MgAl-Layered Double Hydroxide Films on Muscovite Mica: Epitaxial

ARTICLE pubs.acs.org/IECR

MgAl-Layered Double Hydroxide Films on Muscovite Mica: Epitaxial Growth and Catalytic Activity in Acetone Self-Condensation Xiaodong Lei, Zhi L€u, Xiaoxiao Guo, and Fazhi Zhang* State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Box 98, Beijing 100029, China ABSTRACT: A simple method for the immobilization of layered double hydroxides (LDHs) on muscovite mica via strong covalent bonding is described. The crystal structure of the LDH films attached on the substrate was studied by X-ray diffraction (XRD) and attenuated total reflectance-Fourier transform infrared (ATR-FT-IR), and the morphology of the films was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which showed that half-hexagonal shaped LDH platelets grow obliquely on the substrate with a high degree of dispersion. The lattice matching between LDH and muscovite structures suggests that the LDH phase grows epitaxially on the surface of the muscovite and the mechanism of the epitaxial growth process has been analyzed in detail. After being activated by a calcination/rehydration procedure, the rehydrated LDH (RLDH) platelets remain firmly immobilized on the muscovite substrate and retain the half-hexagonal platelet morphology of the LDH precursor. The RLDH/muscovite can act as a solid catalyst and shows higher activity in the aldol condensation of acetone than the powdered RLDH analogue synthesized by the same procedure.

1. INTRODUCTION Layered double hydroxides (LDHs), also known as hydrotalcite-like materials, are generally expressed as [MII1 xMIIIx (OH)2]x+(An )x/n 3 yH2O. The identities of the divalent and trivalent cations (MII and MIII, respectively) and the interlayer anion (An ) together with the value of the stoichiometric coefficient (x) may be varied over a wide range.1 LDHs have attracted increasing attention in recent years owing to their potential applications as catalysts and catalyst supports.2,3 On calcination at about 773 K, LDHs containing interlayer carbonate anions undergo decomposition of the carbonate anions giving mixed metal oxide phases. Subsequent rehydration of these calcined LDHs (CLDHs) at room temperature under nitrogen affords rehydrated LDHs (RLDHs) possessing the original brucite-like layers but with the interlayer anions being hydroxide.4 The activated RLDHs have high base catalytic activity for Claisen-Schmidt condensation, Knoevenagel condensation, and aldol condensation reactions.5 11 All previous studies of RLDHs in catalyzed reactions have used powdered samples. Use of powdered catalysts on an industrial scale gives rise to a number of problems, including high pressure drops, high diffusion resistance, and difficult catalyst separation procedures, and is not amenable to simple scale-up.12 15 If materials such as RLDHs are to be used in practice, it is therefore desirable that they would be fabricated into the macroscopic form to mitigate these problems. There have been several reports of the preparation of LDH films on inorganic substrates, including deposition from Langmuir Blodgett films of LDH layers on mica, deposition on glass from colloidal suspension of LDHs, and formation of a monolayer film of LDHs on Si (100) wafers.16 20 We have previously shown that MgAl-LDH films can be strongly attached on sulfonated polystyrene, NiAl and ZnAl-LDH films can be prepared by using porous anodic alumina/aluminum as both substrate and sole source of aluminum, and MgAl-LDH films can be prepared by r 2011 American Chemical Society

the solvent evaporation and layer-by-layer assembly method on quartz substrates, respectively.21 26 Although the interaction between the films and substrates is strong enough in these cases, the thermal stabilities of the substrates are not sufficient to survive calcination of the surface bonded LDHs during the catalyst activation process. Muscovite (KAl2(Si3Al)O10(OH)2), a type of mica, is a layered aluminosilicate in which negatively charged layers are held together by charge-balancing K+ ions in 12-fold coordination.27 Some of the K+ ions are exposed at the surface and can be exchanged by divalent or trivalent metallic cations, initiating epitaxial film growth. This useful property, along with its inertness, phase stability of muscovite mica good enough near 773 K, relative hardness, and excellent machining properties, makes it an ideal substrate. In this paper, we describe a simple procedure for the epitaxial growth of MgAl-LDH on muscovite. After being activated by a calcination/rehydration procedure, the catalytic properties of the activated RLDH/muscovite samples are investigated by using the aldol condensation of acetone.

