Effect of water on the formamide-intercalation of kaolinite

The molecular structures of low defect kaolinite completely intercalated with formamide and formamide-water mixtures have been determined using a combination of X-ray diffraction, thermoanalytical techniques, DRIFT and Raman spectroscopy. Expansion of the kaolinite to 10.09 A was observed with subtle differences whether the kaolinite was expanded with formamide or formamide-water mixtures. Thermal analysis showed that greater amounts of formamide could be intercalated into the kaolinite in the presence of water. New infrared bands were observed for the formamide intercalated kaolinites at 3648, 3630 and 3606 cm(-1). These bands are attributed to the hydroxyl stretching frequencies of the inner surface hydroxyls hydrogen bonded to formamide with water, formamide and interlamellar water. Bands were observed at similar positions in the Raman spectrum. At liquid nitrogen temperature, the 3630 cm(-1) Raman band separated into two bands at 3633 and 3625 cm(-1). DRIFT spectra showed the hydroxyl deformation mode at 905 cm(-1). Changes in the molecular structure of the formamide are observed through both the NH stretching vibrations and the amide 1 and 2 bands. Upon intercalation of kaolinite with formamide, bands are observed at 3460, 3344, 3248 and 3167 cm(-1) attributed to the NH stretching vibration of the NH involved with hydrogen bonded to the oxygens of the kaolinite siloxane surface. In the DRIFT spectra of the formamide intercalated kaolinites bands are observed at 1700 and 1671 cm(-1) and are attributed to the amide 1 and amide 2 vibrations.     

Identification of superactive centers in thermally treated formamide-intercalated kaolinite

The thermal behavior of a formamide-intercalated mechanochemically activated (dry-ground) kaolinite was investigated by thermogravimetry-mass spectrometry (TG-MS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). After the removal of adsorbed and intercalated formamide, a third type of bonded reagent was identified in the temperature range 230-350 degrees C decomposing in situ to CO and NH3. The presence of formamide decomposition products, as well as CO2 and various carbonates identified by DRIFT spectroscopy, indicates the formation of superactive centers as a result of mechanochemical activation and heat treatment (thermal deintercalation). The structural variance of surface species decreases with the increase of grinding time. The unground mineral contains a small amount of weakly acidic and basic centers. After 3 h of grinding, the number of acidic centers increases significantly, while on further grinding the superactive centers show increased basicity. With the increase of grinding time and treatment temperature the number of bicarbonate- and bidentate-type structures decreases in favor of the carboxylate- and monodentate-type ones.     

The Modification of Hydroxyl Surfaces of Formamide-Intercalated Kaolinites Synthesized by Controlled Rate Thermal Analysis

Controlled rate thermal analysis (CRTA) technology made possible the separation of adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites. X-ray diffraction shows that the CRTA-treated formamide-intercalated kaolinites remain expanded after CRTA treatment. The Raman spectra of the CRTA-treated formamide-intercalated kaolinites are significantly different from those of the intercalated kaolinites with both intercalated and adsorbed formamide. An intense band is observed at 3629 cm(-1), attributed to the inner surface hydroxyls hydrogen bonded to the formamide. Broad bands are observed at 3600 and 3639 cm(-1) and are attributed to the inner surface hydroxyls, which are hydrogen bonded to the adsorbed water molecules. The hydroxyl stretching band of the inner hydroxyl is readily observed at 3621 cm(-1) in the Raman spectra of the CRTA-treated formamide-intercalated kaolinites. The results of thermal analysis show that the amount of intercalated formamide between the kaolinite layers is independent of the presence of water. The Raman bands of the formamide in the CRTA-treated intercalated kaolinites are readily observed. Copyright 2001 Academic Press.     

