The term ‘poly-silsesquioxane’ is related to the elemental silicon/oxygen ratio of RSiO1,5substructures sesqui lat.—one and a half and there-fore designates hybrid materials synthesized
Trang 1Nanostructured polysilsesquioxanes bearing amine and ammonium groups by micelle templating using anionic surfactants†
Thy Phuong Nguyen,abPeter Hesemann,*aThi My Linh Tranband Jo€ el J E Moreaua
Received 3rd December 2009, Accepted 23rd February 2010
First published as an Advance Article on the web 18th March 2010
DOI: 10.1039/b925352a
We report the synthesis of new mesoporous nanostructured polysilsesquioxanes by
hydrolysis–polycondensation procedures of silylated amine or ammonium precursors The
formation of materials with defined architectures and pore arrangements on a mesoscopic length scale
was achieved via soft-templating approaches using anionic surfactants as structure directing agents
For the first time, nanostructured polysilsesquioxanes were obtained with anionic surfactants following
a SI+pathway Structuring was achieved due to electrostatic interactions between the cationic centers
of ammonium precursors and the anionic head group of the sulfate surfactant This study highlights
that specific precursor–surfactant interactions are essential for the formation of nanostructured
materials The obtained new materials are useful for the immobilization of metallic species via the
formation of coordination complexes or anion exchange reactions and therefore have high potential as
heterogeneous catalysts or adsorbents
Introduction
The synthesis of ordered silicates via soft-templating approaches
has attracted tremendous interest since its discovery in 1992.1,2
This strategy opened the door to a large variety of siliceous
materials featuring narrow pore size distribution and regular 2D
or 3D arranged pore structures on a mesoscopic length scale
Simultaneously, polysilsesquioxanes emerged as a new class of
functional organic–inorganic hybrid materials.3,4 These solids,
obtained from bridged silylated organic precursors, are
charac-terized by a homogeneous distribution of organic substructures
within the materials’ framework on a molecular level and contain
covalently linked organic substructures The term
‘poly-silsesquioxane’ is related to the elemental silicon/oxygen ratio of
RSiO1,5substructures (sesqui (lat.)—one and a half) and
there-fore designates hybrid materials synthesized by sol–gel
trans-formation of bridged organic precursors, without addition of
a silica source such as TEOS or TMOS.5In this field, functional
materials bearing chiral, metal complexing and p-conjugated
substructures for applications in heterogeneous asymmetric
catalysis, separation and optics were reported.6–10On the other
side, structured polysilsesquioxanes with defined architectures
from the molecular to the microscopic level have also been
described.11–13
Porous polysilsesquioxanes featuring regular pore architectures were only reported in 1999.14–16These so-called periodic meso-porous organosilicas (PMOs)17,18were originally obtained from rather simple precursors such as 1,2-bis(trialkoxysilyl)ethane, bis(trialkoxysilyl)ethylene, 1,4-bis(trialkoxysilyl)benzene or 2,5-bis(trialkoxysilyl) thiophene.19Special attention was paid to the control of the architecture and morphologies of PMO type materials For example, solids with crystal-like wall structures20–22 and materials displaying controlled size and shape such as nanofibers or coiled shaped particles were recently reported.23–25
More recently, PMO type materials bearing more complex organic substructures have been described, i.e chiral frag-ments,26–30 p-conjugated segments31,32 or chelating entities.33 Bifunctional PMOs bearing more than one type of organic substructure have also been reported The incorporation of multiple bridging groups allows to fine tune the surface proper-ties of PMOs and to achieve the desired functionality and selectivity.34–40 The expression ‘PMO’ refers to the textural properties of this kind of material, in particular to their regular architecture and porosity on a mesoscopic length scale Although several PMO type materials were synthesized by hydrolysis– polycondensation procedures of ‘pure’ bridged silylated precursor molecules, PMOs are in many cases obtained by co-condensation involving bridged organic precursors and silica network formers such as TMOS or TEOS.17 The addition of silica precursors is often necessary in order to generate sufficient mechanical stability which is necessary for the creation of porosity and order within functional siliceous materials espe-cially when flexible and sterically demanding silylated organic substructures were used.41–44
Similar to nanostructured silica phases, PMO type materials are usually synthesized via soft-templating approaches using cationic or nonionic surfactants Structuring of PMOs is gener-ally governed either by electrostatic interactions between cationic
a Institut Charles Gerhardt de Montpellier, UMR CNRS 5253, Equipe
Architectures Mol eculaires et Mat eriaux Nanostructur es, 8, rue de
l’Ecole Normale, 34296 Montpellier Cedex 05, France E-mail: peter.
