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Molecular resolution images of the surfaces of natural zeolites by atomic force microscopy
Microporous and Mesoporous Materials 61 (2003) 79–84 www.elsevier.com/locate/micromeso
Molecular resolution images of the surfaces of natural zeolites by atomic force microscopy M. Voltolini
a,*
, G. Artioli
a,b
, M. Moret
c
a
b
Dipartimento di Scienze della Terra, Universita di Milano, via Botticelli 23, I-20133 Milano, Italy Istituto Sperimentale CNR per la Dinamica dei Processi Ambientali, Sezione di Milano, via Mangiagalli 34, I-20133 Milano, Italy c Dipartimento di Scienza dei Materiali, Universit a di Milano-Bicocca, via Cozzi 53, I-20125 Milano, Italy Received 22 July 2002; received in revised form 4 December 2002; accepted 4 December 2002
Abstract Atomic force microscopy (AFM) was used to characterize the morphological and cleavage surfaces in a number of natural zeolites. The investigated zeolites (stilbite, heulandite, thomsonite, yugawaralite, laumontite, and a few others) show rather interesting and sample-dependent microtopographical features related to the mechanisms involved in the surface growth processes at the molecular level. The results obtained by AFM on stilbite, heulandite, and yugawaralite during the preliminary surface characterization are presented, and the images show that molecular resolution can be achieved and crystallographically interpreted by careful preparation of the sample. Ó 2003 Elsevier Inc. All rights reserved. Keywords: AFM surface imaging; Natural zeolites; Yugawaralite; Stilbite; Heulandite
1. Introduction Studies on zeolite surfaces are aimed to understand the crystallography, the crystal chemistry, and the microtopography of the surface layers, and eventually to interpret the underlying mechanisms of surface growth and transformation. As the crystal surface is the interface where chemisorption, transport, diffusion, and chemical reactions take place, the in situ investigation of crystal surfaces has a fundamental importance in understanding all physico-chemical processes involving the crystal–fluid interactions. In the specific case of zeolites, the understanding and the optimization
*
Corresponding author.
of all applications involving absorption, cation or water exchange, molecular selectivity, crystallization or dissolution, must necessarily be based on the appropriate understanding of surface phenomena. Most zeolite studies are concerned with the bulk structure and properties of the material, because of its internal controlled microporosity. However, many processes such as for example crystal nucleation and growth, are actually governed by surface properties and chemical absorption. Atomic force microscopy (AFM) plays a key-role in the characterization of crystal surfaces, because it allows access to the structural and microstructural features at nanometric resolution. Furthermore many experiments can also be performed in situ, with the crystal in contact with the solution.
1387-1811/03/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S1387-1811(03)00357-3
80
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
The evolution of the microtopographical features can therefore be followed during surface reactions [1,2]. Typically, AFM investigations on zeolites and microporous materials pose a number of problems caused by the strong tip–surface interactions and by the great surface reactivity, which implies an almost universal attraction of impurity molecules on the surface, with subsequent degradation of the image quality. At present only a limited number of papers have been published containing images of zeolite surfaces at the nanoscopic scale. The pioneering work of Mac Dougall et al. [3] provides a few images of natural scolecite, stilbite and faujasite. Other studied natural zeolites are stilbite [4], heulandite [2,5,6,8], and mordenite [7–9]. Some attempts of imaging the surfaces of synthetic zeolites such as LTA and FAU failed to achieve good lateral resolution at the molecular level [8,10–13]. Interestingly, adsorption phenomena in zeolites have already been tackled by using AFM techniques. The systems studied are clinoptilolite and heulandite [14–16]. Moreover, very recently a comparison between zeolites crystals grown in microgravity conditions and under standard gravity has been undertaken [17]. As a preliminary work towards the characterization of natural zeolite surfaces for chemical reactions, the present study investigated the crystal surfaces of three zeolites having similar lamellar morphology. Stilbite, heulandite, and yugawaralite all exhibit tabular habit with the {0 1 0} form being the most developed. The (0 1 0) face is of course a perfect cleavage plane, fit to be investigated by AFM.
