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Deintercalation of Hydrazine-Intercalated Kaolinite in Dry and Moist Air
Journal of Colloid and Interface Science 246, 164–174 (2002) doi:10.1006/jcis.2001.8011, available online at http://www.idealibrary.com on
Deintercalation of Hydrazine-Intercalated Kaolinite in Dry and Moist Air Ray L. Frost,∗,1 J´anos Kristof,† J. Theo Kloprogge,∗ and Erzs´ebet Horvath‡ ∗ Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, 2 George Street, G.P.O. Box 2434, Brisbane, Queensland 4001, Australia; †Department of Analytical Chemistry, University of Veszpr´em, P.O. Box 158, H 8201 Veszpr´em, Hungary; and ‡Research Group for Analytical Chemistry, Hungarian Acadamy of Sciences, P.O. Box 158, H 8201 Veszpr´em, Hungary Received July 19, 2001; accepted October 1, 2001
The deintercalation of hydrazine-intercalated kaolinite has been followed using a combination of X-ray diffraction and diffuse reflectance Fourier transform infrared spectroscopy. Upon intercalation of the kaolinite with hydrazine, the kaolinite layers are ˚ and remain expanded for up to 22 h upon expanded to 10.66 A exposure to moist air. Only upon deintercalation are the peak at ˚ and a minor peak at 9.6 A ˚ observed. Complete deintercala10.39 A tion takes up to 18 days more. Upon intercalation with hydrazine an intense band is observed at 3628 cm−1 and is attributed to the innersurface hydroxyls hydrogen bonded to the hydrazine, which upon deintercalation decreased in intensity. This rate of deintercalation is affected by the presence or absence of moist air. Deintercalation in the presence of water vapor results in the observation of two additional bands at 3550 and 3598 cm−1 , which are attributed to the hydroxyl stretching modes of adsorbed water during deintercalation. The intensity of NH stretching vibrations observed at 3360, 3300, and 3200 cm−1 also decrease in intensity with deintercalation time. Changes in the hydroxyl deformation modes of kaolinite in the 915 cm−1 region and in the HNH deformation modes show strong interactions between the kaolinite surface and the inserting hydrazine molecule. °C 2002 Elsevier Science Key Words: intercalation; hydrazine; kaolinite; hydroxyls; hydrogen bonding; FT-IR spectroscopy; X-ray powder diffraction.
INTRODUCTION
Kaolinite is classified as a nonexpandable clay. The intercalation of kaolinite is an old and ongoing research topic. Among the direct intercalating compounds, hydrazine probably is the most welcomed one due to its fast intercalation rate and high intercalation yields, yet the knowledge about the reaction is the poorest. When molecules such as hydrazine are intercalated between the 1 : 1 layers, some expansion occurs (1–3). Hydrazine intercalation of kaolinite has been studied by research groups, including Ledoux and White (2), Cruz et al. (4, 5), and Johnston and Stone (6). Researchers have shown that kaolinite can be expanded with ˚ (2). Deintercalation occurred through mild hydrazine to 10.4 A heating or by exposure to a controlled vacuum causing the struc˚ (2). Such alteration in interlayer ture to partially collapse to 9.4 A 1
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thickness was complemented by changes in the infrared and Raman spectra (3, 6). More recently Johnston et al. reported an infrared and inelastic neutron scattering study of the 1.03- and 0.95-nm kaolinite–hydrazine intercalation complexes (7). Frost et al. reported the kinetics of deintercalation of hydrazine from hydrazine-intercalated kaolinite (8). Different interpretations of the infrared and Raman spectra of the hydrazine-intercalated complexes have been forthcoming (6, 8). These different interpretations may result from the methodology of synthesis of the hydrazine-intercalated kaolinite complexes. The complex may be prepared using anhydrous hydrazine or by using hydrazine hydrate. The hydrazine molecule interacts with the 1 : 1 layer surfaces through the lone pair of electrons of the nitrogen and the hydrogens of the NH2 group (8, 9). The interaction of the N is not expected to be as strong as that of potassium acetate and vibrational spectroscopic bands higher than 3605 cm−1 are predicted. The interaction of the H in the hydrazine-intercalation complex is expected to be similar to that of the hydrogens in urea (8–11). Thus, there would be no additional hydroxyl bands and no decrease in the intensities of the inner-surface hydroxyls. The question arises as to whether deintercalation would be the same under exposure of the hydrazine-intercalation complex to moist air or under vacuum. In a previous study deintercalation of hydrazine hydrate-intercalated kaolinite was studied. Here the study was undertaken in moist air. The chemistry of the hydrazine-intercalated kaolinite is complex. This complexity results in differences in the attribution of bands in the infrared spectra. Hence new experiments are undertaken to increase our fundamental knowledge of this complexity. Here we report the deintercalation of a hydrazine-intercalated kaolinite as a function of time in the presence and absence of moisture using powder X-ray diffraction (XRD) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). EXPERIMENTAL
The Kaolinite Intercalate The kaolinite used in this study is a low defect kaolinite from Kir´alyhegy in Hungary. This mineral has been previously characterized both by X-ray diffraction and by Raman
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DEINTERCALATION OF HYDRAZINE-INTERCALATED KAOLINITE
spectroscopy (12). The kaolinite was purified through sedimentation and the 2- to 20-µm-sized fraction was selected for intercalation. The intercalate was prepared by mixing 300 mg of kaolinite with 5 cm3 of a 98% hydrazine hydrate aqueous solution for 80 h at room temperature in a magnetic stirrer. The excess solution was decanted and the intercalated kaolinite was immediately subjected to spectroscopic analysis. Two experiments have been conducted. The wet intercalate (i.e., in contact with 98% hydrazine hydrate to avoid deintercalation) was dried in a vacuum oven at room temperature for 30 min. After drying (a powdery sample was obtained) 2–5 mg of the powdery intercalate was mixed with 100 mg KBr for DRIFT and kept for a longer period of time in contact with room air. At certain intervals the spectrum was recorded. In the parallel run, the same mixture (intercalate + KBr) was prepared but kept continuously inside the sample compartment of the FTIR equipment purged continuously with dry air. At intervals the spectrum of this sample was recorded as well. X-Ray Diffraction X-ray diffraction patterns of the intercalated kaolinite at different time intervals after exposure to air were obtained using a Philips PW 1050 type X-ray diffractometer using CuK α radiation operating at 35 kV and 40 mA. It was not possible to undertake the X-ray diffraction patterns under vacuum at this stage. A 1◦ divergence and scatter slit were combined with a normal focus Cu tube at 6◦ take off angle and a 0.2-mm receiving slit (9, 10). The samples were measured in stepscan mode from 2.0◦ 2θ with steps of 0.05◦ up to 40◦ 2θ and a counting time of 2 s. DRIFT Spectroscopy DRIFT analyses were undertaken using a Bio-Rad 60A spectrometer. Five hundred twelve scans were co-added at a resolution of 2 cm−1 with a mirror velocity of 0.3 cm/s. Approxi-
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mately 3 wt% kaolinite or intercalated kaolinite was dispersed in oven-dried spectroscopic grade KBr with a refractive index of 1.559 and a particle size of 5–20 µm. Background KBr spectra were obtained and the sample single beam spectra were ratioed to the background. Spectral manipulations such as baseline adjustment, smoothing, and normalization were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, USA). Band component analysis was undertaken using the Jandel Peakfit software package, 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 Gauss–Lorentz ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations of r 2 greater than 0.995. Graphics are presented using Microsoft Excel. RESULTS AND DISCUSSION
X-Ray Diffraction Results Lattice expansion and contraction. The results of the Xray diffraction analyses of the low defect kaolinite intercalated with hydrazine hydrate and exposed to air for periods of time ranging from Time 0 to 18 days are illustrated in Fig. 1. Data were also collected for periods of up to 1 month. However such data are not shown as the results are similar to the X-ray diffraction patterns of the 18-day pattern. Figure 1 shows the d(001) spacing of both the hydrazineintercalated kaolinite and the deintercalated kaolinite. The Xray diffraction pattern of the hydrazine-intercalated kaolinite clearly shows that the clay has been fully intercalated at ambient temperatures. It is imperative to have 100% intercalation of the kaolinite in an attempt to fully interpret spectroscopic
FIG. 1. X-ray diffraction patterns of the d(001) spacings of kaolinite intercalated with hydrazine and exposed to air for (a) zero time, (b) 3 h, (c) 8 h, (d) 24 h, (e) 104 h, (f) 120 h, (g) 168 h, (h) 11 days, and (i) 1 month.
