Brucite-like Layers Research Articles

Structural and Textural Evolution during Folding of Layers of Layered Double Hydroxides

Layers of a layered double hydroxide, containing aluminum 4-fold coordinated, were partially folded in order to obtain a fibrous hydrotalcite-like compound. The hydrotalcite layers, in the presence of an anionic surfactant (sodium dodecyl sulfate) after hydrothermal treatment for 2 weeks, acquire a mesoporous-like arrangement. The transformation was monitored by techniques sensitive to structural and textural properties. Results suggest that brucite-like layers can be joined throughout unsaturated coordinated aluminum, that is, tetrahedral aluminum which links through hydrogen bonds to form aluminum octahedrally coordinated. The fractal dimension parameter was very sensitive to evolution from layered to fibrous hydrotalcites.

Removal of 2-Chlorophenol from Aqueous Solution by Mg/Al Layered Double Hydroxide (LDH) and Modified LDH

Sorption is a common treatment for removing pollutants from natural environments. Layered double hydroxides (LDHs), which consist of brucite-like positive layers and sodium dodecyl sulfate intercalated with LDH (SDS−LDH), are considered to be potential organic pollutant sorbents. The objectives of this study were (1) to evaluate the impact of removing 2-chlorophenol (2-CP) using Mg3-Al-(NO3) LDH and SDS−LDH and (2) to investigate the removal efficiencies of these two compounds. All fitted sorption data reveal that the second-order model and the Langmuir model best describe the sorption kinetics and isotherms, respectively. By visual MinteqA2 (2000) calculation, the dissociation pKa of 2-CP is 8.56. The experimental results indicate that a high concentration of 2-CP is sorbed by the hydrophilic-hydrophilic physical interaction of LDH when the pH is >8.56; however, the hydrophobic−hydrophobic partition interaction of SDS−LDH is more vital when the pH is <8.56. LDH and SDS−LDH can be removed not only in the ionic form, but also in the molecular form of 2-CP. The efficiencies of LDH and SDS−LDH, in regard to enhancing 2-CP sorption, are strongly dependent on the pH, 2-CP speciation, ionic strength, and metal dissolution. These results are of practical interest, with respect to the selection of sorbents, to optimize aquatic environment remediation technologies.

Synthesis, characterisation and delamination behaviour of lactate-intercalated Mg,Al-hydrotalcite-like compounds

Two series of hybrid organic–inorganic hydrotalcites containing Mg 2+ and Al 3+ in the brucite-like layers (Mg/Al molar ratios of 2:1, 3:1 and 4:1) and lactate (Lc) as counter-anion were synthesized by coprecipitation using Lc/Al molar ratios of 0:1 and 3:1 to prepare the starting solutions. All samples have been characterised by element chemical analysis, powder X-ray diffraction, FT-IR spectroscopy, thermal analysis and morphology analysis (specific surface area measurement, particle size analysis and transmission electron microscopy). Delamination of the synthesized samples after dispersion in water and ultrasound treatment was followed by X-ray diffraction. Delamination has been compared to that shown by samples containing Zn and Al in the brucite-like layers, and it has been found that, contrary to the Zn-containing samples, restacking takes place in all cases upon solvent evaporation.

Preparation and characterization of Mg–Al layered double hydroxides intercalated with benzenesulfonate and benzenedisulfonate

Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with benzenesulfonate (BS –) and benzenedisulfonate (BDS 2–) ions were prepared by coprecipitation and characterized by X-ray diffraction, FT-IR spectroscopy, and chemical analyses. The intercalated BS – and BDS 2– maintained their intrinsic molecular structures within the Mg–Al LDH interlayers. At low intercalation levels, the benzene ring of BS – in BS · Mg–Al LDH was inclined at 30° relative to the plane of the brucite-like layers of Mg–Al LDH. With increasing BS – content, the benzene ring adopted an additional configuration perpendicular to the Mg–Al LDH layers. In BDS-intercalated Mg–Al LDH, the benzene ring of BDS 2– was tilted at 26° relative to the plane of the Mg–Al LDH layers. Intercalation levels of BDS 2– were smaller than those of BS – despite the greater charge density of BDS 2–, which was likely attributable to a greater degree of electrostatic repulsion between intercalated anions.

