Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds
Oxidized with solution of hydrogen peroxide multiwalled carbon nanotubes (MWCNTs) were modified with 2-hydroxyethylmethacrylate (HEMA) or chitosan (CTS). Morphology and surface properties of the pristine and modified MWCNTs have been investigated. The zeta-potential behaviour of MWCNTs was studied a...
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Інститут хімії поверхні ім. О.О. Чуйка НАН України
2010
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| Cite this: | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds / Y. Bolbukh, G. Gunko, G. Prikhod’ko, V. Tertykh, K. László, A. Tóth, B. Koczka // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 4. — С. 389-400. — Бібліогр.: 36 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859742676342013952 |
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| author | Bolbukh, Y. Gunko, G. Prikhod’ko, G. Tertykh, V. László, K. Tóth, A. Koczka, B. |
| author_facet | Bolbukh, Y. Gunko, G. Prikhod’ko, G. Tertykh, V. László, K. Tóth, A. Koczka, B. |
| citation_txt | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds / Y. Bolbukh, G. Gunko, G. Prikhod’ko, V. Tertykh, K. László, A. Tóth, B. Koczka // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 4. — С. 389-400. — Бібліогр.: 36 назв. — англ. |
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| container_title | Хімія, фізика та технологія поверхні |
| description | Oxidized with solution of hydrogen peroxide multiwalled carbon nanotubes (MWCNTs) were modified with 2-hydroxyethylmethacrylate (HEMA) or chitosan (CTS). Morphology and surface properties of the pristine and modified MWCNTs have been investigated. The zeta-potential behaviour of MWCNTs was studied as a function of pH and suspension concentration. After oxidation, the divided nanotubes are found to have uncapped ports decorated with hydroxyl groups mostly. Surface oxygencontaining groups specify the negative zeta-potential in all pH range studied (pH=3-11). The values of zeta-potential display an inverse dependence on the dispersion concentration in acidic and basic solutions. After modification of oxidized MWCNTs with HEMA their isoelectric point is shifted from pH=2 to pH=10. Repeated surface treatment with HEMA (MWCNTs-HEMA-HEMA), along with change of the nature of terminal groups, provides stable surface charge increasing with nanotubes concentration in the pH range of 3-9. The isoelectric point of MWCNTs modified with CTS occurs at pH=4.5. At relatively small zeta-potential values, which become more negative with a decrease in the nanotubes concentration, such suspensions are the most stable.
Досліджено фізико-хімічні властивості, морфологію та характер поверхні вихідних і модифікованих 2-гідроксіетилметакрилатом (HEMA) і хітозаном багатошарових вуглецевих нанотрубок (БШВНТ). Вимірювання дзета-потенціалу БШВНТ проводили при різних рН розчину електроліту і концентраціях суспензії. Показано, що при окисненні БШВНТ відбувається їхнє дроблення з утворенням портів, що обрамлені переважно гідроксильними групами. Кисеньвмісні групи визначають негативний дзета-потенціал окиснених нанотрубок в досліджуваному діапазоні рН (3-11), але залежність дзета-потенціалу від концентрації дисперсії у кислому і основному середовищах обернена. Після модифікування БШВНТ НЕМА ізоелектрична точка зміщується з рН=2 до рН=10. Подовження ланцюжка прикріпленого до нанотрубок модифікатора (БШВНТ-HЕМА-HЕМА) разом із зміною кінцевих функціональних груп забезпечує позитивний і стабільний заряд поверхні, що збільшується симбатно концентрації нанотрубок в діапазоні рН 3-9. Ізоелектрична точка БШВНТ-хітозан близька до рН=4,5. За відносно невеликих значень дзета-потенціалу, який стає більш негативним зі зменшенням концентрації нанотрубок, такі суспензії є найбільш стійкими.
Исследованы физико-химические свойства, морфология и характер поверхности исходных и модифицированных 2-гидроксиэтилметакрилатом (НЕМА) и хитозаном многослойных углеродных нанотрубок (МУНТ). Измерение дзета-потенциала МУНТ проводили при разных рН раствора электролита и концентрациях суспензии. Показано, что при окислении МУНТ происходит их дробление, а образующиеся порты обрамлены преимущественно гидроксильными группами. Кислородсодержащие группы определяют отрицательный дзета-потенциал окисленных нанотрубок в исследуемом диапазоне рН (3-11), но зависимость дзета-потенциала от концентрации дисперсии в кислой и основной средах обратная. После модифицирования МУНТ НЕМА изоэлектрическая точка смещается от рН=2 к рН=10. Удлинение цепочки прикрепленного к нанотрубкам модификатора (МУНТ-НЕМА-НЕМА) вместе с изменением концевых функциональных групп обеспечивает положительный и стабильный заряд поверхности, который увеличивается симбатно концентрации нанотрубок в диапазоне рН 3-9. Изоэлектрическая точка МУНТ-хитозан близка к рН=4,5. При относительно небольшом значении дзета-потенциала, который становится более отрицательным с уменьшением концентрации нанотрубок, такие суспензии являются наиболее устойчивыми.
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Хімія, фізика та технологія поверхні. 2010. Т. 1. № 4. С. 389–400
_____________________________________________________________________________________________
* Corresponding author yukulik@yandex.ru
ХФТП 2010. Т. 1. № 4 389
UDC 544.723:544.77
MULTIWALLED CARBON NANOTUBES
MODIFIED WITH BIOCOMPATIBLE COMPOUNDS
Y. Bolbukh1*, G. Gunko1, G. Prikhod’ko1, V. Tertykh1, K. László2, A. Tóth2, B. Koczka3
1Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine
17 General Naumov Street, Kyiv 03164, Ukraine
2Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics
6-8 Budafoki Street, Budapest 1111, Hungary
3Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics
4 Gellért tér, Budapest 1111, Hungary
Oxidized with solution of hydrogen peroxide multiwalled carbon nanotubes (MWCNTs) were
modified with 2-hydroxyethylmethacrylate (HEMA) or chitosan (CTS). Morphology and surface prop-
erties of the pristine and modified MWCNTs have been investigated. The zeta-potential behaviour of
MWCNTs was studied as a function of pH and suspension concentration. After oxidation, the divided
nanotubes are found to have uncapped ports decorated with hydroxyl groups mostly. Surface oxygen-
containing groups specify the negative zeta-potential in all pH range studied (pH=3-11). The values
of zeta-potential display an inverse dependence on the dispersion concentration in acidic and basic
solutions. After modification of oxidized MWCNTs with HEMA their isoelectric point is shifted from
pH=2 to pH=10. Repeated surface treatment with HEMA (MWCNTs-HEMA-HEMA), along with
change of the nature of terminal groups, provides stable surface charge increasing with nanotubes
concentration in the pH range of 3-9. The isoelectric point of MWCNTs modified with CTS occurs at
pH=4.5. At relatively small zeta-potential values, which become more negative with a decrease in the
nanotubes concentration, such suspensions are the most stable.