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data of a complicated system like the hydrazine–kaolinite intercalate. Hydrazine has been found to very readily adsorb on kaolinite surfaces showing characteristic “intercalation” type spectra and yet the kaolinite was not expanded (this work and Refs. 8–11). In the method of preparation, the hydrazineintercalated kaolinite was dried under vaccuum at 25◦ C. This sample is “dry” in that no excess hydrazine is present and the sample has the appearance of the original kaolinite powder. The d spacing of the hydrazine-intercalated kaolinite was found to ˚ at Time 0 and this figure was constant for the first be 10.66 A 8 h of deintercalation. Only after 22 h of deintercalation did the ˚ This value is in harmony with the d(001) peak shift to 10.39 A. previous studies by the authors and by other research groups (2, 3, 7, 13–15). According to the literature, the intercalate would collapse ˚ as is the case in the preparation of under vacuum to 9.6 A, the hydrazine-intercalation complex in this work (6, 7). One may have expected that the initial d(001) spacing may have ˚ corresponded to this value. However a larger value of 10.66 A was obtained. It must be concluded that the hydrazineintercalation complex absorbed water and reexpanded to this value before the collection of the XRD results. An initial value ˚ for the hydrazine-expanded kaolinite was obtained. of 10.66 A This result differs from previously published results. The value ˚ after a short period of time. It is possible decreases to 10.39 A that after placing the hydrazine-intercalated kaolinite in a vac˚ and uum for 30 min that the complex reexpanded to 10.66 A ˚ then altered to 10.39 A after some molecular rearrangement of the hydrazine and absorbed water in the hydrazine-intercalation complex. This conclusion confirms the concept of the hydrazine molecules keying in to the ditrigonal cavity of the siloxane layer and that this keying may take place even before the collapse of the structure by placing under a vacuum and reduction of the
˚ (6, 7). In the deintercalation prointerlayer spacing to 9.6 A cess, the hydrazine-intercalated kaolinite is quite stable up to at least 8 h, and only after 22 h does the deintercalation process ˚ occur. After 22 h two peaks are observed at 10.39 and 7.4 A. ˚ After the 27-h period the 10.39-A phase is no longer present but the appearance of the deintercalated kaolinite phase at the ˚ peak increases in intensity. In the 96-h period to 7 days, 7.22-A ˚ are three phases with d(001) spacings at 10.4, 7.5, and 7.2 A observed. The first phase is that of the hydrazine-intercalated kaolinite, the second is due to the partially collapsed structure, and the last phase is that of the deintercalated kaolinite. Only after 18 days of air exposure is the hydrazine-intercalated kaolinite completely decomposed. Figure 2 displays the variation of the crystallite size of the d(001) peak of the hydrazine-intercalated kaolinite and the deintercalated hydrazine-intercalated kaolinite as a function of deintercalation time. This intercalate has had its lattice structure destroyed through the intercalation process. Crystallite size is the coherently diffracted domain. The rapid structural degradation of kaolinite is connected with an increase in the mean lattice distortion and is not the consequence of the reduction of the crystallite size. Crystallite size is not equal to particle size. The width of the peak is related to the crystallite size according to the Scherrer equation: L=
λK . β cos θ
L is the mean crystallite dimension in angstroms along a line normal to the reflecting plane, K is a constant close to unity, and β is the width of the reflection at half height expressed in radians of 2θ . Figure 2 displays the changes in the crystallite size as determined by the changes in the
FIG. 2. Variation of crystallite size of the d(001) spacing of hydrazine-intercalated and deintercalated kaolinite as a function of deintercalation time.
DEINTERCALATION OF HYDRAZINE-INTERCALATED KAOLINITE
˚ peak with time of deintercalation. This width of the 10.4-A change is not a linear function with time. This means that the deintercalation process is causing the kaolinite crystal size to ˚ peak width inbecome smaller. On the other hand the 7.2-A creases with time, showing that the deintercalated kaolinite crystallite size is growing with deintercalation time. This process appears to be an exponential growth. Thus a first-order kinetic type process is observed. The crystallite size after 450 h of deintercalation is less than that of the starting material. This proves the deintercalation process causes a disordering of the kaolinite. Considering the different basal spacings it is possible to develop a model for the intercalation of hydrazine based only on geometrical constraints. The hydrazine molecule is basically ditrigonal and planar and may take up a number of orientations within the kaolinite interlayer space. The hydrazine molecule ˚ long, i.e., the length of a N–N may be considered to be 3.53 A ˚ plus twice the length of a N–H bond (1.03 A) ˚ bond (1.47 A) times cos 60◦ . The height of the molecule is the length of the 5 orbitals attributed to the lone pairs of electrons on the nitrogen, ˚ The width of the molecule is the thickness of which is ∼2.9 A. ˚ It is the flat hydrazine molecule, which is approximately 1.5 A. proposed that the different expansions of the kaolinite may correspond to the different possible orientations of the hydrazine molecule within the interlayer space of the kaolinite. It is proposed that the hydrazine molecule enters the kaolinite interlayer ˚ dimension. Then the space as a flat wedge, i.e., using the 1.5-A hydrazine molecule through hydrogen bond interactions reorients within the kaolinite structure causing the expansion. It is possible that the hydrazine then takes up a position with the lone pairs of electrons pointing toward the kaolinite surfaces. The ˚ expansion may result when the lone pair of electrons 10.3-A
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on the nitrogen atoms is pointing directly toward the hydroxyl ˚ is added to 3.53 A. ˚ This would surface. This results when 7.2 A ˚ which was the initial value of the d(001) then make 10.66 A, spacing determined in this work. The reduction of this value ˚ is in harmony with the concept of the hydrazine to 10.39 A molecules keying into the ditrigonal cavity. Such a conclusion fits well with the conclusions of Johnston et al. (6, 7). The question arises as to whether both nitrogens of the hydrazine interact with the hydroxyl surface. It is possible that the lone pair of electrons of both nitrogens form interactions with the hydroxyl surface. However infrared results suggest that both nitrogens are ˚ expansion not exactly equivalent. Another option for the 10.3-A is the presence of two flat lying hydrazine molecules on top of each other. This model seems less likely however. The second ˚ might occur when the hydrogens of the conformation at 9.5 A molecule are pointing toward the siloxane surface. This results ˚ In this model, the lone pair from the addition of 7.2 and 2.5 A. of electrons is parallel to the kaolinite surfaces. These confirmations are solely based on the differences in the hydrazine dimensions. Drift spectroscopic results. In this work, two DRIFT spectroscopic experiments were undertaken: deintercalation of the vacuum-dried hydrazine-intercalated kaolinite (a) under purged dry air and (b) exposed to laboratory air. Figures 3 and 4 show the DRIFT spectra of these two experiments. The deintercalation in dry air is a slow process and even after 3 days the hydrazine-intercalation complex has not completely decomposed. In comparison, the hydrazine-intercalation complex decomposes rapidly when the system is exposed to moist air. What is clearly observed is that in the deintercalation in moist air two additional bands are observed at 3568 and 3599 cm−1 . The intensity of the 3568 cm−1 band increases with time even though
FIG. 3. DRIFT spectra of the OH and NH stretching region of kaolinite intercalated with hydrazine and kept under dry air for (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and (h) 72 h.
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FIG. 4. DRIFT spectra of the OH and NH stretching region of kaolinite intercalated with hydrazine and exposed to moist air for (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 10 h, (f) 24 h, (g) 48 h, and (h) 192 h.
the intercalation complex is decomposing. The 3568 cm−1 band and a band at 3465 cm−1 were previously assigned to the inner-surface hydroxyls of kaolinite–hydrogen bonded to the hydrazine (2). Johnston et al. concurred with such a band attribution. No band at 3465 cm−1 was observed in this work. It is quite evident that the kaolinite intercalates with hydrazine irrespective of whether these two bands are present or not. These bands are only present if water is present. Thus the bands must be assigned to the hydroxyl stretching frequencies of water. The concept that the inner-surface hydroxyls appears as hydrogenbonded hydroxyls with hydrazine as low as 3568 and 3465 cm−1 is rejected. Hydrazine cannot form hydrogen bonds stronger than those of an ionic compound such as potassium acetate. The inner surface hydroxyls of kaolinite–hydrogen bonded to the acetate ion appear at 3605 cm−1 (12). Further if this complex were so strongly bonded then it would not decompose so fast. Another fact is that the NH band positions do not change during decomposition. Thus, if the 3568 cm−1 band were a H-bonded inner-surface OH band occurring/developing during decomposition, then the NH positions should also change. This was not observed. In this work, the concept of the inner surface hydroxyls as hydrogen-bonded hydroxyls with hydrazine as low as 3568 and 3465 cm−1 is in apparent disagreement with other results. Upon intercalation of potassium acetate into kaolinite an intense band is observed at 3605 cm−1 , which is attributed to the inner-surface hydroxyls hydrogen bonded to the acetate ion. Such a bond is strong, making the deintercalation difficult except through washing. Other authors have suggested that bands occur at 3658, 3535, and 3499 cm−1 for dimethyl sulfoxide-intercalated kaolinite, at 3590 cm−1 for formamide-intercalated kaolinite, and in the 3585 to 3560 cm−1 range for urea-intercalated kaolinite and that these bands are attributed to the hydrogen bonding of the inner surface hydroxyls to the inserting molecule. However it is difficult to comprehend how these types of molecules form
hydrogen bonds stronger than those of the acetate of potassium acetate in the intercalation complexes. The authors have previously attributed bands in these positions to water OH stretching vibrations. Thus the two bands observed at 3568 and 3465 cm−1 are ascribed to water vibrational modes in the intercalation complexes. Such observations bring into question the attribution of the 3628 cm−1 band. Figures 3 and 4 clearly show the hydroxyl stretching kaolinite band at 3628 cm−1 . This band is present in the DRIFT spectra during the deintercalation process over the 18-day period of deintercalation. During this time period the ˚ XRD patterns show a d(001) spacing of 10.66 or 10.39 A. ˚ The 9.49 A d(001) spacing is only observed after water is admitted to the system and decomposition is occurring (9–11). Thus we assign the 3628 cm−1 band to the hydroxyl stretching frequency of the inner-surface hydroxyls of kaolinite–hydrogen bonded to hydrazine. There are differences in the spectra reported in this work and that of Johnston and co-workers. In ˚ d(001) spacthis work we associate the 10.66 and 10.39 A −1 ings with the observation of the 3628 cm band in the FTIR spectra. Johnston et al. (6, 7) reports the inner-surface hydroxyl of the hydrazine-intercalated kaolinite for the 10.39˚ phase as 3620 cm−1 . Our observation places the peak at A 3628 cm−1 . Kaolinite hydroxyl stretching. Considerable differences are observed in the spectra of the kaolinite OH stretching region between the hydrazine-intercalated kaolinite exposed to air or maintained in the absence of moist air (Figs. 3 and 4). Figure 5 shows the variation in intensity of the bands as a function of the time of deintercalation. Differences are observed in the intensity of the 3628 cm−1 band attributed to the inner-surface hydroxyls hydrogen bonded to the hydrazine. The decrease in intensity of the band is approximately the same up to 1 h. The decrease in intensity for the sample exposed to moist air is significantly greater than that for the sample exposed to dry air. For example
DEINTERCALATION OF HYDRAZINE-INTERCALATED KAOLINITE
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FIG. 5. Variation of the intensity of the infrared hydroxyl stretching modes of hydrazine-intercalated kaolinite as a function of deintercalation time.
