Sorbents based on modified polysiloxanes

Article abstract of DOI:10.1134/S0020168511030174

Organic-inorganic hybrid sorbents based on a polysiloxane modified with amino and thiourea groups have been synthesized for the first time by a sol-gel process. The structure of the sorbents has been determined by X-ray photoelectron spectroscopy and IR spectroscopy. Their thermal stability has been assessed and the mechanism of their degradation has been elucidated. The structural and adsorption parameters of the sorbents have been evaluated. The results demonstrate that the introduction of amino groups into the structure of the polysiloxane yields an effective sorbent for Pb(II) extraction and enables Cu(II) and Zn(II) separation from Co(II) and Ni(II). The thiourea-modified polysiloxane selectively sorbs Bi(III) (0.1-2 M HCl), Pt(IV) (pH 2), and Pb(II) (pH > 3). Divalent Co, Ni, Cu, and Zn can be sorbed from alkaline solutions.

Full text of DOI:10.1134/S0020168511030174

ISSN 0020ꢀ1685, Inorganic Materials, 2011, Vol. 47, No. 4, pp. 435–441. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L.K. Neudachina, A.Ya. Golub, Yu.G. Yatluk, V.A. Osipova, Yu.A. Berdyugin, E.M. Gorbunova, L.V. Adamova, O.V. Koryakova, M.V. Kuznetsov, 2011,
published in Neorganicheskie Materialy, 2011, Vol. 47, No. 4, pp. 492–498.
Sorbents Based on Modified Polysiloxanes
L. K. Neudachinaa, A. Ya. Goluba, Yu. G. Yatlukb, V. A. Osipovab, Yu. A. Berdyuginb,
E. M. Gorbunovaa, L. V. Adamovaa, O. V. Koryakovab, and M. V. Kuznetsovc
a Gorki Ural State University, pr. Lenina 51, Yekaterinburg, 620083 Russia
b Postovskii Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences,
Akademicheskaya ul. 22, Yekaterinburg, 620990, Russia
c Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences, Pervomaiskaya ul. 91, Yekaterinburg, 620990
eꢀmail: Ludmila.Neudachina@usu.ru
Received June 7, 2010; in final form, September 21, 2010
Abstract—Organic–inorganic hybrid sorbents based on a polysiloxane modified with amino and thiourea
groups have been synthesized for the first time by a sol–gel process. The structure of the sorbents has been
determined by Xꢀray photoelectron spectroscopy and IR spectroscopy. Their thermal stability has been
assessed and the mechanism of their degradation has been elucidated. The structural and adsorption paramꢀ
eters of the sorbents have been evaluated. The results demonstrate that the introduction of amino groups into
the structure of the polysiloxane yields an effective sorbent for Pb(II) extraction and enables Cu(II) and
Zn(II) separation from Co(II) and Ni(II). The thioureaꢀmodified polysiloxane selectively sorbs Bi(III) (0.1–
2 M HCl), Pt(IV) (pH 2), and Pb(II) (pH > 3). Divalent Co, Ni, Cu, and Zn can be sorbed from alkaline
solutions.
DOI: 10.1134/S0020168511030174
INTRODUCTION
such polysiloxanes been investigated. Of particular
interest are the physicochemical characterization and
sorption properties of the following genetically related
sorbents: an unmodified polysiloxane (UMPS,
sorbent I), an aminopropylpolysiloxane (APPS, sorꢀ
bent II), and the aminopropylpolysiloxane modified
with thiourea (PSMT, sorbent III).
Polysiloxanes are unique modern inorganic materiꢀ
als widely used in industrial applications as lubricants,
coatings, and adhesives. In addition, modified polysiꢀ
loxanes are employed in gas chromatography [1] and as
components of membranes in potentiometric sensors
[2]. The study of the properties of organic–inorganic
materials based on silicon compounds for use as chelatꢀ
ing sorbents has been begun comparatively recently [3].
Chemically modified silicas have shown considerable
potential for concentrating transition and noble metal
ions owing to their high mass exchange performance
and the possibility of attaching almost any functional
group [4]. The highest ion exchange capacity among
organic–inorganic sorbents is offered by polysiloxanes.
