Low-defect Kaolinite Research Articles

High- and low-defect kaolinite for brick making: Comparisons of technological properties, phase evolution and microstructure

Kaolinite is among the most common clay minerals in the starting material for fired brick production. The complex geological origin of kaolinite creates different defects in its structure which may affect the sintering behavior and thus, properties of brick products. In this study, two Source Clays (KGa-1 and KGa-2) from the Clay Minerals Society have been employed as kaolinite sources to create a unique KIQF (kaolinite-illite-quartz-feldspar) system. The impacts of kaolinite defects on the microstructure, phase composition, physical, mechanical and thermal properties of fired brick buttons have been investigated. With increased firing temperature, brick products prepared with high-defect kaolinite exhibit steeper decrease of water absorption and increase of bulk density. When the temperature is below 1050 °C, CHK has higher water absorption than that of CLK. The water absorption and bulk density of brick buttons with different kaolinites are comparable (∼11.30 % and ∼ 1.95 g/cm3, respectively) after 1150 °C. For brick buttons (containing different kaolinites) fired at 850, 1050 and 1150 °C, no significant difference is observed in their color, XRD phase composition, or compressive strength. However, at 950 °C, high-defect kaolinite particles in the brick matrix display lower porosity of 41.52 % and a 2D mean pore size of 9.78 µm2 than that of low-defect kaolinite particles (51.19 % and 10.36 µm2, respectively), and this can be attributed to finer particles and a higher amount of Fe (1.08 %) in the former, which promotes vitrification. Smaller pores and a higher amount of spinel formed using high-defect kaolinite have resulted in a 7.1 % higher compressive strength. In addition, between 850 and 1150 °C, the thermal diffusivity of brick buttons with high-defect kaolinite is consistently higher. Thus, 950 °C is a crucial firing temperature when both higher compressive strength and thermal diffusivity of brick buttons are required. In addition, if lower porosity is required, 1050 °C or higher firing temperature is recommended for high-defect kaolinite.

Eco-friendly mechanochemical intercalation of imidazole into kaolinite

In this work, we developed the first simple and eco-friendly mechanochemical solvent-free intercalation of imidazole into low-defect kaolinite. Results obtained by X-ray diffraction showed that imidazole could be intercalated by a co-grinding method with different intercalation ratios (InR) without loss of the stacking between the layers of the kaolinite after the co-grinding. An InR value of 92% was obtained for imidazole after 10 ​h of co-grinding using a ball mill. In addition, SEM and TEM results showed that the mechanical forces led to a decrease in particle size. The mechanochemical intercalation of imidazole into kaolinite was also investigated by Fourier transform infrared spectroscopy (FTIR) and density functional theory calculations, using a cluster model of Al10O38H46 and Si10O30H20 to represent both surfaces of the mineral. Results suggest that imidazole is stabilized into kaolinite interlayer surfaces mainly due to strong n(N)→σ∗(O–H) hydrogen bonding formation with the Al–O surface.

Mechanochemical intercalation of low reactivity kaolinite

Complete urea-intercalation of a low reactivity kaolinite from Birdwood has been carried out by co-grinding with urea in the absence of water (mechanochemical intercalation). The effectiveness of mechanochemical intercalation was compared to solution intercalation by X-ray diffraction (XRD), thermal analysis (TG, DTG), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy and scanning electron microscopy (SEM). In aqueous solution of urea the Birdwood kaolinite was intercalated with difficulty and only 12% intercalation was achieved. After 2h of co-grinding with solid urea, complete (100%) intercalation was attained. The possible explanation of complete intercalation is that co-grinding of Birdwood kaolin with solid urea can remove the high-defect kaolinite coating, which prevents the intercalation of the low-defect kaolinite particles. The mechanochemical treatment increased the degree of intercalation and in parallel reduced the amount of the crystalline kaolinite phase.