after 3 h the intensity for the “wet-air” sample decreased from 90.1 to 42.0%, whereas the sample exposed to dry air decreased from 84.4 to 59.9%. After 10 h of exposure, the intensity for the wet-air sample decreased to below 10%. The intensity for the “dry-air” sample remained at 38%. After 2 days the value was 25%. It is proposed that water influences the rate of deintercalation of the hydrazine-intercalated kaolinite. Johnston et al. ascribed the 3628 cm−1 band to the inner hydroxyls shifted from the normally found position of 3620 cm−1 (6, 7). It is proposed by these authors that the 3620 cm−1 band ˚ phase and the 3628 cm−1 band to the is ascribed to the 10.3 A ˚ 9.5 A phase. In the spectra reported by Johnston et al. the spec˚ phase clearly shows two bands at 3628 cm−1 trum for the 9.5-A with a shoulder at 3620 cm−1 . In other words both the 3620 and ˚ phase. What we 3628 cm−1 bands were present for the 9.5-A observed in the deintercalation of hydrazine-intercalated kaoli˚ nite was both the 3620 and 3628 cm−1 bands for the 10.3-A phase. Hydroxyl Deformation Modes The hydroxyl deformation modes of kaolinite are important in the spectroscopic analysis for the deintercalation of hydrazineintercalated kaolinite. The reason for this is that the hydroxyl stretching modes behave cooperatively with in-phase and out of phase behavior. Such behavior does not occur for the Al–OH deformation modes. For nonintercalated kaolinite two bands are observed at 914 and 936 cm−1 and are assigned to the deformation modes of the inner hydroxyl and the inner-surface hydroxyls, respectively. Figures 6 and 7 display the hydroxyl deformation modes for the deintercalation of hydrazine-intercalated kaolinite. Upon intercalation with hydrazine, an additional band is observed at 895 cm−1 and is assigned to the hydroxyl defor-
mation modes of the inner-surface hydroxyls hydrogen bonded to hydrazine. A low intensity band is also observed at 954 cm−1 . This band corresponds to the ν12 vibrational mode of hydrazine. ˚ In this work, the predominant phase observed was the 10.3-A phase over the Time 0 to 5-day period. This phase is associated with the observation of the 895 cm−1 band. In this work no band was observed at 904 cm−1 as reported by Johnston et al. (7). They associated their observation of the 904 cm−1 band with the partial collapse of the hydrazine-intercalation complex. In this research the band at 913 cm−1 was observed throughout the deintercalation process. We propose that for hydrazine-intercalated kaolinite the innersurface hydroxyl deformation modes observed at 936 cm−1 are simply replaced by the band observed at 895 cm−1 . As deintercalation occurs, the 895 cm−1 band decreases and the 936 cm−1 band increases in intensity. Such variation in intensity is illustrated in Fig. 8. Figure 8 shows that the 914 cm−1 band is constant in intensity whether the hydrazine-intercalated kaolinite is exposed to wet or dry air. The band at 895 cm−1 for the hydrazineintercalation complex exposed to wet air decreases rapidly and concomitantly the band at 936 cm−1 increases in intensity. For the hydrazine-intercalated kaolinite exposed to dry air, there is an apparent rapid change in the first 2 h of deintercalation and then there is a steady decrease in intensity of the 895 cm−1 band with the concomitant increase in the 936 cm−1 band. The rate of decrease in intensity for one band is matched by the rate of increase in the second band. We propose that the 895 cm−1 band is the hydroxyl deformation mode of the inner-surface hydroxyls hydrogen bonded to hydrazine. Upon deintercalation the 895 cm−1 band is replaced by the 936 cm−1 band. No evidence was found in the deintercalation process for the shift of the 936 cm−1 band to a position coinciding with the inner hydroxyl band at 913 cm−1 .
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FIG. 6. DRIFT spectra of the hydroxyl deformation region of hydrazine-intercalated kaolinite exposed to dry air at (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and (h) 72 h.
Water Bending and HNH Deformation Region Figure 9 displays the 1500 to 1700 cm−1 region of hydrazineintercalated kaolinite exposed to moist air. The spectra are of low intensity. Little intensity was observed in this spectral region for the hydrazine-intercalated kaolinite exposed to dry air. The spectral profile is complex and three bands are observed at 1628, 1613, and 1602 cm−1 . At Time 0 two bands are observed at 1613 and 1628 cm−1 with 55.7 and 35.7% relative intensity, respectively. Upon 1 h of deintercalation, an additional band is observed at 1602 cm−1 . Johnston et al. (6, 7) assigned the band observed at 1613 cm−1 to the scissor HNH mode (ν10 mode). A band at 1627 cm−1 was observed by Johnston et al. (6, 7) but
˚ complex. We observe this band throughout the only for the 9.5-A ˚ phase. The position of this deintercalation process for the 10.3-A band depends on the molecular structure of the hydrazine within the intercalation complex. If the hydrazine is anhydrous and no water is adsorbed during the intercalation process then this band would be observed at 1627 cm−1 . However if hydrazine, which normally occurs as a hydrate, contains some water, then a more likely type of molecule will be the [NH2 –NH3 ]δ+ OHδ− unit. Then the HNH scissor modes would not be observed at 1627 cm−1 . In a previous study by the authors, it was shown that the 1627 cm−1 band was present throughout the deintercalation process (9). Figure 10 displays the variation in relative intensity of the three modes. The 1628 cm−1 band may be ascribed to the
FIG. 7. DRIFT spectra of the hydroxyl deformation region of hydrazine-intercalated kaolinite exposed to moist air at (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 10 h, (g) 24 h, (h) 48 h, (i) 3 days, (j) 4 days, (k) 5 days, and (l) 8 days.
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FIG. 8. Variation of the intensity of the infrared hydroxyl deformation modes of hydrazine-intercalated kaolinite as a function of deintercalation time.
HNH scissor mode and decreases in intensity and is lost after 24 h of deintercalation. Both the 1613 and 1595 cm−1 bands grow in relative intensity as the deintercalation process takes place. The increase in intensity of these two bands is in harmony with the increase in intensity of the two hydroxyl stretching bands observed at 3548 and 3598 cm−1 . The 1595 cm−1 band may be assigned to non-hydrogen-bonded water in the interlamellar space. Considerable differences are expressed for the observation ˚ complex as described in and assignment of bands for the 10.3-A this work and that of Johnston and co-workers (6, 7). The reasons for this are not understood, particularly when both groups are ˚ hydrazine-intercalated kaolinite phase. synthesizing a 10.3-A In the 1600 cm−1 region Johnston and co-workers (6, 7) as-
sign the bands to HNH scissor and twist modes. The differences are so large it is as though two different hydrazine-intercalated kaolinites are being synthesized. There are two possible reasons for the differences. One is the presence or absence of water. The hydrazine-intercalated kaolinite complexes synthesized by Johnston et al. (6, 7) do not contain water whereas those prepared by the authors do contain some water. Second, solid loadings may play an important part. The samples prepared by Johnston et al. (6, 7) may contain higher solid loadings. Figure 9 clearly shows the loss of intensity as deintercalation occurs. Thus the attribution of bands in this region to water HOH bending modes is incorrect and as Johnston et al. (6, 7) rightly points out these bands may be attributable to ν3 and ν10 modes of hydrazine. However after some 10 h of deintercalation
FIG. 9. DRIFT spectra of the NH deformation and water bending region of kaolinite intercalated with hydrazine and exposed to moist air for (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 10 h, (g) 24 h, (h) 2 days, (i) 3 days, and (j) 5 days.
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FIG. 10. Variation in the relative intensity of the NH deformation and water bending modes of hydrazine-intercalated kaolinite as a function of deintercalation time.