A DRIFT spectroscopic study of potassium acetate intercalated mechanochemically activated kaolinite

Kaolinite has been mechanochemically activated by dry grinding for periods of time up to 10 h. The kaolinite was then intercalated with potassium acetate and the changes in the structure followed by DRIFT spectroscopy. Intercalation of the kaolinite with potassium acetate is difficult and only the layers, which remain hydrogen bonded, are intercalated. The mechanochemical activation of the kaolinite may be followed by the loss of intensity of the hydroxyl-stretching vibrations. The intensity of the 3695 and 3619 cm(-1) bands reach a minimum after 10 h of grinding. The observation of a band at 3602 cm(-1) is indicative of the intercalation of the kaolinite with potassium acetate. The degree of intercalation decreases with mechanochemical treatment. The effect of exposure of the intercalated mechanochemically activated kaolinite to moist air results in de-intercalation. The effect of the mechanochemical treatment is loss of layer stacking, which prevents the intercalation of the kaolinite.     

Vibrational spectroscopy of formamide-intercalated kaolinites

The vibrational spectroscopy of low and high defect kaolinites fully and partially intercalated with formamide have been determined using a combination of X-ray diffraction, DRIFT and Raman spectroscopy. Expansion of the high defect kaolinite to 10.09 A resulted in a decrease in the peak width of the d(001) peak attributed to a decrease in defect structures upon intercalation. Changes in the defect structures of the low defect kaolinite were observed. Additional infrared bands were observed for the formamide intercalated kaolinites at 3629 and 3606 cm(-1). The 3629 cm(-1) band is attributed to the hydroxyl stretching frequency of the inner surface hydroxyl group hydrogen bonded to the carboxyl group of the formamide. The 3606 cm(-1) band is ascribed to water in the interlayer. Concomitant changes are observed in both the hydroxyl deformation modes and in the carboxyl bands.     

Modification of low- and high-defect kaolinite surfaces: implications for kaolinite mineral processing

A comparison is made of the mechanochemical activation of three low- and one high-defect kaolinite using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. The effect of mechanochemical alteration of the kaolinites is greater for the low-defect kaolinites. The effectiveness of the mechanochemical treatment is represented by the slope of the d(001) peakwidth-grinding time line. High-defect kaolinite is not significantly altered by the grinding treatment. The effect of mechanochemical treatment on peakwidth was independent of the presence of quartz; the quartz acts as an additional grinding medium. The effectiveness of the mechanochemical treatment depends on the crystallinity of the kaolinite. Two processes are identified in the mechanochemical activation of the kaolinite: first the delamination of kaolinite appears to take place in the first hour of grinding and second a recombination process results in the reaggregation of the ground crystals. During this process proton hopping occurs and reaction to form water takes place. This water is then adsorbed and coordinated to surface-active sites created during mechanochemical treatment.     

Modification of kaolinite surfaces through mechanochemical treatment--a mid-IR and near-IR spectroscopic study

The modification of kaolinite surfaces through mechanochemical treatment has been studied using a combination of mid-IR and near-IR spectroscopy. Kaolinite hydroxyls were lost after 10 h of grinding as evidenced by the decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm(-1) and the deformation modes at 937 and 915 cm(-1). Concomitantly an increase in the hydroxyl-stretching vibrations of water is observed. The mechanochemical activation (dry grinding) causes destruction in the crystal structure of kaolinite by the rupture of the O-H, Al-OH, Al-O-Si and Si-O bonds. Evidence of this destruction may be followed using near-IR spectroscopy. Two intense bands are observed in the spectral region of the first overtone of the hydroxyl-stretching vibration at 7065 and 7163 cm(-1). These two bands decrease in intensity with mechanochemical treatment and two new bands are observed at 6842 and 6978 cm(-1) assigned to the first overtone of the hydroxyl-stretching band of water. Concomitantly the water combination bands observed at 5238 and 5161 cm(-1) increase in intensity with mechanochemical treatment. The destruction of the kaolinite surface may be also followed by the loss of intensity of the two hydroxyl combination bands at 4526 and 4623 cm(-1). Infrared spectroscopy shows that the kaolinite surface has been modified by the removal of the kaolinite hydroxyls and their replacement with water adsorbed on the kaolinite surface. NIR spectroscopy enables the determination of the optimum time for grinding of the kaolinite. Further NIR allows the possibility of continual on-line analysis of the mechanochemical treatment of kaolinite.     

