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Porous alumina thin layers using mesophase templating
August 2001
Materials Letters 50 Ž2001. 57–60 www.elsevier.comrlocatermatlet
Porous alumina thin layers using mesophase templating Noureddine Idrissi-Kandri a,b, Andre´ Ayral a,) , Michaela Klotz a , Pierre-Antoine Albouy c , Abdeslam El Mansouri a , Arie Van der Lee a , Christian Guizard a a
LMPM, UMR CNRS 5635, IEM-UMII, CC047, Place Eugene ` Bataillon, F34095 Montpellier cedex 5, France Laboratoire de Chimie Minerale, Faculte´ des Sciences et Techniques Saıss, ´ ¨ B.P. 2202-Atlas, Fes, ´ Morocco c Laboratoire de Physique des Solides, UMR CNRS 8502, UniÕersite´ de Paris-Sud, 91405 Orsay, France
b
Received 3 October 2000; received in revised form 9 November 2000; accepted 14 November 2000
Abstract A method of preparation for alumina thin layers exhibiting an ordered mesoporosity is presented. The synthesis conditions are discussed and the resulting layers are characterised. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Alumina thin layers; Ordered mesoporosity; Mesophase templating
1. Introduction Since the first articles of Beck et al. w1,2x on the synthesis of ordered mesoporous silicate by templating effect, a lot of studies have been devoted to this new class of materials. If the initial syntheses used cationic surfactants to form the templating liquid crystal mesophase, the synthesis conditions were then extended to other types of amphiphilic molecules like neutral surfactant or more recently block copolymers w3,4x. Significant results were also obtained on non-silica oxides w5x. The production of crack-free thin layers of single or mixed oxide is now an important challenge to make way for application of these materials in the field of membranes, sensors or
) Corresponding author. Tel.: q33-467-14-91-43; fax: q33467-14-91-19. E-mail address: [email protected] ŽA. Ayral..
micro-reactors. The sol–gel route has been successfully applied to prepare ordered mesoporous silica layers from diluted gelling solutions w6–8x. In that case, the formation of the templating mesophase occurs with the drying of the layer during the deposition step. In the case of silica layers prepared from highly aqueous sols and using alkyltrimethyl ammonium bromides as surfactants, it has been shown that the sol compositions leading to hexagonal layers can be defined from the corresponding water–surfactant binary diagrams, taking into account the volume fraction of surfactant in the dried layer w8x. Another important criterion is the mean size of the inorganic clusters just before the deposition. This size must be small enough to allow the formation of the mesophases during drying w8x. These synthesis conditions were extended to other ordered silica layers prepared from other types of surfactants, gemini Žwith two cationic polar heads. or non-ionic block copolymers w9,10x. The preparation of ordered porous layers for
00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 4 1 3 - 4
58
N. Idrissi-Kandri et al.r Materials Letters 50 (2001) 57–60
non-silica oxides has been obtained using block copolymers as surfactants and anhydrous chlorides in alcoholic solutions as oxide precursor w5x. The difficulty with the non-silica oxide is to get a sufficient reinforcement of the inorganic walls before the removal of the templating units. If the oxide network is too tenuous, the ordered structure collapses w11x.
