university of groningen mesostructured sillicate-based ......since the discovery of m41s type of...
TRANSCRIPT
University of Groningen
Mesostructured sillicate-based materialsZhang, Zheng
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.
Document VersionPublisher's PDF, also known as Version of record
Publication date:2014
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):Zhang, Z. (2014). Mesostructured sillicate-based materials: studies on mild detemplation methods andadvanced characterization. [S.n.].
CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.
Download date: 20-07-2021
4
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined
study of mild detemplation and structural preservation
In this work the feasibility of the Fenton detemplation on a series of SBA-15 mesophases has been
studied and compared to the conventional calcination. The as-synthesized and detemplated
materials were studied regarding their template content (TGA, CHN), structure (SAXS, TEM), surface
hydroxylation (Blin-Carteret’s approach) and texture (high resolution Argon physisorption). Fenton
detemplation achieves 99% of template removal, leading to highly hydroxylated materials. The
structure can also be better preserved when a second step is applied after the Fenton oxidation. Two
successful approaches are presented: drying in a low-surface-tension solvent (such as n-BuOH) and
hydrothermal stabilization. Both approaches gives rise to similar low structural shrinkage, lower than
calcination and the water-dried Fenton. Nevertheless, the textural features are remarkably different.
The n-BuOH exchange route gives rise to highly hierarchical structures with enhanced
interconnecting pores and the highest surface areas. The hydrothermal stabilization produces large-
pore SBA-15 structures with high pore volume, very low interconnectivity and micropores. Therefore,
the texture can be fine-tuned in this way while the template is removed.
Chapter 4
66
4.1 Introduction
Since the discovery of M41S type of materials in 19921, ordered mesoporous materials (OMMs) have
drawn remarkable attention because of their potential applications in heterogeneous catalysis2,3,
adsorption4, separation5 and as optical and electric devices6. A great breakthrough in OMMs is the
discovery of the SBA-15 structure.7,8 SBA-15 is defined by the same space group (P6mm) as MCM-41, but
is a very different structure in the aspects of synthesis mechanism and textural characteristics.
SBA-15 is synthesized by using amphiphilic triblock copolymers poly(ethylene glycol)-poly(propylene
glycol)-poly(ethylene glycol) (PEO-PPO-PEO) as structure-directing agent in highly acidic aqueous media;
the acid catalyzes the hydrolysis but it is also responsible of the interaction mechanism of the type
(S0H+)(X–I+); where S0 is the block copolymer, HX is the acid and I+ is the silica cationic species. The
hexagonal structure of SBA-15 holds thick walls, which provide better thermal and hydrothermal
stability9. Additionally, SBA-15 has a tunable pore diameter ranging 5-30 nm that can be easily 10,11, which give opportunities to obtain different textual
properties. Especially interesting, SBA-15 has a secondary porosity due to insertion of PEO units into the
silica wall during synthesis12, which is normally described as intra-wall porosity. This intra-wall porosity is
composed of interconnecting small mesopores between the main channels and micropores. The
interconnecting mesopores, sometimes defined as secondary mesopores, have been later confirmed by
making stable carbon CMK-n nano-replicas materials.13, 14 The existence of micropores has been proved
by gas physisorption10,11,15-17 and quantitative X-ray analysis12.
Besides the advantage to be used as hard template to synthesize replicas, the abundant intra-wall
porosity of SBA-15 also contributes greatly to the total surface area and can reduce diffusion limitations
which commonly occur to one dimensional structure, such as MCM-41. 18-21 Some studies have reported
the mechanism of intra-wall porosity formation during synthesis. It was found that SBA-15 synthesized
at intermediate ageing temperatures possesses an optimal intra-wall porosity. Materials aged at
tra-wall and microporosity, with the development of
large-pore diameters and improved hydrothermal stability of the walls.11,17
Two synthetic routes have been reported in order to tune the porosity of mesoporous silicas. One way
to go is to adjust the synthesis conditions to control the self-assembly pathway; the utilization of
swelling agents, such as mesityleen22-26, triisopropylbenzen27,28, alkanes29,30 and amines31 has been
reported in order to produce larger pores. Some of these approaches have been successfully applied to
SBA-15. By using swelling agent during SBA-15 synthesis, both the major mesopores and intra-wall pores
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
67
are increased simultaneously.23,27-29 Nevertheless, the independent adjustment of the primary and
secondary porosity has seldom been reported by using micelle modifiers. Besides the utilization of
organic-based swelling agents, salts have also been reported. Yu et al.32 reports that KCl facilitates the
synthesis of highly ordered silica mesophase. Lately, efforts have been put into the selectively
adjustment of the secondary porosity, which could be very important for mass-transfer limited
applications, as mentioned earlier. Reichhardt et al. described the removal of intra-wall porosity of SBA-
15 by adding NaI during synthesis while maintaining major pore size.33 This procedure gives a similar 2-D
structure as MCM-41 however holding bigger pore diameters and thicker walls. On the other hand, Zhu
et al. published their efforts to fabricate SBA-15 with enhanced interconnectivity by the addition of Poly
(vinyl alcohol) without changing the mesopores.34
A different way to enhance the porosity can be the development of non-thermal detemplation methods.
The organic template species has to be removed to generate the porosity before putting into application.
2 combined with air/O2) is used to oxidize the organic
templates. Such a process completely removes the organic species; however it leads to significant
framework contraction and loss of hydrophilicity35 as a result of thermal condensation. We have shown
that this phenomenon is more severe for SBA-15 mesophases with less condensed structure, which are
aged at relatively lower temperature.36 Therefore, alternative non-thermal detemplation routes, other
than calcination, are still sought. This type of mild methods aims to preserve better the structure
without the need to modify the conventional synthesis protocols.
Several mild methods of detemplation have been reported including solvent extraction36-39, supercritical
fluid extraction40-42, chemically aided and UV-Vis stimulated oxidation43-51 , sonication52, microwave
digesting53 and combined methods54,55. Despite most of these techniques yield acceptable to good
detemplation yields and structural ordering, based on X-ray diffraction, the effect of these mild
approaches on the secondary porosity and surface properties, for the case of SBA-15 is hardly found.
Another mild detemplation method is based on the Fenton chemistry. This was applied to zeolite
BEA56,57 and FER58 (in this case by break down strong complexation equilibria) and some mesoporous
materials50,59,60. The approach serves as detemplation or Fe-incorporation technique, or both. Fenton
chemistry was originally applied in organic pollutant treatment in waste water since it was defined in
1894.61 In this process, extremely oxidizing hydroxyl radicals (OH ) are formed from hydrogen peroxide
catalyzed by Fe (III)/Fe(II) (Eqs. 1.-2; reactions 3 and 4 show two of the possible parallel reactions where
OH are wasted). These radicals can oxidize organics compounds in aqueous solution very effectively, as
Chapter 4
68
well as the block copolymer entrapped within the structure of SBA-15 (eq. 5), where SiOx(OH)2–x
represents an ill condensed network: + + + (1) + + + (2) + + (3) + + (4) ( ) ( 123) + ( ) ( ) + + (5)
We have recently reported the application of the mild Fenton detemplation method to a SBA-15
structure aged at 105 °C.62 The method renders a nearly pristine SBA-15 without structural shrinkage,
low residual template, improved surface area, pore volume and silanol concentration. In this work, we
have extended this approach to a series of SBA-15 mesophases that were aged in the temperature range
of 90 to 130 °C. It turned out that for the low-temperature aged samples, a complete template removal
and full structural preservation cannot be achieved if a second step is applied, in order to compensate
for the capillary tension exerted during drying. Two post-detemplation methods were applied. In one
method, a low-surface-tension solvent exchange before drying is applied, which was successfully applied
on soft MCM-4160. A second novel method was implemented as well, consisting of the application of a
hydrothermal treatment after Fenton detemplation. Both methods will be compared with the calcined
counterparts in aspects of detemplation level, surface hydrophilicity, ordering and textural
characteristics.
