pubs.acs.org/Langmuir © 2009 American Chemical Society
Silylation of Layered Double Hydroxides via a Calcination-Rehydration Route Qi Tao,†,‡,§ Jianxi Zhu,† Ray L. Frost,*,‡ Thor E. Bostrom,‡ R. Mark Wellard,‡ Jingming Wei,† Peng Yuan,† and Hongping He*,†,‡ † Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, P.R. China, ‡Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia, and § Graduate School of Chinese Academy of Sciences, Beijing 100039, P.R. China
Received July 30, 2009. Revised Manuscript Received September 17, 2009 Silylated layered double hydroxides (LDHs) were synthesized through a surfactant-free method involving an in situ condensation of silane with the surface hydroxyl group of LDHs during its reconstruction in carbonate solution. X-ray diffraction (XRD) patterns showed the silylation reaction occurred on the external surfaces of LDHs layers. The successful silylation was evidenced by 29Si cross-polarization magic-angle spinning nuclear magnetic resonance (29Si CP/MAS NMR) spectroscopy, attenuated total reflection Fourier transform infrared (ATR FTIR) spectroscopy, and infrared emission spectroscopy (IES). The ribbon shaped crystallites with a “rodlike” aggregation were observed through transmission electron microscopy (TEM) images. The aggregation was explained by the T2 and T3 types of linkage between adjacent silane molecules as indicated in the 29Si NMR spectrum. In addition, the silylated products show high thermal stability by maintained Si related bands even when the temperature was increased to 1000 °C as observed in IES spectra.
Introduction Layered double hydroxides (LDHs) are lamellar in structure with properties similar to those of natural clays including hydrotalcites (Ht). The Mg2þ in its brucite-like octahedral layer is partly substituted by Al3þ, and the resultant excess charges are balanced by anions held in the interlayer. As a family of compounds, LDHs are commonly expressed as [M1-x2þMx3þ(OH)2]xþAx/nn- 3 mH2O, where M2þ and M3þ are divalent and trivalent cations that occupy octahedral positions in the hydroxide layers, respectively, An- is an interlayer anion, and x is defined as the M3þ/(M2þ þ M3þ) ratio. The unique positively charged layers and excellent anion exchange capacity result in wide applications as adsorbents, ion exchangers, pharmaceutics, catalysts or catalyst supports, and other applications.1-7 In the past decade, clay-based nanomaterials have aroused considerable interests of researchers, because of the improved properties in the resultant materials including increased strength, heat resistance, decreased gas permeability and flammability, and increased biodegradability.8 However, just as with other fillers, the compatibility problem between the hydrophilic LDHs and the hydrophobic polymer will be encountered when LDHs are dispersed into a polymer matrix. One way of overcoming this problem is to modify the LDH surfaces with organic surfactants *Corresponding authors. Phone: (þ86) 85290257. Fax: (þ86) 85290708. Email:
[email protected] (H.H.) or
[email protected] (R.L.F.).
(1) Cavani, F.; Trifiro, F.; Vaccari, A. Catal. Today 1991, 11(2), 173–301. (2) Hutson, N. D.; Speakman, S. A.; Payzant, E. A. Chem. Mater. 2004, 16(21), 4135–4143. (3) Dimotakis, E. D.; Pinnavaia, T. J. Inorg. Chem. 1990, 29(13), 2393–2394. (4) You, Y. W.; Zhao, H. T.; Vance, G. F. J. Mater. Chem. 2002, 12, 907–912. (5) Domingo, C.; Loste, E.; Fraile, J. J. Supercrit. Fluids 2006, 37(1), 72–86. (6) Choudary, B. M.; Chowdari, N. S.; Jyothi, K.; Kantam, M. L. J. Am. Chem. Soc. 2002, 124(19), 5341–5349. (7) Hermosin, M. C.; Pavlovic, I.; Ulibarri, M. A.; Cornejo, J. Water Res. 1996, 30(1), 171–177. (8) Ray, S. S.; Okamoto, M. Prog. Polym. Sci. 2003, 28(11), 1539–1641.