2. Experimental 2.1. Materials Natural crystals of zeolites from secondary crystallization assemblages in basaltic rocks were used as source materials. Provenance localities are: heulandite from Osilo, Sardegna, Italy, yugawaralite from Poona, India, and stilbite from Funningsfjordur, Faer Øer Islands, Denmark. All crystals have well developed tabular habit, and
they were used without any prior chemical treatment. Sample identification and purity was controlled by XRPD on crystals ground from the same specimens. 2.2. Sample preparation and instrumental parameters All the crystal samples were mechanically cleaved with a stainless steel blade just before insertion into the AFM sample cell. AFM measurements were mostly performed in air, although a few tests were also performed with the sample submerged in de-ionized water and in diluted H2 SO4 (0.05 M), HCl (0.1 M), NaOH (0.1 M). No substantial differences were obtained in the two cases. The best results in terms of lateral resolution were obtained in air or in sodium hydroxide solutions; the use of acidic solutions produced several problems of surface contamination. The quality of the cleaved surface is crucial for the imaging experiment: surfaces that allowed high resolution imaging in air also provided high quality images in water or NaOH solutions. The instrument used was a Nanoscope III (Digital Instruments, Santa Barbara, CA) operated in contact mode. Commercially available Si3 N4 triangular cantilevers with pyramidal tips were used, with nominal spring constant k varying from 0.06 to 0.6 N/m. The forces applied on the surfaces were variable (depending on k and the environment); a proper set point value was always chosen to minimize the interaction forces between tip and crystal surface. A key factor was the choice of appropriate values of the scan rate: during this study the scan rate was set at values in the range 3– 40 Hz, using values in the range 12–40 Hz for optimal results when trying to obtain molecular resolution. Images were also recollected using different scan angles in order to check for instrumental artefacts. The x and y-directions of the D piezo-scanner (scan size: 12.5 lm) used for our experiment were calibrated with the conventional calibration grid provided by Digital Instruments; the z-axis was calibrated using the elementary steps on an etched synthetic mica foil. The calibration was checked by imaging the mica sample at molecular resolution.
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
81
To avoid artefacts due to external vibrations the instrument is operating in a quiet place and positioned on a table supported on a specially designed pneumatic suspension system.
, b ¼ 116:4° cell: a ¼ 17:70, b ¼ 17:94, c ¼ 7:42 A [18]). Experiments in various environments were carried out on the Sardinian heulandite crystals, although the best images were obtained in NaOH 0.1 M. They are shown in Fig. 1.
3. Results
3.2. Yugawaralite
3.1. Heulandite
Yugawaralite is here investigated for the first time by AFM. Yugawaralite is another zeolite providing very good clavage surfaces with some b=2 high elementary steps. The measured step is about 0.72(2) nm (yugawaralite cell: a ¼ , b ¼ 111:5° [18]). 6:73, b ¼ 13:95, c ¼ 10:03 A Growth spirals are also frequently observed. The images shown in Fig. 2 were taken in de-ionized water.
Heulandite crystals present a well developed (0 1 0) morphological pinacoid, and after careful cleavage they provide an excellent surface for AFM studies. On the cleaved faces there are flat areas of many lm2 showing elementary steps about 0.91(2) nm high. The measured thickness of these steps nicely corresponds to b=2 (heulandite
Fig. 1. Surface structure of heulandite. The first image (a) is an unfiltered AFM image, the second one (b) is a FTT filtered image with a unit cell outlined, the third (c) is the calculated surface structure and the last (d) is the FFT of the surface image.
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M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
Fig. 2. Yugawaralite surface. The first image (a) is an unfiltered AFM image, a FFT filtered image is shown on the right (b), and the calculated surface structure is presented below (c).
3.3. Stilbite Stilbite has non-perfect cleavage, but nonetheless it provides reasonably flat surfaces when mechanically cleaved. As in heulandite and yugawaralite, the elementary steps observed on the surface are about 0.92(2) nm, that is b=2 high (stilbite cell: b ¼ 127:85° a ¼ 13:61, b ¼ 18:24, c ¼ 11:27 A [18]). The images shown in Fig. 3 were taken in air. Overview of the surface with several growth spirals is shown in Fig. 4.
