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Synthesis and characterization of inorganic membranes and applications
Desalination 184 (2005) 65–69
Synthesis and characterization of inorganic membranes and applications N. Agoudjila*, N. Benmouhouba, A. Larbotb a
Laboratoire de physico-chime des materiaux et environnement. Faculte de chimie Alger email: [email protected] b Laboratoire des materiaux membranaires. CNRS.Montpellier France Received 19 March 2005; accepted 10 April 2005
Abstract The development of membranary technologies had introduced the membrane mineral which are prepared from ceramic materials, they offer many potential advantages over commercial organic polymer membranes for separation processes. Inorganic membranes are very resistant to a wide variety of solvents and are quite stable at hard operating conditions. These features have attracted a great deal of attention from the standpoint of membrane applications. Among the methods of preparation developed, the sol-gel process is appropriate to elaborate thin and porous layers with controllable porosity. The synthesis of gel is based on hydrolysiscondensation reactions indirectly to form a veritable lattice of oxide from molecular precursors. The hydrolysis reaction must be controlled to avoid precipitation of hydrous metal oxide. A true oxide network is formed by chemical bonds in the solution. The deposit thin layers has been realized with a sol prepared with the polymerization of molecular units. The control of sol-gel transition and thermal decomposition has allowed us the synthesis of the mixed oxide ZrO2-SiO2. These results show the great potentiallity of inorganic membrane and allow new applications to be taken into account particulary waste water treatment and gas separation. Crossflow microfiltration and ultrafiltration are becoming of increasing interest to produce drinking water. They can remove bacteria and clarify the water in a single step, so they can reduce appreciably the classic sequences of treatment processes. The structural characterization was studied by differential thermal analysis, infrared spectroscopy, X-ray diffraction and the textural characterization by nitrogen adsorption-desorption allowed us to observe the variation of the surface area, porous volume and pore diameters according to temperature. Scanning electron microscopy observation showed homogeneous layers without cracking. In this paper, some experimental results on the synthesis and characterization of inorganic membrane will be presented. Keywords: Sol-gel, Porous, Membrane
*Corresponding author. Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 22–26 May 2005. European Desalination Society. 0011-9164/05/$– See front matter Ó 2005 Elsevier B.V. All rights reserved doi:10.1016/j.desal.2005.04.034
66
N. Agoudjil et al. / Desalination 184 (2005) 65–69
1. Introduction The aim of this study allows on the one hand to know obtaining conditions and characteristics of vitreous ceramic material by solgel process from alkoxide precursors and on the other hand to contribute to obtain thin and microporous layers. At present, theses processes are applied at the synthesis of material in thin microporous layers shapes, intended to separation, concentration, or purification of chemical species. The microporous ceramics have taken in additional or in substitution the organics membrane a dominating space in the process put into play the selective separations.
EtOH/Acg
Si(OEt) 4
60˚C 0h
Sol
2h
Zr(OPr)4
2h20
Gel
2. Study of the system ZrO2-SiO2 The used alkoxides to obtain this oxide system are the following: Si(OC2H5)4: tetraethoxysilane [Si(OEt)4] Zr(OC3H7)4: tetrapropoxyde of zirconium [Zr(OPr)4] The synthesis difficulty lies in the difference of two alkoxides reactivity as regards of hydrolysis and condensation reactions. We have chosen for a synthesis mode priviliging at maximum of connection formation. Si-O-Zr (Fig. 1). Thus, in a first step the idea is to use up hydrolysis water by forming a maximum of connection of groupings Si-OH. SiðOEtÞ4 þ H2 O ! SiðOEtÞ3 OH þ EtOH Second, Zr(OPr)4 is added to react preferentially with silanol groups following reaction: SiðOEtÞ3 OH þ ZrðOPrÞ4 ! ðOEtÞ3 Si O ZrðOPrÞ3 þ PrOH
Thermal treatment
Oxyde powder Time (hours)
Fig. 1. Steps in preparation of ZrO2-SiO2 mixed oxides powders.