Kaolinite–urea complexes obtained by mechanochemical and aqueous suspension techniques—A comparative study

Intercalation compounds of low- and high-defect kaolinites have been prepared by direct reaction with urea aqueous solution as well as by co-grinding with urea in the absence of water (mechanochemical intercalation). The complexes formed were studied by X-ray diffraction, thermal analysis, DRIFT spectroscopy, and scanning electron microscopy. In aqueous solution the degree of intercalation for the low- and high-defect kaolinites was found to be 77 and 65%, respectively. With mechanochemical intercalation, both kaolinites were almost fully expanded after 1 h of grinding. Based on the results of DRIFT spectroscopy, a structural model for the bonding of urea to the siloxane surface is proposed. The kaolinite–urea intercalation compounds produced by mechanochemical intercalation have crystallite sizes lower than those obtained by the aqueous solution method.     

高岭石/甲酰胺插层的Raman和DRIFT光谱

用Raman和漫反射红外光谱研究高岭石/甲酰胺插层反应机理及插层作用对高岭石微结构的影响.     

Modification of the Kaolinite Hydroxyl Surfaces through the Application of Pressure and Temperature, Part III

Kaolinite hydroxyl surfaces have been modified by the combined application of heat and pressure in the presence of water at 120 degrees C and 2 bars and at 220 degrees C and 20 bars. X-ray diffraction shows that some of the layers are expanded. It is hypothesized that this expansion occurs at the edges of the crystals due to the intercalation of water. The X-ray diffraction data is supported by diffuse reflectance infrared spectroscopy, with additional hydroxyl stretching bands observed around 3550 and 3590 cm-1. These bands are attributed to adsorbed water and to edge-intercalated water. Additional bands are observed in the hydroxyl deformation region around 895 and 877 cm-1. The position of these bands depends on the defect structure of the kaolinite and the conditions under which the kaolinite was thermally treated. Additional water bending vibrations were observed at 1651 and 1623 cm-1 for the thermally treated high-defect kaolinite and at 1682 and 1610 cm-1 for the low-defect kaolinite. The bands at 1651 and 1682 cm-1 are attributed to the bending modes of water coordinated to the kaolinite surface. The role of water in the edge intercalation of water in the high- and low-defect kaolinites is apparently different. Copyright 1999 Academic Press.     

Investigation of mechanochemically modified kaolinite surfaces by thermoanalytical and spectroscopic methods

The effect of mechanochemical activation (dry grinding), formamide intercalation, and thermal deintercalation on high- and low-defect kaolinite surfaces was studied by thermogravimetry and diffuse reflectance Fourier transform infrared spectroscopy. These investigations were completed with specific surface area and pore size distribution measurements. The surface acidity of the ground and the ground-and-intercalated kaolinites was probed with ammonia adsorption. The surface area and the pore volume as well as the amount of adsorbed ammonia increased with the rate of mechanochemical activation. At the same time the thermally deintercalated minerals showed increased surface area but decreased pore volume with the time of grinding. Adsorbed ammonia was detected as ammonium ion in the 1400-1500 cm(-1) spectral range.     

Thermo-infrared-spectroscopy analysis of dimethylsulfoxide-kaolinite intercalation complexes

Dimethylsulfoxide (DMSO) kaolinite complexes of low-and high-defect kaolinites were studied by thermo-IR-spectroscopy analysis. Samples were gradually heated up to 170°C, three hours at each temperature. After cooling to room temperature, they were pressed into KBr disks and their spectra were recorded. From the spectra two types of complexes were identified. In the spectrum of type I complex two bands were attributed to asymmetric and symmetric H-O-H stretching vibrations of intercalated water, bridging between DMSO and the clay-O-planes. As a result of H-bonds between intercalated water molecules and the O-planes, Si-O vibrations of the clay framework were perturbed, in the low-defect kaolinite more than in the high-defect. Type II complex was obtained by the thermal escape of the intercalated water. Consequently, the H-O-H bands were absent from the spectrum of type II complex and the Si-O bands were not perturbed. Type I complex was present up to 120°C whereas type II between 130 and 150°C. The presence of intercalated DMSO was proved from the appearance of methyl bands. These bands decreased with temperature due to the thermal evolution of DMSO but disappeared only in spectra of samples heated at 160°C. Intercalated DMSO was H-bonded to the inner-surface hydroxyls and vibrations associated with this group were perturbed. Due to the thermal evolution of DMSO the intensities of the perturbed bands decreased with the temperature. They disappeared at 160°C together with the methyl bands.     

