Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer
Novel polyorganosiloxanes gels with bifunctional ( ≡SiCH2)3SH/ ≡Si(CH2)3NH2) surface layer have been prepared by a sol-gel technique using silane-ternary systems. The surface properties of the obtained gels are highly reproducible. The effect of the addition of a catalyst was investigat...
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Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2002
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| author | Melnyk (Seredyuk), I. V. Zub, Yu. L. Chuiko, A. A. Van Der Voort, P. |
| author_facet | Melnyk (Seredyuk), I. V. Zub, Yu. L. Chuiko, A. A. Van Der Voort, P. |
| author_institution_txt_mv | [
{
"author": "I. V. Melnyk (Seredyuk)",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "Yu. L. Zub",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "A. A. Chuiko",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "P. Van Der Voort",
"institution": "University of Antwerp"
}
] |
| author_sort | Melnyk (Seredyuk), I. V. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:42:19Z |
| description | Novel polyorganosiloxanes gels with bifunctional ( ≡SiCH2)3SH/ ≡Si(CH2)3NH2) surface layer have been prepared by a sol-gel technique using silane-ternary systems. The surface properties of the obtained gels are highly reproducible. The effect of the addition of a catalyst was investigated, and it is shown that the addition of fluoride ion has a highly beneficial effect on the porous properties of the materials. The synthesized samples have specific surface areas up to 250 m²/g, and have a high potential as selective sorbents for heavy and noble metals (Hg2+, Ag+, Au3+ etc.). |
| first_indexed | 2025-07-22T19:30:11Z |
| format | Article |
| fulltext |
125
NOVEL POLYORGANOSILOXANE XEROGELS WITH
BIFUNCTIONAL ºSi(CH2)3SH/ºSi(CH2)3NH2 SURFACE
LAYER
I.V. Melnyk (Seredyuk)1, Yu.L. Zub1, A.A. Chuiko1, and P. Van Der Voort2
1Institute of Surface Chemistry, National Academy of Sciences
Gen. Naumov Str. 17, 03680 Kyiv-164, UKRAINE
2Laboratory of Adsorption and Catalysis, University of Antwerp (U.I.A.)
Universiteitsplein 1, B- 2610 Wilrijk, BELGIUM
Abstract
Novel polyorganosiloxanes gels with bifunctional (ºSiCH2)3SH/ºSi(CH2)3NH2)
surface layer have been prepared by a sol-gel technique using silane-ternary systems. The
surface properties of the obtained gels are highly reproducible. The effect of the addition of
a catalyst was investigated, and it is shown that the addition of fluoride ion has a highly
beneficial effect on the porous properties of the materials. The synthesized samples have
specific surface areas up to 250 m²/g, and have a high potential as selective sorbents for heavy
and noble metals (Hg2+, Ag+, Au3+ etc.).
Introduction
Sulfur-functionalized silica adsorbents attract much attention because of their ability
to adsorb selectively ions of noble and heavy metals. The selectivity of these adsorbents is
much higher as compared with the oxygen- and nitrogen-containing analogues. Moreover,
sulfur-functionalized silica has an application in chromatography for separation of optical
isomers and for excretion of enzymes and nucleic acids. They are also convenient for
immobilization of biologically active compounds. In addition, the irreversible adsorption of
stable metal complexes with fixed sulfur-containing ligands on a porous support presents an
opportunity for use in heterogeneous catalytic systems [1-4]. Organosilanes can be considered
as ideal precursors for the synthesis of functionalized silicas, as their chemical composition is
widely variable. Organosilanes, contained both S- and N-functions, are therefore very suitable
for the synthesis of selective adsorbents with both chemical functions. The selectivity and
capacity of these adsorbents towards noble metal ions will largely depend on the number and
functionality of the N- and S-functions [1].
So far the studies have mainly dealt with the post-synthesis modification of silica by
grafting a variety of organosilanes to the surface [1-4]. This approach, however, has a number
of disadvantages. Firstly, the surface loading, which may be achieved, is limited by the
amount of hydroxyl groups on the surface. Especially in the case of fumed silica, this
concentration is relatively low. Secondly, the design of the functionalized surface by grafting
methods required several separate stages. Therefore, the one pot synthesis of such adsorbents
is highly appealing. Such synthesis may be made by using of sol-gel technique,
polymerization and gelation of the selected organosilanes [5-6]. In this way, one should be
able to obtain not only a high surface concentration of active groups, but this approach allows
one also to introduce simultaneously the various functional groups. Thus, this approach opens
wide (and new) opportunities for controlled surface design. In this work, we will describe the
126
sol-gel synthesis of polysiloxane adsorbents with aminopropyl [-(CH2)3NH2] and
mercaptopropyl [-(CH2)3SH] surface groups.
