The aim of this work was the preparation of biocompatible micro- and nanoparticles with a hollow in-terrior. The particles must be able to encapsulate and store a chemical payload for a certain time, followed by the release on demand of this payload. In our previous work [13] we have prepared silica microparticles with a hollow core and found that the diffusion across the mesoporous silica shell was strongly dependent on temperature. In this work, we used this dependence and attached iron oxide nanoparticles on the sur-face of the silica shell to create composite iron oxide/silica particles. The iron oxide nanoparticles were able to heat up in the presence of an alternating magnetic field. This property allowed us to use magnetic field as a tool for remote control of diffusion across the particle shell. To avoid spontaneous leakage of encapsu-lated payload in time, we have modified the surface of the composite micropaticles with a layer of palm oil. Palm oil is a phase change material which is solid under 37 °C. We showed that the resultant composite particles are able to store a payload for several months and release a defined quantity on demand by the application of a magnetic field. The particles were characterised in shape, size, heating ability and their mass transport properties.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3557

Kovacik, P.

Soltys, M.

Stepanek, F.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 3, 03NCNN37(3pp) (2013) 
 
 
2304-1862/2013/2(3)03NCNN37(3) 03NCNN37-1  2013 Sumy State University 
Core-shell Structured Composite Silica Micro- and Nanoparticles with Ability Release a De-
fined Quantity „on Demand“ 
 
P. Kovačík*, M. Šoltys, F.Štěpánek 
 
ICT Prague, Laboratory of chemical robotics, Technická 5, 166 28 Prague 
 
(Received 15 February 2013; revised manuscript received 14 April 2013; published online 25 July 2013) 
 
The aim of this work was the preparation of biocompatible micro- and nanoparticles with a hollow in-
terrior. The particles must be able to encapsulate and store a chemical payload for a certain time, followed 
by the release on demand of this payload. In our previous work [13] we have prepared silica microparticles 
with a hollow core and found that the diffusion across the mesoporous silica shell was strongly dependent 
on temperature. In this work, we used this dependence and attached iron oxide nanoparticles on the sur-
face of the silica shell to create composite iron oxide/silica particles. The iron oxide nanoparticles were able 
to heat up in the presence of an alternating magnetic field. This property allowed us to use magnetic field 
as a tool for remote control of diffusion across the particle shell. To avoid spontaneous leakage of encapsu-
lated payload in time, we have modified the surface of the composite micropaticles with a layer of palm oil. 
Palm oil is a phase change material which is solid under 37 °C. We showed that the resultant composite 
particles are able to store a payload for several months and release a defined quantity on demand by the 
application of a magnetic field. The particles were characterised in shape, size, heating ability and their 
mass transport properties.  
 
Keywords: Silica, Radiofrequency field, Controlled release, Encapsulation. 
 
 PACS numbers: 87.50.st, 47.63.mh 
                                               
* kovacikp@vscht.cz 
 
 
1. INTRODUCTION 
 
In recent years there has been an increasing inter-
est in iron oxide/silica composites. Due to their special 
properties such as large surface area and low material 
density these microparticles are very attractive as cata-
lysts [1], microwave absorption materials [2] or in drug 
delivery systems [3]. Major methods for the preparation 
of iron oxide/silica composite microparticles are: sol-gel 
process [4]; layer-by-layer techniques [5]; coprecipita-
tion [6] and surface reaction [7]. 
Coating applied to the surface of materials can im-
prove its properties as it allows control of the interac-
tion of a material with its environment [8]. Nowadays, 
the application range of coatings extends much beyond 
the simple decoration and protection aspects, and func-
tional coatings have become an enabling technology in 
a vast variety of different high-tech areas. Fields in 
which such high-tech coatings are applied range from 
computer chips and hard disk manufacturing [8] to the 
use of special coatings in biomedical and aviation appli-
cations [9]. 
In this work, we introduce a fabrication method of 
hollow composite iron oxide/silica particles. The size, 
morphology and stability of the composite particles was 
systematically investigated and the effect of iron ox-
ide:silica ratio on their heating rate and the release 
kinetics of a model compound (vitamin B12) was de-
termined. 
 