Deintercalation of hydrazine-intercalated kaolinite in dry and moist air

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 expanded to 10.66 A and remain expanded for up to 22 h upon exposure to moist air. Only upon deintercalation are the peak at 10.39 A and a minor peak at 9.6 A observed. Complete deintercalation takes up to 18 days more. Upon intercalation with hydrazine an intense band is observed at 3628 cm(-1) and is attributed to the inner-surface 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.     

H2 generation during dry grinding of kaolinite

H2 generation during mechanochemical treatment of kaolinite by dry grinding was examined by X-ray diffraction analysis, Fourier transform infrared spectroscopy, and BET surface area measurement. The H2 concentration in the mill pot, measured by gas chromatography, increased with grinding time up to a maximum concentration of 156 ppm (0.35 micromol) after 600 min. This H2 generation is considered to occur as a result of three processes: (1) structural destruction characterized by the delamination and loss of hydroxyl groups as a result of dry grinding, (2) transformation of liberated hydroxyls into water molecules by mechanochemical effects such as prototropy, and (3) H2 generation through reaction between surface water molecules and mechanoradicals created by the rupture of Si-O or Al-O-Si bonds. Although the surface area plateaued after 240 min grinding, the H2 concentration continued to increase, indicating that surface mechanoradicals are created during this later grinding stage. Thus, H2 generation can be used as an indicator of mechanoradical formation during mechanochemical treatment.     

Surface modification of mechanochemically activated kaolinites by selective leaching

Low- and high-defect kaolinites mechanochemically activated for different periods of time have been treated with sulfuric acid solution. These modified materials were analyzed using a combination of X-ray diffraction, thermogravimetry, chemical analysis, diffuse reflectance Fourier transform infrared spectroscopy, as well as specific surface area and pore size distribution measurements. In addition to the mechanochemically amorphized part, the disordered and the adequately distorted phases also reacted with sulfuric acid. The specific surface areas of the leached samples of the partially or the completely amorphized materials were found to be greater than those of the thermally amorphized ones. The acid treatment results in a greater total pore volume for the partially amorphized materials than for the totally amorphized mineral. The partially amorphized high-defect kaolinite was proved to be more soluble than the low-defect kaolinite under similar conditions.     

Near-infrared and mid-infrared investigations of Na-dodecylbenzenesulfate intercalated into hydrocalumite chloride (CaAl-LDH-Cl)

Hydrocalumite (CaAl-LDH-Cl) belongs to layered double hydroxides (LDHs). The intercalation of Na-dodecylbenzenesulfate (SDBS) into CaAl-LDH-Cl has been investigated by X-ray diffraction (XRD), mid-infrared (MIR) spectroscopy and near-infrared (NIR) spectroscopy. The mid-infrared spectra indicated that SDBS could be intercalated into CaAl-LDH-Cl, with the same lattice structure to that of CaAl-LDH-Cl, and the interlayer distance of resultant product was expanded to 2.78 nm as confirmed by XRD. The near-infrared spectra (9200-4000 cm(-1)) showed that a special spectral range from 6200 to 5600 cm(-1) and prominent bands of CaAl-LDH-Cl intercalated with SDBS around 8300 cm(-1). This band was assigned to the second overtone of the first fundamental of C-H stretching vibrations of SDBS, and can be used to determinate the result of CaAl-LDH-Cl modified by anionic surfactants. The bands of water stretching vibrations and -OH groups shifted to higher wavenumbers when CaAl-LDH-Cl was intercalated by SDBS, and their intensity of MIR and NIR spectra became lower in intensity.     

