bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adsorption of Chlorinated Phenols from Aqueous Solution By Surfactant-Modified Pillared Clays
Authors: Michot Laurent J. , Pinnavaia Thomas J. 
Published: August 2006

AbstractNew pillared clay-based adsorbents have been prepared by incorporating a nonionic surfactant of general formula C12–14H25–29O(CH2CH2O)5H (commercial name, Tergitol 15S-5), during the synthesis of the aluminum hydroxide pillaring reagent. Different loadings of surfactant have been examined. The presence of the surfactant enhanced the adsorption capacity of the clay toward 3-monochlorophenol from aqueous solution. On the basis of adsorption results for a series of clays with increasing surfactant loadings, the best adsorbent was obtained at a surfactant loading of 255 mg/g of clay. At this loading, the surfactant occupies the micropores, as well as the mesopores and the external surfaces of the pillared clay. Analysis of the adsorption isotherms for 3-monochlorophenol, 3,5-dichlorophenol, 3,4,5-trichlorophenol and pentachlorophenol at different pH shows that the most energetic adsorption sites are the surfactant-occupied micropores between pillars. Additional binding of chlorinated phenols occurs at surfactant sites on external surfaces and mesopores. Upon calcination at 500°C, the clay is converted to a conventional alumina-pillared clay with a basal spacing near 16 Å. This calcined product can be reused as an adsorbent for chlorinated phenols by readsorbing fresh surfactant. The recycled adsorbent exhibits performance properties comparable to the original adsorbent. These results demonstrate the feasibility of utilizing a surfactant-modified pillared clay as a recyclable adsorbent and combustion catalyst for environmental pollutants.
Surface Acidity of Palygorskite-Supported Rhodium Catalysts
Authors: Herrero Juana , Pajares Jesús A. , Blanco Carmen 
Published: August 2006

AbstractInfrared spectra of adsorbed pyridine have been used to obtain qualitative information on the nature of the interaction of pyridine with different rhodium catalysts supported on palygorskite and silica. Based on these data, qualitative definitions of the adsorption sites of these catalysts have been deduced. The catalysts were prepared with natural palygorskite, and palygorskite dehydrated in vacuo at 150°C and 400°C. In this way, catalysts were obtained that had different water contents and, therefore, different acidities. Lewis-bound pyridine was detected by infrared spectroscopy from room temperature to 500°C. The greatest acidity was found in a catalyst prepared with the palygorskite support dehydrated at 150°C before preparation of the catalyst. With this catalyst, strongly hydrogen-bound pyridine was observed when evacuation was carried out at temperatures between 150°C and 300°C. Catalysts prepared with the palygorskite support pretreated at 400°C did not exhibit strongly hydrogen-bound pyridine, and Lewis acidity decreased significantly. As expected, hydrogen-bound pyridine was also detected for rhodium supported on silica. However, it was desorbed at temperatures below 150°C. The results of the acidity studies follow the same pattern as those for 1 -hexene double-bond migration under hydrogénation reaction conditions.
Site Occupancy in Nontronite Studied by Acid Dissolution and Mössbauer Spectroscopy
Authors: Luca Vittorio , MacLachlan Dugald J. 
Published: August 2006

AbstractThe dissolution of two Ca2+-exchanged nontronite samples has been studied in 10% HCl. Early acid-dissolution studies (Osthaus, 1954) have indicated that after two hours of dissolution most of the octahedral Fe3+ (VIFe3+) would be removed leaving mainly tetrahedral Fe3+ (IVFe3+) in the nontronite structure. In the present study, 57Fe Mössbauer spectra of acid-treated samples were recorded and fitted with two octahedral Fe3+ (2 × VIFe3+) and two octahedral and one tetrahedral (2 × VIFe3+, 1 × IVFe3+) doublet models. The Mössbauer spectra of acid-treated Garfield nontronite samples could be adequately fitted with two-doublet models but acid-treated Hohen Hagen nontronite samples could not. Isomer shift and quadrupole splitting values obtained from the two-doublet models corresponded to VIFe3+ and not IVFe3+, as was suggested by the Osthaus (1954) experiment. When an IVFe3+ doublet was included in the model used to fit the Mössbauer spectra of acid-treated Garfield nontronite samples, a slight increase in the intensity of the IVFe3+ doublet occurred with increasing dissolution, but this was much lower than indicated by Osthaus (1954). No trend in the intensity of the IVFe3+ doublet was observed for acid-treated Hohen Hagen nontronite. Therefore, acid treatment appears to remove VIFe3+ and IVFe3+ from the nontronite structure at about the same rate. Mössbauer spectroscopy, infrared spectroscopy and X-ray powder diffraction data indicate that the nontronite that remains undissolved following acid treatment is structurally similar to the untreated nontronite.
Fast and Slow Phosphate Sorption by Goethite-Rich Natural Materials
Authors: Torrent J. , Schwertmann U. , Barrón V. 
Published: August 2006