Experimental
3-aminopropyltriethoxysilane (C2H5O)3Si(CH2)3NH2 (APTES; 99%, Aldrich);
3-mercaptopropyltrimethoxysilane (CH3O)3Si(CH2)3SH (MPTMS; 95%, Aldrich);
tetraethoxysilane Si(OC2H5)4 (TEOS; 98%, Aldrich); (n-C4H9)2Sn(CH3COO)2 (Aldrich);
NH4F (98%, Aldrich); methanol (abs., Aldrich) were used in the sol-gel syntheses.
Xerogel A of poly(3-mercaptopropyl)siloxane was prepared by mixing 21.4 сm3
(0.096 М) TEOS and 9.1 сm3 (0.048 М) MPTMS at ~5°C. 1 g of (n-C4H9)2Sn(CH3COO)2
was added as a catalyst. Afterwards, 4.75 сm3 (0.264 M) of water is added and after 5 minutes
the stirring was stopped, and the solution was aged at room temperature. The formation of the
gel was concluded after 80 days. The gel was separated and vacuum dried at 90oС for 6 h.
Then it was washed by 1 L of water (pH of the last portion of filtrate was 7.0) and dried under
the same condition again. The yield of the white product was 13.6 g.
Xerogel B of poly(3-mercaptopropyl)siloxane was prepared by stirring 0.053 g NH4F
(0.00144 М) in 4.75 сm3 of water and 20 сm3 МеОН, and 9.1 сm3 (0.048 М) MPTMS.
21.4 сm3 (0.096 М) TEOS was slowly added, while keeping the solution at ~5°C. After less
than 1 min the clear solution turned into an elastic gel, which was aged for 24 h. at room
temperature. After washing and vacuum drying at 80oС, the yield of white powdery substance
was 11.1 g.
Synthesis of xerogels with bifunctional surface layer. The organosilanes were added to
20 сm3 of methanol and 0.096 M TEOS, in the concentration described in Table 1.
Afterwards, 4.75 сm3 (0.264 M) of water was added and the stirring was stopped. This gel
formed after a few minutes, it was aged for 24 h. Subsequently, the gel was separated and
vacuum dried at 90oС for 6 h. Then it was washed by 1 L of water and dried under the same
condition again. The yields were respectively: 10.7 g for xerogel C, 11.8 g for xerogel D and
11.1g for xerogel E.
Element analysis of the obtained samples was executed in the Analytical laboratory of
the Faculty of Chemistry of UMIST, U.K. Infrared measurements were performed on a
Nicolet 5PC FT in the transmission mode. Samples were pressed into pellets using KBr.
Thermogravimetric analyses were performed on a Perkin-Elmer at a heating rate of 5°C/min
in a flow of dry air. SEM pictures were taken on a JEOL Superprobe 733. Nitrogen
adsorption-desorption isotherms were recorded on a Quantachrome Autosorb automated gas
adsorption system. Samples were degasses at 120°C prior to the measurement. BET surface
areas [7] and BJH pore size distributions [8] were calculated using commercial software.
Results and discussion
The synthesis of the xerogel A using (n-C4H9)2Sn(CH3COO)2 as a catalyst is
previously described by Parish et al. [9] and Maciel et al. [10, 11]. The synthesis of the
xerogel B (poly(3-mercaptopropyl)siloxane) using fluoride ion as a catalyst has not been
decribed earlier in literature.
The first method has a few unfavorable characteristics. Firstly, often the synthesis
mixture forms two phases, which are sometimes hardly distinguishable. Secondly, the
formation of the gel in the recipe for xerogel is very time-consuming (more than ten days).
Thirdly, the use of (n-C4H9)2Sn(CH3COO)2 as a catalyst results in non-porous xerogels (as
can be inferred from Table 2). Fourthly, as it was shown in [10], the polysiloxane skeleton of
the xerogel A does not have a dense cross-linking and has unhydrolized alkoxy groups.
127
These four points can be considered as serious disadvantages of the method with using
of the (n-C4H9)2Sn(CH3COO)2 catalyst. On the other hand, when fluoride ion is used as a
catalyst, the synthesis of the xerogel proceeds very quickly: a clear, elastic gel is formed after
less than 1 min. Also the other characteristics of xerogel B are superior as compared with the
xerogel A.
1 2
3 4
5 6
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A (´200); 2 - sample C (´300);
3 - sample D (´500); 4 - sample D (´1000); 5 - sample E (´200); 6 -sample E (´1000).