The most effective approach to the preparation of polꢀ
ysiloxanes is sol–gel processing, which allows one to
produce sorbents with controlled pore structure, reduce
the swelling of the material, prevent disintegration of
the matrix through irreversible reactions involving side
groups, and ensure a uniform distribution of sorption
sites over the surface of the matrix [4]. As shown earlier
[5], thioureaꢀmodified polysiloxanes with are capable
EXPERIMENTAL
The starting chemicals used for the synthesis of the
sorbents were 3ꢀaminopropyltriethoxysilane (APTES,
98%, SigmaꢀAldrich) and tetraethyl orthosilicate
(TEOS, 98%, Acros Organics).
Synthesis of the UMPS. TEOS (31.25 g, 150 mmol)
was mixed with propylamine (4.12 cm3, 50 mmol) and
then water (10 cm3, 550 mmol) was added while the
mixture was cooled. The resultant gel was washed with
water at 70–80
1 wt %, ground, and dried to constant nitrogen content
at 100 . In this way, 7.21 g of the UMPS was obtained.
°С until the nitrogen content was below
°С
Synthesis of the APPS. TEOS (6.25 g, 30 mmol) was
mixed with water (3.49 cm3, 83 mmol) while cooling
of effectively extracting platinum from dilute solutions, and then APTES (1.5 cm3, 15 mmol) was added. The
but there have been no systematic studies of the compoꢀ resultant gel was dried to constant weight at 100°С,
sition, structure, or adsorption properties of such sorꢀ washed with water, and again dried. In this way, 3.28 g of
bents, nor has the sorption of transitionꢀmetal ions on the product was obtained.
435

436
NEUDACHINA et al.
Synthesis of the PSMT. The APPS (5.20 g, 17 mmol)
sorbent III,
was ground with hydrochloric acid (0.45 cm3, 19 mmol)
in a mortar. Ammonium thiocyanate was then added,
and the mixture was ground, heated to constant weight at
[2SiO2SiO1.5(CH2)3NH2]n + NH4SCN
HCl; 150
NH Cl
4
°C
150
chloride was negative, and dried to constant weight at
100 . We obtained 5.84 g of the PSMT.
°С ( 2 h), cooled, washed with water until the test for
[2SiO2SiO1.5(CH2)3NHCSNH2]n.
°С
Sorbent II ([2SiO2SiO1.5(CH2)3NH2]n) was preꢀ
pared by a sol–gel process (hydrolytic copolycondensaꢀ
tion of TEOS and APTES). The hydrolysis stage is typꢀ
ically catalyzed by dibutyltin diacetate [6]. However,
gelation then slows down and two phases may form,
IR spectra were measured from 400 to 4000 cm–1 on
a Thermo Nicolet 6700 Fourier transform IR spectromꢀ
eter. The PSMT was characterized by Xꢀray photoelecꢀ
tron spectroscopy (XPS) on a VG ESCALAB MK II
spectrometer (unmonochromatized Mg
radiation, leading to inhomogeneous gelation. Moreover, catalyst
Kα
1, 2
incorporation into xerogels may reduce their porosity.
The use of acids and alkalies as catalysts [7] is unnecesꢀ
sary in this system because the amino group of the
APTES acts as a base. The use of ammonium fluoride as
a catalyst [8] in the presence of methanol accelerates
the sol–gel transition, and no interface is formed, but
the polysiloxanes then have a porous structure only
when TEOS is present in excess. At the same time,
increasing the ratio of the alkoxysilanes reduces the
pore diameter [8], which may hinder the extraction of
large ions. In connection with this, the sorbent was synꢀ
thesized with no catalyst. Because the aminopropyl
group was considered an autocatalytic component [7],
sorbent I was synthesized in the presence of propyꢀ
lamine.
1253.6 eV). The thermal stability of sorbent samples was
assessed at temperatures from 40 to 800 in flowing
C/min using a Netzsch
olos gas analysis system.
The structural and adsorption parameters of the sorꢀ
bents were evaluated from lowꢀtemperature nitrogen
adsorption isotherms obtained using a Tristar 3020
automated surface area analyzer.