3. Structural characterization of mixed oxides ZrO2-SiO2 3.1. By RX diffraction The RX diffraction results in powders treated at different temperatures are summarized in the next chart (Table 1). The tetragonal phase of ZrO2 is more stable in the system of mixed oxides ZrO2-SiO2 than in ZrO2 oxide. It is a transformation of tetragonal phase into the monoclinic phase after thermal treatment at 700 C. But in ZrO2-SiO2 system, the sample contain the tetragonal phase well crystallized without monoclinic
N. Agoudjil et al. / Desalination 184 (2005) 65–69 Table 1 Crystalline phases of SiO2, ZrO2 and ZrO2-SiO2 powders treated at different temperatures Temperature
80 C 400 C 500 C 600 C 700 C 800 C 900 C 1000 C 1300 C 1400 C 1500 C 1600 C
SiO2
ZrO2
ZrO2-SiO2
A A A A A A AþC CþA C C C C
A AþQ Q Q QþM M þ
A A AþQ Q Q Q Q þ
A = Amorphous ; C = Cristobalite; Q = Tetragonal ZrO2; M = Monoclinic ZrO2
67
We notice that desorption isotherm does not coincide with adsorption isotherm, there is appearance of a characteristic hysteresis of a capillary condensation . The observed isotherm for five samples is type IV, is characteristic of mesoporous bodies (Fig. 3). The surface study of the samples treated at different temperatures allows to observe the temperature influence treatment of surface BET, microporous volume and pores diameter. In the range of temperature from 500 to 800 C, we observe a decrease of BET surface (S) and Microporous volume (W) due to densification and consolidation of system (crystallization in a tetragonal phase of ZrO2) (Figs 4 and 5). In fact, densification process leads to reduction of interior energy
phase until 900 C. We notice that the transformation temperature of tetragonal phase to monoclinic phase of ZrO2 is strongly affected by the presence of SiO2 matrix. 3.2. By spectroscopy absorption infra-red We have recorded infra-red spectra for every powder treated at different temperatures (Fig. 2). We notice that connection Si-O-Zr are initially in the gel, this confirms the two alkoxides copolymerization. The band at 970 cm1 is attributed to connection Si-O-Zr vibration, this disappear when the temperature increases [1]. The thin bands at 480–500 and 740 characteristics to the connections vibrations Zr-O-Zr and O-Zr-O [2,3]. From 600 C, we notice only the bands characterized metallic connection M-O-M and O-M-O or M-OH betwen 400 and 1200 cm1, M is the zirconium or silicon. 4. Textural characterization of ZrO2-SiO2 mixed oxides by adsorption/desorption of nitrogen We have drawn adsorption isotherms for five samples treated at different temperatures.
Fig. 2. Infrared Spectra of powders treated at different temperatures.
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N. Agoudjil et al. / Desalination 184 (2005) 65–69
Fig. 5. Evolution of microporous volume as a function of the temperature.
5. Deposits of thin microporous layers
Fig. 3. Absorption isotherm of oxide powder ZrO2SiO2. þ: adsorption; 0: desorption.
and creates a decrease of porosity. The increasing of S and W from 900 C is probably due at structure changing of tetragonal phase of ZrO2 into monoclinic phase, translated by an increase of nitrogen adsorbed quantity, with pores widening. We notice in Fig. 6 that thermal treatment create and widening pores diameter that is in agreement with S and W variation.
Fig. 4. Evolution of BET specific surface area as a function of the temperature.