4.2 Experimental parts
4.2.1 Synthesis of SBA-15 mesophases
Chemicals
All chemical compounds were used as received without further purification: tetraethoxysilane (TEOS,
98%, Aldrich), poly(ethyleneoxide)20-poly(propyleneoxide)70-poly(ethyleneoxide)20 (Pluronic®-P123),
Sigma-Aldrich), hydrochloric acid (HCl, 37 wt. %, ACROS), Iron (III) nitrate nonahydrate (Fe(NO3)3·9H2O,
Riedel-de Haën), hydrogen peroxide (H2O2, 30%, Merck, 1.07209.1000).
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
69
Synthesis
The mesophases were synthesized by the surfactant assisted sol-gel procedure according to the method
reported elsewhere.7, 8 In all experiments the hydrolysis step was identical and the condensation was
systematically varied with the ageing temperature. In a typical experiment, 8 g of P123 were mixed with
240 g HCl (2.0 M) and 60 g of Mili-Q water until a homogenous mixture was obtained. This mixture was
placed in water- 2
gel was: 1.0 SiO2:0.017 P123:5.9 HCl: 204 H2
mixture was then transferred into a 500 ml Teflon bottle and aged under static conditions at various
iltered and the as-obtained solid
was washed with 2 litres of Mili- -15
materials are denoted as Sx-M, where x represents the aging temperature and M indicates mesophase.
Template removal by calcination
kept 6 h at constant temperature, and then cool down to room temperature. The calcination was
performed in a Nabertherm box furnace model LT9/11 equipped with a P330 temperature. The suffix C
is added to the samples code when those are calcined, e.g. S100-C.
Template removal by Fenton oxidation
Before performing the Fenton experiments, the materials were subjected to solvent extraction in
absolute ethanol for 24 h. The details of solvent extraction were described in a former work36. In a
typical Fenton detemplation protocol (method A), a suspension is made by mixing 1.5 g solvent
extracted SBA-15 material and 30 ml Mili-Q water in a round-bottom flask at room temperature. Then
1.5 ml of a Fe (NO3)3 solution (having 1000 ppm iron concentration) was added to the mixture. To this
suspension, 60 ml H2O2 was poured in slowly when stirring. The as-obtained mixture, having ~17 ppm
Fe (III) and 10 vol. % H2O2 -bath equipped with a
condenser. Various treatments were applied after the reaction ended as described in the following
section.
In an alternative method (method B), 1 g of solvent extracted SBA-15 material was mixed with 25 ml
H2O in a round bottom flask at room temperature. The mixture having an Fe(III) concentration of 140
Chapter 4
70
ppm was pre- 2O2 was added stepwisely (5, 10, 15 and finally 20 ml).
The final concentration is ~45 ppm for Fe(III) and 10 vol. % for H2O2..
All experiments were performed by using method A unless it is specified.
4.2.2 Post-detemplation treatments
Direct drying
The aqueous slurry after Fenton-detemplation is centrifu
overnight. The samples obtained in this manner are suffixed with FW, where W comes from water dried.
Hydrothermal treatment
The aqueous slurry after Fenton-detemplation was transferred into a 150 ml Teflon bottle and heated at
-generated pressure. The final silica product was collected by
where HT comes from hydrothermal treatment.
Solvent exchange
After Fenton-detemplation, water was firstly removed by centrifugation. Then around 20 ml n-Butanol
(anhydrous, 99.8%, Sigma-Aldrich) was added into the as-obtained wet solid and stirred for 15 minutes
to reach a good mixing. This solvent-exchange step was repeated for 5 times to reach a thorough
exchange of H2O with n-
overnight.
For the samples detemplated by method B, solvent exchange was carried on by adding 10 mL n-butanol
and stirring for 20 minutes at 70 °C in a test-tube. Subsequently, the mixture was centrifuged and the
24 h. Afterwards the
The samples obtained in this manner are suffixed with FB, where B comes from n-BuOH exchange.
The samples codes and treatments are summarized in Table 1.
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
71
Table 1. Summary of sample codes and their preparative conditions.
Material Method of preparation Sx-M Mesophase: SBA-15 aged at x °C for 24 h, washing and drying. Sx-C Calcination at 550 °C on the Sx-M mesophase. Sx-se Solvent extraction as described elsewhere.36 Sx-seFW Fenton oxidation, dried directly in H2O, on the Sx-se. Sx-seFBD Fenton oxidation, exchange in n-BuOH, drying, on the Sx-se. Sx-seFHT Fenton oxidation, hydrothermal treatment 100 °C 24h, drying, on the Sx-se.
4.2.3 Characterization
Small angle X-ray scattering (SAXS) measurements were performed using a NanoStar instrument (Bruker)
at room temperature. A ceramic fine-focus X-ray tube powered with a Kristallflex K760 generator at 35
kV and 40mA. The primary X-ray flux is collimated using cross-coupled Gobel mirrors and a pinhole of
at the sample position. The sample-detector distance was 104 cm. The scattering is registered by a Hi-
Star position sensitive area detector (Siemens AXS) in the range of 0.1-2.0 nm. After measurement SAXS
spectra are integrated with the Chi method.
The template content was firstly examined by TGA in a Mettler-Toledo analyzer (TGA/SDTA851e).
Typ - -Al2O3 crucible was filled 10 mg of sample. The decomposition of the
template was monitored in air flow of 100 ml/min NTP while the temperature was increased from 30 to
The template content was quantified by CHN analysis as well. Approximately 2 mg of sample was
decomposed into CO2, H2O, and N2. These are later separated in an online gas chromatograph equipped
TM software enables the integration of the chromatogram. The integrated peak height is used in the
calculations using acetanilide (puriss.
Transmission electron microscopy (TEM) images were obtained on a JEOL transmission electron
microscope equipped with a field emission gun operating at 200KV.
The Fe content was evaluated by inductively coupled plasma atomic emission spectroscopy (ICP-AES)
after dissolving the samples in 5 wt.% HF aqueous solution.
Chapter 4
72
Gas sorption isotherms were measured with an ASAP2420 adsorption analyzer (Micromeritcs) by using
for 4 hours. The total pore volume was calculated by
single point at 0.98 p/p0 relative pressure. Brunauer-Emmet-Teller (BET) method was applied for total
surface area. Pore size distribution (PSD), cumulative pore volume distribution (CVD), and cumulative
surface area distribution (CSD) were determined using non-local density functional theory (NLDFT)
developed for oxide surfaces for Argon adsorption.63
4.2.4 Definitions
Detemplation efficiency based on TGA:
= (1 - Sx-FW Sx-se
)×100 (6)
where TGA150-800 is the TGA weight loss between 150 and 800 oC.
