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The influence of ethylene glycol on the preparation of K2SnSi3O9·H2O
Zeolites and Related Materials: Trends, Targets and Challenges Proceedings of 4th International FEZA Conference A. Gédéon, P. Massiani and F. Babonneau (Editors) © 2008 Elsevier B.V. All rights reserved.
301
The influence of ethylene glycol on the preparation of K2SnSi3O9•H2O Zhi Lin Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal. Tel: 351 234401519, Fax: 351 234370084, E-mail: [email protected]
Abstract The influence of ethylene glycol (EG) on the preparation of K2SnSi3O9ǜH2O (AV-6) was studied in this work. The EG content clearly changes the synthesis process. Although the morphology of the samples is similar, the products are mixtures containing AV-6, AV-7 (K2SnSi3O9ǜH2O) and AV-11 (K4Sn2Si6O18). At high EG content, nano crystal of Sn-AV-11, instead of AV-6, is crystallized from the system. The samples were characterized by powder XRD, SEM, solid-state 29Si MAS NMR spectroscopy and thermogravimetric (TG) analysis. Keywords: Silicate, stannosilicate, solvothermal synthesis
1. Introduction Alkali metal silicates (particularly those which are microporous) have received considerable attention in recent years [1]. Their synthesis has been attempted via hydrothermal process and high-temperature solid-state methods. In the hydrothermal synthesis, hydrated cations are considered as template to help the formation of the porous structure. Water also acts as solvent. AV-6 is a microporous solid possessing the structure of mineral umbite [2]. Its structure contains one dimensional 8 member ring channel, and can be used as absorbents and in membrane preparation [3]. In order to modify the morphology of the crystals and search for new materials, ethylene glycol was added in the precursor mixture. At high EG content, Sn-AV-11 [4], instead of AV6, is crystallized from the system. Previously, AV-11 was obtained by calcination of AV-6 or AV-7 [5], or by a two-step hydrothermal synthesis. Here, the influence of ethylene glycol on the preparation of AV-6 and the direct synthesis of nano crystals of Sn-AV-11 in ethylene glycol are reported. The samples were characterized by powder X-ray diffraction (XRD), Scanning electron microscope (SEM), solid-state 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric (TG) analysis.
2. Experimental The influence of ethylene glycol on the preparation of AV-6 was studied using gels with molar compositions 5.5 K2O : 3.0 SiO2 : 1.0 SnO2 : 0-40 EG : 120-5 H2O. The typical synthesis is as follows. A solution was made by dissolving 1.00 g of precipitated silica (93 m/m%, Riedel-de Haën), 3.75 g of KOH (85 m/m%, Aldrich) into 12.88 g of ethylene glycol with proper heating. 1.85 g of SnCl4ǜ5H2O (98 m/m% Riedel-de Räen) were added to above solution with thorough agitation and proper heating. This gel, with a molar composition 5.5 K2O : 3.0 SiO2 : 1.0 SnO2 : 40 EG : 5 H2O, was transferred into Teflon-lined autoclaves and treated at 230 ºC for 3-5 days under static condition without agitation. The autoclaves were cooled down with running water after certain treating
302
Z. Lin
time. The obtained samples were filtered, and washed with distilled water at room temperature, and dried at 60 ºC overnight. The final products are white powder. Powder XRD was performed on a Philips X’pert MPD diffractometer using CuKĮ radiation. The unit cell parameters were refined with programs Powder Cell (PCW) [6]. SEM images and energy dispersive X-ray spectrometry (EDS) were recorded on a Hitachi S-4100 microscope equipped with Rontec EDS system. 29Si MAS NMR spectra were recorded at 79.49 MHz, on an Avance 400 (9.4 T, wide-bore) Bruker spectrometer. 29Si MAS NMR spectra were recorded with 40º radio-frequency (rf) pulses, a spinning rate of 5.0 kHz and 60 s recycle delays. Chemical shifts are quoted in ppm from tetramethylsilane (TMS). Thermogravimetric (TG) curves were measured with a TG-50 Shimadzu analyzer. The samples were heated under air at a rate of 5 ºC/minute.
