Clay Pillaring Research Articles

Structural Transformations of Hydrolysates Obtained from Ti-, Zr-, and Ti, Zr-Solutions Used for Clay Pillaring: Towards Understanding of the Mixed Pillars Nature.

Structural characteristics of hydrolysates formed from the aqueous Ti-, Zr-, and Ti, Zr-pillaring solutions prepared from inorganic precursors (TiCl4 and ZrOCl2), was investigated and compared with that of precipitates obtained from the same solutions after a slight alkalization of pH to the values reported for the conditions of clay pillaring. The materials were recovered by lyophilization and subsequently subjected to calcination at 500, 800 and 1000 °C. Of special interest was the effect of pH on the possible formation of mixed Ti, Zr-oxide species. Powder X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) analysis showed that even a relatively moderate alteration of pH in Ti-, Zr-, or Ti, Zr-precursor solutions caused substantial changes in the outcome of hydrolytic transformations, manifested by different phase and/or chemical composition of the resulting hydrolysates. Analysis of thermal evolution of hydrolysates showed that alkalization facilitated the transformation of anatase into rutile in materials obtained from Ti-pillaring solution, but retarded tetragonal to monoclinic zirconia conversion in samples derived from Zr-pillaring agent. The most striking effect was observed for the mixed Ti, Zr-pillaring solution, where an increase of pH enabled the formation of zirconium titanate as the only crystalline phase, rather than a multiphase mixture of anatase, monoclinic zirconia and zirconium titanate obtained from the more acidic precursor. The finding supports the model of mixed Ti-O-Zr network in props generated in Ti, Zr-pillared montmorillonites.

Studies of organoclays with functionalized pillaring agents

AbstractA series of clay pillaring agents with amino, olefin, and epoxy groups were synthesized. These pillaring agents were used to modify montmorillonite clay by ion‐exchange reactions. TGA studies showed that organoclays with imidazolium pillaring agents have a higher thermal stability than those with ammonium groups. The d‐spacings of organoclays were not affected by the pillaring agent functional groups and were sensitive to the size of pillaring agents. The dynamic‐mechanical properties of the resulting clay/epoxy composites determined by DMA were similar. The addition of these clays to this epoxy resin enhanced the Tg value of the resulting composites and greatly enhanced the storage moduli versus the pure epoxy resin by 1.6–1.8 times at 135°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Morphology, thermal stability and rheology of poly(propylene carbonate)/organoclay nanocomposites with different pillaring agents

Unpillared montmorillonite PGV and five organoclays (Nanocor's Nanomer I.44P, I.24TL and I.34TCN and Southern Clay Product's C25A and C30B) were high shear melt-blended (2.5wt%) into poly(propylene carbonate) (PPC). Solubility parameters of the clay pillaring agents versus that of PPC were used to predict clay/PPC miscibilities and these were compared to XRD and TEM nanoclay dispersion measurements. Clays I.34TCN and C30B, with the highest predicted pillaring agent/PPC miscibilites, had partially exfoliated morphologies. Clays I.24TL, C25A and I.44P, with pillaring agents predicted to be less PPC miscible, were less highly nanodispersed. Quaternary ammonium pillars with two 2-hydroxyethyl groups promoted the best nanodispersion in PPC. 12-Aminododecanoic acid (in I.24TL) promoted the intercalation. Dimethyl dialkyl quaternary ammoniums (in I.44P and C25A) were less effective. Organoclay dispersion improved the thermal stability. The PPC/I.24TL nanocomposite, with the most stable 12-aminododecanoic acid pillar, was the most thermally stable (PPC/I.34TCN and PPC/C30B were the second and third). The nanocomposites exhibited narrower linear viscoelastic zones than PPC and solid-like behaviors in these linear zones.

Optimized procedure for clay pillaring with aluminum species used in depollution

This study presents the improved method of smectite type clays pillaring, using aluminum salts. To achieve this goal, natural clay with a percentage of more than 95% montmorillonite was used. In order to analyze the pillaring process, a thermal procedure was used (thermal programmed desorption). The results of the pillaring process show that a controlled distance between the foliar band structures as long as 18·10–10 m can be obtained. The clays modified by pillaring can be used as molecular sieves in microfiltration processes or as agents in residual water chemical depolluting processes. They also have zeolite properties which make them reusable.

Encapsulation of chiral Mn(III) salen complexes into aluminium pillared clays: Application as heterogeneous catalysts in the epoxidation of styrene

Two chiral manganese(III) salen complexes bearing different chiral diimine bridges, complexes I and II, were encapsulated into three types of Al-pillared clays (Al-PILCs) by in situ generation of the complexes inside the PILCs; one of the PILCs used was derived from a Wyoming clay (Al-WYO) and the other two were from the same original clay Benavila: (i) Al-BEN, where no surfactant was used in the preparation and (ii) Al-TERG, where a polyalchol, i.e. tergitol was used as surfactant to act as an interlayer gallery template. The Al-pillared clay based materials were characterised by different techniques such as FTIR, UV–vis, AA, XPS, XRD and N 2 adsorption at 77 K. They were screened as heterogeneous catalysts in the epoxidation of styrene using iodosylbenzene or m-chloroperbenzoic acid as oxidants. The encapsulated complexes show, in general, moderate alkene conversion (16–40%), but very poor enantiomeric excesses (ee% = 0–14); nevertheless, for complex I encapsulated into Al-TERG using PhIO as oxidant 14 ee% was obtained, which is higher than the value found for the homogeneous phase reaction run under comparable conditions. Characterisation of the catalyst materials after two run suggests partial collapsing of the clay pillars.