2. EXPERIMENTAL DETAILS 2.1. Epitaxial Growth of LDH on Muscovite. Mg(NO3)2 3 6H 2 O and Al(NO3 )3 3 9H 2 O with a Mg 2+ /Al 3+ molar ratio of 2.0 were dissolved in deionized water (200 mL) to give a solution with a total metal cation concentration of 0.06 M, which was placed in a 300 mL glass vessel. Urea ([urea]/[NO3 ] = 4) was dissolved in the above solution. Freshly cleaved muscovite sheets with a size of ∼15 mm 15 mm were suspended in the solution. The container was sealed and maintained at 363 K in Received: November 9, 2011 Accepted: December 15, 2011 Revised: December 12, 2011 Published: December 15, 2011 1275

dx.doi.org/10.1021/ie202566x | Ind. Eng. Chem. Res. 2012, 51, 1275–1280

Industrial & Engineering Chemistry Research

ARTICLE

Figure 1. SEM images of the top (a) and edge (b) of LDH/muscovite and EDS spectra of two selected areas A and B.

an oven for 3 d. After cooling, the muscovite substrates were washed with deionized water and then dried at 363 K for 24 h. The resulting sample is denoted LDH/muscovite. The precipitate of MgAl-CO3-LDH obtained concurrently in the above process was also collected by centrifugation and treated by the same methods. The resulting powder sample is denoted LDH. 2.2. Activation of Samples. The as-prepared LDH/muscovite sample was heated to 773 K in an N2 flow with a heating rate of 10 K/min and kept at this temperature for 8 h. The calcined sample is designated as CLDH/muscovite. The CLDH/muscovite sample was immersed in decarbonated water (80 mL of H2O/10 g of sample) for 5 h at 298 K under an N2 atmosphere. The excess water was removed under vacuum at 298 K for 24 h. The rehydrated MgAl-OH-LDH catalyst is denoted RLDH/ muscovite. The powdered sample LDH was activated by the same calcination/rehydration procedure, and the calcined and rehydrated samples are denoted CLDH and RLDH, respectively. The mica substrate was also alone heated to 773 K for 8 h, then immersed in decarbonated water (80 mL of H2O/10 g of sample) for 5 h at 298 K under an N2 atmosphere. The excess water was removed under vacuum at 298 K for 24 h. 2.3. Characterization. SEM images of the samples were obtained using a Hitachi S-3500N SEM instrument with all samples being sputtered with gold. Elemental analyses of the film samples were performed using an Oxford Link-ISIS300 energy dispersive X-ray spectroscopy (EDS) attachment. AFM images

were recorded with a Nanoscope III scanning probe microscope (Digital Instruments), using Nanoprobe cantilevers/[Si3N4] integral tips with a spring constant of 0.06 nm 1 (Park Scientific). The AFM images were obtained in the constant force mode with the filters off. A “d” scan head was used, which had a maximum scan range of 12 μm 12 μm 4.4 μm. XRD patterns of the samples were recorded on a Shimadzu XRD-6000 diffractometer using Cu Kα radiation (λ = 1.542 Å, 2θ, 7°∼65°, 40 kV, 30 mA). ATR-FT-IR spectra of the samples were recorded on a Bruker Vector 22 spectrometer with an ATR attachment (PIKE). The incident angle was fixed at 318°, and the sample was pressed over the Zn Se crystal. All spectra were recorded from 2000 to 650 cm 1, with a resolution of 4 cm 1 and 50 scans; the background was collected before each spectrum. Elemental analyses for metal elements in powdered samples were performed with a Shimadzu ICPS-7500 inductively coupled plasma (ICP) emission spectrometer on solutions prepared by dissolving the samples in dilute HNO3 (1:1). The RLDH crystal can be dissolved in dilute HNO3 easily, and mica substrate cannot be dissolved by this way. We confirmed dosage of RLDH crystal on muscovite mica by ICP tests using the RLDH dissolving solution. 2.4. Catalytic Tests. The aldol condensation of acetone to diacetone alcohol (DAA) was performed in a 250 mL threenecked flask under an N2 atmosphere at 273 K with the temperature maintained by means of an ice bath. Acetone (2 mol) was added to freshly activated RLDH/muscovite (10 g, we 1276