3. Results and discussion As it can be seen from the reagents, the water always exists in the precursor. Figure 1 displays the products obtained from the mixtures with different EG/H2O ratios. It clearly shows that the EG/H2O ratio in the mixtures has significant influence on resulting products. The studied system crystallized AV-6 when H2O/SnO2 ratio is 120 as described in literature [7]. The mixture of AV-6 and AV-7 [4] was obtained when H2O/SnO2 ratio decreased to 40. With this ratio and replacing water by EG, the amount of AV-7 decreased while AV-11 increased. At lowest water content, water was only introduced by the hydrated reagents. The resulting sample gave powder XRD pattern with very broad line width (Fig 1). With increasing synthesis times, the powder XRD patterns of samples from this precursor were not improved. Figure 2 compares the powder XRD pattern with the one from a typical AV-11 sample which was prepared by calcination of AV-6, clearly indicating that the resulting product possesses AV-11 structure. The estimated cell parameters (a = 10.153±0.005 Å, c = 14.85±0.04 Å) are in the range of ones from literature (a = 10.1587 Å, c = 14.8039 Å) [8]. AV-6 3 H2O AV-7 H2O EG/H2O = 1.1 AV-11 EG/H2O = 2.5 EG/H2O = 8
10
20
30
40
2T / º Figure 1. Powder XRD patterns of products obtained from the mixtures with different EG/H2O ratios.
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The influence of ethylene glycol on the preparation of K2SnSi3 O9 •H2O
SEM image of AV-11 materials obtained in this work, shown in Fig 3a, indicates that the sample contains the aggregates of small particles with the size of nano scale. Therefore, the line broadening in the powder XRD pattern of AV-11 could be due to the small particles size of the sample. Using AV-11 Scherrer formula, the particle size can be estimated and is about 10 nm. This 10 20 30 40 result suggests that the particles of 2T / º about 100 nm in Fig. 3a are probably Figure 2. Powder XRD patterns of polycrystalline, containing much small AV-11 obtained in this experiment (top) ones. Moreover, the particles of AV-11 and from calcinations of AV-6. The sharp obtained in this work are well peak at 2ș 28º is from KCl. distributed. The previously reported AV-11 from a two-step hydrothermal synthesis contains both large and small particles (Fig. 3b). Therefore, this work provides better process to obtain well defined sample.
d
a
c
b
b a
-70
-75
-80
-85
-90
-95
G (ppm)
Figure 3. SEM images of AV-11 obtained in this experiment (a) and by a two-step hydrothermal synthesis (b).
Figure 4. 29Si MAS NMR spectra of assynthesized sample (a), sample after calcination at 600 ºC for 3 h (b), AV-6 (c) and AV-11 (d).
Figure 4 displays the 29Si MAS NMR spectra of as-synthesized sample and the sample after calcination. The NMR spectra of AV-6 and AV-11 are also depicted in figure for comparison. The 29Si MAS NMR spectrum of sample obtained in this work displays a main peak at ca. -82.4 ppm and two additional peaks at ca. -77 and -85.5 ppm. After calcination at 600 ºC for 3 h, the peak at ca. -77 ppm decreased. The 29Si MAS NMR spectrum of AV-11 [4] display two peaks at ca. -82.0 and -82.4 ppm in a 1 : 1 intensity ratio, according with the crystal structure of AV-11, which calls for the presence of two
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Mass loss (wt %)
unique Si(2Si,2M) sites with equal populations. The 29Si MAS NMR spectrum of AV-6 [2] displays three peaks at ca. -84.7, -85.5 and -86.7 ppm. Therefore, the peak at ca. 82.4 ppm can be assigned to AV-11. The loss of resolution may be due to the small crystal size. The peak at ca. -85.5 ppm may result from the low crystalline AV-6, which can not be seen in powder XRD. The peak at ca. -77 ppm is probably from unreacted silicon source. Although the structure of AV-11 contains 7 member ring channel in (40-3) direction, 100 it does not contain water in their structure. The aggregation of nano size particles 98 results in a stable water content in AV-11 sample from this work, which was revealed by TG analysis (Fig 5). This Re-hydrated after 600ºC 96 mass loss is ca. 4.4 % and is reversible. These water molecules may stay at As-prepared intercrystal voids. The total mass loss of 94 25 125 225 325 425 525 625 725 AV-6 material is ca. 5.3 % [2] and the Temperature (ºC) main mass loss is after 250 ºC. Therefore, Figure 5. TG analysis of AV-11. even if we may have low crystalline AV-6 in the sample, the main mass loss here is not from AV-6.