Detemplation efficiency based on CHN:
= (1 - Sx-FW Sx-se
)×100 (7)
where CCHN is the carbon content as determined by CHN analysis.
Shrinkage level: a = ( ) ( ) ( ) × 100 (8)
where a0 is the hexagonal lattice parameter: = 100 (9)
Density of silanols:
For template-free materials (i.e. C, FW and FHT) the silanol group density was evaluated by the Blin-Carteret equation64 (10): OH(groups. nm ) = (10)
Where is the TGA weight loss (wt.%) between 150-800 oC, NA is Avogadro’s number, SBET is the specific surface area using Ar and MWH2O is the molecular weight of water.
Textural parameters:
VT (cm3/g): Total pore volume determined at p/po = 0.98 in the desorption branch. (11)
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
73
SBET (m2/g): Specific surface area determined by the BET model. (12)
DNLDFT (Å): Pore diameter based on the non-local DFT model (NLDFT) (13
V (cm3/g): Micropore volume obtained from the pore volume distribution (PVD) determined by the NLDFT model for pores 20 Å.
(14)
V IW (cm3/g): Intrawall porosity, determined as the pore total volume before the raising step in the pore volume distribution determined by the NLDFT model.
(15)
V IC (cm3/g): Interconnecting porosity defined as VIW – V . (16)
4.3 Results and discussion
4.3.1 Evaluation of the template removal efficiency
The mesophases, before applying the Fenton detemplation, were first subjected to ethanol extraction to
reduce the amount of template, which was found to be between 11.9 and 27.1 wt.% based on TGA after
Figure 1. TGA patterns and corresponding DTGA derivative plots for the samples Sx-FW, x =90-130, after Fenton detemplation.
the extraction. These correspond to 5.1 to 8.8 wt.% based on carbon (Sx-se samples in Table 2). Thus,
solvent extraction reduces the template content in 55-80% as compared to the mesophase (TGA basis).
S90 S95 S100 S110 S130Sx-seFW
200 400 80060070
80
90
100
-0.2
-0.1
0.0
Aging Temperature (x) / °C
Deriv
ate
/ % (°
C)-1
Rela
tive
wei
ght /
%
Chapter 4
74
The template was almost eliminated from the porous network after applying the Fenton treatment. The
carbon content (Table 2) was significantly reduced with a final carbon level of 0.08-0.12 wt.% This
implies that the Fenton detemplation efficiency is about 98-99% ( CHN). Application of harsher
conditions (method B, where the initial Fe concentration is ~8 times higher than in method A) does not
enhance the detemplation efficiency; the carbon contents lies in a comparable range than for method A
(Table 2).
Table 2. Composition of Sx mesophases after Fenton detemplation (method A), evaluated by TGA and CHN analysis, and Fe content.
Ageing T (x) Fe a Sx-se b Sx-seFW b TGA Sx-se c Sx-seFW c,d CHN d wt. % TGA wt.% TGA wt.% % carbon wt % carbon wt. % %
90 0.11 (80) 27.1 3.9 86 7.6 0.08 (0.17) 99 (98) 95 0.10 (83) 17.0 3.8 78 5.8 0.08 (0.03) 99 (99) 100 0.09 (79) 11.9 3.4 71 6.0 0.10 (0.07) 98 (99) 110 0.11 (89) 19.2 3.2 83 5.1 0.12 (0.17) 98 (97) 130 0.07 (61) 12.8 2.7 79 8.8 0.11 (0.16) 99 (98) a. ICP-AES. Values between parenthesis correspond to the percentage of Fe adsorbed from the solution; b. TGA
c. carbon content obtained by CHN elemental analysis (average value of two analyses); d. value in parenthesis corresponds to detemplation method B.
The TGA patterns of the Fenton detemplated materials (Fig. 1) are formed by two weight losses. The
first one accounting 5-10 wt.% is centered at 130 °C, due to the release of physisorbed water.60. A broad
weight loss occurs from 200 until 900 °C (accounting 3-4 wt.%). The detemplation efficiency based on
TGA weight loss was calculated as well ( TGA, Table 2), which was found to range 71-86%. These values
are much smaller than the carbon-based efficiencies. This implies that the broad weight loss at 200-
900 °C is not only due to the residual carbon decomposition but, to a large extent, to the water from the
silanols condensation. Thus, for this type of mild detemplated samples the use of the carbon-based
detemplation efficiency ( CHN) most accurate.
The Fe concentration in the final detemplated samples was determined by ICP-AES, for those treated by
method A. It turns out that the Fe from the solution is adsorbed on the samples. Between 60 to 90% of
the Fe from the Fenton-solution is adsorbed on the samples’ surface, with absolute values ranging 0.07-
0.11 wt.%. This result could explain why not all the template is removed at the applied conditions. Once
the Fe cations (FeIII, FeII) are adsorbed on the material’s surface, its intrinsic Fenton activity decreases; it
is well known that the intrinsic activity of grafted Fe-based Fenton catalysts is inferior to that in solution
using homogeneous-based catalysts. 65
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
75
4.3.2 Silanols concentration
The relatively high weight loss between 200 and 900 °C observed in the TGA pattern indicates that the
material’s surface is highly hydroxylated after Fenton detemplation. The silanols’ concentration can be
calculated from the Blin-Carteret equation,64 which relates the silanols concentration as a function of the
TGA weight loss and surface area. This method was first applied to the calcined (Sx-C) and Fenton
detemplated materials (Sx-seFW). Figure 2 shows the absolute values and trends with the ageing
temperature. There is a decrease of the Si-OH concentration with the ageing temperature. This is
related to the higher degree of network condensation with the increasing ageing temperature, which
implies that less silanols are available on the surface due to the condesantion, which makes the material
more polymerized. We recently proposed that such a higher condensation makes the structure more
resistant to thermal contraction.36 The improved condensation with the synthesis or ageing temperature
have been reported for MCM-4166,67 and JLU-2068-70.
Figure 2. Silanols concentration based on the Blin-Carteret’s approach as a function of the ageing temperature for the calcined (Sx-C), Fenton-water-dried (Sx-seFW) and Fenton plus hydrothermal treatment (Sx-seFHT). Raw data are given in Table A2-2.
In terms of absolute values, the Fenton-derived materials have between 60 and 120 % higher silanol
concentration than the directly calcined counterparts, with a maxium obtained at 100 °C ageing
temperature, of the studied samples.
90 100 110 120 130 1400
2
4
6
8
Si-O
H co
ncen
tratio
n /
wt.%
Aging Temperature (x) / CAging Temperature (x) / °C
Si-O
H c
once
ntra
tion
/ wt.%
0
2
4
6
8
90 100 120110 130
Sx-C
Sx-seFWSx-seFHT
Chapter 4
76
4.3.3 Structural and textural characterization. Effect of the post-detemplation treatment.
Influence on structure and texture after Fenton detemplation.
