Applications of mesoporous titanium phosphonate functionalized with carboxylic groups

Article abstract of DOI:10.1039/c4ra06952h

Mesoporous titanium phosphonate functionalized with -COOH was synthesized by a simple co-condensation process with the use of 2-phosphonoacetic acid and titanium tetrachloride under acid conditions. The obtained mesoporous materials show high surface area and large pore volume, which were supported by XRD, TEM, SEM and N₂ adsorption analysis. The integrity of the organophosphonate groups were further characterized by FTIR and NMR. Palladium nanoparticles were successfully supported onto the materials combined with a metal adsorption-reduction procedure, showing high activity for the Suzuki reaction. Furthermore, the obtained catalyst can be recovered and reused without significant decrease in catalytic activity. This journal is

Full text of DOI:10.1039/c4ra06952h

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Applications of mesoporous titanium phosphonate
functionalized with carboxylic groups
Cite this: RSC Adv., 2014, 4, 44229
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Dongdong Li and Yuping Zhang
Mesoporous titanium phosphonate functionalized with –COOH was synthesized by a simple co-
condensation process with the use of 2-phosphonoacetic acid and titanium tetrachloride under acid
conditions. The obtained mesoporous materials show high surface area and large pore volume, which
were supported by XRD, TEM, SEM and N2 adsorption analysis. The integrity of the organophosphonate
groups were further characterized by FTIR and NMR. Palladium nanoparticles were successfully
supported onto the materials combined with a metal adsorption–reduction procedure, showing high
activity for the Suzuki reaction. Furthermore, the obtained catalyst can be recovered and reused without
significant decrease in catalytic activity.
Received 10th July 2014
Accepted 28th August 2014
DOI: 10.1039/c4ra06952h
www.rsc.org/advances
Introduction
Inorganic–organic hybrid materials have been a hot research
topic because of their combining properties of the inorganic
and organic components.1 These types of materials have the
advantage of possessing a uniform distribution of functional
organic groups within their framework, which allows us to
tailor their density, chemical reactivity, and thermal stability.2
To date, a large number of hybrid porous materials with
various chemical compositions and organic groups have been
well documented, showing interesting properties, such as
catalysts and adsorbents.3 Since the rst periodic mesoporous
organosilicas (PMOs) was reported in 1999, the preparation of
nonsilica-based inorganic–organic hybrid mesoporous mate-
rials has been regarded as one of the recent breakthroughs.4
Compared with the silica-based materials, metal organo-
phosphonates are more promising because of their unique
properties, such as proton conductivity, nonlinear optical
effects, electron transfer, topochemical reactivity and
photochromism.5
Scheme 1 The synthetic route of PAC.
in aqueous solution, which could serve as anchor sites for
adsorbing metal cations.9
In this work, we rst prepared 2-phosphonoacetic acid (PAC)
according to the synthetic route as shown in Scheme 1. Then, we
synthesized high surface area mesoporous titanium phospho-
nate functional with –COOH by a simple co-condensation
process. The synthesized material was fully characterized
using XRD, TEM, N2 adsorption, NMR and FTIR. This meso-
porous titanium phosphonate material exhibited high adsorb-
ing ability on Pd nanoparticles for catalysis, making it a
promising reaction carrier for practical applications.
Experimental section
Carboxylic acid is a well-known reactive group, so carboxyl
functionalized mesoporous materials are of signicant interest
for applications in separation, adsorption, catalysis, drug
delivery, and nanotechnology because of the created negative
charge and polarity.6 Traditional carboxyl-modied meso-
porous materials are more concentrated in silicon-based
materials.7 To date, carboxylic acid functionalized meso-
porous phosphonate has been applied to enzyme adsorption,
such as Shi et al. who have prepared mesoporous aluminum
organophosphates with chiral L-proline groups in the pores.8
Carboxylic groups have strong interaction with cationic species
Materials
Titanium tetrachloride (Tianjin Fengchuan Chemical Co., Ltd.),
ethyl bromoacetate (J&K Chemical Co., Ltd.), triethyl phosphite
(Chengdu Kelong Chemical Reagent Factory), hexadecyl-
trimethylammonium Chloride (CTAC, Tianjin Guangfu Chem-
ical Co., Ltd.). All the materials were purchased without further
purication.