the spectral features in this region, namely, the sharp bands at 1628, 1613, and 1602 cm−1 , are replaced with bands at 1596 and 1613 cm−1 , which are broad with bandwidths of around 33 and 21 cm−1 . The 1613 cm−1 band in the period Time 0 to 6 h is sharp with a bandwidth (FWHH) of 11.2 cm−1 . Thus it is suggested that as deintercalation is occurring the ν10 scissor mode of hydrazine is being replaced by an HOH bending mode in about the same position. At the 10-h position there is a discontinuity of the band component analysis; namely, the 1602 cm−1 band is replaced by the 1595 cm−1 band at the 10-h point. In the spectra reported by Johnston et al. (6, 7), the band at 1616 cm−1 ob˚ ˚ complex shifts to 1613 cm−1 for the 9.5-A served for the 10.3-A −1 complex. A shoulder was also observed at 1627 cm that is not discussed. Further an intense broad feature in the spectra centered at around 1595 cm−1 is not ascribed. The sharp band at 1616 cm−1 is attributable to the antisymmetric scissor mode of hydrazine. Factor group analysis of hydrazine suggests that the free hydrazine molecule will have two scissor modes: the in-phase (ν3 ) and the out of phase (ν10 ) vibrations. The in-phase vibration listed in the paper by Johnston et al. (6) at 1806 cm−1 for liquid hydrazine and reported by others to be at 1603 cm−1 is likely to be of low intensity in the infrared spectra. Thus the two bands observed at 1595 and 1628 cm−1 remain unassigned. These bands are readily assigned to the bending modes of water as has been documented by the author and co-workers (9). One of the fundamental differences between the hydrazineintercalated kaolinites as synthesized by Johnston et al. (6, 7) and Frost et al. (9) is the method of preparation. In the method of preparation by the authors a bulk sample of a kaolinite dried at 150◦ C for 24 h is mixed in hydrazine hydrate under an inert atmosphere. In the method of preparation by Johnston et al. (6, 7), a dilute aqueous suspension of kaolinite is allowed to dry on a zinc selenide disk and then a few drops of anhydrous hydrazine are added to the film of kaolinite. Several possibilities exist for the uptake of water: (a) the hydrazine was not anhydrous, (b) the
kaolinite retained some adsorbed water, or (c) water was taken up during the intercalation process. Nevertheless it appears that the hydrazine-intercalated kaolinite synthesized by Johnston et al. may have taken up water. As previous studies by the authors have shown water is important in the collapse of the 10.3- to ˚ phase (9–11). The broad underlying feature reported by 9.5-A Johnston et al. (7) in the 3200 cm−1 region is better ascribed to the stretching modes of water. Unless the intercalation process is carried out under an inert atmosphere, the hydrazine will easily absorb water from the atmosphere. Amine Stretching Region The NH stretching region for the deintercalation of hydrazineintercalated kaolinite can be observed in Figs. 3 and 4. In this ˚ phase. work the predominant expanded phase is the 10.3-A A low intensity broad band is observed at 2895 cm−1 . This band does not appear to correspond with the band reported by ˚ complex (7). A broad Johnston et al. at 2975 cm−1 for the 10.3-A underlying feature is observed centered around 3250 cm−1 . This band decreases in intensity with deintercalation as can be observed in the spectra. Bands are also observed at 3201, 3301, and 3362 cm−1 . Johnston et al. observed bands at 3368, 3363, 3312, and 3303 cm−1 (7). Johnston did not report a band at 3602 cm−1 and in this work we did not observe a band at 3312 cm−1 . The band observed at ∼3362 cm−1 is asymmetric and may be resolved into two bands at 3357 and 3367 cm−1 . ˚ phase is in good agreement with This splitting for the 10.3-A that reported by Johnston et al. who observed two bands at 3363 and 3368 cm−1 (7). It is concluded from these observations that two types of NH ˚ complex. It may be suggested bands are present for the 10.3-A that the NH units exist in two differing molecular environments: (a) one in which the NH unit is complexed to the kaolinite hydroxyl surface and (b) a second in which the NH is hydrogen
DEINTERCALATION OF HYDRAZINE-INTERCALATED KAOLINITE
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FIG. 11. DRIFT spectra of the HNH scissor and twist regions of hydrazine-intercalated kaolinite at (a) 0 h, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and (h) 72 h.
bonded to other hydrazine molecules or other guest molecules. Deintercalation results in the loss of the broad band centered at 3250 cm−1 . This feature is lost by the 10-h mark for the hydrazine-intercalated kaolinite exposed to moist air. The sharp band at 3302 cm−1 is also lost by this time. Yet the band at 3362 cm−1 is retained even up to the 8-day measurement time. The deintercalation of the hydrazine-intercalated kaolinite in moist air is more rapid than that in dry air. Even after 72 h the dry air deintercalation is not complete.
HNH Twist and Scissor Modes Figure 11 displays part of the HNH scissor and twist modes of the hydrazine-intercalated kaolinite deintercalated after different periods of time. Three bands are observed at 1275, 1315, and 1353 cm−1 . Johnston et al. reported the band at 1276 cm−1 ˚ phase (7). and assigned this band to the partially collapsed 9.5-A ˚ complex throughHowever we observe this band for the 10.3-A out the whole deintercalation process. This band is assigned to
FIG. 12. DRIFT spectra of the SiO and NN stretching regions of hydrazine-intercalated kaolinite at (a) 0 h, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and 72 h.
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an antisymmetric HNH twisting mode. No band is observed at 1305 cm−1 as reported by Johnston et al. (7). A broad low intensity band is observed at 1315 cm−1 . This band is assigned to the symmetric HNH twist (16). In matrix-isolated hydrazine molecules the band is observed at 1299 cm−1 and shifts to 1315 cm−1 upon aggregation of the hydrazine molecules (17). A band at 1350 cm−1 is observed in the spectra for the deintercalation process and corresponds well with the band ascribed by Johnston et al. to 1355 cm−1 (7). SiO and NN Stretching Region for the Deintercalation of Hydrazine-Intercalated Kaolinites The SiO and NN stretching regions of the hydrazineintercalated kaolinite are shown in Fig. 12. The stretching modes of SiO from the kaolinite are observed at 1023, 1054, and 1098 cm−1 . The positions of these bands decrease as deintercalation occurs. There is a shift to lower wavenumbers. This shift is indicative of a bonding of the hydrazine to the siloxane surfaces. The NN stretching vibrations are observed as the broad band centered at 1097 cm−1 . A second band is observed at 1123 cm−1 , which upon deintercalation becomes complex. Two bands are observed after 10 h of deintercalation at 1122 and 1114 cm−1 .
due to rupture of the H bonds between adjacent kaolinite layers. Dehydration of the hydrazine during storage in an inert atmosphere results in a reorientation of the hydrazine in the kaolinite interlayer, resulting in the appearance of a new Raman band at 3626 cm−1 . This band is probably due to the formation of an H bond between the lone nitrogen pair of electrons of the hydrazine and the inner-surface hydroxyls of the kaolinite. It must be kept in mind that the difference between the length and the height of the hydrazine molecule is rather small and the presence of intercalated water (which is always present in hydrazine hydrate) may have a significant impact on the hydrazine– kaolinite intercalate structure. The formation and subsequent intercalation of a [NH2 –NH3 ]δ+ OHδ− unit, based on the fact that hydrazine itself is a weak monoacid base, can also explain the ˚ reflection. It is proposed that the contracformation of the 10.3-A tion of the kaolinite layers takes place in a series of steps, which depends on both the orientation of the hydrazine molecule as it penetrates the interlayer space and the cointercalation of water. At least two discrete conformations of hydrazine are present. ACKNOWLEDGMENTS The financial and infrastructural support of the Queensland University of Technology, Centre for Instrumental and Developmental Chemistry, is gratefully acknowledged.
CONCLUSIONS REFERENCES
Intercalation of kaolinite with hydrazine causes expansion ˚ The kaolinite layers remain of the kaolinite layers to 10.66 A. expanded for up to 22 h upon exposure to air. Only after dein˚ d(001) spacing observed. tercalation commences is the 10.39 A ˚ During the deintercalation process only a minor peak at 9.6 A is found. Upon intercalation with hydrazine an intense band is observed at 3628 cm−1 and is attributed to the inner surface hydroxyls hydrogen bonded to hydrazine, which upon deintercalation decreased in intensity. This rate of deintercalation is affected by the presence or absence of air. Deintercalation in the presence of air results in the observation of two additional bands at 3550 and 3598 cm−1 , which are attributed to the adsorption of water during deintercalation. It is proposed that water is important in the expansion of the ˚ and plays an essential role in the deinterkaolinite to 10.39 A calation process. Intercalation of kaolinite with hydrazine followed by partial decomposition resulted in the expansion of the kaolinite to three different basal spacings at 10.3, 9.5, and ˚ The first two expansions depend on the hydrazine con∼8.0 A. formation in the interlayer space. The amount of each conformation depends on the order of the kaolinite, the length of time for intercalation, and the exposure time to air or inert gases. Based on the observations in the DRIFT spectra it is shown that the ˚ phase is formed by intercalation of the [NH2 –NH3 ]δ+ 10.3-A δ− OH unit. This creates no new bands in the DRIFT spectrum but the bands assigned to the inner-surface hydroxyls disappear
1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
15. 16. 17.
Wada, K., Am. Mineral. 46, 79 (1961). Ledoux, R. L., and White, J. L., J. Colloid Interface Sci. 21, 127 (1966). Olejnik, S., Posner, A. M., and Quirk, J. P., Clay Miner. 8, 421 (1970). Cruz, M., Laycock, A., and White, J. L., in “Proceedings, International Clay Conference, Tokyo,” Vol. 1, pp. 775–789. Israel Univ. Press, Jerusalem, 1969. Cruz, M., Jacobs, H., and Fripiat, J. J., in “Proceedings, International Clay Conference, Madrid, Spain,” p. 35–46. 1972. Johnston, C. T., and Stone, D. A., Clays Clay Miner. 38, 121 (1990). Johnston, C. T., Bish, D. L., Eckert, J., and Brown, L. A., J. Phys. Chem. B 104, 8080 (2000). Frost, R. L., Kloprogge, J. T., Kristof, J., and Horvath, E., Clays Clay Miner. 47, 732 (1999). Frost, R. L., Kristof, J., Paroz, G. N., Tran, T. H., and Kloprogge, J. T., J. Colloid Interface Sci. 208, 216 (1998). Frost, R. L., Kristof, J., and Kloprogge, J. T., Neues Jahrb. Mineral. Monatsh. 2, 49 (1998). Kristof, J., Frost, R. L., Kloprogge, J. T., Horvath, E., and Gabor, M., J. Therm. Anal. 56, 885 (1999). Frost, R. L., Tran, T. H., and Kristof, J., Clay Miner. 32, 587 (1997). Weiss, A., Thielepape, W., Ritter, W., Schafer, H., and Goring, G., Anorg. Allg. Chem. 320, 183 (1963). Weiss, A., Thielepape, W., and Orth, H., in “Proceedings, International Clay Conference Jerusalem I (L. Heller and A. Weiss, Eds.), pp. 277–293. Israel Univ. Press, Jerusalem, 1966. Barrios, J., Plan¸con, A., Cruz, M. I., and Tchoubar, C., Clays Clay Miner. 25, 422 (1977). Durig, J. R., Bush, S. F., and Mercer, E. E., J. Chem. Phys. 44, 4238 (1966). Tipton, T., Stone, D. A., KuBulat, K., and Person, W. B., J. Phys. Chem. 93, 2917 (1989).