After detemplation, the as-obtained template-free mesophases were characterized structurally and
texturally and compared to calcined ones and mesophases. Characterization by SAXS of the mesophases
(Fig. 3, A2-1 and A2-3) reveals a hexagonally packed cylindrical morphology characterized by a distance
Table 3. Argon-based textual properties of SBA-15 obtained under different detemplation routes.a
Material Treatmentsa VT / cm3 ·g-1 SBET / m2·g-1 DNLDFT
/ Å V / cm3 ·g-1 VIW / cm3 ·g-1 VIC
/ cm3 ·g-1
S90 C 1.034 678 106 0.054 0.263 0.209 seFHT 1.242 698 129 0.039 0.246 0.207 seFB 1.265 698 112 0.114 0.352 0.238 seFW 0.910 717 96 0.094 0.268 0.174
S95 C 1.049 724 106 0.085 0.354 0.269 seFHT 1.251 670 129 0.045 0.333 0.288 seFB 1.185 785 114 0.087 0.376 0.289 seFW 0.940 696 96 0.097 0.286 0.189
S100 C 1.170 701 116 0.059 0.379 0.320 seFHT 1.320 638 136 0.028 0.298 0.270 seFB 1.350 822 126 0.080 0.447 0.366 seFW 0.865 733 106 0.107 0.321 0.214
S110 C 1.224 645 126 0.045 0.345 0.300 seFHT 1.339 603 143 0.027 0.386 0.359 seFB 1.355 722 135 0.057 0.387 0.331 seFW 1.230 684 114 0.048 0.349 0.301
S130 C 1.276 509 143 0.020 0.280 0.260 seFHT 1.392 536 150 0.016 0.270 0.254 seFB 1.334 552 143 0.012 0.315 0.303 seFW 1.326 548 143 0.023 0.296 0.274
a. The nomenclature for the different treatments are given in Table 1 and the textural parameters are defined in the experimental part.
After detemplation, the as-obtained template-free mesophases were characterized structurally and
texturally and compared to calcined ones and mesophases. Characterization by SAXS of the mesophases
(Fig. 3, A2-1 and A2-3) reveals a hexagonally packed cylindrical morphology characterized by a distance
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
77
Figure 3. SAXS patterns for the SBA-15 mesophase aged at 90 oC (S90) after various treatments. Two detemplation protocols were applied: A) method A and B) method B. Additional SAXS patterns are given in Fig. A2-1 and A2-2.
between the cylinders of ~12.4 nm, from the position of the 100 reflection, and well-defined secondary
110 and 200 reflections with p6 mm symmetry. Figure 3-a illustrates one example, where several
treatments were applied to the S90 mesophase. The directly calcined material also reveals a similar
0,04 0,06 0,08 0,10 0,12 0,14
Inte
nsity
/ a.
u.
q-factor / Å-1
0,04 0,06 0,08 0,10 0,12 0,14
Inte
nsity
/ a.
u.
q-factor / Å-1
A
B
S90
S90
FW
M
FB FHT
C
seFBseFHTseFWCM
0.04 0.06 0.100.08 0.12 0.14
q-factor / Å-1
Inte
nsity
/a.u
.In
tens
ity/a
.u.
seFBseFWM
Chapter 4
78
Figure 4. A) Argon sorption isotherms at 87 K, B) corresponding pore size distribution (NLDFT); C) cumulative pore volume (NLDFT) and D) cumulative surface area (NLDFT), for S90 after different treatments. Additional graphs can be found in Fig. A2-3.
hexagonal ordering, though the entire pattern shifts towards higher angles due to thermal shrinkage.
The SAXS pattern of the Fenton-derived material (seFW) also has a hexagonal arrangement but the
pattern shifts to higher q-values and the intensity of peaks are remarkably reduced. In the case of
50 100 1500
2
4
6
8
10
PSD NL
DFT/
cm3 g-1
DNLDFT / Å
0.0 0.2 0.4 0.6 0.8 1.00
10
20
30
40
50
Qua
ntity
Ads
orbe
d/m
mol
·g-1
Relative Pressures p/p0
50 100 1500
200
400
600
800
DNLDFT / Å
SAD NL
DFT/
cm2 g-1
50 100 1500.0
0.2
0.4
0.6
0.8
1.0
1.2
PVD
NLDF
T/ cm
3 g-1
DNLDFT / Å
VIW
VICV
CseFWseFBseFHT
S90
B
C
D
A
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
79
detemplation method B, that is harsher than method A, the effect is even more catastrophic since the
100-reflection almost flattens (Fig. 3-b), and the complete disappearance of 110 and 200 secondary
reflections was observed, indicating a fully collapsed structure with severe shrinkage.
In Figure 5 the relative shrinkage in the unit cell ( a0), derived from the SAXS patterns (Fig. 3, A2-1 and
A2-2) is represented as a function of the ageing temperature for various treatments. The relative
shrinkage for the calcined materials decreases with the ageing temperature which is consistent with a
former study; 36 this was explained by the enhanced condensation of the network that makes it more
resistant to thermal deformation. It was remarkable to find that the Fenton–derived materials (series
SeFW) show higher shrinkage than the calcined counterparts in the series, with shrinkages as high as
13%. This effect was noticeable at lower ageing temperature while it disappears at high ageing
temperatures, 110 °C for the series under investigation.
Figure 5. Relative shrinkage ( a0, %) as a function of the ageing temperature for various treatments: calcination (Sx-C), Fenton-warer-dried (Sx-seFW), Fenton and n-BuOH exchange (Sx-seFB) and Fenton and hydrothermal treatment (Sx-seFHT). SAXS patterns are given in Fig. A2-1 and A2-2. Raw data are given in Table A2-2. Fenton protocol: method A.
The overall textural properties using Ar including isotherms, pore size distribution, cumulative pore
volume and cumulative surface area, based on the NLDFT model, are given in Figure 4, Fig. A2-3, and
raw data are compiled in Table 3. It is generally found that the SeFW materials show reduced total pore
90 100 110 120 1300
5
10
15
a0 /
%
Aging Temperature (x) / C
Sx-CSx-seFWSx-seFBSx-seFHT
Sx-CSx-seFWSx-seFBSx-seFHT
Aging Temperature (x) / °C90 100 120110 130
a 0/%
0
5
10
15
Chapter 4
80
volume and decreased mesopore’s diameter compared to the calcined counterparts. This trend is
consistent with the shrinkage of the silica framework with the formation of smaller pore that
contributes less to the pore volume. An exception is found for the S130-seFW that have similar textual
properties than the calcined counterpart due to relatively higher hydrothermal stability. The
microporosity of SeFW samples has increased in all cases due to shrinkage from the structural collapse.
Therefore, these textural trends are in line with the structural changes concluded from SAXS.
The possible explanation for the structural and textual modifications upon Fenton detemplation can be
ascribed to the drying conditions. Figure 6 shows the capillary forces applied on the walls of a
hexagonally arranged mesostructured material during drying. A calculation of the capillary forces
present on the material’s walls under water can be done by means of the Laplace equation; assuming
the major mesoposre diameter is 120 Å, pressures as high as ~150 bar can be generated during drying,
n SBA-15, which
is also known as intra-wall porosity, could suffer even more pressure due to smaller radii according to
Laplace equation. Additionally, the Fenton derived materials have a low degree of polymerization, since
they have not undergone further condensation except under the synthesis steps. All these factors favor
structural damage on the Fenton-derived mesophases, and even collapse when the structure aged at
low temperatures holds smaller pores and low hydrothermal stability.
Figure 6. Illustration of the capillary forces applied on the walls of a hexagonally arranged mesostructured material during drying. The pressure increase ( P) is given by the Laplace equation: r is the radii (half of the pore diameter), is the surface tension and is the contact angle.