Atomic-level studies of the depletion in reactive sites during clay mineral dissolution

Clay mineral dissolution rates can continuously decrease over time as reactive sites located on edges are preferentially depleted under certain pH conditions. Changes in reactive surface area and the difficulties in quantifying this elusive variable have been cited as one key reason for the complexity in developing accurate rate equations for the dissolution of clay minerals. Recently, a solid-state nuclear magnetic resonance (NMR) method has been proposed for counting the number of reactive surface sites on a defined quantity of a clay mineral. Using this solid-state NMR proxy, changes in reactive surface area were monitored for a series of batch dissolution experiments of low-defect kaolinite KGa-1b and Ca-rich bentonite STx-1b, a montmorillonite-rich clay containing an opal-CT impurity, at 21°C and initial pH 3. Kaolinite specific surface area as determined from BET gas isotherm data did not change within error during 80days of dissolution whereas bentonite specific surface area decreased rapidly to about 50% of the original value as interlayer cation concentrations changed. The solid-state NMR proxy revealed decreases in the number of reactive surface sites per gram of kaolinite and bentonite as a function of dissolution time, presumed to be from the preferential dissolution of reactive sites on edges at initial pH 3. This depletion of reactive edge sites can be tied to a concomitant decrease in the rates of release of Si and Al into solution. The quantity of reactive sites can be used to estimate the dissolution rates of kaolinite and bentonite as well as estimate trends in dissolution rates of other clay minerals. These results further highlight the need to quantify the number of reactive sites present on a per gram basis as well as characterize their depletion with time to develop and use dissolution rate models for clay minerals and other heterogeneous materials in the environment.

Clay mineral-enhanced bioremediation of marine oil pollution

Three year old laboratory mixtures of Prestige oil, Atlantic sea water and various types of clay mineral powder (Na- and Ca-smectites, palygorskite, synthetic mica-montmorillonite and a low defect kaolinite) contained significantly lower concentrations of extracted oil than the non-clay containing control. As no significant quantities of oil could be detected in the clay samples following solvent extraction, and no expansion of the viscous oil-treated smectite interlayers could be detected by X-ray diffraction, the measured hydrocarbon content is suggested to provide a reasonable estimate of the total oil present. The observed decrease in the concentration of oil over the reaction period is attributed largely to bacterial digestion rather than to hydrocarbon adsorption, with denser populations of cultured oleophilic bacteria in the more strongly digested samples. Overall, the smectites with high specific surface areas and cation exchange capacities induced the highest degree of oil breakdown, and also stimulated the digestion of the heavier aromatic and resin–asphaltene compounds. The presence of bivalent cations at interlayer sites and hydrated surfaces, including abundant Mg 2+ derived from sea water, is suggested to minimize the thickness of the diffuse ion layer and thus enhance both inorganic and organic nutrient supply from mineral surface to bacterial cell. Adding clay minerals to marine oil pollution is therefore suggested as an effective and economically interesting way of enhancing the bacterial digestion of contaminating spills.

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.

Characterization of changes of low and high defect kaolinite after bioleaching

Two samples of well and poorly ordered kaolinites KG1 and KG2 (designated according to a Handbook for Clay Minerals) have been studied with the aim to describe their structure after biological leaching and removal of iron that decreases the refractoriness of products made of various kaolins. The influence of the biological treatment by silicate bacteria of Bacillus spp. on the process of impurities dissolution was evaluated by the changes occurring on the surface and in the structure of the minerals. The bioleaching of clays and extraction of Fe, Al and Si were performed during 100 days lasting incubation and the products were characterized by XRD, granulometric analyses, EDX and nitrogen adsorption techniques. The qualitative changes of the particles surface charge were measured by the electrophoretic mobility of particles in the electric field.

A new kaolinite order index based on XRD profile fitting

AbstractThe determination of kaolinite order-disorder by X-ray diffraction is problematic due to overlapping peaks from associated kaolin minerals and X-ray amorphous phases. This paper presents a new index (Aparicio-Gala´n-Ferrell index — AGFI), measured on 02land 11lreflections after decomposing individual peaks in the complex diffraction band in an effort to reduce interferences. The new index was tested with three kaolins, of varying structural order, and their admixtures containing different percentages of quartz, feldspar, illite, smectite, chlorite, halloysite and Fe hydroxides and silica gels. The AGFI is highly correlated with the percentage of low-defect kaolinite and the Hinckley Index. It is not as prone to interference by associated minerals and X-ray amorphous phases as other indices. The AGFI can be used to determine kaolinite order-disorder in a wide variety of kaolins and kaolinitic rocks; the only prerequisite is that the kaolinite content should be >10 wt.% in order for the results to be reproducible.