INTRODUCTION
Due to the numerous potential applications
carbon nanotubes (CNTs) have attracted re-
searchers’ interest. Considerable attention has
focused on chemical modification of nanotubes
because it opens new possibilities in fabrication
of new polymeric materials with improved char-
acteristics, in particular for biomedical applica-
tions (sensors, drug delivery systems etc.). Use of
such materials demands the strict functionality of
the components and their biocompatibility [1, 2].
Possessing unique mechanical, electrical, op-
tical properties, carbon nanotubes are severely
limited in processability because they practically
insoluble and infusible, chemically inert, have
poor dispersion capacity in liquid media, as well
as weak interfacial interaction [3]. Grafting the
necessary functional groups to the nanotubes sur-
face allows one to obtain the best dispersion abil-
ity, better stability of suspensions and can regu-
late interaction with the dispersion medium. Es-
pecially it is very important for the polymeric
composites in biomedical applications.
The functionalization of surface with bio-
polymers promises to be one of the most success-
ful methods to improve the CNTs hydrophilicity.
Some biocompatible polymers (or monomers), in
particular chitosan (CTS) or 2-hydroxyethyl-
methacrylate (HEMA), can introduce into surface
layer groups which are capable to form covalent,
ionic and donor-acceptor bonds with bioactive
molecules. Formation of modifying layer on the
nanotubes surface can be realized in several
routes. In the work [4] the nanotubes functionali-
zation was carried out by adsorption coating with
chitosan and following crosslinking of the modi-
fying layer with glutaraldehyde. Such modifica-
tion imparted biphilic properties to the MWCNTs
surface. Obtained modifying layer was stable and
did not affect the original structure of the nano-
tubes. Another way of noncovalent modification
consists in precipitation of chitosan from acidic
solution at pH increasing [5]. At this modification
methodology the determining factor is a deacety-
lation degree of chitosan.
Covalent attachment of modifiers is com-
monly realised through chemically active anchor
Y. Bolbukh, G. Gunko, G. Prikhod’ko et al.
_____________________________________________________________________________________________
390 ХФТП 2010. Т. 1. № 4
groups generated on the nanotubes surface and
ports [6]. Such approach was used for MWCNTs
modification with chitosan in [7]. Covalent bond-
ing was achieved by interaction of chitosan with
acyl chloride (-COCl) groups obtained on surface
during suspending of oxidized MWCNTs in solu-
tion of thionyl chloride. The same approach was
applied in [8] to polyHEMA grafting to walls of
MWCNTs. But it is possible to achieve modifier
covalent attachment by direct interaction of the
polymer (monomer) with the functional groups of
oxidized nanotubes in the presence of a catalyst
[9]. This approach reduces the number of stages
of nanotubes modification.
Because of a recent increase in interest in
preparation and application of aqueous disper-
sions of carbon nanotubes, investigations of
MWCNTs surface charge behaviour at different
pH and suspension concentration were intensi-
fied. As known, the particles are stabilized in the
liquid media by electrostatic repulsion [6] as de-
pendent on zeta potential value which is deter-
mined by a variety of factors including dispersion
concentration. The influence of the solid phase
concentration on the zeta potential remains am-
biguous. Thus, for polystyrene latex, a zeta poten-
tial does not depend on the content of particles in
dispersion [10]. But a tendency to disperse phase
coagulation makes the concentration one of the
defining parameters in the formation of double
electrical layer (DEL). Therefore, for the stable
dispersion obtaining, it is important to know not
only the surface characteristics of modified nano-
tubes but also dependence of a zeta potential
value on the suspension concentration.
In this work we have studied the oxidized
MWCNTs modified with 2-hydroxyethylmeth-
acrylate and chitosan which were obtained via
interaction of the modifying reagents directly
with the oxygen-containing groups on the
MWCNTs surface. The samples obtained were
investigated by scanning electron microscopy
(SEM), energy dispersive X-ray analysis (EDX),
FTIR spectroscopy and low temperature N2 ad-
sorption/desorption. The zeta-potential behaviour
of MWCNTs was studied in KCl solution as a
function of pH and suspension concentration.
EXPERIMENTAL
Materials. MWCNTs were synthesized by
pyrolysis of propylene on ferric catalyst and puri-
fied by mixture of HCl and HF for removing the
residual catalyst and amorphous carbon with the
following washing from acids by water [11].
2-hydroxyethylmethacrylate (HEMA), 2,2'-azo-
isobutyronitrile (AIBN), glutaraldehyde (GA)
were purchased from Fluka. Laboratory prepara-
tion of chitosan was obtained from shrimp shells.
All other chemicals were of analytical grade and
used without additional processing.
MWCNTs functionalization
Oxidation. Purified MWCNTs were dis-
persed in water, and then hydrogen peroxide was
added to suspension. Mixture was heated at 80°C
under stirring for 47 h. The concentration of H2O2
was 30%. The obtained oxidized nanotubes were
filtered under vacuum and dried at 150°C [12].
Modification with HEMA. Oxidized
MWCNTs (0.2 g) were dispersed in 50 ml tolu-
ene, then 2 ml HEMA was added to suspension
with stirring. This mixture was heated to 80°C
and 0.03 ml H2SO4 was added as a catalyst. Proc-
ess of modification was carried out for 8 h at
80°C under reflux. Then sample was filtrated and
washed several times with ethanol, water and
again ethanol. Sample was dried at 60°C until the
solvent was removed. HEMA-functionalized
MWCNTs represented as MWCNTs-HEMA. In
this case the modifying functional layer contains
methacrylic groups that are able to the following
reaction via radical polymerization process [12].
