Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer
Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and purity. By sol-gel processing of these precursors the new functionalized xerogels were synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption method. Mono- and bifunctionalized xero...
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Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2002
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| author | Zub, Yu. L. Melnyk, I. V. Chuiko, A. A. Cauzzi, D. Predieri, G. |
| author_facet | Zub, Yu. L. Melnyk, I. V. Chuiko, A. A. Cauzzi, D. Predieri, G. |
| author_institution_txt_mv | [
{
"author": "Yu. L. Zub",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "I. V. Melnyk",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "A. A. Chuiko",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "D. Cauzzi",
"institution": "Università di Parma"
},
{
"author": "G. Predieri",
"institution": "Università di Parma"
}
] |
| author_sort | Zub, Yu. L. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:42:19Z |
| description | Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and purity. By sol-gel processing of these precursors the new functionalized xerogels were synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption method. Mono- and bifunctionalized xerogels were easily prepared by mixing of precursors in the desired ratios together with tetraethyl orthosilicate. Obtained functional polysiloxanes are perspective materials for metal sorption and hybrid catalysis applications. |
| first_indexed | 2025-07-22T19:30:07Z |
| format | Article |
| fulltext |
35
DESIGN OF FUNCTIONALIZED POLYSILOXANES:
SYNTHESIS AND STUDY ON SULFUR-CONTAINING
XEROGELS WITH MONO- AND BIFUNCTIONAL
SURFACE LAYER
Yu.L. Zub1, I.V. Melnyk1, A.A. Chuiko1, D.Cauzzi2, and G.Predieri2
1Institute of Surface Chemistry, National Academy of Sciences,
Gen. Naumov Str. 17, 03680 Kyiv-164, UKRAINE
2Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Università di Parma, Parco Area delle Scienze, 17/A, 43100 Parma, ITALY
Abstract
Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and
purity. By sol-gel processing of these precursors the new functionalized xerogels were
synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption
method. Mono- and bifunctionalized xerogels were easily prepared by mixing of precursors in
the desired ratios together with tetraethyl orthosilicate. Obtained functional polysiloxanes are
perspective materials for metal sorption and hybrid catalysis applications.
Introduction
Sulfur-containing functional groups anchored to the surface of different matrices
posses as a rule good selectivity in the sorption of analytically important metals. Significant
effort has been made to obtain and investigate sorbents of this class [1-3]. Silicas of different
nature obtained by several methods are often used as support for surface modification.
Seldom in this case the concentration of sulfur-containing groups on the surface is higher than
0.5 mmol/g [2, 3]. For instance, by using the method of “surface assembly” to obtain grafted
sulfur-containing heterocycle ligands, the concentration of such groups on the silica surface
was 2-10 times lower respect to the above-mentioned value. In other words, the sorbtion
capacity of such materials with respect to metal ions was not high ([4] and references therein).
Moreover sides reaction of modifying reagents with surface silanol groups are possible, which
lead to the formation of hydrolytically unstable species.
Therefore it is not surprising that sol-gel method was proposed as an alternative
approach to obtain sulfur-containing sorbents [5]. Many trifunctional silanes of the type
(RO)3SiR' (R – alkyl, and R' – sulfur-containing group) can be prepared for the realization of
this method. Voronkov and collaborators have prepared a number of compounds of such type
and obtained different sulfur-containing xerogels [1, 5]. These sorbents showed high
efficiency in the sorption of Ag(I), Hg(II), Au(III) and platinum groups metals. This synthesis
is performed in one-pot route using hydrolysis of appropriate trifunctional silanes, usually in
basic medium (water or water/dioxane). This, in principle, can lead to partial hydrolysis of
C=S bond. Besides, the specific surface areas of such sorbents were relatively low.
By using sol-gel method, it is easy to vary composition and structure-adsorption
characteristics. In order to use this method we prepared by simple synthesis different
sulfur-containing trifunctional silanes and, for comparison, their oxygen-containing
analogues. By the sol-gel approach we also prepared a number of xerogels with a bifunctional
surface layer in a simple way.
36
Experimental
1. Materials and analytical equipment.
All organic reagents were pure commercial products (Aldrich and Fluka):
n-propylamine (99%); n-dipropylamine (99%); 2-aminobenzothiazole, ABTA (97%);
n-propylisothiocyanate (98%); phenylisocyanate (98%); phenylisothiocyanate (98%);
3-(triethoxysilyl)propylisocyanate, TEPIC (>95%); 3-aminopropyltriethoxysilane, APTES
(99%), N-[3-(trimethoxysilyl)propyl]ethylenediamine, TMPED (97%); tetraethoxysilane,
TEOS (99%).
The solvents were reagents grade and were dried and distilled by standard techniques
before use. All manipulations of reagents containing the trimethoxy- or triethoxysilyl group
(before the sol-gel process) were carried out under dry nitrogen by means of standard
Schlenk-tube techniques.