2. EXPERIMENTAL 
 
2.1 Materials 
 
Tetraethyl orthosilicate (TEOS, 98%), n-octylamine 
(99%), oleic acid (65-88%), acetone (99%), ammonium 
hydroxide solution (25%), iron(III) chloride hexahy-
drate, iron(II) chloride tetrahydrate, n-heptane and 
palm oil were purchased from Sigma-Aldrich. Nitric 
acid (p.a., 65%) and ethanol were purchased from 
Fluka. All chemicals were used as received. Deionized 
water (Aqual 25, 0.07 μS/cm) was used for all reactions 
and treatment processes. 
 
2.2 Synthesis of iron oxide nanoparticles 
 
The iron oxide nanoparticles used for this work 
were prepared by the co-precipitation method [10] and 
stabilized with oleic acid to make them dispersible in 
non-aqueous media. In a typical synthesis, 0.25 g of 
FeCl3.6H2O and 0.125 g of FeCl2.4H2O were dissolved 
in 40 ml of deionised water in a three-neck flask 
equipped with a reflux condenser and heated to 80°C. 
Then 0.2 ml of oleic acid dissolved in 5 ml of acetone 
were added. Iron oxide precipitation was induced by 
adding 5 ml of NH4OH; the mixture was stirred at 500 
rpm for the next 10 min, followed by five additions of 
0.2 ml of oleic acid at 5 minute intervals. The mixture 
was stirred for another 30 min and then cooled down to 
ambient temperature. Dry iron oxide nanoparticles 
dispersible in non-aqueous media were obtained by 
freeze-drying. 
 
2.3 Synthesis of composite iron oxide/silica mi-
croparticles 
 
The fabrication of the composite iron oxide/silica 
microparticles was made in two steps: i) formation of 
hollow-core mesoporous silica microparticles by a liquid 
templating method [11, 12], followed by ii) coating of 
the external silica surface by iron oxide nanoparticles 
 P. KOVACIK, M. SOLTYS, F. STEPANEK PROC. NAP 2, 03NCNN37 (2013) 
 
 
03NCNN37-2 
prepared as described in Section 2.2. The overall syn-
thesis procedure is shown schematically in Fig. 1. In a 
typical synthesis, 10 ml of TEOS (silica precursor) was 
added into 10 ml of octylamine and the mixture was 
stirred at 800 rpm for 3 min at room temperature to 
create a dispersion of octylamine droplets in TEOS. 
This was followed by a quick addition of water (100 ml) 
acidified by 0.2 ml of nitric acid to promote the hydroly-
sis and polycondensation of TEOS around the octyla-
mine droplets. The molar ratio of TEOS:OA:H2O:HNO3 
was 1:1.36:113:0.05. After 3 min of reaction, the result-
ant microparticles were collected by centrifugation (5 
min, 6000 rpm), washed with acetone and dried in air. 
Finally, the particles were calcined at 600 °C for 9 h in 
air to fully remove the organic template. 
 
 
 
Fig. 1 – The scheme of preparation of composite iron oxide/silica particles 
 
2.4 Particle characterisation 
 
Scanning Electron Microscopy (SEM) images were 
taken on a Jeol JCM-5700 scanning electron micro-
scope. The samples were sputter-coated with a 5 nm 
thin film of gold prior to imaging. Some particles were 
mechanically broken by using a mortar with a pestle in 
order to reveal their core-shell structure. The particle 
size distribution was evaluated by the laser diffraction 
particle size analyzer (Horiba Partica LA 950/V2). The 
temperature rise with time of prepared composite mi-
croparticles was measured by a 400 kHz, 2.5 kW gen-
erator of external alternating magnetic field (Power-
Cube 32/400). The permeability of the composite iron 
oxide/silica shell was characterized indirectly by meas-
uring the uptake/release kinetics using UV/VIS spec-
trophotometry (Specord 205 BU). 
 