Raman spectroscopy of potassium acetate-intercalated kaolinites at liquid nitrogen temperature

Raman microscopy has been used to study low and high defect kaolinites and their potassium acetate intercalated complexes at 298 and 77 K. Raman spectroscopy shows significant differences in the spectra of the hydroxyl-stretching region of the two types of kaolinites, which is also reflected in the spectroscopy of the hydroxyl-stretching region of the intercalation complexes. Additional bands to the normally observed kaolinite hydroxyl stretching frequencies are observed for the low and high defect kaolinites at 3605 and 3602 cm(-1) at 298 K. Upon cooling to liquid nitrogen temperature, these bands are observed at 3607 and 3604 cm(-1), thus indicating a weakening of the hydrogen bond formed between the inner surface hydroxyls and the acetate ion. Upon cooling to liquid nitrogen temperature, the frequency of the inner hydroxyls shifted to lower frequencies. Collection of Raman spectra at liquid nitrogen temperature did not give better band separation compared to the room temperature spectra as the bands increased in width and shifted closer together.     

Thermal behavior analysis of kaolinite–dimethylsulfoxide intercalation complex

The thermal behavior of kaolinite?Cdimethylsulfoxide intercalation complex was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FT-IR) spectroscopic analysis. The samples gradually heated up to different temperatures were studied by XRD and FT-IR. The kaolinite?Cdimethylsulfoxide intercalation complex is stable below 130?°C. With the rise in the temperature, the relative intensity of the 1.124-nm peak gradually decreased and disappeared at 200?°C, however, the intensity of the 0.714?nm peak increased in the XRD patterns. In the infrared spectra, the appearance of methyl bands at 3018, 2934, 1428, and 1318?cm^?1 indicates the presence of intercalated dimethylsulfoxide, the intensities of these bands decreased with the temperature rising and remained until around 175?°C, which agree with the XRD and TG?CDSC data.     

Thermo-X-ray-diffraction analysis of dimethylsulfoxide-kaolinite intercalation complexes

DMSO-kaolinite complexes of low- and high-defect Georgia kaolinite (KGa-1 and KGa-2, respectively) were investigated by thermo-XRD-analysis. X-ray patterns showed that DMSO was intercalated in both kaolinites with a d(001)-value of 1.11 nm (type I complex). The samples were gradually heated up to 170°C and diffracted by X-ray at room-temperature. With the rise in temperature, due to the thermal evolution of the guest molecules, the relative intensity of the 1.11 nm peak decreased and that of the 0.72 nm peak (neat kaolinite) increased indicating that the fraction of the non-intercalated tactoids increased. The 1.11 peak disappeared at 130–140°C. During the thermal treatment of both complexes two additional peaks appeared at 110 and 120°C, respectively, with d-values of 0.79–0.94 and 0.61–0.67 nm in DMSO-KGa-1 and 0.81–0.86 and 0.62–0.66 nm in DMSO-KGa-2, indicating the formation of a new phase (type II complex). The new complex was obtained by the dehydration of type I complex and was composed of intercalated DMSO molecules which did not escape. The new peaks disappeared at 150–160°C indicating the complete escape of DMSO.     

Intensities of IR stretching bands as a criterion of polarization and initial chemical activation of adsorbed molecules in acid catalysis. Ethane adsorption and dehydrogenation by zinc ions in ZnZSM-5 zeolite

A DRIFT study of ethane adsorbed by zinc cations in ZnZSM-5 prepared by chemical reaction of the hydrogen form of the zeolite with zinc vapor at 770 K, or by wet ion exchange, reveals unusual spectra of adsorbed C2H6 species. In addition to the weakly perturbed narrow bands in the region of C-H stretching vibrations, these spectra exhibit a very intense broad IR band with a frequency that is more than 200 cm(-1) lower than those of the C-H stretching vibrations of gaseous or physically adsorbed ethane. The very high relative intensity of this band indicates a very strong polarizability of the corresponding vibrational mode. It is concluded that these strongly polarized vibrations are closely connected with the subsequent heterolytic dissociation of ethane at moderately elevated temperatures, resulting in the formation of acidic hydroxyl groups and zinc ethyl fragments. At higher temperatures, the zinc ethyl fragments decomposed, resulting in the formation of zinc hydrides and ethylene. The unusual DRIFT spectrum of the molecular form of ethane adsorption by zinc cations represents a first example of anisotropy of polarizability of adsorbed molecules, which may provide a new explanation for selectivity of the acid-catalyzed reactions. In this connection, it is suggested to use the relative intensities of IR bands of adsorbed molecules as a reactivity index that is directly connected with chemical activation of adsorbed molecules via their polarization by the active sites.