2. Experimental procedure Taking into account the data available in the literature and our previous results on silica, we have prepared alumina thin layers using an ethanolic solution of triblock copolymer of polyŽethylene oxide.polyŽpropylene oxide.-polyŽethylene oxide. type, EO 20 PO 70 EO 20 ŽP123 from Sigma-Aldrich.. This surfactant exhibits a large hexagonal mesophase domain on its binary diagram with water w12x. The inorganic precursor was an Al trihydroxide hydrosol prepared using the synthesis method described elsewhere w13x. The starting sol stabilised at pH s 5 is formed of colloidal particles with a mean hydraulic radius equal to 10 nm. In order to decrease the size of these elemental alumina bricks, the pH of the sol was decreased to pH s 4, which corresponds to the predominance domain for the polycations Al 13 IV Ž ŽAl VI OH. 24ŽH 2 O.12 x 7q . w14x. The presence 12 O4 Al of these species was experimentally confirmed by 27 Al NMR. The decomposition of urea initially present in the sol was able to promote the reinforcement of the Al trihydroxide network during the drying step w11x. The molar ratio surfactantrAl, R, was ranging from 0.009 to 0.021. Thin layers were deposited by dip-coating on flat substrates: thick slides of soda– lime–silica glass and thin silicon wafers Žthickness: 10 mm.. To obtain larger quantities of sample, sols were also poured in wide beakers resulting in cracked thick layers. The samples were first dried at room temperature during 12 h and then for 2 h at 1758C in an oven. The thermal treatment inducing the removal of the surfactant was carried out under nitrogen up to 3508C. It must be noted that the dehydroxylation of the amorphous aluminium trihydroxide occurs at around 4008C and the transition to h-alumina at around 4508C w13x. The thickness of the calcined thin layers is ranging from 0.10 to 0.25 mm as a function of the sol concentration prior to deposition.
The ordered structure of the samples was first investigated with a diffractometer using Cu-K-L3,2 radiation and ur2 u Bragg–Brentano scattering geometry. In order to improve the structural characterisation of the layers, two-dimensional X-ray scattering analyses were performed. The scattering was recorded on photostimulable imaging plates for two different scattering geometries: a normal beam configuration giving access to in-plane preferential orientations and a grazing incident geometry which reveals the out-of-the-plane organisation w15x. The skeletal density of the solid phase was measured by helium pycnometry on calcined powders obtained from thick layers. The bulk density of the thin layers was measured by X-ray reflectometry. The porosity of the calcined thin and thick layers was analysed by nitrogen adsorption. The mesopore size distribution was estimated by analysis of the adsorption and desorption curves using the BJH method w16x, assuming cylindrical pores transmission electron microscopy ŽTEM, JEOL 100CX2. was done on microtomed slides Žthickness 70 nm. of samples embedded in a polymer resin.
3. Results and discussion The thin layers prepared from sols with an intermediate value of R, R s 0.014, are first considered. Using the ur2 u Bragg–Brentano scattering geometry, a large diffraction peak can be observed on the patterns. It is located at 10.5 nm for a layer dried at room temperature. The Bragg spacing decreases to 8.6 nm after drying at 1758C and to 7.3 nm after calcination at 3508C. In addition to this main peak, a second maximum with a very low intensity can be observed at ; dr2, i.e. 3.6 nm for the calcined layer. The two-dimensional X-ray scattering pattern for the calcined layer in normal beam geometry ŽFig. 1a. shows an intense and homogeneous ring located at 17.5 nm Žwhite arrow. and a second very weak ring located at 10.5 nm Žblack arrow.. These positions are in the ratio 1.67, close to 63. A second pattern ŽFig. 1c. was taken at grazing incidence. A diffuse ellipse Žaxes 7.6 and 17.5 nm, respectively. can be observed. Moreover, a reinforcement of the diffracted intensity appears on the large axis. The diagram presented in Fig. 1b is taken in an interme-
N. Idrissi-Kandri et al.r Materials Letters 50 (2001) 57–60
59
Fig. 1. Two-dimensional X-ray scattering patterns for a thin layer calcined at 3508C Ž Rs 0.014; sample-detector distance: 725 mm.. Ža. Normal incidence Žexposition times90 h.; Žb. intermediate incidence: 458 Žexposition times 30 h.; Žc. grazing incidence Žexposition times15 h..
