Large Basal Spacing Research Articles

X‐ray powder diffraction of polymer/layered silicate nanocomposites: Model and practice

AbstractX‐ray powder diffraction in reflection (Bragg–Brentano parafocusing geometry) is extensively used to characterize the structure of polymer/layered silicate nanocomposites (PLSNs). The large basal spacings (d001 > 2.0 nm) necessitates the collection of data at scattering angles (2θ) of less than 10°. The calculation of an ideal scattering profile for PLSNs provides an avenue to ascertain the influence of experimental parameters and the arrangement, organization, concentration, and composition of constituents on the experimentally observed pattern. This enables better experimental technique, more complete utilization of the scattering data, insight into inconsistencies between scattering and microscopy, and minimization of incorrect interpretation or overinterpretation of data. Because of the strong θ dependence of theoretical and experimental factors at low values of 2θ, careful sample preparation and data evaluation are necessary and should be complemented by microscopic observations, especially for PLSNs with low volume fractions of organically‐modified layered silicates (OLS) that are suspected of having exfoliated morphologies. X‐ray powder diffraction in reflection alone is insufficient to completely characterize and ascribe PLSN morphology. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1590–1600, 2002

Orientation of an Organic Anion and Second-Staging Structure in Layered Double-Hydroxide Intercalates

Mg−Al layered double hydroxides (LDHs) intercalated with an anionic azobenzene derivative (AzAA) were prepared, and the arrangement of the incorporated AzAA was investigated by varying the starting AzAA/LDH ratios for two types of LDHs with different Mg/Al mole ratios, Mg/Al = 2.0 (LDH2) and 3.0 (LDH3). The observed basal spacings of the complexes, 8 and 23−25 Å, were ascribed to horizontal (parallel to the layers) and vertical (perpendicular to the layers) orientations of the incorporated AzAA, respectively. In general, the horizontal orientation was observed with low AzAA/LDH ratios and the vertical orientation was observed with higher ratios. For the LDH2 complexes, a large basal spacing of 33 Å was observed with intermediate AzAA/LDH ratios, that is, 0.5 and 0.75, which was interpreted as an alternate stacking of the two types of interlayers (“1:1 ordered interstratification” or “second staging”). In the case of the LDH3 complexes having a smaller layer-charge density, second staging was not found with the intermediate AzAA/LDH ratios; instead, two separated phases, 8 and 23 Å, were obtained. TEM images for the complexes with basal spacings of 33 and 25 Å were consistent with the proposed structure model.

Comments on “Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce And La” By J.L. Valverde, P. Cañizares, M.R. Sun Kou, and C.B. Molina

Valverde et al. (2000) recently reported on the preparation and characterization of Al-pillared smectites modified with Ce and La. Pillaring of clays with Al polyoxocations (Keggin type Al13) and a large variety of other complexing cations has been reported many times since the seventies. McCauley (1988) described in a patent the preparation of thermally stable pillared clays with large basal spacings of ~28 A , followed by publications by Sterte (1991a, 1991b) and Booij and coworkers (Booij et al., 1996a, 1996b). These authors used hydrothermally treated or refluxed solutions containing the Al polyoxocation and the rare earth elements in the form of their chloride salts. The presence of cerium or lanthanum seems to promote polymerization of the Al polyoxocation. Until now however, nobody has been able to assess the structure of the newly formed pillaring molecules. Although the inter-layer spacing is about twice that of the normal Al-pillared clay, chemical analyses indicate smaller amounts of Ce and La than expected from polymerization of the Al polymer alone. Several other studies on the combination of Al pillars with Ce or La resulted in the formation of pillared clays with basal spacings characteristic of Al-pillared clays. However, catalytic activity is enhanced owing to Ce or La ( e.g., Gonzalez et al., 1992; Mendioroz et al., 1993; Trillo et al., 1993). Unfortunately, Valverde and coworkers (Valverde et al., 2000) missed most …

Alkyl Derivatives of Boehmite Having the Second Stage Structure

The reaction of aluminum alkoxide in straight-chain primary alcohols at elevated temperatures yielded the alkyl derivatives of boehmite [AlO(OH)1-x (OR) x ], a class of intercalation compound where the guest moieties are covalently bonded to the host boehmite layers. The addition of small amounts of water to the reaction system yielded another phase having a larger basal spacing. XRD, IR, and elemental analysis showed that the products had the boehmite layer structure with the alkyl moieties incorporated between the boehmite layers. IR spectra of the products also exhibited bands due to hydrogen bonding between the boehmite layers. These results suggest that the products are the alkyl derivatives of boehmite having the second stage structure. Because water in the reaction medium facilitated the hydrolysis of intermediate aluminum alkoxides, the product with the second stage structure had smaller alkyl/Al ratio and therefore had smaller basal spacing than that expected from the corresponding first stage product.