°С
argon at a heating rate of 10
°
STA 409 Luxx/QMS 403 C A
ё
To prepare a platinum(IV) solution, a weighed
amount of platinum metal was dissolved in heated aqua
regia. After boiling down the solution to dryness, conꢀ
centrated hydrochloric acid and crystalline sodium
chloride were added, the solution was again boiled
down to dryness, the dry residue was dissolved in hydroꢀ
chloric acid (1 : 1), and the solution volume was brought
to the mark with water in a volumetric flask. Metal soluꢀ
tions were prepared using appropriate salts of reagent
grade or higher purity. The solutions were standardized
chelatometrically. The acidity of the sorption solutions
was adjusted with a universal buffer mixture. Exact soluꢀ
tion pH values were determined by an Iꢀ130M ionꢀselecꢀ
tive meter. The background electrolyte used was potasꢀ
sium chloride. The sorption solutions were held in conꢀ
tact with the sorbent for 2 h. The amount of metal sorbed
was calculated from the difference between the initial and
equilibrium concentrations. The latter was determined
spectrophotometrically (Helios Alpha) and spectrometꢀ
rically (iCAP 6500 AES and Solaar M6 AAS).
Sorbent III ([2SiO2SiO1.5(CH2)3NHCSNH2]n) was
prepared by modifying the amino groups of sorbent II
with thiourea residues.
The synthesized sorbents had the form of white (I
and II) or yellowish (III) powders. The reduced conꢀ
tents of the atoms in sorbent III in comparison with the
nominal composition (table) points to a significant conꢀ
tent of absorbed water. The C/S ratio exceeds the nomꢀ
inal value. One possible reason for this is that sorbent III
contained aminopropyl groups that had not reacted
with the ammonium thiocyanate. The N/S atomic ratio
(2.38) exceeds the value that would be expected from
the structure of the thiourea group, which confirms the
presence of unmodified amino groups.
From the content of side groups, one can estimate
the maximum sorption capacity of the sorbent at
monolayer coverage.
RESULTS AND DISCUSSION
The sorbents were synthesized according to the folꢀ
lowing schemes:
The strong IR absorption band at 1000–1200 cm–1
(Fig. 1a) and its higher frequency shoulder (1200–
1250 cm–1) are commonly attributed to stretching
modes of the siloxane bonds in a matrix grafted with
molecules containing methylene groups [9]. The presꢀ
ence of such groups is supported by the absorption band
near 800 cm–1 [10]. There is a group of absorption
bands in the C–H stretching region (2800–3000 cm–1).
The broad band in the range 3000–4000 cm–1 cannot
be unambiguously assigned to O–H or N–H bonds, but
sorbent I,
+ H O, CH (CH ) NH
2 2
2
3
–EtOH
2
Si(OEt)4
sorbent II,
SiO2,
Si(OEt)4 + (EtO)3Si(CH2)3NH2
[2SiO2SiO1.5(CH2)3NH2]n,
H O
2
–EtOH
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SORBENTS BASED ON MODIFIED POLYSILOXANES
Elemental analysis of the polysiloxanes
437
Elemental analysis data, wt %: found (calculated)
Concentration of side
groups*, mmol/g
Sorbent
C/N molar ratio C/S molar ratio
Si
C
H
N
S
I
42.00
(46.74)
2.18
(–)
0.89
(–)
0.6
(–)
–
4.24
(–)
–
–
0.43
(–)
II
34.68
(36.57)
15.04
(15.64)
3.41
(3.50)
5.28
(6.10)
–
3.32
(2.99)
3.77
(4.57)
III
30.71
(29.13)
12.02
(16.61)
3.06
(3.14)
6.12
(9.73)
5.85
(11.08)
2.29
(1.99)
5.48
(3.99)
2.18
(2.91)
* Calculated from the elemental analysis data (from the relative amounts of the starting reagents).
all of the spectra contain the
δ(OH) band at 1620– sis loop [14] observed in the case of the APPS is due to
1650 cm–1, and the (NH) mode at 1560 cm–1 is charꢀ
δ
its porous structure and reflects the presence of uniꢀ
formly packed agglomerates of nearly monodisperse
spherical particles. This material has a rather broad pore
size distribution (Fig. 3, curve II). The H2 hysteresis
acteristic of nitrogenꢀcontaining species. The Si–O(H)
bonds show up near 940–960 cm–1. We failed to identify
the thiourea group in the structure of the PSMT
because of the overlap of thioamide groups: [ν(C–N) + loop in the isotherm of the PSMT is typical of many
ν
(C=S)] with
ν
(Si–O–Si);
δ(NH2)
ν(C=S) with ν(Si–C), and
porous adsorbents (e.g., inorganic oxides or porous
glasses), but the structural characteristics of the material
are difficult to describe [14]. Curve III in Fig. 3 repreꢀ
sents a narrow pore size distribution, but the peak has a
small shoulder on the largeꢀdiameter size, due to the
presence of two types of pores. The isotherm of the
ν(N–C–N) with
.