Deintercalation of Hydrazine-Intercalated Kaolinite in Dry and Moist Air Ray L. Frost,∗,1 J´anos Kristof,† J. Theo Kloprogge,∗ and Erzs´ebet Horvath‡ ∗ Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, 2 George Street, G.P.O. Box 2434, Brisbane, Queensland 4001, Australia; †Department of Analytical Chemistry, University of Veszpr´em, P.O. Box 158, H 8201 Veszpr´em, Hungary; and ‡Research Group for Analytical Chemistry, Hungarian Acadamy of Sciences, P.O. Box 158, H 8201 Veszpr´em, Hungary Received July 19, 2001; accepted October 1, 2001
The deintercalation of hydrazine-intercalated kaolinite has been followed using a combination of X-ray diffraction and diffuse reflectance Fourier transform infrared spectroscopy. Upon intercalation of the kaolinite with hydrazine, the kaolinite layers are ˚ and remain expanded for up to 22 h upon expanded to 10.66 A exposure to moist air. Only upon deintercalation are the peak at ˚ and a minor peak at 9.6 A ˚ observed. Complete deintercala10.39 A tion takes up to 18 days more. Upon intercalation with hydrazine an intense band is observed at 3628 cm−1 and is attributed to the innersurface hydroxyls hydrogen bonded to the hydrazine, which upon deintercalation decreased in intensity. This rate of deintercalation is affected by the presence or absence of moist air. Deintercalation in the presence of water vapor results in the observation of two additional bands at 3550 and 3598 cm−1 , which are attributed to the hydroxyl stretching modes of adsorbed water during deintercalation. The intensity of NH stretching vibrations observed at 3360, 3300, and 3200 cm−1 also decrease in intensity with deintercalation time. Changes in the hydroxyl deformation modes of kaolinite in the 915 cm−1 region and in the HNH deformation modes show strong interactions between the kaolinite surface and the inserting hydrazine molecule. °C 2002 Elsevier Science Key Words: intercalation; hydrazine; kaolinite; hydroxyls; hydrogen bonding; FT-IR spectroscopy; X-ray powder diffraction.
INTRODUCTION
Kaolinite is classified as a nonexpandable clay. The intercalation of kaolinite is an old and ongoing research topic. Among the direct intercalating compounds, hydrazine probably is the most welcomed one due to its fast intercalation rate and high intercalation yields, yet the knowledge about the reaction is the poorest. When molecules such as hydrazine are intercalated between the 1 : 1 layers, some expansion occurs (1–3). Hydrazine intercalation of kaolinite has been studied by research groups, including Ledoux and White (2), Cruz et al. (4, 5), and Johnston and Stone (6). Researchers have shown that kaolinite can be expanded with ˚ (2). Deintercalation occurred through mild hydrazine to 10.4 A heating or by exposure to a controlled vacuum causing the struc˚ (2). Such alteration in interlayer ture to partially collapse to 9.4 A 1
To whom correspondence should be addressed. E-mail: [email protected].
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thickness was complemented by changes in the infrared and Raman spectra (3, 6). More recently Johnston et al. reported an infrared and inelastic neutron scattering study of the 1.03- and 0.95-nm kaolinite–hydrazine intercalation complexes (7). Frost et al. reported the kinetics of deintercalation of hydrazine from hydrazine-intercalated kaolinite (8). Different interpretations of the infrared and Raman spectra of the hydrazine-intercalated complexes have been forthcoming (6, 8). These different interpretations may result from the methodology of synthesis of the hydrazine-intercalated kaolinite complexes. The complex may be prepared using anhydrous hydrazine or by using hydrazine hydrate. The hydrazine molecule interacts with the 1 : 1 layer surfaces through the lone pair of electrons of the nitrogen and the hydrogens of the NH2 group (8, 9). The interaction of the N is not expected to be as strong as that of potassium acetate and vibrational spectroscopic bands higher than 3605 cm−1 are predicted. The interaction of the H in the hydrazine-intercalation complex is expected to be similar to that of the hydrogens in urea (8–11). Thus, there would be no additional hydroxyl bands and no decrease in the intensities of the inner-surface hydroxyls. The question arises as to whether deintercalation would be the same under exposure of the hydrazine-intercalation complex to moist air or under vacuum. In a previous study deintercalation of hydrazine hydrate-intercalated kaolinite was studied. Here the study was undertaken in moist air. The chemistry of the hydrazine-intercalated kaolinite is complex. This complexity results in differences in the attribution of bands in the infrared spectra. Hence new experiments are undertaken to increase our fundamental knowledge of this complexity. Here we report the deintercalation of a hydrazine-intercalated kaolinite as a function of time in the presence and absence of moisture using powder X-ray diffraction (XRD) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). EXPERIMENTAL
The Kaolinite Intercalate The kaolinite used in this study is a low defect kaolinite from Kir´alyhegy in Hungary. This mineral has been previously characterized both by X-ray diffraction and by Raman
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DEINTERCALATION OF HYDRAZINE-INTERCALATED KAOLINITE
spectroscopy (12). The kaolinite was purified through sedimentation and the 2- to 20-µm-sized fraction was selected for intercalation. The intercalate was prepared by mixing 300 mg of kaolinite with 5 cm3 of a 98% hydrazine hydrate aqueous solution for 80 h at room temperature in a magnetic stirrer. The excess solution was decanted and the intercalated kaolinite was immediately subjected to spectroscopic analysis. Two experiments have been conducted. The wet intercalate (i.e., in contact with 98% hydrazine hydrate to avoid deintercalation) was dried in a vacuum oven at room temperature for 30 min. After drying (a powdery sample was obtained) 2–5 mg of the powdery intercalate was mixed with 100 mg KBr for DRIFT and kept for a longer period of time in contact with room air. At certain intervals the spectrum was recorded. In the parallel run, the same mixture (intercalate + KBr) was prepared but kept continuously inside the sample compartment of the FTIR equipment purged continuously with dry air. At intervals the spectrum of this sample was recorded as well. X-Ray Diffraction X-ray diffraction patterns of the intercalated kaolinite at different time intervals after exposure to air were obtained using a Philips PW 1050 type X-ray diffractometer using CuK α radiation operating at 35 kV and 40 mA. It was not possible to undertake the X-ray diffraction patterns under vacuum at this stage. A 1◦ divergence and scatter slit were combined with a normal focus Cu tube at 6◦ take off angle and a 0.2-mm receiving slit (9, 10). The samples were measured in stepscan mode from 2.0◦ 2θ with steps of 0.05◦ up to 40◦ 2θ and a counting time of 2 s. DRIFT Spectroscopy DRIFT analyses were undertaken using a Bio-Rad 60A spectrometer. Five hundred twelve scans were co-added at a resolution of 2 cm−1 with a mirror velocity of 0.3 cm/s. Approxi-
165
mately 3 wt% kaolinite or intercalated kaolinite was dispersed in oven-dried spectroscopic grade KBr with a refractive index of 1.559 and a particle size of 5–20 µm. Background KBr spectra were obtained and the sample single beam spectra were ratioed to the background. Spectral manipulations such as baseline adjustment, smoothing, and normalization were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, USA). Band component analysis was undertaken using the Jandel Peakfit software package, 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 Gauss–Lorentz ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations of r 2 greater than 0.995. Graphics are presented using Microsoft Excel. RESULTS AND DISCUSSION
X-Ray Diffraction Results Lattice expansion and contraction. The results of the Xray diffraction analyses of the low defect kaolinite intercalated with hydrazine hydrate and exposed to air for periods of time ranging from Time 0 to 18 days are illustrated in Fig. 1. Data were also collected for periods of up to 1 month. However such data are not shown as the results are similar to the X-ray diffraction patterns of the 18-day pattern. Figure 1 shows the d(001) spacing of both the hydrazineintercalated kaolinite and the deintercalated kaolinite. The Xray diffraction pattern of the hydrazine-intercalated kaolinite clearly shows that the clay has been fully intercalated at ambient temperatures. It is imperative to have 100% intercalation of the kaolinite in an attempt to fully interpret spectroscopic
FIG. 1. X-ray diffraction patterns of the d(001) spacings of kaolinite intercalated with hydrazine and exposed to air for (a) zero time, (b) 3 h, (c) 8 h, (d) 24 h, (e) 104 h, (f) 120 h, (g) 168 h, (h) 11 days, and (i) 1 month.