Elemental analyses (C, N, H, S) were performed with a Carlo Erba EA 1108
automated analyzer. Thermal analysis was performed in the range 20-800oC with a heating
rate of 5oC min-1 in an air stream using Perkin-Elmer Thermal System. IR spectra were
recorded on a Nicolet NEXUS FTIR spectrometer using thin films or KBr disks. 1H NMR
spectra were obtained with a Bruker AC-300 instrument. Mass spectra were recorded on a
Finnigan SSQ 710 mass spectrometer. Energy dispersive X-ray (EDX) microanalyses and
scanning electron microscopy (SEM) images were obtained by the electron microscopy
microanalyses system JEOL 6400 EDS.
BET surface areas [6] were measured using a Micromeritics 2200 equipment from
nitrogen adsorption at the temperature of liquid nitrogen, after degassing the samples in a
nitrogen stream at 423K for about 1 h.
2. Preparation of trialkoxysilanes.
2.1. (EtO)3Si(CH2)3NCS
The synthesis of this compound was performed following to the published method
with minor changes [7]. n-Hexane instead of diethyl ether was used to extract the liquid
isothiocyanate that was subsequently obtained as the yellow oil, by filtering the suspension
and evaporating the hexane under vacuum.
2.2. [(EtO)3Si(CH2)3NH]2C=O (I).
In a 100 ml Schlenk flask 0.025 mol of APTES was dissolved under nitrogen in 10 ml
of dry hexane and cooled using an ice-bath. 0.025 mol of TEPIC in 10 ml of hexane were
added dropwise with stirring. A white precipitate was formed after 5 min. The suspension was
kept for 30 min in an ice-bath, filtered, washed with 10 ml of cold hexane and dried in
vacuum. From the filtrate an additional portion of white product can be obtained. Total yield
is quantitative. Melting point: 63-65oC. Elemental analysis (calcd for C19H44N2O7Si2):
C, 48.25 (48.60); H, 9.86 (9.46); N, 5.94 (6.00); Si, 11.41 (12.00). 1H NMR (CDCl3, d/ppm ):
0.62 (m, SiCH2), 1.21 (t, CH3), 1.61 (m, CH2), 3.14 (m, CH2N), 3.80 (q, CH2O), 4.50 (m,
NH). MS, m/z (%): 498(35), 470(72), 468(45), 424(100), 422(85), 245(18), 219(15), 174(15).
IR, cm-1: 3336 vs (very strong) (nNH), 2975 vs, 2928 vs, 2885 vs (nCH), 1620 vs (nCO),
1596 vs (nasNCN, B band), 1289 m (medium) (nsNCN+nNH, C band), 1104 vs, 1076 vs
(nSiO).
2.3. [(EtO)3Si(CH2)3NH]2C=S (II).
0.025 M of (EtO)3Si(CH2)3NCS was dissolved under nitrogen in 10 ml of dry hexane
and added to solution of 0.025 M of APTES in 10 ml of hexane. The solution was allowed to
react for 1 h with stirring and then heated for 1 h at 60oC. After cooling and evaporating the
hexane under vacuum the light-yellow oil distilled in vacuum. Yield was 95%. 1H NMR
(CDCl3, d/ppm): 0.64 (m, SiCH2), 1.21 (t, CH3), 1.71 (m,CH2), 3.42 (m,CH2N), 3.80 (q,
CH2O), 6.0 (m, NH). MS, m/z (%): 498(35), 470(72), 468(45), 424(100), 422(85), 245(18),
37
219(15), 174(15). IR, cm-1: 3272 m, br (nNH), 2976 vs, 2928 vs, 2886 vs (nCH), 1554 vs
(nasNCN, B band), 1295 m, 1268 w (weak) (nsNCN+nNH, C band), 1103 vs, 1079 vs (nSiO).
2.4. (EtO)3Si(CH2)3NHC(O)NHC3H7-n (III).
In a 100 ml Schlenk flask 0.030 mol of n-propylamine was dissolved under nitrogen in
10 ml of hexane and cooled using an ice-bath. 0.025 M of TEPIC in 10 ml of hexane was
added dropwise with stirring. An exothermic reaction took place. The solution was stirred for
15 min at ice-bath temperature and then for 3 h at room temperature. A white waxy product
was obtained after the solvent was completely evaporated under vacuum. Yield is
quantitative. Elemental analysis (calcd for C13H30N2O4Si): C, 46.63 (50.95); H, 10.32 (9.87);
N, 9.73 (9.14). 1H NMR (CDCl3, d/ppm): 0.55 (m, SiCH2), 0.83 (m, CH3(CH2)2N),
1.14 (t,CH3), 1.40 (m, CH3CH2CH2N), 1.51 (m,CH2), 3.00-3.10 (m,CH2N), 3.74 (q,CH2O),
5.31 (m,NHC3H7), 5.37 (m,NHC3H6). MS, m/z (%): 335(8), 306(12), 265(6), 261(100),
245(6), 220(5), 202(8), 163(12). IR, cm-1: 3344 vs (nNH), 2974 vs, 2928 vs, 2880 vs (nCH),
1630 vs (nCO), 1579 vs, br (bright) (nasNCN, B band), 1278m, 1262m (nsNCN+nNH,
C band), 1103 vs, 1079vs (nSiO).