diate orientation with an incident angle of 458. One observes two ellipses of lower eccentricity. Refereeing to our previous work on silica layers w15x and assuming hexagonal mesophases as initial templating structure, these X-ray scattering results can be interpreted as follows. The drying and further thermal treatments induce an important unidirectional shrinkage of the layers in a direction perpendicular to the substrate resulting in a compression of the 2D hexagonal arrangement of the micellar cylinders. Moreover, the observed reinforcement of the diffracted intensity on the large axis at grazing incidence can be related to a preferential initial orientation of the micellar cylinders parallel to the layer interfaces. The skeletal density is equal to ; 2.0 g cmy3 for a sample calcined at 3508C. This value is in good agreement with the nature of solid phase, i.e. amorphous aluminium trihydroxide, if it is compared to the density of the crystallised aluminium trihydroxide, 2.4–2.5 g cmy3 . The porosity of calcined thin and thick layers with R s 0.014 was analysed. The nitrogen adsorption–desorption isotherms exhibit all the same shape ŽFig. 2., with a important hysteresis loop, as previously observed on ordered mesoporous alumina prepared by a different route w5x. The mean pore BJH diameters determined from the adsorption branch are equal to 7.9 and 7.3 nm for the thick and the thin layers, respectively. The mean pore BJH diameters determined from the desorption branch are both equal to 3.5 nm. The difference between adsorption and desorption is clearly incompatible with the existence of open cylindrical pores. Because of the lack of precision in the weight of analysed thin layers, the total pore volume was estimated from the isotherm corresponding to the thick layers Žfor silica samples w8x, a low difference of pore volume was
Fig. 2. Nitrogen adsorption–desorption isotherm for a thick layer calcined at 3508C Ž Rs 0.014..
observed between thin and thick layers.. The total porosity calculated using the previously determined skeletal density is equal to 43%. This value is in good agreement with the density of the thin layer measure by X-ray reflectometry, 1.1 g cmy3 . The calculation of the wall density using the method described in Ref. w8x leads to a value very close to that of the skeletal density. The porosity of the alumina walls is so very low. A previous study on mesoporous silica layers prepared from hexagonal mesophases evidenced the lack of connectivity between the mesopores w17x. The important hysteresis loop observed in the case of alumina could thus be explained by both this lack of connectivity between the mesopores and the very low porosity of the alumina walls. So the mesopore emptying is shifted to low relative pressure. TEM image of a calcined
Fig. 3. TEM image of a thin layer calcined at 3508C Ž Rs 0.014..
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N. Idrissi-Kandri et al.r Materials Letters 50 (2001) 57–60
thin layer is shown in Fig. 3. This image is quite different of that of the rectilinear and parallel cylindrical pores observed for hexagonal phases prepared from cationic surfactants w8,15x. This difference can be related to the lower stiffness of the micelles formed from non-ionic surfactants. From the density of the alumina walls and the molar ratio R, we have calculated the surfactant volume fractions in the dried layers w8x. The volume fractions giving rise to an ordered layer range from 0.55 to 0.75. This interval coincides exactly with the domain of formation of ordered silica layers using the same surfactant w10x and also with the domain of existence of the hexagonal phase in the corresponding surfactant–water binary diagram w12x.
4. Conclusion These first results demonstrate that ordered mesoporous alumina layers can be prepared from alumina hydrosols using the templating effect of a mesophase formed by self-association of triblock copolymers. The synthesis conditions can be predicted taking into account simple geometrical criteria based on the size of the inorganic clusters before deposition and on the volume fraction of surfactant in the dried layer.
Acknowledgements The authors thank Ms. C. Menager and M. ´ Lavergne for performing the electron micrographs ŽUniversite´ Pierre et Marie Curie- Paris VI, France..