Figure 2a shows a wideꢀscan XPS spectrum of the
surface of the PSMT. The binding energies ( b) of the Si
Si 2 and O 1 electron levels (102.7 and 532.3 eV,
respectively) are close to those reported for poly(dimeꢀ
E
p
s
thylsiloxane) [11] and an aminopropylpolysiloxane [12] UMPS has a type H4 hysteresis loop, which reflects the
but differ from the Si 2
ica gels (103.3 and 533.3 eV, respectively [13]). The С 1
spectrum has two peaks, at 284.6 and 286.8 eV. These
states seem to be related to surface carbon contaminaꢀ
p and O 1s binding energies in silꢀ
presence of slitꢀshaped pores. The pore size distribution
is relatively narrow, with a wellꢀdefined wing on the
smallꢀdiameter side (Fig. 3, curve I).
s
tion. The XPS spectrum in the N 1
s
region (Fig. 2b)
(399.60 eV,
The average pore diameter decreases in the order
APPS (dpore = 19.3 nm) > UMPS (dpore = 10.7 nm) >
NH3+
indicates that the PSMT contains
88%) and NH2 (398.15 eV, 12%). The material also
PSMT (dpore = 5.7 nm). The pore volume decreases in
contains sulfur and chlorine, with the S 2
levels at 162.0 and 198.0 eV, respectively.
p and Cl 2p
the same order. The specific surface area increases in
the order APPS < PSMT < UMPS. In the three sorꢀ
bents, the pore diameter lies in the range 2–50 nm.
Therefore, the sorbents are mesoporous according to
Dubinin’s classification.
The lowꢀtemperature nitrogen adsorption–desorpꢀ
tion isotherms were sꢀshaped, with a capillary condenꢀ
sation hysteresis loop (in the relative pressure ranges
0.65–0.95, 0.8–1.0, and 0.45–0.95 for sorbents I, II,
and III, respectively). According to the IUPAC classifiꢀ
cation [14], they were type IV isotherms. Such isoꢀ
therms are characteristic of mesoporous sorbents and
represent a polymolecular adsorption process accomꢀ
The specific surface area of the sorbents (UMPS,
113.1 m2/g; APPS, 77.7 m2/g; PSMT, 107.2 m2/g) is
smaller in comparison with modified silicas [15] but
considerably exceeds that of the polysiloxane prepared
panied by capillary condensation. The type H1 hystereꢀ by Dobryanskaya et al. [8].
INORGANIC MATERIALS Vol. 47
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438
NEUDACHINA et al.
(а)
I
I I
I I I
3000
2000
Wavenumber, cm–1
1000
(b)
I
II
III
796.0
444.5
1076.4
1000
3000
2000
Wavenumber, cm–1
Fig. 1. IR spectra of the (I) UMPS, (II) APPS, and (III) PSMT (a) before and (b) after heat treatment at 800°С.
In the derivative thermogravimetry (DTG) curves of hermic peaks in the differential thermal analysis (DTA)
the three sorbents, the lowest temperature weight loss curves. Exposure to temperatures from 170 to 430
peak is located at 100–130 (Fig. 4) and is due to the leads to the thermal oxidation of the terminal amine
release of physisorbed water, as supported by the endotꢀ and thiourea groups, resulting in a weight loss in the
°С
°С
INORGANIC MATERIALS Vol. 47
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2011

SORBENTS BASED ON MODIFIED POLYSILOXANES
O 1
439
s
(а)
O(KVV
)
C 1
S 2s
s
Si 2p
Si 2
N 1
s
S 2
p
s
Cl 2
p
0
100
200
300
400
500
600
700
800
900
1000
Binding energy, eV
(b)
N 1
s
NH+3
(Eb = 399.6 eV)
NH2
(Еb = 398.15 eV)
390
395
400
Binding energy, eV
405
410
Fig. 2. (a) Wideꢀscan and (b) N 1s XPS spectra of the PSMT (MgKα Xꢀray source, 1253.6 eV).
