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The combination of mechanochemical and ultrasonic treatment was applied to synthesize CaAlFe-layered triple hydroxides with carbonate or chloride anions in the interlamellar space. The optimal parameters of the preparation were explored by altering the initial ratio of the metal ions and the temperature of ultrasonic irradiation. The resulting triple hydroxides were characterized by X-ray diffractometry, infrared and X-ray absorption spectroscopies, thermogravimetric analysis and scanning electron microscopy. The products were close-to-phase-pure CaAlFe-layered triple hydroxides. Elevation of the temperature transformed the CaAlFe-Cl(-)-layered triple hydroxide to rare oxyhalides (Ca2FeO3Cl and Ca12Al14O32Cl2)., (Copyright © 2016 Elsevier B.V. All rights reserved.)

It has been generally accepted for long that water molecules are integral parts of layered double hydroxides (LDHs). It is even thought that in the absence of water molecules, there is no LDH structure. It is shown in this contribution that via the solvolysis of Mg- or Ca-alkoxides and Al-alkoxide with methanol or propanol and co-precipitated in methanolic methoxide, water-free LDH-like structures could be constructed. These novel LDH-like materials proved to be more active and selective catalysts in a Knoevenagel condensation than the corresponding 'classical' LDHs. Synthesis, thought to be not possible to prepare, characterization and a catalytic application of water-free LDHs are described. Water molecules are replaced by small alcohol molecules in the interlayer space. [ABSTRACT FROM AUTHOR]

Ni(II)-containing layered double hydroxides (LDHs) were synthesized with various methods with the intention of placing the Ni(II) ions in different positions in/on the LDH. Ni(II) was introduced as a lattice-modifier into CaAl-, CaFe- and MgAl-LDHs or in the interlayer space in form of a complex anion or as the divalent component of NiAl-LDH or as surface dopant. The materials were structurally characterized by various instrumental methods; however, the final proof of lattice modification was proven by the Suzuki–Miyaura and the Heck coupling reactions. Each as-prepared catalyst was active and selective towards the coupling products with or without various additives. They could be recycled except the surface-doped material, in which intense leaching of the Ni(II) content was observed on reuse. Ni(II)-containing LDHs are active and recyclable catalysts in the Suzuki and Heck coupling reactions—this is the final proof that the Ni(II) ions are constituents of the lattice. [ABSTRACT FROM AUTHOR]

Abstract CaFe-layered double hydroxide (CaFe-LDH) was prepared by the co-precipitation technique and was treated mechanochemically in a mixer mill. The impacts of grinding frequency (3–21 Hz) and duration of milling (5–240 min) were mapped to learn about the deterioration steps of the layered structure. The possibility of structural reconstruction of the mechanochemically disordered chloride-containing LDH was tested in distilled water as well as in nitrate-containing aqueous solution. The main methods to follow the deformation and the rearrangement process were X-ray diffractometry and infrared spectroscopy, but electron microscopy techniques and thermal analysis were also applied to better understand and visualize the disruption and reconstitution of the LDH framework. Graphical abstract Unlabelled Image Highlights • Studying mechanochemical treatment on CaFe-LDH • Successful structural rehabilitation of the milled samples • Intercalation of nitrate guest anion during the reconstruction • Increased specific surface area in the regained LDH system [ABSTRACT FROM AUTHOR]

Abstract An ultrasonically-assisted mechanochemical method was further improved to increase the yield of high-quality ZnAl 2 -LDH with carbonate interlayer anions. In the LDH formation, the rarely studied temperature, power and pulse character of ultrasound irradiation were investigated to determine the optimal parameters for the synthesis. The as-prepared samples were milled with varying the grinding frequency in order to convert the layered hydroxide structure into ZnAl 2 O 4 spinel. This was the first time that ZnAl 2 O 4 spinel formation was induced mechanochemically. The main method to identify the effects of ultrasonic and mechanochemical treatments was X-ray diffractometry; however, infrared spectroscopy, scanning electron microscopy, and thermal analysis were also applied to follow and compare the mechanochemically induced spinel formation to the more frequently used heat treatment. Graphical abstract The thermal and the mechanochemical transformations of ZnAl-LDH to ZnAl spinel were followed and the resulting materials were compared. Image 1 Highlights • Developing further the ultrasonic mechano-preparation of aluminium-rich ZnAl 2 -LDH. • Mapping the ultrasonic irradiation characteristics on LDH formation. • ZnAl 2 O 4 spinel generation by mechanical and heat treatment of the as-prepared LDH. • Following the LDH degradation and evolution of spinel on two routes by XRD, IR, SEM. [ABSTRACT FROM AUTHOR]

