Qinfu Liu

MAS NMR study of surface-modified calcined kaolin

Abstract Calcined kaolins, modified by a silane coupling agent, were analyzed by magic angle spinning nuclear magnetic resonance (MAS NMR) and compared to unmodified samples. The results show no chemical shift for 29 Si, whereas there is a marked change for 27 Al. The chemical shifts of 5.44 and 65.69 ppm of 27 Al in unmodified samples are respectively moved to 3.8–4.4 and 54.6–59.9 ppm after modification. This is attributed to changes in the chemical environment around the surface Al ions on the calcined kaolin resulting from chemical bonding of the silane coupling agent molecules to the Al. The results demonstrate that MAS NMR is a useful technique for characterizing the surface modification mechanisms of minerals.

Delamination of kaolinite–potassium acetate intercalates by ball-milling

Structural changes in intercalated kaolinite after wet ball-milling were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area (SSA) and Fourier transform infrared spectroscopy (FT-IR). The X-ray diffraction pattern at room temperature indicated that the intercalation of potassium acetate into kaolinite caused an increase of the basal spacing from 0.718 to 1.42 nm, and with the particle size reduction. The surface area increased sharply with the intercalation and delamination by ball-milling. The wet ball-milling kaolinite after intercalation did not change the structural order, and the particulates have high aspect ratio according SEM images.

A spectroscopic comparison of selected Chinese kaolinite, coal bearing kaolinite and halloysite : a mid-infrared and near-infrared study

Mid-infrared (MIR) and near-infrared (NIR) spectroscopy have been compared and evaluated for differentiating kaolinite, coal bearing kaolinite and halloysite. Kaolinite, coal bearing kaolinite and halloysite are the three relative abundant minerals of the kaolin group, especially in China. In the MIR spectra, the differences are shown in the 3000-3600 cm⁻¹ between kaolinite and halloysite. It cannot obviously differentiate the kaolinite and halloysite, leaving alone kaolinite and coal bearing kaolinite. However, NIR, together with MIR, gives us the sufficient evidence to differentiate the kaolinite and halloysite, especially kaolinite and coal bearing kaolinite. There are obvious differences between kaolinite and halloysite in all range of their spectra, and they also show some difference between kaolinite and coal bearing kaolinite. Therefore, the reproducibility of measurement, signal to noise ratio and richness of qualitative information should be simultaneously considered for proper selection of a spectroscopic method for mineral analysis.

Infrared and infrared emission spectroscopic study of typical Chinese kaolinite and halloysite.

The structure and thermal stability between typical Chinese kaolinite and halloysite were analysed by X-ray diffraction (XRD), infrared spectroscopy, infrared emission spectroscopy (IES) and Raman spectroscopy. Infrared emission spectroscopy over the temperature range of 300-700°C has been used to characterise the thermal decomposition of both kaolinite and halloysite. Halloysite is characterised by two bands in the water bending region at 1629 and 1648 cm(-1), attributed to structural water and coordinated water in the interlayer. Well defined hydroxyl stretching bands at around 3695, 3679, 3652 and 3625 cm(-1) are observed for both kaolinite and halloysite. The 550°C infrared emission spectrum of halloysite is similar to that of kaolinite in 650-1350 cm(-1) spectral region. The infrared emission spectra of halloysite were found to be considerably different to that of kaolinite at lower temperatures. These differences are attributed to the fundamental difference in the structure of the two minerals.

Mechanism of kaolinite sheets curling via the intercalation and delamination process.

Kaolinite naturally occurs in the plate form for the interlayer hydrogen bond and the distortion and adaption of tetrahedron and octahedron. But kaolinite sheets can be exfoliated to nanoscrolls artificially in laboratory through multiple-step displacement intercalation. The driving force for kaolinite sheet to be curled nanoscroll originates from the size discrepancy of Si-O tetrahedron and Al-O octahedron. The displacement intercalation promoted the platy kaolinite sheets spontaneously to be scrolled by eliminating the interlayer hydrogen bond and atomic interaction. Kaolinite nanoscrolls are hollow tubes with outer face of tetrahedral sheet and inner face of octahedral sheet. Based on the theoretical calculation it is firstly reported that the minimum interior diameter for a single kaolinite sheet to be scrolled is about 9.08 nm, and the optimal 24.30 nm, the maximum 100 nm, which is verified by the observation of scanning electron microscope and transmission electron microscope. The different adaption types and discrepancy degree between tetrahedron and octahedron generate various curling forces in different directions. The nanoscroll axes prefer the directions as [100], [11¯0], [110], [31¯0], and the relative curling force are as follows, [31¯0]>[100]=[11¯0]>[110].