4. Conclusions Ethylene glycol has clear influence on the synthesis of stannosilicates. AV-11 has been directly prepared via solvothermal synthesis using ethylene glycol as solvent. The product contains particles in nano scale.
Acknowledgment This work was financially supported by FCT, POCI2010 and FEDER.
References [1] J. Rocha, Z. Lin, in: Giovanni Ferraris and Stefano Merlino (Eds.), Micro- and Mesoporous Mineral Phases, Rev. Mineral Geochem., 57 (2005) 173. [2] Z. Lin, J. Rocha, A. Valente, Chem. Commun., (1999) 2489. [3] V. Sebastian, Z. Lin, J. Rocha, C. Téllez, J. Santamaría, J. Coronas, Chem. Mater., 18(10) (2006) 2472. [4] Z. Lin, A. Ferreira, J. Rocha, J. Solid State Chem., 175 (2003) 258. [5] Z. Lin, J. Rocha, J. D. Pedrosa de Jesus, A. Ferreira, J. Mater. Chem., 10 (2000) 1353. [6] W. Kraus, G., Nolze, Federal Institute for Materials Research and Testing, Rudower Chaussee 5 (2000) 12489, Berlin, Germany. [7] Z. Lin, J. Rocha, in: A. Galarneao, F. Di Renzo, F. Fajula, J. Vedrine (Eds.), Zeolites and mesoporous materials at the dawn of the 21st century, Studies in Surface Science and Catalysis 135 (2001) 246. [8] A. Ferreira, Z. Lin, M. R. Soares, J. Rocha, Mate. Sci. Forum, 443-444 (2004) 329.
301
The influence of ethylene glycol on the preparation of K2SnSi3O9•H2O Zhi Lin Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal. Tel: 351 234401519, Fax: 351 234370084, E-mail: [email protected]
Abstract The influence of ethylene glycol (EG) on the preparation of K2SnSi3O9ǜH2O (AV-6) was studied in this work. The EG content clearly changes the synthesis process. Although the morphology of the samples is similar, the products are mixtures containing AV-6, AV-7 (K2SnSi3O9ǜH2O) and AV-11 (K4Sn2Si6O18). At high EG content, nano crystal of Sn-AV-11, instead of AV-6, is crystallized from the system. The samples were characterized by powder XRD, SEM, solid-state 29Si MAS NMR spectroscopy and thermogravimetric (TG) analysis. Keywords: Silicate, stannosilicate, solvothermal synthesis
1. Introduction Alkali metal silicates (particularly those which are microporous) have received considerable attention in recent years [1]. Their synthesis has been attempted via hydrothermal process and high-temperature solid-state methods. In the hydrothermal synthesis, hydrated cations are considered as template to help the formation of the porous structure. Water also acts as solvent. AV-6 is a microporous solid possessing the structure of mineral umbite [2]. Its structure contains one dimensional 8 member ring channel, and can be used as absorbents and in membrane preparation [3]. In order to modify the morphology of the crystals and search for new materials, ethylene glycol was added in the precursor mixture. At high EG content, Sn-AV-11 [4], instead of AV6, is crystallized from the system. Previously, AV-11 was obtained by calcination of AV-6 or AV-7 [5], or by a two-step hydrothermal synthesis. Here, the influence of ethylene glycol on the preparation of AV-6 and the direct synthesis of nano crystals of Sn-AV-11 in ethylene glycol are reported. The samples were characterized by powder X-ray diffraction (XRD), Scanning electron microscope (SEM), solid-state 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric (TG) analysis.
