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3. Author's personal copy
Spray-dried porous silica microspheres functionalised by phosphonic acid groups
Inna V. Melnyk a,⇑
, Mohamed Fatnassi b
, Thomas Cacciaguerra b
, Yuriy L. Zub a
, Bruno Alonso b,⇑
a
Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, 17 General Naumov Street, Kyiv 03164, Ukraine
b
Institut Charles Gerhardt de Montpellier – UMR 5253 (CNRS/ENSCM/UM2/UM1) 8, rue de l’Ecole Normale, 34296 Montpellier Cedex 5, France
a r t i c l e i n f o
Article history:
Received 7 July 2011
Received in revised form 17 October 2011
Accepted 16 November 2011
Available online 30 November 2011
Keywords:
Spray-drying
Mesoporous materials
Sol–gel
Phosphonic acid
a b s t r a c t
Porous silica-based microspheres with pore surfaces functionalized by phosphonic acids are obtained for
the first time from a direct co-condensation route using two alkoxide precursors (Si(OEt)4 and
Si(OEt)3(CH2)2P(O)(OEt)2), surfactant self-assembly and spray-drying methods. The synthesis employs
octadecyltrimethylammonium bromide as template agent. The post-treatment of the microspheres in
boiling concentrated hydrochloric acid insures the hydrolysis of the ethoxy groups initially bound to
phosphorus in the organophosphonate–siloxane precursor, without destroying the morphological and
textural properties. Final porous materials have the chemical structure [SiO1.81(OZ)0.38]0.91[SiO1.35(OZ)0.29
(CH2)2P(O)(OH)2]0.09 (with Z @ H or Et), and posses interesting textural properties: SBET = 747 m2
gÀ1
, and
dp = 2.3 nm.
Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction
Mesoporous materials obtained by surfactant’s micelle templat-
ing methods and possessing pore surfaces functionalized by com-
plexing groups are of wide interest [1–11]. For sorption and
separation technologies, the shape and the particle size plays a key
role in both the internal and external diffusion of the chemical spe-
cies. Spray-drying is a simple, continuous and scalable process [12]
that can be used for the production of mesoporous microspheres
[13,14]. The surfactant nature (ionic character, size, hydrophilic-
lipophilic balance) and quantity will determine the textural proper-
ties [14]. In turn, this will allow in optimizing the diffusion of the
species to be complexed inside the materials. In addition, the selec-
tivity and efficiency of the complexation is insured by the nature of
the functional groups covering the pore surface. The two main strat-
egies to functionalize silica pore surfaces consist in either a grafting
step on already formed porous samples, either a direct co-condensa-
tion route allowing the formation of the final material more directly.
The advantages and drawbacks of both strategies have been already
discussed [2]. The co-condensation route is attractive by the more
homogeneous spatial distribution of functional groups that can be
expected. However, the control of the textural properties is more dif-
ficult, in particular because of the additional interactions between
the functional groups and the surfactants or the organometallic pre-
cursors. Also, the functional groups can be incorporated in not acces-
sible areas. We have already solved these problems for the
incorporation of small organic groups (Me, Ph) using a co-condensa-
tion route and spray-drying siloxane oligomers’ sols [15]. The idea
was to separate in time the hydrolysis of the tetralkoxysilane (Q
units’ precursors) allowing for the formation of the siloxane oligo-
mers possessing an optimal size for the final morphological and tex-
tural properties, and the co-condensation on these oligomers of the
organosiloxane units bearing the desired functional groups (T units).
This idea was extended later to the mercaptopropyl organic groups
[16]. And the thiol functional groups incorporated were able to
quickly complex silver cations in stoichiometric amounts.
In this article, we report our first results on the direct functional-
ization of silica’s surfaces with phosphonic acid groups inside spray-
dried mesoporous microspheres. Compared to previous works on
spray-dried functionalized mesoporous microspheres [15–18],
there is a supplementary difficulty as it is necessary to hydrolyze
the phosphonate ester groups incorporated by the co-condensation
route, without destroying the texture and structure of the materials.