dx.doi.org/10.1021/ie202566x |Ind. Eng. Chem. Res. 2012, 51, 1275–1280


ARTICLE

confirmed that there are 0.2 0.3 g of RLDH on 10 g of muscovite by ICP tests) or freshly activated RLDH (0.3 g) and calcined/rehydrated pristine mica (10 g) under a flow of N2 in order to exclude atmospheric carbon dioxide. The mixture of products was analyzed by a gas chromatograph/mass spectrometer (GC/MS-QP2010, Shimadzu). Iso-octane was used as an internal standard in order to calculate the amount of DAA formed. There was no detectable amount of mesityl oxide (MO) or other byproduct observed.

3. RESULTS AND DISCUSSION 3.1. Structure and Morphology of LDH Films on Muscovite. MgAl-CO3-LDH are formed as large hexagonal platelets

when urea is slowly hydrolyzed by heating in solutions containing Mg2+ and Al3+ cations.28 30 When this process was carried out at 363 K in the presence of freshly cleaved muscovite sheets, the SEM images (Figure 1) of the resulting material (LDH/ muscovite) show that well-dispersed half-hexagonal shaped platelets grew obliquely on the substrate. The EDS spectra of two selected areas of the LDH/muscovite sample, area A on the naked surface of the muscovite and area B on a part of the surface occupied by one of the platelets, are also shown in Figure 1, and details of the elemental composition are given in Table 1. In area A, the measured Mg/Al ratio was zero and the Si/Al ratio 1.41, confirming that only muscovite was present. In area B, the Mg/Al and Si/Al ratios were 0.89 and 0.73, respectively, suggesting the presence of both the muscovite substrate and attached MgAl-CO3-LDH phase. Deducting the Al content attributed to the muscovite according to the Si/Al ratio in area A, the Mg/Al ratio of the LDH platelet present in area B is about 1.83. Elemental analysis by ICP showed that the Mg/Al molar ratios in the LDH films are about 1.85, in agreement with the EDS measurement. Table 1. Elemental Composition of the Two Selected Areas Obtained from EDS (Elemental Molar Ratios; No Fe Was Detected) element