References w1x C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 Ž1992. 710. w2x J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 Ž1992. 10834. w3x M. Templin, A. Franck, A. Du Chesne, H. Leist, Y. Zhang, R. Ulrich, V. Schadler, U. Wiesner, Science 278 Ž1997. ¨ 1795. w4x D. Zhao, P. Yang, N. Melosh, J. Feng, B.F. Chmelka, G.D. Stucky, Adv. Mater. 10 Ž1998. 1380. w5x P. Yang, D. Zhao, D.I. Margolese, B.F. Chmelka, G.D. Stucky, Chem. Mater. 11 Ž1999. 281. w6x M. Ogawa, Chem. Commun. Ž1999. 1149. w7x Y. Lu, R. Ganguli, C.A. Drewien, M.T. Anderson, C.J. Brinker, W. Gong, Y. Guo, H. Soyez, B. Dunn, M.H. Huang, J.I. Zinks, Nature 389 Ž1997. 364. w8x M. Klotz, A. Ayral, C. Guizard, L. Cot, J. Mater. Chem. 10 Ž2000. 66. w9x M. Klotz, Thesis, University of Montpellier, France, 2000. w10x M. Klotz, N. Idrissi-Kandri, A. Ayral, C. Guizard, Mater. Res. Soc. Symp. Proc., vol. 628, in press Želectronic article already available.. w11x S. Acosta, A. Ayral, C. Guizard, L. Cot, J. Sol–Gel Sci. Technol. 8 Ž1996. 195. w12x B. Chu, Z. Zhou, in: V.M. Nace ŽEd.., Nonionic Surfactants Polyoxoalkylene Block Copolymers, Marcel Dekker, New York, 1996, 67. w13x N. Idrissi-Kandri, A. Ayral, C. Guizard, E.H. El Ghadraoui, L. Cot, Mater. Lett. 40 Ž1999. 52. w14x J.Y. Bottero, J.M. Cases, F. Flessinger, J.E. Poirier, J. Phys. Chem. 84 Ž1980. 29. w15x M. Klotz, P.A. Albouy, A. Ayral, C. Menager, D. Grosso, A. ´ Van der Lee, V. Cabuil, F. Babonneau, C. Guizard, Chem. Mater. 12 Ž2000. 1721. w16x S. Lowell, J.E. Shields, Powder Surface Area and Porosity, Chapman & Hall, London, 1984. w17x M. Klotz, A. Ayral, C. Guizard, L. Cot, Sep. Purif., submitted for publication.
Materials Letters 50 Ž2001. 57–60 www.elsevier.comrlocatermatlet
Porous alumina thin layers using mesophase templating Noureddine Idrissi-Kandri a,b, Andre´ Ayral a,) , Michaela Klotz a , Pierre-Antoine Albouy c , Abdeslam El Mansouri a , Arie Van der Lee a , Christian Guizard a a
LMPM, UMR CNRS 5635, IEM-UMII, CC047, Place Eugene ` Bataillon, F34095 Montpellier cedex 5, France Laboratoire de Chimie Minerale, Faculte´ des Sciences et Techniques Saıss, ´ ¨ B.P. 2202-Atlas, Fes, ´ Morocco c Laboratoire de Physique des Solides, UMR CNRS 8502, UniÕersite´ de Paris-Sud, 91405 Orsay, France
b
Received 3 October 2000; received in revised form 9 November 2000; accepted 14 November 2000
Abstract A method of preparation for alumina thin layers exhibiting an ordered mesoporosity is presented. The synthesis conditions are discussed and the resulting layers are characterised. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Alumina thin layers; Ordered mesoporosity; Mesophase templating
1. Introduction Since the first articles of Beck et al. w1,2x on the synthesis of ordered mesoporous silicate by templating effect, a lot of studies have been devoted to this new class of materials. If the initial syntheses used cationic surfactants to form the templating liquid crystal mesophase, the synthesis conditions were then extended to other types of amphiphilic molecules like neutral surfactant or more recently block copolymers w3,4x. Significant results were also obtained on non-silica oxides w5x. The production of crack-free thin layers of single or mixed oxide is now an important challenge to make way for application of these materials in the field of membranes, sensors or
) Corresponding author. Tel.: q33-467-14-91-43; fax: q33467-14-91-19. E-mail address: [email protected] ŽA. Ayral..