2.5. (EtO)3Si(CH2)3NHC(S)NHC3H7-n (IV).
In a 100 ml Schlenk flask 0.025 mol of APTES was dissolved under nitrogen in 30 ml
of ethanol. To this solution, 0.025 M of n-C3H7NCS dissolved in 10 ml ethanol was added
with stirring. An exothermal reaction took place. The resulting solution was boiled for 1 h.
After cooling, the solvent was completely evaporated under vacuum. By staying some time in
vacuum the clear transparent oil transformed into a white waxy solid. Yield was quantitative.
Elemental analysis (calcd for C13H30N2O3SSi): N, 8.41 (8.68); S, 9.47 (9.94). 1H NMR
(CDCl3, d/ppm): 0.55 (m, SiCH2), 0.84 (m, CH3(CH2)2N), 1.11 (t, CH3),
1.51 (m, CH3CH2CH2N), 1.60 (m, CH2), 3.00-3.33 (m, CH2N), 3.71 (q, CH2O), 6.20 (br s,
NHC3H7), 6.30 (br s, NHC3H6). MS, m/z (%): 325(8), 324(30), 333(85), 322(100), 277(16),
163(20). IR, cm-1: 3267 vs, br (nNH), 2973 vs, 2928 vs, 2885 vs (nCH), 1556 vs, br
(nas NCN, B band), 1294 m, 1268 m (nsNCN+nNH, C band), 1103 vs, 1079 vs (nSiO).
2.6. (EtO)3Si(CH2)3NHC(O)NHC6H5 (V).
0.025 M C6H5NCO was added dropwise under nitrogen to a solution of 0.025 M of
APTES in 15 ml ethanol with stirring. An exothermic reaction took place. The solution was
allowed to react for 30 min and then the solvent was completely evaporated under vacuum.
The transparent oil formed and after staying in vacuum gave a white solid. Yield is
quantitative. M.P. is 44-46oC. Elemental analysis (calcd for C16H28N2O4Si): C, 56.71 (56.44);
H, 8.53 (8.29); N, 8.16 (8.23). 1H NMR (CDCl3, d/ppm): 0.62 (m, SiCH2), 1.20 (t, CH3),
1.62 (m, CH2), 3.20 (m, CH2N), 3.79 (q, CH2O), 5.34 (m, NH), 6.95 (br s, NHC6H5),
7.00-7.05, 7.23-7.30 (m, C6H5). MS, m/z (%): 542(75), 503(20), 370(72), 341(100), 324(46),
295(100), 293(43), 202(42), 93 (20). IR, cm-1: 3351 vs, br, 3310 s (strong) (nNH), 3077 w,
3039 w (nCH arom), 2971 vs, 2924 vs, 2883 vs (nCH aliph), 1644 vs (nCO), 1559 vs, br
(nasNCN, B band), 1237 m (nsNCN+nNH, C band), 1108 vs, 1079 vs, br (nSiO).
2.7. (EtO)3Si(CH2)3NHC(S)NHC6H5 (VI).
The synthesis of this compound was performed following to the published method [8]
from APTES and C6H5NCS. Under staying in vacuum the product was obtained as a
pale-yellow viscous liquid, giving satisfactory spectroscopic data. 1H NMR (CDCl3, d/ppm):
0.58 (m, SiCH2), 1.16 (t, CH3), 1.68 (m, CH2), 3.61 (m, CH2N), 3.71 (q, CH2O), 6.24 (br s,
NH), 7.18-7.28, 7.37-7.42 (m, C6H5), 8.02 (br s, NHC6H5). MS, m/z (%): 356(100), 311(32),
218(10), 176(16), 163(30), 152(12), 135(15), 93(10). IR, cm-1: 3275 s, br, 3212 sh (shoulder),
br (nNH), 3062 w, 3039 w (nCH arom), 2975 vs, 2926 vs, 2887 vs (nCH aliph), 1537 vs
(nasNCN, B band), 1242 m (nsNCN+nNH, C band), 1103 vs, 1079 vs, br (nSiO).
38
2.8. (EtO)3Si(CH2)3NHC(O)NHCNSC6H4 (VII).
In a 100 ml Schlenk flask 0.025 mol of ABTA was dissolved under nitrogen in 30 ml
of CH3CN. To this light yellow-green solution 0.025 mol of TEPIC was added dropwise with
stirring. The resulting solution was refluxed for 2 h. After cooling the solvent was completely
evaporated under vacuum. The residue was dissolved in 10 ml of warm ethanol and filtered.
The filtrate was evaporated under vacuum yielding a light-green solid in 90% yield. M.P. is
79-81oC. Elemental analysis (calcd for C17H27N3O4SSi): C, 50.91(51.39); H, 6.62(6.8);
N, 10.49(10.58); S, 8.14(8.06); Si, 7.54(7.05). 1H NMR (CDCl3, d/ppm ): 0.70 (m, SiCH2),
1.22 (t, CH3), 1.73 (m, CH2), 3.37 (m, CH2N), 3.82 (q, CH2O), 7.19-7.24, 7.34-7.40,
7.69-7.73 (m, C6H5), 11.14 (br s, NH). MS, m/z (%): 426(16), 398(100), 353(25), 351(48),
247(8), 222(18), 202(8), 176(10), 150(37). IR, cm-1: 3325 vs, br (nNH), 3056 w (nCH arom),
2976 vs, 2929 vs, 2889 vs (nCH aliph), 1700 vs, br (nCO), 1540 vs, br (nasNCN, B band),
1272 m, 1251 m (nsNCN+nNH, C band), 1103 vs, 1079 vs (nSiO).
