Thin films of nickel–aluminum-containing layered double hydroxide (NiAl-LDH) have been prepared on nickel foil and nickel foam substrates by secondary (seeded) growth of NiAl-LDH seed layer. The preparation procedure consists of deposition of LDH seeds from a colloidal suspension on the substrate by dip coating, followed by hydrothermal treatment of the nanocrystals to form the LDH film. The secondary grown film is found to provide a higher crystallinity and more uniform composition of metal cations in the film layer than the in situ grown film on seed-free substrate under identical hydrothermal conditions. A systematic investigation of the film evolution process reveals that the crystallite growth rate is relatively fast for the secondary grown film because of the presence of LDH nanocrystal seeds. Electrochemical performance of the resulting NiAl-LDH films as positive electrode material was further assessed as an example of their practical applications. The secondary grown film electrode delivers improved recharge–discharge capacity and cycling stability compared with that of the in situ grown film, which can be explained by the existence of a unique microstructure of the former. Our findings show an example for the effective fabrication of LDH film with controllable microstructure and enhanced application performance through a secondary (seeded) growth procedure.

•Composite films of SiO2/LDH have been fabricated on aluminum substrate by a two-step preparation method.•Micropore defects between LDH crystallites in the in situ grown LDH film were filled gradually after dip-coating with SiO2 sol-gel.•The SiO2/LDH composite film has remarkable anticorrosion property for aluminum metal.•The defect-sealing effect of SiO2 coating can enhance the barrier property of LDH film, and then restrain the penetration of corrosive agent through the LDH film to the metal substrate.Developing composite films with good integrity is of great importance for the requirement of effective protection of metal materials. Herein, we report the fabrication of composite films of silica/layered double hydroxide (SiO2/LDH) on aluminum substrate by a two-step preparation method, in which MgAl-LDH crystallites were first in situ grown on aluminum surface, then SiO2 layer was deposited on LDH-coated substrate film by sol-gel dip-coating technique. The rough surface of the as-prepared LDH film has many pore defects in the size of micro meters. After dip-coating with SiO2 sol-gel, the micropores between LDH crystallites were mostly sealed. The composite films have remarkable anticorrosion property for aluminum metal, in comparison with the single LDH and SiO2 film. With the increasing of SiO2 coating times, the protective effect of the composite film strengthens gradually. This could be due to the synergism between the in situ grown LDH film, working as a rigid frame for depositing of SiO2 sol-gel, and the SiO2 layer, giving excellent barrier property to the composite film because of its better compactness.Download high-res image (85KB)Download full-size image

Double-confined nickel nanocatalyst Ni/Ni(Al)Ox/AlOx, with metal Ni nanoparticles implanted in the weakly crystalline Ni(Al)Ox matrix and embedded in amorphous AlOx networks, was facilely fabricated by hydrogen reduction of the NiAl-LDH precursor at a controlled temperature. Direct structure imaging of Ni and Al species revealed that subnanometer Ni0 clusters nucleate initially in the Ni(Al)Ox matrix. Subsequent growth of Ni0 clusters proceeds at the expense of the surrounding Ni(Al)Ox, accompanied by consecutive transfer of Al3+ from the central part to the near-surface, suggesting a mechanism of ion reverse migration. The Ni(Al)Ox interfacial shell is proposed to provide a strong connection with the metallic Ni and the AlOx network, improving the hydrogen adsorption capacity of the double-confined Ni catalyst and consequently the catalytic activity for dimethyl terephthalate hydrogenation to dimethyl cyclohexane-1,4-dicarboxylate, a prominent modification reagent and intermediate in the polymer industry. The findings should be of great importance to both designing novel confined catalysts and understanding the structure–activity correlation.