According to Refs. [19,20], nanoparticles made of silica with
phosphonic groups using a template synthesis are used in the
development of drug delivery systems [20] and as filling materials
in order to enhance proton conductivity [19]. Therefore, the devel-
opment of methods for the synthesis of mesoporous silica micro-
spheres with pore surfaces functionalized by phosphonic acids,
and the further study of their properties, as suggested in this paper,
is an important task.
2. Experimental
2.1. Syntheses
2.1.1. Sol preparation
In a typical synthesis, tetraethoxysilane 11.24 g (TEOS,
Si(OC2H5)4, 98%, Aldrich), isopropanol 36.12 g (i
PrOH, 99.9%, APC)
1387-1811/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.micromeso.2011.11.038
⇑ Corresponding authors. Tel.: +38 (0)44 4229630; fax: +38 (0)44 4243567 (I.V.
Melnyk), tel.: +33 (0)4 67 16 34 68; fax: +33 (0)4 67 16 34 70 (B. Alonso).
E-mail addresses: melnyk_inna@isc.gov.ua (I.V. Melnyk), bruno.alonso@enscm.fr
(B. Alonso).
Microporous and Mesoporous Materials 152 (2012) 172–177
Contents lists available at SciVerse ScienceDirect
Microporous and Mesoporous Materials
journal homepage: www.elsevier.com/locate/micromeso
4. Author's personal copy
and an acidic aqueous solution 10.81 g (HCl, 0.1 M) are mixed to-
gether. The solution is stirred in a closed vessel at 297 K during
46.5 h. Diethylphosphanatoethyltriethoxysilane 1.97 g (DPETES,
(C2H5O)3Si(CH2)2P(O)(OC2H5)2, 95%, Aldrich) is then added. Again,
the solution is stirred in a closed vessel at room temperature dur-
ing a 5.5 h. Octadecyltrimethylammonium bromide 3.78 g (OTAB,
[CH3(CH2)17N(CH3)3]Br, 99%, Fluka) is added and dissolved under
vigorous stirring 15 min before spray-drying. The molar propor-
tions TEOS:DPETES:H2O:OTAB are fixed to 0.9:0.1:10:0.16.
As described previously we use i
PrOH as solvent because it gives
more ordered textures rather than other small alcohols within our
spray-drying conditions [21]. Acid catalysts are used for EISA pro-
cesses and for co-condensation reactions. HCl is chosen here be-
cause of its volatility.
2.1.2. Spray-drying
Spray-drying was undertaken using a Büchi Mini-Spray Dryer
B-290 apparatus fitted with a two-fluid nozzle (inner diameter of
0.7 mm, sol and compressed air volume flow rates fixed to 0.34
and 357 L hÀ1
respectively), and an inert loop containing a de-
humidifier and a solvent condensation unit. The spray-drying gas
was dried nitrogen. The inlet and outlet temperatures were 373
and 333 K respectively. An overpressure of 3 kPa before gas filter-
ing insured small particle residence times (%1 s), and particle col-
lection by a cyclone. The collected powders are dried for 72 h at
333 K (final yield about 70%). They correspond to sample A.
OTAB from the as-synthesized material was removed by stirring
the sample in boiling ethanol for 3 h and four times (100 cm3
EtOH
per 1 g of a sample). The hot suspension was filtered and the pre-
cipitate was dried in air for 3 days (sample B). For the hydrolysis of
ester groups the derived powder material was refluxed in concen-
trated HCl (10 cm3
HCl per 1 g of a sample). After this a precipitate
was filtered, washed with 4 dm3
of distilled water and dried in vac-
uum at 353 K for 6 h (sample C). All the procedures have been
found to be reproducible.