This opportunity was used at the next stage of modi-
fication. So, the monomer HEMA (2 ml) was added
to toluene dispersion (50 ml) of MWCNTs-HEMA
(0.2 g) in the AIBN presence. Such type repeated
modification results in change of functionality of the
modifying layer. The process was conducted under
the same conditions. This sample is represented as
MWCNTs-HEMA-HEMA.
Modification with chitosan. Oxidized
MWCNTs (0.6 g) were ultrasonicated for 30 min
in the chitosan (0.2 g) solution in acetic acid (2%).
The dispersion was slowly stirring during one hour
for chitosan adsorption on nanotubes. Then the
ammonium solution drop-by-drop was added to
dispersion until pH became 8. After this procedure
the mixture was heated to 60°C and glutaraldehyde
(0.2 g) was added. In this way chitosan adsorbed
on oxidized nanotubes was cross-linked by glu-
taraldehyde. Obtained nanotubes were washed
several times in acid and water in order to remove
unreacted polymer followed by drying at 60°C to
yield the final product. Obtained sample is repre-
sented as MWCNTs-CTS.
Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 391
Characterizations of MWCNTs. The surface
morphological image and elemental composition
of MWCNTs were obtained using scanning elec-
tron microscope (SEM) and energy dispersive
X-ray (EDX) analysis (JEOL JSM-5500LV, Ja-
pan) after gold plating at an accelerating voltage
of 25 kV. Before plating the samples were dis-
persed and maintained on copper grids with dou-
ble-sided adhesive black carbon tape. Quanta-
chrome NOVA® Surface Area Analyzer was used
to determine the MWCNTs structural characteris-
tics by N2 adsorption/desorption at 77 K. Specific
surface area values and a pore size distribution
were obtained by the Barrett, Joyner and Halenda
(BJH) equation using the desorption isotherm.
The surface functional groups of nanotubes
were detected by a Fourier transform infrared
(FTIR) spectrometer (Nicolet NEXUS FTIR) in
the frequency range of 4000–400 cm-1 with the
resolution of 8.0 cm-1, the average number of
scans was 50. Samples were mixed with KBr be-
fore taking measurements.
The zeta-potential values of pure and func-
tionalized carbon nanotubes were determined at
the different concentrations of nanotubes disper-
sion in sodium chloride aqueous solution
(0.01 M) using a Zeta-analyzer (Zetaplus, Brook-
haven, USA). Samples were ultrasonicated
(22 kHz, 90% power and mood sweep) for
30 min before taking measurements. The pH of
the MWCNTs dispersion was adjusted from 3 to
11 by adding 1 M potassium hydroxide or hydro-
chloric acid. Electrophoretic mobility of disper-
sions was measured to determine the zeta-
potential using the Smoluchowski equation.
RESULTS AND DISCUSSION
Morphology study. SEM images of purified
MWCNTs at the different magnifications are
shown in Fig. 1. As is easy to see, after sonication
in toluene MWCNTs adhere to one another in
plate-like particles due to intermolecular interac-
tions. As could be expected, nanotubes in such
particles are ramified and entangled (Fig. 1b),
however, individual nanotubes are also visible.
Treatment of nanotubes with hydrogen per-
oxide is an alternative to the use of mineral acids
for oxidation. The hydrogen peroxide could be-
have as reducing or oxidizing agent with pre-
dominance of the oxidizing properties [13]. The
side benefit of such approach is the absence of
pollutants at an input of the oxidizer solution.
a
b
Fig. 1. SEM images of purified MWCNTs at the dif-
ferent magnifications (×500 – a, ×30000 – b)
Decrease in debundling and break of nano-
tubes were marked after MWCNTs oxidation
(Fig. 2a,b). SEM images of the oxidized
MWCNTs display the long (near 1.5 µm) as well
as shorter (0.5 µm) nanotubes with the average
diameter about 0.1 µm. The absence of big bun-
dles and relatively narrow length distribution al-
lows one to consider the sample as uniform.
Fig. 3 shows the N2 adsorption/desorption iso-
therms (a, b) and the pore size distributions (c)
obtained for purified (a) and oxidized MWCNTs
(b). As will readily be observed, the adsorption
isotherms exhibit a type II shape [14]. The reversi-
ble type II isotherm is typical of the nonporous or
macroporous adsorbent. But observed shoulder at
the very low p/p0 (about 0.01) testifies to the pres-
ence of micropores or pores with diameter near
low bounder of the mesoporous scale. At p/p0 =
0.9
the isotherms display a sharp increment showing
mesoporous nature of the samples. A small closed
adsorption/desorption hysteresis loop is also ob-
served at p/p0 above 0.2. Hysteresis is closest to the
H3 type (according to the IUPAC classification)
which is usually associated with the slit-like pores.
Y. Bolbukh, G. Gunko, G. Prikhod’ko et al.
_____________________________________________________________________________________________
392 ХФТП 2010. Т. 1. № 4
a
b
Fig. 2. SEM images of oxidized MWCNTs at the differ-
ent magnifications (×10000 – a, ×30000 – b)
The nanotubes surface characteristics ob-
tained from N2 adsorption/desorption isotherms
(Fig. 3a, b) indicate the change of the specific
surface area (S) of purified MWCNTs from 150
to 240 m2/g after oxidation. Pore size distribution
curve (Fig. 3c, curve 1) for the purified
MWCNTs has two major peaks at 3.4 and 33 nm
but the latter pores have a low volume. Narrow
pore size distribution testified about the nano-
tubes structure uniformity. Small total pore vol-
ume VΣ (0.55 cm3/g) and relatively high specific
surface area suggest that the mentioned pores are
constitute the inner cavities on the nanotubes ports
[15] which are formed during catalyst removal.
Specific surface area of oxidized nanotubes
had increased insignificantly (about 60%).
