Pillared Clays Research Articles

Preparation and characterization of pillared montmorillonite: application in adsorption of cadmium

This work concerns the pillaring of Algerian montmorillonite with polyhydroxymetal such as aluminum and chromium and its application in adsorption of inorganic polluant in the water : the cadmium. A systematic study of different parameters was undertaken such as the ratio of Cr/Al (5, 10, 20, 50 and 80 mmoles/g) ; Cr/Al (0, 0.2, 0.6, 1.2 and 5 mol/mole), aging time of metallic hydrolysis (1, 4, 24 and 36 h) and temperature (25, 40, 60 and 95°C). The obtained pillared clays were characterized by X-ray diffraction, physisorption of nitrogene at 77 K and by transmission electronic microscopy. It has been shown that a high temperature and a long time of metallic polymerization (before the intercalation) are in favor to a good pillaring. Indeed, the chromium polymer resulted by the hydrolysis under 95°C for 36 h leads (after intercalation and burn-off at 150°C) to a pillared clays with an interesting and stable textural properties ( d 001 = 19.13 Å, A sp = 196 m 2/g when calcined at 300°C). The effect of ratio Cr/Al shows that its increase is not favorable to the expansion of clay layers. When the ratio Cr/Al goes from 0.2 to 1.2, the basal spacing decreases from 17.8 to 16Å. The samples which have optimal properties were used as adsorbent of heavy metal. In this part of work, a systematic study optimizing the adsorption was also realized. The equilibrium time reaches 20, 40 and 80 min for the clays Mont.Al-Cr (Cr/Al = 0); Mont.Al-Cr (Cr/Al = 0.2) and Mont.Cr respectively. The adsorption yield is about 91%, 27% and 10% for an adsorption at 20 min for the abovementioned clays respectively. These results reveals that the Al pillared clay (Cr/Al = 0) has a better affinity toward the cadmium in our conditions.

Isomerization of 1-butene catalyzed by ion-exchanged, pillared and ion-exchanged/pillared clays

A natural smectite clay (STx-1, USA) was ion-exchanged with Al, Fe or pillared with polyoxocations of the same metals. Samples were also prepared by combining these two treatments. The prepared solids were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), TPD of ammonia and N2 adsorption. The catalytic activity was evaluated by using the isomerization of 1-butene at 300 °C. XRF results showed an increase in the content of Al or Fe thus giving evidence that these metals were effectively exchanged or deposited over the starting material. Al- and Fe-pillared clays showed a significant increase of the surface area. Ion-exchanged clays showed similar surface areas to that of the starting clay. From XRD patterns only the Al-pillared clay gave an increase of the d-spacing. The synthesized pillared clays were superior catalysts for the isomerization of 1-butene than the ion-exchanged clays; the ion-exchanged/pillared clays showed a similar catalytic behavior as that of the parent pillared clays. The Al-pillared clay was the best catalyst for the reaction and its efficiency was related to the high acidity and high surface area.

Direct immobilisation versus covalent attachment of a Mn(III) salen complex onto an Al-pillared clay and influence in the catalytic epoxidation of styrene

A Mn(III) salen complex was immobilised onto an aluminium-pillared clay (Al-WYO) by three different methodologies: method A (catalyst A2), direct immobilisation of the complex into the Al-WYO; method B (catalyst A4), covalent anchoring through cyanuric chloride (CC); and method C (catalyst A7), covalent attachment onto a 3-aminopropyltriethoxysilane (APTES) modified Al-WYO mediated by CC. All the materials were characterised by XPS and FTIR; the Mn content of the materials with the immobilised complex was determined by AAS. FTIR and XPS spectra confirmed the organo-functionalisation of Al-WYO and complex immobilisation in the parent and organo-modified Al-PILCs. Direct immobilisation of the complex into the Al-WYO (method A) leads to the highest immobilisation efficiency ( η = 37.5%) compared with the anchoring procedures using the two spacers, methods B and C, which gave η = 7.4% and 8.7%. Nevertheless, the surface Mn contents are always higher than those obtained by bulk analysis, suggesting that in all materials the complexes are located within the most external pores. The Mn(III) salen-based pillared clays were tested in catalytic epoxidation reaction of styrene using iodosylbenzene as the oxygen source and were reused for several cycles. The catalyst A2 was the best heterogeneous catalyst among the catalysts prepared since it showed similar substrate conversion and styrene epoxide selectivity to the homogeneous counterpart; the heterogeneous catalysts A4 and A7 showed considerably lower values for these parameters. The styrene epoxide yields decrease in the order, A2 ≫ A4 > A7, which might be associated with some pernicious catalytic activity of the organo-modified supports (A3 and A6). Moreover, A2 could be reused for four times with a slight decrease in its catalytic activity and with almost no leaching of the active phase.