Synthesis of Ga2O3-pillared fluorine micas

Synthesis of gallium oxide pillared fluorine micas has been undertaken by using hydroxogallium solutions having different OH/Ga ratios and aging conditions as pillaring agents. The gallium oxide pillared fluorine micas obtained from aged hydroxogallium solutions have larger basal spacings and higher specific surface areas than those obtained from freshly prepared hydroxogallium solutions. Thermal durability of the pillared structure depends on the aging conditions of the hydroxogallium solutions; thermal durability of the pillared micas was enhanced by using the solutions aged under the optimized conditions. The pillared micas obtained from the hydroxogallium solution (OH/Ga = 2.0) aged at room temperature for 24 hours retained larger basal spacings and specific surface areas even after heated up to 750 °C.

Synthesis and characterization of a new mesoporous alumina-pillared titanate with a double-layer arrangement structure

Direct reaction of a colloidal suspension of an exfoliated layered titanate with an aluminium polyoxocation solution produced an ordered phase with a large basal spacing of 2.6 nm. Taking into account the starting Al/titanate molar ratio this swelling can be ascribed to the intercalation of double layers of Al13 polyoxocations between the titanate sheets. Heat-treatment at 600 °C resulted in an alumina-pillared titanate with specific surface areas ranging from 270 to 300 m2 g−1 and a pore volume of 0.25 mL g−1 (liquid nitrogen). The material was mainly mesoporous, the predominant pores having a diameter close to 4.0 nm. The acidity of the pillared titanate was ca. 0.60 mmol of protons g−1.

Organic Derivatives of Layered Inorganics Having the Second Stage Structure

The reaction of gibbsite (a modification of Al(OH)3) in glycol at elevated temperatures yielded the glycol derivative of boehmite together with a small amount of well-crystallized boehmite and a residue of unreacted gibbsite. The addition of water to the medium increased the reactivity of gibbsite and yielded a novel phase having a large basal spacing. Pure product of this phase was obtained by the reaction of microcrystalline gibbsite (<0.2 μm) in 75 vol % ethylene glycol−water or in 95% 1,4-butanediol−water at 250 °C for 2 h. XRD analysis showed that the products had the boehmite layer structure and that the difference between the basal spacings of the present products and those of the corresponding glycol derivatives of boehmite obtained in pure glycols was about the same as the thickness of a boehmite layer. IR spectra of the present products exhibited a band due to hydrogen bonding between the boehmite layers. These results suggest that the products are the glycol derivatives of boehmite having the second stage structure. 2-Methoxyethyl and 2-(dimethylamino)ethyl derivatives of boehmite having the second stage structure were also formed by the similar reactions in 2-methoxyethanol and N,N-dimethylethanolamine, respectively.

Formation of Organic Anion-pillared Layered Zinc Hydroxides by Coprecipitation.

From the viewpoints of removal, recovery and preconcentration of organic anions (An-) in water, the direct fixation into the precipitates of layered zinc hydroxide by a coprecipitation has quantitatively been investigated. When the solution of 8-200 mmol dm-3 Zn (NO3)2 was added dropwise into the solution of 1-250 mmol dm-3 organic anions at 25°C with stirring, the saturated aliphatic carboxylate ions with long carbon chain such as sebacate and dodecanedioate, the aromatic carboxylate ions such as terephthalate and also the anionic surfactants such as dodecylbenzenesulfonate and dodecyl sulfate were incorporated highly in the layered zinc hydroxide precipitates. The optimum conditions were found as follows; Z n2+/ A 2- molar ratio:>1.6, Zn2+/A- molar ratio> 3.2, and pH 6-7. The pecipitates were also found to have the layer structure with large basal spacings, which crystallinity being quite high in spite of the low reaction temperature. The guest organic anions were thought to be incorporated in a perpendicular or tilted configuration to the zinc hydroxide layers or botallackite type layers as a monolayer or bilayer by coordinating their anionic functional group, to Zn2+ ion in the host layers. Therefore, if the solutions contained a lot of inorganic anions, the coprecipitation of the organic anions was not influenced and the excellent selectivity for organic anions was observed. In conclusion, the possible fixation method based on the new mechanism (coprecipitation as pillared-layered zinc hydroxides) can be proposed.