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data of a complicated system like the hydrazine–kaolinite intercalate. Hydrazine has been found to very readily adsorb on kaolinite surfaces showing characteristic “intercalation” type spectra and yet the kaolinite was not expanded (this work and Refs. 8–11). In the method of preparation, the hydrazineintercalated kaolinite was dried under vaccuum at 25◦ C. This sample is “dry” in that no excess hydrazine is present and the sample has the appearance of the original kaolinite powder. The d spacing of the hydrazine-intercalated kaolinite was found to ˚ at Time 0 and this figure was constant for the first be 10.66 A 8 h of deintercalation. Only after 22 h of deintercalation did the ˚ This value is in harmony with the d(001) peak shift to 10.39 A. previous studies by the authors and by other research groups (2, 3, 7, 13–15). According to the literature, the intercalate would collapse ˚ as is the case in the preparation of under vacuum to 9.6 A, the hydrazine-intercalation complex in this work (6, 7). One may have expected that the initial d(001) spacing may have ˚ corresponded to this value. However a larger value of 10.66 A was obtained. It must be concluded that the hydrazineintercalation complex absorbed water and reexpanded to this value before the collection of the XRD results. An initial value ˚ for the hydrazine-expanded kaolinite was obtained. of 10.66 A This result differs from previously published results. The value ˚ after a short period of time. It is possible decreases to 10.39 A that after placing the hydrazine-intercalated kaolinite in a vac˚ and uum for 30 min that the complex reexpanded to 10.66 A ˚ then altered to 10.39 A after some molecular rearrangement of the hydrazine and absorbed water in the hydrazine-intercalation complex. This conclusion confirms the concept of the hydrazine molecules keying in to the ditrigonal cavity of the siloxane layer and that this keying may take place even before the collapse of the structure by placing under a vacuum and reduction of the
˚ (6, 7). In the deintercalation prointerlayer spacing to 9.6 A cess, the hydrazine-intercalated kaolinite is quite stable up to at least 8 h, and only after 22 h does the deintercalation process ˚ occur. After 22 h two peaks are observed at 10.39 and 7.4 A. ˚ After the 27-h period the 10.39-A phase is no longer present but the appearance of the deintercalated kaolinite phase at the ˚ peak increases in intensity. In the 96-h period to 7 days, 7.22-A ˚ are three phases with d(001) spacings at 10.4, 7.5, and 7.2 A observed. The first phase is that of the hydrazine-intercalated kaolinite, the second is due to the partially collapsed structure, and the last phase is that of the deintercalated kaolinite. Only after 18 days of air exposure is the hydrazine-intercalated kaolinite completely decomposed. Figure 2 displays the variation of the crystallite size of the d(001) peak of the hydrazine-intercalated kaolinite and the deintercalated hydrazine-intercalated kaolinite as a function of deintercalation time. This intercalate has had its lattice structure destroyed through the intercalation process. Crystallite size is the coherently diffracted domain. The rapid structural degradation of kaolinite is connected with an increase in the mean lattice distortion and is not the consequence of the reduction of the crystallite size. Crystallite size is not equal to particle size. The width of the peak is related to the crystallite size according to the Scherrer equation: L=
λK . β cos θ
L is the mean crystallite dimension in angstroms along a line normal to the reflecting plane, K is a constant close to unity, and β is the width of the reflection at half height expressed in radians of 2θ . Figure 2 displays the changes in the crystallite size as determined by the changes in the
FIG. 2. Variation of crystallite size of the d(001) spacing of hydrazine-intercalated and deintercalated kaolinite as a function of deintercalation time.
DEINTERCALATION OF HYDRAZINE-INTERCALATED KAOLINITE
˚ peak with time of deintercalation. This width of the 10.4-A change is not a linear function with time. This means that the deintercalation process is causing the kaolinite crystal size to ˚ peak width inbecome smaller. On the other hand the 7.2-A creases with time, showing that the deintercalated kaolinite crystallite size is growing with deintercalation time. This process appears to be an exponential growth. Thus a first-order kinetic type process is observed. The crystallite size after 450 h of deintercalation is less than that of the starting material. This proves the deintercalation process causes a disordering of the kaolinite. Considering the different basal spacings it is possible to develop a model for the intercalation of hydrazine based only on geometrical constraints. The hydrazine molecule is basically ditrigonal and planar and may take up a number of orientations within the kaolinite interlayer space. The hydrazine molecule ˚ long, i.e., the length of a N–N may be considered to be 3.53 A ˚ plus twice the length of a N–H bond (1.03 A) ˚ bond (1.47 A) times cos 60◦ . The height of the molecule is the length of the 5 orbitals attributed to the lone pairs of electrons on the nitrogen, ˚ The width of the molecule is the thickness of which is ∼2.9 A. ˚ It is the flat hydrazine molecule, which is approximately 1.5 A. proposed that the different expansions of the kaolinite may correspond to the different possible orientations of the hydrazine molecule within the interlayer space of the kaolinite. It is proposed that the hydrazine molecule enters the kaolinite interlayer ˚ dimension. Then the space as a flat wedge, i.e., using the 1.5-A hydrazine molecule through hydrogen bond interactions reorients within the kaolinite structure causing the expansion. It is possible that the hydrazine then takes up a position with the lone pairs of electrons pointing toward the kaolinite surfaces. The ˚ expansion may result when the lone pair of electrons 10.3-A
167
on the nitrogen atoms is pointing directly toward the hydroxyl ˚ is added to 3.53 A. ˚ This would surface. This results when 7.2 A ˚ which was the initial value of the d(001) then make 10.66 A, spacing determined in this work. The reduction of this value ˚ is in harmony with the concept of the hydrazine to 10.39 A molecules keying into the ditrigonal cavity. Such a conclusion fits well with the conclusions of Johnston et al. (6, 7). The question arises as to whether both nitrogens of the hydrazine interact with the hydroxyl surface. It is possible that the lone pair of electrons of both nitrogens form interactions with the hydroxyl surface. However infrared results suggest that both nitrogens are ˚ expansion not exactly equivalent. Another option for the 10.3-A is the presence of two flat lying hydrazine molecules on top of each other. This model seems less likely however. The second ˚ might occur when the hydrogens of the conformation at 9.5 A molecule are pointing toward the siloxane surface. This results ˚ In this model, the lone pair from the addition of 7.2 and 2.5 A. of electrons is parallel to the kaolinite surfaces. These confirmations are solely based on the differences in the hydrazine dimensions. Drift spectroscopic results. In this work, two DRIFT spectroscopic experiments were undertaken: deintercalation of the vacuum-dried hydrazine-intercalated kaolinite (a) under purged dry air and (b) exposed to laboratory air. Figures 3 and 4 show the DRIFT spectra of these two experiments. The deintercalation in dry air is a slow process and even after 3 days the hydrazine-intercalation complex has not completely decomposed. In comparison, the hydrazine-intercalation complex decomposes rapidly when the system is exposed to moist air. What is clearly observed is that in the deintercalation in moist air two additional bands are observed at 3568 and 3599 cm−1 . The intensity of the 3568 cm−1 band increases with time even though
FIG. 3. DRIFT spectra of the OH and NH stretching region of kaolinite intercalated with hydrazine and kept under dry air for (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and (h) 72 h.
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FIG. 4. DRIFT spectra of the OH and NH stretching region of kaolinite intercalated with hydrazine and exposed to moist air for (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 10 h, (f) 24 h, (g) 48 h, and (h) 192 h.
the intercalation complex is decomposing. The 3568 cm−1 band and a band at 3465 cm−1 were previously assigned to the inner-surface hydroxyls of kaolinite–hydrogen bonded to the hydrazine (2). Johnston et al. concurred with such a band attribution. No band at 3465 cm−1 was observed in this work. It is quite evident that the kaolinite intercalates with hydrazine irrespective of whether these two bands are present or not. These bands are only present if water is present. Thus the bands must be assigned to the hydroxyl stretching frequencies of water. The concept that the inner-surface hydroxyls appears as hydrogenbonded hydroxyls with hydrazine as low as 3568 and 3465 cm−1 is rejected. Hydrazine cannot form hydrogen bonds stronger than those of an ionic compound such as potassium acetate. The inner surface hydroxyls of kaolinite–hydrogen bonded to the acetate ion appear at 3605 cm−1 (12). Further if this complex were so strongly bonded then it would not decompose so fast. Another fact is that the NH band positions do not change during decomposition. Thus, if the 3568 cm−1 band were a H-bonded inner-surface OH band occurring/developing during decomposition, then the NH positions should also change. This was not observed. In this work, the concept of the inner surface hydroxyls as hydrogen-bonded hydroxyls with hydrazine as low as 3568 and 3465 cm−1 is in apparent disagreement with other results. Upon intercalation of potassium acetate into kaolinite an intense band is observed at 3605 cm−1 , which is attributed to the inner-surface hydroxyls hydrogen bonded to the acetate ion. Such a bond is strong, making the deintercalation difficult except through washing. Other authors have suggested that bands occur at 3658, 3535, and 3499 cm−1 for dimethyl sulfoxide-intercalated kaolinite, at 3590 cm−1 for formamide-intercalated kaolinite, and in the 3585 to 3560 cm−1 range for urea-intercalated kaolinite and that these bands are attributed to the hydrogen bonding of the inner surface hydroxyls to the inserting molecule. However it is difficult to comprehend how these types of molecules form
hydrogen bonds stronger than those of the acetate of potassium acetate in the intercalation complexes. The authors have previously attributed bands in these positions to water OH stretching vibrations. Thus the two bands observed at 3568 and 3465 cm−1 are ascribed to water vibrational modes in the intercalation complexes. Such observations bring into question the attribution of the 3628 cm−1 band. Figures 3 and 4 clearly show the hydroxyl stretching kaolinite band at 3628 cm−1 . This band is present in the DRIFT spectra during the deintercalation process over the 18-day period of deintercalation. During this time period the ˚ XRD patterns show a d(001) spacing of 10.66 or 10.39 A. ˚ The 9.49 A d(001) spacing is only observed after water is admitted to the system and decomposition is occurring (9–11). Thus we assign the 3628 cm−1 band to the hydroxyl stretching frequency of the inner-surface hydroxyls of kaolinite–hydrogen bonded to hydrazine. There are differences in the spectra reported in this work and that of Johnston and co-workers. In ˚ d(001) spacthis work we associate the 10.66 and 10.39 A −1 ings with the observation of the 3628 cm band in the FTIR spectra. Johnston et al. (6, 7) reports the inner-surface hydroxyl of the hydrazine-intercalated kaolinite for the 10.39˚ phase as 3620 cm−1 . Our observation places the peak at A 3628 cm−1 . Kaolinite hydroxyl stretching. Considerable differences are observed in the spectra of the kaolinite OH stretching region between the hydrazine-intercalated kaolinite exposed to air or maintained in the absence of moist air (Figs. 3 and 4). Figure 5 shows the variation in intensity of the bands as a function of the time of deintercalation. Differences are observed in the intensity of the 3628 cm−1 band attributed to the inner-surface hydroxyls hydrogen bonded to the hydrazine. The decrease in intensity of the band is approximately the same up to 1 h. The decrease in intensity for the sample exposed to moist air is significantly greater than that for the sample exposed to dry air. For example
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169
FIG. 5. Variation of the intensity of the infrared hydroxyl stretching modes of hydrazine-intercalated kaolinite as a function of deintercalation time.
