- Email: [email protected]
Effect of various templates on the formation of mesoporous benzene-silica hybrid material
Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.
429 429
Effect of various templates on the formation of mesoporous benzene-silica hybrid material K.-F. Zhou a , Q.-H. Xia a '*, H.-B. Zhu a , D. Hu a and Z.-M. Liu b * a
Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, China b Dalian Institute of Chemical Physics, Academia Sinica, Dalian 116023, China.
The chain length of the template seriously affected the formation of mesoporous benzene-silica hybrid material from a basic medium under our experimental conditions. Only Ci6 surfactant could template a PMO solid with XRD peaks at low angles of 26 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. PMO materials could not be formed by [CnH2n+i(CH3)3N+, n=8, 12, 22] and [(CnH2n+i)4NOH, n = 2, 4], but the recovered organosilica solids possessed similar infrared framework vibrations and XRD peaks at high angles of ca. 20=11.5, 23.4, 35.4°. In an acidic medium mesoporous benzene-silica hybrid materials could be mediated by [CnH2n+i(CH3)3N+, n=12, 16], in which C ]6 templated a 3D-cage like mesopore structure, similar to SBA-1. Keywords: mesoporous benzene-silica, PMO, MCM-41, SBA-1 1. Introduction Inagaki et al. reported the surfactant-mediated synthesis of a benzene-silica hybrid PMO material in 2002 [1]. Since then, much effort has been focused on the research of various organic-inorganic hybrid periodic mesoporous organosilicas (PMO) using some organic silicate esters as starting materials [2]. Those PMO materials are thought to consist of crystal-like wall structures, as evidenced mainly by XRD patterns, where additional four sharp peaks emerge at d=1.6, 3.8, 2.5 and 1.9 A (29 = 10-70°), different from those of MCM-41. The literature proposed that the self-assembly of organosilane BTEB molecules formed the periodic structure in the walls of the mesoporous benzene-silica, probably because hydrophobic and hydrophilic interactions directed the selfassembly of BTEB molecules [1]. Our present results show that the formation
430
of mesoporous benzene-silica hybrid solid in a basic medium could be similar to that of MCM-41, while in an acidic medium similar to that of SB A-1. 2. Experimental Section The used alkyl ammoniums included [CnH2n+i(CH3)3NBr, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4) ], and organosilica source was 1,4-bis(triethoxysilyl) benzene (BTEB, 98 wt%, self-made [3]). The synthesis of PMO in a basic medium was carried out in the following procedure. Appropriate amount of surfactant was first dissolved in the solution consisting of 120 g of distilled water and 7 ml of 3 M aqueous NaOH at 25°C. While stirring vigorously, 3.24 g of BTEB was well dispersed into the basic solution. The molar composition was 0.806BTEB: 0.63surf.: 2.1NaOH : 667H2O. The stirring was continued for another 24 h, then the suspension was statically refluxed at 90°C for a period of 72-240 h. Thereafter, the white solid was recovered by filtration, washed repeatedly with distilled water, and dried at 100°C overnight. The surfactant molecules were removed by extraction through stirring the as-prepared solids in the solution of 200 ml ethanol and 6 ml concentrated HC1 (36%) at60°C for 6 h, followed by filtration and drying at 80 °C for 5 h. This extraction was repeated twice. In an acidic medium mesoporous benzene-silica materials were synthesized in the presence of [CnH2n+i(CH3)3N+, n=12,16]. Under stirring the surfactant was dissolved in the solution consisting of 10 ml concentrated HC1 and 36 ml water at 0, 23, 30 and 60°C, respectively. While stirring vigorously, 2.25 g of BTEB was dispersed into the acidic solution. The molar composition was 5.6BTEB: 3.3surf.: 323.6HC1: 2000H2O. The stirring was continued for another 24 h, and then the suspension was statically aged for 72 h at 0, 23, 30 and 90 °C, respectively. Finally, the recovered solid underwent identical treatments as described above. All the solid samples were well characterized by XRD, IR, BET, TEM and 13C CP MAS NMR techniques. 3. Results and Discussion In a basic medium the addition of Ci6H33(CH3)3N+ achieved benzene-silica PMO material, while the use of both [CnH2n+,(CH3)3N+, n=8,12,22] and [(CnH2n+i)4NOH, n=2,4] did not yield any mesoporous solid. Figure 1 compares XRD patterns and IR spectra of six solids templated by [CnH2n+i(CH3)3N+, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4] in the basic medium, in which six samples show similar IR framework vibrations. The sample synthesized with Ci6 exhibits an XRD pattern of highly ordered PMO solid, but others mediated by Cg, C12, C22 and [(CnH2n+04NOH, n=2,4] do not show any mesoporous characteristic. These samples show similar diffraction peaks at high angles of ca 20=11.5, 23.4 and 35.4°, while the PMO induced by Q 6 contains diffraction peaks at low angles of 26= 2.0, 3.6 and 4.2°, similar to ordered MCM-41.