Silylated pillared clay (SPILC): A novel bentonite-based inorgano–organo composite sorbent synthesized by integration of pillaring and silylation

This research examines the feasibility of synthesizing inorgano–organo composites based on bentonite-silylated pillared interlayered clays (SPILCs) by pre-pillaring of bentonite with the Keggin ion (hydroxyaluminum polycation) and then silylating with alkylchlorosilanes. The results of organic carbon content analysis, FTIR, XRD, and DTA/TG indicated that the silyl group can be successfully grafted to the inner surface of pillared interlayered clays (PILCs) through reaction with the OH groups of the pillars and the d-spacing of synthesized PILCs and SPILCs were almost the same. SPILCs have both the higher organic carbon content relative to original bentonite and PILCs and the better surface and pore properties relative to surfactants-modified organobentonites. A comparison of the modifier demand of SPILCs and CTMAB-bentonites indicated that the silylation of PILCs was a modifier-economized process for organically modification of bentonite. The heat-resistant temperature of SPILCs, 508 °C for OTS-Al-PILC and 214 °C for TMCS-Al-PILC, are more excellent organobentonites. Unlike the partition-predominated sorption mechanisms of organobentonites, both adsorption and partition are important components of sorption mechanism of SPILCs. The VOC sorption capacity of SPILCs is approximately same with that of organobentonites and the hydrophobicity of SPILCs is superior to that of PILCs.

Oxidation of cyclohexane with molecular oxygen in presence of characterized macrocyclic heteronuclear FeCu complex catalyst ionically bonded to zirconium pillared montmorillonite clay

Heteronuclear macrocyclic complex of iron and copper, FeCuL(NO 3) 24H 2O [L = (CH 3C 6H 2CH 2O(CH 2) 3N) 2] was synthesized and characterized using CHN and X-ray crystallography. A general scheme for bonding the complexes ionically on acidified montmorillonite clay was evolved and the thermogravimetric analysis of the final catalyst showed that it was stable up to 400 °C. The increased thermal and chemical stability of the complex bonded to the clay has been explained through enhanced interactive energy between them and its higher catalytic efficiency has been demonstrated through the following reaction. The oxidation of cyclohexane in presence of this catalyst using molecular oxygen in the absence of intiators, promoters and coreactants was studied in the temperature range of 150–210 °C. All commercial catalyst reported are known to form cyclohexanol and cyclohexanone in about equimolar ratio, but with our catalyst, cyclohexanone along with small amount of uncharacterized waste products (D) were formed and the selectivity of the former decreases (due to the formation of large amount of D) with increase in temperature. The experimental data were analyzed against different kinetic scheme available in literature and the rate constants of the best scheme were determined using Genetic Algorithm. From the experiments carried out at different temperatures and pressures, we found that for every rate constant, an Arrhenius type relation (independent of reactor pressure) could be established.

Pillared Materials from Layer Titanosilicates?

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Depollution of uranyl polluted waters using pillared clays

This paper reports on the use of clays pillared with copper polyhydroxycations in the depollution of waters polluted with radioactive elements. The pillared clays have very good surface properties which recommend them for use in cationic depollution. The article includes a kinetic study on the depollution of radioactive polluted waters, studying the influence of temperature on the process. The pillared clays are prepared from Romanian clay originally from Valea Chioarului deposits; the experiments have used an autochthonous material in an unconventional performant depollution technology.