after 3 h the intensity for the “wet-air” sample decreased from 90.1 to 42.0%, whereas the sample exposed to dry air decreased from 84.4 to 59.9%. After 10 h of exposure, the intensity for the wet-air sample decreased to below 10%. The intensity for the “dry-air” sample remained at 38%. After 2 days the value was 25%. It is proposed that water influences the rate of deintercalation of the hydrazine-intercalated kaolinite. Johnston et al. ascribed the 3628 cm−1 band to the inner hydroxyls shifted from the normally found position of 3620 cm−1 (6, 7). It is proposed by these authors that the 3620 cm−1 band ˚ phase and the 3628 cm−1 band to the is ascribed to the 10.3 A ˚ 9.5 A phase. In the spectra reported by Johnston et al. the spec˚ phase clearly shows two bands at 3628 cm−1 trum for the 9.5-A with a shoulder at 3620 cm−1 . In other words both the 3620 and ˚ phase. What we 3628 cm−1 bands were present for the 9.5-A observed in the deintercalation of hydrazine-intercalated kaoli˚ nite was both the 3620 and 3628 cm−1 bands for the 10.3-A phase. Hydroxyl Deformation Modes The hydroxyl deformation modes of kaolinite are important in the spectroscopic analysis for the deintercalation of hydrazineintercalated kaolinite. The reason for this is that the hydroxyl stretching modes behave cooperatively with in-phase and out of phase behavior. Such behavior does not occur for the Al–OH deformation modes. For nonintercalated kaolinite two bands are observed at 914 and 936 cm−1 and are assigned to the deformation modes of the inner hydroxyl and the inner-surface hydroxyls, respectively. Figures 6 and 7 display the hydroxyl deformation modes for the deintercalation of hydrazine-intercalated kaolinite. Upon intercalation with hydrazine, an additional band is observed at 895 cm−1 and is assigned to the hydroxyl defor-
mation modes of the inner-surface hydroxyls hydrogen bonded to hydrazine. A low intensity band is also observed at 954 cm−1 . This band corresponds to the ν12 vibrational mode of hydrazine. ˚ In this work, the predominant phase observed was the 10.3-A phase over the Time 0 to 5-day period. This phase is associated with the observation of the 895 cm−1 band. In this work no band was observed at 904 cm−1 as reported by Johnston et al. (7). They associated their observation of the 904 cm−1 band with the partial collapse of the hydrazine-intercalation complex. In this research the band at 913 cm−1 was observed throughout the deintercalation process. We propose that for hydrazine-intercalated kaolinite the innersurface hydroxyl deformation modes observed at 936 cm−1 are simply replaced by the band observed at 895 cm−1 . As deintercalation occurs, the 895 cm−1 band decreases and the 936 cm−1 band increases in intensity. Such variation in intensity is illustrated in Fig. 8. Figure 8 shows that the 914 cm−1 band is constant in intensity whether the hydrazine-intercalated kaolinite is exposed to wet or dry air. The band at 895 cm−1 for the hydrazineintercalation complex exposed to wet air decreases rapidly and concomitantly the band at 936 cm−1 increases in intensity. For the hydrazine-intercalated kaolinite exposed to dry air, there is an apparent rapid change in the first 2 h of deintercalation and then there is a steady decrease in intensity of the 895 cm−1 band with the concomitant increase in the 936 cm−1 band. The rate of decrease in intensity for one band is matched by the rate of increase in the second band. We propose that the 895 cm−1 band is the hydroxyl deformation mode of the inner-surface hydroxyls hydrogen bonded to hydrazine. Upon deintercalation the 895 cm−1 band is replaced by the 936 cm−1 band. No evidence was found in the deintercalation process for the shift of the 936 cm−1 band to a position coinciding with the inner hydroxyl band at 913 cm−1 .
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FIG. 6. DRIFT spectra of the hydroxyl deformation region of hydrazine-intercalated kaolinite exposed to dry air at (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and (h) 72 h.
Water Bending and HNH Deformation Region Figure 9 displays the 1500 to 1700 cm−1 region of hydrazineintercalated kaolinite exposed to moist air. The spectra are of low intensity. Little intensity was observed in this spectral region for the hydrazine-intercalated kaolinite exposed to dry air. The spectral profile is complex and three bands are observed at 1628, 1613, and 1602 cm−1 . At Time 0 two bands are observed at 1613 and 1628 cm−1 with 55.7 and 35.7% relative intensity, respectively. Upon 1 h of deintercalation, an additional band is observed at 1602 cm−1 . Johnston et al. (6, 7) assigned the band observed at 1613 cm−1 to the scissor HNH mode (ν10 mode). A band at 1627 cm−1 was observed by Johnston et al. (6, 7) but
˚ complex. We observe this band throughout the only for the 9.5-A ˚ phase. The position of this deintercalation process for the 10.3-A band depends on the molecular structure of the hydrazine within the intercalation complex. If the hydrazine is anhydrous and no water is adsorbed during the intercalation process then this band would be observed at 1627 cm−1 . However if hydrazine, which normally occurs as a hydrate, contains some water, then a more likely type of molecule will be the [NH2 –NH3 ]δ+ OHδ− unit. Then the HNH scissor modes would not be observed at 1627 cm−1 . In a previous study by the authors, it was shown that the 1627 cm−1 band was present throughout the deintercalation process (9). Figure 10 displays the variation in relative intensity of the three modes. The 1628 cm−1 band may be ascribed to the
FIG. 7. DRIFT spectra of the hydroxyl deformation region of hydrazine-intercalated kaolinite exposed to moist air at (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 10 h, (g) 24 h, (h) 48 h, (i) 3 days, (j) 4 days, (k) 5 days, and (l) 8 days.
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171
FIG. 8. Variation of the intensity of the infrared hydroxyl deformation modes of hydrazine-intercalated kaolinite as a function of deintercalation time.
HNH scissor mode and decreases in intensity and is lost after 24 h of deintercalation. Both the 1613 and 1595 cm−1 bands grow in relative intensity as the deintercalation process takes place. The increase in intensity of these two bands is in harmony with the increase in intensity of the two hydroxyl stretching bands observed at 3548 and 3598 cm−1 . The 1595 cm−1 band may be assigned to non-hydrogen-bonded water in the interlamellar space. Considerable differences are expressed for the observation ˚ complex as described in and assignment of bands for the 10.3-A this work and that of Johnston and co-workers (6, 7). The reasons for this are not understood, particularly when both groups are ˚ hydrazine-intercalated kaolinite phase. synthesizing a 10.3-A In the 1600 cm−1 region Johnston and co-workers (6, 7) as-
sign the bands to HNH scissor and twist modes. The differences are so large it is as though two different hydrazine-intercalated kaolinites are being synthesized. There are two possible reasons for the differences. One is the presence or absence of water. The hydrazine-intercalated kaolinite complexes synthesized by Johnston et al. (6, 7) do not contain water whereas those prepared by the authors do contain some water. Second, solid loadings may play an important part. The samples prepared by Johnston et al. (6, 7) may contain higher solid loadings. Figure 9 clearly shows the loss of intensity as deintercalation occurs. Thus the attribution of bands in this region to water HOH bending modes is incorrect and as Johnston et al. (6, 7) rightly points out these bands may be attributable to ν3 and ν10 modes of hydrazine. However after some 10 h of deintercalation
FIG. 9. DRIFT spectra of the NH deformation and water bending region of kaolinite intercalated with hydrazine and exposed to moist air for (a) 0 min, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 10 h, (g) 24 h, (h) 2 days, (i) 3 days, and (j) 5 days.
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FIG. 10. Variation in the relative intensity of the NH deformation and water bending modes of hydrazine-intercalated kaolinite as a function of deintercalation time.