Mild oxidation of tetrahydrothiophene to sulfolane over V-, Mo- and W-containing layered double hydroxides

Abstract A series of layered double hydroxides (LDH) with Mg 2+ and Al 3+ cations in the brucite-like layer and W-, V- and Mo-oxospecies in the interlayer gallery were prepared, characterized and tested as catalysts for the sulfolane synthesis by mild sulfoxidation of tetrahydrothiophene (THT) with H 2 O 2 . The structural and textural properties of solids and the nature of the metal species were investigated by X-ray diffraction (XRD), N 2 adsorption, thermogravimetric analysis (TGA), diffuse reflectance ultraviolet spectroscopy (DRUV), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalytic activity was evaluated in the liquid-phase THT oxidation with dilute H 2 O 2 in various organic solvents and temperature range of 20–30 °C. The best performances in terms of catalytic activity and stability were obtained with WO 4 2− -containing LDH catalyst.

Preparation of Ni(II)/Ti(IV) layered double hydroxide at high supersaturation

Ni(II)/Ti(IV) carbonate layered double hydroxide with high crystallinity has been synthesized by high supersaturation method. The structure and chemical composition of the compound have been characterized by PXRD, FT-IR, ICP-AES, SEM, N 2 adsorption–desorption isotherms, UV–vis, TG–DTA, and in situ HT-XRD techniques. It is found that Ti(IV) ions are incorporated into the brucite-like layer and the high positive charge of the layers has no obvious effect on the basal spacing. But the substitution of Ti(IV) for Ni(II) in the layer decreases the thermal stability of the resulting LDH materials.

Synthesis of Cd/(Al+Fe) layered double hydroxides and characterization of the calcination products

Layered double hydroxides (LDHs) containing Cd(II), Al(III), and Fe(III) in the brucite-like layers with different starting Fe/Al atomic ratios and with nitrate as counteranion have been prepared following the coprecipitation method at a constant pH value of 8. An additional Cd(II),Al(III)-LDH sample interlayered with hexacyanoferrate(III) ions has been prepared by ionic exchange at pH 9. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), and FT-IR spectroscopy. Their thermal stability has been assessed by thermogravimetric and differential thermal analyses (TG-DTA) and mass spectrometric analysis of the evolved gases. The PXRD patterns of the solids calcined at 800 °C show diffraction lines corresponding to Cd(Al)O and spinel-type materials, which precise nature (CdAl 2O 4, Cd 1− x Fe 2+ x O 4, or Cd x Fe 2.66O 4) depends on location and concentration of iron in the parent material or precursor.

Composition and anion ordering in some Fe II–III hydroxysalt green rusts (carbonate, oxalate, methanoate): The fougerite mineral

Main features of Fe II–III hydroxysalts (green rusts) are obtained from XRD. Moreover, Mössbauer spectroscopy revealed that several Fe II sites exist. The structure is classified in green rusts one and two (GR1 and GR2) according to the stacking sequence of Fe(OH) 2 brucite-like layers depending on the shape and type of anions inserted within interlayers. Long range order as determined for hydroxysulphate GR2(SO 4 2−) is extended to distributions of cations and anions within GR1s even though these are not observed by XRD. Abundances of Fe II and Fe III environments within GR1s that intercalate carbonate, oxalate and methanoate (formate) are found for compositions [Fe 6 IIFe 2 III(OH) 16] 2+·[CO 3 2−·5H 2O] 2−, [Fe 4 IIFe 2 III(OH) 12] 2+·[CO 3 2−·3H 2O] 2−, [Fe 6 IIFe 2 III(OH) 16] 2+·[C 2O 4 2−·4H 2O] 2− and [Fe 5 IIFe 2 III(OH) 14] 2+·[2HCOO −·3H 2O] 2−, which correspond to orders α, β and γ where the cation distances are (2 × a 0), (√3 × a 0) or a mixture of both, with a ferric molar ratio x = {[Fe III]/[Fe total]} = 1/4, 1/3 and 2/7, respectively. Anion distributions within interlayers are devised and long range orders in other layered double hydroxides could questionably be extended from these models. The formula [Fe 6 II (1− x) Fe 6 x IIIO 12H 2(7−3 x) ] 2+·[CO 3 2−·3H 2O] 2− for the fougerite mineral, which is the oxyhydroxycarbonate obtained by deprotonation of Fe II–III hydroxycarbonate [Fe 4 IIFe 2 III(OH) 12] 2+·[CO 3 2−·3H 2O] 2− where x ∈ [1/3,2/3] is confirmed.

