Inner-surface OH Research Articles

Influence of Synthesis Conditions on the Formation of a Kaolinitemethanol Complex and Simulation of its Vibrational Spectra

AbstractKaolinite is often used as a base for the synthesis of new organo-mineral nanomaterials designed for applications in industry and in environmental protection. To make the mineral structure more likely to interact with organic molecules, a kaolinite-methanol complex (KM) can be used. In the present study, different experimental procedures were tested to investigate the formation of the KM. The kaolinitedimethyl sulfoxide intercalation compound (KDS), either wet or dried, was used as a pre-intercalate. The samples obtained were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, CHNS elemental analysis, 13C CP-magic angle spinning nuclear magnetic resonance (MAS NMR), and 27Al and 29Si MAS NMR techniques. The method of density functional theory with dispersion corrections (DFT-D2) was used to explain the structure and to simulate the vibrational spectra of KM. Theoretical results were compared with experimental data. The most effective formation of the KM (d001 = 11.1 Å — wet; d001 = 8.7 Å — dried) was observed when the dried KDS precursor was used. In such conditions the degree of intercalation reached ~98% after 24 h of reaction time. As indicated by the CHNS elemental analysis, ~1/6 of the inner-surface OH groups were grafted by OCH3 groups. The esterification reaction was less efficient at higher temperatures or when wet KDS was used. In the latter case, the excess of very polar dimethyl sulfoxide molecules prevented intercalation of methanol and further grafting. Detailed analysis of the results of theoretical simulations revealed that the reaction of the KDS with methanol led to the formation of kaolinite with both grafted methoxy groups and intercalated methanol, and water molecules in the interlayer space. The spectra calculated revealed the contribution of individual vibrational modes into the complex bands, i.e. the energy of C-H vibrations was in the order: νasCHmet > νasCHmtx > νsCHmet > νsCHmtx.

Separation of Adsorbed and Intercalated Hydrazine in Hydrazine-Hydrate Intercalated Kaolinite by Controlled-Rate Thermal Analysis

The thermal behavior of a low-defect kaolinite fully expanded with hydrazine-hydrate has been investigated in a nitrogen atmosphere at a constant, preset decomposition rate of 0.15 mg/min. Under controlled-rate thermal analysis (CRTA) conditions, it was possible to distinguish between loosely bonded (adsorbed) and strongly bonded (intercalated) reagent. The loosely bonded reagent is connected to the internal and external surfaces of the expanded mineral and is present as a space filler between the sheets of the delaminated mineral. The strongly bonded hydrazine-hydrate is connected to the kaolinite inner-surface OH groups by the formation of hydrogen bonds. Based on the thermoanalytical results, three different types of bonded reagent could be distinguished in the complex. Type 1 reagent (approximately 0.20 mol hydrazine-hydrate/mol inner-surface OH) is liberated between approximately 50 and 70 °C. Type 2 reagent is lost between approximately 70 and 85 °C, corresponding to a quantity of 0.12−0.15 mol hydr...

New data on the kaolinite-potassium acetate complex

AbstractThe intercalation complex of kaolinite and potassium acetate (KAc) was studied by HTXRD, IR spectroscopy and DTA-TG. The HTXRD patterns indicate that the 14.06 Å basal spacing of the complex contracts to 11.77 Å and 9.35 Å after heating at 60°C. The DTA-TG data indicate that water is present in these new complexes, the decomposition of which occurs between 290°C and 400°C. Modifications observed in the high-frequency region of the spectra obtained after heating suggest that K ions occupy the ditrigonal holes in the OH surface of the kaolinite layers, whereas water is probably located between the KAc layer and the OH surface of the kaolinite. This structural arrangement would favour the H-bonding between inner-surface OH groups and water and justifies the presence of new bands at lower frequencies. Electrostatic interactions between the keyed K ions and O of the inner OH groups would justify the modifications of the 3619 cm-1 OH-stretching band.