It is of economic and environmental interest to develop novel integrated methodologies allowing one-pot synthesis process with single catalyst. Herein, we report our attempt to catalytically hydrogenate dimethyl terephthalate (DMT) into 1,4-cyclohexanedimethanol (CHDM), a linker molecule for polyester fibers which can be produced in practice by a two-step process with two reactors, using supported trimetallic RuPtSn/Al2O3 catalysts in one batch reactor. The catalytic hydrogenation reaction is carried out by two consecutive reaction stages with different reaction temperature and pressure in the batch reactor. The results of catalytic performance and sample characterization by XRD, TPR, and HRTEM demonstrate that trimetallic RuPtSn catalysts show a synergistic effect on the catalytic hydrogenation of DMT to CHDM. Ru4Pt2Sn8/Al2O3 catalyst sample presents higher CHDM yield. A possible mechanism of hydrogenation reaction, which may contain two distinct catalytic active sites related with Ru metal particles, is also provided.

Generation of bimetallic sites on supported catalysts has been proved to be capable of enhancing catalytic performance when compared to those of the corresponding monometallic ones. Herein we report the preparation of novel Al2O3-supported NiCo bimetallic catalysts (NiCo/Al2O3) derived from Ni2+Co2+Al3+-containing layered double hydroxides (NiCoAl-LDHs) precursors, which were in situ grown on the surface and in the pore canals of microspherical γ-Al2O3, and their catalytic performance for selective hydrogenation of pyrolysis gasoline. Bimetallic NiCo/Al2O3 derived from LDHs precursor exhibited the better catalytic performance than the sample prepared by impregnation. The appropriate amounts of substitution of nickel for cobalt improved the catalytic activity and stability dramatically, indicating the synergistic effects of nickel and cobalt in terms of the hydrogenation reactivity. The enhanced reducibility and smaller particles for NiCo/Al2O3 samples derived from LDHs precursor were proposed to suppress the coke formation during the hydrogenation reaction, leading to improve catalytic activity and stability.

The geometrical structure and electronic properties of a series of AuN (N = 1–8) clusters supported on a Mg2+, Al3+-containing layered double hydroxides (MgAl–LDH) are investigated using density functional theory. The Au clusters are supported on two typical crystal faces of the LDH platelet, the basal {0001} and the lateral \( \{ 10\,\bar{1}\,0\} \) crystal face, respectively, corresponding to the top and edge site of monolayer MgAl–LDH lamella for the sake of simplicity. It is revealed that an increase in the charge transfer from the LDH lamella to the AuN clusters at the edge site rather than clusters on the top surface, demonstrating a preferential adsorption for AuN clusters at the edge of LDH lamella. Moreover, the calculated adsorption energy of the AuN clusters on the LDH lamella increases with the cluster size, irrespective of the adsorption site. The investigation on the interaction between O2 and AuN clusters on the LDH lamella is further carried out for understanding the catalytic oxidation properties of the LDH-supported Au catalyst. The formation of reactive O2− species, a necessary prerequisite in catalytic oxidation of CO, by O2 bridging two Au atoms of AuN clusters indicates that the LDH-supported Au catalyst has the required characteristics of a chemically active gold catalyst in CO oxidation.

Pd nanoparticles supported on basic layered double hydroxide (LDH) as highly efficient and reusable catalysts are prepared and characterized. The layered structure of LDH support could be reconstructed to different extent by controlling the activation conditions, which presented changing quantity of Brønsted-base sites. Besides, with the changing calcination temperature the LDH substrate imposed a restricted nano-size effect on the supported Pd particles under identical reduction condition, which demonstrated a convenient approach for controlling the size of supported Pd particles. The resulting Pd/LDH samples were tested as heterogeneous catalysts for solvent-free oxidation of benzyl alcohol using molecular oxygen. The sample with a larger amount of Brønsted-base sites is more active in the oxidation of benzyl alcohol, and after five catalytic runs it still gives benzaldehyde in excellent yields. The promotional effect of Brønsted-base sites of the LDH support on the catalytic activity for benzyl alcohol oxidation over Pd/LDH is studied.