Analogous results were found by other authors
[16] for MWCNTs oxidized with acids and were
explained as an effect of interparticle repulsions
of nanotubes resulting in smaller-sized "globs" of
nanotubes. But in our case after oxidation the
nanotubes are splintered (Fig. 2) and the pores
0
100
200
300
400
0 0,2 0,4 0,6 0,8 1
Relative Pressure (p/ps)
V
o
lu
m
e
A
d
so
rb
ed
(
cm
3 /g
)
a
0
400
800
1200
1600
0 0,2 0,4 0,6 0,8 1
Relative Pressure (p/ps)
V
o
lu
m
e
A
d
so
rb
ed
(c
m
3 /g
)
b
0
0,002
0,004
0,006
0,008
0,01
0 50 100 150 200
Pore Radius (Å)
d
V
(r
)
(c
m
3 /Å
/g
)
1
2
c
Fig. 3. The nitrogen adsorption–desorption isotherms
of purified (a) and oxidized (b) MWCNTs and
pore size distribution (c) for purified (1) and
oxidized (2) nanotubes
volume and pores diameter are increased in
nearly 4 times. After oxidation the average pore
diameter is 29.4 nm (Fig. 3c, curve 2) and
VΣ=2.03 cm3/g (BJH). Nitrogen isotherm for oxi-
dized sample (Fig. 3b) indicated the adsorption
hysteresis in the p/p0 range of 0.6 to 0.99. So, the
sample is mainly mesoporous. The increase in
both pore volume and diameter could testify
about caps opening in nanotubes oxidized at the
ends. This assertion is confirmed by XPS data
presented below (Table).
Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 393
Table. Elemental composition of MWCNTs using
XPS data
Content, %
Sample
Е=
284.3 eV
C–C
Е=
285.0 eV
C=C
Е=
286.0–286.5
eV
C–OН,
С–О–С
Е=
90.1–290.4
eV
C=O,
O–C=O
MWCNTs
purified 48.7 3.95 8.04 39.3
MWCNTs
oxidized
38.13 15.39 33.15 13.33
a
b
c
Fig. 4. SEM images of MWCNTs modified with HEMA
(MWCNTs-HEMA) at the different magnifications
(×300 – a, ×10000 - b, ×30000 – c)
SEM images of nanotubes modified with
HEMA display the aggregates with layered struc-
ture (Fig. 4). Perhaps agglomeration of oxidized
nanotubes during modification with the HEMA
was caused by bound monomers or oligomers
interaction which can envelop nanotubes and en-
tangle to one-another. MWCNTs coated with chi-
tosan are shown in Fig. 5.
a
b
c
Fig. 5. SEM images of MWCNTs modified with chitosan
(MWCNTs-CTS) at the different magnifications
(×300 – a, ×10000 – b, ×30000 – c)
Y. Bolbukh, G. Gunko, G. Prikhod’ko et al.
_____________________________________________________________________________________________
394 ХФТП 2010. Т. 1. № 4
The composite obtained is the pellet with di-
ameter of 50–150 µm. At the chosen synthesis
conditions the nanotubes are introduced into
polymer domains, and polymer beams with
d=1 µm surrounded by linear chains are observed.
Surface chemistry of modified MWCNTs.
The SEM/EDX technique was applied for obtain
information about the elemental composition of
surfaces (within an information depth of around
8 nm). Obtained results testified that samples
contained residual quantity of S and Cl (0.17 and
0.93 at %) which were introduced with solutions
during purification and washing. Low content of
Fe on the MWCNTs surface (0.49 at %) permits
to assert that the sample was enough purified
from catalyst.
XPS results (Table) testify domination of
C=O and C–O=C groups on purified MWCNTs.
In FTIR spectra (Fig. 6, spectrum 1) the band
with the absorption maxima at 1639 cm-1 attrib-
uted to the benzene derivatives and the band at
1465 cm-1 pointed on the presence of О–С=О
groups. The weak band at 1270 cm-1 and broad
one at 1122 cm-1 are attributed to vibrations of
C–O–C groups.
550105015502050
Wavenumber (cm-1)
A
bs
o
rb
an
ce
16
3
9
16
1
9
1
4
6
5
1
1
22
1
0
9
5
1
6
5
0
15
7
0
1
1
7
4
1
02
2
1
2
1
3
22
Fig. 6. FTIR spectra of the purified (1) and oxidized
MWCNTs (2)
After oxidation, splitted nanotubes without
caps should have the ports fringed with oxygen-
containing groups. XPS data obtained (Table)
testify that during nanotubes treatment with hy-
drogen peroxide the nanotubes ports were mostly
oxidized [12]. In the sample C–OH and C–O–C
groups predominated over C=O ones in accor-
dance with the literature data [17, 18], and per-
centage of the phenolic groups is increased in
comparison with untreated nanotubes.
The FTIR spectrum of the oxidized
MWCNTs (Fig. 6, spectrum 2) shows the band
at 1650 cm-1 attributed to the benzene deriva-
tives stretching and the band at 1570 cm-1. The
adsorption bands localized at 1450 cm-1 (C–H)
attributed to bending vibrations of benzene ring
and band at 1022 cm-1 corresponded to tangen-
tial C–H bending vibrations in mono-substituted
benzene. The band at 1465 cm-1 points on the
presence О–С=О groups and the bands at
1174 cm-1(C–O) and 1095 сm-1 (C–O–C) are as-
sociated with the ring vibrations in ortho-
disubstituted benzene with attached hydroxyl and
lactone groups [19, 20].
It is conceivable that the monomer HEMA is
preferentially attached to the relatively reactive tube
ends or defect sites of nanotubes such as ether, car-
bonyl (lactone) or hydroxyl groups. IR spectra of
MWCNTs functionalized with HEMA show the
absorption at 1630 cm-1 (C=C) and 1604 cm-1
(COO) assigned to bound –О–С(О)–C(CH3)=CH2
groups (Fig. 7).
45095014501950245029503450
Wavenumber (cm-1)
A
b
so
rb
a
nc
e
32
55
1
63
9
16
19
29
30
35
60
2
85
8
1
2
3
29
68
14
15
Fig. 7. FTIR spectra of MWCNTs-HEMA (1),
MWCNTs-HEMA-HEMA (2) and MWCNTs-
CTS (3)
The band at 1385 cm-1 corresponding to
the bending vibrations of C–H bonds in –СН3
groups confirms the presence of methacrylic
groups in the modifying layer. Narrow band
with an intermediate intensity at 1465 cm-1 is
attributed to О–С=О groups. Availability of
C–O–C bonds and –OH groups attached to
benzene rings is confirmed by the bands at
1095 and 1022 cm-1. The absorption band with
maximum at 1369 cm−1 attributed to vibrations
of C–H bonds in –СН2–ОН groups and bands
at 1570 and 1480 cm-1 corresponding to C–H
bonds vibrations in substituted benzene indi-
cated HEMA attachment to nanotubes [8, 21].