Large pore REE/Al pillared bentonites: Preparation, structural aspects and catalytic properties

Ce Al and La Al pillared bentonites were prepared by cation-exchange of different bentonites with hydrothermally treated (130–160°C for 16–136 h) solutions containing mixtures of aluminiumchlorohydrate (ACH) and REE (Ce and La)-salts. After calcination at 500°C the pillared clays are characterised by basal spacings of 24.8–25.7 Å, and have BET surface areas of approximately 430 m 2/g. The pillared products are hydrothermally stable to at least 500°C. The large basal spacings and surface areas are due to the formation of large REE/Al containing polyoxycations. The formation of this cation is favoured by high initial Al concentrations (≥3.7 M) and an OH Al molar ratio of approximately 2.5. Ce Al or La Al ratios can be as low as 1 30 . Hydroconversion of n-heptane indicated that the activity of these materials is higher than that of a conventional Pt loaded amorphous silica alumina (ASA) reference catalyst. The selectivity is strongly dependant on the type of starting clay. In industrial hydrocracking of normal feedstock, a Ni W loaded REE/Al pillared clay catalyst showed slightly higher initial activity than the ASA reference catalyst. However, the pillared clay catalyst showed rapid deactivation due to coke-formation, which reduced the surface area and pore volume. Additionally coke formation may be facilitated by the relatively high iron content of the pillared bentonite (3.43 wt%).

Preparation, Structural Characteristics and Catalytic Properties of Large-Pore Rare Earth Element (Ce, La)/Al-Pillared Smectites

AbstractCe/Al- and La/Al-pillared smectites were prepared by cation exchange of bentonite, saponite and laponite with hydrothermally treated (130–160 °C for 16–136 h) solutions containing mixtures of aluminumchlorohydrate (ACH) and Ce3+-/and La3+-salts. After calcination at 500 °C, the pillared products are characterized by basal spacings between 24.8 and 25.7 Å and surface areas of approximately 430 m2 g−1. The products are hydrothermally stable at 500 °C after 2 h in steam. The large basal spacings are due to the formation of a large Ce/La-bearing Al-polyoxocation, whose formation is favored by initially high Al concentrations ≥3.7 M and an OH/Al molar ratio of approximately 2.5. The Ce/Al or La/Al molar ratios can be as low as 1/30. 27Al nuclear magnetic resonance (NMR) spectroscopy has shown that the polyoxocation has a higher Altetrahedral/Aloctahedral ratio than the Keggin structure Al13, which may partly explain the higher stability compared to normal Al-pillared clays. Hydroconversion of n-heptane indicated that the activity of the Pt-loaded pillared products is higher than that of a conventional Pt-loaded amorphous silica-alumina catalyst. Selectivity is strongly dependent on the type of starting clay and its acidity. In industrial hydrocracking of normal feedstock, a Ni/W-loaded Ce/Al-pillared bentonite catalyst showed rapid deactivation due to coke-formation reducing the surface area and the pore volume. Additionally, coke-formation is facilitated by the relatively high iron content of the pillared bentonite (3.43 wt% Fe2O3).

Nanolayer Ordering in an Epoxy-Exfoliated Clay Hybrid Composite

A new class of epoxy-clay nanocomposites have been prepared from alkylammonium exchanged fluorohectorite clays. These nanocomposites have usually large and regular basal spacings up to 105 {angstrom} platelet separation. The extra large separation of the clay nanolayers results in reinforcement of the polymer matrix, the reinforcing effect being comparable to that of disordered phased nanocomposites. It is now possible to define two general classes of exfoliated clay nanocomposites, namely those with long range nanolayer ordering, and those with little or no long range ordering. Long range ordering is indicated by the XRD patterns that have multiple 00l harmonies whereas disordered composites exhibit little or no 00l diffraction. Regardless of the presence of X-ray Bragg diffraction, exfoliated polymer-clay nanocomposites form when adjacent clay nanolayers are separated by a distance that precludes the possibility of interlayer communication through the association of galleries cations.