4. Discussion and conclusion AFM has proven to be an appropriate and useful technique to investigate zeolite surfaces in terms of microtopography, although to reach a spatial res-
olution of sufficient quality to interpret the surface structure at near-atomic level very flat and clean surfaces have to be selected [7]. Imaging of other natural and synthetic zeolites (i.e. chabazite, NaLTA, laumontite) did not produce nanometric resolution images at the lattice scale, probably because of degree of roughness of the surfaces at the atomic level. The best resolution achieved when imaging the (0 1 0) surface of yugawaralite (Fig. 2) is limited for the same reason. In the yugawaralite image the single tetrahedral vertices, probably surface hydroxyl groups, can not be resolved and only groups of two tetrahedra are visible. In the stilbite images (Fig. 3) the single tetrahedra can be identified, and the resemblance of the calculated and the FFT filtered image is evident. The environmental fluid in contact with the surface does not seem to greatly improve the final
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
83
Fig. 3. Stilbite surface. The first image (a) is a (0 1 0) area at molecular resolution, the second image (b) was FFT filtered. The calculated structure (c) and its FFT (d) are shown below.
Fig. 4. Stilbite (0 1 0) cleavage surface. The microtopographic image (a) at the left exhibits elementary steps having b=2 height, which are generated by several dislocation sources. The image at the right (b) represents one of such steps at molecular resolution.
quality of the images with respect to those imaged in air, provided that the selected surface is flat and clean. In general, an acceptable spatial resolution
can be obtained in air, although working with a fluid cell can provide more stability and limit the forces acting on the surface. The use of acidic
84
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
fluids, even if very diluted and operating on chemically resistant zeolites, always produces a little surface etching. In spite of keeping the surface clean, some reaction products are formed at the surface, quickly degrading the quality of the images. Basic solutions like NaOH 0.1 M seem to produce better results, as previously observed by other authors [19]. AFM studies of the (0 1 0) surfaces of three natural zeolites at molecular resolution were completed, as a preliminary step into interpreting the behaviour of zeolite surfaces in contact with aqueous solutions. The scarcity of high resolution images of zeolites in the literature is to be related to the difficulty of obtaining appropriate surfaces for AFM imaging. The study will progress by following in situ chemical reactions such as adsorption and dissolution on zeolite surfaces.
[3]
[4] [5]
[6] [7]
[8] [9]
[10] [11]
Acknowledgements The work has been carried out in the frame of the project ‘‘Mineral surface chemical reactions: intercalation and sorption processes’’ (Coordinator Prof. G. Artioli), and financed by MURST COFIN 2000.
[12]
[13] [14]
[15]
References [1] S. Yamamoto, S. Sugiyama, O. Matsuoka, K. Kohmura, T. Honda, Y. Banno, H. Nozoye, J. Phys. Chem. 100 (1996) 18474. [2] M. Voltolini, M. Moret, G. Artioli, in: R. Aiello, G. Giordano, F. Testa (Eds.), Impact of Zeolites and Other Porous Materials on the New Technologies at the Beginning of the New Millennium, Studies in Surface
[16] [17]
[18] [19]