micro-reactors. The sol–gel route has been successfully applied to prepare ordered mesoporous silica layers from diluted gelling solutions w6–8x. In that case, the formation of the templating mesophase occurs with the drying of the layer during the deposition step. In the case of silica layers prepared from highly aqueous sols and using alkyltrimethyl ammonium bromides as surfactants, it has been shown that the sol compositions leading to hexagonal layers can be defined from the corresponding water–surfactant binary diagrams, taking into account the volume fraction of surfactant in the dried layer w8x. Another important criterion is the mean size of the inorganic clusters just before the deposition. This size must be small enough to allow the formation of the mesophases during drying w8x. These synthesis conditions were extended to other ordered silica layers prepared from other types of surfactants, gemini Žwith two cationic polar heads. or non-ionic block copolymers w9,10x. The preparation of ordered porous layers for
00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 4 1 3 - 4
58
N. Idrissi-Kandri et al.r Materials Letters 50 (2001) 57–60
non-silica oxides has been obtained using block copolymers as surfactants and anhydrous chlorides in alcoholic solutions as oxide precursor w5x. The difficulty with the non-silica oxide is to get a sufficient reinforcement of the inorganic walls before the removal of the templating units. If the oxide network is too tenuous, the ordered structure collapses w11x.
2. Experimental procedure Taking into account the data available in the literature and our previous results on silica, we have prepared alumina thin layers using an ethanolic solution of triblock copolymer of polyŽethylene oxide.polyŽpropylene oxide.-polyŽethylene oxide. type, EO 20 PO 70 EO 20 ŽP123 from Sigma-Aldrich.. This surfactant exhibits a large hexagonal mesophase domain on its binary diagram with water w12x. The inorganic precursor was an Al trihydroxide hydrosol prepared using the synthesis method described elsewhere w13x. The starting sol stabilised at pH s 5 is formed of colloidal particles with a mean hydraulic radius equal to 10 nm. In order to decrease the size of these elemental alumina bricks, the pH of the sol was decreased to pH s 4, which corresponds to the predominance domain for the polycations Al 13 IV Ž ŽAl VI OH. 24ŽH 2 O.12 x 7q . w14x. The presence 12 O4 Al of these species was experimentally confirmed by 27 Al NMR. The decomposition of urea initially present in the sol was able to promote the reinforcement of the Al trihydroxide network during the drying step w11x. The molar ratio surfactantrAl, R, was ranging from 0.009 to 0.021. Thin layers were deposited by dip-coating on flat substrates: thick slides of soda– lime–silica glass and thin silicon wafers Žthickness: 10 mm.. To obtain larger quantities of sample, sols were also poured in wide beakers resulting in cracked thick layers. The samples were first dried at room temperature during 12 h and then for 2 h at 1758C in an oven. The thermal treatment inducing the removal of the surfactant was carried out under nitrogen up to 3508C. It must be noted that the dehydroxylation of the amorphous aluminium trihydroxide occurs at around 4008C and the transition to h-alumina at around 4508C w13x. The thickness of the calcined thin layers is ranging from 0.10 to 0.25 mm as a function of the sol concentration prior to deposition.
The ordered structure of the samples was first investigated with a diffractometer using Cu-K-L3,2 radiation and ur2 u Bragg–Brentano scattering geometry. In order to improve the structural characterisation of the layers, two-dimensional X-ray scattering analyses were performed. The scattering was recorded on photostimulable imaging plates for two different scattering geometries: a normal beam configuration giving access to in-plane preferential orientations and a grazing incident geometry which reveals the out-of-the-plane organisation w15x. The skeletal density of the solid phase was measured by helium pycnometry on calcined powders obtained from thick layers. The bulk density of the thin layers was measured by X-ray reflectometry. The porosity of the calcined thin and thick layers was analysed by nitrogen adsorption. The mesopore size distribution was estimated by analysis of the adsorption and desorption curves using the BJH method w16x, assuming cylindrical pores transmission electron microscopy ŽTEM, JEOL 100CX2. was done on microtomed slides Žthickness 70 nm. of samples embedded in a polymer resin.
