Narrow Results

The thermal behavior of Mg and Al layered double hydroxide with interlayer hydrogen phosphate (abb. as Mg/Al-HPO₄-LDH) is investigated below 1273 K by means of XRD, TG-DTA, SEM and FT-IR. The basal spacing of Mg/Al-HPO4-LDH decreases with increasing heating temperature stepwise in two stages; from 1.07 nm at 293 K to 0.85 nm at 333 K in the first stage and to 0.73 nm between 373 K and 443 K in the second one. The LDH becomes amorphous above 443 K until Mg₃ (PO₄)₂, MgO and MgAl₂O₄ (spinel) appear at 1273 K. SEM images of the LDH show plate-like crystallites both before and after heating at 473 K.

Intercalation of hydrogen phosphate (HPO₄) into Mg/Al-Layered Double Hydroxides (LDH) with DodecylBenzeneSulfonate (DBS) was investigated with regard to anion exchange, rehydration and a combination of delamination and anion exchange. HPO₄ could not be intercalated into the interlayer space of LDH with DBS when using either anion exchange or rehydration methods. However, HPO₄ was successfully intercalated into the Mg/Al-LDH using a combination of delamination and anion exchange methods.

An exfoliated layered double hydroxides/poly(methyl methacrylate) (LDHs/PMMA) nanocomposite was prepared by in situ solution polymerization of methyl methacrylate (MMA) in the presence of 4-vinylbenzenesulfonate intercalated LDHs(MgAl-VBS LDHs). MgAl-VBS LDHs was prepared by the ion exchange method, and the structure and composition of the MgAl-VBS LDHs were determined by X-ray diffraction (XRD), infrared spectroscopy and elemental analysis. XRD and transmission electron microscopy (TEM) were employed to examine the structure of LDHs/PMMA nanocomposite. It was indicated that the LDHs layers were well exfoliated and dispersed in the PMMA matrix. The grafting of PMMA onto LDHs was confirmed by the extraction result and the weight fraction of grafted PMMA increased as the weight fraction of LDHs in the nanocomposites increased.

Nano-ordered hybrid films of layered double hydroxide (LDH) nanosheets and two types of anionic dye molecules, i.e. tetrakis(4-carboxyphenyl)porphyrin (TCPP) and 1,3,6,8-pyrenetetrasulfonic acid (PTSA), were prepared by a layer-by-layer deposition (LBL) method. Photo-induced energy transfers (PET) between the PTSA and TCPP layers were investigated for two differently stacked structures of the TCPP/LDH/PTSA hybrid films, i.e. (a) PTSA/LDH multilayers independently stacked on the TCPP/LDH multilayers to form (TCPP/LDH)_n/(PTSA/LDH)_n and (b) TCPP/LDH and PTSA/LDH monolayers deposited alternately to form [(TCPP/LDH)/(PTSA/LDH)]_n hybrid films, which were both prepared by varying the successive and alternate stacking of the (TCPP/LDH) and (PTSA/LDH) unit layers. A Foerster type resonance energy transfer is observed in the present hybrid films, where the efficiency of PET was strongly affected by changing the distance between the TCPP and PTSA molecules in the (TCPP/LDH)₃/(PSS/LDH)_m/(PTSA/LDH)₃ hybrid films (m = 1−10) obtained by the insertion of the photochemically inert poly(styrenesulfonic acid) (PSS) and LDH hybrid layers, i.e. the insertion of (PSS/LDH)_m between the (TCPP/LDH)₃ and (PTSA/LDH)₃ layers.

Sintering of the active metallic nanoparticles and carbon deposition are the key problems faced for CO methanation catalysts. For overcoming those problems, bimetallic nanocatalyst is a promising route. In this work, a series of Al₂O₃ supported Ni-Co alloy catalysts were prepared by reducing NiCoAl layered double hydrotalcite (LDHs), and characterized with X-ray diffraction (XRD), temperature programmed reduction TPR, N₂ adsorption-desorption, transmission electron microscopy (TEM) and temperature programed oxidation (TPO) techniques. The resultant catalysts were mesoporous with nanoparticles of Ni-Co alloy ranging from 7.9nm to 9.2nm which were highly dispersed in alumina matrix. The sample Ni₇Co₃-Al₂O₃ catalysts showed very good catalytic performance during the stability test at 500/600${}^{\circ }$C for 300h, meanwhile exhibited excellent anti-sintering ability and anti-carbon deposition ability, owing to the formation of Ni-Co alloy and the feature of LDHs. This strategy for improving anti-sintering and anti-carbon deposition should be extendable for catalysts of other reactions.