0.20
0.15
0.10
III
I
II
0.05
0
5
10
15
20
25
30
Pore diameter, nm
Fig. 3. Pore size distributions of the (I) UMPS, (II) APPS, and (III) PSMT.
INORGANIC MATERIALS Vol. 47 No. 4 2011

440
NEUDACHINA et al.
0
100 200 300 400 500 600 700 800
log
1
D
I
7
1
2
6
0.05
0.10
0.15
0.20
5
1
2
3
DTG
DTG
DTG
UMPS
APPS
3
4
PSMT
0
Zn
3
4
4
5
6
DSC
DSC
DSC
UMPS
2
Pt
APPS
Co
1
PSMT
5
–1
Cu
Ni
0
ENDO
6
–1
0
1
2
3
4
5
6
7
8
9
10 11
pH
0
100 200 300 400 500 600 700 800
Temperature
, °C
log
4
D
Pb
II
Fig. 4.
(
1
2
–
,
3
5
) DTG and ( ) DSC curves of the (
) APPS, and (3, 6) PSMT.
4
–
6
1, 4)
Co
UMPS, (
3
three sorbents, particularly in PSMT. At temperatures
above 400 , all of the residual organics burn out, givꢀ
2
Ni
°С
1
ing rise to exothermic peaks in the DTA curves. Moreꢀ
over, at these temperatures the residual silanol groups
may condense. The assumed disintegration mechanism
was confirmed by mass spectrometry. The net weight
loss in the APPS reached 26%, which is very close to the
weight loss (about 24%) calculated under the assumpꢀ
tion that all of the side groups were eliminated and all of
the silanol groups were condensed. A similar picture
was observed for the PSMT. The quantitative burnout of
functional groups is supported by the IR spectra in
Fig. 1b: the O–H, N–H, and C–H modes disappear,
and only the modes of the siloxane backbone persist.
The thermal stability of the matrix in the temperature
range studied is indirectly supported by the small weight
loss, within 10%, in the unmodified polysiloxane.
Bi
0
Pt
–1
–2
Zn
Cu
–3
3
11
10
pH
0
2
6
9
1
5
7
4
8
log
6
D
III
Pb
Bi
5
4
3
2
1
The specifics of the sorption properties of the three
materials are well illustrated by the plots of the distribuꢀ
tion coefficient against solution pH for heavyꢀmetal
and platinum(IV) ions in Fig. 5. Sorbent I is not selecꢀ
tive for any of the ions studied (Fig. 5, panel I). The
introduction of amino groups into the structure of the
polysiloxane (sorbent II) yields a very effective sorbent
for Pb(II) extraction (the Pb distribution coefficient
reaches 104) (Fig. 5, panel II). In addition, it can be
used to separate Cu(II) and Zn(II) from Co(II) and
Ni(II) at pH 7–10. Sorbent III (Fig. 5, panel III)
enables selective extraction of Bi(III) (0.1–2 M HCl),
Pt(IV) (pH 2), and Pb(II) (pH > 3). Divalent Co, Ni,
Cu, and Zn ions can be sorbed from alkaline solutions.
Copper has the largest distribution coefficient, which
Pt
Cu
Co
Ni
Zn
3
2
1
0
1
2
3
4
5
6
7
8
9
10
pH
[HCl], M
Fig. 5. Acid–base dependence of metal ion sorption by the
(I) UMPS, (II) APPS, and (III) PSMT: = 0.0200 g,
g
sorb
d
= 0.075–0.100 mm,
τ
= 2 h.
grain
INORGANIC MATERIALS Vol. 47
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2011

SORBENTS BASED ON MODIFIED POLYSILOXANES
441
5. Golub, A.Ya., Neudachina, L.K., Yatluk, Yu.G., and
Berdyugin, Yu.A., Sorption of Platinum(IV) Ions by A
New Organosilicon Sorbent Containing Silylpropyl
allows one to separate copper from the other
tion metals in the absence of Pb.
3d transiꢀ
Thiourea Groups, Sorbtsionnye Khromatogr. Protsessy
,
2006, vol. 6, no. 6, pp. 1151–1156.
CONCLUSIONS
6. Khatib, I.S. and Parish, R.V., Insoluble Ligands and
Their Application: I. A Comparison of SilicaꢀImmobiꢀ
lized Ligands and Functionalized Polysiloxanes, J. Orgaꢀ
nomet. Chem., 1989, vol. 369, pp. 9–16.