Mg

O

Al

Si

K

area A area B

0 9.84

57.38 69.08

15.26 11.11

21.53 8.08

5.82 1.88

The SEM image of the edge of the LDH/muscovite sample (Figure 1b) confirms that the half-hexagonal LDH sheets are obliquely joined to the muscovite, with the thickness of the LDH film being of the order of several micrometers. The surface morphology of the LDH/muscovite sample was further investigated by AFM (Figure 2), and the profile images of three selected lines show that the tilt angle of the LDH sheets with respect to the surface of the muscovite substrate is in the range 40° to 60°. The dimensions of the LDH platelets as determined by AFM are in the range 1 to 4 μm, consistent with the SEM images in Figure 1. The crystal structure of the films attached on the substrate was studied by XRD (Figure 3) and FT-IR (Figure 4). Though much lower than the diffraction peaks of muscovite substrate (Figure 3A), the characteristic reflection peaks corresponding to the (003) and (006) planes of LDH phase can still be observed (Figure 3B,C). The LDH films is confirmed by the XRD pattern of the powder scraped from the muscovite substrate (Figure 3D); symmetric reflection peaks of (00l) and (0kl) planes together with (110) and (113) reflection peaks reveal a typical MgAl-CO3LDH phase, a profile similar to those presented by hydrotalcitelike compounds.29 Likewise, the FT-IR spectrum of the powder scraped from the muscovite substrate (Figure 4) is consistent with the reported spectra of MgAl-CO3-LDHs.31,32 The broad absorption band centered around 3460 cm 1 is associated with the hydroxyl stretching band υ(OHstr), arising from metal hydroxyl groups and hydrogen-bonded interlayer water molecules. Another absorption band at 1356 cm 1 can be assigned to the υ3 (asymmetric stretching) mode of CO32 ions in the interlayer galleries. The other bands observed in the range 500 800 cm 1 can be attributed to M-O, M-O-M, and O-M-O lattice vibrations. The XRD and FT-IR data, together, suggest that the halfhexagonal platelet films formed on the surface of the muscovite substrate are indeed MgAl-CO3-LDH. Indexed in a hexagonal cell with rhombohedral symmetry, cell parameters of the MgAl-CO3LDH will be a = 3.04 Å (d110 = 1.52 Å) and c = 22.62 Å (d003 = 7.54 Å), corresponding to an interlayer distance of 7.54 Å that is typical for MgAl-CO3-LDHs. In the case of the muscovite supported films, the fact that the half-hexagonal MgAl-CO3-LDH platelets are obliquely attached to the surface via their edges suggests that they have been epitaxially grown onto the muscovite via a strong chemical

Figure 2. AFM image of LDH/muscovite and profiles of three selected lines. 1277



ARTICLE

interaction. SEM images of the films obtained after calcination at 773 K (CLDH/muscovite) and subsequent rehydration of this sample at room temperature (RLDH/muscovite) are shown in Figure 5. In each case, the samples both retain the half-hexagonal platelet morphology and remain attached obliquely to the

muscovite. Since considerable thermal stresses are associated with a temperature change of ∼500 K, these two observations support the hypothesis that the LDHs have been epitaxially grown on the muscovite surface via a strong chemical interaction. The ATR-FT-IR spectra of the LDH/muscovite, CLDH/ muscovite,and RLDH/muscovite samples are shown in Figure 6. The absorption band at 1352 cm 1 in the spectrum of LDH/ muscovite (Figure 6A) can be attributed to the υ3 (asymmetric stretching) mode of CO32 ions in the interlayer galleries,31,32 consistent with the spectrum (Figure 4) of the powder scraped from the surface of the muscovite. This peak is absent in the spectra of CLDH/muscovite and RLDH/muscovite (Figure 6B, C, confirming that CO32 ions in the interlayer galleries decompose on calcination and are not reincorporated during the rehydration process. The bands at about 1538 cm 1 in Figure 6B,C ndicate the formation of MgO or Mg-OH.

Figure 3. XRD patterns of (A) muscovite, (B, C) LDH/muscovite, and (D) powder scraped from the substrate. (Part C is the glancing angle diffraction pattern of LDH/muscovite from 7° to 30°).

Figure 4. FT-IR spectrum of the powder scraped from the substrate in LDH/muscovite.

Figure 6. ATR-FT-IR spectra of (A) LDH/muscovite, (B) CLDH/ muscovite,and (C) RLDH/muscovite.

Figure 5. SEM images of (A) CLDH/muscovite and (B) RLDH/muscovite. 1278



ARTICLE

Figure 7. Surface structure of muscovite.

Figure 9. Plots of conversion of acetone to DAA versus time at 273 K with RLDH/muscovite film (acetone/(RLDH/muscovite) = 2 mol/10 g, we confirmed that there are 0.2 0.3 g of RLDH on 10 g of muscovite by ICP tests) and RLDH powder (acetone/RLDH powder = 2 mol/0.3 g).