3. RESULTS 
 
3.1 Size and morphology of prepared particles 
 
The silica particles as well as the resultant compo-
site iron oxide/silica microparticles had a spherical 
shape (Fig. 2) with a relatively narrow size distribution 
(Fig. 4). The mean particle diameter was 26 m for 
microparticles and 250 nm for nanoparticles. Five dif-
ferent composite particle samples with increasing iron 
oxide/silica ratio were prepared and further character-
ized (Table 1). 
 
Table 1 – Sample codes and corresponding iron oxide/silica 
particle ratios used for the preparation of the composite mi-
croparticles. 
 
Sample 
Used mass ratio 
silica vs. iron oxide 
1 1:0.0 
2 1:0.1 
3 1:0.2 
4 1:0.4 
5 1:0.8 
 
 
 
Fig. 2 – Composite silica microparticles, they core/shell structure and the detail from TEM microscopy on the surface of the com-
posite shell. 
 CORE-SHELL STRUCTURED COMPOSITE SILICA MICRO- AND… PROC. NAP 2, 03NCNN37 (2013) 
 
 
03NCNN37-3 
 
 
Fig. 3 – First two images are pure silica nanoparticles and the last one is composite iron oxide/silica nanoparticles. 
 
3.2 Radiofrequency induced release 
 
The composite particles loaded with the model 
compound (vitamin B12) can be stored in the dry state 
for several months without a loss of functionality. 
Once rehydrated, a step change in the release rate 
can be induced by the application of the RF magnetic 
field, which causes local heating of the micrcoparti-
cles. Figure 4 shows the time-dependence of the quan-
tity released in the case of seven cycles consisting of 5 
min of RF field ON, followed by 20 min of RF field 
OFF. While essentially no release was observed dur-
ing the “cold” periods, a step change in the released 
quantity was achieved in each of the “hot” periods. 
The relative amount released during each step was 
gradually lower as the concentration difference be-
tween the particle core and the surrounding bulk 
decreases. The amount released in each step also 
depends on the composition of the particles, i.e. on the 
iron oxide:silica ratio, which determines the tempera-
ture achieved when the RF field is on. The higher the 
ratio and therefore the heating rate, the higher the 
amount released after a given number of steps. Thus, 
the quantity released can be controlled relatively 
accurately both by the initial particle composition and 
by the RF trigger sequence. 
 
 
 
Fig. 4 – Radiofrequency induced release form composite iron 
oxide/silica microparticles. 
 
AKNOWLEDGEMENTS 
 
Financial support from the European Research 
Council (Grant No. 200580-Chobotix) and from a grant 
for Specific University Research (MSMT 21/2013) is 
gratefully acknowledged. This research has also re-
ceived funding from the European Union Seventh 
Framework Programme (FP7/2007-2013) under grant 
agreement 318671 (MICREAgents). 
 