Science and Catalysis, vol. 142, Elsevier Science, Amsterdam, 2002, p. 1721. J.E. Mac Dougall, S.D. Cox, G.D. Stucky, A.L. Weisenhorn, P.K. Hansma, W.S. Wise, Zeolites 11 (1991) 429. M. Komiyama, K. Tsujimichi, Y. Oumi, M. Kubo, A. Miyamoto, Appl. Surf. Sci. 121/122 (1997) 543. S. Yamamoto, S. Sugiyama, O. Matsuoka, T. Honda, Y. Banno, H. Nozoye, Micropor. Mesopor. Mater. 21 (1998) 1. G. Binder, L. Scandella, A. Schumacher, N. Kruse, R. Prins, Zeolites 16 (1996) 2. S. Yamamoto, O. Matsuoka, S. Sugiyama, T. Honda, Y. Banno, H. Nozoye, Chem. Phys. Lett. 260 (1996) 208. S. Sugiyama Ono, O. Matsuoka, S. Yamamoto, Micropor. Mesopor. Mater. 48 (2001) 103. S. Sugiyama, S. Yamamoto, O. Matsuoka, T. Honda, H. Nozoye, S. Qiu, J. Yu, O. Terasaki, Surf. Sci. 377–379 (1997) 140. J.R. Agger, N. Pervaiz, A.K. Cheetham, M.W. Anderson, J. Am. Chem. Soc. 120 (1998) 10754. M.W. Anderson, J.R. Agger, J.T. Thornton, N. Forsyth, Angew. Chem. Int. Ed. Engl. 35 (1996) 1210. S. Sugiyama, S. Yamamoto, O. Matsuoka, H. Nozoye, J. Yu, G. Zhu, S. Qiu, O. Terasaki, Micropor. Mesopor. Mater. 28 (1999) 1. M.W. Anderson, J.R. Agger, N. Hanif, O. Terasaky, Micropor. Mesopor. Mater. 48 (2001) 1. A.L. Weisenhorn, J.E. Mac Dougall, S.A.C. Gould, S.D. Cox, W.S. Wise, J. Massie, P. Maivald, V.B. Elings, G.D. Stucky, P.K. Hansma, Science 247 (1990) 1330. E.J. Sullivan, D.B. Hunter, R.S. Bowman, Clays Clay Mineral. 45 (1997) 42. M. Komiyama, T. Shimaguchi, T. Koyama, M. Gu, J. Phys. Chem. 100 (1996) 15198. J. Warzywoda, M. Valcheva-Traykova, G.A. Rossetti, N. Bacß, R. Joesten, S.L. Suib, A. Sacco, J. Crystal Growth 220 (2000) 150. G. Gottardi, E. Galli, Natural Zeolites, Springer-Verlag, Berlin, 1985. L. Scandella, N. Kruse, R. Prins, Surf. Sci. Lett. 281 (1993) L331.
Molecular resolution images of the surfaces of natural zeolites by atomic force microscopy M. Voltolini
a,*
, G. Artioli
a,b
, M. Moret
c
a
b
Dipartimento di Scienze della Terra, Universita di Milano, via Botticelli 23, I-20133 Milano, Italy Istituto Sperimentale CNR per la Dinamica dei Processi Ambientali, Sezione di Milano, via Mangiagalli 34, I-20133 Milano, Italy c Dipartimento di Scienza dei Materiali, Universit a di Milano-Bicocca, via Cozzi 53, I-20125 Milano, Italy Received 22 July 2002; received in revised form 4 December 2002; accepted 4 December 2002
Abstract Atomic force microscopy (AFM) was used to characterize the morphological and cleavage surfaces in a number of natural zeolites. The investigated zeolites (stilbite, heulandite, thomsonite, yugawaralite, laumontite, and a few others) show rather interesting and sample-dependent microtopographical features related to the mechanisms involved in the surface growth processes at the molecular level. The results obtained by AFM on stilbite, heulandite, and yugawaralite during the preliminary surface characterization are presented, and the images show that molecular resolution can be achieved and crystallographically interpreted by careful preparation of the sample. Ó 2003 Elsevier Inc. All rights reserved. Keywords: AFM surface imaging; Natural zeolites; Yugawaralite; Stilbite; Heulandite
1. Introduction Studies on zeolite surfaces are aimed to understand the crystallography, the crystal chemistry, and the microtopography of the surface layers, and eventually to interpret the underlying mechanisms of surface growth and transformation. As the crystal surface is the interface where chemisorption, transport, diffusion, and chemical reactions take place, the in situ investigation of crystal surfaces has a fundamental importance in understanding all physico-chemical processes involving the crystal–fluid interactions. In the specific case of zeolites, the understanding and the optimization
*
Corresponding author.
of all applications involving absorption, cation or water exchange, molecular selectivity, crystallization or dissolution, must necessarily be based on the appropriate understanding of surface phenomena. Most zeolite studies are concerned with the bulk structure and properties of the material, because of its internal controlled microporosity. However, many processes such as for example crystal nucleation and growth, are actually governed by surface properties and chemical absorption. Atomic force microscopy (AFM) plays a key-role in the characterization of crystal surfaces, because it allows access to the structural and microstructural features at nanometric resolution. Furthermore many experiments can also be performed in situ, with the crystal in contact with the solution.