In this work, organic–inorganic hybrid ultrathin transparent films (UTFs), produced by layer-by-layer (LBL) assembly of the europium inclusion complex of $\beta$-cyclodextrin ($\beta$-CD) and Mg–Al-layered double hydroxide (MgAl–NO₃–LDHs) nanosheets, are reported. UV-visible (UV-Vis) absorption and fluorescence spectroscopy show orderly growth of the europium inclusion complex of $\beta$-CD/layered double hydroxide (EICC/LDH) films with an increasing number of deposition cycles. X-ray diffraction and scanning electron microscopy measurements indicate that the films feature periodic layered structures with uniform surface morphology. Moreover, when EICC is assembled with inorganic rigid LDH nanosheets, the lifetimes are prolonged due to the isolation effect, and the UTFs are transparent with high brightness, which indicate that these films could serve as new optical materials.

In this work, the Ni–Mn layered double hydroxide (Ni–Mn LDH) nanopetals are fabricated on three-dimensional reduced graphene oxide/Ni foam (RGO/NF) by one-step hydrothermal method, in which the suspension of graphene oxide (GO) is directly reduced by nickel foam (NF) to obtain NF/RGO. The composite, which consists of interconnected Ni–Mn LDH nanopetals, forms a macroporous structure. Such an open space can promote electrolyte dispersion and ion diffusion of active substances, thus enhancing capacitance performance. Remarkable, during crystal growth, RGO can not only provide active sites for Ni–Mn LDH nanopetals, but also effectively connect Ni–Mn LDH nanopetals to NF, further promoting the electrochemical behavior of composite material. Moreover, RGO possess reasonable chemical stability which can improve the mechanical properties of the composite to obtain good stability. The experimental results show that the NF/RGO electrode material with Ni–Mn LDH nanopetals has excellent specific capacitance of 2250Fg${}^{-1}$ at 1Ag${}^{-1}$, good rate performance (the capacitance retention rate is still 64.0% at 10Ag${}^{-1})$ and excellent cycle life (45.1% at 10Ag${}^{-1}$ after 5000 cycles). NR/NM–LDH is used as the positive electrode and activated carbon is used as the negative electrode to assemble the asymmetric supercapacitor, the proper power density and energy density indicates that the NR/NM–LDH composite has great potential as an electrode material for supercapacitors.

Hierarchical hollow nano-/micro-architectures with complex multishelled structures are highly desirable for achievement of various functionalities. However, it is still a great challenge to integrate multinary compositions into a nonspherical hollow structure with complex multishells. Herein, we developed an effective strategy to construct hierarchical double-shelled NiCo-layered double hydroxides@MSiO₃ (NiCo-LDH@MSiO₃, M = Ni, Cu, Mn) hollow polyhedral nanocages with inner NiCo-LDH and outer MSiO₃ layers. Our design principle involved a one-pot synthesis of Co-based zeolitic imidazolate framework-67@SiO₂ (ZIF-67@SiO${}_2)$ core@shell polyhedrons and a subsequent two-step in situ chemical conversion reaction process. Benefiting from the structural merits including high specific surface area, abundant mass diffusion pathways, and the unique hierarchical hollow structures, the double-shelled NiCo-LDH@MSiO₃ hollow polyhedral cages exhibited significant adsorption capacity of Congo red. Especially, the maximum adsorption capacity of the double-shelled NiCo-LDH@NiSiO₃ hollow polyhedral cages could reach up to 510.6mg/g, implying a high efficiency for the removal of Congo red from aqueous solution and a potential application in water treatment.

