmaꢀAldrich); analytical grade 25% aqueꢀ
ous ammonia solution (NH4OH) (Sigma TEK), 95% ethanol
manufacturer LLC "Gippokrat"), special purity grade acetoniꢀ
trile and analytical grade toluene were also used. The deionized
water was obtained on a combined membrane unit of DVSꢀM/
(
The maximum current value at potential of 0.55 V served
as the analytical signal of ferrocene group oxidation on the
NC surface. The calibration plot was obtained for the
quantity of electricity spent for the ferrocene group oxidaꢀ
tion versus its concentration in the initial modifying susꢀ
1
NA(18)ꢀN MedianaꢀFilter series, Moscow.
All aqueous solutions were prepared using deionized water.
Equipment. The IKA Eurostar digital 2482000 overhead stirꢀ
rer was used for stirring the nanoparticles and nanocomposite
suspensions containing the magnetic core and for the preparaꢀ
tion of nanocomposites by emulsion polymerization; an IKA
СꢀMAG HS7 magnetic stirrer with an ETSꢀD5 thermometer
was used for stirring and heating liquids and emulsions; an Ultraꢀ
sonic processor 500 W ultrasonic homogenizer with microꢀ
processor control (Sigma—Aldrich) was used for obtaining emulꢀ
sions and suspensions.
The electrochemical investigations were carried out using
an IVAꢀ5 inversion voltammetry analyzer (IVA, Ekaterinburg) and
an Autolab type III potentiostat/galvanostat (The Netherlands).
A thickꢀfilm graphite electrode was used as a working elecꢀ
trode. The Ag/AgCl saturated electrode and glassy carbon rod
served as a reference and auxiliary electrodes, respectively.
The procedure of working electrode preparation. The preparaꢀ
tion of test sample suspension was carried out as follows: 0.005 g
of the sample was dispersed in 5 mL of dispersion medium, then
the suspension was treated with ultrasound during 2 min.
The modification of working electrodes performed by applyꢀ
ing 10 L of a test sample suspension on the electrode working
area followed by drying in air up to the total evaporation of
disperse medium.
–
1
pension: 1; 2; 4.5; 6; 10 g L
.
Q = 2•10–8 C – 2•10–8
(
Sr = 8.3%, n = 5, p = 0.95).
During the cyclic scan of electrode potential the
current of ferrocene group oxidation at first sharply drops
then gradually decreases to the background value, which
testifies to the removal of oxidation product from the nearꢀ
electrode layer.
Thus, the approaches to synthesis and modification of
nanocomposites were used whose combination allows one
to obtain the magnetic electroactive nanocomposite parꢀ
ticles with a uniform polymer coating without using the
tough conditions, corrosive environments and sophistiꢀ
cated apparatus. The application of the covalent grafting
of the modifying compound ("signal forming label") gives
stable coating on the surface of magnetite nanoparticles
and provides their electroactivity.
The procedures for synthesis of the nanocomposite parꢀ
ticles based on Fe O with different polymer coatings
Microscopic studies were carried out with a Quantaꢀ200 scanꢀ
ning electron microscope (FEI Company, USA) and Jeol
JEMꢀ1400 (Japan), FEI MORGAGNI 286(D) (FEI Company,
USA) transmission electron microscopes.
The nanoparticle samples for the investigations were preꢀ
pared by the adsorption method on the copper grid formvar subꢀ
strate which was placed on a test suspension drop of 20 L volume
and kept for 30 s. The suspension excess was removed with the
filter paper from the edge of grid after separation from the drop.
Microscopic and microdiffraction studies were carried out on
the same surface site of the sample.
3
4
(
polypyrrole; poly(vinylbenzyl chloride) modified by quinꢀ
oline; silica modified by ferrocene) were developed.
The analytical electrochemical signals were detected
for all obtained nanocomposites.