128
The proposed synthesis method has significant advantages in comparison with
a method described by Voronkov`s group for the grafting of polymercaptomethylsiloxane and
polymercaptoethylsiloxane [12-14]. Authors [12-14] used single-component systems, which
essentially narrow the opportunities of a flexible design on a surface and influence the
structural-adsorptive characteristics of the formed xerogels. Moreover, Voronkov’s approach
can cause a partial decomposition of the functional groups.
Xerogels C, D and E were prepared without the addition of a catalyst [15], since the
bifunctional aminosilanes create an autocatalytic effect. In other words, the amino group of
the silane catalyses its own grafting to the surface, as it was described in [4]. Washing water
pH value was the following: for the sample C in the beginning of washing – 8.4, in the end –
7.0; for a sample of D – 9.2 and 9.2 respectively; for the sample E – 9.8 and 10.2 respectively.
Fig. 1 shows the SEM microphotos of these 4 samples. Clear trends can be observed in
these pictures. The xerogel A consists of irregular particles, frequently of triangular shape
with sharp edges. The particle size is 150-200 µm. Looking at the samples C ® E
microphotos an increasing connectivity between particles is observed: from 50-100 mm (C) up
to agglomerates with the size 400 mm and more (E). Also, the content of aminopropyl groups
grows from C to E. Therefore, we assume that the increasing number of amino groups and
therefore the increasing pH during the synthesis results in a higher solubility of the silica
matrix resulting in smoother particles bound together.
In Table 1 the results of the element analysis are summarized. These results show
clearly that the obtained products have approximately the same concentration of functional
groups that the primary synthesis mixture. So, for the sample C it makes 3.47 (in an original
mixture - 3.0), for D - 1.12 (1.0) and for E - 0.36 (0.33).
Table 1. Composition of obtained xerogels and contents of functional groups.
Sample
Molar ratio of
ТEОS/МPТМS/
АPТES
Element analysis data,
in wt. %
1CNH2
mmol/g
2CNH2
mmol/g
CSH
mmol/g
С Н N S Si
А 2 / 1 / 0 12.8 4.0 - 10.4 29.8 - - 4.00
B 2 / 1 / 0 15.5 3.0 - 12.6 28.4 - - 4.50
C 2 / 0.75 / 0.25 15.0 3.4 1.4 9.1 31.9 0.95 0.77 3.30
D 2 / 0.5 / 0.5 14.6 3.4 2.6 6.2 32.5 1.80 1.54 2.14
E 2 / 0.25 / 0.75 14.6 3.4 4.0 2.9 32.8 2.80 2.86 1.00
1 from the data of the element analysis on nitrogen
2 from the data of acid-base titration
It also shows that the mercaptopropyl functional groups is less susceptible to washing
procedures (more strongly bound) as compared with aminopropyl groups. Besides, acid-base
titration proved that all amino functions are active and available on the surface, irrespective of
ratio MPTMS/APTES during synthesis. The IR spectra of the materials are presented in
Fig. 2.
For all sample, strong absorption in the 1000-1200 cm-1 region is observed and
assigned to three-dimensional skeleton of siloxane bonds [16]. The presence of propyl chains
is obvious from set of bands of a weak intensity in 1300-1500 cm-1 region and two
(sometimes - three) bands of medium intensity in 2800-3000 cm-1 region. The latter bands are
129
assigned to stretching vibrations ns,as(CH). In the IR spectrum of the xerogel A (Fig. 2, А)
shows a low-intensity absorption band at 2565 cm-1, assigned to n(SH).
Fig. 2. IR spectra of xerogels A, C, D, and E.
Upon reducing the of MPTMS concentration in the synthesis mixture, its intensity
decreases to almost absent in the IR spectrum of xerogel E (Fig. 2, E). All substances contain
water, as can be seen from the d(Н2О) vibrations at 1600-1650 cm-1 and the broad band about
3000 cm-1 of n(ОH) of the adsorbed water. Samples of D and E (Fig. 2, D and E) show slight
absorption at ~3300 and ~3375 cm-1; which can be assigned to the symmetric and asymmetric
stretching vibrations of N-H in the amino groups. These bands are absent in the IR spectrum
of the xerogel А. The weak band at 1560 cm-1 in samples D and E becomes more intense as
a function of the loading of amino groups and is assigned to the d(RNН3
+) of the
alkylammonium cations, which are formed on the surface of polyaminosiloxanes [17].
The thermo-analytical curves for the synthesized xerogels are given in Fig. 3 and 4.