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or/and coupling agents to change the hydrophilic surfaces of LDHs to hydrophobic ones. Silylation, also known as silane grafting, is one of the most efficient approaches to modify the surface of many inorganic materials including glass, silicon chips, metals, and clays,9-14 especially when the organosilanes are with nucleophilic groups (e.g., 3-aminopropyltriethoxysilane, NH2(CH2)3Si(OC2H5)3, APS).15-19 In this case, organosilane not only can increase the hydrophobicity of substrates by the surface grafting but also can help to bond with the polymers through the amino groups. Therefore, this method has been extensively applied in chromatography, antimicrobials, catalysts, immobilized enzymes, and fiber reinforced composites. In contrast to the case of cationic clay minerals (for example, smectite group minerals and minerals from the serpentine group),12,20,21 very few studies have been conducted on the grafting of silane onto the surface of LDHs,22,23 the only (9) Frost, R. L.; Mendelovici, E. J. Colloid Interface Sci. 2006, 294(1), 47–52. (10) Kluth, G. J.; Sung, M. M.; Maboudian, R. Langmuir 1997, 13(14), 3775– 3780. (11) Mendelovici, E.; Frost, R. L. J. Colloid Interface Sci. 2005, 289(2), 597–599. (12) Mendelovici, E.; Frost, R. L.; Kloprogge, J. T. J. Colloid Interface Sci. 2001, 238(2), 273–278. (13) Pape, P. G.; Plueddemann, E. P. J. Adhes. Sci. Technol. 1991, 5(10), 831–42. (14) Tegelstroem, H.; Wyoeni, P. I. Electrophoresis 1986, 7(2), 99. (15) Angloher, S.; Kecht, J.; Bein, T. Chem. Mater. 2007, 19(23), 5797–5802. (16) Ingall, M. D. K.; Honeyman, C. H.; Mercure, J. V.; Bianconi, P. A.; Kunz, R. R. J. Am. Chem. Soc. 1999, 121(15), 3607–3613. (17) Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Science 2007, 318(5849), 426–430. (18) Oh, S.; Kang, T.; Kim, H.; Moon, J.; Hong, S.; Yi, J. J. Membr. Sci. 2007, 301(1-2), 118–125. (19) Yeon, Y. R.; Park, Y. J.; Lee, J. S.; Park, J. W.; Kang, S. G.; Jun, C. H. Angew. Chem., Int. Ed. 2008, 47(1), 109–112. (20) He, H. P.; Zhou, Q.; Martens, W. N.; Kloprogge, T. J.; Yuan, P.; Yunfei, X. F.; Zhui, J. X.; Frost, R. L. Clays Clay Miner. 2006, 54(6), 691–698. (21) Mendelovici, E.; Frost, R. L. J. Colloid Interface Sci. 2005, 289(2), 597–599. (22) Park, A. Y.; Kwon, H.; Woo, A. J.; Kim, S. J. Adv. Mater. 2005, 17(1), 106– 109. (23) Wypych, F.; Bail, A.; Halma, M.; Nakagaki, S. J. Catal. 2005, 234(2), 431– 437.
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anionic clays existing in nature considering their higher surface charge.24 An improved approach is to exchange long alkyl chain anions into the interlayer of LDHs, which not only can enlarge the interlayer space but also can change the property of the LDH surface from hydrophilic to hydrophobic.25 As a result, the organosilane molecules may be introduced into the clay interlayer to react with the hydroxyl groups on the solid surface.26,27 Furthermore, the exfoliation of LDH layers may occur during grafting, which is very important to improve the mechanical property of the resultant clay-based nanocomposites. Previously, an in situ coprecipitation approach was developed to graft silane onto the LDH surface, using surfactant anion interlayered LDHs as a precursor.25,28,29 Silylation products with different morphology and features were obtained successfully. However, extra treatment must be adopted to drive away the unwanted surfactant anions. Herein, a surfactant-free silylation approach is presented based upon the “structure memory effect” property of LDHs.30 The silylation reaction was carried out in situ, during the reconstruction of LDHs via a rehydration procedure. The goal of this research work is to develop a simple and universal approach for synthesis of clay-based nanocomposites through silylation of LDH types of minerals.