7. ElꢀNahhal, I.M. and ElꢀAshgar, N.M., A Review on
PolysiloxaneꢀImmobilized Ligand Systems: Synthesis,
Characterization and Applications, J. Organomet.
Chem., 2007, vol. 692, pp. 2861–2886.
8. Dobryanskaya, G.I., Mel’nik, I.V., Zub, Yu.L., et al.,
Effect of the Si(OC2H5)4/(CH3O)3Si(CH2)3SH Ratio
on the Structure and Adsorption Properties of the
Resultant Xerogels and the Accessibility of Functional
Groups in Their Surface Layer, Zh. Fiz. Khim., 2006,
vol. 80, no. 6, pp. 1071–1077.
Mesoporous polysiloxanes with a large specific surꢀ
face area have been synthesized for the first time by a
sol–gel process. The matrix of the sorbents is thermally
stable up to 800°С. The presence of functional groups
lowers the thermal stability of the materials. The polysiꢀ
loxane functionalized with amino groups is an effective
sorbent for Pb extraction. The introduction of thiourea
groups enables the sorbent to be used to extract soft
Lewis acids, such as bismuth and platinum.
ACKNOWLEDGMENTS
9. Safa, K., Bahadori, A., Tofangdarzadeh, S., and Nasirtꢀ
abrizi, M., Trisyl Modification of Epoxyꢀ and Chloromꢀ
ethylꢀPolysiloxanes, J. Iran. Chem. Soc., 2008, vol. 5,
no. 1, pp. 37–47.
This work was supported by the Federal Agency for
Education through the federal targeted program Scienꢀ
tists and Teachers of Innovative Russia, 2009–2013
,
state contract no. P278, July 23, 2009.
10. Bois, L., Bonhomme, A., Ribes, A., et al., Functionalꢀ
ized Silica for Heavy Metal Ions Adsorption, Colloids
Surf., A, 2003, no. 221, pp. 221–230.
REFERENCES
11. Beamson, G. and Briggs, D., High Resolution XPS of
Polymers. The Scienta ESCA300 Database, New York:
Wiley, 1992.
12. ElꢀNahhal, I.M., Chechimi, M.M., Cordier, C., and
Dodin, G., XPS, NMR and FTIR Structural Characterꢀ
ization of PolysiloxaneꢀImmobilized Amine Ligand Sysꢀ
tem, J. NonꢀCryst. Solids, 2000, vol. 275, pp. 142–146.
13. Noller, H., Lercher, J.A., and Vinek, H., Acidic and
Basic Sites of Main Group Mixed Metal Oxides, Mater.
Chem. Phys., 1988, vol. 18, nos. 5–6, pp. 577–593.
14. Gregg, S.J. and Sing, K.S.W., Adsorption, Surface Area,
and Porosity, New York: Academic, 1982.
1. ElꢀNasser, A.A. and Parish, R.V., Solid Polysiloxane
Ligands Containing Glycineꢀ or Iminodiacetateꢀ
Groups: Synthesis and Application to Binding and Sepaꢀ
ration of Metal Ions, J. Chem. Soc., Dalton Trans., 1999,
no. 19, pp. 3463–3466.
2. Colilla, M., Darder, M., Aranda, P., et al., AminoꢀPolyꢀ
siloxane Hybrid Materials As Carbon Composite Elecꢀ
trodes for Potentiometric Detection of Anions, J. Mater.
Chem., 2005, vol. 15, pp. 3844–3851.
3. Zub, Yu.I. and Parish, R.V., Functionalized Polysiloxane
Sorbent: Preparation, Structure, Properties and Use,
Stud. Surf. Sci. Catal., 1996, vol. 99, pp. 285–299.
15. Losev, V.N., Silicas Chemically Modified with Sulfurꢀ
Containing Groups for Preconcentration, Separation,
and Determination of Noble and Nonferrous Metals,
4. Kudryavtsev, G.V., Bernadyuk, S.Z., and Lisichkin, G.V.,
Ion Exchangers Based on Modified Mineral Carriers,
Usp. Khim., 1989, vol. 58, no. 4, pp. 684–709.
Extended Abstract of Doctoral (Chem.) Dissertation
,
Tomsk: TPU, 2007.
INORGANIC MATERIALS Vol. 47
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