431 C-22 5000 5000 -
C-16
Intensity /cps
SB 4000 -
C-12 C-8
' 3000 3000 -
C-4 C-2
C-16 C-22 C-12 C-8
2000 1000 1000 -
4000 400 4000 3600 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400
0 0
-1 WAVENUMBER / / cm-1
C-4
C-2 5
10
15 15
20 25 20 25 2θ 2θ/°/°
30
35
40
Figure 1. Effect of basic medium on IR spectra and XRD patterns of samples. -Ph-Ph* band * Side band
*
ULU *
*
300 300
250 250
200 200
150 150
100 100 ppm ppm
50
0
-50 -50
Figure 2. 1 3 C CP MAS NMR spectrum. 13/-
Figure 3. TEM image of 3D-cage pore.
C CP MAS NMR spectrum of thus-synthesized PMO solid contains only one signal at 133.2 ppm, with some side bands, due to the phenylene carbon (Fig. 2). The formation of benzene-silica PMO solid from a basic medium was affected by the chain length of the template. The PMO solid induced by C 1 6 had well-defined mesopores averaging 31 A, a pore volume of 0.46 cm3/g, and a surface area of 858 m2/g. Surface area (m2/g) and pore volume (crnVg) of other organosilica solids were (342.8, 0.18)for C 22 , (595.6, 0.62)for C 12 , (233.2, 0.35) for C8, (541.2, 1.17) for (C4H9)4NOH, (504.4, 0.93) for (C 2 H 9 ) 4 NOH without detectable mesopore. This seems to indicate a possible mechanism, i.e. BTEB molecules were first hydrolyzed by aqueous base to form negatively-charged benzene-silica hybrid colloidal particles with a certain degree of polymerization, which then surrounded positively-charged rod-like micelles in the solution to array hexagonally into integrated mesoporous framework.
432 C-16 (60°C, (60°C, 90°C)
^f
5000
Intensity/cps
^T\
C-16 (30°C, 30°C) C-16 (0°C, 30°C)
4000 . 4000
C-16 (0°C, 0°C) C-12 (23°C, 23°C)
3000
°C) C-16 (30°C, 30 C-16(30°C, 30°C) C-16(0°C, C-16 (0°C, 00°C) °C) C-16(0°C, 30°C) °C) C-16 (0°C, 30 C-16 (60 (60°C, 90°C) °C, 90 °C) C-16 C-12 °C, 23 °C) C-12 (23 (23°C, 23°C)
2000 • 1000 1000 •
4000 3600 400 4000 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400 -1 WAVENUMBER/cm WAVENUMBER /cm-1
0 0 0
2
4
6
8
10
2θ /° 2θ/°
Figure 4. Effect of acidic medium on IR spectra and XRD patterns of samples.
In an acidic medium mesoporous benzene-silica hybrid materials could be formed in the presence of d e ^ C F t ^ N * and Ci2H25(CH3)3N+. After the removal of tern plate molecules by extraction, the sample templated by Ci6 exhibits three diffraction peaks at low angles of ca. 20 = 2.02, 2.24, 2.44°, similar to those of a 3D-cage SBA-1, obviously different from that induced by Cn with only a broad XRD peak at ca. 2.92° 20 (Fig. 4). IR spectra in Fig. 4 show the similarity of their infrared framework vibrations, and the difference from those in Fig. 1. The use of C]6 was beneficial to the formation of benzenesilica solid from an acidic medium, which was evidenced by TEM image in Fig. 3. This material possessed a 3D-cage like pore structure [4], with a pore size of ca. 28 A, a pore volume of 0.31 cm /g, and a surface area of 529.3 m /g. 4. Conclusion The formation of mesoporous benzene-silica solid from a basic medium was affected by the chain length of organic templates, in which only Ci 6 effectively templated a PMO solid with XRD peaks at low angles of 20 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. Six samples displayed similar diffraction peaks at high angles of ca. 2#=11.5, 23.4, 35.4°, which seems to propose the similarity of formation processes of PMO and ordered MCM-41 in the basic solution. In an acidic medium mesoporous benzene-silica materials could be mediated by [CnH2n+i(CH3)3N+, n=12,16], in which only Ci6 templated a 3Dcage like mesopore structure similar to SBA-1. 5. References [1] [2] [3] [4]
S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. F. Fajula and F. Di Renzo, Microporous Mesoporous Mater., 82 (2005) 227. K. J. Shea, D. A. Loy and O. Webster, J. Am. Chem. Soc, 114 (1992) 6700. Y. Goto and S. Inagaki, Microporous Mesoporous Mater., 89 (2006) 103.