Hence, the modifying layer of the MWCNTs-
HEMA includes both methacrylate and ester
groups as well as phenolic and hydroxyl
groups. The absence in the IR spectrum the
bands corresponding to polymer (Fig. 7, spec-
Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 395
trum 1) allows one to assume that the modify-
ing layer consists of molecules of the monomer
or oligomers.
After repeated MWCNTs-HEMA modifica-
tion with HEMA in the presence of the initiator of
radical polymerization there are the bands at 1730
and 1060 cm-1 attributed to the C=O and C–O–C
groups in the modifying reagent molecules An
increase of the relative intensity of the bands of –
CH2– groups and an appearance of the band near
894 cm-1 testify about the modifier grafting by
interaction with vinyl groups of the preliminarily
immobilized molecules. The presence of bands at
894 and 786 cm-1 indicates the formation of
polymer chains.
After MWCNTs modification with chitosan
FTIR spectra (Fig. 7, spectrum 3) clearly show
new absorption at 3552–3417 cm-1 that is typical
of N–H vibrations in –NHCO. Appearance in
spectrum of MWCNTs-CTS several peaks at
3600–3300 cm-1 indicates the formation of in-
termolecular hydrogen bonds. Strong peaks
1639, 1619, 1415 and 624 cm-1 were also ob-
served. Weak broad absorbance at 1137 cm-1 and
sharp band at 624 cm-1, attributed to C–O–C and
O–C–O vibrations, indicates the esters presence.
The results confirm the MWCNTs capsulation by
chitosan.
Surface charge of modified MWCNTs.
The measurement of zeta-potential of the nano-
tubes in water is complicated by low stability
of the dispersion, but these data give useful in-
formation about surface charge properties. As
known, zeta-potential depends on the type and
concentration of the electrolyte [22, 23], nano-
tubes concentration in suspension. Fig. 8 de-
picts zeta potential of purified MWCNTs taken
at the different concentrations of the suspension
in KCl solution (pH=7.1). Each point is average
zeta potential value from 10 measurements
(within a measuring time of 7 min). With an
increase of the suspension concentration up to
0.7 mg/ml the zeta potential changes slightly,
but the relative error of measurements is sig-
nificantly augmenting and at C = 0.8 mg/ml a
sign of the surface charge is reversed. Fluctua-
tions in the values of zeta potential during
measuring, detected also by authors [16, 24],
may be caused by the nanotubes tendency to
coagulation. It can be assumed that the various
values of zeta-potentials are related to nanotube
agglomerates of different sizes.
pH=7.1
-80
-60
-40
-20
0
20
40
60
80
0 0,2 0,4 0,6 0,8 1
Concentration (mg/ml)
Z
et
a
p
o
te
n
ti
al
(
m
V
)
-30
-25
-20
-15
-10
-5
0
1 3 5 7 9 11
pH
Z
et
a
p
o
te
n
ti
al
(
m
V
)
0.2 mg/ml
0.1mg/ml
a b
pH=3.2
-35
-25
-15
-5
5
15
25
35
0 0,1 0,2 0,3 0,4 0,5
Concentration ( mg/ml)
pH=7.1
Z
et
a
p
o
te
n
ti
al
(
m
V
)
-50
-40
-30
-20
-10
0
0 0,1 0,2 0,3
Concentration ( mg/ml)
pH=9
pH=11
Z
et
a
p
o
te
n
ti
al
(
m
V
)
c d
Fig. 8. Dependences of zeta potential of purified (a)
and oxidized (b–d) MWCNTs on suspension
concentration in 0.01 mol/l KCl solution (a, с,
d) and on medium pH (b)
According to the literature data [25], as-
produced carbon nanotubes have the isoelectric
point (IEP) in the pH range of 5–8 and with in-
creasing of pH the zeta potential becomes more
negative, probably because of adsorption of hy-
droxide ions on the MWCNTs surface. Usually,
after purification the presence of acidic groups
shifts IEP to the lowest pH values [25]. As was
shown in [26], purified nanotubes have small and
positive zeta-potential in the acidic medium with
IEP in the pH range of 2–3. For tested herein pu-
rified MWCNTs IEP was about pH=3. After oxi-
dation, the presence of oxygen-containing groups
shifts the isoelectric point to values often below
pH=2 what is close to the value presented in [27].
The oxidized MWCNTs exhibit negative charge
in the whole pH range investigated and till pH=7
the zeta potential values are increased with pH
growth what correlate with the literature data. It
can be explained by dissociation of the hydroxyl
groups. It will impart the negative charge to the
nanotubes surface. The character of the curve
(Fig. 8b) in pH range of 3–7 is similar to those of
the plots obtained in [16, 26, 28, 29] for oxidized
nanotubes. The low potential values (in the range
from -10 to -25 mV) demonstrate that the
MWCNTs are less sensitive to protons (H+) and
hydroxide anions (OH−) [30]. It is usual when the
functional groups are primary ketones, aldehydes,
alcohols or esters [31, 32], because these groups
are electrically neutral and do not dissociate in
the pH range of 2–12. The dependences of the
zeta potential for nanotubes under study testify
Y. Bolbukh, G. Gunko, G. Prikhod’ko et al.
_____________________________________________________________________________________________
396 ХФТП 2010. Т. 1. № 4
that oxidized nanotubes contain mainly alcohol
and ester groups.
As known, zeta potential values of colloidal
particles are increased with the suspension con-
centration decrease [22]. The results obtained for
oxidized MWCNTs correlate with this observa-
tion in the acidic media: when suspension con-
centration increases zeta potential becomes more
positive (Fig. 8c) and the IEP shifts to higher pH.
IEP for the suspension with concentration of
0.4 mg/ml was near pH=4. Positive zeta potential
(Fig. 8c, pH 3.2) is characteristic of nanotubes
with the low content of oxygen-containing
groups, and it is defined by an increase in the ag-
glomerates size with enhancement of the suspen-
sion concentration. Diffusion of counterions in-
side agglomerates is complicated and the degree
of the functional groups dissociation is reduced.