hesemann@enscm.fr; Fax: +33 4 67 14 43 53; Tel: +33 4 67 14 72 17
b Faculty of Chemistry, Hanoi University of Science, 19 Le Thanh Tong,
Hanoi, Vietnam
† Electronic supplementary information (ESI) available: 1 H NMR and
FT-IR spectra of precursor 1; FT-IR spectrum of material A;
TGA-plots of materials A, B and C; BJH dV/dlog(D) pore volume
distribution of materials A–E; 29 Si OP MAS NMR spectra and 13 C CP
MAS NMR spectra of materials B, D and E, 29 Si OP MAS NMR
spectrum of material C See DOI: 10.1039/b925352a
Trang 2surfactants and anionic silanolates in basic reaction media
(S+I-pathway) or by hydrogen bonding between di- or triblock
copolymer and silanols under acidic conditions (S0I0-pathway).17
Here we report the first example for the design of ordered pore
arrangements within polysilsesquioxanes using anionic structure
directing agents following an SI+-pathway This approach
fundamentally differs from other synthetic strategies for the
formation of PMO type materials We show that the formation
of structured solid phases can be induced by strong electrostatic
interactions between anionic surfactant and the organo-ionic
part of a cationic precursor molecule Contrary to conventional
PMO synthesis, in this study, the silyl groups have no or little
influence on the formation of nanostructured solid phases
Since several years, our special concern is the elaboration of
nanostructured siliceous materials bearing ionic substructures.45–48
Here, we report that cationic ammonium precursor in the
pres-ence of anionic structure directing agents lead to
poly-silsesquioxanes displaying hexagonally arranged pore structures
A related strategy has been used for the synthesis of
nano-structured silicas,49,50 but anionic surfactant templated
meso-porous polysilsesquioxanes have never been reported yet
We studied in particular the syntheses of mesoporous
nanostructured functionalized PMO materials from the
tris-(3-(trimethoxysilyl)propyl)amine precursor 1 and the cationic
ammonium precursors 2 and 3 (Scheme 1) As all materials were
synthesized by hydrolysis–polycondensation of the sole
precur-sors without addition of silica precurprecur-sors such as TEOS or
TMOS, the obtained solids can be described as mesoporous
nanostructured polysilsesquioxanes
2 Experimental
General details
3-Aminopropyltrimethoxysilane, 3-(chloropropyl)-trimethoxysilane
and the anionic surfactant sodium hexadecyl sulfate (containing
40% sodium stearyl sulfate) were purchased at ABCR The
surfactants P123 and CTAB were purchased at Aldrich.1H and
13C spectra in solution were recorded on Bruker AC 250 or
Bruker Avance 400 spectrometers at room temperature
Deuterated chloroform was used as solvent for liquid NMR
experiments and chemical shifts are reported as d values in parts
per million relative to tetramethylsilane IR samples were
prepared as KBr pellets FT-IR spectra were measured on
a Perkin-Elmer 1000 FT-IR spectrometer MS-ESI were
measured on Water Q-Tof mass spectrometer
Solid state 13C and 29Si CP MAS NMR experiments were
recorded on a Varian VNMRS 400 MHz solid spectrometer
using a two channel probe with 7.5 mm ZrO2rotors The 29Si
solid state NMR spectra were recorded using both CP MAS and
One Pulse (OP) sequences with samples spinning at 6 kHz CP
MAS was used to get high signal to noise ratio with 5 ms contact time and 5 s recycling delay For OP experiments, p/6 pulse and
60 s recycling delay were used to obtain quantitative information
on the silane–silanol condensation degree The 13C CP MAS spectra were obtained using 5 ms contact time, 5 s recycling delay and 5 kHz spinning rate The number of scans was in the range 1000–3000 for29Si OP MAS spectra and of 2000–4000 for13C CP MAS spectra Nitrogen sorption isotherms at 77 K were obtained with a Micromeritics ASAP 2020 apparatus Prior to measurement, the samples were degassed for 18 hours at 100C The surface areas (SBET) were determined from BET treatment in the range 0.04–0.3 p/p0 and assuming a surface coverage of nitrogen molecules estimated to be 13.5 A˚2 Pore size distribu-tions were calculated from the adsorption branch of the isotherms using the BJH method The pore width was estimated
at the maximum of the pore size distribution TEM images were obtained using JEOL 1200 EX II (120 kV) XRD experiments were carried out with an Xpert-Pro (PanAnalytical) diffrac-tometer equipped with a fast X’celerator detector using Cu-Ka radiation TGA experiments were performed with a TA Instru-ments Q50 apparatus The samples were heated under an air stream from 50 to 800C with a heating rate of 10C min1
Precursor syntheses Tris(3-(trimethoxysilyl)propyl)amine 1 A mixture of 10.0 g (55.6 mmol) of 3-aminopropyltrimethoxysilane, 38.8 g (196 mmol)
of 3-chloropropyltrimethoxysilane and 28.8 g (224 mmol) of ethyl-diisopropylamine was heated (115C) with stirring during
4 days After this time, the starting materials have totally been consumed The reaction mixture was cooled to room tempera-ture The formed salts were precipitated by addition of 300 mL of pentane The suspension was filtered and the solvents were evaporated The crude product was finally distilled under reduced pressure to give the title compound as a yellow viscous liquid Yield: 25.2 g (50 mmol, 90%) 1H NMR (400 MHz, CDCl3) d 0.54 (m, 6H), 1.46 (m, 6H), 2.34 (m, 6H), 3.50 (s, 27H);