Experimental Section Synthesis of Materials. 1. Synthesis of Mg6Al2(OH)16CO3 3 4H2O (LDH). The hydrotalcites were prepared by 28
coprecipitation as reported previously. About 0.039 mol of Mg(NO3)2 3 6H2O (99.0%, Ajax Finechem, Australia) and 0.013 mol of Al(NO3)3 3 9H2O (98.0%, Sigma-Aldrich) with a molar ratio of 3:1 (Mg2þ/Al3þ) were dissolved in 44 mL distilled water (solution A). About 0.01 mol of NaOH (99.0%, Chem-Supply, Australia) was dissolved in 50 mL of distilled water (solution B). At room temperature, solution B and solution A were dropped into 50 mL of distilled water with vigorous stirring. The pH value of the mixture was kept at 10 pH units. After filtration and washing with distilled water, the gel-like resulting products were dried at 75 °C (denoted as LDH). The mixed metallic oxides (LDO) were obtained by calcination of as-synthesized LDH at 500 °C for 6 h. 2. Synthesis of Silylated LDH (LDO-Si). About 1.0 g of LDO was put into a 50 mL solution containing about 0.015 mol of Na2CO3 (99.5%,Merck, Australia). With stirring, a solution with 0.014 mol APS (98.0%, Sigma-Aldrich, US) and 50 mL of C2H5OH (99.5%, Merck, Australia) was added drop by drop. After stirring for 6 h, the gel-like resulting product was washed water and centrifuged at 4000 rpm (2300 rcf) for 10 min. The centrifuge-washing cycles were repeated until 1 L of water was consumed. The resultant gel-like products were dried at 75 °C (denoted as LDO-Si). Characterization of Materials. Powder X-ray diffraction (XRD) patterns were recorded using a Bruker D8 Advance diffractometer with Cu KR radiation (λ = 1.5406°), operating at 40 kV and 40 mA. The incident beam was monochromated through a 0.020 mm Ni filter then passed through a 0.04 rad Soller (24) Li, C.; Wang, G.; Evans, D. G.; Duan, X. J. Solid State Chem. 2004 177(12), 4569–4575. (25) Zhu, J. X.; Yuan, P.; He, H. P.; Frost, R.; Tao, Q.; Shen, W.; Bostrom, T. J. Colloid Interface Sci. 2008, 319(2), 498–504. (26) Wypych, F.; Bail, A.; Halma, M.; Nakagaki, S. J. Catal. 2005, 234(2), 431– 437. (27) Park, A. Y.; Kwon, H.; Woo, A. J.; Kim, S. J. Adv. Mater. 2005, 17(1), 106– 109. (28) Tao, Q.; He, H. P.; Frost, R. L.; Yuan, P.; Zhu, J. X. Appl. Surf. Sci. 2009, 255(7), 4334–4340. (29) Tao, Q.; Yuan, J.; Frost, R. L.; He, H.; Yuan, P.; Zhu, J. Appl. Clay Sci. 2009, 45(4), 262–269. (30) Chibwe, K.; Jones, W. J. Chem. Soc., Chem. Commun. 1989, 14, 926–927.
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slit, a 1.0 mm fixed mask with a 1.0° divergence slit, and a 0.2° antiscatter slit. Patterns were acquired between 1° and 76° (2θ) at a scan speed of 1.5° min-1 with an increment of 0.01°. Each of the samples (about 1.5 g) was held on a poly(methyl methacrylate) (PMMA) holder and oriented with a slide before testing. Transmission electron microscopy (TEM) images were obtained using a JEOL1200 electron microscope operating at an acceleration voltage of 100 kV. The specimens for TEM observation were prepared by the following procedure. The clay sample was dispersed in 95% ethanol for 5 min, and then a drop of sample suspension was dropped onto a carbon-coated copper grid, which was left to dry for 10 min and then transferred into the microscope. 1 H decoupled solid state 29Si cross polarization magic-angle spinning nuclear magnetic resonance (29Si CP/MAS NMR) spectroscopy was conducted on a 400-MR NMR spectrometer (Direct Drive model; Varian Inc., CA), operating at 79.43 MHz for 29Si, with the tancpx pulse sequence in a 5 mm silicon nitride rotor spinning at 2.5 kHz. Tetramethylsilane (TMS) was used as an external reference. Acquisition parameters included 102 400 transients were acquired with an acquisition time of 0.05 s and a relaxation delay of 1 s. Spinal-64 decoupling was used with a cross-polarization time of 3 ms. A total of 2000 data points were recorded over a spectral width of 500 ppm. Data were processed using the Nuts software package (Acorn NMR), and band component analysis was undertaken using the Jandel “Peakfit” software package (Erkrath, Germany) which enabled the type of fitting function to be selected and allowed specific parameters to be fixed or varied accordingly. Band fitting was done using a Lorentz-Gauss cross-product function with the minimum number of component bands used for the fitting process. The Lorentz-Gauss ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations (r2) greater than 0.995. Band fitting of the spectra is quite reliable providing there is some band separation or changes in the spectral profile. Infrared spectra (IR) were obtained using a Nicolet Nexus 870 FTIR spectrometer with a smart endurance single bounce