The small weight losses at 100°C (A - 2.6%; B- 1.1%; C - 3.1%; D - 4.4%; E - 5.3%) is
assigned to the desorption of water. For the xerogel B the weak exothermal band at 280oС is
more pronounced than for the xerogel A (see Fig. 3). The intensive burning out of surface
layer for the sample B would begin at 250oС, while for A - at 265oС. Though the total weight
losses for both samples are very similar (for A -27.2%; for B- 26.5%), two exothermal effects
are observed for sample A above 500°C. It is possible that the reason of these differences is
the presence of porosity in the sample causing the large availability of function groups.
Besides, for the synthesis of the xerogel A, (n-С4Н9)2Sn(CH3COO)2 was used as a catalyst).
Moessbauer spectroscopy [18] has shown that this molecule remains incorporated/adsorbed
on the final gel. Sample E contains the least amount of mercapto groups. The thermograms of
samples C and D (Fig. 4, C and D) have only one strong exothermal effect at 350oС.
Thus, the surface layer of the xerogels with a ratios of functional groups SH/NН2 3:1
and 2:2 are the most thermally steady. Poly(3-aminopropyl)siloxane, obtained at the ratio
130
TEOS/APTES 2:1, has one exothermal peak at 270oС [19]. Thus, it is possible to assume an
effect of synergism in the C and D samples.
Fig. 3. Thermoanalytical curves for xerogels A and B.
Fig. 4. Thermoanalytical curves for xerogels C, D and E.
The structure-adsorption characteristics of the xerogels obtained are represented in
Table 2. Sample A, prepared by an use of the Sn-catalyst, is not porous at all.
Polymercaptomethylsiloxane, synthesized in an alkaline conditions (of single-component
system) [12]), has a specific surface area of 80 m2/g (on n-hexane) and 162 m2/g (on argon).
The xerogels C, D and E, containing bifunctional surface layer, have very high surface areas
131
and pore volumes (see Table 2). All samples with bifunctional surface layer have a
capillary-condensation hysteresis (Fig. 5), pointing to the presence of mesopores.
Table 2. Structure-adsorption characteristics of synthesized samples.
Sample S sp ,
m2/g
Vs, cm3/g deff , nm
A < 1 - -
B 216 0.152 2.8
C 214 0.358 6.7
D 217 0.302 5.6
E 234 0.675 11.5
It is interesting to note that for the xerogel E, containing the smallest amount of amino
groups, the hysteresis curve is broader and shifted to larger relative pressures (see Fig. 5). The
average pore size is nearly twice as large as that for the samples C and D (Table 2), and is
very close to the pore size for polyaminosiloxanes, obtained in the same conditions [19]. Also,
the surface areas slightly increase from sample C to E, and thus Ssp. values grow from 214 up
to 234 m2/g with an increasing of amino groups contents (Table 2).
Fig. 5. Isotherms of nitrogen adsorption for the samples C, D and E.
The pore size distributions for the samples are shown in Fig. 6. For the sample B with
a monofunctional surface layer this distribution is very narrow and the average pore size lies
at the boundary between micro- and mesopores (see Table 2). With an introduction into
surface layer of aminopropyl groups (sample C), a biporous structure occurs with two
different types of mesopores. At higher contents of amino groups (sample D, Fig. 6) the
biporous structure is still maintained. However, for the sample with the maximum content of
amino groups in surface layer (Fig. 6, E), a monoporous system with large mesopores is
observed again. It is interesting to note that in samples C and D, containing bifunctional
surface layer, the effective diameter of the samllest mesopores is close to the mesopores of a
0
50
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150
200
250
300
350
400
450
500
0,00E+00 1,00E-01 2,00E-01 3,00E-01 4,00E-01 5,00E-01 6,00E-01 7,00E-01 8,00E-01 9,00E-01 1,00E+00
P/Po
ad
so
rb
ed
v
ol
um
e
ga
s
(c
m
3 /g
)
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E
132
sample, containing only mercaptopropyl groups. Therefore, we must conclude that in those
intermediate cases, there is no simple correlation between the composition of the initial gel
and the composition and structural- adsorptive properties of the final xerogels
Fig. 6. Pore size distributions for the samples B, C, D, and E.
Fig. 6. Pore size distributions for the samples B, C, D, and E.
Conclusion
Polyorganosiloxanes with bifunctional surface layers have been synthesized in
one-stage synthesis method. It is shown that the relative concentration of both functional
groups can be varied in a wide range (SH/NН2 ratios were 4:0; 3:1; 2:2; and 1:3). Such
bifunctional xerogels have a high potential for the selective adsorption of various metal ions
in aqueous media. Synthesized xerogels have high specific surface areas and pore volumes.