1387-1811/03/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S1387-1811(03)00357-3
80
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
The evolution of the microtopographical features can therefore be followed during surface reactions [1,2]. Typically, AFM investigations on zeolites and microporous materials pose a number of problems caused by the strong tip–surface interactions and by the great surface reactivity, which implies an almost universal attraction of impurity molecules on the surface, with subsequent degradation of the image quality. At present only a limited number of papers have been published containing images of zeolite surfaces at the nanoscopic scale. The pioneering work of Mac Dougall et al. [3] provides a few images of natural scolecite, stilbite and faujasite. Other studied natural zeolites are stilbite [4], heulandite [2,5,6,8], and mordenite [7–9]. Some attempts of imaging the surfaces of synthetic zeolites such as LTA and FAU failed to achieve good lateral resolution at the molecular level [8,10–13]. Interestingly, adsorption phenomena in zeolites have already been tackled by using AFM techniques. The systems studied are clinoptilolite and heulandite [14–16]. Moreover, very recently a comparison between zeolites crystals grown in microgravity conditions and under standard gravity has been undertaken [17]. As a preliminary work towards the characterization of natural zeolite surfaces for chemical reactions, the present study investigated the crystal surfaces of three zeolites having similar lamellar morphology. Stilbite, heulandite, and yugawaralite all exhibit tabular habit with the {0 1 0} form being the most developed. The (0 1 0) face is of course a perfect cleavage plane, fit to be investigated by AFM.
2. Experimental 2.1. Materials Natural crystals of zeolites from secondary crystallization assemblages in basaltic rocks were used as source materials. Provenance localities are: heulandite from Osilo, Sardegna, Italy, yugawaralite from Poona, India, and stilbite from Funningsfjordur, Faer Øer Islands, Denmark. All crystals have well developed tabular habit, and
they were used without any prior chemical treatment. Sample identification and purity was controlled by XRPD on crystals ground from the same specimens. 2.2. Sample preparation and instrumental parameters All the crystal samples were mechanically cleaved with a stainless steel blade just before insertion into the AFM sample cell. AFM measurements were mostly performed in air, although a few tests were also performed with the sample submerged in de-ionized water and in diluted H2 SO4 (0.05 M), HCl (0.1 M), NaOH (0.1 M). No substantial differences were obtained in the two cases. The best results in terms of lateral resolution were obtained in air or in sodium hydroxide solutions; the use of acidic solutions produced several problems of surface contamination. The quality of the cleaved surface is crucial for the imaging experiment: surfaces that allowed high resolution imaging in air also provided high quality images in water or NaOH solutions. The instrument used was a Nanoscope III (Digital Instruments, Santa Barbara, CA) operated in contact mode. Commercially available Si3 N4 triangular cantilevers with pyramidal tips were used, with nominal spring constant k varying from 0.06 to 0.6 N/m. The forces applied on the surfaces were variable (depending on k and the environment); a proper set point value was always chosen to minimize the interaction forces between tip and crystal surface. A key factor was the choice of appropriate values of the scan rate: during this study the scan rate was set at values in the range 3– 40 Hz, using values in the range 12–40 Hz for optimal results when trying to obtain molecular resolution. Images were also recollected using different scan angles in order to check for instrumental artefacts. The x and y-directions of the D piezo-scanner (scan size: 12.5 lm) used for our experiment were calibrated with the conventional calibration grid provided by Digital Instruments; the z-axis was calibrated using the elementary steps on an etched synthetic mica foil. The calibration was checked by imaging the mica sample at molecular resolution.
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
81
To avoid artefacts due to external vibrations the instrument is operating in a quiet place and positioned on a table supported on a specially designed pneumatic suspension system.