Synthesis of 4-Chlorophenoxyacetate-Zinc-Aluminium-Layered Double Hydroxide Nanocomposite: Physico-Chemical and Controlled Release Properties

Layered organic-inorganic hybrid nanocomposite material was synthesised using 4-chlorophenoxyacetate (4CPA) as guest anion intercalated into the Zn-Al layered double hydroxide inorganic host by direct co-precipitation method at pH = 7.5 and Zn to Al molar ratio of 4. Both PXRD and FTIR results confirmed that the 4CPA was successfully intercalated into the Zn-AI-LDH interlayer. As a result, a well-ordered nanolayered organic-inorganic hybrid nanocomposite, with the expansion of the basal spacing from 8.9 angstroms in the layered double hydroxide to 20.1 angstroms in the resulting nanocomposite was observed. The FTIR spectrum of the nanocomposite (ZAC) showed that it composed spectral features of Zn-AI-LDH (ZAL) and 4CPA. The nanocomposites synthesized in this work are of mesoporous-type containing 39.8% (w/w) of 4CPA with mole fraction of Al3+ in the inorganic brucite-like layers (xAI) of 0.224. The release studies showed a rapid release of the 4CPA for the first 600 min, and more sustained thereafter. The total amount of 4CPA released from the nanocomposite interlayer into the aqueous solution were 21%, 66%, and 72% in 0.0001, 0.00025, and 0.0005 M sodium carbonate, respectively. In distilled water, about 75, 35, and 57% of 4CPA could be released in 1000 min, when the pH of the release media was set at 3, 6.25, and 12, respectively. In comparison with a structurally similar organic moiety with one more chlorine atom at the 2-position of the aromatic ring, namely 2,4-dichlorophenoxyacetate (24D), the 4CPA showed a slower release rate. The slightly bulkier organic moiety of 24D together with the presence of chlorine atom at the 2-position presumably had contributed to its higher release rate, and it seems that these factors may be exploited for tuning the release rate of intercalated guest anions with similar properties. This study suggests that layered double hydroxide can be used as a carrier for an active agent and the chemical structure of the intercalated moiety can be used to tune the desired release kinetics of the beneficial agent.

Metatungstate and tungstoniobate-containing LDHs: Preparation, characterisation and activity in epoxidation of cyclooctene

Polyoxometalates (POMs) H 2W 12O 40 6− and W 4Nb 2O 19 4− have been intercalated between the brucite-like layers of Mg, Al and Zn, Al hydrotalcites by anion exchange, starting from the corresponding nitrate precursors. The solids have been characterised by Powder X-ray Diffraction (PXRD), Fourier Transform infrared (FT-IR) spectroscopy, N 2 adsorption–desorption at −196 °C and thermogravimetric (TG) and differential thermal analyses (DTA), and have been tested in the epoxidation of cyclooctene using H 2O 2 or t-BuOOH as oxidants. The results show that both anions are effectively located in the interlayer space maintaining their pristine structures without depolymerisation. Upon intercalation of such large anions microporosity is developed and subsequently an increase in the specific surface areas is also observed. In general, the prepared materials possess catalase and epoxidation activity, with ZnAl-intercalated H 2W 12O 40 6− giving the best results in terms of epoxide yield (17% at 24 h). Product selectivity is different for the intercalated and free POMs, the latter yielding 1,2-cyclooctanediol as the only product, whereas the former produces only the epoxide. The epoxidation reaction seems to be catalysed in homogeneous phase by the POM.