Adsorption of carbon dioxide of 1-site and 3-site models in pillared clays: A Gibbs ensemble Monte Carlo simulation

Adsorption behavior of carbon dioxide confined in pillared clays is analyzed by using constant pressure Gibbs ensemble Monte Carlo (GEMC) method. In our simulation, 1-site and 3-site models are used to represent carbon dioxide. At the 1-site model, carbon dioxide is described as a Lennard–Jones (LJ) sphere, while at the 3-site model, carbon dioxide is modeled as a three-sites linear chain represented by EPM2 potential considering the quadrapolar effect. The potential model from Yi et al. for pillared clays is used to emphasize its quasi two-dimensional structure. Comparing the calculated results from the 1-site and the 3-site models at T = 228.15 and 258.15 K, we observe that the adsorption amount from the two models is the same basically. However, the local density presents a significant difference, because the shoulder in the main peak near the wall from 3-site model can reflect the orientation of carbon dioxide. Accordingly, in the systematical investigation to explore the effect of porosity and pore width on the adsorption of carbon dioxide in pillared clays, the 3-site model was only used. We observe that for a narrow pore of H = 1.02 nm , each isotherm shape displays type I curve, suggesting that it is not inflected by the porosity. However, for the larger pores of H = 1.70 and H = 2.38 nm , the increase of the porosity alters the shape of adsorption isotherms from a simple linear relation to the first order jump, indicating that the porosity is of very important factor to affect adsorption and phase behavior of fluids confined in pillared clays. The excess adsorptions of carbon dioxide at supercritical temperatures of T = 323.15 and 348.15 K are also investigated. We find that the maximum exists for each excess isotherm, and the optimal pressure corresponding to the maximum increases with the pore width. However, the porosity has no significant effect on the optimal pressure.

Effect of the modification of ZrO2-containing pillared clay with Pt and Cu atoms on the properties of inorganic complex intermediates in the selective catalytic reduction of nitrogen oxides with propylene according to in situ IR-spectroscopic data

It was found that only bridging and bidentate nitrate complexes were formed on the surface of Pt,Cu/ZrO2-pillared interlayered clay (ZrO2-PILC) upon the interaction with a flow of the (0.2% NO + 2.5% O2)/N2 mixture, whereas monodentate and nitrosyl complexes were not detected. The concentration of nitrate complexes on Pt,CU/ZrO2-PILC was higher and the strength of their bond to the surface was weaker than those on unmodified ZrO2-PILC. Isopropoxide and acetate complexes and coordinatively bound acetone were formed on the surface in the interaction of Pt,Cu/ZrO2-PILC with a flow of the (0.2% C3H6 + 2.5% O2)/N2 mixture. The supporting of Pt and Cu onto zirconium dioxide pillars resulted in considerable changes in the concentration and the temperature region of the existence of hydrocarbon surface compounds, as compared with ZrO2-PILC. Under reaction conditions at relatively low temperatures, isopropoxide and nitrate intermediates on the surface of Pt,Cu/ZrO2-PILC formed a complex structurally similar to adsorbed dinitropropane. At elevated temperatures, a surface nitromethane complex was formed in the interaction of the acetate complex with nitrate species. The spectrokinetic measurements demonstrated that the apparent rate constants of consumption of nitrate and nitroorganic complexes considerably increased on going from ZrO2-PILC to Pt,Cu/ZrO2-PILC. Moreover, the constants of consumption of nitroorganic and nitrate complexes were similar for both of the catalysts. This fact suggests that, on the test catalysts, nitroorganic complexes were reaction intermediates in the selective catalytic reduction of NOx (NOx SCR) with hydrocarbons. The found differences in the activation species and thermal stabilities of reactants can explain different activities of ZrO2-PILC and Pt,Cu/ZrO2-PILC in the SCR reaction of NOx with propylene in an excess of oxygen.