AbstractAlthough phosphate sorption by goethite and other less-abundant Fe oxides strongly influences the concentration of this anion in the soil solution and aquatic environments, relatively little is known on the P-sorption characteristics of natural goethites. For this reason, we examined the P-sorption capacity and time course of P sorption of 10 goethite-rich soil, ferricrete and lake ore samples, in which the content and nature of mineral impurities were unlikely to affect P sorption significantly. Phosphate sorption could be adequately described by a modified Freundlich equation including a time term. The amount of P sorbed after 1 day of equilibration at a concentration of 1 mg P/liter ranged widely (0.36–2.04 /μmol P/m2). The total P sorbed after 75 days of equilibration varied less, in relative terms (1.62–3.18μmol P/m2), i.e., a higher slow sorption tended to compensate for a lower initial (fast) sorption. Total sorbed P (X̄ = 2.62, SD = 0.52μmol P/m2) was similar to the sorption capacity of synthetic goethites, suggesting a common sorption mechanism and the predominance of one type of crystal face, which, according to previous transmission electron microscope observations, might be the (110).The extent of the slow reaction correlated to the ratio between micropore surface area and total surface area, as well as to oxalate-extractable Fe, which is an estimation of the ferrihydrite content. Ferrihydrite impurities might affect the slow reaction by contributing to the microporosity of some samples. Silicate adsorbed on the surface of the goethites was readily desorbed during phosphate sorption and did not significantly affect the extent of the slow sorption process.
Effects of Layer Charge, Charge Location, and Energy Change on Expansion Properties of Dioctahedral Smectites
Authors: Sato Tsutomu , Watanabe Takashi , Otsuka Ryohei 
Published: August 2006

AbstractExpansion properties often homoionic smectites that differed in amount and location of layer charge were examined by X-ray powder diffraction analysis at various relative humidities, or after glycerol or ethylene glycol solvations. Except for K-samples with glycerol solvation, and Na- and Ca-samples with ethylene glycol, differences in the basal spacings are observed in samples having similar layer charge. These results show that the basal spacings are larger when the layer charge is located in octahedral sites than when it is in tetrahedral sites. This suggests that expansion is due to the combined effects of the charge location and amount.The effects of layer charge magnitude and location on expansion were represented by an energy change (expansion energy: ΔEr) during the hydration and solvation processes. Plots of basal spacings versus ΔEr show a reasonable relationship; the spacings generally decrease stepwise as the value of ΔEr increases. The basal spacings of K-samples with glycerol solvation, Na-saturated and K-saturated samples at 100% RH are apt to contract stepwise with increasing value of ΔEr. For these samples, the figures showing the relationship between each expanded phase and the charge characteristics are obtained from the isoquants of ΔEr, given the boundary of the expanded phases. A behavior test using these figures may be combined with the Greene-Kelly test to estimate the amount and the location of the layer charge of common smectites.
Composition and Properties of Synthetic Hydrotalcites
Authors: Misra C. , Perrotta A. J. 
Published: August 2006

AbstractHydrotalcites of high aluminum content have been synthesized from aluminate liquors of varying composition and activated magnesia obtained by calcination of hydroxide or hydroxycarbonate precursors. Lattice parameter measurements and chemical analyses of 21 synthetic hydrotalcites show that the aluminum substitution $$\left( {\rm{X = \frac{{Al}}{{Al + Mg}}}} \right)$$ for most of the products is about 0.35, which is at the maximum experimentally-observed limit of solid solubility. Pillared hydrotalcites were also prepared by molybdate, Chromate, and silicate anion replacement. A maximum distance of 10.4 Å between the brucite-like layers was observed for the Mo7O246− intercalated material.
An Electron Optical Investigation of the Alteration of Kaolinite to Halloysite
Authors: Singh Balbir , Gilkes R. J. 
Published: August 2006