2.2. Characterization
X-Ray diffraction (XRD) powder patterns were collected on a
DRON 4-07 diffractometer using Cu-Ka radiation, 2h scanning
was carried out in the region of 1.0–8.0° at a speed of 0.5° minÀ1
.
Complementary small angle XRD patterns were obtained from a
Bruker AXS D8 diffractometer.
Transmission electron microscopy (TEM) analysis was under-
taken on a JEOL 1200 EX2 microscope operating at 100 kV. After
grinding, the calcined samples were embedded in a resin and cut
into slices ($70 nm thick) with an ultramicrotome.
The morphology is studied by scanning electron microscopy
(HITACHI 4800 S or JEOL JSM-6060LA electron microscopes) or
by light scattering granulometry (Malvern Mastersizer 2000).
IR spectra in the 4000–400 cmÀ1
region were recorded on a
spectrometer Thermo Nicolet Nexus FTIR using diffuse reflectance
‘‘SMART Collector’’ at a resolution of 8 cmÀ1
. Samples were mixed
with pre-calcined KBr in a ratio of 1:20.
1
H (m0 @ 400.1 MHz), 29
Si (m0 @ 79.5 MHz) and 31
P (m0 @ 162.0
MHz) solid-state NMR MAS spectra were recorded on a Varian
400 spectrometer. 1.6 mm rotors span at 40 kHz were used for
1
H and 31
P experiments, and 7.5 mm rotors span at 4–5 kHz for
29
Si. 1
H single pulse sequences employed 90° pulses (2.5 ls) and
5 s recycle delays. 29
Si single pulse sequences employed 30° pulses
(1.7 ls) and 60 s recycle delays. 31
P single pulse sequences em-
ployed 45° pulses (1 ls) and 10 s recycle delays. 1
H, 29
Si and 31
P
chemical shifts were referenced using the secondary references:
adamantane (d = 1.75 ppm), TMS (d = 0 ppm) and K2HPO4
(d = 4.1 ppm), respectively. Deconvolution of NMR spectra and
XRD patterns were done using the least square fitting procedures
implemented in the dmfit software freely available from the web
(http://www.nmr.cemhti.cnrs-orleans.fr/dmfit/).
The siloxane condensation degree c is defined as the average
fraction of siloxane Si–O–Si bonds around the Si units over all
the possible siloxane bonds. For the Q units it is calculated using:
c ¼
X
ði:%QÞ
h i
= imax
X
ð%QÞ
h i
where i is the number of siloxane bonds around the related Qi
silox-
ane unit, and imax the maximum of these bonds (imax = 4 for Q units).
‘‘% Qi
’’ are the percentages for each unit type. They are obtained
from 29
Si NMR spectrum deconvolution using the dmfit software
and Gaussian peaks of variable position, amplitude and width.
The same procedure is used for the T units, replacing Qi
by Ti
and
using imax = 3.
N2 sorption isotherms measured at 77 K were recorded using a
Micromeritics Tristar apparatus. Sample outgassing was achieved
at 323 K until a stable static vacuum of 3mTorr (0.4 Pa) was
reached.
Elemental analyses were done at the CNRS facility ‘‘Service Cen-
tral d’Analyse’’ (Vernaison, France).
3. Results and discussion
3.1. Sol preparation
Our first goal was to produce sols containing siloxane oligomers
with optimal characteristics (size, surface) [21,22] and bearing the
phosphonate groups. Siloxane sols are prepared through hydrolysis
and condensation reactions starting with alkoxide monomer pre-
cursors. The alkoxides TEOS and DPETES form respectively Q units
Si(OZ)4 and T units Si(OZ)3CH2CH2PO(OEt)2 (Z @ H, R). As shown in
Scheme 1, these alkoxides are added at two different steps in order
to produce siloxane oligomers possessing Q units at their core, and
co-condensed T units at their surface [15,16]. Most of the parame-
ters of the sol preparation (Scheme 1) are fixed according to the ex-
pected properties or to our previous knowledge on spray-dried
microspheres; namely: f = 0.1; h = 10; i = 10; s = 0.16; D2 % 6 h.