, b ¼ 116:4° cell: a ¼ 17:70, b ¼ 17:94, c ¼ 7:42 A [18]). Experiments in various environments were carried out on the Sardinian heulandite crystals, although the best images were obtained in NaOH 0.1 M. They are shown in Fig. 1.
3. Results
3.2. Yugawaralite
3.1. Heulandite
Yugawaralite is here investigated for the first time by AFM. Yugawaralite is another zeolite providing very good clavage surfaces with some b=2 high elementary steps. The measured step is about 0.72(2) nm (yugawaralite cell: a ¼ , b ¼ 111:5° [18]). 6:73, b ¼ 13:95, c ¼ 10:03 A Growth spirals are also frequently observed. The images shown in Fig. 2 were taken in de-ionized water.
Heulandite crystals present a well developed (0 1 0) morphological pinacoid, and after careful cleavage they provide an excellent surface for AFM studies. On the cleaved faces there are flat areas of many lm2 showing elementary steps about 0.91(2) nm high. The measured thickness of these steps nicely corresponds to b=2 (heulandite
Fig. 1. Surface structure of heulandite. The first image (a) is an unfiltered AFM image, the second one (b) is a FTT filtered image with a unit cell outlined, the third (c) is the calculated surface structure and the last (d) is the FFT of the surface image.
82
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
Fig. 2. Yugawaralite surface. The first image (a) is an unfiltered AFM image, a FFT filtered image is shown on the right (b), and the calculated surface structure is presented below (c).
3.3. Stilbite Stilbite has non-perfect cleavage, but nonetheless it provides reasonably flat surfaces when mechanically cleaved. As in heulandite and yugawaralite, the elementary steps observed on the surface are about 0.92(2) nm, that is b=2 high (stilbite cell: b ¼ 127:85° a ¼ 13:61, b ¼ 18:24, c ¼ 11:27 A [18]). The images shown in Fig. 3 were taken in air. Overview of the surface with several growth spirals is shown in Fig. 4.
4. Discussion and conclusion AFM has proven to be an appropriate and useful technique to investigate zeolite surfaces in terms of microtopography, although to reach a spatial res-
olution of sufficient quality to interpret the surface structure at near-atomic level very flat and clean surfaces have to be selected [7]. Imaging of other natural and synthetic zeolites (i.e. chabazite, NaLTA, laumontite) did not produce nanometric resolution images at the lattice scale, probably because of degree of roughness of the surfaces at the atomic level. The best resolution achieved when imaging the (0 1 0) surface of yugawaralite (Fig. 2) is limited for the same reason. In the yugawaralite image the single tetrahedral vertices, probably surface hydroxyl groups, can not be resolved and only groups of two tetrahedra are visible. In the stilbite images (Fig. 3) the single tetrahedra can be identified, and the resemblance of the calculated and the FFT filtered image is evident. The environmental fluid in contact with the surface does not seem to greatly improve the final
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
83
Fig. 3. Stilbite surface. The first image (a) is a (0 1 0) area at molecular resolution, the second image (b) was FFT filtered. The calculated structure (c) and its FFT (d) are shown below.
Fig. 4. Stilbite (0 1 0) cleavage surface. The microtopographic image (a) at the left exhibits elementary steps having b=2 height, which are generated by several dislocation sources. The image at the right (b) represents one of such steps at molecular resolution.
quality of the images with respect to those imaged in air, provided that the selected surface is flat and clean. In general, an acceptable spatial resolution
can be obtained in air, although working with a fluid cell can provide more stability and limit the forces acting on the surface. The use of acidic
84
M. Voltolini et al. / Microporous and Mesoporous Materials 61 (2003) 79–84
fluids, even if very diluted and operating on chemically resistant zeolites, always produces a little surface etching. In spite of keeping the surface clean, some reaction products are formed at the surface, quickly degrading the quality of the images. Basic solutions like NaOH 0.1 M seem to produce better results, as previously observed by other authors [19]. AFM studies of the (0 1 0) surfaces of three natural zeolites at molecular resolution were completed, as a preliminary step into interpreting the behaviour of zeolite surfaces in contact with aqueous solutions. The scarcity of high resolution images of zeolites in the literature is to be related to the difficulty of obtaining appropriate surfaces for AFM imaging. The study will progress by following in situ chemical reactions such as adsorption and dissolution on zeolite surfaces.