Host-guest composite materials were prepared applying the anionic forms of Ni(II)-amino acid ( l-histidine, l-cysteine, and l-tyrosine) as the guests and CaAl-layered double hydroxide (CaAl-LDH) as the host. The syntheses were performed either by introducing the amino acid anions first and then constructing the metal ion-amino acid complexes or intercalating the pre-prepared complexes in anionic forms. The pristine as well as the composite LDH samples were structurally characterized by X-ray diffractometry, mid IR spectroscopy and scanning electron microscopy. The structural features of the interlayer complexes were studied by UV-Vis, inductively coupled plasma optical emission, mid and far IR and X-ray absorption spectroscopies as well as energy-dispersed X-ray analysis. On the basis of the acquired data, structural models were constructed. The composites were applied as catalysts in the liquid-phase oxidation of cyclohexene applying peracetic acid and the in situ formed iodosyl benzene as oxidants. Using peracetic acid afforded epoxide, while applying iodosyl benzene provided cis diol as the major or exclusive oxidation product. The catalysts displayed good recycling properties. [ABSTRACT FROM AUTHOR]

L-Cysteinate-intercalated CaAl-layered double hydroxide (LDH) was prepared by the co-precipitation method producing highly crystalline hydrocalumite phase with a well-pillared interlayer gallery. The obtained materials were characterized by X-ray diffractometry, IR as well as Raman spectroscopies. By performing interlamellar oxidation reactions with peracetic acid as oxidant, oxidation of cysteinate to cystinate in aqueous and cysteinate sulfenic acid in acetonic suspensions occurred. The oxidations could be performed under mild conditions, at room temperature, under neutral pH and in air. It has been shown that the transformation pathways are due to the presence of the layered structure, that is, the confined space of the LDH behaved as molecular reactor. [ABSTRACT FROM AUTHOR]

An ultrasonically-enhanced mechanochemical method was developed to synthesize CaFe-layered double hydroxides (LDHs) with various interlayer anions (CO 3 2− , NO 3 − , ClO 4 − , N 3 − , F − , Cl − , Br − and I − ). The duration of pre-milling and ultrasonic irradiation and the variation of synthesis temperature in the wet chemical step were investigated to obtain the optimal parameters of preparation. The main method to characterize the products was X-ray diffractometry, but infrared and synchrotron-based X-ray absorption spectroscopies as well as thermogravimetric measurements were also used to learn about fine structural details. The synthesis method afforded successful intercalation of the anions, among others the azide anion, a rarely used counter ion providing a system, which enables safe handling the otherwise highly reactive anion. The X-ray absorption spectroscopic measurements revealed that the quality of the interlayered anions could modulate the spatial arrangement of the calcium ions around the iron(III) ions, but only in the second coordination sphere. [ABSTRACT FROM AUTHOR]

From aqueous NaOH/Ca(OH) 2 /NaAl(OH) 4 mixtures, after allowing short reaction times we observed the precipitation of Ca(OH) 2 (s) at lower, and a mixture of Ca(OH) 2 (s) and a layered double hydroxide, hydrocalumite (HC) at higher aluminate concentrations. From the maximum aluminate concentration, at which the equilibrium solid phase is still portlandite ( i.e. , further increase in the aluminate concentration results in HC appearing in the precipitate beside the portlandite), the concentration based solubility products of two polymorphs of HC with the formula of [Ca 2 Al(OH) 6 ]OH· n H 2 O (differing in n ) has been estimated and was found to be log L HC =−11.4 at 25 °C and −12.1 at 75 °C, respectively (where L HC =[Ca 2+ ] 2 [Al(OH) 4 − ][OH − ] 3 ) and at constant ionic strength (I=1 M NaCl). To the best of our knowledge, this is the first published estimate for the solubility product of hydrocalumite. Additionally, from the composition obtained for NaOH/Ca(OH) 2 /NaAl(OH) 4 mother liquors in equilibrium with Ca(OH) 2 (s), attempts were made to extract the formation constant of the ion pair CaAl(OH) 4 + . It was found, that the effects caused by the supposed formation of this solution species are too small to be reliably determined, which allowed an upper estimate for its formation constant, K , to be suggested in the temperature range of 25–75 °C ( K <200 and 40 M −1 at 25 and 75 °C, respectively). [ABSTRACT FROM AUTHOR]