Based on this hypothesis, the first apparent solution is reducing the capillary force to a minimum extent.
Basically, there is three main factors in the Laplace equation that can be changed: as radii, surface
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
81
tension constant and contact angle. Among these three factors, the major mesopore diameter is
dependent on aging temperature which has been adjusted at the range of
process. The simplest choices left are to adjust the value of surface tension constant and contact angle.
Both factors are physical properties that heavily depend on the applied solvent. So there is no doubt
that a solvent with smaller surface tension is highly desirable; as it was applied recently for soft MCM-
41.60 Another possible solution is to improve hydrothermal stability of silica mesophases to resist better
the damaging pressure from drying. Both approaches will be discussed in the following sections.
Approach I: Influence on structure and texture by solvent exchange after Fenton detemplation.
The main cause of structural and textual damage appears to be the capillary force as we discussed in the
former section. Therefore, solvent exchange has been performed immediately after Fenton oxidation to
the wet sample before drying. Among possible options, n-butanol (n-BuOH) was chosen as it is an
optimal solvent for this study; the reason for this choice is due to low surface tension ( n-BuOH =24.6
dyn/cm) which is only one-third of this value for water ( water =72.8 dyn/cm). Also, the relatively high
boiling-point of n-BuOH
solvents co-exist during the drying process. After the solvent is settled, two methods have been applied
in the subsequent solvent-exchange step corresponding to detemplation methods A and B respectively.
In method A, n-butanol exchange is performed as 5 washing steps at room temperature while method B
involves an extra equilibration st
guarantee a thorough exchange.
The samples after n-BuOH exchange were measured by SAXS as shown in Figure 3, for the S90
mesophase. By using method A, S90-seFB shows a q[100] value clearly smaller than directly dried (S90-
seFW) and calcined samples, but still the position of the q-factor for the 100 reflection is somewhat
higher than the precursor. That indicates that S90-seFB possess less shrinkage than the S90-seFW due to
the reduced pressure from the capillary forces. Nevertheless, the slight difference of q [100] peak
position, when compared with corresponding precursors (P in Fig. 3) demonstrates that the framework
contraction still exists. The calculated cell parameters (Table A2-2) shows that the shrinkage level of S90-
seFB is much less ( a0=5.8 %) than either calcined (10.1%) or S90-seFW (13.0%) samples.
On the other hand, exchange method B resulted in a better structural preservation for the same
mesophase. As shown in Figure 3-b, S90-seFB gives a nearly identical SAXS pattern as the precursor with
well-defined 100, 110 and 200 reflections. This improvement is not surprising since 24-hours equilibrium
Chapter 4
82
step for method B possibly promotes the efficiency of solvent exchange greatly. Consequently, water in
silica mesophases was more thoroughly exchanged by n-BuOH in method B rather than method A; and
the existence of water during drying, as we stated earlier, is the main cause of structural and textual
damage. So the structural damage after a more thorough solvent-exchange in method B becomes more
negligible.
When we extend the method A to four additional mesophases (Figure A2-1a and A2-2), similar
improvement is observed compared to the corresponding seFW and calcined counterparts; however,
the improvement is less prominent than for S90 since the mesophases get stable with the ageing
temperature. So for samples aged at relatively higher temperatures, S110 and S130, the n-BuOH shows
less visible improvement compared to the water drying (seFW) according to SAXS patterns. The effect of
the n-BuOH exchange is clearly demonstrated in Figure 5, where the relative shrinkage of the seFB series
is much lower than the seFW and inferior than the calcined materials, as a result of the better drying
conditions. The effect disappears with the ageing temperature, and eventually the sample S130 is
insensitive to calcination, FW or FB due to its high hydrothermal stability. It is noteworthy that method B
provided spectacular results in the sense that no shrinkage was obtained for the complete series (Fig. 3
and Fig. A2-1, b). However, from a practical stand point, we opted to study the texture of samples
derived from method A, since it is a much faster protocol. TEM pictures (Figure 7) for the S100-C and
S100-seFB shows a similar porous structure which is consistent with SAXS patterns.
Detailed textual information for these materials can be found in Table 3 and Fig. A2-2. The shape of
the isotherms was in all cases similar; type IV with H1 hysteresis, representing solids with cylindrical
pore geometry with relatively high pore size uniformity and facile pore connectivity (Fig. A2-2, a).71 The
pore sizes for the seFB were always larger than for the calcined and seFW, in that order (Fig. A2-2, b);
though the differences disappears at higher ageing temperatures. This indicates a less contracted
structure for the seFB series. The cumulative pore volume curves are consistent with the total pore
volume, seFB > C > seFW.
Approach II: Influence on structure and texture of in-situ hydrothermal treatment after
Fenton detemplation.
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
83
Another method developed to avoid the structural damage is a post hydrothermal treatment. The
purpose of this step is to obtain a structure with further condensation; in other words, with better
hydrothermal stability. Amorphous silica bears silanol groups on the surface as well as exposed siloxane
(Si-O-Si) bonds.72 The former one is hydrophilic and dominates the silica surface properties while the
latter one is normally considered as hydrophobic. The condensation level was evaluated by the Blin-
Carteret’s approach (Fig. 2). The condensation extent of hydrothermally treated samples (Sx-seFHT) is
intermediate between the Sx-seFW and Sx-C; which indicates that the hydrothermal step reduces the
surface Si-OH and condense the structure further by creating siloxane bonds.
Figure 7. TEM pictures for S100 after: a) calcination (S100-C); b) Fenton-detemplation via method A plus n-butanol exchange (S100-seFB).
From the ordering point of view, the hydrothermal treatment preserves the hexagonal structure (Fig. 3,
A2-1 and A2-2) and the observed relative shrinkage is also low, in the same order as that found for the
Sx-seFB series (Fig. 5). A similar dependency with the ageing temperature could be appreciated for this
treatment. Therefore this approach seems to be effective in avoiding capillary-tension induced
shrinkage. The shape of the adsorption isotherms are also similar, of the type IV with H1 hysteresis but
20 nm20 nm
20 nm20 nm20 nm20 nm
(a.)
(b.)
20 nm20 nm
Chapter 4
84
the hydrothermal treatment gave rise to an enlargement of the pore size with a decrease of the
micropore volume. This is consistent with the well-known trends of the effect of the ageing temperature
as reported by Galarneau et al.11 Thus, bigger pores are formed at expense of eliminating microporosity.
Figure 8. Textural parameter derived from Ar physisoprtion: A) total pore volume; B) specific surface area; C) micropore volume and D) Interconnecting porosity.