Layered double hydroxides (LDHs), members of a family of two-dimensional anionic clay with flexibility in composition, have found a wide variety of applications in industry, including as additives in polymers, as precursors to magnetic materials, in biology and medicine, in catalysis, and in environmental remediation. A detailed understanding of the mechanism of the LDH formation should gain deep insight on the synthetic methodologies of the material and further allow the properties of the resulting LDH to be tailored to specific applications. Herein, we report a systematic investigation of the formation mechanism of the typical MgAl-LDH by urea precipitation method from a magnesium and aluminum precursor salt solution. It is revealed that, at the first stage of the synthesis, amorphous colloidal hydroxide aluminum is formed from the aluminum precursor salt solution. Then, the amorphous hydroxides are transformed into the crystallites of oxide-hydroxide aluminum boehmite γ-AlOOH, accompanying the continuous incorporation of surrounding Mg2+ into the sheet of the lamellar γ-AlOOH, leading to the charge imbalance of the sheet, which destroys the hydrogen bonds existing between the sheets. Subsequently, the carbonate ions in the solution are intercalated into the interlayer galleries by an electrostatic interaction for balancing the sheet charge, resulting in an initial LDH phase with alveolate-like structure. Finally, the main layers stack to build a three-dimensional network with the positive charge being balanced by the carbonate ions arranged in the hydrated interlayer galleries, and the integrated plate-like structure of LDH is formed. Throughout the above-mentioned processes, the incorporation of magnesium ions into the sheet of the lamellar boehmite can play a primary role for the formation of LDH crystallites.Keywords: formation mechanism; HRTEM; hydrotalcite; lamellar; layered double hydroxides; nucleation;

A simple method for the immobilization of layered double hydroxides (LDHs) on muscovite mica via strong covalent bonding is described. The crystal structure of the LDH films attached on the substrate was studied by X-ray diffraction (XRD) and attenuated total reflectance-Fourier transform infrared (ATR-FT-IR), and the morphology of the films was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which showed that half-hexagonal shaped LDH platelets grow obliquely on the substrate with a high degree of dispersion. The lattice matching between LDH and muscovite structures suggests that the LDH phase grows epitaxially on the surface of the muscovite and the mechanism of the epitaxial growth process has been analyzed in detail. After being activated by a calcination/rehydration procedure, the rehydrated LDH (RLDH) platelets remain firmly immobilized on the muscovite substrate and retain the half-hexagonal platelet morphology of the LDH precursor. The RLDH/muscovite can act as a solid catalyst and shows higher activity in the aldol condensation of acetone than the powdered RLDH analogue synthesized by the same procedure.

Acrylonitrile–butadiene–styrene (ABS) resin is widely used as an important engineering thermoplastic polymer in various industrial applications, but suffers from easily burning and generating a large amount of smoke and toxic gases. Here we report a utilization of hydrotalcite-like MgA1- and ZnMgA1-layered double hydroxides (MgA1- and ZnMgA1-LDHs) as an inorganic flame retardant to ABS resin. The LDHs were prepared by a scalable method involving separate nucleation and aging steps (SNAS). The performances of the LDHs/ABS composites were evaluated by measuring limiting oxygen index (LOI), smoke density (Dm), heat release rate (HRR), and average mass loss rate (av-MLR). The results obtained show that both LDH/ABS composites exhibit higher LOI and lower Dm values, lower values of pk-HRR and av-MLR, and a prolonged combustion time, in comparison with the pristine ABS. Comparison between MgAl- and ZnMgAl-LDH-containing composites shows that the introduction of Zn2+ is able to facilitate flame retardance, smoke suppression efficiency, and tensile strength elongation rate of the ZnMgAl-LDH/ABS composite. Our results show that LDHs may be used as a type of promising inorganic flame retardant to enhance smoke suppression and flame retardant for ABS resin.Graphical AbstractHighlights► MgA1- and ZnMgA1-LDHs were ultilized as an flame retardant to ABS resin. ► Both LDH/ABS composites exhibit enhanced perormances compared with the pristine ABS. ► Introduction of Zn2+ of LDH is able to further facilitate the enhancement.

A cobalt–iron layered double-hydroxide (CoFe-LDH) film with c-axis orientation has been fabricated through a solvent evaporation method and an oriented CoFe2O4/CoO nanocomposite film formed in a subsequent thermal treatment process. The resulting product is composed of nanosized ferromagnetic (FM) CoFe2O4 particles embedded in antiferromagnetic (AFM) CoO matrix with (111)-orientation. A topotactic transformation from the LDHs precursor film to the CoFe2O4/CoO nanocomposite film was proposed to cause an exchange coupling between the FM CoFe2O4 and AFM CoO phases in the nanocomposite, leading to an enhanced magnetic stability of the CoFe2O4, as shown by the higher value of the blocking temperature (TB, >400 K) compared with the values reported in previous studies for pure CoFe2O4 nanoparticles with similar size. Furthermore, the orientation of the CoFe2O4/CoO nanocomposite film is found to be attributed to the magnetic anisotropy when the magnetic field was applied on different directions. Such an improvement in magnetic stability has the potential to facilitate practical applications of FM spinel ferrite/AFM oxide nanocomposite films at room temperature.