2. Experimental The influence of ethylene glycol on the preparation of AV-6 was studied using gels with molar compositions 5.5 K2O : 3.0 SiO2 : 1.0 SnO2 : 0-40 EG : 120-5 H2O. The typical synthesis is as follows. A solution was made by dissolving 1.00 g of precipitated silica (93 m/m%, Riedel-de Haën), 3.75 g of KOH (85 m/m%, Aldrich) into 12.88 g of ethylene glycol with proper heating. 1.85 g of SnCl4ǜ5H2O (98 m/m% Riedel-de Räen) were added to above solution with thorough agitation and proper heating. This gel, with a molar composition 5.5 K2O : 3.0 SiO2 : 1.0 SnO2 : 40 EG : 5 H2O, was transferred into Teflon-lined autoclaves and treated at 230 ºC for 3-5 days under static condition without agitation. The autoclaves were cooled down with running water after certain treating
302
Z. Lin
time. The obtained samples were filtered, and washed with distilled water at room temperature, and dried at 60 ºC overnight. The final products are white powder. Powder XRD was performed on a Philips X’pert MPD diffractometer using CuKĮ radiation. The unit cell parameters were refined with programs Powder Cell (PCW) [6]. SEM images and energy dispersive X-ray spectrometry (EDS) were recorded on a Hitachi S-4100 microscope equipped with Rontec EDS system. 29Si MAS NMR spectra were recorded at 79.49 MHz, on an Avance 400 (9.4 T, wide-bore) Bruker spectrometer. 29Si MAS NMR spectra were recorded with 40º radio-frequency (rf) pulses, a spinning rate of 5.0 kHz and 60 s recycle delays. Chemical shifts are quoted in ppm from tetramethylsilane (TMS). Thermogravimetric (TG) curves were measured with a TG-50 Shimadzu analyzer. The samples were heated under air at a rate of 5 ºC/minute.
3. Results and discussion As it can be seen from the reagents, the water always exists in the precursor. Figure 1 displays the products obtained from the mixtures with different EG/H2O ratios. It clearly shows that the EG/H2O ratio in the mixtures has significant influence on resulting products. The studied system crystallized AV-6 when H2O/SnO2 ratio is 120 as described in literature [7]. The mixture of AV-6 and AV-7 [4] was obtained when H2O/SnO2 ratio decreased to 40. With this ratio and replacing water by EG, the amount of AV-7 decreased while AV-11 increased. At lowest water content, water was only introduced by the hydrated reagents. The resulting sample gave powder XRD pattern with very broad line width (Fig 1). With increasing synthesis times, the powder XRD patterns of samples from this precursor were not improved. Figure 2 compares the powder XRD pattern with the one from a typical AV-11 sample which was prepared by calcination of AV-6, clearly indicating that the resulting product possesses AV-11 structure. The estimated cell parameters (a = 10.153±0.005 Å, c = 14.85±0.04 Å) are in the range of ones from literature (a = 10.1587 Å, c = 14.8039 Å) [8]. AV-6 3 H2O AV-7 H2O EG/H2O = 1.1 AV-11 EG/H2O = 2.5 EG/H2O = 8
10
20
30
40
2T / º Figure 1. Powder XRD patterns of products obtained from the mixtures with different EG/H2O ratios.
303
The influence of ethylene glycol on the preparation of K2SnSi3 O9 •H2O
SEM image of AV-11 materials obtained in this work, shown in Fig 3a, indicates that the sample contains the aggregates of small particles with the size of nano scale. Therefore, the line broadening in the powder XRD pattern of AV-11 could be due to the small particles size of the sample. Using AV-11 Scherrer formula, the particle size can be estimated and is about 10 nm. This 10 20 30 40 result suggests that the particles of 2T / º about 100 nm in Fig. 3a are probably Figure 2. Powder XRD patterns of polycrystalline, containing much small AV-11 obtained in this experiment (top) ones. Moreover, the particles of AV-11 and from calcinations of AV-6. The sharp obtained in this work are well peak at 2ș 28º is from KCl. distributed. The previously reported AV-11 from a two-step hydrothermal synthesis contains both large and small particles (Fig. 3b). Therefore, this work provides better process to obtain well defined sample.
d
a
c
b
b a
-70
-75
-80
-85
-90
-95
G (ppm)
Figure 3. SEM images of AV-11 obtained in this experiment (a) and by a two-step hydrothermal synthesis (b).