 
REFERENCES 
 
1. Sadasivan S., Sukhorukov G.B., J. Colloid Interface Sci. 
304, 437 (2006). 
2. Fuertes A.B., Valdés-Solís T., Sevilla M., J. Phys. Chem. C 
112, 3648 (2008). 
3. Zhou J., Wu W., Caruntu D., Yu M.H., Martin A., Chen 
J.F., O’Connor C.J., Zhou W.L, J. Phys. Chem. C 111, 
17473 (2007). 
4. Chen I., Wang C., Chen C.Y., Scr. Mater. 58, 37 (2008). 
5. Caruso F., Spasova M., Susha A., Chem. Mater. 13, 109 
(2001). 
6. Wu W., Caruntua D., Martin A., Yu M.H., Connor C.J.O., 
Zhou W.L., Chen J.F., J. Magn. Magn. Mater. 311, 578 
(2007). 
7. Lin C.R., Wang C.C., Chen I.H., J. Appl. Phys. 99, 08N707 
(2006). 
8. Advincula R.C., Brittain W.J., Kaster K.C., Rühe J., Poly-
mer brushes (Wiley-VCH, Weinheim”, 2004). 
9. Zhulina E.B., Singh C., Balasz A.C, Macromolecules, 26, 
6338 (1996).  
10. Maity D., Agrawal D.C., J. Magn. Magn. Mater. 308, 46 (2007). 
11. Kovačík P, Kremláčková Z, Štěpánek F. Microporous and 
Mesoporous Materials., 159, 119 (2012). 
12. Cheng X, Liu S, Lu L, Sui X, Meynen V, Cool P, et al. 
Microporous and Mesoporous Materials., 98, 41 (2007). 
13. Kovačík P., Kremláčková Z., Štěpánek F., Micropor. Meso-
por. Mater. 159, 119 (2012). 
 


English

Core-shell Structured Composite Silica Micro- and Nanoparticles with Ability Release a De fined Quantity „on Demand“