13C NMR (CDCl3) d 6.70, 20,14, 50.48, 57.00; FT-IR(KBr)
nmax/cm1 2944, 2841, 2804, 1465, 1192, 1089, 820; HRMS [ESI+, m/z] calcd for C18H46NO9 (M + H)+ 504.2480, found 504.2509
Methyl-(tris(3-trimethoxysilyl)propyl) ammonium iodide 2 At room temperature and under argon, 6.8 g (48 mmol) of iodo-methane are added carefully to 20.0 g (40 mmol) of tris(3-tri-methoxysilyl)propyl) amine 1 The reaction mixture was stirred
at room temperature for 15 h After this time, the volatiles were pumped off The title compound was obtained as a brownish oil after repeated washing with pentane and drying under high vacuum at 50 C Yield: 24.8 g (38.4 mmol, 96%) 1H NMR (CDCl3) d 0.64 (t, 2H, J¼ 8.2 Hz), 1.74 (m, 2H, J ¼ 8.2 Hz), 3.19 (s, 3H), 3.36 (m, 2H, J ¼ 6.0 Hz), 3.52 (s, 27H) 13C NMR (CDCl3) d 5.51, 16.12, 48.90, 50.79, 63.18; MS-ESI (m/z (%)) 518.3 (100) [M+]; HRMS (ESI, m/z) [M]+ calcd for
C10H30NO9Si3+ (fully hydrolyzed product) 329.1228, found 392.1218
Tetrakis(3-(trimethoxysilyl)propyl)ammonium iodide 3 At room temperature and under argon, 12.7 g (44 mmol) of
Scheme 1 Structures of the neutral amine precursor 1 and the ionic
ammonium precursors 2 and 3.
Trang 33-iodopropyltrimethoxysilane were added to 20.0 g (40 mmol) of
tris(3-trimethoxysilyl)propyl) amine 1 The reaction mixture was
heated to 120C and stirred at this temperature for 24 h After
cooling to room temperature, the title compound was obtained
as an oil after repeated washing with pentane and drying under
high vacuum at 50C Yield: 30.4 g/38.1 mmol (95%).1H NMR
(CDCl3) d 0.67 (t, 2H, J¼ 7.8 Hz), 1.75 (m, 2H, J ¼ 7.8 Hz), 3.26
(m, 2H), 3.52 (m, 27H).13C NMR (CDCl3) d 5.59, 16.04, 50.74,
60.72; MS-ESI (m/z (%)) 666.4 (100) [M+]; HRMS (ESI, m/z)
[M]+calcd for C24H60NO12Si4+, 666.3193, found, 666.3197
Materials’ syntheses
Material A 1.00 g (1.98 mmol) of precursor 1 was added to
a solution of 531 mg sodium hexadecyl sulfate (containing
approx 40% of sodium stearyl sulfate) in 35.8 mL of distilled
water and 4.0 mL of 1 M hydrochloric acid at 60C A white
precipitate formed after one minute The formed suspension was
vigorously stirred for further 20 min, and filtered The surfactant
was eliminated by repeated washing with a solution consisting of
200 mL ethanol/10 mL conc hydrochloric acid The material was
finally treated with 200 mL ethanol/30 mL ammonia (10 wt% sol
in water) in order to get the amine containing silica hybrid
material A after drying Yield: 405 mg
The materials D and E were synthesized in a similar way from
the precursors 2 and 3, respectively
Material B CTAB (362 mg) was dissolved in a solution of
23.7 mL of distilled water and 0.3 mL of NH3(25 wt% solution in
water) This mixture was stirred during 60 min to give a
homo-geneous solution 1.00 g (1.98 mmol) of precursor 1 was added to
this solution at room temperature A white precipitate appeared
after several minutes The suspension was vigorously stirred for
a further 2 h and finally allowed to stand at 70 C for 72 h
Material B was isolated in the same way as described for material
A Yield: 532 mg
Material C Firstly an aqueous solution of P123 was prepared
from 48.2 g hydrochloric acid (37%), 215 mL of water and 8.7 g
of P123 To 4.61 g of this solution were added 800 mg
(1.58 mmol) of precursor 1 A white precipitate is formed after
30 min The suspension was stirred for a further 20 h at 40C and
was allowed to stand at 70C during 72 h Material C was
iso-lated in the same way as described for material A Yield: 387 mg
3 Results and discussion
Precursor syntheses
The synthesis of the trisilylated amine precursor 1 was achieved
by alkylation of the commercially available
3-amino-propyltrimethoxysilane with 3-chloropropyl-trimethoxysilane in
the presence of ethyl-diisopropyl amine The crude precursor 1
was purified by distillation under reduced pressure The
ammo-nium precursors 2 and 3 were synthesized from the trisilylated
amine 1 by alkylation using either methyl iodide or
3-iodopropyl-trimethoxysilane The ammonium salts 2 and 3 were obtained
after washing with pentane and subsequent drying in high purity
and excellent yields
Synthesis of amine and ammonium based polysilsesquioxanes
We then used the three precursors 1–3 for the synthesis of pol-ysilsesquioxanes
Firstly, sol–gel processing of precursor 1 was performed under different reaction conditions Three hybrid materials were obtained by hydrolysis–polycondensation of the pure precursor 1 using anionic (60% sodium hexadecyl sulfate/40% sodium stearyl sulfate), cationic (CTAB) and neutral (P123) surfactants, yielding the materials A, B and C, respectively The syntheses of materials A and C were performed in acidic reaction media whereas material B was prepared in a basic reaction mixture