Electron spin resonance study of copper acetylacetonate adsorbed on clays

Two clays have been studied by means of a copper acetylacetonate probe. Swelling clays (montmorillonites) and non-swelling clays (kaolinites) have been investigated. KaoliniteNa (KlNa) shows a clear interaction with the copper complex. At room temperature, the electron spin resonance (ESR) spectra of KlCa do not show a real axial symmetry. In spite of the large basal spacing of the montmorillonites (Na, Ca, and Zr) the spectra are less well resolved than those of kaolinite. The tensor components g ¶ , g ⊥, A ¶ and A ⊥ are obtained by numerical simulation of the spectra. Adapted parameters are calculated in order to determine the magnitude and nature of the interaction of the copper complex with the clays.

Intercalation of methacrylamide into sodium, calcium and alkylammonium exchanged montmorillonites

Methacrylamide was intercalated into hydrophilic and organophilic exchanged forms of montmorillonite from various solvents. The increase of the basal spacing depends on the interlayer cation and the polarity of used solvent. The largest basal spacing ( d 001=3.35 nm) was observed for the long-chain alkylammonium montmorillonite and polar organic solvents. The alkyl chain length of the alkylammonium cation is a limiting factor for the interlayer expansion. An attempt was made to polymerize intercalated monomer by gamma-ray initiation. Subsequently, an additional swelling of the silicate structure was observed. Decomposition products of intercalated material and long-chain alkylamides were identified in the acetone extract. The additional swelling seems to be related to the gamma-ray initiated reaction products in the interlayer space.

MAS n.m.r. and i.r. studies of pillared clays

The silica- or alumina-pillared clays with a definite surface area and a larger basal spacing may be prepared by the gel dispersion method. The changes of i.r. and MAS n.m.r. spectra of these pillared clays before and after calcination at a higher temperature showed that the clays were exchanged with metal-hydroxide sols, that no characteristics changes were observed in the clay structure, and that it is only a cation-exchange process, but on subsequent high-temperature treatment at 450°C, obvious changes in MAS n.m.r. 29Si or 27Al spectra and i.r. framework vibration spectra appeared, so some changes in the clay structure did take place. It is suggested that during the calcination, a chemical reaction between tetrahedral sheets of the clays (with or without AI IV substitution) and the pillaring agents (pillars) takes place, forming the three-dimensional network structure.

Clay Mineral Type and Organic Compound Sorption by Hexadecyltrimethlyammonium‐Exchanged Clays

AbstractIn order to relate mineralogy to sorbent efficiency, organo‐clays were prepared from reference vermiculite, illite, smectite, and kaolinite clay minerals using the organic cation hexadecyltrimethylammonium (HDTMA). Adsorption isotherms using 14C‐HDTMA indicated stoichiometric adsorption of HDTMA up to the cation‐exchange capacity (CEC). Organo‐clays were prepared by adding HDTMA equivalent to the CEC and were evaluated as sorbents for nonionic organic compounds (NOCs) dissolved in water. X‐ray diffraction analysis of the HDTMA clays revealed basal spacings of 28 Å for the vermiculite and 23, 20, and 18 Å for the high‐charge, intermediate‐charge, and low‐charge smectites, respectively. The HDTMA vermiculite, illite, and smectites were all highly effective sorbents for NOCs, whereas Mg smectite was ineffective. The sorption isotherms of benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, t‐butylbenzene, naphthalene, and biphenyl on the HDTMA clays indicated that sorption occurred by partition interactions with the HDTMA‐derived organic phase. In general, both the greater HDTMA content and the larger basal spacings of high‐charge HDTMA clays increased NOC sorption. Mineral‐charge effects on the sorption of unsubstituted aromatic compounds (benzene, naphthalene, and biphenyl) were less evident than for alkyl‐benzenes. Greater sorption of the alkylbenzenes by high‐charge HDTMA clays can be attributed to the capability of the large basal spacings to accommodate larger solute molecules. The formation of organic cation exchanged soil clays derived from vermiculite, illite, or smectite may greatly improve the ability of soils to immobilize organic contaminants.