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 3, 03NCNN37(3pp) (2013)   2304-1862/2013/2(3)03NCNN37(3) 03NCNN37-1  2013 Sumy State University Core-shell Structured Composite Silica Micro- and Nanoparticles with Ability Release a De-fined Quantity „on Demand“  P. Kovačík*, M. Šoltys, F.Štěpánek  ICT Prague, Laboratory of chemical robotics, Technická 5, 166 28 Prague  (Received 15 February 2013; revised manuscript received 14 April 2013; published online 25 July 2013)  The aim of this work was the preparation of biocompatible micro- and nanoparticles with a hollow in-terrior. The particles must be able to encapsulate and store a chemical payload for a certain time, followed by the release on demand of this payload. In our previous work [13] we have prepared silica microparticles with a hollow core and found that the diffusion across the mesoporous silica shell was strongly dependent on temperature. In this work, we used this dependence and attached iron oxide nanoparticles on the sur-face of the silica shell to create composite iron oxide/silica particles. The iron oxide nanoparticles were able to heat up in the presence of an alternating magnetic field. This property allowed us to use magnetic field as a tool for remote control of diffusion across the particle shell. To avoid spontaneous leakage of encapsu-lated payload in time, we have modified the surface of the composite micropaticles with a layer of palm oil. Palm oil is a phase change material which is solid under 37 °C. We showed that the resultant composite particles are able to store a payload for several months and release a defined quantity on demand by the application of a magnetic field. The particles were characterised in shape, size, heating ability and their mass transport properties.   Keywords: Silica, Radiofrequency field, Controlled release, Encapsulation.   PACS numbers: 87.50.st, 47.63.mh                                                * kovacikp@vscht.cz   1. INTRODUCTION  In recent years there has been an increasing inter-est in iron oxide/silica composites. Due to their special properties such as large surface area and low material density these microparticles are very attractive as cata-lysts [1], microwave absorption materials [2] or in drug delivery systems [3]. Major methods for the preparation of iron oxide/silica composite microparticles are: sol-gel process [4]; layer-by-layer techniques [5]; coprecipita-tion [6] and surface reaction [7]. Coating applied to the surface of materials can im-prove its properties as it allows control of the interac-tion of a material with its environment [8]. Nowadays, the application range of coatings extends much beyond the simple decoration and protection aspects, and func-tional coatings have become an enabling technology in a vast variety of different high-tech areas. Fields in which such high-tech coatings are applied range from computer chips and hard disk manufacturing [8] to the use of special coatings in biomedical and aviation appli-cations [9]. In this work, we introduce a fabrication method of hollow composite iron oxide/silica particles. The size, morphology and stability of the composite particles was systematically investigated and the effect of iron ox-ide:silica ratio on their heating rate and the release kinetics of a model compound (vitamin B12) was de-termined.  2. EXPERIMENTAL  2.1 Materials  Tetraethyl orthosilicate (TEOS, 98%), n-octylamine (99%), oleic acid (65-88%), acetone (99%), ammonium hydroxide solution (25%), iron(III) chloride hexahy-drate, iron(II) chloride tetrahydrate, n-heptane and palm oil were purchased from Sigma-Aldrich. Nitric acid (p.a., 65%) and ethanol were purchased from Fluka. All chemicals were used as received. Deionized water (Aqual 25, 0.07 μS/cm) was used for all reactions and treatment processes.  2.2 Synthesis of iron oxide nanoparticles  The iron oxide nanoparticles used for this work were prepared by the co-precipitation method [10] and stabilized with oleic acid to make them dispersible in non-aqueous media. In a typical synthesis, 0.25 g of FeCl3.6H2O and 0.125 g of FeCl2.4H2O were dissolved in 40 ml of deionised water in a three-neck flask equipped with a reflux condenser and heated to 80°C. Then 0.2 ml of oleic acid dissolved in 5 ml of acetone were added. Iron oxide precipitation was induced by adding 5 ml of NH4OH; the mixture was stirred at 500 rpm for the next 10 min, followed by five additions of 0.2 ml of oleic acid at 5 minute intervals. The mixture was stirred for another 30 min and then cooled down to ambient temperature. Dry iron oxide nanoparticles dispersible in non-aqueous media were obtained by freeze-drying.  2.3 Synthesis of composite iron oxide/silica mi-croparticles  The fabrication of the composite iron oxide/silica microparticles was made in two steps: i) formation of hollow-core mesoporous silica microparticles by a liquid templating method [11, 12], followed by ii) coating of the external silica surface by iron oxide nanoparticles  P. KOVACIK, M. SOLTYS, F. STEPANEK PROC. NAP 2, 03NCNN37 (2013)   03NCNN37-2 prepared as described in Section 2.2. The overall syn-thesis procedure is shown schematically in Fig. 1. In a typical synthesis, 10 ml of TEOS (silica precursor) was added into 10 ml of octylamine and the mixture was stirred at 800 rpm for 3 min at room temperature to create a dispersion of octylamine droplets in TEOS. This was followed by a quick addition of water (100 ml) acidified by 0.2 ml of nitric acid to promote the hydroly-sis and polycondensation of TEOS around the octyla-mine droplets. The molar ratio of TEOS:OA:H2O:HNO3 was 1:1.36:113:0.05. After 3 min of reaction, the result-ant microparticles were collected by centrifugation (5 min, 6000 rpm), washed with acetone and dried in air. Finally, the particles were calcined at 600 °C for 9 h in air to fully remove the organic template.    