AbstractParallel-oriented and exceptionally long (> 10 μm) tubes of halloysite occur in the pallid zone of a deeply-weathered lateritic profile on granite in southwest Australia.Transmission electron microscopy and selected-area electron diffraction of ultrathin sections showed that kaolinite plates within pseudomorphs of mica crystals had fractured at irregular intervals along the a crystallographic axis to produce laths elongated along the b axis. The laths near the edges of the pseudomorphs were less constrained by the pseudomorph and had rolled to produce halloysite tubes. The tubes varied in diameter and degree of roundness. Some tubes were polyhedral rather than cylindrical in cross section. The length and number of planar faces in a tube and the angle between faces varied, exhibiting no consistent pattern.Tubes in dispersed clay samples showed two types of twinning. In the first type, tubes and associated laths were joined together side by side. In the second type, single tubes bifurcated into two individual tubes. It is proposed that the first type of twinning occurred by folding of adjacent laths that remained joined together while the second type occurred due to exfoliation of a thick lath followed by folding of the exfoliated lath fragments into tubes.Analytical electron microscopy showed that the chemical compositions of halloysite tubes, laths, and kaolinite plates were similar with the average cation exchange capacity of single tubes being small (4.5 meq/100 g) but higher than values for laths (2.8 meq/100 g) and plates (1.9 meq/100 g).
Structural and Magnetic Properties of Ferrihydrite
Authors: Pankhurst Q. A. , Pollard R. J. 
Published: August 2006

Abstract57Fe Mössbauer spectra of two synthetic samples of ferrihydrite, recorded at 4.2 K in applied fields of up to 9 T, have been analysed by a mean-field model. The samples exhibit two and six X-ray diffraction peaks. It is shown that only one ferric ion site is present in the mineral, and that in this site the ions are octahedrally coordinated. The spectra show the presence of different magnetic states: ferrimagnetism in two-line ferrihydrite, and antiferromagnetism in six-line ferrihydrite. The ferrimagnetism in two-line ferrihydrite is analysed in terms of random fluctuations arising from the small numbers of ferric ions per particle, and it is shown that the different magnetic states may arise purely as a result of these fluctuations.
Occurrence and Palaeohydrological Significance of Authigenic Kaolinite in the Aldebaran Sandstone, Denison Trough, Queensland, Australia
Authors: Baker Julian C. , Golding Suzanne D. 
Published: August 2006

AbstractThin section, XRD, SEM, and isotopic techniques have been used to study authigenic kaolinite occurring in reservoir sandstones of the Lower Permian Aldebaran Sandstone. Where the unit is no longer an active aquifer, kaolinite is an intermediate-stage phase, and is highly depleted in deuterium (δDSMOW = −115 to −99‰) and 18O (δ18OSMOW = +7.8 to +8.9‰), indicating that precipitation must have been from meteoric water. Deep penetration of this water is linked to Late Triassic deformation and uplift of the Denison Trough sequence, an event which led to exposure of the Aldebaran Sandstone by the Early Jurassic prior to its re-burial beneath Jurassic and Cretaceous sedimentary rocks. The same water was probably involved in the creation of secondary porosity in the interval.Where the Aldebaran Sandstone is presently undergoing meteoric flushing, kaolinite is relatively enriched in deuterium (δDSMOW = −104 to −93‰) and 18O (δ18OSMOW = +11.7 to +14.6‰), reflecting precipitation largely from post-Mesozoic meteoric water which was isotopically heavier than the Mesozoic water involved in intermediate-stage kaolinite precipitation. This temporal shift in meteoric water isotopic composition is related to the northward drift of the Australian continent to lower latitudes since the Mesozoic Era.
Electric Charge and Surface Characteristics of Hydroxyaluminosilicate- and Hydroxyaluminum-Vermiculite Complexes
Authors: Inoue Katsuhiro , Satoh Chiaki 
Published: August 2006