Synthesis of ethyl-2-(diethoxyphosphoryl)acetate
A mixture of ethyl bromoacetate (2.2 g, 13.2 mmol) and triethyl
phosphite (2.19 g, 13.2 mmol) was heated in a ame-dried ask
to 90 ꢀC for 10 h. The mixture was allowed to cool down to afford
the desired product (2.83 g, 98%). 1H NMR (CDCl3, 300 MHz): d
Department of Materials Science, Jilin University, Changchun, 130012, P. R. China.
E-mail: lidongdong@jlu.edu.cn; Tel: +86-43185168540
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1.297–1.375 (m, 9H), 2.923–3.000 (d, 2H), 4.130–4.241 (m, 6H). measured on a Micromeritics Gemini V analyzer. Transmission
13C NMR (75 MHz, CDCl3): 165.7, 62.6, 61.4, 33.5, 16.2, 14.0.
electron microscopy (TEM) images were recorded with a JSM-
3010 electron microscope. Scanning electron microscopy
(SEM) images were recorded with a JSM-6700F electron micro-
scope. Infrared (IR) measurements of the samples dispersed in
KBr pellets were performed on a Perkin-Elmer spectrum 430
FTIR spectrometer. Solid-state 31P MAS NMR experiments were
taken on a Varian Innity-plus 300 spectrometer operating at
resonance frequency of 121.4 MHz, using a chemagnetic 4 mm
double-resonance probe with a spinning rate of 8 kHz. 13C MAS
experiments were performed on a Varian Innity-plus 400
spectrometer at a resonance frequency of 100.6 MHz using a 5
mm probe with a spinning rate of 8 kHz. The 13C and 31P
chemical shis were referenced to hexamethylbenzene (HMB)
and 85% H3PO4, respectively.
Synthesis of 2-phosphonoacetic acid (PAC)
Ethyl-2-(diethoxyphosphoryl)acetate (2.3 g, 10 mmol) and HCl
(50 mL) was heated to reux for 9 h, aer cooling to room
temperature the water was removed by distillation under reduced
pressure. The crude product was added to ethyl acetate (100 mL)
to stir at room temperature, then the white suspension was l-
trated and washed with ethyl acetate, the resulting white powder
was dried under vacuum (1.3 g, 93%). 1H NMR (D2O, 300 MHz): d
2.950–3.019 (d, 2H). 13C NMR (75 MHz, D2O): 168.7, 32.3.
Synthesis of mesoporous titanium phosphonate
functionalized with carboxylic groups (TiP)
In a typical synthesis procedure, CTAC (0.2 g, 0.625 mmol) and
PAC (0.14 g, 1 mmol) were added into deionized water (9 mL)
with vigorous stirring, and then TiCl4 (P/Ti molar ratio: 1.2/1) of
ethanol (2 mL) solution was added very slowly. The mixture was
placed in an ice water bath to slow down the hydrolysis of TiCl4,
and the pH value was adjusted to be ca. 4.0. A homogenous
colloidal solution was obtained aer another 3 h of stirring. The
obtained mixture was transferred to a Teon-lined autoclave
and crystallized statically at 120 ꢀC under autogenous pressure
for about 24 h. Then, the obtained precipitate was ltered and
reuxed in ethanol for 24 h to remove the template. The mes-
oporous titanium phosphonate functionalized with carboxylic
Results and discussion
The compound PAC was prepared according to the synthetic
route as shown in Scheme 1. Then, it was introduced into
mesoporous titanium phosphonate through P–O–Ti covalent
bonds by a one-pot condensation process by using CTAC as the
surfactant (Scheme 2). Aer removing the surfactant, the
material functionalized with carboxylic groups was obtained,
marked as TiP. The content of PAC introduced in TiP deter-
mined by ICP analysis was 1.2 mol gꢁ1 (Table 1).