Fig. 1 – The scheme of preparation of composite iron oxide/silica particles  2.4 Particle characterisation  Scanning Electron Microscopy (SEM) images were taken on a Jeol JCM-5700 scanning electron micro-scope. The samples were sputter-coated with a 5 nm thin film of gold prior to imaging. Some particles were mechanically broken by using a mortar with a pestle in order to reveal their core-shell structure. The particle size distribution was evaluated by the laser diffraction particle size analyzer (Horiba Partica LA 950/V2). The temperature rise with time of prepared composite mi-croparticles was measured by a 400 kHz, 2.5 kW gen-erator of external alternating magnetic field (Power-Cube 32/400). The permeability of the composite iron oxide/silica shell was characterized indirectly by meas-uring the uptake/release kinetics using UV/VIS spec-trophotometry (Specord 205 BU).  3. RESULTS  3.1 Size and morphology of prepared particles  The silica particles as well as the resultant compo-site iron oxide/silica microparticles had a spherical shape (Fig. 2) with a relatively narrow size distribution (Fig. 4). The mean particle diameter was 26 m for microparticles and 250 nm for nanoparticles. Five dif-ferent composite particle samples with increasing iron oxide/silica ratio were prepared and further character-ized (Table 1).  Table 1 – Sample codes and corresponding iron oxide/silica particle ratios used for the preparation of the composite mi-croparticles.  Sample Used mass ratio silica vs. iron oxide 1 1:0.0 2 1:0.1 3 1:0.2 4 1:0.4 5 1:0.8    Fig. 2 – Composite silica microparticles, they core/shell structure and the detail from TEM microscopy on the surface of the com-posite shell.  CORE-SHELL STRUCTURED COMPOSITE SILICA MICRO- AND… PROC. NAP 2, 03NCNN37 (2013)   03NCNN37-3   Fig. 3 – First two images are pure silica nanoparticles and the last one is composite iron oxide/silica nanoparticles.  3.2 Radiofrequency induced release  The composite particles loaded with the model compound (vitamin B12) can be stored in the dry state for several months without a loss of functionality. Once rehydrated, a step change in the release rate can be induced by the application of the RF magnetic field, which causes local heating of the micrcoparti-cles. Figure 4 shows the time-dependence of the quan-tity released in the case of seven cycles consisting of 5 min of RF field ON, followed by 20 min of RF field OFF. While essentially no release was observed dur-ing the “cold” periods, a step change in the released quantity was achieved in each of the “hot” periods. The relative amount released during each step was gradually lower as the concentration difference be-tween the particle core and the surrounding bulk decreases. The amount released in each step also depends on the composition of the particles, i.e. on the iron oxide:silica ratio, which determines the tempera-ture achieved when the RF field is on. The higher the ratio and therefore the heating rate, the higher the amount released after a given number of steps. Thus, the quantity released can be controlled relatively accurately both by the initial particle composition and by the RF trigger sequence.    Fig. 4 – Radiofrequency induced release form composite iron oxide/silica microparticles.  AKNOWLEDGEMENTS  Financial support from the European Research Council (Grant No. 200580-Chobotix) and from a grant for Specific University Research (MSMT 21/2013) is gratefully acknowledged. This research has also re-ceived funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement 318671 (MICREAgents).   REFERENCES  1. Sadasivan S., Sukhorukov G.B., J. Colloid Interface Sci. 304, 437 (2006). 2. Fuertes A.B., Valdés-Solís T., Sevilla M., J. Phys. Chem. C 112, 3648 (2008). 3. Zhou J., Wu W., Caruntu D., Yu M.H., Martin A., Chen J.F., O’Connor C.J., Zhou W.L, J. Phys. Chem. C 111, 17473 (2007). 4. Chen I., Wang C., Chen C.Y., Scr. Mater. 58, 37 (2008). 5. Caruso F., Spasova M., Susha A., Chem. Mater. 13, 109 (2001). 6. Wu W., Caruntua D., Martin A., Yu M.H., Connor C.J.O., Zhou W.L., Chen J.F., J. Magn. Magn. Mater. 311, 578 (2007). 7. Lin C.R., Wang C.C., Chen I.H., J. Appl. Phys. 99, 08N707 (2006). 8. Advincula R.C., Brittain W.J., Kaster K.C., Rühe J., Poly-mer brushes (Wiley-VCH, Weinheim”, 2004). 9. Zhulina E.B., Singh C., Balasz A.C, Macromolecules, 26, 6338 (1996).  10. Maity D., Agrawal D.C., J. Magn. Magn. Mater. 308, 46 (2007). 11. Kovačík P, Kremláčková Z, Štěpánek F. Microporous and Mesoporous Materials., 159, 119 (2012). 12. Cheng X, Liu S, Lu L, Sui X, Meynen V, Cool P, et al. Microporous and Mesoporous Materials., 98, 41 (2007). 13. Kovačík P., Kremláčková Z., Štěpánek F., Micropor. Meso-por. Mater. 159, 119 (2012).  

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Core-shell Structured Composite Silica Micro- and Nanoparticles with Ability Release a De fined Quantity „on Demand“

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