• The preparation of MnIn-LDHs applying air/N 2 /H 2 atmosphere was optimized. • The physico-chemical properties of the LDH with various Mn:In molar ratio was characterized in detail. • MnM(III)-LDHs (M: Al, Sc, Cr, Fe, Ga) were successfully synthesised by using the optimized parameters. • Outstanding catalytic activity of the LDHs was found in hydroquinone oxidation. • MnIn- and MnCr-LDHs showed the highest photocatalytic contributions under UV–Vis light. The preparation of a new member of the hydrotalcite supergroup, i.e. , MnIn-LDHs with Mn:In molar ratios from 5:2 to 8:2 was developed for the first time, by using the co-precipitation technique. The effect of the presence of air, N 2 or H 2 was systematically tested. The physico-chemical properties of the solids were characterized in detail. The application of reductive atmosphere proved to be vital for achieving phase-pure products. While the thermal behavior of the LDHs with different Mn:In molar ratios were largely similar, the increasing Mn:In ratio resulted in decreasing direct optical band gaps from 4.06 to 3.14 eV. By using the optimized conditions found for MnIn-LDHs, Mn 4 M(III)-LDHs were also prepared with M = Al, Sc, Cr, Fe, Ga. The catalytic performance of the various Mn(II)-based LDHs were tested under dark and UV–Vis-illuminated conditions for the transformation of hydroquinone in acetonitrile medium. The photocatalytic mechanism over MnIn-LDHs was studied by radical trapping tests, indicating the photogenerated holes play an important role in the decomposition of hydroquinone and even benzoquinone. The incorporation of Sc(III), Cr(III) and Fe(III) resulted in catalysts with outstanding performance both with and without illumination; under these conditions several metal oxides/semiconductors (like BiVO 4, Bi 2 WO 6 , SrTiO 3 , Bi 2 O 3 , SnO 2 , WO 3 , In 2 O 3 , ZnO and Degussa P25 TiO 2) and even the nonmetallic g-C 3 N 4 proved to be inactive. The largest photocatalytic contributions were measured for the Mn 4 Cr- and Mn 4 In-LDHs. The selectivity and yield of the benzoquinone formation was found to be the largest in the case of the Mn 4 Al-, Mn 4 Fe- and Mn 4 In-LDHs using UV–Vis light source. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Successful synthesis of pristine and Fe(III)-amino acid intercalated CaAl-LDHs. • Models of the intercalated complexes based on the results of a range of experimental methods. • Successful applications the oxidations of cyclohexene and in Ullmann coupling. • The organic-inorganic composites proved to be efficient and recyclable catalysts. Abstract Synthesis of intercalated composites were carried out using CaAl-LDH (layered double hydroxide) as host and the anionic form of Fe(III)-amino acid complexes as guest materials. Intercalation was attempted with two methods either introducing the preformed complexes or constructing the complex among the layers of the LDH. After optimization of the synthesis parameters, structural characterization was performed by X-ray diffractometry, scanning electron microscopy as well as mid and far infrared spectroscopies. Quantitative data about the intercalated complexes were collected by chemical analysis and X-ray absorption spectroscopy investigating the near edge region as well as the extended fine structure. Structural models based on characterization measurements are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann-type etherification coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities. [ABSTRACT FROM AUTHOR]

• Develop of mechanochemical preparation of the nickel-poor/aluminum-rich LDHs. • Synthesis of bromide, iodide, perchlorate, sulfamate containing LDHs for the first time. • Detailed structural, thermal and optical characterizations of the solids. • Influence of quality of interlayer anions on the CO 2 hydrogenation pathways. • Comparative catalytic study of the LDHs and co-precipitated NiAl-hydroxides. A simple synthetic route of preparing NiAl 4 -layered double hydroxides (LDHs) was developed. First, Al(OH) 3 was pretreated by using high-energy dry-milling. This was followed by impregnation with moderately concentrated aqueous Ni-salt solutions with different counter anions under mild conditions. Using this protocol, beside the already known NiAl 4 -LDHs with chloride, nitrate, sulfate interlamellar anions, bromide, iodide, perchlorate and sulfamate ion intercalated versions were also possible to be prepared for the first time. Catalysts obtained from these LDHs proved to be active in CO 2 hydrogenation reaction. The quality of interlayer anions was found to exert a profound effect on the topotactic transformation of LDHs, the in situ reduction of nickel and the formation of spinel-type oxides. Catalysts from sulfate and sulfamate containing NiAl 4 -LDHs possessed outstandingly high (>90 %) CO selectivity independently from the reaction temperatures, while those obtained from nitrate and perchlorate containing LDHs facilitated mostly and robustly the formation of methane. [Display omitted] [ABSTRACT FROM AUTHOR]