diamond attenuated total reflection (ATR) cell. Spectra over the 4000-525 cm-1 range were obtained by the coaddition of 64 scans with a resolution of 4 cm-1 and a mirror velocity of 0.6329 cm s-1. Infrared emission spectroscopy (IES) was carried out on a Nicolet spectrometer, which was modified by replacing the IR source with an emission cell. Approximately 0.2 mg samples were spread as thin layers on an about 6 mm diameter platinum surface in a N2 atmosphere. The emission spectra were collected at intervals of 50 °C over the range 100-1000 °C. Considering both precision and time efficiency, the spectra were acquired by coaddition of 1024 scans for the temperature from 100 to 250 °C (about 10 min 34 s each time), 128 scans for the temperature from 300 to 500 °C (about 1 min 19 s), and 64 scans for the temperature from 550 to 1000 °C (about 40 s), with a resolution of 4 cm-1. More detailed descriptions of the cell and principles of the emission experiment are available in the literature.31,32
Results and Discussion XRD Results. The X-ray diffraction patterns of synthesized silylation products are shown in Figure 1. The XRD pattern of Ht displays a typical and well ordered layer structure with a basal spacing (d003) of 7.9 A˚ (Figure 1a). This value matches well with the standard ICDD reference pattern 00-022-0700 (hydrotalcite, synMg6Al2(OH)16CO3 3 H2O). After calcination, a series of d00 L peaks corresponding to LDH are replaced by characteristic patterns of magnesium oxide (ICDD reference code: 01-075-1525) and aluminum oxide (marked with an asterisk). These indicated that (31) Vassallo, A. M.; Coleclarke, P. A.; Pang, L. S. K.; Palmisano, A. J. Appl. Spectrosc. 1992, 46(1), 73–78. (32) Frost, R. L.; Vassallo, A. M. Clays Clay Miner. 1996, 44(5), 635–651.
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Figure 3. Solid state 29Si CP/MAS NMR spectrum of LDO-Si.
Figure 1. XRD patterns of LDH (a), LDO (b), and LDO-Si (c) (the reference patterns and codes are from the ICDD).
Figure 2. TEM images of LDH (a) and LDO-Si (b). Scale bars represent 20 nm.
the pristine LDH structure is destroyed (Figure 1b). When calcined materials (LDO) were exposed to a sodium carbonate solution, the original LDH structure was reconstituted (Figure 1c). All the reflections of LDO-Si are intensified, indicating a higher crystallinity of the resultant sample. It also implies that the condensation between surface hydroxyl groups of LDH and the silanols have little influence on the structure of the final product throughout its reconstruct procedure. The broadening of the reflection may due to the variation of the particle sizes as deduced in TEM images. No interlayer expansion is noticed in LDO-Si (d003 is 7.8 A˚), indicating that APS molecules are only located on the external surface of LDO-Si.29 TEM Images. The differences in morphology of samples before and after calcination were investigated using transmission electron microscopy (Figure 2). Nanoscale flat crystal particles which included some irregular hexagonal crystals were observed in images of the original LDH (Figure 2a). All these particles displayed smooth surfaces and were oriented randomly on the grid support films. Significant changes were observed in the silylation samples. These samples showed aggregated needle shaped or folded ribbonlike crystallites with a length of about 60-100 nm (Figure 2b) instead of the large and more rounded Langmuir 2010, 26(4), 2769–2773
Table 1. Solid State 29Si CP/MAS NMR Chemical Shifts (ppm), Peak Assignments of Oxane Bond Type Using Tn Notations, and Relative Population of Oxane Type for LDO-Si
Scheme 1. Silylation of LDHs via a Process of Calcination-Rehydration of LDHs
particles in pristine LDH. The orientations of the LDO-Si needle crystallites suggest that they may bond to form a “rodlike” aggregation (Figure 2b). This methodology of silylated LDHs offers a method of synthesizing nanorods based upon the modification of LDHs. The morphology and texture differences can be easily understood by considering the calcination, rehydration, and condensation processes (Scheme 1). In LDHs, crystallite growth along the a and b axes is more favorable in order to maximize the exposure of OH groups to the aqueous phase, so that the hexagonal morphology is formed. With exposure of LDO to carbonate anions, it begins to reconstruct the structure of the LDHs; meanwhile, APS hydrolyzes to form silanol, silandiol, and silantriol. Soon afterward, the silanols are adsorbed to the neoformative DOI: 10.1021/la902812g
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Figure 4. FTIR spectra of LDH (a), LDO (b), and LDO-Si (c, d).