New Techniques for Studying the Intercalation of Kaolinites from Georgia with Formamide

AbstractA new technique utilizing Raman microscopy and Fourier transform infrared (FTIR) microsacopy is described. This technique uses thin films of oriented clay aggregates on glass slides suitable also for X-ray diffraction (XRD). Raman microscopy proved the most useful technique providing both better resolution of the OH-stretching bands and greater spectral resolution. Kaolinites from Washington County, Georgia, with varying defect structures involving layer stacking were intercalated with formamide and additional Raman bands were observed at 3610 and 3627 cm−1. A concomitant decrease in the inner-surface OH band intensities at 3695 and 3685 cm−1 occurred. These bands are attributed to the inner-surface OH hydrogen bonded to the formamide molecule through the C=O group. The 3627 cm−1 band is sharp with a half width of 7.5 cm−1 and comprises 11% of the total normalized band area. When two additional OH bands are observed at 3610 and 3627 cm−1 two C=O bands at 1674 and 1658 cm−1 are observed also. The two additional Raman inner-surface OH bands were not observed in the IR spectra. However, a band of low intensity was observed at 3590 cm−1. Models for the intercalation of formamide in kaolinites are proposed.

New Data on the Kaolinite-Potassium Acetate Complex

The intercalation complex of kaolinite and potassium acetate (KAc) was studied by HTXRD, IR spectroscopy and DTA-TG. The HTXRD patterns indicate that the 14.06 Aa basal spacing of the complex contracts to 11.77 Aa and 9.35 Aafter heating at 60 degrees C. The DTA-TG data indicate that water is present in these new complexes, the decomposition of which occurs between 290 degrees C and 400 degrees C. Modifications observed in the high-frequency region of the spectra obtained after heating suggest that K ions occupy the ditrigonal holes in the OH surface of the kaolinite layers, whereas water is probably located between the KAc layer and the OH surface of the kaolinite. This structural arrangement would favour the H-bonding between inner-surface OH groups and water and justifies the presence of new bands at lower frequencies. Electrostatic interactions between the keyed K ions and O of the inner OH groups would justify the modifications of the 3619 cm (super -1) OH-stretching band.

Differing Effects of Particle Size and Shape in the Infrared and Raman Spectra of Kaolinite

A B S T R ACT : Infrared (IR) spectra of well-ordered kaolinites generally show four OH-stretching frequencies, near 3697, 3670, 3652 and 3620 cm i. Raman spectra of the same kaolinites mostly show an additional band near 3686 cm -~, which, in the coarsely crystalline Keokuk kaolinite, largely replaces the 3695 cm -I band. It is shown that the 3686 cm ~ band can be ascribed to a transverse optical crystal vibration involving the in-phase stretching vibration of the three inner-surface hydroxyl groups in the unit-cell. Raman exciting radiation, commonly of wavelength near 500 nm, can excite this crystal vibration in crystals of comparable and greater thickness. Infrared studies are usually made on clay-size (<2 ~tm) particles, which have mean thicknesses of 30-150 nm. Infrared radiation of wavelength near 2.7 gm can only excite whole crystal vibrations perpendicular to the plates. The in-phase vibration of inner-surface OH groups in the whole-crystal mode lies at 3697 cm -1, which is the same frequency as that of the longitudinal optical mode in macroscopic crystals.