Figure 4. 29Si MAS NMR spectra of assynthesized sample (a), sample after calcination at 600 ºC for 3 h (b), AV-6 (c) and AV-11 (d).
Figure 4 displays the 29Si MAS NMR spectra of as-synthesized sample and the sample after calcination. The NMR spectra of AV-6 and AV-11 are also depicted in figure for comparison. The 29Si MAS NMR spectrum of sample obtained in this work displays a main peak at ca. -82.4 ppm and two additional peaks at ca. -77 and -85.5 ppm. After calcination at 600 ºC for 3 h, the peak at ca. -77 ppm decreased. The 29Si MAS NMR spectrum of AV-11 [4] display two peaks at ca. -82.0 and -82.4 ppm in a 1 : 1 intensity ratio, according with the crystal structure of AV-11, which calls for the presence of two
304
Z. Lin
Mass loss (wt %)
unique Si(2Si,2M) sites with equal populations. The 29Si MAS NMR spectrum of AV-6 [2] displays three peaks at ca. -84.7, -85.5 and -86.7 ppm. Therefore, the peak at ca. 82.4 ppm can be assigned to AV-11. The loss of resolution may be due to the small crystal size. The peak at ca. -85.5 ppm may result from the low crystalline AV-6, which can not be seen in powder XRD. The peak at ca. -77 ppm is probably from unreacted silicon source. Although the structure of AV-11 contains 7 member ring channel in (40-3) direction, 100 it does not contain water in their structure. The aggregation of nano size particles 98 results in a stable water content in AV-11 sample from this work, which was revealed by TG analysis (Fig 5). This Re-hydrated after 600ºC 96 mass loss is ca. 4.4 % and is reversible. These water molecules may stay at As-prepared intercrystal voids. The total mass loss of 94 25 125 225 325 425 525 625 725 AV-6 material is ca. 5.3 % [2] and the Temperature (ºC) main mass loss is after 250 ºC. Therefore, Figure 5. TG analysis of AV-11. even if we may have low crystalline AV-6 in the sample, the main mass loss here is not from AV-6.
4. Conclusions Ethylene glycol has clear influence on the synthesis of stannosilicates. AV-11 has been directly prepared via solvothermal synthesis using ethylene glycol as solvent. The product contains particles in nano scale.
Acknowledgment This work was financially supported by FCT, POCI2010 and FEDER.
References [1] J. Rocha, Z. Lin, in: Giovanni Ferraris and Stefano Merlino (Eds.), Micro- and Mesoporous Mineral Phases, Rev. Mineral Geochem., 57 (2005) 173. [2] Z. Lin, J. Rocha, A. Valente, Chem. Commun., (1999) 2489. [3] V. Sebastian, Z. Lin, J. Rocha, C. Téllez, J. Santamaría, J. Coronas, Chem. Mater., 18(10) (2006) 2472. [4] Z. Lin, A. Ferreira, J. Rocha, J. Solid State Chem., 175 (2003) 258. [5] Z. Lin, J. Rocha, J. D. Pedrosa de Jesus, A. Ferreira, J. Mater. Chem., 10 (2000) 1353. [6] W. Kraus, G., Nolze, Federal Institute for Materials Research and Testing, Rudower Chaussee 5 (2000) 12489, Berlin, Germany. [7] Z. Lin, J. Rocha, in: A. Galarneao, F. Di Renzo, F. Fajula, J. Vedrine (Eds.), Zeolites and mesoporous materials at the dawn of the 21st century, Studies in Surface Science and Catalysis 135 (2001) 246. [8] A. Ferreira, Z. Lin, M. R. Soares, J. Rocha, Mate. Sci. Forum, 443-444 (2004) 329.