The last aspect of this study has been devoted to offered possibilities by ZrO2-SiO2 system in a realization of thin microporous layers. These layers present interest in a domain of inorganic membranes domain as far as they have characteristics with high chemical and mechanical resistances. These layers have been deposited in porous support in alumina a presenting the pores diameter of 0.2 mm on the usable face for the deposit. The membrane deposit has been realized with a sol prepared with P.E.M process (Polymerization of Molecular Entity). Scanning electron spectroscopy observation showed homogenous layers, without cracking, with a thickness of 2 mm (Fig. 7) We obtain at 600 C the pore diameter of 100 nm (Fig. 8).
Fig. 6. Evolution of pores diameter as a function of the temperature.
N. Agoudjil et al. / Desalination 184 (2005) 65–69
69
Fig. 7. Micrography of the layer obtained at 600 C.
Fig. 8. Cross section of the layer obtained at 600 C.
6. Conclusion
References
We have chosen to study this system mixed oxides ZrO2-SiO2 for their interesting properties and the interest which may bring in the domain of inorganic membranes chemical and mechanical high resistance. The obtained results by adsorption/desorption of nitrogen showed that texturals characteristics are linked at structurals changes. The presence of SiO2 stabilizes the tetragonal phase until 900 C and confers to the system a high resistance to the thermal shocks. The deposit tests of thin layers in the macroporous support have showed homogeneous layers, without cracking with a thickness of 2 mm. The Sol-Gel processes are particulary well suited at the realization of thin microporous layers.
[1] S.W. Lee and R.A. Condrate Sr., J Mater Sci., 2951 (1988) 23. [2] M. Jansen and E. Guenther, Chem Mater., 2110 (1995) 7. [3] F. Babonneau, J. Maquet and J. Livage, J Chem Mater., 1050 (1995) 7. [4] C.J. Brinker and G.W. Sherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing. Academic Press, New York, 1990. [5] C. Guizard, A. Julbe and A. Ayral, J Mater Sci., 55 (1999) 9. [6] J. Kims and Y.S. Lin, J Mater Sci., 75 (1998) 139. [7] H.H. Kung and E.I. Ko, Am Chem Soc., 421 (1995) 34. [8] J. Livage, M. Henry and C. Schanchez, Prog Solid-State Chem., 259 (1988) 18.
Synthesis and characterization of inorganic membranes and applications N. Agoudjila*, N. Benmouhouba, A. Larbotb a
Laboratoire de physico-chime des materiaux et environnement. Faculte de chimie Alger email: [email protected] b Laboratoire des materiaux membranaires. CNRS.Montpellier France Received 19 March 2005; accepted 10 April 2005
Abstract The development of membranary technologies had introduced the membrane mineral which are prepared from ceramic materials, they offer many potential advantages over commercial organic polymer membranes for separation processes. Inorganic membranes are very resistant to a wide variety of solvents and are quite stable at hard operating conditions. These features have attracted a great deal of attention from the standpoint of membrane applications. Among the methods of preparation developed, the sol-gel process is appropriate to elaborate thin and porous layers with controllable porosity. The synthesis of gel is based on hydrolysiscondensation reactions indirectly to form a veritable lattice of oxide from molecular precursors. The hydrolysis reaction must be controlled to avoid precipitation of hydrous metal oxide. A true oxide network is formed by chemical bonds in the solution. The deposit thin layers has been realized with a sol prepared with the polymerization of molecular units. The control of sol-gel transition and thermal decomposition has allowed us the synthesis of the mixed oxide ZrO2-SiO2. These results show the great potentiallity of inorganic membrane and allow new applications to be taken into account particulary waste water treatment and gas separation. Crossflow microfiltration and ultrafiltration are becoming of increasing interest to produce drinking water. They can remove bacteria and clarify the water in a single step, so they can reduce appreciably the classic sequences of treatment processes. The structural characterization was studied by differential thermal analysis, infrared spectroscopy, X-ray diffraction and the textural characterization by nitrogen adsorption-desorption allowed us to observe the variation of the surface area, porous volume and pore diameters according to temperature. Scanning electron microscopy observation showed homogeneous layers without cracking. In this paper, some experimental results on the synthesis and characterization of inorganic membrane will be presented. Keywords: Sol-gel, Porous, Membrane
*Corresponding author. Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 22–26 May 2005. European Desalination Society. 0011-9164/05/$– See front matter Ó 2005 Elsevier B.V. All rights reserved doi:10.1016/j.desal.2005.04.034
66
N. Agoudjil et al. / Desalination 184 (2005) 65–69
1. Introduction The aim of this study allows on the one hand to know obtaining conditions and characteristics of vitreous ceramic material by solgel process from alkoxide precursors and on the other hand to contribute to obtain thin and microporous layers. At present, theses processes are applied at the synthesis of material in thin microporous layers shapes, intended to separation, concentration, or purification of chemical species. The microporous ceramics have taken in additional or in substitution the organics membrane a dominating space in the process put into play the selective separations.