LDH layers and/or condensed with the surface hydroxyl groups to generate the silylated LDHs (LDO-Si). In this case, the (ab) plane becomes hydrophobic due to the adsorption of APS. This change leads to growth along the c axis, which is low energy and kinetically accessible behavior, forming ribbonlike particles.33 APS has three siloxane bonds; therefore, it can condense with neighboring silanols as well as with surface hydroxyl groups of LDHs. As a result, an intermolecular Si-O-Si linkage matrix is formed between two (or more) adjacent silylated LDHs. 29 Si CP/MAS NMR. For a better understanding of the oligomeric species formed between APS and LDH, the 29Si CP/ MAS NMR technique was applied to the silylated product, LDOSi (Figure 3). Tn notations (n = 0, 1, 2, and 3, which represents the number of “O bridge” structures formed between silane and the LDH surface and/or neighbor silane as summarized in Table 1) are used to describe the different kinds of siloxane bonds formed between APS and the substrate or the neighboring APS.27 The possible products, generated from hydrolysis of APS and condensations between APS and silica in aqueous solution, are discussed in the literature.34,35 The NMR peaks of LDO-Si are assigned considering the differences of chemical shift and the reaction solvents with those reported,27,34,35 and the relative populations of each type of siloxane bond are summarized according to peak fitting results (Table 1). In contrast to the reported cases,27,34,35 the hydrolyzed monodentate APS molecule (T1) is detected by a peak shown at -50 ppm (parts per million) and with a high relative population (34.1%). A possible explanation for a remaining ethoxy group is that ethanol was used to dissolve APS before exposure to aqueous solution, which can hamper APS against hydrolysis.36 The schemes for T2 (-56 ppm) and T3 (-66 ppm) peaks are proposed considering the easier intermolecular condensation of APS in aqueous solution compared to that in nonaqueous solution.34 The signal at -66 ppm (33) Xu, Z. P.; Braterman, P. S. J. Mater. Chem. 2003, 13(2), 268–273. (34) Dehaan, J. W.; Vandenbogaert, H. M.; Ponjee, J. J.; Vandeven, L. J. M. J. Colloid Interface Sci. 1986, 110(2), 591–600. (35) Vrancken, K. C.; Decoster, L.; Vandervoort, P.; Grobet, P. J.; Vansant, E. F. J. Colloid Interface Sci. 1995, 170(1), 71–77. (36) Salon, M. C. B.; Abdelmouleh, M.; Boufi, S.; Belgacem, M. N.; Gandini, A. J. Colloid Interface Sci. 2005, 289(1), 249–261.
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could be due to the structure as shown in Table 1, or triple coordination of silicon to the LDH surface. However, the later structure is easy to form in a nonaqueous system, in which the silane molecules can be physisorbed to the surface of solid to form three Si-O-M covalent bonds. While in the aqueous system, the preorganization of silane molecules would happen before grafting, giving rise to the formation of dimerized chains.34,37 So the structures are preferred as in Table 1. The favored T2 type of siloxane bonds (50.8%) in this case is the most obvious difference with reaction in nonaqueous solution.27 The latter two types of oligomers well explain the aggregation of ribbonlike particles observed in the TEM image (Figure 2b). IR and IES Analysis. FTIR spectra of the LDH, LDO, and their silylated product LDO-Si are shown in Figure 4. For LDH (Figure 4a), a broad band centered at 3450 cm-1 is attributed to the O-H vibration mode of the hydroxyl group and water molecules. Water deformation is recorded at ∼1638 cm-1. The band located at 1351 cm-1 is attributed to the asymmetric stretching mode (ν3) of the carbonate ion. The bands below 700 cm-1 are due to the vibration of M-O (M = Mg2þ, Al3þ). After calcination, vibrations of hydroxyl groups and carbonate anions lose intensity apparently due to partial destruction of the LDH structure and decomposition of interlayer anions38 (Figure 4b). The rehydration procedure with the coexistence of APS restacks the LDH structure and forms siloxane bonds between LDH and APS (Figure 4c and d). A series of bands arising from APS are detected in the silylated product, including asymmetric and symmetric stretching vibra tions of CH2- (around 2935 cm-1), scissoring modes of -NH2 (1565 cm-1), and stretching modes of Si-O-Si, Si-O-M, and the other Si-O related vibrations (1040 and 1004 cm-1)28 (Figure 4c and d). Besides, stretching mode of -NH2 is expected at around 3300 cm-1, but with the overlap of -OH related bands, it cannot be distinguished easily in this case. While the more detailed spectroscopic character of the silylated sample is investigated by infrared emission spectroscopy analysis (37) Dkhissi, A.; Esteve, A.; Jeloaica, L.; Esteve, D.; Rouhani, M. D. J. Am. Chem. Soc. 2005, 127(27), 9776–9780. (38) Tao, Q.; Zhang, Y. M.; Zhang, X.; Yuan, P.; He, H. P. J. Solid State Chem. 2006, 179(3), 708–715.