Figure 8. Proposed structure of LDH/muscovite based on the lattice match between MgAl-LDH and the muscovite phases.

3.2. Growth Mechanism of LDH Films on Muscovite. The charge-balancing K+ cations at the surface of muscovite are exposed.27,33,34 It is to be expected that these K+ ions can be substituted by Al3+ because of the stronger electrostatic attraction of the latter with layer oxygen sites, which will promote the initial nucleation of an LDH phase and allow MgAl-CO3-LDH films to be grown on the muscovite surface attached by Al O M (M = Si or Al) bonds between the AlO6 octahedra of the LDH and (Si, Al)O4 tetrahedra of muscovite by sharing of O atoms. Muscovite exists as the 2M1 polytype, having a monoclinic structure with the space group (C2/c) with the cell parameters being a = 5.2 Å, b = 9.0 Å, c = 20.1 Å, and β = 95.7°.35 37 The distance between two neighboring O atoms on the basal surface of muscovite is about 2.6 Å (Figure 7). For MgAl-LDH, the distance between two neighboring O atoms is in the range of 3.02 3.07 Å, depending on the Mg/Al ratio.1,38 For the materials reported here, where Mg/Al = 2, a value of about 3.04 Å is expected. The lattice mismatch between the LDH and muscovite phases is about 14.5%, which is regarded as sufficiently low to allow epitaxial growth, for example, Matsuki et al. have reported that gallium nitride can be heteroepitaxially grown on muscovite even although there is a lattice mismatch of 43%.39 Figure 8 illustrates the proposed lattice-matched structure of the LDH and the muscovite phases. Because the framework O atoms of the (Si, Al)O4 tetrahedra on the basal surface of muscovite are

shared by the AlO6 octahedra of the LDH, the films can only adopt a tilted orientation with respect to the muscovite surface. 3.3. Catalytic Activity Tests. The catalytic activity of RLDH/ muscovite film was studied by using the aldol condensation reaction of acetone to diacetone alcohol (DAA) at 273 K as a probe reaction, the catalytic properties of the RLDH powder prepared under the same calcination and rehydration conditions were also studied for comparison. The mica substrate alone was also treated by the same calcination/rehydration process. We found that the thermal-treated mica did not have any catalytic properties. As shown in Figure 9, the plots of acetone conversion against time are similar for the two catalysts, showing an initial rapid increase and eventually reached a constant value. The performance of the RLDH/muscovite film catalyst was slightly superior to that of acetone conversion and reached 23.0% after 460 min, which is very close to the thermodynamic equilibrium conversion (The conversion of acetone to DAA is reversible, with the equilibrium strongly favoring acetone and temperature. The equilibrium conversion is 23.1% at 273 K.),40 while that with the RLDH powder catalyst reached only 22.8% after 560 min. We have previously argued that the ordered array of acid base hydroxyl pairs on the basal surface of activated MgAl-LDH comprises the main active sites for the reaction of acetone to give DAA:41 a pair of acetone molecules are first adsorbed on a neighboring acid base hydroxyl pair on the surface of the RLDHs and then react at the catalyst surface. In a liquid solid interphase reaction, especially at lower temperatures, transportation of matter usually dominates the overall rate because diffusion is a temperature-activated process.42 Because the RLDH sheets are firmly immobilized on, and well dispersed over, the surface of the muscovite substrate, the basal surfaces of the RLDH sheets grown on the muscovite are more exposed than those of the RLDH powder and the mass transfer resistance for RLDH/muscovite film is lower than that for the RLDH powder. Accordingly, the diffusion of acetone molecules to, and the backdiffusion of DAA molecules from, the active sites on the RLDH/ muscovite film catalyst reaction zone are faster than in the case of the RLDH powder, and thus the overall rate of reaction with the film catalyst is higher than that observed with the RLDH powder catalyst. 1279