Fig. 1 shows the X-ray diffraction patterns of TiP and TiP–Pd
samples. It can be seen that the samples exhibit only one single
broad low-angle reection at 2q ¼ 1.5ꢀ (Fig. 1a), indicating these
hybrid materials have a “wormlike” mesoporous structure,
which may be because the incorporation of PAC disturbed the
formation of a well-ordered structure. With the incorporation of
Pd nanoparticles, the intensity of the diffraction peak decreased
and produces a large platform (Fig. 1b), suggesting more
disordered structure of TiP–Pd.
ꢀ
groups was obtained aer drying at 60 C, marked as TiP.
Catalysis experiments
Preparing palladium nanoparticles on the support TiP:palla-
dium(II) chloride (10 mg, 0.056 mmol) and NaCl (70 mg, 1.2
mmol) were dissolved in water (10 mL) for 15 min under a
nitrogen atmosphere. TiP (200 mg) was then added to the
solution and further stirred for 1 h at room temperature. The
reaction mixture was ltered, washed with ethanol, and dried
overnight under vacuum. Then, the material was dispersed in
ethanol (10 mL), and a freshly prepared 0.05 M NaBH4 ethanol
solution (5 mL) was slowly added with vigorous stirring. Aer
reduction for about 6 h, the mixture was ltered and washed
thoroughly with deionized water and dried under vacuum at
room temperature. The amount of Pd loaded in TiP was
0.12 mmol gꢁ1 according to the ICP analysis.
In a typical reaction, p-iodoanisole (50 mg, 0.21 mmol) was
reacted with a slight excess of boronic acid derivative (0.32 mmol)
at 80 ꢀC in DMF (2 mL) in the presence of K2CO3 (78 mg) and the
catalyst (10 mg), and the reaction mixture was stirred under N2.
Aer reacting for about 2 h, the mixture was cooled to room
temperature. The catalyst was ltered and washed with EtOAc.
The pure product was isolated by column chromatography.
Scheme 2 The synthesized route of Pd nanoparticles supported on
mesoporous titanium phosphonate.
Table
1 Physicochemical data for surfactant-extracted TiP and
TiP–Pd
Characterizations
Sample PAC mol gꢁ1 Pd mmol gꢁ1 SBET m2 gꢁ1 V cm3 gꢁ1 DBJH nm
Powder X-ray diffraction (XRD) patterns were recorded on a
Rigaku D/MAX 2500/PC X-ray diffractometer with Cu Ka radia-
TiP
TiP–Pd 1.2
1.2
—
0.12
458
300
0.53
0.33
2.6
2.5
tion. N2 adsorption–desorption isotherms at 77
K were
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volume of 0.53 cm3 gꢁ1 and corresponding pore size distribu-
tion displays only one well-dened peak centered at 2.6 nm.
When Pd nanoparticles were incorporated into the material, its
N2 adsorption is lower and the pore size distribution is slightly
decreased. The textural parameters of TiP and TiP–Pd are
summarized in Table 1.
The spherical particles morphology of the material TiP was
characterized by scanning electron microscopy (SEM) at
different magnication, as shown in Fig. 3. The TEM micro-
graph (Fig. 4a) indicates that all the spherical particles are
attached together and the presence of “wormlike” pore struc-
ture with about 2–3 nm, which is well consistent with XRD and
N2 adsorption. Aer loading Pd nanoparticles, there is no
apparent change in the materials. As seen in the high magni-
cation TEM image (Fig. 4b), the Pd nanoparticles are clearly
distinguishable with the average size around 5 nm. This may be
a consequence of the good stability effect of carboxylic groups to
the palladium nanoparticles.
Fig. 1 Low angle XRD patterns of (a) TiP, and (b) TiP–Pd; (inset picture)
wide angle of TiP–Pd.
Fig. 5 is the FTIR spectra of TiP and PAC. According to the
literature, the broad band at 3405 cmꢁ1 can be attributed
mainly to the –OH stretching vibration of the residual water.
The strong band at 1718 cmꢁ1 is attributed to the –COOH
stretching vibration.10 The wide band at 1034 cmꢁ1 is the
characteristic of Ti–O–P framework vibration. In brief, the FTIR
data supports the conclusion that the organophosphonate PAC
was successfully incorporated into the materials.