3. Preparations of xerogels.
3.1. SiO2/[SiO3/2(CH2)3NH]2C=O (2 : 1) (MI).
0.025 mol of APTES was dissolved under nitrogen in 10 ml of ethanol and to this
solution 0.025 mol of TEPIC in 10 ml of ethanol was added dropwise under stirring. An
exothermal reaction took place. After 30 min the resulting solution was cooled using an ice-
bath and added of a solution of 0.0278 g NH4F in 2.48 ml (0.1375 mol) of water. After
stirring for some seconds, 0.05 mol of the cold TEOS was added to this solution. After
reaching homogeneity the clear resulting solution was left to reach room temperature.
Gelation occurred in less that 10 min, giving a slight opalescent gel. After 24 h the gel was
crushed and dried under vacuum at 60/70/80oC, for 2 h at each temperature. Then it was
crushed again, washed with 500 ml of water and dried under vacuum at 70/80/90oC for 2 h at
each temperature. 10.9 g of white solid were obtained.
3.2. SiO2/[SiO3/2(CH2)3NH]2C=O (4 : 1) (MID).
This xerogel was obtained by the same method of 3.1 with the following changes:
0.0125 mol of APTES was dissolved in 10 ml of ethanol and to this solution 0.0125 mol of
TEPIC in 5 ml of ethanol was added; 0.0189 g NH4F in 2.14 ml (0.1188 mol) of water was
used; xerogel was washed with 500 ml of water. Yield was 6.5 g.
3.3. SiO2/[SiO3/2(CH2)3NH]2C=S (4 : 1) (MIID).
0.025 mol of APTES was dissolved under nitrogen in 20 ml of ethanol and to this
solution 0.025 mol of [(EtO)3Si(CH2)3NH]2C=S (obtained in 2.3) in 20 ml of ethanol was
added dropwise under stirring. After 30 min stirring the reaction mixture was heated for 1 h at
60oC and only after that it was cooled using an ice-bath and added of a solution of 0.0278 g
NH4F in 4.28 ml (0.2375 mol) of water. After stirring some seconds, 0.10 mol of the cold
TEOS was added to this solution. After reaching homogeneity the clear resulting solution was
left to reach room temperature. Gelation occurred in less that 50 min, giving a slight
opalescent gel. After 24 h the gel was crushed and dried under vacuum at 60/70/80o C, for 2 h
at each temperature. Then it was crushed again, washed with 1000 ml of water and dried
under vacuum at 60/70/80oC for 2 h at each temperature. 13.5 g of light-yellow solid was
obtained.
3.4. SiO2/SiO3/2(CH2)3NHC(O)NHC3H7-n (2 : 1) (MIII).
0.025 mol (EtO)3Si(CH2)3NHC(O)NHC3H7-n (obtained in 2.4) was dissolved in 20 ml
ethanol and cooled with an ice-bath. To this solution, 0.0278 g of NH4F dissolved in 2.48 ml
of water was added and after some seconds of stirring, in which the solution stayed clear,
0.05 mol of cold TEOS was added with stirring. Gelation occurred in less than 5 min. After
24 h the gel was crushed and dried under vacuum at 60/70/80oC (for 2 h at each temperature).
39
Then it was crushed again, washed with 500 ml of water and dried under vacuum at
70/80/90oC (for 2 h at each temperature). Yield of white product was 7.9 g.
3.5. SiO2/SiO3/2(CH2)3NHC(O)NHC3H7-n (4 : 1) (MIIID).
This xerogel was obtained using the method described in 3.4 with the following
changes: trifunctional silane was dissolved in 30 ml ethanol; the water amount was 4.28 ml
(0.2375 mol), and TEOS amount was 0.10 mol; xerogel was washed with 1000 ml of water.
Yield was 10.7 g.
3.6. SiO2/SiO3/2(CH2)3NHC(O)NHC3H7-n/ SiO3/2(CH2)3NH2 (4 : 1 : 1) (BIII).
0.025 mol of (EtO)3Si(CH2)3NHC(O)NHC3H7-n (obtained in 2.4) was dissolved in
20 ml ethanol and cooled with an ice-bath. A second solution of TEOS/APTES
(0.10/0.025 mol) was prepared and cooled. 4.95 ml of water was added to the first solution
and after several second the second was added to the mixture. A milk-white gel was obtained
in 20 min. After 24 h it was crushed and dried in vacuum at 60/70/80oC (for 2 h at each
temperature). Then it was crushed again, washed with 1000 ml of water and dried under
vacuum at 80/90/105oC (for 2 h at each temperature). Yield of white product was 10.5 g.