Under such conditions, the DEL is formed in
boundary layer of the aggregates and neutraliza-
tion of the surface charge is realized at the lower
concentration of the counter-ions. With decrease
in the nanotubes concentration, the surface acces-
sibility is increased and for the DEL formation
more counter-ions are required.
Above pH=7 an effect of the suspension con-
centration on zeta-potential (Fig. 8d) is higher:
potential becomes more positive with a decrease
in the concentration. Nanotubes suspensions was
found to be more stable in the alkaline media in
comparison with those in the acidic media, and at
the concentrations above 0.2 mg/ml the zeta po-
tential measurements became impossible because
of low transparency of the suspensions.
Hence, the nanotubes oxidation improved the
MWCNTs stability in aqueous suspension, but
this stability strongly depends on the nanotubes
ability to coagulation and the nature of the sur-
face functional groups. It should be marked that
largest values of zeta-potential (-29.34 mV) cor-
responding the best stability of dispersion have
reached at рН=11.
Zeta potential of MWCNTs-HEMA (Fig. 9a)
was positive until pH=9 with IEP close to pH=10.
Similarity of the obtained pH-dependence with
such dependence for nanotubes suspensions with
the Disperbyk-2150 dispersant in the ethanol so-
lution [21] is paid an attention. Positive surface
charge was also achieved by the use of non-ionic
surfactant Pluronic 123 or cationic surfactant
CTAB (SWCNTs covered by CTAB display a
ζ-potential of 61.5 mV) [33]. However, for
MWCNTs-HEMA the low potential values (15 to
-20 mV) were detected in all range of pH that is
insufficient for suspension stability (stability from
electrostatic considerations is achieved for zeta
potential values beyond the -15 to 15 mV range).
Positive surface charge of MWCNTs-HEMA in-
dicates a low ionization of the modifying layer in
the wide pH range of 3–9, consequently, the oxy-
gen-containing groups, capable to dissociation,
are replaced (or screened) by the modifier mole-
cules. Grafted HEMA, likely copolymer Disper-
byk-2150, behaves as a cationic surfactant and
shields the nanotubes surface with lyophobic
methacrylate groups.
-30
-20
-10
0
10
20
1 3 5 7 9 11pH
Z
et
a
p
o
te
n
ti
al
(
m
V
)
С=0.4 mg/ml
C=0.1 mg/ml
pH=7.1
0
2
4
6
8
10
12
0 0,1 0,2 0,3 0,4 0,5
Concentration ( mg/ml)
Z
et
a
p
o
te
n
ti
al
(
m
V
)
a b
0
5
10
15
20
25
30
1 3 5 7 9 11pH
Z
et
a
p
o
te
n
ti
al
(
m
V
)
C=0.4 mg/ml
-30
-20
-10
0
10
20
30
1 3 5 7 9 11pH
C=0.2 mg/ml
C=0.1 mg/ml
Z
et
a
p
o
te
n
ti
al
(
m
V
)
c d
Fig. 9. Dependences of zeta potentials of MWCNTs-HEMA
(a), MWCNTs-HEMA-HEMA (b, c) and MWCNTs-
CTS (d) on medium pH (a, с, d) and on suspension
concentration (b)
According to the results obtained, the zeta-
potential is diminished with the suspension con-
centration decrease, and the dispersion stability is
reduced at pH below 10 (Fig. 9a). For MWCNTs-
HEMA this dependence is linear and insignifi-
cant. However, with the modifier molecules elon-
gation (MWCNTs-HEMA-HEMA sample) de-
crease in the zeta potential value was more sub-
stantial (Fig. 9b). It is significant that at the low-
est suspension concentration the zeta potential
values were close to zero and with less disper-
sion. DEL becomes more stable with the suspen-
sion concentration decrease.
For the MWCNTs-HEMA-HEMA sample
zeta potential is positive throughout the pH
range studied (Fig. 9c). Similar results were re-
ported in [33] where the zeta-potential distribu-
tion for carbon nanotubes wrapped by cationic
surfactant CTAB was presented. Zeta potential
Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 397
values of MWCNTs-HEMA-HEMA in the pH
range of 5–9 were significantly higher in com-
parison with the MWCNTs-HEMA sample.
MWCNTs-HEMA-HEMA forms fairly stable
dispersion in water (Fig. 9a, c). The least sus-
pension stability was observed at pH=3 and
pH=11.
For the MWCNTs-HEMA-HEMA sample
the highest value of zeta potential was detected at
pH 9 (Fig. 9c). With the following pH increase
the potential tends to zero and the IEP for this
sample was found above pH=11. Perhaps, at this
pH the polymer chains became more linear that
results in the DEL compaction.
With pH increase the solubility of chitosan
is decreased and it could reduce the suspension
stability. However the MWCNTs-CTS suspen-
sion was shown to be stable throughout the pH
range studied. The IEP was in the pH range of
4–5 depending on the suspension concentration
(Fig. 9d). In spite of small values of the zeta po-
tential in the pH range of 7–11 at C=0.2 mg/ml,
nanotubes sedimentation was not observed. The
suspension was the least stable at pH=5.2 that
was close to IEP. Chemical and conformational
changes of CTS, while changing pH, may be
responsible for such dispersion behaviour. Usu-
ally chitosan is precipitated at pH above 6.5.
Some properties of the chitosan-MWCNTs sys-
tem have been studied in [34]. In the acidic solu-
tions adsorbed onto MWCNTs surface chitosan
acts as a polymeric cationic surfactant and stabi-
lizes the nanotubes suspension. The polymeric
chains of CTS repulse one another in the acidic
solution owing to –NH2 groups protonation.
Groups –NH3
+ are gradually deprotonated with
pH increasing, and then MWCNTs-CTS precipi-
tate because of intramolecular hydrogen bonding.
In the basic solution, both –NH3
+ and –COOH
groups of chitosan are deprotonated forming
–NH2 and –COO– groups. The negatively
charged –COO– groups could also promote to
formation of the homogeneous dispersion of car-
bon nanotubes. When the medium pH was close
to the isoelectric point, the –NH2 and –COOH
groups form intramolecular and intermolecular
complexes, and nanotubes sedimentation takes
place [35].
Cross-linking of adsorbed chitosan with
glutaraldehyde results in lowering of amino
groups content. Properties of the obtained sam-
ple are comparable with the characteristics of
the nanotubes modified with cellulose [36].