EtOH/Acg
Si(OEt) 4
60˚C 0h
Sol
2h
Zr(OPr)4
2h20
Gel
2. Study of the system ZrO2-SiO2 The used alkoxides to obtain this oxide system are the following: Si(OC2H5)4: tetraethoxysilane [Si(OEt)4] Zr(OC3H7)4: tetrapropoxyde of zirconium [Zr(OPr)4] The synthesis difficulty lies in the difference of two alkoxides reactivity as regards of hydrolysis and condensation reactions. We have chosen for a synthesis mode priviliging at maximum of connection formation. Si-O-Zr (Fig. 1). Thus, in a first step the idea is to use up hydrolysis water by forming a maximum of connection of groupings Si-OH. SiðOEtÞ4 þ H2 O ! SiðOEtÞ3 OH þ EtOH Second, Zr(OPr)4 is added to react preferentially with silanol groups following reaction: SiðOEtÞ3 OH þ ZrðOPrÞ4 ! ðOEtÞ3 Si O ZrðOPrÞ3 þ PrOH
Thermal treatment
Oxyde powder Time (hours)
Fig. 1. Steps in preparation of ZrO2-SiO2 mixed oxides powders.
3. Structural characterization of mixed oxides ZrO2-SiO2 3.1. By RX diffraction The RX diffraction results in powders treated at different temperatures are summarized in the next chart (Table 1). The tetragonal phase of ZrO2 is more stable in the system of mixed oxides ZrO2-SiO2 than in ZrO2 oxide. It is a transformation of tetragonal phase into the monoclinic phase after thermal treatment at 700 C. But in ZrO2-SiO2 system, the sample contain the tetragonal phase well crystallized without monoclinic
N. Agoudjil et al. / Desalination 184 (2005) 65–69 Table 1 Crystalline phases of SiO2, ZrO2 and ZrO2-SiO2 powders treated at different temperatures Temperature
80 C 400 C 500 C 600 C 700 C 800 C 900 C 1000 C 1300 C 1400 C 1500 C 1600 C
SiO2
ZrO2
ZrO2-SiO2
A A A A A A AþC CþA C C C C
A AþQ Q Q QþM M þ
A A AþQ Q Q Q Q þ
A = Amorphous ; C = Cristobalite; Q = Tetragonal ZrO2; M = Monoclinic ZrO2
67
We notice that desorption isotherm does not coincide with adsorption isotherm, there is appearance of a characteristic hysteresis of a capillary condensation . The observed isotherm for five samples is type IV, is characteristic of mesoporous bodies (Fig. 3). The surface study of the samples treated at different temperatures allows to observe the temperature influence treatment of surface BET, microporous volume and pores diameter. In the range of temperature from 500 to 800 C, we observe a decrease of BET surface (S) and Microporous volume (W) due to densification and consolidation of system (crystallization in a tetragonal phase of ZrO2) (Figs 4 and 5). In fact, densification process leads to reduction of interior energy
phase until 900 C. We notice that the transformation temperature of tetragonal phase to monoclinic phase of ZrO2 is strongly affected by the presence of SiO2 matrix. 3.2. By spectroscopy absorption infra-red We have recorded infra-red spectra for every powder treated at different temperatures (Fig. 2). We notice that connection Si-O-Zr are initially in the gel, this confirms the two alkoxides copolymerization. The band at 970 cm1 is attributed to connection Si-O-Zr vibration, this disappear when the temperature increases [1]. The thin bands at 480–500 and 740 characteristics to the connections vibrations Zr-O-Zr and O-Zr-O [2,3]. From 600 C, we notice only the bands characterized metallic connection M-O-M and O-M-O or M-OH betwen 400 and 1200 cm1, M is the zirconium or silicon. 4. Textural characterization of ZrO2-SiO2 mixed oxides by adsorption/desorption of nitrogen We have drawn adsorption isotherms for five samples treated at different temperatures.