3.7. SiO2/SiO3/2(CH2)3NHC(S)NHC3H7-n (2 : 1) (MIV).
0.025 mol of (EtO)3Si(CH2)3NHC(S)NHC3H7-n (obtained in 2.5) was dissolved in
20 ml ethanol and cooled using an ice-bath. The preparation followed to the one reported
in 3.4. Gelation occurred in less than 10 min. Yield of slightly yellow solid was 8.2 g.
3.8. SiO2/SiO3/2(CH2)3NHC(S)NHC3H7-n (4 : 1) (MIVD).
It was obtained by method described in 3.5 with the following changes: trifunctional
silane was dissolved in 30 ml of ethanol, the water amount was 4.28 ml (0.2375 mol), and
TEOS quantity was 0.10 mol; aging time was 48 h. Yield was 11.4 g.
3.9. SiO2/SiO3/2(CH2)3NHC(S)NHC3H7-n/ SiO3/2(CH2)3NH2 (4 : 1 : 1) (BIV).
This xerogel was obtained according to 3.6 with the following changes: 30 ml of
ethanol was used. Yield of white product was 12.2 g.
3.10. SiO2/SiO3/2(CH2)3NHC(O)NHC3H7-n/SiO3/2(CH2)3NHC(S)NHC3H7-n (4:1:1) (BIII/IV).
0.025 mol (EtO)3Si(CH2)3NHC(O)NHC3H7-n (obtained in 2.4) was dissolved in 20 ml
of ethanol and added to a solution of 0.025 mol of (EtO)3Si(CH2)3NHC(S)NHC3H7-n
(obtained in 2.5) in 20 ml of ethanol. The resulting solution was cooled and was added of a
solution of 0.0278 NH4F in 4.95 ml (0.275 mol) of water. After obtaining solution
homogeneity 0.10 mol of cold TEOS was added to that solution with stirring. Gelation
occurred in 12 min. After 24 h the gel was crushed and dried in vacuum at 60/70/80oC (for 2 h
at each temperature). Then it was crushed again, washed with 1000 ml of water and dried
under vacuum at 70/80/90oC (for 2 h at each temperature). Yield of slight-yellow product was
16.2 g.
3.11. SiO2/SiO3/2(CH2)3NHC(S)NHC6H5 (2 : 1) (MVI).
0.025 mol of (EtO)3Si(CH2)3NHC(S)NHC6H5 (obtained in 2.7) was dissolved in 20 ml
of ethanol and cooled using an ice-bath. Then the synthesis was performed according to 3.4.
Gelation occurred in 5 min. Yield was 8.7 g.
3.12. SiO2/SiO3/2(CH2)3NHC(S)NHC6H5 (4 : 1) (MVID).
0.025 mol of (EtO)3Si(CH2)3NHC(S)NHC6H5 (obtained in 2.7) was dissolved in 30 ml
of ethanol and cooled using an ice-bath. Then the synthesis was performed according to 3.5.
Gelation occurred in 5 min. Yield of white product was 12.1 g.
3.13. SiO2/SiO3/2(CH2)3NHC(S)NHC6H5 (8 : 1) (MVID’).
0.025 mol of (EtO)3Si(CH2)3NHC(S)NHC6H5 (obtained in 2.7) was dissolved in 40 ml
of ethanol and cooled using an ice-bath. Then the synthesis was performed according to 3.12
with the following changes: the water amount was 7.88 ml ( 0.4375 mol ), and TEOS quantity
was 0.20 mol. Gelation occurred in 10 min. Yield of slight-yellow product was 19.6 g.
3.14. SiO2/SiO3/2(CH2)3NHC(S)NHC6H5/SiO3/2(CH2)3NH2 (4 : 1 : 1) (BVI).
40
The synthesis of this xerogel was performed like in 3.6 with the following changes:
30 ml of ethanol was used. Gelation occurred in 15 min. Yield of white product was 15.0 g.
3.15. SiO2/SiO3/2(CH2)3NHC(O)NHC6H5/SiO3/2(CH2)3NHC(S)NHC6H5 (4 : 1 : 1) (BV/VI).
0.025 mol of (EtO)3Si(CH2)3NHC(O)NHC6H5 (obtained in 2.6) was dissolved in
20 ml of ethanol and mixed with a solution of 0.025 mol of (EtO)3Si(CH2)3NHC(S)NHC6H5
(obtained in 2.7) in 20 ml of ethanol. The resulting solution was cooled with an ice-bath and
then added of a solution of 0.0278 g of NH4F in 4.95 ml of water. After obtaining solution
homogeneity, 0.10 mol of the cold TEOS were added to the previous solution. Gelation
occurred in less than 7 min. After 24 h the gel was crushed and dried in vacuum at 60/70/80oC
(for 2 h at each temperature). Then it was crushed again, washed with 1000 ml of water and
dried under vacuum at 70/80/90oC (for 2 h at each temperature). Yield of slightly-yellow
product was 18.3 g.