With decrease in concentration of MWCNTs-
CTS suspension the value of the zeta potential
(as an absolute value) is increased. This indi-
cates an interaction between aggregates in the
suspension. Comparison of the results obtained
for the modified nanotubes allows one to con-
clude that modification with chitosan provides
the most stable aqueous suspensions of carbon
nanotubes.
CONCLUSION
Modification of oxidized MWCNTs with
HEMA and chitosan could be used to change
surface charge, to disperse nanotubes homo-
geneously in suspension and to impart them
biocompatibility. The data presented testify
that during oxidation with hydrogen peroxide
the tangles of nanotubes are crushed, ports are
opened while the modification with polymers
resulted in formation of agglomerates. For all
the samples, a decrease of the suspension con-
centration leads to shift of the zeta potential
value into the negative range. The interaction
between particles (aggregates) into suspension
has a significant effect on the DEL structure.
For each sample there is the concentration
when the dispersion is the most stable. After
the oxidized MWCNTs modification with
HEMA the isoelectric point is shifted to
pH=10. Elongation the modifier chains at-
tached to nanotubes (MWCNTs-HEMA-
HEMA), along with change of the terminal
groups nature, provides the positive and stable
surface charge increase in nanotubes concen-
tration at pH range of 3–9. For nanotubes
modified with polymer the zeta potential de-
pends on the conformation of the grafted
molecules, since at the different pH the poly-
mer chains can be expanded or collapsed. In-
crease of the zeta potential value provides en-
hancement of the dispertion stability. An ex-
ception to the general dependences found for
the zeta potential values was detected for the
chitosan-modified nanotubes. The isoelectric
point of the MWCNTs modified with chitosan
was close to pH=4.5. At relatively small zeta-
potential values, which became more negative
with decrease in nanotubes concentration, such
suspensions were the most stable due to fea-
tures of the modifier morphology and the na-
ture of terminal groups.
Y. Bolbukh, G. Gunko, G. Prikhod’ko et al.
_____________________________________________________________________________________________
398 ХФТП 2010. Т. 1. № 4
ACKNOWLEDGEMENT
This work was partly supported by FP7
Marie Curie Actions People Project "Hybrid
nanocomposites and their applications – Compo-
situm", Grant Agreement Number PIRSES-GA-
2008-230790. Special gratitude to György
Bosznai (Department of Physical Chemistry and
Materials Science, Budapest University of Tech-
nology and Economics, Hungary) for help in ad-
sorption measurements.
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400 ХФТП 2010. Т. 1. № 4
Багатошарові вуглецеві нанотрубки,
модифіковані біосумісними речовинами
Ю. Больбух, Г. Гунько, Г.П. Приходько,
В.А. Тьортих, Х. Ласло, А. Тоз, Б. Koчка
Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України
вул. Генерала Наумова 17, Київ 03164, Україна, yukulik@yandex.ru
Будапештський університет технології і економіки, кафедра фізичної хімії та матеріалознавства
вул. Будафокі 6-8, Будапешт 1111, Угорщина
Будапештський університет технології і економіки, Кафедра неорганічної та аналітичної хімії
пл. Св. Геллерта 4, Будапешт 1111, Угорщина
Досліджено фізико-хімічні властивості, морфологію та характер поверхні вихідних і модифіко-
ваних 2-гідроксіетилметакрилатом (HEMA) і хітозаном багатошарових вуглецевих нанотрубок
(БШВНТ). Вимірювання дзета-потенціалу БШВНТ проводили при різних рН розчину електроліту і
концентраціях суспензії. Показано, що при окисненні БШВНТ відбувається їхнє дроблення з утворен-
ням портів, що обрамлені переважно гідроксильними групами. Кисеньвмісні групи визначають нега-
тивний дзета-потенціал окиснених нанотрубок в досліджуваному діапазоні рН (3-11), але залеж-
ність дзета-потенціалу від концентрації дисперсії у кислому і основному середовищах обернена. Піс-
ля модифікування БШВНТ НЕМА ізоелектрична точка зміщується з рН=2 до рН=10. Подовження
ланцюжка прикріпленого до нанотрубок модифікатора (БШВНТ-HЕМА-HЕМА) разом із зміною кін-
цевих функціональних груп забезпечує позитивний і стабільний заряд поверхні, що збільшується сим-
батно концентрації нанотрубок в діапазоні рН 3-9. Ізоелектрична точка БШВНТ-хітозан близька до
рН=4,5. За відносно невеликих значень дзета-потенціалу, який стає більш негативним зі зменшенням
концентрації нанотрубок, такі суспензії є найбільш стійкими.
Многослойные углеродные нанотрубки,
модифицированные биосовместимыми веществами
Ю. Больбух, Г. Гунько, Г.П. Приходько,
В.А. Тертых, К. Ласло, А. Тоз, Б. Koчка
Институт химии поверхности им. А.А. Чуйко Национальной академии наук Украины
ул. Генерала Наумова 17, Киев 03164, Украина, yukulik@yandex.ru
Будапештский университет технологии и экономики, кафедра физической химии и материаловедения,
ул. Будафоки 6-8, Будапешт 1111, Венгрия
Будапештский университет технологии и экономики, кафедра неорганической и аналитической химии
пл. Св. Геллерта 4, Будапешт 1111, Венгрия
Исследованы физико-химические свойства, морфология и характер поверхности исходных и мо-
дифицированных 2-гидроксиэтилметакрилатом (НЕМА) и хитозаном многослойных углеродных на-
нотрубок (МУНТ). Измерение дзета-потенциала МУНТ проводили при разных рН раствора электро-
лита и концентрациях суспензии. Показано, что при окислении МУНТ происходит их дробление, а
образующиеся порты обрамлены преимущественно гидроксильными группами. Кислородсодержащие
группы определяют отрицательный дзета-потенциал окисленных нанотрубок в исследуемом диапа-
зоне рН (3-11), но зависимость дзета-потенциала от концентрации дисперсии в кислой и основной
средах обратная. После модифицирования МУНТ НЕМА изоэлектрическая точка смещается от
рН=2 к рН=10. Удлинение цепочки прикрепленного к нанотрубкам модификатора (МУНТ-НЕМА-
НЕМА) вместе с изменением концевых функциональных групп обеспечивает положительный и ста-
бильный заряд поверхности, который увеличивается симбатно концентрации нанотрубок в диапазо-
не рН 3-9. Изоэлектрическая точка МУНТ-хитозан близка к рН=4,5. При относительно небольшом
значении дзета-потенциала, который становится более отрицательным с уменьшением концентра-
ции нанотрубок, такие суспензии являются наиболее устойчивыми.