All obtained materials are mesoporous.
Acknowledgement
PVDV acknowledges the FWO-Vlaanderen for the financial support.
References
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13. Finn L.P., Slinyakova I.B., Voronkov M.G., Vlasova N.N., Кletsko F.P., Кirillov A.I., and
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Results and discussion
Results and discussion
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A ((200); 2 - sample C ((300); 3 sample D ((500); 4 - sample D ((1000); 5 - sample E ((200); 6 -sample E ((1000).
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A ((200); 2 - sample C ((300); 3 sample D ((500); 4 - sample D ((1000); 5 - sample E ((200); 6 -sample E ((1000).
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A ((200); 2 - sample C ((300); 3 sample D ((500); 4 - sample D ((1000); 5 - sample E ((200); 6 -sample E ((1000).
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A ((200); 2 - sample C ((300); 3 sample D ((500); 4 - sample D ((1000); 5 - sample E ((200); 6 -sample E ((1000).
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A ((200); 2 - sample C ((300); 3 sample D ((500); 4 - sample D ((1000); 5 - sample E ((200); 6 -sample E ((1000).
Fig. 1. SEM microphotos of xerogels obtained: 1 - sample A ((200); 2 - sample C ((300); 3 sample D ((500); 4 - sample D ((1000); 5 - sample E ((200); 6 -sample E ((1000).
Sample
A
Acknowledgement
References
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| id | oai:ojs.pkp.sfu.ca:article-90 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2025-07-22T19:30:11Z |
| publishDate | 2002 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/44/ce5728c4eab79245047606e14ccd7344.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-902018-11-27T09:42:19Z Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer Melnyk (Seredyuk), I. V. Zub, Yu. L. Chuiko, A. A. Van Der Voort, P. Novel polyorganosiloxanes gels with bifunctional ( ≡SiCH2)3SH/ ≡Si(CH2)3NH2) surface layer have been prepared by a sol-gel technique using silane-ternary systems. The surface properties of the obtained gels are highly reproducible. The effect of the addition of a&nbsp;catalyst was investigated, and it is shown that the addition of fluoride ion has a highly beneficial effect on the porous properties of the materials. The synthesized samples have specific surface areas up to 250 m²/g, and have a high potential as selective sorbents for heavy and noble metals (Hg2+, Ag+, Au3+ etc.). Novel polyorganosiloxanes gels with bifunctional ( ≡SiCH2)3SH/ ≡Si(CH2)3NH2) surface layer have been prepared by a sol-gel technique using silane-ternary systems. The surface properties of the obtained gels are highly reproducible. The effect of the addition of a&nbsp;catalyst was investigated, and it is shown that the addition of fluoride ion has a highly beneficial effect on the porous properties of the materials. The synthesized samples have specific surface areas up to 250 m²/g, and have a high potential as selective sorbents for heavy and noble metals (Hg2+, Ag+, Au3+ etc.). Novel polyorganosiloxanes gels with bifunctional ( ≡SiCH2)3SH/ ≡Si(CH2)3NH2) surface layer have been prepared by a sol-gel technique using silane-ternary systems. The surface properties of the obtained gels are highly reproducible. The effect of the addition of a&nbsp;catalyst was investigated, and it is shown that the addition of fluoride ion has a highly beneficial effect on the porous properties of the materials. The synthesized samples have specific surface areas up to 250 m²/g, and have a high potential as selective sorbents for heavy and noble metals (Hg2+, Ag+, Au3+ etc.). Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2002-06-12 Article Article application/pdf https://surfacezbir.com.ua/index.php/surface/article/view/90 Surface; No. 7-8 (2002): Chemistry, Physics and Technology of Surface; 125-133 Поверхность; № 7-8 (2002): Химия, физика и технология поверхности; 125-133 Поверхня; № 7-8 (2002): Хімія, фізика та технологія поверхні; 125-133 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/90/89 Авторське право (c) 2002 I.V. Melnyk (Seredyuk), Yu.L. Zub, A.A. Chuiko, P. Van Der Voort |
| spellingShingle | Melnyk (Seredyuk), I. V. Zub, Yu. L. Chuiko, A. A. Van Der Voort, P. Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title | Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title_alt | Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title_full | Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title_fullStr | Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title_full_unstemmed | Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title_short | Novel polyorganosiloxane xerogels with bifunctional Si(CH2)3SH/Si(CH2)3NH2 surface layer |
| title_sort | novel polyorganosiloxane xerogels with bifunctional si(ch2)3sh/si(ch2)3nh2 surface layer |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/90 |
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