AbstractHydroxyaluminosilicate (HAS) ions prepared from hydroxy-Al (HyA) ions and orthosilicic acid at different NaOH/Al molar and Si/Al atomic ratios were fixed in the interlayer spaces of vermiculite (Vt). The electric charge and surface characteristics of HAS-Vt and HyA-Vt complexes formed were investigated in the pH range of 4 to 8. At pH 4 to 6, the magnitude of negative charge (CEC) of HAS-Vt and HyA-Vt complexes was drastically reduced by a HAS- or HyA-interlayer formation of Vt. At pH 7 to 8, especially in NaOH/Al molar ratio of 2.5, the magnitude of negative charge was from 62 to 89% of CEC in untreated Vt, suggesting that part of HAS or HyA ions fixed on Vt was excluded from its interlayer spaces. The positive charge did not develop on HAS-Vt and HyA-Vt complexes at pH between 4 and 8. The fixation of HAS or HyA ions on Vt caused the significant reduction of its total and internal surface areas as well as the slight increase of its external surface area. The HAS- or HyA-fixation in the interlayer spaces of Vt was confirmed by X-ray diffraction analysis. Our results provided evidence of a possibility that Vt could fix HAS ions in the same way as HyA ions, transforming to chloritized-Vt. These interlayer materials could play a significant role in modifying the surface and mineralogical properties and cation exchange capacity of clays and soils.
Dehydration of Hydroxy-Interlayered Vermiculite as a Function of Time and Temperature
Authors: Harris W. G. , Hollien K. A. , Bates S. R. , Acree W. A. 
Published: August 2006

AbstractNonexchangeable polymers in interlayers of expansible phyllosilicates influence thermal dehydration in ways not completely understood. Thermal dehydration of hydroxy-interlayered vermiculite (HIV) from Florida soils, for example, results in irreversible d001 shifts. This study was conducted to characterize HIV dehydration as a function of time (t) and temperature (T), and to determine how reversibility of dehydration is affected by elevated T. Clay-sized HIV from 3 soils was heated incrementally and d-spacing shifts (Δd) were monitored by X-ray diffraction (XRD) at low relative humidity (RH). Samples were then mounted on a metal heating strip in the XRD focal plane and scanned repeatedly at constant T levels to monitor Δd with t. Finally, Δd in response to RH shifts from <5% to >85% was determined at 25°C and at elevated temperatures. Incremental heating revealed a Δd plateau roughly corresponding to the z dimension of hexameric octahedrally coordinated Al. The initial slope of Δd-vs-t curves increased with T. The same maximum Δd reached at 200°C was reached at 160°C, but more slowly. All samples exhibited reversible and irreversible dehydration, the former being attributable to sites in equilibrium with external vapor and the latter to sites requiring heat for desorption. Reversible sites were not perturbed by moderate heating, but were apparently eliminated by polymer dehydroxytation. The dehydration behavior of HIV could be explained by steric resistance of water vapor diffusion within a tortuous interlayer polymeric network. Alternatively, new polymer/oxygen-surface bonds exceeding the hydration energy of interlayer components could form via heat-induced re-articulation of polymer/oxygen-surface bonds at smaller basal spacings.
Mössbauer Spectra of Soil Kaolins from South-Western Australia
Authors: St. Pierre Tim G. , Singh Balwant , Webb John , Gilkes Bob 
Published: August 2006

AbstractSix well-characterized soil kaolins from widely separated sites in south-western Australia and four reference kaolins were studied by 57Fe Mössbauer spectroscopy at room temperature after removal of non-structurally-bound iron with dithionite-citrate-bicarbonate solution. The soil kaolins and one of the reference kaolins were also studied at temperatures near 16 K. The soil kaolins were remarkably similar in crystal size, crystallinity, dehydroxylation temperature, cation exchange capacity, surface area and iron content. Müssbauer spectra of the soil kaolins at room temperature were also essentially identical consisting of a quadrupole-split doublet superimposed on a broad component which indicated that all of the iron was present as Fe(III) and that slow paramagnetic relaxation effects were present. Mean values for the chemical isomer shift and quadrupole splitting of the doublet for the soil kaolins were 0.33 and 0.55 mm/s respectively which indicates that the iron is in the octahedral sites of the kaolin lattice. The spectra of the soil kaolin samples at temperatures near 16 K showed a further slowing down of the paramagnetic relaxation and confirmed that no discrete iron oxide minerals were present.Mössbauer spectra of the four reference kaolins at room temperature showed a doublet component similar to those for the soil kaolins. Three of them showed evidence for other spectral components including, in two cases, a component due to the presence of Fe(II).
The Influence of Aluminum on Iron Oxides. Part XVI: Hydroxyl and Aluminum Substitution in Synthetic Hematites
Authors: Stanjek Helge , Schwertmann Udo 
Published: August 2006