It is known that when the first aging time D1 varies, the extent
of hydrolysis and condensation reactions varies, and hence the
characteristics of the siloxane oligomers (size, pendent reactive
groups) [21–23]. Smaller sol aging times usually lead to delayed
gelification and solidification processes. As a consequence, more
ordered textures are obtained, but also more agglomerated mor-
phologies. In the case of phosphonic functionalized spray-dried sil-
icas, we have tested three different aging times D1: 24, 48 and 72 h.
When decreasing the aging time, we observe an increase in texture
ordering (thinner and better resolved peaks), but also an increase
in spheres’ agglomeration (higher particles’ diameter in average),
Scheme 1. Sol preparation.
I.V. Melnyk et al. / Microporous and Mesoporous Materials 152 (2012) 172–177 173
5. Author's personal copy
as expected [22]. The aging time D1 = 48 h is here a good
compromise.
We also studied the effect of alkyltrimethylammonium bromide
surfactant chain length n on the texture. We observe that the cell
parameter estimated from XRD increases as a function of n
(Fig. 1) as also expected and following a trend already found for
some other inorganic [24,25] or hybrid [26,27] mesoporous mate-
rials (with p6m phases). In that sense, the use of surfactants with
variable chain length is an interesting opportunity for the modula-
tion of the pore sizes. However, the degree of ordering also de-
creases when decreasing n, as it could be observed previously
[24]. Although this effect might be counterbalanced by introducing
a constant volume fraction of surfactant instead of a constant mo-
lar proportion s, we only consider the longer octadecyltrimethy-
lammonium bromide surfactant in the following.
In our standard synthesis, the sol is then prepared using
TEOS:DPETES:H2O:OTAB with molar proportions 0.9:0.1:10:0.16,
following Scheme 1 and the D1 and D2 aging times (48 and 6 h).
After spray-drying, the collected powder is dried for 72 h at
333 K and results in sample A.
3.2. Post-syntheses treatments
In order to remove the surfactant and to liberate the porosity,
but also to hydrolyze the phosphonate groups, we plan and opti-
mize a series of post-treatments on our as-synthesized micro-
spheres (sample A). After different trials, we end up with the
following successful procedure. The extraction of most of the sur-
factant molecules was achieved using hot and refluxing ethanol
(sample B). Further, the hydrolysis of the phosphonate ester into
a phosphonic function was realized using harsh and simple condi-
tions by stirring the sample into boiling and concentrated HCl
(37.5%). In the final sample C, elemental analyses confirmed that
the molar ratio P/Si remains equal to 0.10 (±0.01). It should be
noted that the boiling in ethanol does not result in complete re-
moval of template OTAB according to IR spectroscopy (see below).
Its characteristic absorption bands disappear only in the IR spec-
trum of sample C.
3.3. Morphology
The functionalized porous particles have a spherical morphol-
ogy as observed by SEM and light scattering. Average micro-
sphere’s diameters are around 1 lm (number-average size
distribution). It is important to notice that after the different
post-treatments, the final sample C is made of well separated
microspheres (Fig. 2). This morphology and dimensions favor a
high diffusion of the chemicals from the solution to the core of
the particles, as it can be expected for sorption applications.
3.4. Texture
The X-Ray diffractogram of un-treated sample A (Fig. 3(a)) pres-
ent a main and wide peak at low angle ($2°) and smaller wide
peaks (at $4°). This pattern can be assigned to a mixture of meso-
phase domains: ordered (p6mm space group, diffracting peaks:
100, 110, 200) and non-ordered (scattering peaks). This feature
is typical of surfactant templated silica microspheres obtained
through spray-drying [15,21,22]. After ethanol treatment, the dif-
fraction peaks related to the ordered phase have almost disap-
peared (single scattering peak observed at small angle). Both
samples B and C might correspond then to homogeneous non-
ordered phases. This is confirmed by TEM analysis on sample C
(Fig. 3(b)). No ordered domain was observed in any part of the cut-
ted microspheres. The N2 adsorption–desorption isotherms of sam-
ple C are of type II according to IUPAC convention [28]. Indeed, the
pore size is only slightly above the micropore range (dp = 2.3 nm).