However, the comparison of the textural features reveals differences between the n-BuOH and
hydrothermal treatment. This can be appreciated in Fig. 8 where the surface area, total pore volume,
micropore volume and interconnecting pores are compared among the various detemplation
approaches, for the series of mesophases. In terms of total pore volume both post-detemplation
approaches produces the highest values with a maximum for S130. The highest microporosity was found
at low ageing temperatures for the SeFW due to the significant collapse and formation of micropores;
SeFB possesses a better defined structure with an intermediate fraction of microprores while those are
severely depleted after the hydrothermal treatment. The specific surface area for all the treatments do
have a maximum at around 100 °C ageing temperature; the SeFB shows the highest value with 822 m2.g-
Aging Temperature (x) / °C90 100 120110 130
V μ/ c
m3 g
-1
0
0.04
0.08
0.12C
0
4
8
2
Aging Temperature (x) / °C90 100 120110 130
V IC
/ cm
3 g-1
0
0.1
0.2
0.3
0.4D
90 100 110 120 130
V T /
cm3 g
-1
0
0.4
0.8
1.2
Sx AS B
ET /
m2 g
-10
200
400
600
800
CFWFBFHT
CseFWseFBseFHTB
90 100 110 120 1300
0
0
0
0
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
85
1 that was minimal for the seFHT series. The interconnecting pores, defined as those mesopores smaller
than the main channel, was estimated and it turns out that the optimal interconnecting porosity is
maximized for the S100-seFB with a value of 0.366 cm3.g-1 which represents 27% of the total pore
volume. A second candidate is the S110-seFHT with 0.359 cm3.g-1 with 27% of the total pore volume as
well.
4.3.4 Mechanistic insights about the structural changes upon the various post-treatments.
When we take a look at all methods including calcination and the Fenton related routes, it is clear that a
mild detemplation itself is not enough to obtain well-preserved structures despite of the full template
removal. The two post treatments we developed can greatly preserve the structures. Most interestingly,
the porosity is improved preferably in different fashions.
The mechanistic pathways including all the situations presented in this study are summarized in Figure 9.
When calcination is performed (process ), the structure is highly condensed and gets contracted
while having a good ordering and hierarchical porosity; the template is fully oxidized in this process. The
Fenton detemplation is quite effective in removing the template with only trace amount iron left on the
surface, likely as FeOx oxides species. The drying process can be devastating to the structure when the
SBA-15 mesophases after Fenton-detemplation are dried in water (process ). Therefore a less
ordered structure, or even totally disordered, is obtained in case of drying directly after Fenton
detemplation (Material E). The reason for this damage is because of the large capillary forces generated
during water evaporation within the pores; the effect is more pronounced for low-ageing temperature
materials while it disappears at high ageing temperatures. After exchanging water with n-butanol
(Material D), the capillary forces can be significantly reduced, thus the final dried material holds a better
preserved hierarchial structure (Material G), including quasi-pristine cell parameter, with enhanced
interconnecting pores and the highest specific surface area. The hydrothermal treatment is another
method to avoid the damage. The as-obtained SBA-15s are more condensed with higher cell parameter,
enhanced diameter of major mesopores and minimized secondary porosity, consequently having the
smallest surface area (material F).
Chapter 4
86
Figure 9. Transformation pathways of the SBA-15 mesophase after various detemplation routes discussed in this study: SBA-15 mesophase after solvent extraction (A, Sx-se); A after calcination (B, Sx-C); A after Fenton oxidation containing water (C); C after drying (E, Sx-seFW); C after n-BuOH exchange (D); D after drying (G, Sx-seFB); C after hydrothermal ageing and drying (F, Sx-seFHT). Nomenclature: CAL (calcination), FD (Fenton detemplation), SE (solvent exchange), D100 (dried at 100 oC), HT100/24 (hydrothermally treated at 100 oC for 24 h).
4.4 Conclusions
Full template removal (99%) of SBA-15 mesophases without thermal calcination is achieved in this work
after applying a Fenton-chemistry based detemplation method. The structural preservation can only be
achieved if a post-detemplation methodology is applied, due to the intense capillary forces when drying
in a water-based medium. Two routes have been successfully applied to overcome this: n-BuOH
exchange to dry the mesophase in a low-surface tension medium or the application of a hydrothermal
step after the Fenton detemplation in order to condense further the structure and become more
resistant to the capillary forces. Both approaches preserve better the structure in terms of the relative
shrinkage that is smaller than calcination, and Fenton water dried, but give rise to different type of
porosities. The n-BuOH exchange produces high surface areas and hierarchical porous structures with
enhanced interconnecting pores while the hydrothermal treatment yields materials with less
interconnectivity, larger pore sizes and consequently high pore volumes.
seF BE
H2O
a0
DNLDFT
C.
n-BuOH
D.
B. E. F. G.
CAL D100HT100/24,
D100 D100
Template Pluronic P123
A.
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
87
References
1. Kresge, C.; Leonowicz, M.; Roth, W.; Vartuli, J.; Beck, J. Ordered Mesoporous Molecular-Sieves Synthesized by a Liquid-Crystal Template Mechanism. Nature 1992, 359, 710-712.
2. Corma, A. From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem. Rev. 1997, 97, 2373-2419.
3. Taguchi, A.; Schuth, F. Ordered mesoporous materials in catalysis. Micropor. Mesopor. Mat. 2005, 77, 1-45.
4. Hartmann, M. Ordered mesoporous materials for bioadsorption and biocatalysis. Chem. Mater. 2005, 17, 4577-4593.
5. Davis, M. Ordered porous materials for emerging applications. Nature 2002, 417, 813-821.
6. Klichko, Y.; Liong, M.; Choi, E.; Angelos, S.; Nel, A. E.; Stoddart, J. F.; Tamanoi, F.; Zink, J. I. Mesostructured Silica for Optical Functionality, Nanomachines, and Drug Delivery. J Am Ceram Soc 2009, 92, S2-S10.
7. Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279, 548-552.
8. Zhao, D. Y.; Huo, Q. S.; Feng, J. L.; Chmelka, B. F.; Stucky, G. D. Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures. J. Am. Chem. Soc. 1998, 120, 6024-6036.
9. Zhang, F.; Yan, Y.; Yang, H.; Meng, Y.; Yu, C.; Tu, B.; Zhao, D. Understanding effect of wall structure on the hydrothermal stability of mesostructured silica SBA-15. J. Phys. Chem. B 2005, 109, 8723-8732.
10. Kruk, M.; Jaroniec, M.; Ko, C. H.; Ryoo, R. Characterization of the porous structure of SBA-15. Chem. Mater. 2000, 12, 1961-1968.
11. Galarneau, A.; Cambon, H.; Di Renzo, F.; Fajula, F. True microporosity and surface area of mesoporous SBA-15 silicas as a function of synthesis temperature. Langmuir 2001, 17, 8328-8335.
12. Imperor-Clerc, M.; Davidson, P.; Davidson, A. Existence of a microporous corona around the mesopores of silica-based SBA-15 materials templated by triblock copolymers. J. Am. Chem. Soc. 2000, 122, 11925-11933.
13. Jun, S.; Joo, S. H.; Ryoo, R.; Kruk, M.; Jaroniec, M.; Liu, Z.; Ohsuna, T.; Terasaki, O. Synthesis of new, nanoporous carbon with hexagonally ordered mesostructure. J. Am. Chem. Soc. 2000, 122, 10712-10713.
14. Joo, S.; Choi, S.; Oh, I.; Kwak, J.; Liu, Z.; Terasaki, O.; Ryoo, R. Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles. Nature 2001, 412, 169-172.
Chapter 4
88
15. Silvestre-Albero, A.; Jardim, E. O.; Bruijn, E.; Meynen, V.; Cool, P.; Sepulveda-Escribano, A.; Silvestre-Albero, J.; Rodriguez-Reinoso, F. Is There Any Microporosity in Ordered Mesoporous Silicas? Langmuir 2009, 25, 939-943.
16. Ravikovitch, P.; Neimark, A. Characterization of micro- and mesoporosity in SBA-15 materials from adsorption data by the NLDFT method. J. Phys. Chem. B 2001, 105, 6817-6823.