Evidences for decarbonation and exfoliation of layered double hydroxide in N, N-dimethylformamide–ethanol solvent mixture

The behavior of a Hydrotalcite-like material (carbonate-containing Mg,Al-layered double hydroxide) in N, N-dimethylformamide (DMF)–ethanol mixture, at ambient temperature, has been investigated. The releasing of CO 2 and production of a formate-containing material occurred mainly for 1:1 (v/v) solvent mixture. Decarbonation of Hydrotalcite is promoted by DMF hydrolysis followed by neutralization of brucite-like layers through HCOO − intercalation. Translucent colloidal dispersion of LDH nanoparticles from the formate-containing phase was characterized by transmission electron (TEM) and atomic force (AFM) microscopies. The absence of (00ℓ) reflection at X-ray diffraction (XRD) pattern for dried colloidal dispersion indicated delamination of Hydrotalcite. The restacked sample exhibited broad reflections and typical hydroxide ordered layers non-basal (110) diffraction peaks. A LDH-HCOO − material was also prepared and characterized by FTIR and FT-Raman spectroscopies. Decarbonation and exfoliation of Hydrotalcite in N, N-dimethylformamide–ethanol mixed solvent provide an interesting method for preparation of new intercalated LDH materials.

Syntheses of new peroxo-polyoxometalates intercalated layered double hydroxides for propene epoxidation by molecular oxygen in methanol

A new type of layered double hydroxides intercalated by peroxo-polyoxometalates was synthesized by treating PdMAl-[PW 11O 39] (M = Mg 2+ or Zn 2+) with 30% H 2O 2. XRD, FT-IR, and 31P MAS NMR revealed that the interlayer anion [PW 11O 39] 7− was converted mainly to {PO 4[WO(O 2) 2] 4} 3− and [W 2O 3(O 2) 4(H 2O) 2] 2−. 27Al MAS NMR revealed that the brucite-like layers did not collapse during synthesis. PdMgAl-[PW 4 + W 2] showed 91.5% selectivity for propene oxide at 47.5% conversion during propene epoxidation by O 2 in methanol at 353 K for 10 h. The catalytic ability of PdMgAl-[PW 4 + W 2] can be attributed to the presence of highly active Pd particles in the brucite-like layers that generate H 2O 2 in situ, the strong epoxidation ability of interlayer peroxo-polyoxometalates with dilute H 2O 2, and the promotion effect of the basic MgAl-type brucite-like layers toward alkene epoxidation. Moreover, PdMgAl-[PW 4 + W 2] can be separated and reused by filtration without leaching active components into the solvent.

Ba2Co9O14: New Inorganic Building Blocks with Magnetic Ordering through Super-Super Exchanges Only

Ba2Co2+3Co3+6O14 has been prepared by conventional solid-state reaction between BaO2 and CoO. Its crystal structure has been refined from single-crystal X-ray diffraction data and powder neutron diffraction, a = 5.6963(8) A, c = 28.924(6) A, space group R3m, Z = 3, R1 = 4.44%, wR2 = 10.96%. It shows evidence of new building blocks called T‘ (ch‘h‘c stacking sequence of cubic O4 and hexagonal BaO3 layers) by analogy with the related T-blocks (hh‘h‘h) of the barium hexaferrites. T‘ consists of CoII,IIIO2 brucite-like layers pillared by CoIIO4 tetrahedra and CoIII3O12 octahedral trimers. Below TN = 39 K, tetrahedral and octahedral high spin CoII (S = 3/2) diluted in the framework mainly containing low spin CoIII (S = 0) interact through CoII−O−O−CoII through super-super exchanges (SSE) only. The analysis of the competition between the multiple SSE paths has been performed through geometrical considerations. The magnetic moments are lying antiferromagnetically in the a,b plane in good agreement with the magn...