AbstractSynthetic hematites with Al substitutions between 0 and 18 mol % were synthesized at different temperatures and water activities. The cell-edge lengths a for different synthesis conditions decreased linearly with increasing Al substitution. The regression lines, however, had different slopes and intercepts: the series with the highest synthesis temperature (1270 K) had the most negative slope. With increasing Al substitution, the hematites contained increasing amounts of non-surface water. Significant correlations were found between these chemically determined water contents and the deviations of the unit-cell parameters a, c, and V relative to the corresponding 1270 K regression lines. To explain the measured X-ray peak intensities, structural OH had to be included into the theoretical calculations. From intensity ratios normalized to I113, it is possible to determine the structural OH separately from the Al substitution, which can be assessed by the shift of the cell-edge lengths relative to the 1270 K regression lines. The incorporation of Al and OH into the hematite structure induces strain, which was quantified by X-ray diffraction.
Preparation and Characterization of Reduced-Charge Hectorites
Authors: Jaynes William F. , Traina Samuel J. , Bigham Jerry M. , Johnston Cliff T. 
Published: August 2006

AbstractA series of reduced-charge (RC) hectorites were prepared by multiple heat (250°C) treatments of Mg-saturated hectorites (SHCa-1 ). Cation exchange capacity (CEC) measurements and alkylammonium exchange indicated that a decrease in layer charge occurred with each Mg-250 treatment. Chemical analyses showed that decreases in structural Li and increases in structural Mg contents coincided with charge reduction. Fluorescence measurements of adsorbed quinoline indicated that the hectorite surface was acidified during charge reduction; hydroxyl group deprotonation is a possible source for the acidity. Fourier transform infrared spectra (FTIR) indicated that the Mg-250 treatment induced the loss of structural Li and shifted the SiO stretch band to a position similar to that in talc. The relative intensities of the OH and SiO stretch bands in FTIR spectra suggest that some of the hydroxyl groups in hectorite were lost, possibly by deprotonation. However, thermogravimetric data (TG) reveal no significant difference in the hydroxyl contents of the hectorites.The FTIR spectra, CEC, layer charge, chemical, and TG data all supported the view that Mg substitution for octahedral Li occurred which resulted in a more “talc-like” structure. Charge reduction in smectites is evidently a general phenomenon and can be induced by heat treatment with the proper exchangeable cation. The ability to reduce the charge of hectorites makes it possible to prepare a series of clays which vary in charge but lack structural Fe. Such RC smectites should be suitable for expandable clay mineral studies which utilize spectroscopic techniques that are sensitive to Fe content.
Polymerization and Transalkylation Reactions of Toluene on Cu(II)-Montmorillonite
Authors: Tipton T. , Gerdom L. E. 
Published: August 2006

AbstractProducts resulting from the reaction of toluene with Cu(II)-montmorillonite were analyzed using GC/MS, HPLC/MS, GPC, and FTIR methods. Numerous oligomers of toluene were observed, extending at least as high as the resolution limit (1500 g/mol) of the GPC column. The FTIR spectrum of the nonvolatile components of the extract was very similar to that of liquid toluene. GC/MS data on the volatile components revealed dimers, trimers, and a multitude of transmethylated products. Oligomerization proceeded via both ring-ring (i.e., polyphenyl) and ring-methyl linkages. The primary trans-methylated products were tert-butylbenzene and isopropylxylene, indicating a competition between ringand side-chain methylations. The side-chain substitutions cannot be explained in terms of the aromatic radical cation intermediate which typically forms in arene/clay reactions. A consideration of alkylbenzene reactions observed in various other media suggests that the present transmethylation reactions occur via a benzyl cation intermediate.
The Coordination of Aluminum Ions in the Palygorskite Structure
Authors: Güven Necip , de la Caillerie Jean-Baptiste d'Espinose , Fripiat Jose J. 
Published: August 2006

AbstractNMR spectra of PF1-1 Floridan palygorskite strongly suggest that Al3+ occurs only in octahedral coordination. X-ray microanalysis of the palygorskite fibers indicate a chemical composition defined by the atomic ratios: Mg/Si = 0.34, Al/Si = 0.27, and Fe/Si = 0.04. Considering the NMR and CEC data in this report along with the previously published results of IR and Mössbauer spectroscopic studies, the following structural formula is proposed for PF1-1 palygorskite:
$${\rm{(M{g_{2.12}}A{l_{1.68}}F{e^{3 + }}_{0.24}{\square _{0.96}})S{i_8}{O_{20}}{(OH)_2}{(O{H_2})_4}}}$$
where □ represents the vacant Ml octahedral sites in the structure, and Al3+ and Fe3+ are all exclusively assigned to the octahedral sites.