4. CONCLUSIONS MgAl-CO3-LDH films have been immobilized on the surface of muscovite with a high degree of dispersion. The structures of the LDH and muscovite phases suggest that they are sufficiently closely lattice-matched to allow epitaxial growth of the LDH sheets on the muscovite surface. The as-prepared LDH/muscovite sample can be activated by a calcination/rehydration procedure. The resulting RLDH sheets remain firmly attached to the muscovite substrate and retain their original half-hexagonal plateshaped morphology. The RLDH/muscovite film shows a higher catalytic activity in the self-condensation of acetone than the RLDH powder catalyst synthesized under the same conditions. Thus RLDH/muscovite film is a potential candidate for use as a solid catalyst for the aldol condensation of acetone and other base catalyzed reactions. ’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: (+86) 10-64425385. Phone: (+86) 10-64425105.

’ ACKNOWLEDGMENT We acknowledge generous financial support from the National Natural Science Foundation of China and the 973 Program (Grant No. 2011CBA00506). ’ REFERENCES (1) Evans, D. G.; Slade, R. C. T. Struct. Bonding (Berlin) 2006, 119, 1–87. (2) Roeffaers, M. B. J.; Sels, B. F.; Uji-i, H.; Schryver, F. C.; Jacobs, P. A.; Vos, D. E.; Hofkens, J. Nature 2006, 439 (7076), 572–575. (3) Sels, B.; Vos, D.; Jacobs, P. A. Catal. Rev. 2001, 43 (4), 443–488. (4) Braterman, P. S.; Xu, Z. P.; Yarberry, F. Handbook of Layered Materials; Marcel Dekker Inc: New York, 2004; pp 373 374. (5) Climent, M. J.; Corma, A.; Iborra, S.; Velty, A. J. Catal. 2004, 221 (2), 474–482. (6) Kantam, M. L.; Choudary, B. M.; Reddy, C. V.; Rao, K. K.; Figueras, F. Chem. Commun. 1998, 998 (9), 1033–1034. (7) Abello, S.; Medina, F.; Tichit, D.; Ramirez, J. P.; Groen, J. C.; Sueiras, J. E.; Salagre, P.; Cesteros, Y. Chem.—Eur. J. 2005, 11 (2), 728–739. (8) Roelofs, J. C. A. A.; Lensveld, D. J.; Van Dillen, A. J.; Jong, K. P. J. Catal. 2001, 203 (1), 184–191. (9) Prinetto, F.; Tichit, D.; Teissier, R.; Coq, B. Catal. Today 2000, 55 (1 2), 103–116. (10) Winter, F.; Van Dillen, A. J.; Jong, K. P. Chem. Commun. 2005, 5 (31), 3977–3979. (11) Abello, S.; Medina, F.; Tichit, D.; Perez-Ramírez, J.; Cesteros, Y.; Salagre, P.; Sueiras, J. E. Chem. Commun. 2005, 5 (11), 1453–1455. (12) Williams, J. L. Catal. Today 2001, 69 (1 4), 3–9. (13) Centi, G.; Perathoner, S. CATTECH 2003, 7 (3), 78–89. (14) Centi, G.; Perathoner, S. Catal. Today 2003, 79 80, 3–13. (15) Meille, V. Appl. Catal., A 2006, 315 (1), 1–17. (16) He, J. X.; Kobayashi, K.; Takahashi, M.; Villemure, G. Thin Solid Films 2001, 397 (1 2), 255–265. (17) He, X. J.; Yamashita, S.; Jones, W.; Yamagishi, A. Langmuir 2002, 18 (5), 1580–1586. (18) Gardner, E.; Huntoon, K. M.; Pinnavaia, T. J. Adv. Mater. 2001, 13 (16), 1263–1266. (19) Lee, J. H.; Rhee, S. W.; Jung, D. Y. Chem. Commun. 2003, 3 (21), 2740–2741. (20) Lee, J. H.; Rhee, S. W.; Jung, D. Y. Chem. Mater. 2004, 16 (19), 3774–3779.