Insight into morphology and structure of different particle sized kaolinites with same origin.

The particle size, morphology, crystallinity order and structural defects of four kaolinite samples are characterized by the techniques including particle size analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The particle size of four kaolinite samples gradually increases. Four samples all belong to the ordered kaolinite and show a decrease in structural order with the increase of kaolinite particle size. The changes of structural defect are proved by the increase of the band splitting in Raman spectroscopy, the decrease of the intensity of absorption bands in infrared spectroscopy, and the decrease of equivalent silicon atom and the increase of non-equivalent aluminum atom in MAS NMR spectroscopy. The differences in morphology and structural defect are attributed to the broken bonds of Al-O-Si, Al-O-Al and Si-O-Si and the Al substitution for Si in tetrahedral sheets.

An infrared spectroscopic comparison of four Chinese palygorskites.

Infrared spectroscopy has been used to characterize and compare four palygorskite mineral samples from China. The position of the main bands identified by infrared spectra is similar, but there are some differences in intensity, which are significant. In addition, several additional bands are observed in the spectra of palygorskite and their impurities. This variability is attributed to differences in the geological environment, such as the degree of weathering and the extent of transportation of the minerals during formation or deposition, and the impurity content in these palygorskites. The bands of water and hydroxyl groups in these spectra of palygorskite samples have been studied. The characteristic band of palygorskite is observed at 1195 cm(-1). Another four bands observed at 3480, 3380, 3266 and 3190 cm(-1) are attributed to the water molecules in the palygorskite structure. These results suggest that the infrared spectra of palygorskites mineral from different regions are decided not only by the main physicochemical properties of palygorskite, but also by the amount and kind of impurities.

Molecular-Level Investigation of the Adsorption Mechanisms of Toluene and Aniline on Natural and Organically Modified Montmorillonite.

The present work reports the adsorption mechanisms of aniline and toluene in dry and hydrated montmorillonite (MMT-Na and MMT-Na-W) and tetramethylammonium-cation-modified MMT (MMT-TMA) as determined through density functional theory. These theoretical investigations explicitly demonstrate that cation-π interactions between Na(+)/TMA(+) cations and aromatics play the key role in adsorption of organics over MMT-Na and MMT-TMA. Weak hydrogen bonds between the H atoms of organics and basal O atoms of tetrahedral silicate also stabilize the location of organics. The combination of interactions between water and basal O atoms and between organics and water molecules in hydrated MMT complexes strengthens the adsorption of organics on MMT, resulting in higher formation energies in hydrated organically intercalated MMTs than in the corresponding dry complexes. The adsorption of organics also changes frontier orbital distributions and consequently promotes the preferential occurrence of reactions on the organics rather than on the MMT layers. These adsorption mechanisms predicted by theoretical investigation can be used to explicate the adsorption of aromatic organics on aluminosilicates with different external environment.

The origins of kaolinite-rich rocks associated with coal measures in China

Abstract Kaolinite-rich rocks are widespread in Chinese coal-bearing strata. Three main types of deposits are recognized. Those deposits identified as flint clays are several metres thick and show lateral variations in bed composition. The kaolinite is thought to have formed mainly on the adjacent landmass, but some crystallization of gels within the basin is not ruled out. Tonsteins, which formed from the in situ alteration of airfall volcanic ashes, are very common in the coal measures and are up to 0.5 m thick. Finally, kaolinite deposits are described where the development of kaolin is related to weathering of coals either close to or at the present land surface.

The molecular structure of chloritoid: A mid-infrared and near-infrared spectroscopic study

The mineral chloritoid collected from the argillite in the bottom of Yaopo Formation of Western Beijing was characterized by mid-infrared (MIR) and near-infrared (NIR) spectroscopy. The MIR spectra showed all fundamental vibrations including the hydroxyl units, basic aluminosilicate framework and the influence of iron on the chloritoid structure. The NIR spectrum of the chloritoid showed combination (ν+δ)OH bands with the fundamental stretching (ν) and bending (δ) vibrations. Based on the chemical component data and the analysis result from the MIR and NIR spectra, the crystal structure of chloritoid from western hills of Beijing, China, can be illustrated. Therefore, the application of the technique across the entire infrared region is expected to become more routine and extend its usefulness, and the reproducibility of measurement and richness of qualitative information should be simultaneously considered for proper selection of a spectroscopic method for the unit cell structural analysis.