The BET specific surface area SBET is 747 m2
gÀ1
and Vs = 0.17
cm3
gÀ1
.
3.5. Siloxane network
From 29
Si NMR spectra (Fig. 4), we conclude that the molar pro-
portion of Q and T units fixed in solution to 9:1 is preserved over
the different treatments as also concluded from elemental analyses
(vide supra). In that sense, our procedure for anchoring T on Q units’
oligomers is effective and robust. In addition, by comparing and
modeling the 29
Si NMR spectra of samples A and C, we noticed that
the condensation degree increases from 0.84 to 0.91, and from 0.82
to 0.90 for Q and T units respectively. The post-treatments favor in-
deed the extent of the polycondensation process.
The existence of three-dimensional polysiloxane network in the
samples is confirmed by the presence of the most intense absorp-
tion band in the region 1030–1080 cmÀ1
of IR spectra (Fig. 5),
which refers to mas(SiOSi). When polysiloxane samples contain sil-
icon atoms surrounded by O3SiC, this absorption band usually has
a broad intense high-frequency shoulder [29] (Fig. 5).
3.6. Surface groups
DPETES is identified by the absorption band of m(P@O) at
1241 cmÀ1
in the IR spectrum [30]. For the IR spectra of xerogels,
containing the surface functional groups „Si(CH2)2P(O)(OC2H5)2
or „Si(CH2)2P(O)(OH)2 [30], this absorption band shifts to
30
32
34
36
38
40
42
44
46
48
50
11 12 13 14 15 16 17 18 19
Chain length n
Cellparametera(A)
Fig. 1. Variations in cell parameter a (p6mm space group considered) and
surfactant chain length n. The line results from a least squares regression fit
(a = 2.08 n + 9.29 Å, with v2
> 0.99).
Fig. 2. Morphology of functionalized microspheres. SEM micrographs of sample C.
174 I.V. Melnyk et al. / Microporous and Mesoporous Materials 152 (2012) 172–177
6. Author's personal copy
low-frequency region (because of the participation of „P@O in
hydrogen bond) and often cannot be identified. This is because it
is masked by the intense high-frequency shoulder of mas(SiOSi)
band (see above). The same situation is observed for the samples
A, B, and C (Fig. 5): the band corresponding to „P@O groups (at
1220 cmÀ1
) overlaps with vibrational band arising from polysilox-
ane network (in the region 1100–1200 cmÀ1
).
Moreover, the presence of „Si(CH2)2P(O)(OC2H5)2 functional
groups in the surface layer ensures the appearance of five absorp-
tion bands of medium intensity in the range 1350–1500 cmÀ1
of IR
spectra, four of which (at $1370, $1395, $1445, and $1480 cmÀ1
)
are associated with variations of ethoxygroups near phosphorus
atom [30]. However, for sample A the last two of them are masked
by an intense absorption band at 1480 cmÀ1
, characteristic for
deformation vibrations of methylene groups of OTAB (Fig. 5). This
is also observed for sample B, indicating incomplete removal of the
template by boiling with ethanol (Fig. 5). In the IR spectrum of
sample C, there is only one low-intensity absorption band at
$1413 cmÀ1
in this region (Fig. 5), which can be assigned to defor-
mation vibrations d((Si)CH2) of ethyl fragment in „Si(CH2)2P(O)@
groups [31]. The presence of this later band in the spectrum of C
and the absence of the four bands testify to the completeness of
hydrolysis of ester groups. We note that at about 1645 cmÀ1
there
is the absorption band d(H2O) in the IR spectra, indicating the pres-
ence of water. In the IR spectrum of C, it seems to overlap with the
absorption band corresponding to one of the oscillation fragment –
P(O)(OH)2 [31]. The presence of water, participating in hydrogen
bonds, is confirmed by the broad absorption band above
3100 cmÀ1
in the IR spectra (Fig. 5).