In spite of numerous investigations on the various processes of the thermal decomposition and rehydration of layered double hydroxides (LDHs) by a variety sophisticated experimental means, many details are still unexplored and some contradictions are still unresolved. In this work, our efforts were focussed on clarifying the composition, structure and properties of thermally decomposed metaphases originating from CaFe–LDH, heat treated in the 373–973 K temperature range. The structure reconstruction ability of mixed metal oxide phases obtained after heat treatments was also investigated, mainly concentrating on the changes in the microenvironment of Fe(III), in the presence of controlled amount of water vapour (i.e., at different relative humidities). All samples were characterised by X-ray diffractometry, and the iron-containing phases were studied by 57 Fe Mössbauer spectroscopy. [ABSTRACT FROM AUTHOR]

The intercalation/encapsulation of the anionic forms of diclofenac and naproxen anti-inflammatory drugs into CaFe-layered double hydroxides (LDHs) were investigated by four techniques. A novel mechanochemically-aided pathway was used and compared to the conventional co-precipitation, direct anion exchange and dehydroxylation-rehydration routes. The evolved average crystal thicknesses (23–35 nm) showed good correlation with the high drug-loading content (26–55% w /w) of the LDH solids. The as-prepared hybrid nanocomposites were studied in detail by X-ray diffractometry, Fourier-transform infrared and Raman spectroscopies, scanning electron microscopy, thermogravimetric and dynamic light scattering analyses. The drug−LDH solids were dispersed in hydrogels and the light microscopic size analysis imaged particles mainly of area between 5 and 10 μm2. In Franz diffusion cells, the in vitro drug release tests (collated by the Korsmeyer–Peppas kinetic model) registered slow release of the organic molecules from the external surface and the interlayer region of the LDH particles highly depending on the applied intercalation techniques. Compared to hydrogels without LDH solids, the liberation of drug molecules were found to be 15–70% slower from their LDH-capsulated forms. Raman mapping of the ex vivo human skin penetration tests visualized the transdermal route of the drug molecules and attested their accumulation in the epidermis and upper zone of the dermis from the LDH − hydrogel preparations. [Display omitted] • Diclofenac and naproxen were successfully intercalated into biocompatible CaFe-LDH. • Mechanochemically-aided and conventional synthesis routes were compared. • Structural, morphological and thermal characterization was carried out. • In vitro test proved prolonged drug release from the hydrocalumite capsulated forms. • Ex vivo study attested enhanced accumulation in the upper region of the skin. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intercalation of β-isocupreidinate among the layers of CaAl-LDH. • Intercalation of β-isocupreidinate among the layers of silylated CaAl-LDH. • Structural characterization (XRD, SEM, two types of IR techniques) of the composites. • Using the composites as catalysts in Michael addition producing chiral adducts. • Studying their recycling abilities and the structural changes upon reuse. β-isocupreidinate (β-iCu) anions having well-known structure and catalytic activity in various asymmetric reactions, were incorporated into the interlayer gallery of hydrocalumite (CaAl-LDH) by the partial delamination-restacking method. Silylation of the outer surface of the LDH with trimethyl silane was also employed to avoid the adsorption of β-iCu on the outer surface and to block the basic sites there. The obtained materials were characterized by a range of instrumental methods (X-ray diffractometry, scanning electron microscopy, ATR-IR and grazing incidence IR spectroscopies). The catalytic activities of the composites were tested in the asymmetric Michael addition of β-nitrostyrene and ethyl 2-fluoroacetoacetate. The β-iCu-pillared LDHs proved to be active and recyclable catalysts with very good diastereoselectivities and acceptable and in 2-propanol very good enantioselectivities. The silylated composite retained its activity and diastereoselectivity even in the third repeated run, when heptane was the solvent. [ABSTRACT FROM AUTHOR]