Au catalysts with layered double hydroxide (LDH) as support were fabricated and the crystal faces feature of LDH platelets was revealed to have a crucial effect on the location and particle size of gold nanoparticles (AuNPs). A preferential deposition of AuNPs with a narrow size distribution was formed on the lateral {101̅0} faces of LDH platelets. Catalytic property evaluation of the resulting Au/LDH samples showed that the conversion of styrene with tert-butyl hydroperoxide (TBHP) to styrene oxide (SO) occurred on the AuNPs with particle size of 2−3 nm, mainly deposited on the lateral faces of LDH support.Keywords: Au nanoparticles; crystal face; homogeneous deposition-precipitation; layered double hydroxide; styrene epoxidation

CaAl-layered double hydroxide (CaAl-LDH) has recently been proposed as potential concrete hardening accelerators, because of the similarity in the AFm phase (a family of hydrated calcium aluminate phases) that occurs in hydrated cement. The applications of the promising materials require synthesis routes to be capable of producing large-scale, byproduct-free, and easy-to-handle CaAl-LDH. Herein, we report a general and scalable synthesis of pure CaAl-LDH via an organic/water solution. The possibility of the formation of CaAl-LDH is addressed in terms of the prevention of ethanol from the generation of CaCO3 byproduct. The morphology and crystallinity of CaAl-LDH are tuned by varying different pH value, ethanol/water volumetric content, crystallization time, and temperature. A proper synthesis condition (for example, an ethanol/water volume ratio of 4:1, a pH value of 10.5–11.5, an aging time of 24 h, and a crystallization temperature of 70 °C) are optimized, and further readily scaled up, by a factor of up to 20, with respect to the initial starting materials. Our results of pure CaAl-LDH in different organic/water solutions may open up a means to produce promising concrete hardening accelerators in large amounts.

Zirconium phenylphosphonate (ZrPP) films with different crystallite orientations have been fabricated on unmodified and surface-sulfonated polystyrene (PS) substrates by an in situ hydrothermal crystallization method. On the unmodified PS substrate, a monolayer film with the hexagonal ab planes of the ZrPP crystallites parallel to the PS can be obtained by restricting the crystallization time. After a longer crystallization time, the ZrPP films adopt a bilayer arrangement, with the ab planes of the ZrPP crystallites in the lower layer being parallel to the substrate, and the ab planes of the ZrPP crystallites in the upper layer being perpendicular to the substrate. On the surface-sulfonated PS, however, the ZrPP crystallites form a monolayer film with their ab planes perpendicular to the substrate irrespective of the crystallization time. We suggest that the different interactions between the ZrPP crystallites and the two substrates, namely the π–π interactions between the phenyl groups in the ZrPP surface and those in the unmodified PS substrate, and the coordinate interactions between the lone pairs of electrons on oxygen atoms in the sulfonate groups on the sulfonated PS and vacant coordination sites on Zr atoms on the edges of ZrPP crystallites, are responsible for the different morphologies of the monolayer films on the unmodified and sulfonated substrates. Two distinct growth mechanisms are proposed which can satisfactorily account for the different crystallite orientations in the two ZrPP films.