The mesoporous structure was further conrmed by
nitrogen adsorption at 77 K. Fig. 2 exhibits the N2 adsorption–
desorption isotherms and the corresponding pore size distri-
bution curves of the materials. The isotherm of TiP is type IV
according to the IUPAC classication, with the H2 hysteresis
loop at relative low pressure, characteristic of mesoporous
materials. It has a specic BET surface area of 458 m2 gꢁ1, pore
The maintenance of organic groups in the synthesized
materials was further conrmed by 31P and 13C MAS NMR
spectra (Fig. 6). Fig. 6a shows the 31P MAS NMR spectra of TiP,
presenting one peak at around 17 ppm, which can be assigned
to the organic phosphorus species. In 13C MAS NMR spectra,
TiP shows a peak at 177 ppm attributed to the carbon in
–COOH and –COOꢁ groups. The signals at 36 ppm are related
to the carbon atoms between the carboxyl group and the
Fig. 3 The SEM images of the support TiP at different magnification.
Fig. 2 (a) N2 adsorption–desorption isotherms of TiP, TiP–Pd at 77 K
and (b) corresponding pore size distribution curves (BJH method).
Fig. 4 The TEM images of (a) TiP, (b) TiP–Pd.
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Fig. 5 The FTIR spectra of (a) TiP and (b) PAC sample.
Fig. 7 XPS Pd 3d spectra of TiP–Pd samples.
Table 2 The coupling reactions of p-iodoanisole with various aryl-
boronic acids
Entry
1
3
Yield (%)
1
2
H
92
97
p-OMe
3
4
5
o-OMe
p-Ac
98
98
94
p-NO2
various arylboronic acids were carried out under an N2
atmosphere. As shown in Table 2, the reaction afforded
almost a 100% yield, showing that this material is an effective
catalyst carrier for palladium nanoparticles. Furthermore, the
catalyst can be reused for ve cycles without signicant loss in
Fig. 6 31P MAS NMR spectra and 13C MAS NMR spectra of TiP.
phosphonic group. In summary, the 31P and 13C MAS NMR
data not only support the presence of organophosphonate in
the structures, but also conrm the integrity of PAC aer the
template removal.
Carboxyl groups are uniformly distributed on the surface
of TiP, which are good ligands for inorganic species. Thus, the
synthesized materials may nd potential applications in the
elds of catalysis. In this work, we used this material to
adsorb palladium(II) ion and reduce it to the zero valent
examined by XRD (Fig. 1, inset) and X-ray photoelectron
spectroscopic (XPS) technique (Fig. 7). We can see the
appearance of diffraction peaks at 39.4ꢀ, 46.1ꢀ because of Pd
in the metallic state (Fig. 1, inset). The presence of new Pd
3d3/2 and Pd 3d5/2 peaks at lower binding energies of 340.6 eV
and 335.1 eV further indicates that Pd metals are formed.11
Fig. 4b shows that the palladium nanoparticles are almost 5
nm, which may show catalytic activity on the Suzuki reaction.
On the basis of the optimized reaction conditions, the
coupling reactions between a range of p-iodoanisole and Fig. 8 The reusability of the catalyst.
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activity by taking p-iodoanisole and phenylboronic acid, for
example, demonstrating the efficiency of the catalyst (Fig. 8).
K. Yasuda, K. Hirao and T. Yazawa, J. Am. Ceram. Soc.,
2004, 87, 504.
3 B. Lee, Y. Kim, H. Lee and J. Yi, Microporous Mesoporous
Mater., 2001, 50, 77; X. B. Ma, J. Liu, L. S. Xiao, R. Chen,
J. Q. Zhou and X. K. Fu, J. Mater. Chem., 2009, 19, 1098;
B. Malvi, B. R. Sarkar, D. Pati, R. Mathew, T. G. Ajithkumar
and S. S. Gupta, J. Mater. Chem., 2009, 19, 1409.