In this paper, well-defined Mg-Al LDHs nanosheets with high yield are prepared by the following sequential procedures: hydrothermal preparation of Mg-Al-CO${}_3^{2-}$ LDHs, followed by expanding interlayer spacing by NH₄NO₃ treatment. The results show that the concentration of the layer expansion agent (NH₄NO${}_3)$ and the exfoliation solvent play a key role in the exfoliation result. The basal spacing changed from 0.758nm to the range of 0.758–0.895nm when the concentration of NH₄NO₃ was increased up to 5 M, which infers that the increase of layer space is caused by the synergy of NH${}_4^{+}$ and NO${}_3^{-}$. Among the three exfoliation solvents (formamide, N-methyl pyrrolidone and isopropyl alcohol), formamide showed the highest exfoliation effect. From the characteristic XRD patterns, the as-obtained colloidal aggregates of the exfoliated nanosheets do not show the characteristic diffractions of LDHs, while the typical peaks at 10.562${}^{\circ }$, 20.032${}^{\circ }$ and 21.185${}^{\circ }$ assigned to LDHs are observed after drying of the colloidal aggregates. Moreover, a transparent LDH film is also successfully prepared by coating colloidal aggregates of nanosheets on a glass substrate without using any adhesive. The stable film exhibits the strong adsorption ability of Methyl Orange.

The study on the evolution of natural ferroan brucite (MgFe(OH)${}_2)$ was beneficial to discovering the function of brucite in the geologic cycle and directing the reasonable utilization of brucite resources. In this study, natural MgFe(OH)₂ was characterized in detail and Rietveld refinement was employed to determine the precise content and existing environment of Fe${}^{2+}$. The reaction products of MgFe(OH)₂ under various atmospheric conditions, including CO₂, O₂ and a mixed atmosphere of CO₂ and O₂ were innovatively investigated to gain insights into the evolution process and the crucial role played by Fe${}^{2+}$. Accordingly, the evolution mechanism of MgFe(OH)₂ under different atmospheres was afforded based on the characterization and molecular simulations like electron transfer and binding energy. Fe${}^{2+}$ in MgFe(OH)₂ layers could be oxidized by O₂ easily and give positive layers, CO${}_3^{2-}$ produced by CO₂ dissolving in water simultaneously was attracted to finally produce CO${}_3^{2-}$ intercalated MgFe- layered double hydroxides (MgFe-CO${}_3^{2-}$-LDHs) which could be used as adsorbents, catalysts and so on. This process was supported by thermodynamics and also the dominant evolution route due to the dynamic reason. The existence of Fe${}^{2+}$ in MgFe(OH)₂ resulted in the diversity of the evolution products. This work highlighted the composition and structure of evolution products of natural MgFe(OH)₂ under different environment as well as its possible application field.

In this paper, Ce-doped CdAl layered double hydroxide (LDH) was first synthesized and the derivative CdO/Al₂O₃/CeO₂ composite oxide was prepared by calcining Ce-doped CdAl LDH. The structure, morphology and chemical state of the Ce doped CdAl LDH and CdO/Al₂O₃/CeO₂ were also investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), solid state nuclear magnetic resonance (SSNMR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The gas sensing properties of CdO/Al₂O₃/CeO₂ to ethanol were further studied and compared with CdO/Al₂O₃ prepared from CdAl LDH, CeO₂ powder as well as the calcined Ce salt. It turns out that CdO/Al₂O₃/CeO₂ sensor shows best performance in ethanol response. Besides, CdO/Al₂O₃/CeO₂ possesses short response/recovery time (12/72 s) as well as remarkable selectivity in ethanol sensing, which means composite oxides prepared from LDH are very promising in gas sensing application.

In this paper, flower-like layered double hydroxides were synthesized with eggshell membrane assistant. The as-prepared samples were characterized by a series of techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Thermal gravity-differential thermal analysis and Nitrogen sorption/desorption. The resulting layered double hydroxides were composed of nanoplates with edge-to-face particle interactions. The specific surface area and total pore volume of the as-prepared flower-like layered double hydroxides were 160m²/g and 0.65m³/g, respectively. The adsorption capacity of flower-like layered double hydroxides to Congo Red was 258mg/g, which was higher than that of layered double hydroxides synthesized by the traditional method.