From these first characterizations, we can conclude that the
general formula of the siloxane skeleton in sample C is
[SiO2Àn/2(OZ)n]0.9[SiO1.5Àm/2(OZ)m(CH2)2P(O)(OH)2]0.1, with Z @ (H
1 2 3 4 5 6
100
110 200
Intensity(a.u.)
2theta (o
)
2 4 6 8
2theta (o
)
Intensity(a.u.)
А
B
C
0.0 0.2 0.4 0.6 0.8 1.0
0
50
100
150
200
250
VolumeN2
adsorbed(cm
3
/g)
Relative Pressure (P/Po)
(e)
(a) (b)
Fig. 3. Texture of functionalized microspheres: (a) XRD pattern for samples A, (b) XRD patterns for samples A, B and C, (c) TEM micrograph of sample A, (d) TEM micrograph
of sample C, (e) N2 sorption (d) desorption (s) isotherms at 77 K of sample C.
I.V. Melnyk et al. / Microporous and Mesoporous Materials 152 (2012) 172–177 175
7. Author's personal copy
or Et). From the estimated siloxane condensation degrees, we have:
n = 4 (1Àc) = 0.38 and m = 3 (1Àc) = 0.29. The molar ratio is P/Si is
0.10 from elemental analyses, and 0.09 from NMR. Therefore, the
more condensed formula can be written [SiO1.81(OZ)0.38]0.91
[SiO1.35(OZ)0.29(CH2)2P(O)(OH)2]0.09.
From 1
H spectra we are also able to follow the effects of the
post-synthetic treatments (Fig. 6). In particular, we observe a
strong decrease in the relative intensity of bands associated to
the surfactant molecule OTA+
. Also, a band related to water mole-
cules in interaction with silanol groups [17,32–34] is emerging
after hydrolysis of the phosphonate ester groups, indicating possi-
bly a higher degree of hydrophilicity.
31
P solid-state NMR MAS spectra are presented in Fig. 7. In the
spectrum of sample A, a main wide peak is located at 35 ppm and
is related to pendent ethyl phosphonate functional groups -
CH2PO(OEt)2 [35–37]. It also presents a wider peak at 27 ppm
which relative area is 10% of the signal. This feature – two peaks
8 to 10 ppm away in 10:1 proportions – is relatively common for
silica surfaces functionalized by phosphonate esters [36] or phos-
phonic acid [36,38–40] functional groups. The smallest peak is usu-
ally related to phosphonate or phosphonic groups in interaction
with silica [36,40], in relatively good agreement with former stud-
ies in solution [38]. Here we carefully assign the shoulder to a dis-
tribution of –CH2PO(OEt)2Ày(OSi)y moieties with 1 6 y 6 2. After
ethanol post-treatment, sample B has almost the same 31
P spec-
trum, only the relative areas of the two peaks significantly change.
The increase of the shoulder assigned to –CH2PO(OEt)2Ày(OSi)y can
be an effect of the higher temperature used for surfactant extrac-
tion. After acid post-treatment, the whole 31
P spectrum of sample
C is shifted. The main peak is located now at 32 ppm, the typical
value for the pendent phosphonic acid functional groups –
CH2PO(OH)2 [36,37,40–42]. In accordance with above, the shoulder
is assigned to a distribution of –CH2PO(OH)2Ày(OSi)y groups with
1 6 y 6 2. Its relative area (15%) shows that part of the phosphonic
functional groups might not be free for further complexation pro-
cesses. Overall, 31
P analysis demonstrates without ambiguity that
the hydrolysis of the phosphate ester into phosphonic acid func-
tional groups is fully achieved with our acid post-synthesis
treatment.