3. Results and discussion The thin layers prepared from sols with an intermediate value of R, R s 0.014, are first considered. Using the ur2 u Bragg–Brentano scattering geometry, a large diffraction peak can be observed on the patterns. It is located at 10.5 nm for a layer dried at room temperature. The Bragg spacing decreases to 8.6 nm after drying at 1758C and to 7.3 nm after calcination at 3508C. In addition to this main peak, a second maximum with a very low intensity can be observed at ; dr2, i.e. 3.6 nm for the calcined layer. The two-dimensional X-ray scattering pattern for the calcined layer in normal beam geometry ŽFig. 1a. shows an intense and homogeneous ring located at 17.5 nm Žwhite arrow. and a second very weak ring located at 10.5 nm Žblack arrow.. These positions are in the ratio 1.67, close to 63. A second pattern ŽFig. 1c. was taken at grazing incidence. A diffuse ellipse Žaxes 7.6 and 17.5 nm, respectively. can be observed. Moreover, a reinforcement of the diffracted intensity appears on the large axis. The diagram presented in Fig. 1b is taken in an interme-
N. Idrissi-Kandri et al.r Materials Letters 50 (2001) 57–60
59
Fig. 1. Two-dimensional X-ray scattering patterns for a thin layer calcined at 3508C Ž Rs 0.014; sample-detector distance: 725 mm.. Ža. Normal incidence Žexposition times90 h.; Žb. intermediate incidence: 458 Žexposition times 30 h.; Žc. grazing incidence Žexposition times15 h..
diate orientation with an incident angle of 458. One observes two ellipses of lower eccentricity. Refereeing to our previous work on silica layers w15x and assuming hexagonal mesophases as initial templating structure, these X-ray scattering results can be interpreted as follows. The drying and further thermal treatments induce an important unidirectional shrinkage of the layers in a direction perpendicular to the substrate resulting in a compression of the 2D hexagonal arrangement of the micellar cylinders. Moreover, the observed reinforcement of the diffracted intensity on the large axis at grazing incidence can be related to a preferential initial orientation of the micellar cylinders parallel to the layer interfaces. The skeletal density is equal to ; 2.0 g cmy3 for a sample calcined at 3508C. This value is in good agreement with the nature of solid phase, i.e. amorphous aluminium trihydroxide, if it is compared to the density of the crystallised aluminium trihydroxide, 2.4–2.5 g cmy3 . The porosity of calcined thin and thick layers with R s 0.014 was analysed. The nitrogen adsorption–desorption isotherms exhibit all the same shape ŽFig. 2., with a important hysteresis loop, as previously observed on ordered mesoporous alumina prepared by a different route w5x. The mean pore BJH diameters determined from the adsorption branch are equal to 7.9 and 7.3 nm for the thick and the thin layers, respectively. The mean pore BJH diameters determined from the desorption branch are both equal to 3.5 nm. The difference between adsorption and desorption is clearly incompatible with the existence of open cylindrical pores. Because of the lack of precision in the weight of analysed thin layers, the total pore volume was estimated from the isotherm corresponding to the thick layers Žfor silica samples w8x, a low difference of pore volume was
Fig. 2. Nitrogen adsorption–desorption isotherm for a thick layer calcined at 3508C Ž Rs 0.014..
observed between thin and thick layers.. The total porosity calculated using the previously determined skeletal density is equal to 43%. This value is in good agreement with the density of the thin layer measure by X-ray reflectometry, 1.1 g cmy3 . The calculation of the wall density using the method described in Ref. w8x leads to a value very close to that of the skeletal density. The porosity of the alumina walls is so very low. A previous study on mesoporous silica layers prepared from hexagonal mesophases evidenced the lack of connectivity between the mesopores w17x. The important hysteresis loop observed in the case of alumina could thus be explained by both this lack of connectivity between the mesopores and the very low porosity of the alumina walls. So the mesopore emptying is shifted to low relative pressure. TEM image of a calcined
Fig. 3. TEM image of a thin layer calcined at 3508C Ž Rs 0.014..