17. Galarneau, A.; Cambon, N.; Di Renzo, F.; Ryoo, R.; Choi, M.; Fajula, F. Microporosity and connections between pores in SBA-15 mesostructured silicas as a function of the temperature of synthesis. New J. Chem. 2003, 27, 73-79.
18. Lin, K.; Pescarmona, P. P.; Vandepitte, H.; Liang, D.; Van Tendeloo, G.; Jacobs, P. A. Synthesis and catalytic activity of Ti-MCM-41 nanoparticles with highly active titanium sites. J. Cata. 2008, 254, 64-70.
19. De Cremer, G.; Roeffaers, M. B. J.; Bartholomeeusen, E.; Lin, K.; Dedecker, P.; Pescarmona, P. P.; Jacobs, P. A.; De Vos, D. E.; Hofkens, J.; Sels, B. F. High-Resolution Single-Turnover Mapping Reveals Intraparticle Diffusion Limitation in Ti-MCM-41-Catalyzed Epoxidation. Angew. Chem. -Int. Edit. 2010, 49, 908-911.
20. De Cremer, G.; Bartholomeeusen, E.; Pescarmona, P. P.; Lin, K.; De Vos, D. E.; Hofkens, J.; Roeffaers, M. B. J.; Sels, B. F. The influence of diffusion phenomena on catalysis A study at the single particle level using fluorescence microscopy. Catal. Today 2010, 157, 236-242.
21. Lin, K.; Pescarmona, P. P.; Houthoofd, K.; Liang, D.; Van Tendeloo, G.; Jacobs, P. A. Direct room-temperature synthesis of methyl-functionalized Ti-MCM-41 nanoparticles and their catalytic performance in epoxidation. J. Cata. 2009, 263, 75-82.
22. Schmidt-Winkel, P.; Lukens, W.; Yang, P.; Margolese, D.; Lettow, J.; Ying, J.; Stucky, G. Microemulsion templating of siliceous mesostructured cellular foams with well-defined ultralarge mesopores. Chem. Mater. 2000, 12, 686-696.
23. Fan, J.; Yu, C. Z.; Wang, L. M.; Tu, B.; Zhao, D. Y.; Sakamoto, Y.; Terasaki, O. Mesotunnels on the silica wall of ordered SBA-15 to generate three-dimensional large-pore mesoporous networks. J. Am. Chem. Soc. 2001, 123, 12113-12114.
24. Fan, J.; Yu, C. Z.; Gao, T.; Lei, J.; Tian, B. Z.; Wang, L. M.; Luo, Q.; Tu, B.; Zhou, W. Z.; Zhao, D. Y. Cubic mesoporous silica with large controllable entrance sizes and advanced adsorption properties. Angew. Chem. -Int. Edit. 2003, 42, 3146-3150.
25. Kruk, M.; Hui, C. M. Synthesis and characterization of large-pore FDU-12 silica. Micropor. Mesopor. Mat. 2008, 114, 64-73.
26. Huang, L.; Yan, X.; Krut, M. Synthesis of Ultralarge-Pore FDU-12 Silica with Face-Centered Cubic Structure. Langmuir 2010, 26, 14871-14878.
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
89
27. Cao, L.; Man, T.; Kruk, M. Synthesis of Ultra-Large-Pore SBA-15 Silica with Two-Dimensional Hexagonal Structure Using Triisopropylbenzene As Micelle Expander. Chem. Mater. 2009, 21, 1144-1153.
28. Cao, L.; Kruk, M. Synthesis of large-pore SBA-15 silica from tetramethyl orthosilicate using triisopropylbenzene as micelle expander. Colloid Surface A 2010, 357, 91-96.
29. Kruk, M.; Cao, L. Pore size tailoring in large-pore SBA-15 silica synthesized in the presence of hexane. Langmuir 2007, 23, 7247-7254.
30. Mandal, M.; Kruk, M. Versatile approach to synthesis of 2-D hexagonal ultra-large-pore periodic mesoporous organosilicas. J. Mater. Chem. 2010, 20, 7506-7516.
31. Sayari, A.; Kruk, M.; Jaroniec, M.; Moudrakovski, I. New approaches to pore size engineering of mesoporous silicates. Adv Mater 1998, 10, 1376-+.
32. Yu, C.; Tian, B.; Fan, J.; Stucky, G.; Zhao, D. Salt effect in the synthesis of mesoporous silica templated by non-ionic block copolymers. Chem. Commun. 2001, 2726-2727.
33. Reichhardt, N.; Kjellman, T.; Sakeye, M.; Paulsen, F.; Smatt, J.; Linden, M.; Alfredsson, V. Removal of Intrawall Pores in SBA-15 by Selective Modification. Chem. Mater. 2011, 23, 3400-3403.
34. Zhu, J.; Kailasam, K.; Xie, X.; Schomaecker, R.; Thomas, A. High-Surface-Area SBA-15 with Enhanced Mesopore Connectivity by the Addition of Poly(vinyl alcohol). Chem. Mater. 2011, 23, 2062-2067.
35. Schueth, F.; Sing, K. S. W.; Weitkamp, J. In Handbook of Porous Solids 1551; Wiley -VCH: 2002; pp 1551.
36. Zhang, Z.; Yin, J.; Heeres, H. J.; Melian-Cabrera, I. Thermal detemplation of SBA-15 mesophases. Effect of the activation protocol on the framework contraction. Micropor. Mesopor. Mat. 2013, 176, 103-111.
37. Doyle, A.; Hodnett, B. K. Synthesis of 2-cyanoethyl-modified MCM-48 stable to surfactant removal by solvent extraction: Influence of organic modifier, base and surfactant. Micropor. Mesopor. Mat. 2003, 58, 255-261.
38. Ji, H.; Fan, Y. Q.; Jin, W. Q.; Chen, C. L.; Xu, N. P. Synthesis of Si-MCM-48 membrane by solvent extraction of the surfactant template. J. Non-Cryst. Solids 2008, 354, 2010-2016.
39. Knofel, C.; Lutecki, M.; Martin, C.; Mertens, M.; Hornebecq, V.; Llewellyn, P. L. Green solvent extraction of a triblock copolymer from mesoporous silica: Application to the adsorption of carbon dioxide under static and dynamic conditions. Micropor. Mesopor. Mat. 2010, 128, 26-33.
40. Lu, X. B.; Zhang, W. H.; Xiu, J. H.; He, R.; Chen, L. G.; Li, X. Removal of the template molecules from MCM-41 with supercritical fluid in a flow apparatus. Ind. Eng. Chem. Res. 2003, 42, 653-656.
Chapter 4
90
41. van Grieken, R.; Calleja, G.; Stucky, G. D.; Melero, J. A.; Garcia, R. A.; Iglesias, J. Supercritical fluid extraction of a nonionic surfactant template from SBA-15 materials and consequences on the porous structure. Langmuir 2003, 19, 3966-3973.
42. Huang, Z.; Huang, L.; Shen, S.; Poh, C.; Hidajat, K.; Kawi, S.; Ng, S. High quality mesoporous materials prepared by supercritical fluid extraction: effect of curing treatment on their structural stability. Micropor. Mesopor. Mat. 2005, 80, 157-163.