Adsorption of diuron and its degradation products from aqueous solution by surfactant-modified pillared clays

Adsorption of the herbicide diuron and its three degradation products: 3-(3,4-dichlorophenyl)-1-methylurea, 1-(3,4-dichlorophenyl) urea and 2,4-dichloroanilin on three organo–inorgano-clay minerals, was investigated. These surfactant-modified pillared clays (SMPC) were prepared by intercalation of polycations of aluminum(III), iron(III) or titanium(IV) into the interlamellar space of a montmorillonite, followed by co-adsorption of cetyl trimethylammonium bromide. The adsorption capacity of these new microporous solids was considerably enhanced especially with Ti- or Fe-SMPC. The adsorption isotherms of diuron and its derivatives at different pH were performed on each SMPC. These isotherms are typically S-type curves and suggested a hydrophobic adsorption mechanism. A comparative study of adsorption of the four compounds on each SMPC adsorbent shows the high adsorption capacity of diuron in comparison with its degradation products. This new generation of adsorbents could thus be considered as powerful competitors to activated carbon for the water treatment of industrial effluents in acidic medium.

Functionalized clay heterostructures for reducing cadmium and lead uptake by plants in contaminated soils

Natural and synthetic clay minerals have been transformed into Si-pillared mesoporous structures and then grafted with SH functions, for heavy metal ion trapping in polluted soils. The techniques and the limits encountered were detailed, with assessments of transformations by FTIR spectrometry and X-ray diffraction analyses. Adsorption isotherms of Cd 2+ and Pb 2+ were measured after 1 day shaking in calcium nitrate suspensions. Tests of Cd and Pb plant uptake were pursued by ray-grass cultivation on polluted soil amended or not with a functionalized synthetic beidellite during 3 months. Natural beidellite, hectorite and vermiculite were transformed into SH-grafted pillared clays but difficulties were encountered to keep a regular and significant interlayer distance until the last step. The well crystalline high-charge vermiculite of Santa Olalla (Spain), after Li-saturation, exchange with alkyl-ammonium cations, formation and grafting of interlayer Si-pillars, showed the highest capacity of Cd 2+ and Pb 2+ fixation among the 3 functionalized tested clay minerals. The cadmium uptake by ray-grass grown on polluted soil has been quite depressed by amendments with 0.17 or 0.5% of functionalized synthetic beidellite, but these amendments were inefficient for lead.

EVALUATION OF TOLUENE ADSORPTIVITY OF POROUS PILLARED CLAYS IN COMPARISON WITH OTHER POROUS SILICAS

Adsorption and desorption behaviors of toluene were investigated for porous pillared clays, such as organic-pillared clays (silica- or silica/alumina-pillared kanemite, and porous clay nanocomposites) and compared with those of silicalite, β-zeolite, ordered mesoporous silica, and silica aerogel to examine their abilities as adsorbents for volatile organic compounds (VOCs). Toluene adsorption isotherms of these materials showed that all the porous pillared clays adsorbed toluene in the relatively low pressure region (p/p 0 < 0.01) and much higher than the other porous materials, owing to the flat toluene molecule. No other significant differences were observed in the adsorption rates of the porous pillared clays. DTA-TG analyses of the porous pillared clays revealed a weak ability to entrap toluene up to 373 K. Lower retention of VOCs at raised temperatures allows the porous pillared clays to regenerate more easily for repeated use.

Influence of acidity of montmorillonite and modified montmorillonite clay minerals for the conversion of longifolene to isolongifolene

Isolongifolene and various other isolongifolene-based products are commercially important chemicals that find applications in perfumery and fragrance industry. These important commodity chemicals are generally prepared by homogeneous catalyzed reactions of longifolene in liquid phase. In the present study, role of acidity and acid distribution on montmorillonite, pillared interlayered clay and modified pillared clay catalysts have been studied for the first time in vapor phase system for the conversion of longifolene to isolongifolene. The number and strength of acid sites of montmorillonite clay mineral have been modified by steps of synthesis and by cations selection. Reaction of Al- pillared montmorillonite with Ru3+ yielded a catalyst with significantly higher distribution of weak acid sites while fortification of montmorillonite with Ce3+ and La3+ had little effect on total acidity and its distribution. In the present study, an attempt has been made to correlate the activity of the catalysts with total acidity, number and strength of the acid for the conversion of longifolene to isolongifolene. NH3 TPD determined the concentration and strength of acid sites.