It has to be mentioned that the trisilylated amine 1 is virtually an ionic precursor as it forms the corresponding ammonium salt in acidic medium Consequently, the materials A and C are formed from the ammonium salt of precursor 1 The amine functions were generated after hydrolysis–polycondensation by basic treatment with an ethanol/ammonia solution
In order to confirm the structural integrity of the immobilized trialkylamine entities after the hydrolysis–polycondensation processes, we performed solid state NMR experiments with the materials A–C The 29Si OP MAS and 13C CP MAS spectra obtained with material A are given in Fig 1 and 2 The 29Si spectrum shows two signals at58.4 ppm and 66.7 ppm related
to T2and T3sites, respectively The higher intensity was observed for T3substructures, indicating high condensation degree of the solid The complete absence of Q-resonances in the29Si spectrum indicates that no Si–C bond cleavage occurred during the hydrolysis–polycondensation and reflects the high chemical stability of the precursor towards acidic hydrolysis–poly-condensation conditions
The13C CP MAS spectrum of material A (Fig 2, top) shows three signals at 10.4, 20.6 and 57.5 ppm characteristic for n-propyl chains of the precursor These values are in good agreement with the shifts observed in the liquid NMR spectrum
of the precursor 1 (Fig 2, bottom) Furthermore, the absence of other signals than those related to the hydrolyzed precursor 1 strongly suggests complete elimination of the surfactant and confirms the absence of residual or newly formed triethoxysilyl groups Similar spectra were obtained both with materials
B and C (see ESI†).29Si OP MAS spectra of these solids showed higher intensities of T3signals The highest condensation degree was observed in the case of material B, synthesized in basic
Fig 1 29 Si OP MAS NMR spectrum of material A.
Trang 4reaction media Q-Signals were not observed These results
confirm the chemical integrity of the immobilized amine
substructures and reflect high chemical stability of the precursor
under the hydrolysis–polycondensation reactions
The thermogravimetric analysis of the materials (see ESI†)
shows TGA-plots with very similar shape for all three materials
The solids show relatively low thermal stability under an air
stream The decomposition starts at 240C, and the total weight
loss in all three cases was found to be around 40%, which is in
very good agreement with the expected value (39.3%) This result
also reflects the complete elimination of the structure directing
agents from the as-made materials by washing In this way, the
thermogravimetric analysis of the materials A, B and C also
confirms the results obtained by solid state NMR experiments
Hydrolysis–polycondensation of this trisilylated precursor
using various structure directing agents led to materials featuring
different textures Fig 3 shows the X-ray diffractograms of the
hybrid materials obtained from the pure precursor 1 using
anionic (60% sodium hexadecyl sulfate/40% sodium stearyl
sulfate), cationic (CTAB) and neutral (P123) surfactants,
yielding the materials A, B and C, respectively While amorphous
materials were obtained using CTAB and P123 (Fig 3, B and C),
structured solids were obtained with anionic surfactants (Fig 3,
A) In this latter case, the formation of the solid takes place
according to a SI+pathway The presence of ammonium groups
formed by protonation of the amine precursor under acid hydrolysis conditions led to enhanced interactions between the anionic surfactant and the cationic precursor and enabled the formation of a nanostructured material showing a high degree of regularity on a mesoscopic scale The X-ray diffractogram of this solid shows a pattern with a sharp and intense reflection at 2q¼ 2.41corresponding to a d-spacing of 3.66 nm and weaker reflections at 2q¼ 4.18 and 2q ¼ 4.82 (d-spacings 2.11 and 1.83 nm, respectively), characteristic for the (100), (110) and (200) reflections of materials with hexagonal architecture From these values, the distance between two pore centers in material
A can be calculated to be 4.2 nm
Further information concerning the texture of the materials
A, B and C were obtained by nitrogen sorption experiments The adsorption isotherms are shown in Fig 4, the pore size distribution curves are shown in Fig 5 and the surface properties are summarized in Table 1 All three materials are highly porous solids with specific surface areas in the range from 700 to
1200 m2 g1 Materials B and C show nitrogen uptake over
a relatively large p/p0 range Both adsorption–desorption isotherms show hysteresis phenomena indicating mesoporosity The materials show specific surface areas of 700 and 875 m2g1 displaying relatively broad pore size distributions centered at
12 and 4.2 nm, respectively (Fig 5, middle and right) In contrast, the nitrogen sorption isotherm of material A shows a type 4 isotherm with a relatively sharp adsorption step in the range from p/p0 ¼ 0.14–0.2, indicating essentially micro- and super-microporosity and a relatively narrow pore size distribution The pore volume can be estimated to be 0.57 mL g1 The specific
Fig 2 13 C liquid NMR spectrum of precursor 1 (bottom) and 13 C CP
MAS NMR spectrum of material A (top).