Thermal decomposition of layered double hydroxides (LDHs) is a way of fabricating mixed metal oxide (MMO) nanocomposite materials composed of metal oxide and spinel phases. A detailed understanding of the mechanism of the transformation of the LDH precursor to the MMO should allow the properties of the resulting MMO nanocomposites to be tailored to specific applications. Here we report a systematic investigation of the structure, composition, and morphology evolution from ZnAl-LDHs to ZnO-based MMO nanocomposites composed of ZnO and ZnAl2O4 on calcination at different temperatures. The nucleation and oriented growth of ZnO crystallites and the formation of ZnAl2O4 were monitored by high resolution transmission electron microscopy (HRTEM) combined with selected-area electron diffraction (SAED), in situ X-ray diffraction (XRD), solid-state 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR), and thermogravimetric and differential thermal analyses (TG−DTA). The layered structure of the LDH precursor was maintained as the temperature was increased from room temperature to 180 °C. Upon further heating from 200 to 400 °C, ZnO nuclei doped with Al3+ were first formed as an amorphous phase and then underwent oriented growth along the ⟨101̅0⟩ direction. The high aspect ratio of the LDH platelets is responsible for the oriented growth of the resulting ZnO crystallites. On further increasing the calcination temperature, Zn2+ ions were continuously released from the amorphous phase resulting in the formation of crystalline ZnO nanoparticles doped with Al3+, which are homogeneously dispersed throughout the amorphous phase. When the calcination temperature reached 500 °C, Al3+ ions were released from the ZnO-like structure resulting in the formation of ZnAl2O4 spinel and the crystallinity of the spinel increased gradually with increasing temperature. Sintering of ZnO and ZnAl2O4, with concomitant loss of the platelet-like morphology, occurred below 800 °C. UV−visible spectroscopy showed that the ZnO/ZnAl2O4 nanocomposite prepared by calcination of the ZnAl-LDH precursor at 800 °C has superior UV-blocking properties to both commercial ZnO and a physical mixture of ZnO and ZnAl2O4.

The performance of solid catalysts and catalyst supports is generally believed to be dependent on their morphology, surface area, and architecture. In order to fully exploit their attractive properties in actual practical applications, layered zirconium phosphate materials should be fabricated into macroscopic form. Here, we report the fabrication of microscopic spheres of α-zirconium phosphate (α-ZrP) by a spray-drying process. The layered α-ZrP nanoparticles were originally obtained using a synthesis route involving separate nucleation and aging steps (SNAS). The resulting products are composed of nanosize α-ZrP particles aggregated into solid microspheres with a diameter of 5–45 μm and a sphericity of 0.80. After calcination at 573 K, surface area of 43.8 m2/g could be obtained for α-ZrP microspheres, which is larger than that of the α-ZrP powder after similar thermal treatment (36.2 m2/g). Furthermore, the number of acidic sites of the α-ZrP microspheres is greater than for the α-ZrP powder due to its unique textual properties and higher surface area. The acylation reaction of fatty acid methyl esters (methyl stearate) with ethanolamine to form monoethanolamides was chosen as a probe reaction to evaluate the catalytic activity of the resulting microspherical α-ZrP materials, which showed high activity compared to the sample in the form of powders, with about 92.9% methyl stearate conversion at 393 K for 12 h. The enhanced performance in the reaction is determined by the large surface area and the increased number of acidic sites in the multiple-scales porosity of α-ZrP microspheres.α-Zirconium phosphate (α-ZrP) micropheres were fabricated by a two-step route involving separate nucleation and aging steps(SNAS) and spray-drying. After being calcined at 573 K, the α-ZrP micropheres exhibit better catalytic activity in acylation of amino derivatives than similar α-ZrP powder due to higher surface area and increased acidity.

The in situ crystallization technique has been utilized to fabricate zirconium phenylphosphonate (ZrPP) films with their hexagonal crystallite perpendicular to the copper substrate. The micro/nano roughness surface structure, as well as the intrinsic hydrophobic characteristic of the surface functional groups, affords ZrPP films excellent hydrophobicity with water contact angle (CA) ranging from 134° to 151°, without any low-surface-energy modification. Particularly, in the corrosive solutions such as acidic or basic solutions over a wide pH from 2 to 12, no obvious fluctuation in CA was observed for all the ZrPP film. The k values of the hydrophobic ZrPP films are in the low-k range (k < 3.0), meeting the development of ultra-large-scale integration (ULSI) circuits. The hydrophobicity feature is proposed to bear ZrPP film a more stable low-k value in an ambient atmosphere. Besides, the polarization current of ZrPP films is reduced by 2 orders of magnitude, compared to that of the untreated copper substrate. Even deposited in a vacuum oven for 30 days at room temperature, ZrPP films also show excellent corrosion resistance, indicating a stable anticorrosion property.