3.16. SiO2/SiO3/2(CH2)3NHC(O)NHCNSC6H4 (2 : 1) (MVII).
The solution of 0.025 mol of the initial trifunctional silane was obtained according to
2.8. The residue obtained after complete evaporation of CH3CN was dissolved in 40 ml of
warm ethanol, filtered and cooled in an ice-bath. Then it was added of a solution of 0.0278 g
of NH4F in 2.48 ml of water. After 10-15 sec 0.05 mol of cold TEOS was added to the
previous solution. Gelation occurred in 15 min. After 24 h the gel was crushed and dried in
vacuum at 60/70/80oC (for 2 h at each temperature). Then it was crushed again, washed with
500 ml of water and dried under vacuum in the same conditions. Yield of slightly-green
product was 10.2 g.
3.17. SiO2/SiO3/2(CH2)3NHC(O)NHCNSC6H4 (4 : 1) (MVIID).
This xerogel was obtained according to 3.16 with the following changes: 4.28 ml
(0.2375 mol) of water and 0.10 mol of TEOS were used; the xerogel was washed using
1000 ml of water; the second drying was performed at 70/80/90oC (2 h at each temperature).
Yield was 13.0 g.
3.18. SiO2/SiO3/2(CH2)3NHC(O)NHCNSC6H4/SiO3/2(CH2)3NH(CH2)2NH2 (4 : 1 : 1) (BVII).
This xerogel was obtained according to 3.16 with the following changes in method:
the catalyst was not used; the water amount was 4.95 ml (0.275 mol); TEOS was previously
mixed with TMPED (0.10/0.025 M). Gelation occurred in less than 20 min. The second
drying was performed at 70/80/90oC (2 h at each temperature). Yield was 17.2 g.
Results and discussion
For the synthesis of trialkoxysilanes with oxygen- and sulfur-containing functional
groups we used the well-known reaction of primary amines with isothiocyanates (see
Scheme 1). This reaction as a rule does not show the formation of by-products, often goes at
room temperature and allows one to obtain a wide spectra of trifunctional silanes with high
yield.
Solv
(RO)3Si(CH2)3NH2 + S(O)CN-R'' ¾¾® (RO)3Si(CH2)3NHC(S(O))NHR'' (1)
Thus we obtained triethoxysilanes which contain R'' radicals such as n-C3H7 (O I;
S II ); C6H5 (O III; S IV); (CH2)3Si(OC2H5)3 (O V; S VI); CNSC6H4 (O VII). It should
be noted that V and VI were synthesized earlier [9-12] using the transamination reaction. In
this case V was obtained as an oil with 12.2 % yield. Using the reaction (1), independently
from the solvent (n-hexane or benzene), it crystallizes as a white solid (melting point
61-63oC) in quantitative yield. Spectral characteristics of this product are consistent with
those described in [12] except the NH position in 1H NMR spectrum; for the crystalline
product this signal is shifted to strong fields (an analogous situation is observed for
substance IV, 1H NMR spectrum of which was described in [8]). A single strong band in the
41
range 3000-4000 cm-1 was identified in the IR spectrum of this substance, which is attributed
to n(NH). After drying in vacuum, this substance does not dissolve well in alcohols,
benzene, etc. The product is air and moisture stable. Also substance IV was earlier described
as an oil [8] and a solid product [13]. However our goal consisted in obtaining
triethoxysilanes precursors for sol-gel synthesis that, as a rule, did not need special
purification. Their purity according to spectral data was quite satisfactory for the further use.
At the same time it should be said that most triethoxysilanes can form oils, because they
contain traces of solvents, for example ethanol, which can be seen in 1H NMR spectra.
However in our case that was not a problem because they were prepared in ethanol, which is
the solvent used for the further gels obtaining.
All the precursors used in this work have been characterized by IR spectroscopy due
to their intense and typical functional-group absorption bands. NHC(O)NHR'' groups show a
strong, narrow n(NH) absorption band in the range 3200-3400 cm-1. In the case of
NHC(S)NHR'' groups the n(NH) band is broader and less intense. Secondly, in the range
1500-1700 cm-1 we observe the nas(NCN) and n(CO) absorption bands [14, 15]. In the case of
S-containing silanes, the nas(NCN) is a single broad band (also in the case of different groups
on the nitrogen atoms). For the O-containing silanes we observe two strong and narrow
absorption bands.
In the 1H NMR spectra of the synthesized precursors, the NH-groups absorption is
present at low field (>4.5 ppm). In the case of symmetrical (thio)urea (V and IV substances)
the two NH have the same chemical shifts, in the case of (thio)urea with substituents of
different nature (I – IV substances) there are two signals. For VII substance despite of the
different nature of the substituents only one broad signal is observed at about 11.0 ppm,
probably because of exchange processes.
All the obtained precursors were used in the synthesis of gels. By the reaction of
hydrolytic co-condensation, we prepared two- and three-component xerogels, where by
component we mean the silane-containing precursors (see Scheme 2):
H2O/F-
Si(OC2H5)4 + (C2H5O)3Si(CH2)3NHC(O or S)NHR'' + (C2H5O)3Si(CH2)3R''' ¾¾¾®
- C2H5OH
¾¾® SiO2/ SiO3/2(CH2)3NHC(O or S)NHR''/SiO3/2(CH2)3R''', (2)
where R'' = n-C3H7; C6H5; (CH2)3Si(OC2H5)3; CNSC6H4 and R''' = -NH2 or -NH(CH2)2NH2.