Fig 3 X-Ray diffractograms of the solids A, B and C (top to bottom).
Fig 4 Nitrogen adsorption–desorption isotherms of materials A, B and C.
Fig 5 Pore size distribution curves of the materials A, B and C.
Trang 5surface area SBETcan be estimated to be 1220 m2g1and the BJH
average pore diameter 22 A˚ XRD, TEM and nitrogen sorption
experiments give concordant results and indicate that material A
is a highly porous solid featuring a regular hexagonal
architec-ture with an average pore diameter of 22 A˚ (Fig 5, left) and wall
thickness of approx 20 A˚
Thus, the characterization of the materials A–C indicates that
the amine precursor 1 can be used for sol–gel processing without
chemical decomposition or bond cleavage of the organic
substructure Hydrolysis–polycondensation of compound 1 led
to the formation of highly porous materials The main result of
this study concerns the structuring of the materials The
gener-ation of solid phases displaying a highly regular architecture on
a mesoscopic length scale and narrow pore size distribution was
only observed with anionic structure directing agents under
acidic reaction conditions This result can clearly be attributed to
specific interactions between the cationic ammonium precursor
and the anionic surfactant as illustrated in Scheme 2
On the other side, the formation of materials with pore
diameters in the range of 4 nm is rather typical for template
assisted hydrolysis–polycondensation using nonionic surfactants
as observed in the synthesis of material C.51However, the
lyo-tropic arrangement of the surfactant in the
hydrolysis–poly-condensation mixture seems to be disturbed by the presence of
the protonated precursor as the obtained solids do not show
a regular architecture Finally, the utilization of CTAB gives the
material with the largest average pore diameter It has to be
stressed that the formation of material B took place under
alkaline reaction conditions Contrary to the syntheses of the
materials A and C, this reaction involves the sol–gel
trans-formation of the neutral amine precursor 1 The trans-formation of
materials displaying pore diameters bigger than 10 nm is rather
untypical for the utilization of cationic CTAB surfactant and
suggests the formation of larger aggregates in the hydrolysis– polycondensation mixtures
These results prompted us to generalize this new strategy for the synthesis of structured materials using the cationic precursors
2 and 3 in the presence of anionic surfactants Hydrolysis– polycondensation reactions were carried out under similar reaction conditions as applied for the synthesis of material A using a mixture of 60% sodium hexadecyl sulfate/40% sodium stearyl sulfate as structure directing agent in acidic media In this way, the materials D and E were obtained from the precursors
2 and 3, respectively
The characterization of the obtained solids by 29Si and13C solid state NMR spectroscopy indicated the structural integrity
of the immobilized ammonium substructures Contrary to the materials A, B and C, synthesized from the amine precursor 1, the29Si OP MAS spectra of the materials D and E show higher intensities for the T2 signals This result indicates a lower condensation degree in the case of the materials obtained from tetraalkylammonium precursors 2 and 3 This result can be attributed to the basic treatment of the materials A, B and C either during hydrolysis–polycondensation or during washing giving a higher condensation degree in these materials
The X-ray diffractograms of these two new materials D and E are shown in Fig 6 together with a diffractogram of material A Whereas the diffractogram of material A clearly displays the reflections characteristic for materials with hexagonal architec-tures (vide supra), the reflections in the diffractogram of material
D are less well defined The (100) reflection in the diffractogram
of this material is broader, and the (110) and (200) reflections can hardly be identified The diffractogram of material E only shows
Table 1 Surface properties of the materials A–E
Material S BET /m 2 g 1 Used surfactant/reaction mixture Average pore diameter b /A˚ Pore volume/cm 3 g 1 Texture
a
The used anionic surfactant was a mixture of 60% sodium hexadecyl sulfate/40% sodium stearyl sulfate.bPore diameters were calculated by the BJH method from the adsorption branch of the isotherms The materials A, B and C were obtained from precursor 1, whereas the materials D and E were obtained from the precursors 2 and 3, respectively.