Polynuclear hydroxyaluminum-montmorillonite complexes: Formation of 18.8 Å and 28 Å pillared structures

Polynuclear hydroxyaluminum-montmorillonite complexe were prepared by treating Na-saturated montmorillonite with partially neutralized solutions of Al-containing monomer and polynuclear hydroxyaluminum species. The polynuclear hydroxyaluminum cations were preferably adsorbed by montmorillonite over monomer Al. The maximum quality of the polynuclear hydroxyaluminum adsorbed was ≈400 meq Al/100 g of montmorillonite and was independent of OH/Al molar ratios of hydroxyaluminum solutions. Three types of complexes were characterized by X-ray diffraction analysis; 18.8 Å phase, 28 Å phase and an intermediate phase. Initial conditions for drying suspensions containing complexes were found to be determining factors for the type of solid complex formed. Extremely dry conditions favored the formation of the 18.8 Å phase, whereas ambient conditions produced the intermediate phase. On aging, these phases were gradually transformed to the 28 Å phase. Upon heating at 700°C the 18.8 Å phase was converted to the 28 Å phase. The calculated average chemical composition of the polynuclear hydroxyaluminum cations adsorbed in montmorillonite layers was [Al(OH) 0.56+ 2.44] n. The quantity of the maximum adsorption, ≈400 meq, was only a quarter of the quantity of the interlayer cations required to form a chlorite structure which has a layer thickness of 14.2 Å. In spite of low amounts of hydroxy-Al adsorbed, the observed large basal spacings indicated that the complexes found in the present investigation must have pillared structures. From X-ray data, the height of the pillars was found to be ≈9.2 Å. This and chemical data suggested that the Johansson's model molecule [Al 13O 4(OH) 24(H 2O) 12] 7+, was most suitabl e for the pillar. If this is the case, then one molecule occupied an area of 12–13 montmorillonite unit cells at every layer in the 18.8 Å phase, whereas two cations occupied the corresponding area at every second layer in the 28 Å phase. Therefore, a transformation from the 18.8 Å phase to the 28 Å phase could be explained by the migration of the cations from an interlayer space of the 18.8 Å phase to one layer above or below.

Adsorption and Acidic Properties of Clays Pillared With Oxide Sols

AbstractInterlayers of montmorillonite were pillared with TiO2, SiO2-TiO2and SiO2-Fe2O3sols. The pillared structures were thermally stable at least up to 500°C and retained unusually large basal spacings in the range of 24–45Å and surface areas as high as 300–500 m2/g. The TiO2pillared clay showed Type IV adsorption isotherm for nitrogen. Although SiO2-TiO2and SiO2-Fe2O3pillared clays had basal spacings much larger than that of TiO2pillared clay, these mixed oxide pillared clays had small pores and exhibited Type I isotherm. The acidic strength distributions were determined by a titration method using n-butylamine and Hammett indicators. All of the pillared clays had large acidities, but the acidic strength decreased in the following order: TiO2- SiO2» SiO2-Fe2O3pillared clays. Temperature-programmed desorption (TPD) spectra of ammonia were measured and interpreted in relation to the acidity distribution. Infrared spectra of pyridine adsorbed on TiO2pillared clay indicated that the acidity predominantly arises from Lewis acid sites.

Mountkeithite, a new pyroaurite-related mineral with an expanded interlayer containing exchangeable MgSO4