Reaction paths of the formation and consumption of nitroorganic complex intermediates in the selective catalytic reduction of nitrogen oxides with propylene on zirconia-pillared clays according to in situ spectroscopic data

It was found that the adsorption and catalytic properties of nanosized ZrO2 particles as the pillar constituents of ZrO2-pillared clay and bulk ZrO2 are essentially different. The interaction of NO with the surface of bulk ZrO2 resulted in the formation of three types of nitrate complexes. Only two nitrate species were formed on ZrO2-pillared clay (the monodentate species was absent). Only an acetate complex was formed in the interaction of a mixture of propylene and oxygen with the surface of bulk ZrO2, whereas an isopropoxide complex was the main propylene activation species on ZrO2-pillared clay. On the surface of ZrO2-pillared clay, isopropoxide and nitrate intermediates formed a complex structurally similar to adsorbed dinitropropane. On the surface of bulk ZrO2, acetate and monodentate nitrate complexes formed a complex structurally similar to adsorbed nitromethane. The dinitropropane complex on ZrO2-pillared clay was consumed in reactions with surface nitrates. The decomposition reaction of a dinitropropane compound with the formation of acetate complexes and ammonia predominated on the surface containing no nitrate complexes in the absence of NO + O2 from a gas phase. The found differences in reactant activation species and their thermal stabilities explained differences in the activities of bulk ZrO2 and nanosized ZrO2 particles as pillars in pillared clay in the course of the selective catalytic reduction of nitrogen oxides with propylene in an excess of oxygen.

Pillaring of high charge density synthetic micas (Na-4-mica and Na-3-mica) by intercalation of oxides nanoparticles

Porous metal oxides synthesized by pillaring the high charge density synthetic micas, Na-4-mica and Na-3-mica, were reported for the first time. The interlayer spaces of mica layers are pre-expanded with n-octylammonium cation, which are subsequently replaced by pillar precursors (iron polyhydroxy cation or Fe 3+-deposited silica sols) to form intercalation compounds. Heating the precursors at 773 K resulted in the formation of Fe 2O 3 or Fe 2O 3–SiO 2 pillared micas having a high surface area (57–130 m 2/g), high porosity and good thermal stability. Characterization with XRD, TEM, and N 2 adsorption experiments suggests that the resultant pillared micas consist of fragmented pillared clay forming a “house-of-cards” structure. The acidic property of the pillared micas was tested by TPD of ammonia, and the result shows that pillaring of Na-4-mica with Fe 2O 3 or Fe 2O 3–SiO 2 causes a significant increase in the acid amount.

The use of $$O_2^{\begin{array}{*{20}c}--\\\cdot \\ \end{array} } $$ radical anions as spin probes for testing nanostructured materials based on zirconium oxide

The conditions of formation of $$O_2^{\begin{array}{*{20}c}--\\\cdot \\ \end{array} } $$ radical anions on the surface of zirconium oxide systems including nanostructured pillared clays, in interaction with hydrogen peroxide and an NO + O2 mixture of gases were studied by the EPR method. The special features of the formation of these radicals depending on the phase composition, structure, and degree of hydroxylation of the surface are discussed.

Copper- and iron-pillared clay catalysts for the WHPCO of model and real wastewater streams from olive oil milling production

The properties of copper-based pillared clays (Cu-PILC) have been studied and compared with those of the analogous iron-based clays (Fe-PILC) in the wet hydrogen peroxide catalytic oxidation (WHPCO) of model phenolic compounds (p-coumaric and p-hydroxybenzoic acids) and real olive oil milling wastewater (OMW). These two catalysts show comparable performances in all these reactions, although they show some differences in the rates of the various steps of reaction. In particular, Cu-PILC shows a lower formation of oxalic acid (main reaction intermediate) with respect to Fe-PILC. Both catalysts show no leaching of the transition metal differently from other copper-based catalysts prepared by wetness impregnation on oxides (alumina, zirconia) or ion-exchange of clays (bentonite) or zeolite ZSM-5. No relationship was observed between copper reducibility in the catalyst and the performance in WHPCO, as well as between the rate of copper leaching and catalytic behavior. Cu-PILC shows a comparable activity to dissolved Cu2+ ions, although the turnover number is lower assuming that all copper ions in Cu-PILC are active. Cu-PILC shows a high resistance to leaching and a good catalytic performance, which was attributed to the presence of copper essentially in the pillars of the clay. A high efficiency in H2O2 use in the first hour of reaction with the participation of dissolved O2 in solution was also shown. For longer reaction times, however, the efficiency of H2O2 use considerably decreases.