4 T. Y. Ma, X. Z. Lin and Z. Y. Yuan, J. Mater. Chem., 2010, 20,
7406; B. Z. Tian, X. Y. Liu, B. Tu, C. Z. Yu, J. Fan, L. M. Wang,
S. H. Xie, G. D. Stucky and D. Y. Zhao, Nat. Mater., 2003, 2,
159; X. Shi, J. Liu, C. M. Li and Q. H. Yang, Inorg. Chem.,
2007, 46, 7944.
Conclusions
In conclusion, high surface area mesoporous titanium orga-
nophosphonate materials functionalized with a carboxyl group
have been synthesized by the use of cationic surfactant CTAC as
the structure-directing agent. Organic carboxyl groups maintain
their integrity in the mesoporous materials, which was an
effective ligand for palladium nanoparticles. The as-prepared
nanosized palladium particles have a narrow size distribution
(5 nm), showing high catalytic activity on the Suzuki reaction.
Importantly, the catalyst can be reused for several times without
the sharp loss of catalytic activity. Because the carboxyl group is
a particularly useful reactive group, this material may nd a
wide range of potential applications in other elds, such as
biomedicine etc.
5 T. Y. Ma, X. J. Zhang, G. S. Shao, J. L. Cao and Z. Y. Yuan, J.
´
Phys. Chem. C, 2008, 112, 3090; V. F. D. Alvaro and
R. A. W. Johnstone, J. Mol. Catal. A: Chem., 2008, 280, 131.
6 S. Sumiya, Y. Kubota, Y. Oumi, M. Sadakane and T. Sano,
Appl. Catal., A, 2010, 372, 82; Z. Yan, S. Y. Tao, J. X. Yin
and G. T. Li, J. Mater. Chem., 2006, 16, 2347.
7 S. Fiorilli, B. Camarota, D. Perrachon, M. C. Bruzzoniti,
E. Garronez and B. Onidaz, Chem. Commun., 2009, 4402;
I. Kornarakis, G. Sopasis, C. J. Miliosb and G. S. Armatas,
RSC Adv., 2012, 2, 9809; C. C. Ting, C. H. Chung and
H. M. Kao, Chem. Commun., 2011, 47, 5897.
8 X. Shi, J. Yang and Q. H. Yang, Eur. J. Inorg. Chem., 2006,
1936.
Acknowledgements
This work is supported by the China Postdoctoral Science
Foundation (801141002416).
9 M. C. Bruzzoniti, A. Prelle, C. Sarzanini, B. Onida, S. Fiorilli
and E. Garrone, J. Sep. Sci., 2007, 30, 2414; M. C. Bruzzoniti,
C. Sarzanini, A. M. Torchia, M. Teodoro, F. Testa, A. Virga
and B. Onida, J. Mater. Chem., 2011, 21, 369; H. Wang,
Y. F. Yu, Q. W. Chen and K. Cheng, Dalton Trans., 2011, 40,
559.
Notes and references
1 A. P. Wight and M. E. Davis, Chem. Rev., 2002, 102, 3589;
10 S. C. Shen, P. S. Chow, S. G. Kim, K. W. Zhu and R. B. H. Tan,
J. Colloid Interface Sci., 2008, 321, 365; S. Fiorilli, B. Onida,
B. Bonelli and E. Garrone, J. Phys. Chem. B, 2005, 109, 16725.
11 A. J. Amali and R. K. Rana, Green Chem., 2009, 11, 1781;
F. W. Zhang, J. Jin, X. Zhong, S. W. Li, J. R. Niu, R. Li and
J. T. Ma, Green Chem., 2011, 13, 1238.
¨
F. Hoffmann, M. Cornelius, J. Morell and M. Froba, Angew.
Chem., Int. Ed., 2006, 45, 3216; J. A. Melero, R. van Grieken
and G. Morales, Chem. Rev., 2006, 106, 3790; A. Burns,
H. Ow and U. Wiesner, Chem. Soc. Rev., 2006, 35, 1028.
2 R. K. Zeidan, S. J. Hwang and M. E. Davis, Angew. Chem., Int.
Ed., 2006, 45, 6332; T. Kikukawa, K. Kuraoka, K. Kawabe,
This journal is © The Royal Society of Chemistry 2014
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