The results of the study showed that the nanocomposꢀ
ites modified by ferrocene: 1) have much smaller size
(
20—30 nm) and more uniform coating in comparison
with the other nanocomposites; 2) make it possible to

Electroactive nanocomposites based on Fe O
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013 2335
3
4
Synthesis of magnetite nanocomposites by coprecipitation
Nanocomposites of different sizes were obtained by varying
(
general procedure). Nanoparticles of Fe O were obtained by
the mass ratio of (Fe O )—pyrrole nanoparticle: 2 : 1 (sample 3),
3 : 2 (sample 4), 1 : 1 (sample 5), 4 : 5 (sample 6).
3
4
3
4
2
3
coprecipitation method by adding dropwise a 25% NH OH
4
solution to an aqueous solution containing 4.5 wt% FeCl and
After that the volume of dispersive medium was measured
(the amount of water in which the reaction proceeds) for the
selected 1 : 1 ratio of (Fe O )—pyrrole nanoparticle. The folꢀ
3
2
.25 wt% FeCl . The reactants were used in stoichiometric raꢀ
2
tios (except ammonia which was taken in small excess) accordꢀ
ing to equation (1).
3
4
lowing mass ratios were used: Fe O —water nanoparticle 1 : 125
3
4
Synthesis of nanocomposites with polymer coating based on
poly(vinylbenzyl chloride) modified by quinoline (general proceꢀ
dure). Before carrying out the polymerisation reaction the magꢀ
netite particle surface were hydrophobized. Oleic acid (3 mL)
(sample 7), 1 : 250 (sample 8), and 1 : 500 (sample 9).
The presence of polymer coating on nanoparticles was conꢀ
firmed by IR spectroscopy data. All nanocomposite spectra had
–
1
similar characteristic bands, typical IR spectrum, /cm : 3389,
was added to a suspension of Fe O4 nanoparticles (0.5 g) in
1574 (=NH), 1309—1218 (—C=C—), 571 (Fe O ).
3
3
4
2
00 mL of deionized water, mixed with the help of overhead
Synthesis of nanocomposites with silica coating modified by
ferrocene (general procedure). The magnetite nanoparticles
(0.5 g) were dispersed in 80 mL of 95% ethanol, then 0.5 mL of
stirrer up to decoloration of the water phase (nanoparticles miꢀ
grate to the oleic acid drops). Then the oleic acid excess was
consecutively washed off with water and ethanol with the magꢀ
netic separation of nanoparticles.
The magnetite nanoparticles modified by oleic acid were
dispersed in the mixture of 1.3 mL of paraꢀvinylbenzyl chloride,
tetraethoxysilane and 1 mL of 25% NH OH solution were added
4
(see Scheme 4). The mixture was refluxed with stirring for 10 h.
The unreacted tetraethoxysilane was removed by washing three
times with ethanol, then with toluene. The nanocomposite was
separated by magnetic separation.
0
.13 mL of 1,4ꢀdivinylbenzene, and 0.2 mL of cyclohexane (lipoꢀ
philic phase), and then mixed with the water phase (0.1 g of
sodium dodecyl sulfate emulsifier solution in 50 mL of water)
under ultrasonic irradiation (see Scheme 1). The radical polyꢀ
merization was futher initiated by adding the redox system conꢀ
taining 0.015 g of Na S O and 0.0238 g of Na S O . The proꢀ
[3ꢀ(Ferrocenylamide)propyl]triethoxysilane was obtained by
2
9
the well known method based on amidation of ferrocenecarbꢀ
oxylic acid chloride with various amines (see Scheme 5). The
oxalyl chloride (1.5 mmol) solution containing DMF (0.2 mmol)
in 5 mL of dried CH Cl was added dropwise to a intensively
2
2
3
2
2
8
2
2
cess was carried out with stirring during 12 h at 80 C. The samꢀ
ple was dried on a watch crystal at room temperature, the comꢀ
pletion of drying was performed under vacuum over P O .