Synergism of Clay and Heteropoly Acids as Nano-Catalysts for the Development of Green Processes with Potential Industrial Applications

A large number of inorganic oxides, mixed oxides, including alumina, silica, titania, zirconia, zeolites, carbon, clays and ion exchange resins have been employed as both supports and solid acid catalysts. Clay structure collapses at high temperatures and has to be stablilized. The thermal stability and pore size issues were addressed by pillaring of clays. Natural clays are acid treated or ion-exchanged to be used as solid acids, and the acidity and pore structure are dependent on the treatment methodology. Another important class of catalysts is the heteropoly acids (HPA), which are employed as homogeneous or heterogeneous catalysts, having both acid and redox properties. The focus of the current paper is to address the work done in our laboratory on the synergism between clays and heteropoly acids for the development of green processes. A comparison is also provided for the activity of these catalysts with other solid acids. Several alkylation, acylation, isomerization, condensation, dehydration, esterification, nitration and oxidation reactions which are useful in a wide spectrum of industries such as bulk, intermediates, dyes, plasticizer, pharmaceuticals, perfumes, flavours and other fine chemicals were investigated to improve the selectivity of the desired products.

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 …

Structure of Zirconia Nanoparticles used for Pillaring of Clay

ABSTRACTSAXS and EXAFS were applied to study genesis of polynuclear zirconium hydroxyspecies in pillaring solutions as dependent upon the zirconium concentration, addition of alkaline-earth chlorides and aging. After the montmorillonite clay pillaring, the structure of zirconium nanopillars was characterized by applying X-ray structural analysis, UV-Vis, FTIRS of adsorbed CO and nitrogen adsorption isotherms. Main pillaring species appear to be nanorods comprised of several Zr4 tetramers. Basic structural features of the tetramers are preserved in zirconia nanoparticles fixed between alumosilicate layers in pillared clays. In calcined samples, those nanoparticles contain only bridging hydroxyls and/or oxygen anions responsible for bonding within pillars and between pillars and clay sheets.

Non-aggressive pillaring of clays with zirconium acetate. Comparison with alumina pillared clays

A non-aggressive method of intercalation of smectitic clays with zirconium oligomers from the hydrolysis of a commercial solution of zirconium acetate is presented. Two saponites and a montmorillonite have been selected as the starting materials. The conditions of the intercalation process, pH=3.3 and room temperature, seem to allow a high polymerization degree of the intercalation zirconium species without significantly affecting the layer clay structures. Basal spacings in the 14–24 Å range are obtained for the zirconia pillared clays after thermal treatment at 500°C. Moreover, the specific surface areas and specific micropore volumes of the zirconia pillared clays reached values up to 300 m 2/g and 0.140 cm 3/g, respectively. The amounts of ZrO 2 fixed varied between 27% and 36% of the weight of the pillared samples. The textural properties of the zirconium intercalated clays were compared with that of their aluminum intercalated counterparts, resulting in higher specific surface areas and micropore volumes for the zirconia pillared saponites calcined at 500°C.

The Al Pillaring of Clays. Part I. Pillaring with Dilute and Concentrated Al Solutions

AbstractSaponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemistry or Al. Pillared saponite is obtained after exchange with refluxed Al solutions; while for hectorite, Al solutions treated with ammonium acetate give a pillared product with 1.8–1.9 nm spacing and thermal stability up to 873 K. In both types of solutions, the Keggin ion Al cluster is a minority species or totally absent. The typical 1.8–1.9 nm spacing is only obtained after washing. The quality of the pillared material can be judged from its thermal stability, its surface area, and the width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. The latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated conditions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.

The origins of house and home?

Abstract Excavations in course at the site of Qermez Dere in north Iraq have revealed a stratified sequence dating from the end of the epi‐palaeolithic period into the earliest centuries of the early neolithic. A sequence of subterranean houses belonging in the latter part of that time‐span (8250–7900 bc) is remarkable for the elaborate care and effort spent on their construction, maintenance and demolition/replacement. Each house was kept very clean, and there is a distinct lack of debris and even the equipment of everyday life. Each house was equipped with one or more non‐structural clay pillars. At the end of the series six weathered human crania were placed on the floor of the last house as it was being obliterated. These very early neolithic houses are contrasted with those of the preceding epi‐palaeolithic of the Levant, and it is suggested that they represent an important change in the perception of the house as home and the focus of attitudes and activities of symbolic social significance concerned with the conservation of property and the continuity and solidarity of the owning family.

Comparison of the photochemical and photophysical properties of clays, pillared clays, and zeolites

Uranyl-containing pillared clays, uranyl-exchanged clays, and zeolites have been used to photooxidize solutions of ethanol and diethyl ether. Product analysis indicates that uranyl ions in the clay pillars produce a more selective catalyst than materials obtained by inserting uranyl ion in the interlamellar spacings of the clay. Mechanisms are proposed to distinguish reactivity and selectivity differences of these photocatalysts. Incorporation of uranyl ions does not significantly affect the cracking properties of pillared clay catalysts.