MgAl-Layered double hydroxide (LDH) films with different orientations on the two sides of a glass substrate, one of which was modified with poly(vinyl alcohol), have been obtained by a one-step in situ hydrothermal crystallization method, and the growth mechanisms of the two films are discussed.

Magnesium/aluminum layered double hydroxide (LDH) films have been prepared in situ by means of urea hydrolysis using aluminum metal as both the substrate and sole source of aluminum. Scanning electron microscopy (SEM) images showed that the LDH crystallites are almost perpendicular to the substrate and interlaced with each other forming a network of vacant pockets. The film showed outstanding mechanical strength and high adhesion with the substrate. After being calcined at 500 °C, MgAl mixed metal oxide (MMO) films were obtained which retained the morphology of the precursor films. The values of dielectric constant (k) of the MgAl-MMO films were measured and showed low values in the range 2.0−4.7 arising from the low density of the interlaced structure. The effect of varying the preparation conditions of the LDH precursor films on the microstructure and k-value of the corresponding MMO films was investigated by varying the metal ion concentration, crystallization time, and crystallization temperature. The MMO films became more compact with increasing metal ion concentration and crystallization time, which resulted in increased k-values.

A zinc−aluminum layered double hydroxide (ZnAl-LDH)/alumina bilayer film has been fabricated on an aluminum substrate by a one-step hydrothermal crystallization method. The LDH film was uniform and compact. XRD patterns and SEM images showed that the LDH film was highly oriented with the c-axis of the crystallites parallel to the substrate surface. The alumina layer existing between the LDH film and the substrate was formed prior to the LDH during the crystallization process. Polarization measurements showed that the bilayer film exhibited a low corrosion current density value of 10−8 A/cm2, which means that the LDH/alumina bilayer film can effectively protect aluminum from corrosion. Electrochemical impedance spectroscopy (EIS) showed that the impedance of the bilayer was 16 MΩ, meaning that the film served as a passive layer with a high charge transfer resistance. The adhesion between the film and the substrate was very strong which enhances its potential for practical application.

In order to fully exploit their attractive properties in actual practical applications, layered double hydroxide (LDH) materials should be fabricated into macroscopic form. A magnesium−aluminum layered double hydroxide (MgAl-LDH) containing interlayer carbonate anions has been obtained using a synthesis route involving separate nucleation and aging steps, and microspheres of the material formed in a subsequent spray drying process. The resulting products are composed of nanosized LDH particles aggregated into solid microspheres with a diameter of 10−50 μm, a sphericity of 0.84, modal pore access diameter of 87.9 nm, surface area of 43 m2/g, and total pore volume of 1.29 cm3/g. The presence of an accessible diffusion pathway in the macropore domain of the LDH microspheres offers the possibility of enhanced performances in a wide range of applications. Furthermore, the spherical morphology of the materials was retained when the LDHs were converted into solid base catalysts by calcination and subsequent rehydration, indicating the robust nature of the macroscopic particles.

Mixed metal oxide (MMO) films containing Ni2+ and Al3+ have been fabricated by a simple process involving calcination of layered double hydroxide (LDH) film precursors at 300−600 °C for 4 h in air. Scanning electron microscopy (SEM) reveals that the resulting Ni/Al−O thin films maintain the original nestlike morphology of the precursor films without any deformation of the microstructure during the thermal decomposition process. After surface treatment with an aqueous solution of sodium laurate, the wettability of the NiAl-LDH and Ni/Al−O thin film surfaces changes from hydrophilic to hydrophobic. Moreover, whereas the NiAl-LDH film exhibits a low adhesion for water (Cassie−Baxter behavior) after surface modification, the Ni/Al−O films exhibit a high adhesion for water (Wenzel behavior). A possible explanation for this phenomenon has been suggested.