As a solvent, ethanol was used and NH4F as a catalyst. The ratio F-/Si was usually 1/100 or
less. The amount of water was one half of the one needed for complete hydrolysis of all
ethoxy groups [16].
The gels obtained have opalescent, which is characteristic for the sol-gel process in
basic or nucleophilic medium. After ageing (usually for 24 h) the gels were crushed, dried in
vacuum, crushed again, washed with water and dried again at vacuum. The drying conditions
for sulfur-containing gels were softer then in other cases. Elemental analysis (C, H, N, S) data
for the obtained xerogels are given in Table 1.
The synthesized xerogels can be divided into two groups related with the composition
of their surface layer; xerogels with monofunctionalized (M) and bifunctionalized (B) surface
layers. Xerogels M are hydrophobic and posses a small value of specific surface area (Ssp)
when TEOS/trifunctional silane ratio was 2:1. Therefore xerogels with higher
TEOS/trifunctional silane ratio (4 : 1; MD xerogels) were prepared and they show hydrophilic
properties. Also xerogels with a bifunctional surface layer (B), displayed hydrophilic
character of their surface.
42
All the xerogels were obtained as light powdery materials, which, as a rule, are easily
suspended in air. Sometimes sulfur-containing xerogels posses a pale-yellow color. In Fig. 1
SEM pictures are shown. They are typical for such xerogels and indicate that they consist of
particles of different size with sharp edges, with finely dispersed small grains.
a b c
Fig. 1. Scanning electron micrograph for the sample BIV: 25x (a); 1100x (b) and 5500x (c)
Fig. 2. IR spectra of MID; MIID; MIVD.
43
Table 1. Elemental analysis data and specific surface area of the obtained xerogels.
Xerogels
abbrevia-
tions
Composition of reacting
mixture and ratio of
components
Elemental analysis data
(wt.%)
C H N S
C/N/S ratio 1Cf.g.
mmol
g-1
Ssp.
m2 g-1
MI
MID
BI
MII
MIID
BII
BI/II
MIV
MIVD
MVID'
BIV
BIII/IV
MV
MVD
MVID
MVII
MVIID
BVII
TEOS/I (2:1)
TEOS/I (4:1)
TEOS/I/APTES (4:1:1)
TEOS/II (2:1)
TEOS/II (4:1)
TEOS/II/APTES (4:1:1)
TEOS/I/II (4:1:1)
TEOS/IV (2:1)
TEOS/IV (4:1)
TEOS/IV (8:1)
TEOS/IV/APTES (4:1:1)
TEOS/III/IV (4:1:1)
TEOS/V (2:1)
TEOS/V (4:1)
TEOS/VI (4:1)
TEOS/VII (2:1)
TEOS/VII (4:1)
TEOS/VII/TMPED(4:1:1)
24.74 5.02 7.54 -
18.53 3.37 5.16 -
14.93 3.26 5.31 -
24.64 4.68 7.49 9.19
20.60 3.75 5.89 9.44
18.96 4.01 6.33 2.67
25.49 5.13 7.64 4.38
31.31 4.03 6.82 8.37
24.64 3.15 5.21 6.51
17.22 2.23 3.38 1.96
25.24 3.48 6.53 6.11
32.85 4.22 6.94 5.13
26.74 5.39 5.83 -
14.44 3.38 4.53 -
15.67 3.65 4.41 7.02
32.03 3.43 9.03 7.16
25.14 2.76 6.92 7.36
27.58 4.36 9.65 5.61
7.6/2.0/-
8.4/2.0/-
9.8/3.0/-
7.1/1.9/1.0
5.8/1.4/1.0
19.0/5.4/1.0
15.5/4.0/1.0
10.1/1.9/1.0
10.1/1.8/1.0
23.5/3.9/1.0
11.0/2.4/1.0
17.1/3.1/1.0
10.7/2.0/-
7.4/2.0/-
6.0/1.4/1.0
11.9/2.9/1.0
9.1/2.2/1.0
13.2/3.9/1.0
2.9
1.9
1.3
3.2
3.3
0.9
1.4
2.2
2.9
0.6
2.0
1.7
2.2
1.7
2.4
2.4
2.5
1.9
<1
189
109
<1
175
276
70
<1
1Concentration of functional group in mmol g-1 (from elemental analysis data).
Table 2. Main absorption bands in IR spectra of synthesized xerogels (cm-1)
and their assignment.