429 429
Effect of various templates on the formation of mesoporous benzene-silica hybrid material K.-F. Zhou a , Q.-H. Xia a '*, H.-B. Zhu a , D. Hu a and Z.-M. Liu b * a
Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, China b Dalian Institute of Chemical Physics, Academia Sinica, Dalian 116023, China.
The chain length of the template seriously affected the formation of mesoporous benzene-silica hybrid material from a basic medium under our experimental conditions. Only Ci6 surfactant could template a PMO solid with XRD peaks at low angles of 26 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. PMO materials could not be formed by [CnH2n+i(CH3)3N+, n=8, 12, 22] and [(CnH2n+i)4NOH, n = 2, 4], but the recovered organosilica solids possessed similar infrared framework vibrations and XRD peaks at high angles of ca. 20=11.5, 23.4, 35.4°. In an acidic medium mesoporous benzene-silica hybrid materials could be mediated by [CnH2n+i(CH3)3N+, n=12, 16], in which C ]6 templated a 3D-cage like mesopore structure, similar to SBA-1. Keywords: mesoporous benzene-silica, PMO, MCM-41, SBA-1 1. Introduction Inagaki et al. reported the surfactant-mediated synthesis of a benzene-silica hybrid PMO material in 2002 [1]. Since then, much effort has been focused on the research of various organic-inorganic hybrid periodic mesoporous organosilicas (PMO) using some organic silicate esters as starting materials [2]. Those PMO materials are thought to consist of crystal-like wall structures, as evidenced mainly by XRD patterns, where additional four sharp peaks emerge at d=1.6, 3.8, 2.5 and 1.9 A (29 = 10-70°), different from those of MCM-41. The literature proposed that the self-assembly of organosilane BTEB molecules formed the periodic structure in the walls of the mesoporous benzene-silica, probably because hydrophobic and hydrophilic interactions directed the selfassembly of BTEB molecules [1]. Our present results show that the formation
430
of mesoporous benzene-silica hybrid solid in a basic medium could be similar to that of MCM-41, while in an acidic medium similar to that of SB A-1. 2. Experimental Section The used alkyl ammoniums included [CnH2n+i(CH3)3NBr, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4) ], and organosilica source was 1,4-bis(triethoxysilyl) benzene (BTEB, 98 wt%, self-made [3]). The synthesis of PMO in a basic medium was carried out in the following procedure. Appropriate amount of surfactant was first dissolved in the solution consisting of 120 g of distilled water and 7 ml of 3 M aqueous NaOH at 25°C. While stirring vigorously, 3.24 g of BTEB was well dispersed into the basic solution. The molar composition was 0.806BTEB: 0.63surf.: 2.1NaOH : 667H2O. The stirring was continued for another 24 h, then the suspension was statically refluxed at 90°C for a period of 72-240 h. Thereafter, the white solid was recovered by filtration, washed repeatedly with distilled water, and dried at 100°C overnight. The surfactant molecules were removed by extraction through stirring the as-prepared solids in the solution of 200 ml ethanol and 6 ml concentrated HC1 (36%) at60°C for 6 h, followed by filtration and drying at 80 °C for 5 h. This extraction was repeated twice. In an acidic medium mesoporous benzene-silica materials were synthesized in the presence of [CnH2n+i(CH3)3N+, n=12,16]. Under stirring the surfactant was dissolved in the solution consisting of 10 ml concentrated HC1 and 36 ml water at 0, 23, 30 and 60°C, respectively. While stirring vigorously, 2.25 g of BTEB was dispersed into the acidic solution. The molar composition was 5.6BTEB: 3.3surf.: 323.6HC1: 2000H2O. The stirring was continued for another 24 h, and then the suspension was statically aged for 72 h at 0, 23, 30 and 90 °C, respectively. Finally, the recovered solid underwent identical treatments as described above. All the solid samples were well characterized by XRD, IR, BET, TEM and 13C CP MAS NMR techniques. 3. Results and Discussion In a basic medium the addition of Ci6H33(CH3)3N+ achieved benzene-silica PMO material, while the use of both [CnH2n+,(CH3)3N+, n=8,12,22] and [(CnH2n+i)4NOH, n=2,4] did not yield any mesoporous solid. Figure 1 compares XRD patterns and IR spectra of six solids templated by [CnH2n+i(CH3)3N+, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4] in the basic medium, in which six samples show similar IR framework vibrations. The sample synthesized with Ci6 exhibits an XRD pattern of highly ordered PMO solid, but others mediated by Cg, C12, C22 and [(CnH2n+04NOH, n=2,4] do not show any mesoporous characteristic. These samples show similar diffraction peaks at high angles of ca 20=11.5, 23.4 and 35.4°, while the PMO induced by Q 6 contains diffraction peaks at low angles of 26= 2.0, 3.6 and 4.2°, similar to ordered MCM-41.