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procedure can be found in TG/DTG/DTA curves of LDO-Si (Figure S1, Supporting Information).
Conclusions
Figure 5. IES spectroscopy of LDO-Si: (a) 100 °C, (b) 150 °C,
(c) 200 °C, (d) 250 °C, (e) 300 °C, (f) 350 °C, (g) 400 °C, (h) 450 °C, (i) 500 °C, (j) 550 °C, (k) 600 °C, (l) 650 °C, (m) 700 °C, (n) 750 °C, (o) 800 °C, (p) 850 °C, (q) 900 °C, (r) 950 °C, and (s) 100 °C.
(Figure 5). The spectroscopic character changes during thermal decomposition of the sample can be clearly revealed by the signal changes. IES spectra show that the surface adsorbed water moisture (3340 cm-1) disappeared as the temperature was increased up to 150 °C,28 and the surface hydroxyl groups (3700-3300 cm-1) decreased in intensity gradually, synchronized with the -CH2 groups from APS (2926, 2867, and 1530 cm-1) up to 600 °C. The decarbonation procedure finished at around 350 °C with the disappearance of the band at 1347 cm-1 (assigned to the ν3 stretching of CO32-). A series of bands corresponding to Si bonds to different atoms are clearly displayed in the IES spectra, such as at 1508, 1417, 1186-980, and 858 cm-1. Among these, the band at 999 cm-1 is also detected via FTIR spectroscopy and is attributed to Si-O-M stretching vibrations;28 the bands at 1186 and 858 cm-1are suggested to be assigned to Si-O-Si and M-(Si-O)n-M stretching modes, respectively. With a rise in temperature, the silicates/silica phase replaces the silylated product. The increase in intensity in the two bands located at 1508 and 1417 cm-1 can be attributed to overtones of Si-O and Si-O-Si symmetric stretching modes of LDO-Si, respectively. All these Si related bands are distinguishable even when the temperature goes up to 1000 °C, implying the higher thermal stability in the resultant product. The mass loss and the phase transformation information during the heating
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APS silylated LDHs have been synthesized via a surfactant-free method. The method involves rehydration of calcinated LDHs in carbonate solution. The silylated product is generated with the formation of LDHs by an in situ condensation of silane with the surface hydroxyl groups. The resultant materials show aggregated needle or ribbon shaped crystallites in the TEM images. The linkages of Si-O-Si are formed by intermolecular condensation of APS as shown by T2 and T3 signals in the 29Si NMR spectrum. These signals and the occurrence of a Si-O-M vibration at around 1004 cm-1 in the FTIR spectrum (999 cm-1 in IES) of the silylated LDH are important evidence for the success of the silylation procedure. In addition, the silylated LDH shows a higher thermal stability as all the Si related bands are distinguishable when the temperature is increased up to 1000 °C. The present study shows that a certain kind of novel clay-based nanomaterial can be synthesized by rehydration of calcinated LDHs simultaneously with a silylation procedure. These nanomaterials have potential applications in many industrial fields including claybased nanocomposites, adsorbents for removal of organic contaminants from water, flame retarding materials, and layered double hydroxide polymer nanocomposites.39,40 Acknowledgment. This is contribution No. IS-1122 from GIGCAS. The financial and infrastructure support of the National Science Fund for Distinguished Young Scholars (Grant No. 40725006) and Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-yw-112) is acknowledged. The financial and infrastructure support of the Queensland University of Technology Inorganic Materials Research Program of the School of Physical and Chemical Sciences is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding. Q.T. is grateful to The China Scholarship Council for the overseas funding to visit QUT. Supporting Information Available: TG/DTG/DTA curves of LDO-Si and the related descriptions. This material is available free of charge via the Internet at http://pubs. acs.org. (39) Wypych, F.; Satyanarayana, K. G. J. Colloid Interface Sci. 2005, 285(2), 532–543. (40) , S.; , D.; Seeley, G. Chem. Commun. 2002, 14, 1506–1507.
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