3.7. Accessibility of surface groups
From acid base titration on sample C, the quantity of accessible
phosphonic functional groups to water is 0.9 mmol gÀ1
; a value
that is very close to the total amount of phosphonic functional
groups from elemental analysis on P (1.0 mmol gÀ1
). The small dif-
ference (ca. 10%) could arise from the presence of P–O–Si linkages
discussed above. However 90% of phosphonic groups in the sample
C is available and can participate in complexation reactions. Fur-
ther on, the sorption properties towards lanthanide ions in solution
have been studied in a parallel work [43].
4. Conclusions
Based on the foregoing we can conclude that the spray-drying
method is successfully developed for producing spherical silica-
based sorbents containing a surface layer made of phosphonic acid
functional groups. It was established that the use octadecyltrime-
thylammonium bromide as the template agent in the spray-drying
procedure, associated to post-treatments allows the formation of
microspheres with a porous structure in the micro-/meso-limit
(dp = 2.3 nm) and a high specific surface area (SBET = 747 m2
gÀ1
).
The use of boiling hydrochloric acid in the last post-treatment al-
lows for a complete hydrolysis of the ester phosphonate groups
29
Si chemical shift / ppm
A
C
-150-130-110-90-70-50-30
T units
Q units
Fig. 4. Solid-state 29
Si NMR spectra of samples A (top) and C (bottom).
Fig. 5. FTIR spectra of functionalized microspheres, samples A, B and C.
1
H chemical shift / ppm
A
B
C
-20246810
CH3-CH2-……CH2-CH2-CH2…
CH3-N…
H2O HOSi…
Fig. 6. Solid-state 1
H NMR spectra (from top to bottom: samples A, B and C).
176 I.V. Melnyk et al. / Microporous and Mesoporous Materials 152 (2012) 172–177
8. Author's personal copy
without a concomitant destruction of the siloxane skeleton and the
porous structure. After the different steps, the chemical structure
as deducted from 29
Si NMR is [SiO1.81(OZ)0.38]0.91
[SiO1.35(OZ)0.29(CH2)2P(O)(OH)2]0.09 (with Z @ H or Et). Using 31
P
solid-state NMR MAS spectroscopy it was shown that approxi-
mately, 15% of phosphonic acid groups interact with the siloxane
surface with the possible formation of new bonds –P–O–Si–. This
feature decreases the accessibility of the phosphonic functional
groups only in small proportions. The obtained spray-dried micro-
spheres are perspective under study of the removal of lanthanide
and actinide ions from aqueous solutions.
Acknowledgements
CNRS and NAS of Ukraine are gratefully acknowledged for fund-
ing bilateral collaboration (project no 23996). I.V. Melnyk and Yu.L.
Zub thank State Target Scientific and Technical Program of NAS of
Ukraine ‘‘Nanotechnologies and Nanomaterials’’ (project 6.22.5.42)
for partial financial support of this research. P. Peralta and P. Ga-
veau from ICG Montpellier are acknowledged for their help in
spray-drying and NMR experiments, respectively.
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31
P chemical shift / ppm
1020304050
δ = 35 ppm
~90 %
δ = 35 ppm
~80 %
δ = 32 ppm
~85 %
δ = 27 ppm
~10 %
δ = 28 ppm
~20 %
δ = 23 ppm
~15 %
A
B
C
Fig. 7. Solid-state 31
P NMR spectra (from top to bottom: samples A, B and C). The
given isotropic chemical shifts and relative percentage areas are obtained after
spectrum deconvolution using pseudo-Voigt functional groups.
I.V. Melnyk et al. / Microporous and Mesoporous Materials 152 (2012) 172–177 177
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