Rietveld Refinement of the Kaolinite Structure at 1.5 K

AbstractThe crystal structure of Keokuk kaolinite, including all H atoms, was refined in space group C1 using low-temperature (1.5 K) neutron powder diffraction data (λ = 1.9102 Å) and Rietveld refinement/difference-Fourier methods to Rwp = 1.78%, reduced χ2 = 3.32. Unit-cell parameters are: a = 5.1535(3) Å, b = 8.9419(5) Å, c = 7.3906(4) Å, α = 91.926(2)°, β = 105.046(2)°, γ = 89.797(2)°, and V = 328.70(5) Å3. Unit-cell parameters show that most of the thermal contraction occurred along the [001] direction, apparently due to a decrease in the interlayer distance. The non-H structure is very similar to published C1 structures, considering the low temperature of data collection, but the H atom positions are distinct. The inner OH group is essentially in the plane of the layers, and the inner-surface OH groups make angles of 60°–73° with the (001) plane. Difference-Fourier maps show minor anisotropy of the inner-OH group in the [001] direction, but the inner-surface OH groups appear to have their largest vibrational (or positional disorder) component parallel to the layers. Although no data indicate a split position of any of the H sites in kaolinite, there is support for limited random positional disorder of the H atoms. However, these data provided no support for a space group symmetry lower than C1.

Attribution of the OH stretching bands of kaolinite

AbstractExamination of the infrared spectra of synthetic kaolinites, with various degrees of substitution of hydroxyls by OD groups, allows a more detailed attribution of the stretching bands due to inner-surface hydroxyls of kaolinite. Among the three innersurface OH groups of the unit cell, two are nearly perpendicular to the sheet and give coupled vibrations which are responsible for the bands around 3695 and 3670 cm−1; the band near 3655 cm−1 is due to the other hydroxyl, which is lying close to the sheet.

Infra-red study of the interaction between caesium chloride and kaolinite

The interaction of CsCl with kaolinite leads to delamination of the tactoid followed by hydration of the kaolinite layer. A kaolinite-CsCl-H2O complex is obtained. The 3700, 3674 and 3657 cm–1 OH stretching bands of kaolinite are shifted to 3606, 3588 and 3507 cm–1. The AlOH deformation bands are also shifted from 937 and 912 cm–1 to 900 cm–1. These shifts may be due to weak hydrogen bonding between the sorbed water molecules and the inner-surface OH groups. Most of the bands which are associated with perpendicular vibrations are sharpened.

A study of hydroxyl groups in kaolin minerals utilizing selective deuteration and infrared spectroscopy

AbstractThe OH-OD exchange of kaolin minerals through contact with D2O introduced into interlayer space via intersalation resulted in a partial shift of the OH absorption bands. The total decrease in OH absorbance upon deuteralion was 52, 56, and 47% for the kaolinite, dickite-nacrite, and halloysite respectively, but the percentage decrease differed for the different absorption maxima of any one mineral. A secondary OH—OD exchange in the deuterated specimens was also observed upon heating to 350 and 400° C. These data together with the lack of deuteration in montmorillonite, and available orientation data on the kaolin OH groups by infrared spectroscopy, suggest that only two-thirds of the inner-surface OH groups form the interlayer OH—O bonds.

Infrared studies of hydrogen bonding interaction between kaolinite surfaces and intercalated potassium acetate, hydrazine, formamide, and urea

Expansion of kaolinite by intercalation of urea, formamide, hydrazine, and potassium acetate permits infrared studies of deuterium exchange and hydrogen bonding interaction of CO and NH 2 groups with the internal mineral surfaces. Intercalation of kaolinite with potassium acetate increases the d 001 spacing from 7.13 A. to 11.6 A., and the 3695 cm. −1 absorption band is shifted to 3600 cm. −1 owing to weak hydrogen bonding between the acetate anion and the OH groups. Intercalation of hydrazine within the kaolinite structure increases the ν(NH 2) stretching frequency from 3338 cm. −1 for the liquid to 3365 cm. −1 for the intercalated molecules. The asymmetric and symmetric ν(NH 2) stretching frequencies of liquid formamide are shifted from 3420 and 3340 cm. −1 to 3500 and 3380 cm. −1, respectively, in the formamide-kaolinite complex. In the urea-kaolinite complex, the asymmetric and symmetric ν(NH 2) stretching frequencies at 3500 and 3380 cm. −1 correspond to NH 2 groups interacting with the oxygens located on the basal tetrahedral layer; bands at 3520 and 3415 cm. −1 are assigned to similar NH 2 groups involved in weak hydrogen bonding with the inner-surface OH.