Fig 6 X-Ray diffractograms of the solids A, D and E (top to bottom).
Scheme 2 Sol–gel processing of cationic precursors using anionic
structure directing agents according to an S I + pathway.
Trang 6a broad (100) reflection The position of the (100) reflections is
nearly unchanged in all three cases This result clearly indicates
a decreasing structural regularity in these materials in the order
A–D–E The material A obtained from the amine precursor 1
shows the highest order whereas material E obtained from the
tetrasilylated ammonium precursor 3 is the lowest structured
material in this series
These results were confirmed by electron microscopy
Scan-ning electron microscopy (SEM) micrograph of material A
(Fig 7, upper-left) shows agglomerated particles with a diameter
of approx 1 mm TEM image of a Cu(I)-impregnated sample of
A shows a regular hexagonal array of 2D aligned channels with
high degree of structural regularity (Fig 7, upper-right) The
SEM micrograph of material E (Fig 7, lower-left) shows a rough
material with agglomerated particles of much smaller size in the
range of 100–200 nm The TEM micrograph (Fig 7, lower-right)
shows a porous material with a less defined architecture
Although well structured domains are visible by transmission
electron microscopy, the X-ray diffractogram of material E
indicates the formation of a material with low long-range order
The results obtained from XRD and TEM concerning the
texture of the materials A, D and E were confirmed by nitrogen
sorption experiments The isotherms of the materials are as given
in Fig 8 The isotherm of material A shows a type 4 isotherm
with a relatively sharp adsorption step in the range from
p/p0¼ 0.14–0.2 A similar isotherm was obtained with material
D However, this material shows lower nitrogen uptake
indi-cating lower specific surface area and pore volume Accordingly,
the specific surface area SBETof this material was found to be
only 574 m2g1 In contrast, the isotherm obtained with material
E displays no inflexion at 0.1 < p/p0< 0.15 as observed in the
isotherms of A and D, but only a lower defined N2uptake at
relative pressures p/p0< 0.3 This phenomenon indicates broader
pore size distribution within material E The specific surface area
of this material was found to be slightly lower as in the case of
material A (SBET ¼ 908 m2 g1) The surface properties of the
materials D and E are summarized in Table 1 together with the
data for the materials A–C
These results clearly indicate that sterical shielding of the cationic center by alkyl chains within the compounds 1, 2 and 3 has a direct impact on the texture in the materials obtained from sol–gel processing of these precursors As illustrated in Scheme 3, the trialkylammonium salt formed from precursor 1 allows the highest surfactant–precursor interaction Furthermore,
a hydrogen bonding contribution between precursor and anionic surfactant cannot be excluded In contrast, the cationic tetraal-kylammonium groups of precursors 2 and 3 limit the surfactant– precursor interaction and therefore led to the formation of lower structured solids, in particular in the case of the tetraalkylammonium salt 3
Another indication for the decisive influence of ionic precursor–surfactant interaction on the structuring of the PMO type materials was obtained from hydrolysis–polycondensation procedures in alkaline reaction media Precursors 1 and 2 were transformed into the corresponding hybrid materials in the presence of hexadecyl sulfate anions Whereas the material D-OH, obtained from 2, showed similar architecture compared
to the related material D (Fig 9), the X-ray diffractogram of material A-OH, obtained from precursor 1, does not show any reflections This result highlights that the presence of a cationic center within the precursor is essential for the generation of structured phases as it enables ionic interactions with the anionic structure directing agents
Fig 7 SEM (left) and TEM (right) images of material A (upper) and E
(lower).
Fig 8 Nitrogen adsorption–desorption isotherms of material A, D and E.
Scheme 3 Ionic precursor–surfactant interactions between the proton-ated form of precursor 1 (upper) and precursor 3 (lower) with long-chain substituted sulfonates.