CaAl-layered double hydroxide (CaAl-LDH), one of anionic functional layered materials, has recently been proposed as potential concrete hardening accelerators. Previous laboratory synthesis shows the necessity of employing a protective nitrogen atmosphere to avoid the formation of large amounts of CaCO3 byproduct. Here, we present a preparation of pure CaAl-LDHs which are readily free of contamination by CaCO3. The CaAl-LDHs were prepared via a scalable method of separate nucleation and aging steps (SNAS) by facile introduction of a mixed ethanol/water media. The application of the as-prepared CaAl-LDHs was investigated as a hardening accelerator in concrete. Standard tests of the compressive and flexural strengths of the cement mortars showed that specimens containing CaAl-LDHs as a hardening accelerator exhibited a greatly enhanced performance in respect of early compressive strength and early flexural strength; and the values increased by 61% and 71%, respectively compared to the pristine concrete specimen. The enhanced performances were addressed in terms of the results in situ X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry.

In order to fully exploit the green characteristics of solid base catalysts they should be fabricated into macrostructured rather than powder form. Magnesia-rich magnesium aluminate spinel (MgO·MgAl2O4) framework catalysts with tunable basicity have been prepared by using γ‐Al2O3 macrospheres (0.5–1.0 mm in diameter) as a hard template. The process involves in situ growth of magnesium–aluminum layered double hydroxides (MgAl-LDHs) in the channels of the γ‐Al2O3 macrospheres by the urea hydrolysis method, followed by calcination, tuning of the basicity through etching of excess aluminum with aqueous alkali and a final calcination step. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), elemental analysis and low temperature N2 adsorption–desorption studies demonstrate that the composite MgO·MgAl2O4 materials are composed of nanosized rod-like particles aggregated into a spherical framework. Catalytic reactivity was investigated by using methanolysis of soybean oil as probe reaction. The MgO·MgAl2O4 composite shows a higher biodiesel yield compared to an MgO/MgAl2O4/γ‐Al2O3 material with the same loading of magnesium prepared by a conventional impregnation method. The enhanced catalytic activity of the former material can be ascribed to its higher basicity, specific surface area, pore volume and pore size.

A hybrid film containing a substituted azobenzene, 7-[(trifluoromethoxyphenylazo)phenoxy]pentanoate anion (CF3AZO-), intercalated in a layered double hydroxide (LDH) film immobilized on a porous anodic alumina/aluminum (PAO/Al) substrate has been prepared by an anion-exchange reaction of a ZnAl–NO3–LDH/PAO/Al precursor film with the sodium salt of CF3AZO- anions under mild conditions. The hybrid LDH film was characterized by scanning electron microscopy, powder X-ray diffraction and Fourier transform infrared spectroscopy. TG–DTA, UV–visible spectroscopy and CIE 1976 L*a*b* color difference (ΔE) tests indicated that the intercalated ZnAl–CF3AZO–LDH showed enhanced thermo-stability and photo-stability compared to the pristine CF3AZO salt. Irradiation with UV light led to a switch in wettability of the film from superhydrophobic to hydrophilic and this process could be reversed by subsequent irradiation with visible light.

Films of layered double hydroxides (M/Al-LDHs) with M=Ni, Zn have been fabricated on a porous anodic alumina/aluminum (PAO/Al) substrate via an in situ crystallization technique. The Ni/Al-LDH film has an orientation in which the ab-faces of the platelets are all perpendicular to the substrate whilst the LDH crystallites in the Zn/Al-LDH film are randomly orientated. Furthermore, the interlayer galleries of Ni/Al-LDH contain CO32- anions whereas NO3− anions were found in the interlayer galleries of Zn/Al-LDH. These differences between the Ni/Al-LDH and Zn/Al-LDH films are, at first sight, surprising because the films were fabricated under identical experimental conditions. Two different mechanisms, homogeneous nucleation and the heterogeneous nucleation, have been proposed in order to account for the different growth processes of the Ni/Al-LDH and Zn/Al-LDH films, respectively. The two distinct growth mechanisms can satisfactorily account for the different crystallite orientations and types of interlayer ion in the M/Al-LDH (M=Ni, Zn) films.

MgAl-Layered double hydroxide (LDH) films with different orientations on the two sides of a glass substrate, one of which was modified with poly(vinyl alcohol), have been obtained by a one-step in situ hydrothermal crystallization method, and the growth mechanisms of the two films are discussed.