Estudo por microscopia eletrônica das transformações durante a queima de argilas altamente aluminosas brasileiras

Duas argilas altamente aluminosas gibbsíticas, utilizadas em produtos refratários, foram estudadas por métodos óptico-eletrônicos, com a finalidade de caracterizar a seqüência de fases formadas durante transformações térmica. As argilas na forma de pós foram queimadas sobre placas de platina entre 200 ºC e 1500 ºC e com resfriamento programado. Após o aquecimento a 300 ºC, foi possível distinguir no microscópio eletrônico de transmissão entre cristais hexagonais de gibbsita e de caulinita, tendo o mesmo tamanho e forma. As transformações de fase da gibbsita e os cristais de caulinita pouco defeituosos seguem series independentes até 1100 ºC / 1200 ºC. Foi fácil distinguir morfologicamente os pseudomorfos das aluminas-chi e -kapa dos pseudomorfos dos cristais da caulinita e da metacaulinita no intervalo 400 ºC / 800 ºC. Cristais de espinélio alongados podem ser caracterizados dentro dos pseudomorfos da metacaulinita a 900 ºC. A mulita, em ambas as argilas, aumenta em teor e nas dimensões dos cristais de 900 ºC / 1550 ºC, enquanto o teor de alumina-alfa cresce até 1300 ºC e decresce em seguida até 1550 ºC, indicando haver interações entre as diversas fases, especialmente entre sílica e alumina-alfa.

The Effect of Pressure on Order/Disorder in Kaolinite Under Wet and Dry Conditions

AbstractWell ordered kaolinite was isostatically and uniaxially pressurized up to 13,200 kg/cm2 for 10 min in dry conditions and the effects of pressure on kaolinite order were determined by analyzing the shapes of two-dimensional diffraction bands on X-ray powder diffraction patterns. Increased pressure decreased the percentage of low-defect kaolinite phase, and isostatic pressure proved to be more effective than uniaxial pressure in increasing disorder, e.g. the degree of disorder resulting from 2000 kg/cm2 isostatic pressure was equivalent to that caused by a 3200 kg/cm2 uniaxial pressure. Also, the effect of high pressure was similar to that obtained with lower pressures applied several times (e.g. the effect of applying 8500 kg/cm2 pressure for 10 min was comparable to using 3200 kg/cm2 pressure five times).In addition, six kaolinites of different structural order were isostatically pressurized up to 4000 kg/cm2 for 10 min, both in dry and wet (water) conditions. Under dry conditions, changes in structurally ordered kaolinite were comparable to those cited above whereas kaolinite pressurized in wet conditions showed a moderate improvement in structural order.These results may contribute to our understanding of kaolinite behavior during burial diagenesis and low-grade metamorphism. In addition, these results can also be used in industry to improve kaolin technological properties that depend on kaolinite structural order by application of appropriate industrial pressure processes.

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.

Influence of the particle-size reduction by ultrasound treatment on the dehydroxylation process of kaolinites

Kaolinites from well-known sources (KGa-1 and KGa-2) were used to study the influence of the particle-size reduction on the dehydroxylation process. Size reduction of particles was obtained by ultrasound treatment to avoid the effect of the progressive amorphization of the structure, which takes place with the traditional grinding treatment. The particle-size reduction causes an increase of the mass loss between 140 and 390°C attributed to the loss of the hydroxyl groups exposed on the external surface of kaolinite; a shift to lower temperatures of the endothermic effect related with the mass loss between 390 and 600°C; and a shift of the end of dehydroxylation to lower temperatures. The first modification can be explained by an increase of the number of hydroxyls exposed on the external surface of kaolinite which is proportional to the new surface generated in the particle reduction process, whereas the shift of the dehydroxylation to lower temperatures is related to the reduction of the dimensions of the particles which favour the diffusion controlled mechanisms. Comparing between the DTA curves to the TG curves of the studied samples shows that the observed modifications in the thermal properties induced by the particle-size reduction are greater for the low-defect kaolinite. The intensity of these modifications depends on the effectiveness of the ultrasound treatment.