Trang 7We report the synthesis of new periodic mesoporous organosilica
based on amine and ammonium building blocks These materials
were obtained by hydrolysis–polycondensation procedures of the
pure amine or ammonium precursors without addition of silica
network formers The importance of the study is two-fold
Firstly, we describe the synthesis of functional mesoporous
hybrid materials with high potential in catalysis and separation,
in particular for the immobilization of metallic species via the
formation of coordination complexes or anion exchange
reac-tions Nanostructured silica containing amine functions are
versatile materials for diverse applications in heterogeneous
catalysis and separation,52–56and silica hybrid materials bearing
cationic substructures are versatile solid phases for anion
exchange reactions and have therefore found widespread
utili-zation as exchange resins.57–61 The immobilization of anionic
catalytic species via anion exchange reactions gives rise to the
formation of heterogeneous catalysts.62,63Regarding the
forma-tion of the nanostructured and mesoporous materials, we
describe here the first synthesis of periodic mesoporous
orga-nosilicas using anionic surfactants as structure directing agents
following an SI+-mechanism This study highlights that specific
precursor–surfactant interactions in the sol solution are essential
for the formation of structured materials We show that the
substitution pattern of the cationic ammonium center has high
importance for the interaction with the anionic template, which
is determinant for the architecture of the formed materials The
materials displaying highest structural regularity were obtained
from protonated trialkylammonium precursors The use of
a related tetrapropylammonium precursor containing a more
shielded cationic nitrogen center led to solids with worm-like
architectures under identical hydrolysis–polycondensation
conditions In general, this approach opens the door for the
elaboration of new porous and nanostructured solids bearing
ionic functional groups
Acknowledgements
The authors thank P Gaveau (Institut Charles Gerhardt de
Montpellier) for solid state NMR measurements P Hesemann
thanks the ’Reseau de Recherche 3, Chimie pour le
Developpement Durable’ of the CNRS for financial support
Notes and references
1 C T Kresge, M E Leonowicz, W J Roth, J C Vartuli and
J S Beck, Nature, 1992, 359, 710–712.
2 Y Wan and D Y Zhao, Chem Rev., 2007, 107, 2821–2860.
3 K J Shea, D A Loy and O Webster, J Am Chem Soc., 1992, 114, 6700–6710.
4 R J P Corriu, J J E Moreau, P Thepot and M Wong Chi Man, Chem Mater., 1992, 4, 1217–1224.
5 U Diaz, T Garcia, A Velty and A Corma, J Mater Chem., 2009,
19, 5970–5979.
6 P Hesemann and J J E Moreau, Tetrahedron: Asymmetry, 2000, 11, 2183–2194.
7 A Brethon, P Hesemann, L Rejaud, J J E Moreau and M Wong Chi Man, J Organomet Chem., 2001, 627, 239–248.
8 J C Broudic, O Conocar, J J E Moreau, D Meyer and M Wong Chi Man, J Mater Chem., 1999, 9, 2283–2285.
9 X Sallenave, O J Dautel, G Wantz, P Valvin, J P Lere-Porte and
J J E Moreau, Adv Funct Mater., 2009, 19, 404–410.
10 O J Dautel, J P Lere-Porte, J J E Moreau and M Wong Chi Man, Chem Commun., 2003, 2662–2663.
11 J J E Moreau, L Vellutini, M Wong Chi Man and C Bied, Chem.– Eur J., 2003, 9, 1594–1599.
12 J J E Moreau, L Vellutini, M Wong Chi Man, C Bied,
J L Bantignies, P Dieudonne and J L Sauvajol, J Am Chem Soc., 2001, 123, 7957–7958.
13 J J E Moreau, L Vellutini, M Wong Chi Man and C Bied, J Am Chem Soc., 2001, 123, 1509–1510.
14 T Asefa, M J MacLachan, N Coombs and G A Ozin, Nature,
1999, 402, 867–871.
15 S Inagaki, S Guan, Y Fukushima, T Ohsuna and O Terasaki,
J Am Chem Soc., 1999, 121, 9611–9614.
16 B J Melde, B T Holland, C F Blanford and A Stein, Chem Mater., 1999, 11, 3302–3308.
17 F Hoffmann, M Cornelius, J Morell and M Froba, Angew Chem., Int Ed., 2006, 45, 3216–3251.
18 W J Hunks and G A Ozin, J Mater Chem., 2005, 15, 3716–3724.
19 O Dag, C Yoshina-Ishii, T Asefa, M J MacLachlan, H Grondey,
N Coombs and G A Ozin, Adv Funct Mater., 2001, 11, 213–217.
20 S Inagaki, S Guan, T Ohsuna and O Terasaki, Nature, 2002, 416, 304–307.
21 S Fujita and S Inagaki, Chem Mater., 2008, 20, 891–908.
22 M A Wahab and C B He, Soft Mater., 2009, 7, 79–92.
23 P Mohanty and K Landskron, Nanoscale Res Lett., 2009, 4, 169– 172.
24 P Mohanty and K Landskron, Nanoscale Res Lett., 2009, 4, 1524– 1529.
25 E B Cho, D Kim and M Jaroniec, J Phys Chem C, 2008, 112, 4897–4902.
26 A Ide, R Voss, G Scholz, G A Ozin, M Antonietti and A Thomas, Chem Mater., 2007, 19, 2649–2657.
27 S MacQuarrie, M P Thompson, A Blanc, N J Mosey,
R P Lemieux and C M Crudden, J Am Chem Soc., 2008, 130, 14099–14101.
28 S Polarz and A Kuschel, Adv Mater., 2006, 18, 1206–1209.
29 P Y Wang, X Liu, J Yang, Y Yang, L Zhang, Q H Yang and
C Li, J Mater Chem., 2009, 19, 8009–8014.