Fig. 2. Infrared Spectra of powders treated at different temperatures.
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N. Agoudjil et al. / Desalination 184 (2005) 65–69
Fig. 5. Evolution of microporous volume as a function of the temperature.
5. Deposits of thin microporous layers
Fig. 3. Absorption isotherm of oxide powder ZrO2SiO2. þ: adsorption; 0: desorption.
and creates a decrease of porosity. The increasing of S and W from 900 C is probably due at structure changing of tetragonal phase of ZrO2 into monoclinic phase, translated by an increase of nitrogen adsorbed quantity, with pores widening. We notice in Fig. 6 that thermal treatment create and widening pores diameter that is in agreement with S and W variation.
Fig. 4. Evolution of BET specific surface area as a function of the temperature.
The last aspect of this study has been devoted to offered possibilities by ZrO2-SiO2 system in a realization of thin microporous layers. These layers present interest in a domain of inorganic membranes domain as far as they have characteristics with high chemical and mechanical resistances. These layers have been deposited in porous support in alumina a presenting the pores diameter of 0.2 mm on the usable face for the deposit. The membrane deposit has been realized with a sol prepared with P.E.M process (Polymerization of Molecular Entity). Scanning electron spectroscopy observation showed homogenous layers, without cracking, with a thickness of 2 mm (Fig. 7) We obtain at 600 C the pore diameter of 100 nm (Fig. 8).
Fig. 6. Evolution of pores diameter as a function of the temperature.
N. Agoudjil et al. / Desalination 184 (2005) 65–69
69
Fig. 7. Micrography of the layer obtained at 600 C.
Fig. 8. Cross section of the layer obtained at 600 C.
6. Conclusion
References
We have chosen to study this system mixed oxides ZrO2-SiO2 for their interesting properties and the interest which may bring in the domain of inorganic membranes chemical and mechanical high resistance. The obtained results by adsorption/desorption of nitrogen showed that texturals characteristics are linked at structurals changes. The presence of SiO2 stabilizes the tetragonal phase until 900 C and confers to the system a high resistance to the thermal shocks. The deposit tests of thin layers in the macroporous support have showed homogeneous layers, without cracking with a thickness of 2 mm. The Sol-Gel processes are particulary well suited at the realization of thin microporous layers.
[1] S.W. Lee and R.A. Condrate Sr., J Mater Sci., 2951 (1988) 23. [2] M. Jansen and E. Guenther, Chem Mater., 2110 (1995) 7. [3] F. Babonneau, J. Maquet and J. Livage, J Chem Mater., 1050 (1995) 7. [4] C.J. Brinker and G.W. Sherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing. Academic Press, New York, 1990. [5] C. Guizard, A. Julbe and A. Ayral, J Mater Sci., 55 (1999) 9. [6] J. Kims and Y.S. Lin, J Mater Sci., 75 (1998) 139. [7] H.H. Kung and E.I. Ko, Am Chem Soc., 421 (1995) 34. [8] J. Livage, M. Henry and C. Schanchez, Prog Solid-State Chem., 259 (1988) 18.