Xerogel n(NH)+n(OH) n(CH) n(CO) nas (NCN) n(SiO)
MI
MID
BI
MII
MIID
BII
BI/II
MIV
MIVD
MVID’
BIV
BIII/IV
MV
MVD
MVID
MVII
MVIID
BVII
3373
3380, 3440
3303, 3362
3283
3327
3289, 3357
3323
3258
3301, 3383
3385
3272
3316, 3385
3371
3415
3384
3267, 3360
3271, 3365
3290, 3368
2870, 2936, 2969
2876, 2936, 2976
2880, 2939, 2965
2874, 2933, 2965
2880, 2936, 2968
2877, 2939, 2965
2876, 2933, 2970
2873, 2932, 2965
2894, 2936, 2980
2896, 2941, 2992
2879, 2933, 2965
2885, 2943, 2992
2975, 2933, 2891
2895, 2933, 2985
2896, 2925, 2978
2882, 2937, 2972
2880, 2940, 2977
2880, 2940, 2980
1636
1639
1639
-
-
-
1653
-
-
-
-
1665
1652
1660
-
1683
1684
1706
1574
1574
1574
1559
1558
1559
1535
1540
1543
1550
1540
1546
1570
1580
1567
1539
1539
1548
1072, 1134
1077, 1164
1059, 1144
1074, 1141
1079, 1162
1064, 1141
1070, 1125
1128
1077, 1164
1075, 1160
1070, 1145
1051, 1133
1074, 1102
1068
1072
1070, 1130
1075, 1140
1048, 1133
44
Fig. 3. Thermograms of MID, MIID, MIVD and BIV.
C : N : S ratio, calculated using elemental analysis data (Table 1), indicates that all the
functional groups are incorporated on the surface of the xerogels. Their presence is confirmed
by IR spectroscopy data. Table 2 shows the positions of main absorption bands, which were
found in IR spectra and their assignment. The strong absorption bands in the range
1500-1700 cm-1 were useful for identification. IR spectra of all the xerogels show in the range
1000-1180 cm-1 the strongest absorption band (which usually compares with a shoulder on the
left side of the band). The appearance of this band is typical of three-dimensional siloxane
skeleton [17]. Fig. 2 shows IR spectra for some synthesized xerogels.
Xerogels, prepared from precursors with O-containing functional groups, display, as
expected, more high thermal stability as compared with appropriate S-containing substances.
In Fig. 3 some examples of thermograms are shown.
In Table 1 values of Ssp are represented. As expected, 2 : 1 system shows a low or very
low specific surface area. Ssp is higher for 4 : 1 : 1 ternary and 4 : 1 binary systems. The
highest value of Ssp is found for the 8 : 1 system.
Conclusions
By simple reaction new xerogel precursors were prepared and obtained in satisfactory
yield and purity. By using these precursors in the sol-gel process we could obtain
surface-functionalized xerogel with the desired silicon/function ratio and relative
composition. Their properties will be investigated in the field of metal-sorption and metal
hybrid catalysis, trying to relate them to their surface composition and structure.
45
Acknowledgement
Financial support for Yu.L. Zub by CNR-NATO is gratefully acknowledged.
References
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Università di Parma, Parco Area delle Scienze, 17/A, 43100 Parma, ITALY
Università di Parma, Parco Area delle Scienze, 17/A, 43100 Parma, ITALY
Introduction
Experimental
Conclusions
References
|
| id | oai:ojs.pkp.sfu.ca:article-81 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2025-07-22T19:30:07Z |
| publishDate | 2002 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/22/12373ffd58d2bfdbe3e7bc3b7b28ad22.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-812018-11-27T09:42:19Z Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer Zub, Yu. L. Melnyk, I. V. Chuiko, A. A. Cauzzi, D. Predieri, G. Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and purity. By sol-gel processing of these precursors the new functionalized xerogels were synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption method. Mono- and bifunctionalized xerogels were easily prepared by mixing of precursors in the desired ratios together with tetraethyl orthosilicate. Obtained functional polysiloxanes are perspective materials for metal sorption and hybrid catalysis applications. Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and purity. By sol-gel processing of these precursors the new functionalized xerogels were synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption method. Mono- and bifunctionalized xerogels were easily prepared by mixing of precursors in the desired ratios together with tetraethyl orthosilicate. Obtained functional polysiloxanes are perspective materials for metal sorption and hybrid catalysis applications. Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and purity. By sol-gel processing of these precursors the new functionalized xerogels were synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption method. Mono- and bifunctionalized xerogels were easily prepared by mixing of precursors in the desired ratios together with tetraethyl orthosilicate. Obtained functional polysiloxanes are perspective materials for metal sorption and hybrid catalysis applications. 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/81 Surface; No. 7-8 (2002): Chemistry, Physics and Technology of Surface; 35-45 Поверхность; № 7-8 (2002): Химия, физика и технология поверхности; 35-45 Поверхня; № 7-8 (2002): Хімія, фізика та технологія поверхні; 35-45 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/81/79 Авторське право (c) 2002 Yu.L. Zub, I.V. Melnyk, A.A. Chuiko, D.Cauzzi, G.Predieri |
| spellingShingle | Zub, Yu. L. Melnyk, I. V. Chuiko, A. A. Cauzzi, D. Predieri, G. Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title | Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title_alt | Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title_full | Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title_fullStr | Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title_full_unstemmed | Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title_short | Design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| title_sort | design of functionalized polysiloxanes: synthesis and study on sulfur containing xerogels with mono- and bifunctional surface layer |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/81 |
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