For the creation of electroactive label on the nanoparticles
surface coated with poly(vinylbenzyl chloride), 1 mL of quinoꢀ
line was added to 0.1 g of nanocomposite particles in 3 mL of
acetonitrile followed by refluxing (see Scheme 2). The reagent
excess was removed by washing with acetonitrile, then the sample
was dried.
stirred ferrocenecarboxylic acid suspension (1 mmol) in 10 mL
of dried CH Cl in argon atmosphere at 0 C. The reaction mixꢀ
2
2
ture was stirred for 20 min at 0 C, and the solution became
brightred. Next the solvent was evaporated to dryness under deꢀ
creased pressure. The obtained ferrocenyl chloride was dissolved
2
5
in 25 mL of dried CH Cl2 and added dropwise to a mixture
2
of aminopropyltriethoxysilane (1.3 mmol) and triethylamine
(2 mmol) in 10 mL of dried CH Cl at 0 C. The suspension was
2
2
stirred for 20 min at 0 C, then for 2 h at room temperature, after
Nanocomposites of different sizes were obtained by varying
the mass ratio of (Fe O )—monomer (paraꢀvinylbenzyl chloride)
that it was concentrated in a vacuum. The obtained residue was
subjected to column chromatography on SiO . The solvent was
3
4
2
nanoparticle: 1 : 10 (sample 1) and 3 : 10 (sample 2).
The water to lipophilic phase ratio was 3 : 100.
evaporated to dryness under decreased pressure to give yellow
crystals. Yield 0.26 g (60%), m.p. 81 C. Eluent: hexane—ethyl
The presence of polymer coating on nanoparticles was conꢀ
firmed by IR spectroscopy data. All spectra of obtained nanoꢀ
composites have similar characteristic bands, typical IR specꢀ
acetate (2 : 8) (R 0.3). The product was identified as [3ꢀ(ferroꢀ
f
1
13
cenylamide)propyl]triethoxysilane on the basis of H, C NMR
spectra and elemental analysis data. All obtained data coincide
–
1
30
trum, /cm : 2920.1 (Csp3—H), 1444.2 (—C=Cꢀbenzene ring
with the earlier published.
bonds), 1130.2 (—C—O—), 554.7 (Fe O ), (—C—Cl).
Grafting of ferrocene derivative was performed in anhydrous
toluene. [3ꢀ(Ferrocenoylamino)propyl]triethoxysilane (0.03 g)
was added to 0.1 g of a suspension of nanoparticles coated
with silicon oxide in toluene. The reaction was carried out at
the toluene boiling point and with stirring during 12 h (see
Scheme 6).
The obtained sample 10 was purified by washing with toluꢀ
ene three times followed by the magnetic separation of nanoꢀ
composite. The sample was dried at 70 C.
3
4
Synthesis of nanocomposites with electroactive polymer coatꢀ
ing based on polypyrrole (general procedure). Pyrrole (0.1 mL)
and a solution of iron(III) chloride (1.2 g) of hexahydrate in 5 mL
of water were added to a suspension containing 0.1 g of magneꢀ
tite nanoparticles in 50 mL of water under ultrasonic (US) irraꢀ
diation (see Scheme 3). The reaction was carried out under ulꢀ
trasonic irradiation.
For the purification of composite nanoparticles from the
pyrrole monomer remaining after polymerization and other comꢀ
ponents of reaction mixture, the nanocomposite was precipitatꢀ
ed using magnetic separation, the supernatant fluid was decantꢀ
ed, the nanocomposite was washed 5 times with water and then
The presence of silica coating on Fe O was confirmed by
3
4
–
1
the IR spectroscopy data. IR spectrum, /cm : region
3365 (Si—OH), region 1565 (=NH), 1062 (Si—O—C), region
578 sm– (Fe O ), 1157, 1180 (Fc—Alc).
1
3
4
3
times with ethanol. The precipitate was separated by magnetic
separation.
The sample was dried on a watch crystal at room temperaꢀ
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Received May 23, 2013;
in revised form October 15, 2013