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.

The effects of grinding on the structure of a low-defect kaolinite

Numerous studies have demonstrated the presence of at least two distinct kaolinites in individual kaolinite samples, one a low-defect material and the other a moderate- to high-defect material. Other studies have shown that some kaolinites contain the lowest-defect material in the coarsest size fractions whereas others contain the lowest-defect kaolinite in the finest fractions. In an attempt to clarify possible mechanisms for producing such kaolinite samples, we have used powder X-ray diffraction to study the effects of mechanical grinding on the nature of layer stacking in the >40 μm fraction of the American Petroleum Institute kaolinite standard no. 9 from Mesa Alta, New Mexico. This material is relatively rich in a low-defect kaolinite. Hand grinding for 10 min plus grinding under acetone for up to an additional 34 min in an automatic agate grinder produced significant changes in its diffraction pattern. However, further dry grinding in a ball mill for 10 min produced material that was almost totally disordered, based on measures such as the Hinkley index. The diffraction patterns of the wet-ground materials showed evidence of increasing disorder that could be modeled best as a physical mixture of low- and high-defect material, consistent with a physical mixture of the original ordered phase with varying amounts of a highly disordered material. Disorder in the high-defect kaolinite is caused by the interstratification of normal kaolinite layers with their enantiomorphs. Contrary to expectations, grinding of kaolinite does not produce a progressive increase in disorder for all of the crystallites present in a sample. Instead, grinding apparently creates increased amounts of a disordered kaolinite that coexist with relatively unaffected material. There is no evidence for the occurrence of an intermediate disordered phase. Contrary to previous reports, disorder caused by physical stress does not include random layer displacements of ±b/3.

In Situ Characterization and Differentiation of Kaolinites in Lateritic Weathering Profiles Using Infrared Microspectroscopy

AbstractLateritic weathering kaolinites have been characterized in situ and differentiated for the first time by means of infrared microspectroscopy (IRMS). Four classical OH-stretching bands have been observed in the Fourier transform infrared (FTIR) spectra, at 3695, 3668, 3650 and 3620 cm−1, denoted ν1, ν2, ν3 and ν4, respectively, plus a band at 3595 cm−1 associated with the octahedral substitution of Fe3+ for Al3+. Infrared microspectroscopy of thin-sections of lateritic weathering profiles provides useful information on the types of kaolinite present in different horizons of the profile. The spectra obtained from large well-ordered kaolinite crystals look like those obtained by diffuse reflectance in that, compared with the KBr disk spectra of <2 µm powders, bands at 3668 and 3650 cm−1 are enhanced, and the strong absorption of KBr disks at 3695 cm−1 is replaced by a broad weaker band from 3700–3680 cm−1. In laterites, these large well-ordered kaolinites often exhibit a band at 3595 cm−1 indicative of significant Fe3+ substitution for Al3+ in the structure. The IR microspectra obtained from regions of small, more poorly-ordered kaolinites do not differ so markedly from that of KBr disks. All show enhanced absorption around 3650 cm−1 compared with well-ordered kaolinites, indicating that the disorder is due, at least in part, to domains of dickite-like and/or nacrite-like stacking in their structure. The 3595 cm−1 band is always weaker than that of the well-ordered kaolinite in the same profile. The IRMS data from well-characterized reference kaolinites show that the ratio Aν2/Aν3 is a pertinent IR order index for kaolinites. The larger this index, the larger is the area of the 3595 cm−1 band, and the larger and the more ordered is the kaolinite sample. It is suggested that the diversity of FTIR spectra observed reflects intergrowths of kaolinite-dickite polymorphs, or at least mixtures of high- and low-defect kaolinites which are frequently encountered in the lateritic geosphere rather than pure kaolinitic phases. The largest kaolinites having secondary crystallized in voids are the most ordered and the most ferruginous and have been considered as useful mineralogical tracers of the recent evolution of old lateritic terrains.