60
N. Idrissi-Kandri et al.r Materials Letters 50 (2001) 57–60
thin layer is shown in Fig. 3. This image is quite different of that of the rectilinear and parallel cylindrical pores observed for hexagonal phases prepared from cationic surfactants w8,15x. This difference can be related to the lower stiffness of the micelles formed from non-ionic surfactants. From the density of the alumina walls and the molar ratio R, we have calculated the surfactant volume fractions in the dried layers w8x. The volume fractions giving rise to an ordered layer range from 0.55 to 0.75. This interval coincides exactly with the domain of formation of ordered silica layers using the same surfactant w10x and also with the domain of existence of the hexagonal phase in the corresponding surfactant–water binary diagram w12x.
4. Conclusion These first results demonstrate that ordered mesoporous alumina layers can be prepared from alumina hydrosols using the templating effect of a mesophase formed by self-association of triblock copolymers. The synthesis conditions can be predicted taking into account simple geometrical criteria based on the size of the inorganic clusters before deposition and on the volume fraction of surfactant in the dried layer.
Acknowledgements The authors thank Ms. C. Menager and M. ´ Lavergne for performing the electron micrographs ŽUniversite´ Pierre et Marie Curie- Paris VI, France..
References w1x C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 Ž1992. 710. w2x J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 Ž1992. 10834. w3x M. Templin, A. Franck, A. Du Chesne, H. Leist, Y. Zhang, R. Ulrich, V. Schadler, U. Wiesner, Science 278 Ž1997. ¨ 1795. w4x D. Zhao, P. Yang, N. Melosh, J. Feng, B.F. Chmelka, G.D. Stucky, Adv. Mater. 10 Ž1998. 1380. w5x P. Yang, D. Zhao, D.I. Margolese, B.F. Chmelka, G.D. Stucky, Chem. Mater. 11 Ž1999. 281. w6x M. Ogawa, Chem. Commun. Ž1999. 1149. w7x Y. Lu, R. Ganguli, C.A. Drewien, M.T. Anderson, C.J. Brinker, W. Gong, Y. Guo, H. Soyez, B. Dunn, M.H. Huang, J.I. Zinks, Nature 389 Ž1997. 364. w8x M. Klotz, A. Ayral, C. Guizard, L. Cot, J. Mater. Chem. 10 Ž2000. 66. w9x M. Klotz, Thesis, University of Montpellier, France, 2000. w10x M. Klotz, N. Idrissi-Kandri, A. Ayral, C. Guizard, Mater. Res. Soc. Symp. Proc., vol. 628, in press Želectronic article already available.. w11x S. Acosta, A. Ayral, C. Guizard, L. Cot, J. Sol–Gel Sci. Technol. 8 Ž1996. 195. w12x B. Chu, Z. Zhou, in: V.M. Nace ŽEd.., Nonionic Surfactants Polyoxoalkylene Block Copolymers, Marcel Dekker, New York, 1996, 67. w13x N. Idrissi-Kandri, A. Ayral, C. Guizard, E.H. El Ghadraoui, L. Cot, Mater. Lett. 40 Ž1999. 52. w14x J.Y. Bottero, J.M. Cases, F. Flessinger, J.E. Poirier, J. Phys. Chem. 84 Ž1980. 29. w15x M. Klotz, P.A. Albouy, A. Ayral, C. Menager, D. Grosso, A. ´ Van der Lee, V. Cabuil, F. Babonneau, C. Guizard, Chem. Mater. 12 Ž2000. 1721. w16x S. Lowell, J.E. Shields, Powder Surface Area and Porosity, Chapman & Hall, London, 1984. w17x M. Klotz, A. Ayral, C. Guizard, L. Cot, Sep. Purif., submitted for publication.