43. Keene, M. T. J.; Denoyel, R.; Llewellyn, P. L. Ozone treatment for the removal of surfactant to form MCM-41 type materials. Chem. Commun. 1998, 2203-2204.
44. Buchel, G.; Denoyel, R.; Llewellyn, P. L.; Rouquerol, J. In situ surfactant removal from MCM-type mesostructures by ozone treatment. J. Mater. Chem. 2001, 11, 589-593.
45. Yang, L.; Wang, Y.; Luo, G.; Dai, Y. Simultaneous removal of copolymer template from SBA-15 in the crystallization process. Micropor. Mesopor. Mat. 2005, 81, 107-114.
46. Xiao, L.; Li, J.; Jin, H.; Xu, R. Removal of organic templates from mesoporous SBA-15 at room temperature using UV/dilute H2O2. Micropor. Mesopor. Mat. 2006, 96, 413-418.
47. Lu, A. H.; Li, W. C.; Schmidt, W.; Schuth, F. Low temperature oxidative template removal from SBA-15 using MnO(4)(-)solution and carbon replication of the mesoporous silica product. J. Mater. Chem. 2006, 16, 3396-3401.
48. Xie Li-Li; Li Qing-Hua; Yuan Hao; Wang Li-Jun; Tian Zhen; Bing Nai-Ci UV/ozone Treatment on the Removal of the Organic Template from Mesoporous SBA-15. Acta Chimica Sinica 2008, 66, 2113-2116.
49. Xu, J.; Chen, M.; Liu, Y. M.; Cao, Y.; He, H. Y.; Fan, K. N. Vanadia supported on H2O2-detemplated mesoporous SBA-15 as new effective catalysts for the oxidative dehydrogenation of propane. Micropor. Mesopor. Mat. 2009, 118, 354-360.
50. Liu, Y. M.; Xu, J.; He, L.; Cao, Y.; He, H. Y.; Zhao, D. Y.; Zhuang, J. H.; Fan, K. N. Facile Synthesis of Fe-Loaded Mesoporous Silica by a Combined Detemplation-Incorporation Process through Fenton's Chemistry. J. Phys. Chem. C 2008, 112, 16575-16583.
51. Kecht, J.; Bein, T. Oxidative removal of template molecules and organic functionalities in mesoporous silica nanoparticles by H2O2 treatment. Micropor. Mesopor. Mat. 2008, 116, 123-130.
52. Jabariyan, S.; Zanjanchi, M. A. A simple and fast sonication procedure to remove surfactant templates from mesoporous MCM-41. Ultrason. Sonochem. 2012, 19, 1087-1093.
53. Tian, B. Z.; Liu, X. Y.; Yu, C. Z.; Gao, F.; Luo, Q.; Xie, S. H.; Tu, B.; Zhao, D. Y. Microwave assisted template removal of siliceous porous materials. Chem. Commun. 2002, 1186-1187.
54. Yang, C. M.; Zibrowius, B.; Schmidt, W.; Schuth, F. Consecutive generation of mesopores and micropores in SBA-15. Chem. Mater. 2003, 15, 3739-3741.
Mesoporous Materials SBA-15 with enhanced hierarchical porosity: a combined study of mild detemplation and structural preservation
91
55. Yang, C. M.; Zibrowius, B.; Schmidt, W.; Schuth, F. Stepwise removal of the copolymer template from mesopores and micropores in SBA-15. Chem. Mater. 2004, 16, 2918-2925.
56. Melian-Cabrera, I.; Kapteijn, F.; Moulijn, J. One-pot catalyst preparation: combined detemplating and Fe ionexchange of BEA through Fenton's chemistry. Chem. Commun. 2005, 2178-2180.
57. Melian-Cabrera, I.; Kapteijn, F.; Moulijn, J. Room temperature detemplation of zeolites through H2O2-mediated oxidation. Chem. Commun. 2005, 2744-2746.
58. Melian-Cabrera, I.; Espinosa, S.; Garcia-Montelogo, F.; Kapteijn, F.; Moulijn, J. Ion exchanged Fe-FER through H2O2-assisted decomplexation of organic salts. Chem. Commun. 2005, 1525-1527.
59. Zhang, Z.; Heeres, H. J.; Melián-Cabrera, I. V. In In Comprehensive detemplation studies of SBA-15 combining aspects of template removal and structural order preservation; Fourth International Symposium on Advanced micro- and mesoporous materials ; 2011; .
60. Perez, L. L.; Ortiz-Iniesta, M. J.; Zhang, Z.; Agirrezabal-Telleria, I.; Santes, M.; Heeres, H. J.; Melian-Cabrera, I. Detemplation of soft mesoporous silica nanoparticles with structural preservation. J. Mater. Chem. a 2013, 1, 4747-4753.
61. H.J.H.Fenton, M. A. Oxidation of Tartaric Acid in presence of Iron. J. Chem. Soc. , Trans. 1894, 65, 899-910.
62. Zhang, Z.; Santangelo, D. L.; ten Brink, G.; Kooi, B. J.; Moulijn, J. A.; Melián-Cabrera, I. On the drug adsorption capacity of SBA-15 obtained from various detemplation protocols. Mater. Lett. 2014, 131, 186-189.
63. Micromeritics Co. ASAP 2420, Norcross, GA.
64. Blin, J. L.; Carteret, C. Investigation of the silanols groups of mesostructured silica prepared using a fluorinated surfactant: Influence of the hydrothermal temperature. J. Phys. Chem. C 2007, 111, 14380-14388.
65. Walter Z. Tang Physicochemical Treatment of Hazardous Wastes; CRC Press: 2003; .
66. Mokaya, R. Improving the stability of mesoporous MCM-41 silica via thicker more highly condensed pore walls. J. Phys. Chem. B 1999, 103, 10204-10208.
67. Mokaya, R. Hydrothermally stable restructured mesoporous silica. Chem. Commun. 2001, 933-934.
68. Han, Y.; Li, D. F.; Zhao, L.; Song, J. W.; Yang, X. Y.; Li, N.; Di, Y.; Li, C. J.; Wu, S.; Xu, X. Z.; Meng, X. J.; Lin, K. F.; Xiao, F. S. High-temperature generalized synthesis of stable ordered mesoporous silica-based materials by using fluorocarbon-hydrocarbon surfactant mixtures. Angew. Chem. -Int. Edit. 2003, 42, 3633-3637.
Chapter 4
92
69. Yang, X. Y.; Zhang, S. B.; Qiu, Z. M.; Tian, G.; Feng, Y. F.; Xiao, F. S. Stable ordered mesoporous silica materials templated by high-temperature stable surfactant micelle in alkaline media. J. Phys. Chem. B 2004, 108, 4696-4700.
70. Li, D. F.; Han, Y.; Song, H. W.; Zhao, L.; Xu, X. Z.; Di, Y.; Xiao, F. S. High-temperature synthesis of stable ordered mesoporous silica materials by using fluorocarbon-hydrocarbon surfactant mixtures. Chem-Eur. J. 2004, 10, 5911-5922.
71. Kruk, M.; Jaroniec, M. Gas adsorption characterization of ordered organic-inorganic nanocomposite materials. Chem. Mater. 2001, 13, 3169-3183.
72. Schueth, F.; Sing, K. S. W.; Weitkamp, J. In Handbook of Porous Solids 1354; Wiley -VCH: 2002; pp 1354.