ARTICLE

(21) Lei, X.; Yang, L.; Zhang, F.; Evans, D. G.; Duan, X. Chem. Lett. 2005, 34 (12), 1610–1611. (22) Chen, H.; Zhang, F.; Fu, S.; Duan, X. Adv. Mater. 2006, 18 (23), 3089–3093. (23) Zhang, F.; Zhao, L.; Chen, H.; Xu, S.; Evans, D. G.; Duan, X. Angew. Chem., Int. Ed. 2008, 47 (13), 2466–2469. (24) Li, S.; Lu, J.; Wei, M.; Evans, D. G.; Duan, X. Adv. Funt. Mater. 2010, 20 (17), 2848–2856. (25) Yan, D.; Lu, J.; Wei, M.; Han, J.; Ma, J.; Li, F.; Evans, D. G.; Duan, X. Angew. Chem., Int. Ed. 2009, 48 (17), 3073–3076. (26) Yan, D.; Lu, J.; Ma, J.; Wei, M; Evans, D. G.; Duan, X. Angew. Chem., Int. Ed. 2011, 50 (3), 720–723. (27) Purton, J. A.; Allan, N. L.; Blundy, J. D. J. Mater. Chem. 1997, 7 (9), 1947–1951. (28) Ogawa, M.; Kaiho, H. Langmuir 2002, 18 (11), 4240–4242. (29) Pagano, M. A.; Forano, C.; Besse, J. P. J. Mater. Chem. 2003, 13 (8), 1988–1993. (30) Costantino, U.; Marmottini, F.; Nocchetti, M.; Vivani, R. Eur. J. Inorg. Chem. 1998, 10, 1439–1446. (31) Titulaer, M. K.; Jansen, J. B. H; Geus, J. W. Clays Clay Miner. 1994, 42 (3), 249–258. (32) Yang, W. S.; Kim, Y.; Liub, P. K.T.; Sahimia, M. T.; Tsotsis, T. Chem. Eng. Sci. 2002, 57 (15), 2945–2953. (33) Wang, J.; Kalinichev, A. G.; Kirkpatrick, R. J. Geochim. Cosmochim. Acta 2006, 70 (3), 562–582. (34) Friedrich, F.; Heissler, S.; Faubel, W.; N€uesch, R.; Weidler, P. G. Vib. Spectrosc. 2007, 43 (2), 427–434. (35) Berle, J. D.; Tetterhorst, R. Mineral. Mag. 1968, 36, 883–886. (36) Guggenheim, S.; Chang, Y.; Van Gross, A. H. F. Am. Mineral. 1987, 72 (5 6), 537–550. (37) Kuwahara, Y. Phys. Chem. Miner. 1999, 26 (2), 198–205. (38) Pausch, I.; Lohse, H. H.; Sch€urmann, K.; Allmann, R. Clays Clay Miner. 1986, 34 (5), 507–510. (39) Matsuki, N.; Kim, T. W.; Ohta, J.; Fujioka, H. Solid State Commun. 2005, 136 (6), 338–341. (40) Podrebarac, G.; Ng, G. F. T. T.; Rempel, G. L. Chem. Eng. Sci. 1997, 52 (17), 2991–3002. (41) Lei, X. D.; Zhang, F. Z.; Yang, L.; Guo, X. X.; Tian, Y. Y.; Fu, S. S.; Li, F.; Evans, D. G.; Duan, X. AIChE J. 2007, 53 (4), 932–940. (42) Loukopoulos, V.; Gavril, D.; Karaiskakis, G.; Katsanos, N. A. J. Chromatogr., A 2004, 1061 (1), 55–73.

1280


MgAl-Layered Double Hydroxide Films on Muscovite Mica: Epitaxial

Recommend Documents