Adsorption and intercalation of Acid Blue 9 on Mg–Al layered double hydroxides of variable metal composition

Layered double hydroxides (LDHs) of the type [ Mg 1 - X Al X ( OH ) 2 ] X + [ ( CO 3 2 - ) X / 2 · m H 2 O ] with variable Mg/Al molar ratios have been prepared by co-precipitation of Mg 2+ and Al 3+ ions at constant pH. The ability of these compounds to adsorb Acid Blue 9 has been evaluated by UV–Vis spectrophotometry, FT-IR spectroscopy, powder X-ray diffraction analysis, N 2 adsorption/desorption analysis, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy and atomic absorption spectroscopy. Optimum adsorption of Acid Blue 9 (AB9) was achieved for LDHs produced from mixtures containing Mg and Al in molar ratios varying from 3.1 to 4.4. LDHs with such compositions giving an equilibrium binding constant ( K a) of ca. 1.2 × 10 5 M −1 with a maximum monolayer coverage ( C m) of ca. 7.6 × 10 −2 mmol g −1. This observation was correlated to the surface area, phase purity, pore size and volume, particle size and the surface morphology of the LDHs. Powder XRD analysis after adsorption of 1.85 mM Acid Blue 9 in 20% (v/v) glycerol–H 2O solvent system indicated that the dye was not intercalated between the brucite-like layers as no change was evident in the d (003) spacing. Thus, at this low concentration surface adsorption of the dye is occurring. Powder XRD analysis revealed that intercalation was achieved at 76 mM dye concentration in the same solvent system for materials with Mg:Al molar ratios between 3.1 and 5.6. This results in an expansion of the interlayer spacing from ca. 8 Å to 19 Å to accommodate the AB9 anion. For the sample produced from a 3:1 mixture of Mg/Al, thermal gravimetric and elemental/micro analyses revealed that the new hybrid material has the composition [Mg 3.0Al 1.0(OH) 7.5][(CO 3) 0.62 · 3.2H 2O · 1.5Glycerol · 0.1Acid Blue 9].

Mössbauer investigations of natural and synthetic tochilinite and valleriite

Samples of natural and synthetic tochilinites and valleriites were investigated by Mossbauer spectroscopy. Synthesis of tochilinite was carried out at different temperatures and Fe/Mg ratio in the initial mixture. The relative amounts of obtained phases as functions of Mg atom relative content in the initial mixture were derived. It was shown that Mg atoms preferred to occupy one of two nonequivalent positions in brucite-like layers when entering the tochilinite structure. Parameters of hyperfine interaction were determined for valleriite and crystal chemical identification of 57Fe subspectra was carried out.

Investigations of sulfide minerals with layered structure by Mössbauer spectroscopy methods

Samples obtained as a result of the tochilinite synthesis process were investigated by 57Fe Mossbauer spectroscopy. Tochilinite, magnetite and troilite were obtained in investigated samples. The dependences of phase relative content on different content of Mg atoms in the initial mixture were received. It was found that Mg atoms stabilized tochilinite structure. It was shown that magnesium atom entering into tochilinite structure led to Fe atom redistribution in brucite-like layer. It was confirmed that in tochilinite structure equal number of sulfide and brucite-like layers conjugated.

Azoic dyes hosted on hydrotalcite-like compounds: Non-toxic hybrid pigments

Layered double hydroxides with the hydrotalcite type structure and a Mg:Al ratio of three have been prepared with an azoic dye (methyl orange) stabilized on the external surface. Methyl orange was incorporated by reconstruction from a mildly calcined LDH-CO 3 precursor. The solids have been characterized by powder X-ray diffraction and FTIR, UV–vis and 27Al, 13C CP/MAS NMR spectroscopies. Hartree–Fock calculations were performed in order to investigate the guest-host arrangement. Results show that the methyl orange molecule is in configuration trans and that the carbons in α- and β-positions, relative to the azo group, are interacting directly with brucite-like layers. Hydrotalcite shows a very high affinity for retention of azoic dyes. Another advantage offered by the stabilization of methyl orange anions in hydrotalcites compounds is that they are shielded from acid attacks.