Raman spectroscopy of dimethyl sulphoxide and deuterated dimethyl sulphoxide at 298 and 77 K

Raman spectroscopy was used to determine the molecular behaviour of DMSO and DMSO-d6, and to compare it with that of DMSO in DMSO-intercalated kaolinites. For DMSO at 298 K two bands are observed at 2994 and 2913 cm−1 and are assigned to the antisymmetric and symmetric CH stretching modes. At 77 K the degeneracy of these bands is lost. Bands are now observed as antisymmetric bands at 3001, 2995 and 2988 cm−1 and symmetric bands at 2923, 2909 and 2885 cm−1, respectively. For the DMSO-intercalated low-defect kaolinite, the 2913 cm−1 band resolves into five component bands at 2882, 2907, 2917, 2920 and 2937 cm−1. The CD antisymmetric and symmetric stretching modes in the 298 K spectrum are found at 2250 and 2125 cm−1, respectively. Both bands show some asymmetry and further bands may be resolved at 2256 and 2244 cm−1 in the antisymmetric stretching region and at 2118 cm−1 in the symmetric stretching region. The spectra of the SO stretching region of DMSO and DMSO-d6 are complex with a band profile centred at 1050 cm−1. Three bands are curve resolved at 1058, 1042 and 1026 cm−1 attributed to the unassociated monomer and the out-of-phase and the in-phase vibrations of the dimer, respectively. Upon cooling to liquid nitrogen temperature, these three bands are observed at 1057, 1038 and 1019 cm−1. The spectra of the SO stretching region of DMSO-d6 are more complex because of the overlap of the DCD deformation modes with the SO stretching modes. The antisymmetric and symmetric stretching CS modes of DMSO are observed at 698 and 667 cm−1, shifting at 77 K to 705 and 672 cm−1. It is concluded that the structure of DMSO in DMSO-intercalated kaolinite is different from those of both liquid DMSO at 298 K and solid DMSO measured at 77 K. Copyright © 2002 John Wiley & Sons, Ltd.

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...

Sorption of Cd–cysteine complexes by kaolinite

The effect of cysteine on the adsorption of Cd(II) by kaolinite was examined at 25 °C using a low-defect kaolinite from Minas Gerais (Brazil) and a high-defect kaolinite from Berici Hills (Italy). The chemical data demonstrated that the amount of Cd–cysteine detected on kaolinite increases rapidly during the first few hours with a first-order reaction, thereafter adsorption becomes linear with time for low-defect kaolinite and slows rapidly for high-defect kaolinite. In low-ordered kaolinite, the Cd–cysteine is intercalated in the structure. Evidence of these changes was also observed by differential thermal analysis (DTA). The thermal decomposition of the Cd–cysteine adsorbed on the kaolinites was studied by analysing the evolved gases. The mass spectra of both samples show the evolution of NO (or CH 3CH 3, m/ z=30), CO 2 ( m/ z=44), and SO 2 ( m/ z=64) between 150 and 300 °C and of H 2O ( m/ z=18), CO 2 ( m/ z=44) and SO 2 ( m/ z=64) in the temperature range between 400 and 700 °C. The high-defect kaolinite also caused the evolution of molecular units with m/ z=34 (H 2S) and m/ z=76 (N 2O 3).

Modification of the Hydroxyl Surface in Cesium Acetate Intercalated Kaolinite

Changes in the hydroxyl surfaces of cesium acetate intercalated kaolinite have been studied over the ambient to predehydroxylation temperature range using a combination of FTIR and Raman spectroscopy, combined with X-ray diffraction. Upon intercalation of a low-defect kaolinite with cesium acetate, the kaolinite layers expanded to 14.0 A. Upon heating the intercalate to 50 °C, the kaolinite expands to 17.0 A. Over the temperature range 100−200 °C, a third phase with a d(001) spacing of 12.80 A was observed. These expansions are reversible, and upon cooling the intercalation complex and upon exposure to air for sufficient lengths of time, the d(001) spacing returned to 14.0 A. These expansions are in harmony with thermal decomposition measurements. Diffuse reflectance spectroscopy shows that the cesium acetate intercalated kaolinite is almost completely intercalated and that the thermal treatment of the intercalate is reversible. The Raman spectrum of the hydroxyl stretching region of the intercalated kaol...

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.