Oxidation of cyclohexene with molecular oxygen catalyzed by cobalt porphyrin complexes immobilized on montmorillonite

Composite materials were prepared by intercalating cationic porphyrinato cobalt complexes with the substituents of the quaternary ammonium salt of heterocyclic amine into a montmorillonite interlayer. Using these clay interlayer-fixed porphyrinato cobalt complexes as catalyst, the epoxidation of cyclohexene by oxygen molecules was examined. The prepared intercalation compounds have mesopores with an average diameter of about 12 nm, and their specific surface area increased in proportion to the amount of the intercalated porphyrinato cobalt complexes. It was proven that the porphyrinato cobalt complex was intercalated between montmorillonite layers functioned as a pillaring agent. A pillared clay catalyst, which was prepared by intercalating a [meso-tetrakis(1-ethyl-3-pyridinio)porphyrinato] cobalt complex into the montmorillonite interlayer, showed the highest catalytic activity forming 1,2-epoxycyclohexane preferentially in the presence of isobutyraldehyde. It is suggested that montmorillonite contributes to the stabilization of the porphyrinato cobalt complex, and also plays a role in accelerating oxidation by activating oxygen molecules by way of constructing a reaction field that is regulated three-dimensionally through electrostatic interaction with guest molecules.

Adsorption and desorption behaviors of flavor molecules into a microporous pillared clay mineral and the application to flavor capsule composites

We have investigated adsorption and desorption behaviors of Hinokitiol, Vanillin and 3-Phenyl-2-propen-1-ol (POO) into microporous montmorillonite pillared with tetramethylammonium ions (TMA-Mnt) in order to examine the ability of TMA-Mnt to retain volatile flavor molecules, with a view to applying TMA-Mnt as a capsule for the preparation of flavor/polymer composites. The treatment of TMA-Mnt with Hinokitiol, Vanillin and POO in n-hexane at 313 K caused the adsorption of these molecules on the internal and external surfaces of TMA-Mnt. Their adsorption isotherms, having Langmuir adsorption form, revealed that these compounds occupy 62–131, 23–62 and 38–102% of these total capacities in TMA-Mnt. Differential thermal analysis and thermo gravimetric (DTA–TG) measurements of the resultant Hinokitiol/, Vanillin/ and POO/TMA-Mnt compounds showed that exothermic peaks and weight losses due to the decomposition or desorption of these molecules were observed above their sublimation temperatures. This indicates that their desorptions were suppressed above the sublimation temperatures owing to their immobilization in TMA-Mnt. Detailed analyses revealed that the adsorption of these compounds into the micropores decreases their volatility at higher temperatures, demonstrating the ability of TMA-Mnt to retain the volatile flavor compounds. Hinokitiol/TMA-Mnt compound was subsequently mixed with molten poly(ethylene terephthalate) (PET) to examine the desorption behavior of Hinokitiol molecules from the PET composite. A comparison of Hinokitiol/TMA-Mnt/PET and Hinokitiol/PET exposed to temperatures of 333, 373 and 413 K showed that the desorption of Hinokitiol molecules was suppressed in Hinokitiol/TMA-Mnt/PET due to their entrapment in the micropores of TMA-Mnt, while the molecules were easily desorbed from Hinokitiol/PET. Consequently, we have found that TMA-Mnt successfully encapsulates volatile flavor compounds in a polymer composite.

Pt-containing pillared clay catalysts for CO oxidation

Platinum has been introduced into pillared clay as a complex with the organosilicon amine N’-[3-(trimethoxysilyl)propyl]diethyltriamine, as a complex with the organosilicon amine and zirconyl chloride, as an ammine complex, and by impregnation with a chloroplatinic acid solution followed by hydrogen reduction. The catalytic activity of the Pt-containing clays in CO oxidation in excess hydrogen was also studied. The last procedure yields the most active Pt-containing pillared clay. Calcium has been introduced into pillared clay by ion exchange, and it was found that the catalytic activity of the clay decreases with increasing Ca content.