[3]
[4] [5]
[6] [7]
[8] [9]
[10] [11]
Acknowledgements The work has been carried out in the frame of the project ‘‘Mineral surface chemical reactions: intercalation and sorption processes’’ (Coordinator Prof. G. Artioli), and financed by MURST COFIN 2000.
[12]
[13] [14]
[15]
References [1] S. Yamamoto, S. Sugiyama, O. Matsuoka, K. Kohmura, T. Honda, Y. Banno, H. Nozoye, J. Phys. Chem. 100 (1996) 18474. [2] M. Voltolini, M. Moret, G. Artioli, in: R. Aiello, G. Giordano, F. Testa (Eds.), Impact of Zeolites and Other Porous Materials on the New Technologies at the Beginning of the New Millennium, Studies in Surface
[16] [17]
[18] [19]
Science and Catalysis, vol. 142, Elsevier Science, Amsterdam, 2002, p. 1721. J.E. Mac Dougall, S.D. Cox, G.D. Stucky, A.L. Weisenhorn, P.K. Hansma, W.S. Wise, Zeolites 11 (1991) 429. M. Komiyama, K. Tsujimichi, Y. Oumi, M. Kubo, A. Miyamoto, Appl. Surf. Sci. 121/122 (1997) 543. S. Yamamoto, S. Sugiyama, O. Matsuoka, T. Honda, Y. Banno, H. Nozoye, Micropor. Mesopor. Mater. 21 (1998) 1. G. Binder, L. Scandella, A. Schumacher, N. Kruse, R. Prins, Zeolites 16 (1996) 2. S. Yamamoto, O. Matsuoka, S. Sugiyama, T. Honda, Y. Banno, H. Nozoye, Chem. Phys. Lett. 260 (1996) 208. S. Sugiyama Ono, O. Matsuoka, S. Yamamoto, Micropor. Mesopor. Mater. 48 (2001) 103. S. Sugiyama, S. Yamamoto, O. Matsuoka, T. Honda, H. Nozoye, S. Qiu, J. Yu, O. Terasaki, Surf. Sci. 377–379 (1997) 140. J.R. Agger, N. Pervaiz, A.K. Cheetham, M.W. Anderson, J. Am. Chem. Soc. 120 (1998) 10754. M.W. Anderson, J.R. Agger, J.T. Thornton, N. Forsyth, Angew. Chem. Int. Ed. Engl. 35 (1996) 1210. S. Sugiyama, S. Yamamoto, O. Matsuoka, H. Nozoye, J. Yu, G. Zhu, S. Qiu, O. Terasaki, Micropor. Mesopor. Mater. 28 (1999) 1. M.W. Anderson, J.R. Agger, N. Hanif, O. Terasaky, Micropor. Mesopor. Mater. 48 (2001) 1. A.L. Weisenhorn, J.E. Mac Dougall, S.A.C. Gould, S.D. Cox, W.S. Wise, J. Massie, P. Maivald, V.B. Elings, G.D. Stucky, P.K. Hansma, Science 247 (1990) 1330. E.J. Sullivan, D.B. Hunter, R.S. Bowman, Clays Clay Mineral. 45 (1997) 42. M. Komiyama, T. Shimaguchi, T. Koyama, M. Gu, J. Phys. Chem. 100 (1996) 15198. J. Warzywoda, M. Valcheva-Traykova, G.A. Rossetti, N. Bacß, R. Joesten, S.L. Suib, A. Sacco, J. Crystal Growth 220 (2000) 150. G. Gottardi, E. Galli, Natural Zeolites, Springer-Verlag, Berlin, 1985. L. Scandella, N. Kruse, R. Prins, Surf. Sci. Lett. 281 (1993) L331.