AbstractMountkeithite [(Mg,Ni)9(Fe3+,Cr,Al)3(OH)24]3+[(CO{in3,SO4)1.5(Mg,Ni)2(SO4)2(H2O)11]3− occurs with pyrite, magnetite, magnesite, hexahydrite, and morenosite in a low-temperature hydrothermal vein system in the Mount Keith disseminated nickel sulphide deposit, Western Australia. Electron-microprobe analyses gave the following average composition: MgO 31.7, NiO 6.1, CuO 0.1, Cr2O3 6.1, Fe2O3 8.3, Al2O3 2.6, SO3 14.7; microanalysis for C and H gave CO2 3.9, H2O 30.6; total 104.1. The X-ray powder diffraction pattern has the following strongest lines: 11.30(10), 5.63(8), 4.63(2), 3.765(6), 2.645(4), 2.545(4), 1.554(5), and 1.505(3); these can be indexed on a hexagonal cell with a = 10.698 Å, c = 22.545 Å.Mountkeithite occurs as friable aggregates and rosettes composed of soft, pearly to translucent, pale pink to white flakes with perfect basal cleavage. Optical properties are uniaxial negative with ɛ = 1.51 and ω = 1.52; weakly dichroic from colourless to palest pink. Specific gravity is 2.12 (calc. 1.95). Mountkeithite is soluble, with efferves-cence, in dilute HCl. Mountkeithite changes to a pyroaurite-like phase, with a 7.8.Å basal spacing when immersed in water, but can be changed back to an 11.3 Å phase by immersion in 1M MgSO4; mountkeithite also collapses to a 7.8 Å basal spacing under vacuum. Phases similar to mountkeithite have been synthesized by immersing grains of stichtite in 1M MgSO4, at 20, 50, 105, and 200°C.The structure of mountkeithite is interpreted as consisting of positively charged brucite-like hydroxyl layers, containing both divalent and trivalent cations, separated by about 7 Å-thick, negatively charged interlayers containing carbonate and sulphate anions, magnesium sulphate, and water. Carrboydite, motukoreaite, and hydrohonessite are minerals with similarly large basal spacings of 10–11 Å, and are also believed to have pyroaurite-related structures with expanded interlayers.

CLAY-INORGANIC STUDIES. II. HYDROXY ALUMINUM PHOSPHATE–MONTMORILLONITE COMPLEX

Two specimens of hydroxy aluminum phosphate interlayer materials in montmorillonite clay were prepared with 7.20 meq Al and 11.29 meq H3PO4/g clay and with 14.40 meq Al and 22.58 meq H3PO4/g clay, and the resulting complexes studied by chemical and mineralogical methods. Both interlayer materials were slightly positively charged and except for different water contents their chemical compositions were almost identical. They contained Al, PO4 and H2O and a minor amount of Ca and approximated hydrous AlPO4∙nH2O. The mole ratios of Al:Ca:PO4:OH were 1.00:0.08:0.92:0.24 and 1.00:0.05:0.91:0.24, respectively. The interlayer materials appeared to be loosely packed and distributed sparsely in interspaces of the montmorillonite. The degree of packing was greater for the preparation with the larger amount of interlayer material. The materials increased the montmorillonite basal spacing to 23.3 Å under air-dry condition (30–40% relative humidity) but did not affect the lateral dimensions. The basal spacing varied somewhat with relative humidity at room temperature and decreased markedly as water was driven off by heating. Heat treatments between room temperature and 300 C sharply reduced the d001 spacings to 16.7 Å which persisted up to 700 C. It is postulated that the large basal spacings occur because the hydrated interlayer materials have a framework structure with tunnels along the c-axis. This being so, changes in the spacings with different humidities might result from the movement of water molecules among interstitial spaces existing around and between the loosely distributed molecules of interlayer material. The 16.7 Å spacing for the dehydrated phase corresponds to the sum of 7.0 Å, the edge dimension of an orthorhombic anhydrous AlPO4 and 9.7 Å, the silicate layer thickness.

Hydrous Sodium Silicates from Lake Magadi, Kenya: Precursors of Bedded Chert

Two new hydrous sodium silicates, NaSi(7)O(13)(OH)(3).3H(2)O (magadiite) and NaSi(11)O(20.5)(OH)(4).3H(2)O (kenyaite), were found in lake beds at Lake Magadi, Kenya. Both are well-crystallized layered silicates with large basal spacings. Concretions within the magadiite bed consist of kenyaite or quartz (chert) in the center, surrounded by kenyaite. In dilute acids magadiite and kenyaite are converted to 6SiO(2).H(2)O (SH), the first known crystalline hydrate of silica. The magadiite bed probably represents a chemical precipitate from alkaline brines. Percolating waters convert magadiite to kenyaite and eventually to chert. Thus a mechanism has been outlined for the formation of bedded chert deposits through inorganic precipitation. Alternations between silica-rich and iron-rich bands of iron formations may be due to concentration cycles in alkaline lakes.