Dehydrochlorination behavior of a chloride ion-intercalated hydrotalcite-like compound during thermal decomposition

We prepared a chloride ion-intercalated hydrotalcite-like compound (Cl −-HT) in a co-precipitation reaction, and investigated its thermal properties using thermogravimetry-differential thermal analysis (TG–DTA) and simultaneous thermogravimetry-mass spectrometry (TG-MS). In addition, we examined the effects of temperature and atmosphere on the dehydrochlorination of Cl −-HT during thermal treatment. The thermal decomposition of the Cl −-HT was divided into three stages: the evaporation of surface adsorbed water and interlayer water in the Cl −-HT, the dehydroxylation of the brucite-like octahedral layers in the Cl −-HT, and the elimination of HCl from the Cl −-HT. H 2O was produced at four steps: the evaporation of surface adsorbed water and interlayer water in the first stage, two steps of H 2O production caused by the dehydroxylation of the parts of Cl −-HT with properties similar to Mg(OH) 2 and Al(OH) 3, respectively, in the second stage, and H 2O production due to the dehydroxylation of the part of Cl −-HT with properties similar to Al(OH) 3 in the third stage. HCl was produced at two steps: the dehydrochlorination of the parts of Cl −-HT with properties similar to AlOCl and Mg(OH)Cl, respectively, in the third stage. Hydrochloric acid was obtained from the Cl −-HT on thermal treatment. The degree of dehydrochlorination of the Cl −-HT increased with temperature. The degree was greater under water vapor than under nitrogen at all temperatures, indicating that water vapor promoted the dehydrochlorination of Cl −-HT. However, the concentration of hydrochloric acid obtained under water vapor was lower than that under nitrogen.

Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides

Layered double hydroxides (LDH) with Mg 2+ and Al 3+ cations in the brucite-like layer and W-containing anions in the interlayer have been prepared by direct ion exchange of a MgAl-NO 3 LDH precursor with tungstate anions. The W-containing catalysts have been characterised by elemental chemical analysis, powder X-ray diffraction, Raman and UV-DR spectroscopies, thermogravimetric analysis and nitrogen adsorption. The results indicate the presence of both WO 4 2− and W 7O 24 6− anions in the interlayer gallery. The catalytic oxidation of organic sulfides and thiophene derivatives using hydrogen peroxide as oxidizing agent, in the presence of W-containing layered double hydroxide as catalyst, was investigated using various organic solvents miscible with water. It was found that W-containing LDHs are active catalysts promoting the fast oxidation of sulfur containing organic compounds with 30% H 2O 2 under very mild reaction conditions, but the catalytic activity depends on the nature of the W-containing anions. Other factors, like as the structure of the sulfur-containing organic compounds, the reaction temperature and solvent also influence the catalytic conversion.

Synthesis, characterization and reaction behaviour of lamellar AFm phases with aliphatic sulfonate-anions

The addition of alkanesulfonates as admixtures to cementitious materials allows the formation of new lamellar phases (AFm), which was proofed by X-ray diffraction (XRD). The course of hydration was investigated by heat flow calorimetry. The layered structures of AFm phases are composed of brucite-like main layers and interlayers containing alkanesulfonate ions and additional H 2O molecules. These structural not necessary H 2O molecules release gradually at definite steps with increasing temperature. With varying relative humidity the layer thickness c′ of short aliphatic chained calcium aluminate alkanesulfonate hydrates changes considerably, whereas large organic molecules dominate the layer thickness of those with longer aliphatic chains. By means of the increase of layer thickness with increasing chain lengths it is possible to determine the tilt angles of the aliphatic chains in the interlayers.