the spectral features in this region, namely, the sharp bands at 1628, 1613, and 1602 cm−1 , are replaced with bands at 1596 and 1613 cm−1 , which are broad with bandwidths of around 33 and 21 cm−1 . The 1613 cm−1 band in the period Time 0 to 6 h is sharp with a bandwidth (FWHH) of 11.2 cm−1 . Thus it is suggested that as deintercalation is occurring the ν10 scissor mode of hydrazine is being replaced by an HOH bending mode in about the same position. At the 10-h position there is a discontinuity of the band component analysis; namely, the 1602 cm−1 band is replaced by the 1595 cm−1 band at the 10-h point. In the spectra reported by Johnston et al. (6, 7), the band at 1616 cm−1 ob˚ ˚ complex shifts to 1613 cm−1 for the 9.5-A served for the 10.3-A −1 complex. A shoulder was also observed at 1627 cm that is not discussed. Further an intense broad feature in the spectra centered at around 1595 cm−1 is not ascribed. The sharp band at 1616 cm−1 is attributable to the antisymmetric scissor mode of hydrazine. Factor group analysis of hydrazine suggests that the free hydrazine molecule will have two scissor modes: the in-phase (ν3 ) and the out of phase (ν10 ) vibrations. The in-phase vibration listed in the paper by Johnston et al. (6) at 1806 cm−1 for liquid hydrazine and reported by others to be at 1603 cm−1 is likely to be of low intensity in the infrared spectra. Thus the two bands observed at 1595 and 1628 cm−1 remain unassigned. These bands are readily assigned to the bending modes of water as has been documented by the author and co-workers (9). One of the fundamental differences between the hydrazineintercalated kaolinites as synthesized by Johnston et al. (6, 7) and Frost et al. (9) is the method of preparation. In the method of preparation by the authors a bulk sample of a kaolinite dried at 150◦ C for 24 h is mixed in hydrazine hydrate under an inert atmosphere. In the method of preparation by Johnston et al. (6, 7), a dilute aqueous suspension of kaolinite is allowed to dry on a zinc selenide disk and then a few drops of anhydrous hydrazine are added to the film of kaolinite. Several possibilities exist for the uptake of water: (a) the hydrazine was not anhydrous, (b) the
kaolinite retained some adsorbed water, or (c) water was taken up during the intercalation process. Nevertheless it appears that the hydrazine-intercalated kaolinite synthesized by Johnston et al. may have taken up water. As previous studies by the authors have shown water is important in the collapse of the 10.3- to ˚ phase (9–11). The broad underlying feature reported by 9.5-A Johnston et al. (7) in the 3200 cm−1 region is better ascribed to the stretching modes of water. Unless the intercalation process is carried out under an inert atmosphere, the hydrazine will easily absorb water from the atmosphere. Amine Stretching Region The NH stretching region for the deintercalation of hydrazineintercalated kaolinite can be observed in Figs. 3 and 4. In this ˚ phase. work the predominant expanded phase is the 10.3-A A low intensity broad band is observed at 2895 cm−1 . This band does not appear to correspond with the band reported by ˚ complex (7). A broad Johnston et al. at 2975 cm−1 for the 10.3-A underlying feature is observed centered around 3250 cm−1 . This band decreases in intensity with deintercalation as can be observed in the spectra. Bands are also observed at 3201, 3301, and 3362 cm−1 . Johnston et al. observed bands at 3368, 3363, 3312, and 3303 cm−1 (7). Johnston did not report a band at 3602 cm−1 and in this work we did not observe a band at 3312 cm−1 . The band observed at ∼3362 cm−1 is asymmetric and may be resolved into two bands at 3357 and 3367 cm−1 . ˚ phase is in good agreement with This splitting for the 10.3-A that reported by Johnston et al. who observed two bands at 3363 and 3368 cm−1 (7). It is concluded from these observations that two types of NH ˚ complex. It may be suggested bands are present for the 10.3-A that the NH units exist in two differing molecular environments: (a) one in which the NH unit is complexed to the kaolinite hydroxyl surface and (b) a second in which the NH is hydrogen
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FIG. 11. DRIFT spectra of the HNH scissor and twist regions of hydrazine-intercalated kaolinite at (a) 0 h, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and (h) 72 h.
bonded to other hydrazine molecules or other guest molecules. Deintercalation results in the loss of the broad band centered at 3250 cm−1 . This feature is lost by the 10-h mark for the hydrazine-intercalated kaolinite exposed to moist air. The sharp band at 3302 cm−1 is also lost by this time. Yet the band at 3362 cm−1 is retained even up to the 8-day measurement time. The deintercalation of the hydrazine-intercalated kaolinite in moist air is more rapid than that in dry air. Even after 72 h the dry air deintercalation is not complete.
HNH Twist and Scissor Modes Figure 11 displays part of the HNH scissor and twist modes of the hydrazine-intercalated kaolinite deintercalated after different periods of time. Three bands are observed at 1275, 1315, and 1353 cm−1 . Johnston et al. reported the band at 1276 cm−1 ˚ phase (7). and assigned this band to the partially collapsed 9.5-A ˚ complex throughHowever we observe this band for the 10.3-A out the whole deintercalation process. This band is assigned to
FIG. 12. DRIFT spectra of the SiO and NN stretching regions of hydrazine-intercalated kaolinite at (a) 0 h, (b) 1 h, (c) 2 h, (d) 3 h, (e) 6 h, (f) 11 h, (g) 24 h, and 72 h.
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an antisymmetric HNH twisting mode. No band is observed at 1305 cm−1 as reported by Johnston et al. (7). A broad low intensity band is observed at 1315 cm−1 . This band is assigned to the symmetric HNH twist (16). In matrix-isolated hydrazine molecules the band is observed at 1299 cm−1 and shifts to 1315 cm−1 upon aggregation of the hydrazine molecules (17). A band at 1350 cm−1 is observed in the spectra for the deintercalation process and corresponds well with the band ascribed by Johnston et al. to 1355 cm−1 (7). SiO and NN Stretching Region for the Deintercalation of Hydrazine-Intercalated Kaolinites The SiO and NN stretching regions of the hydrazineintercalated kaolinite are shown in Fig. 12. The stretching modes of SiO from the kaolinite are observed at 1023, 1054, and 1098 cm−1 . The positions of these bands decrease as deintercalation occurs. There is a shift to lower wavenumbers. This shift is indicative of a bonding of the hydrazine to the siloxane surfaces. The NN stretching vibrations are observed as the broad band centered at 1097 cm−1 . A second band is observed at 1123 cm−1 , which upon deintercalation becomes complex. Two bands are observed after 10 h of deintercalation at 1122 and 1114 cm−1 .
due to rupture of the H bonds between adjacent kaolinite layers. Dehydration of the hydrazine during storage in an inert atmosphere results in a reorientation of the hydrazine in the kaolinite interlayer, resulting in the appearance of a new Raman band at 3626 cm−1 . This band is probably due to the formation of an H bond between the lone nitrogen pair of electrons of the hydrazine and the inner-surface hydroxyls of the kaolinite. It must be kept in mind that the difference between the length and the height of the hydrazine molecule is rather small and the presence of intercalated water (which is always present in hydrazine hydrate) may have a significant impact on the hydrazine– kaolinite intercalate structure. The formation and subsequent intercalation of a [NH2 –NH3 ]δ+ OHδ− unit, based on the fact that hydrazine itself is a weak monoacid base, can also explain the ˚ reflection. It is proposed that the contracformation of the 10.3-A tion of the kaolinite layers takes place in a series of steps, which depends on both the orientation of the hydrazine molecule as it penetrates the interlayer space and the cointercalation of water. At least two discrete conformations of hydrazine are present. ACKNOWLEDGMENTS The financial and infrastructural support of the Queensland University of Technology, Centre for Instrumental and Developmental Chemistry, is gratefully acknowledged.
CONCLUSIONS REFERENCES
Intercalation of kaolinite with hydrazine causes expansion ˚ The kaolinite layers remain of the kaolinite layers to 10.66 A. expanded for up to 22 h upon exposure to air. Only after dein˚ d(001) spacing observed. tercalation commences is the 10.39 A ˚ During the deintercalation process only a minor peak at 9.6 A is found. Upon intercalation with hydrazine an intense band is observed at 3628 cm−1 and is attributed to the inner surface hydroxyls hydrogen bonded to hydrazine, which upon deintercalation decreased in intensity. This rate of deintercalation is affected by the presence or absence of air. Deintercalation in the presence of air results in the observation of two additional bands at 3550 and 3598 cm−1 , which are attributed to the adsorption of water during deintercalation. It is proposed that water is important in the expansion of the ˚ and plays an essential role in the deinterkaolinite to 10.39 A calation process. Intercalation of kaolinite with hydrazine followed by partial decomposition resulted in the expansion of the kaolinite to three different basal spacings at 10.3, 9.5, and ˚ The first two expansions depend on the hydrazine con∼8.0 A. formation in the interlayer space. The amount of each conformation depends on the order of the kaolinite, the length of time for intercalation, and the exposure time to air or inert gases. Based on the observations in the DRIFT spectra it is shown that the ˚ phase is formed by intercalation of the [NH2 –NH3 ]δ+ 10.3-A δ− OH unit. This creates no new bands in the DRIFT spectrum but the bands assigned to the inner-surface hydroxyls disappear
1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
15. 16. 17.
Wada, K., Am. Mineral. 46, 79 (1961). Ledoux, R. L., and White, J. L., J. Colloid Interface Sci. 21, 127 (1966). Olejnik, S., Posner, A. M., and Quirk, J. P., Clay Miner. 8, 421 (1970). Cruz, M., Laycock, A., and White, J. L., in “Proceedings, International Clay Conference, Tokyo,” Vol. 1, pp. 775–789. Israel Univ. Press, Jerusalem, 1969. Cruz, M., Jacobs, H., and Fripiat, J. J., in “Proceedings, International Clay Conference, Madrid, Spain,” p. 35–46. 1972. Johnston, C. T., and Stone, D. A., Clays Clay Miner. 38, 121 (1990). Johnston, C. T., Bish, D. L., Eckert, J., and Brown, L. A., J. Phys. Chem. B 104, 8080 (2000). Frost, R. L., Kloprogge, J. T., Kristof, J., and Horvath, E., Clays Clay Miner. 47, 732 (1999). Frost, R. L., Kristof, J., Paroz, G. N., Tran, T. H., and Kloprogge, J. T., J. Colloid Interface Sci. 208, 216 (1998). Frost, R. L., Kristof, J., and Kloprogge, J. T., Neues Jahrb. Mineral. Monatsh. 2, 49 (1998). Kristof, J., Frost, R. L., Kloprogge, J. T., Horvath, E., and Gabor, M., J. Therm. Anal. 56, 885 (1999). Frost, R. L., Tran, T. H., and Kristof, J., Clay Miner. 32, 587 (1997). Weiss, A., Thielepape, W., Ritter, W., Schafer, H., and Goring, G., Anorg. Allg. Chem. 320, 183 (1963). Weiss, A., Thielepape, W., and Orth, H., in “Proceedings, International Clay Conference Jerusalem I (L. Heller and A. Weiss, Eds.), pp. 277–293. Israel Univ. Press, Jerusalem, 1966. Barrios, J., Plan¸con, A., Cruz, M. I., and Tchoubar, C., Clays Clay Miner. 25, 422 (1977). Durig, J. R., Bush, S. F., and Mercer, E. E., J. Chem. Phys. 44, 4238 (1966). Tipton, T., Stone, D. A., KuBulat, K., and Person, W. B., J. Phys. Chem. 93, 2917 (1989).