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| id | nasplib_isofts_kiev_ua-123456789-29022 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 2079-1704 |
| language | English |
| last_indexed | 2025-12-01T18:48:52Z |
| publishDate | 2010 |
| publisher | Інститут хімії поверхні ім. О.О. Чуйка НАН України |
| record_format | dspace |
| spelling | Bolbukh, Y. Gunko, G. Prikhod’ko, G. Tertykh, V. László, K. Tóth, A. Koczka, B. 2011-11-28T21:21:54Z 2011-11-28T21:21:54Z 2010 Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds / Y. Bolbukh, G. Gunko, G. Prikhod’ko, V. Tertykh, K. László, A. Tóth, B. Koczka // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 4. — С. 389-400. — Бібліогр.: 36 назв. — англ. 2079-1704 https://nasplib.isofts.kiev.ua/handle/123456789/29022 544.723:544.77 Oxidized with solution of hydrogen peroxide multiwalled carbon nanotubes (MWCNTs) were modified with 2-hydroxyethylmethacrylate (HEMA) or chitosan (CTS). Morphology and surface properties of the pristine and modified MWCNTs have been investigated. The zeta-potential behaviour of MWCNTs was studied as a function of pH and suspension concentration. After oxidation, the divided nanotubes are found to have uncapped ports decorated with hydroxyl groups mostly. Surface oxygencontaining groups specify the negative zeta-potential in all pH range studied (pH=3-11). The values of zeta-potential display an inverse dependence on the dispersion concentration in acidic and basic solutions. After modification of oxidized MWCNTs with HEMA their isoelectric point is shifted from pH=2 to pH=10. Repeated surface treatment with HEMA (MWCNTs-HEMA-HEMA), along with change of the nature of terminal groups, provides stable surface charge increasing with nanotubes concentration in the pH range of 3-9. The isoelectric point of MWCNTs modified with CTS occurs at pH=4.5. At relatively small zeta-potential values, which become more negative with a decrease in the nanotubes concentration, such suspensions are the most stable. Досліджено фізико-хімічні властивості, морфологію та характер поверхні вихідних і модифікованих 2-гідроксіетилметакрилатом (HEMA) і хітозаном багатошарових вуглецевих нанотрубок (БШВНТ). Вимірювання дзета-потенціалу БШВНТ проводили при різних рН розчину електроліту і концентраціях суспензії. Показано, що при окисненні БШВНТ відбувається їхнє дроблення з утворенням портів, що обрамлені переважно гідроксильними групами. Кисеньвмісні групи визначають негативний дзета-потенціал окиснених нанотрубок в досліджуваному діапазоні рН (3-11), але залежність дзета-потенціалу від концентрації дисперсії у кислому і основному середовищах обернена. Після модифікування БШВНТ НЕМА ізоелектрична точка зміщується з рН=2 до рН=10. Подовження ланцюжка прикріпленого до нанотрубок модифікатора (БШВНТ-HЕМА-HЕМА) разом із зміною кінцевих функціональних груп забезпечує позитивний і стабільний заряд поверхні, що збільшується симбатно концентрації нанотрубок в діапазоні рН 3-9. Ізоелектрична точка БШВНТ-хітозан близька до рН=4,5. За відносно невеликих значень дзета-потенціалу, який стає більш негативним зі зменшенням концентрації нанотрубок, такі суспензії є найбільш стійкими. Исследованы физико-химические свойства, морфология и характер поверхности исходных и модифицированных 2-гидроксиэтилметакрилатом (НЕМА) и хитозаном многослойных углеродных нанотрубок (МУНТ). Измерение дзета-потенциала МУНТ проводили при разных рН раствора электролита и концентрациях суспензии. Показано, что при окислении МУНТ происходит их дробление, а образующиеся порты обрамлены преимущественно гидроксильными группами. Кислородсодержащие группы определяют отрицательный дзета-потенциал окисленных нанотрубок в исследуемом диапазоне рН (3-11), но зависимость дзета-потенциала от концентрации дисперсии в кислой и основной средах обратная. После модифицирования МУНТ НЕМА изоэлектрическая точка смещается от рН=2 к рН=10. Удлинение цепочки прикрепленного к нанотрубкам модификатора (МУНТ-НЕМА-НЕМА) вместе с изменением концевых функциональных групп обеспечивает положительный и стабильный заряд поверхности, который увеличивается симбатно концентрации нанотрубок в диапазоне рН 3-9. Изоэлектрическая точка МУНТ-хитозан близка к рН=4,5. При относительно небольшом значении дзета-потенциала, который становится более отрицательным с уменьшением концентрации нанотрубок, такие суспензии являются наиболее устойчивыми. This work was partly supported by FP7 Marie Curie Actions People Project "Hybrid nanocomposites and their applications – Compositum", Grant Agreement Number PIRSES-GA-2008-230790. Special gratitude to György Bosznai (Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, Hungary) for help in adsorption measurements. en Інститут хімії поверхні ім. О.О. Чуйка НАН України Хімія, фізика та технологія поверхні Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds Багатошарові вуглецеві нанотрубки, модифіковані біосумісними речовинами Многослойные углеродные нанотрубки, модифицированные биосовместимыми веществами Article published earlier |
| spellingShingle | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds Bolbukh, Y. Gunko, G. Prikhod’ko, G. Tertykh, V. László, K. Tóth, A. Koczka, B. |
| title | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds |
| title_alt | Багатошарові вуглецеві нанотрубки, модифіковані біосумісними речовинами Многослойные углеродные нанотрубки, модифицированные биосовместимыми веществами |
| title_full | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds |
| title_fullStr | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds |
| title_full_unstemmed | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds |
| title_short | Multiwalled Carbon Nanotubes Modified with Biocompatible Compounds |
| title_sort | multiwalled carbon nanotubes modified with biocompatible compounds |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/29022 |
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