431 C-22 5000 5000 -
C-16
Intensity /cps
SB 4000 -
C-12 C-8
' 3000 3000 -
C-4 C-2
C-16 C-22 C-12 C-8
2000 1000 1000 -
4000 400 4000 3600 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400
0 0
-1 WAVENUMBER / / cm-1
C-4
C-2 5
10
15 15
20 25 20 25 2θ 2θ/°/°
30
35
40
Figure 1. Effect of basic medium on IR spectra and XRD patterns of samples. -Ph-Ph* band * Side band
*
ULU *
*
300 300
250 250
200 200
150 150
100 100 ppm ppm
50
0
-50 -50
Figure 2. 1 3 C CP MAS NMR spectrum. 13/-
Figure 3. TEM image of 3D-cage pore.
C CP MAS NMR spectrum of thus-synthesized PMO solid contains only one signal at 133.2 ppm, with some side bands, due to the phenylene carbon (Fig. 2). The formation of benzene-silica PMO solid from a basic medium was affected by the chain length of the template. The PMO solid induced by C 1 6 had well-defined mesopores averaging 31 A, a pore volume of 0.46 cm3/g, and a surface area of 858 m2/g. Surface area (m2/g) and pore volume (crnVg) of other organosilica solids were (342.8, 0.18)for C 22 , (595.6, 0.62)for C 12 , (233.2, 0.35) for C8, (541.2, 1.17) for (C4H9)4NOH, (504.4, 0.93) for (C 2 H 9 ) 4 NOH without detectable mesopore. This seems to indicate a possible mechanism, i.e. BTEB molecules were first hydrolyzed by aqueous base to form negatively-charged benzene-silica hybrid colloidal particles with a certain degree of polymerization, which then surrounded positively-charged rod-like micelles in the solution to array hexagonally into integrated mesoporous framework.
432 C-16 (60°C, (60°C, 90°C)
^f
5000
Intensity/cps
^T\
C-16 (30°C, 30°C) C-16 (0°C, 30°C)
4000 . 4000
C-16 (0°C, 0°C) C-12 (23°C, 23°C)
3000
°C) C-16 (30°C, 30 C-16(30°C, 30°C) C-16(0°C, C-16 (0°C, 00°C) °C) C-16(0°C, 30°C) °C) C-16 (0°C, 30 C-16 (60 (60°C, 90°C) °C, 90 °C) C-16 C-12 °C, 23 °C) C-12 (23 (23°C, 23°C)
2000 • 1000 1000 •
4000 3600 400 4000 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400 -1 WAVENUMBER/cm WAVENUMBER /cm-1
0 0 0
2
4
6
8
10
2θ /° 2θ/°
Figure 4. Effect of acidic medium on IR spectra and XRD patterns of samples.
In an acidic medium mesoporous benzene-silica hybrid materials could be formed in the presence of d e ^ C F t ^ N * and Ci2H25(CH3)3N+. After the removal of tern plate molecules by extraction, the sample templated by Ci6 exhibits three diffraction peaks at low angles of ca. 20 = 2.02, 2.24, 2.44°, similar to those of a 3D-cage SBA-1, obviously different from that induced by Cn with only a broad XRD peak at ca. 2.92° 20 (Fig. 4). IR spectra in Fig. 4 show the similarity of their infrared framework vibrations, and the difference from those in Fig. 1. The use of C]6 was beneficial to the formation of benzenesilica solid from an acidic medium, which was evidenced by TEM image in Fig. 3. This material possessed a 3D-cage like pore structure [4], with a pore size of ca. 28 A, a pore volume of 0.31 cm /g, and a surface area of 529.3 m /g. 4. Conclusion The formation of mesoporous benzene-silica solid from a basic medium was affected by the chain length of organic templates, in which only Ci 6 effectively templated a PMO solid with XRD peaks at low angles of 20 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. Six samples displayed similar diffraction peaks at high angles of ca. 2#=11.5, 23.4, 35.4°, which seems to propose the similarity of formation processes of PMO and ordered MCM-41 in the basic solution. In an acidic medium mesoporous benzene-silica materials could be mediated by [CnH2n+i(CH3)3N+, n=12,16], in which only Ci6 templated a 3Dcage like mesopore structure similar to SBA-1. 5. References [1] [2] [3] [4]
S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. F. Fajula and F. Di Renzo, Microporous Mesoporous Mater., 82 (2005) 227. K. J. Shea, D. A. Loy and O. Webster, J. Am. Chem. Soc, 114 (1992) 6700. Y. Goto and S. Inagaki, Microporous Mesoporous Mater., 89 (2006) 103.