30 J Morell, S Chatterjee, P J Klar, D Mauder, I Shenderovich,
F Hoffmann and M Froba, Chem.–Eur J., 2008, 14, 5935–5940.
31 T Tani, N Mizoshita and S Inagaki, J Mater Chem., 2009, 19, 4451–4456.
32 N Mizoshita, Y Goto, M P Kapoor, T Shimada, T Tani and
S Inagaki, Chem.–Eur J., 2009, 15, 219–226.
33 J Alauzun, A Mehdi, C Reye and R J P Corriu, J Mater Chem.,
2007, 17, 349–356.
34 H G Zhu, D J Jones, J Zajac, R Dutartre, M Rhomari and
J Roziere, Chem Mater., 2002, 14, 4886–4894.
35 M C Burleigh, S Jayasundera, M S Spector, C W Thomas,
M A Markowitz and B P Gaber, Chem Mater., 2004, 16, 3–5.
36 J Morell, M Gungerich, G Wolter, J Jiao, M Hunger, P J Klar and M Froba, J Mater Chem., 2006, 16, 2809–2818.
37 E B Cho, D Kim and M Jaroniec, Langmuir, 2007, 23, 11844– 11849.
38 O Olkhovyk and M Jaroniec, Ind Eng Chem Res., 2007, 46, 1745– 1751.
Fig 9 X-Ray diffractograms of the solids D, D-OH and A-OH (top to
bottom).
Trang 839 R M Grudzien, B E Grabicka, S Pikus and M Jaroniec, Chem.
Mater., 2006, 18, 1722–1725.
40 B E Grabicka and M Jaroniec, Microporous Mesoporous Mater.,
2009, 119, 144–149.
41 O Olkhovyk and M Jaroniec, J Am Chem Soc., 2005, 127, 60–
61.
42 W Whitnall, L Cademartiri and G A Ozin, J Am Chem Soc.,
2007, 129, 15644–15649.
43 K Landskron and G A Ozin, Science, 2004, 306, 1529–1532.
44 C Baleizao, B Gigante, D Das, M Alvaro, H Garcia and
A Corma, Chem Commun., 2003, 1860–1861.
45 B Gadenne, P Hesemann, V Polshettiwar and J J E Moreau, Eur.
J Inorg Chem., 2006, 3697–3702.
46 V Polshettiwar, P Hesemann and J J E Moreau, Tetrahedron Lett.,
2007, 48, 5363–5366.
47 T P Nguyen, P Hesemann, P Gaveau and J J E Moreau, J Mater.
Chem., 2009, 19, 4164–4171.
48 A El Kadib, P Hesemann, K Molvinger, J Brandner, C Biolley,
P Gaveau, J J E Moreau and D Brunel, J Am Chem Soc.,
2009, 131, 2882–2892.
49 C Gao, Y Sakamoto, O Terasaki, K Sakamoto and S Che,
J Mater Chem., 2007, 17, 3591–3602.
50 S Che, A E Garcia-Bennett, T Yokoi, K Sakamoto, H Kunieda,
O Terasaki and T Tatsumi, Nat Mater., 2003, 2, 801–805.
51 D Y Zhao, Q S Huo, J L Feng, B F Chmelka and G D Stucky,
J Am Chem Soc., 1998, 120, 6024–6036.
52 D Brunel, A C Blanc, A Galarneau and F Fajula, Catal Today,
2002, 73, 139–152.
53 D Brunel, Microporous Mesoporous Mater., 1999, 27, 329–344.
54 K Moller and T Bein, Chem Mater., 1998, 10, 2950–2963.
55 G E Fryxell, J Liu, T A Hauser, Z M Nie, K F Ferris,
S Mattigod, M L Gong and R T Hallen, Chem Mater., 1999,
11, 2148–2154.
56 A M Liu, K Hidajat, S Kawi and D Y Zhao, Chem Commun.,
2000, 1145–1146.
57 Y H Ju, O F Webb, S Dai, J S Lin and C E Barnes, Ind Eng Chem Res., 2000, 39, 550–553.
58 B Lee, H J Im, H M Luo, E W Hagaman and S Dai, Langmuir,
2005, 21, 5372–5376.
59 T H Kim, M Jang and J K Park, Microporous Mesoporous Mater.,
2008, 108, 22–28.
60 A Walcarius and V Ganesant, Langmuir, 2006, 22, 469–477.
61 J Kramer, N E Dhladhia and K R Koch, Sep Purif Technol.,
2006, 49, 181–185.
62 K Yamaguchi, C Yoshida, S Uchida and N Mizuno, J Am Chem Soc., 2005, 127, 530–531.
63 R Ciriminna, P Hesemann, J J E Moreau, M Carraro,
S Campestrini and M Pagliaro, Chem.–Eur J., 2006, 12, 5220–5224.