Properties Of Layered Double Hydroxides Research Articles

Effect of Synthesis Method on Properties of Layered Double Hydroxides Containing Ni(III)

Unstable oxidation state +3 of nickel can be stabilized in the structure of layered double hydroxides, the resulting crystallinity and properties being dependent on the synthesis method. Three different wet chemical methods (co-precipitation at variable pH, co-precipitation followed by hydrothermal treatment, co-precipitation with microwave treatment) were used to synthesize Mg/Ni–Al layered double hydroxides containing triply charged nickel cations. Lattice parameters of the samples synthesized by various methods were found to differ from each other by about 1.5%. The most crystallized sample was obtained by hydrothermal synthesis. The oxidation state of nickel in the LDH samples was confirmed by XPS. TEM mapping gave evidence of the uniform distribution of nickel in all the samples. The LDHs’ reduction with hydrogen and thermal transformations of the phase composition and morphology of LDHs were studied in detail. The properties of the samples synthesized by the different methods were shown to be quite similar.

Effect of drying step on layered double hydroxides properties: Application in reactive dye intercalation

Freeze-dried sulfate intercalated layered double hydroxides (LDH) phase was synthetized by coprecipitation method via direct intercalation of sulfate anion. The effect of freeze-drying process on LDH properties was investigated. The resulting phase was evaluated for its efficiency in the intercalation of the reactive azo dye, Remazol Brilliant Red F3B (RR-F3B). The freeze-dried phase exhibited a low crystallinity and narrow particle size distribution compared to conventional LDH phases. The freezing step led to highly aggregated nanoparticles with a characteristic distance d003 of 8.12 Å. The preferential arrangement of the intercalated dye species was examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The results showed that RR-F3B molecules were partially accommodated between the LDH layers as single-layer with horizontal orientation. The effect of drying on morphological and structural properties can be attributed to several stresses during freezing and drying steps.

Tuning the Adsorption Properties of Layered Double Hydroxides to Tailor Highly Active Oxygen Bifunctional Electrocatalysts

Herein a new class of CoNx-C/NiFe2O4 bifunctional electrocatalysts was synthesized by calcination of CoPcTs/Ni2Fe-LDH precursor at 700°C under nitrogen atmosphere. A series of the CoPcTs/Ni2Fe-LDH precursors were prepared by adsorption of cobalt phthalocyanine tetrasulfonate (CoPcTs) on Ni2Fe-LDH. The synergistic effect between CoNx and NiFe2O4 compound, in the CoNx-C/NiFe2O4-120 hybrid composite showed excellent ORR and OER catalytic activity. The ΔE (oxygen electrode activity parameter for evaluating the overall electrocatalytic activity and reversibility of a bifunctional electrocatalyst) value for CoNx-C/NiFe2O4-120 is 0.92 V.

Fatigue Properties of Layered Double Hydroxides Modified Asphalt and Its Mixture

This study investigated the influence of layered double hydroxides (LDHs) on the fatigue properties of asphalt mixture. In this paper, different aging levels (thin film oven test (TFOT) and ultraviolet radiation aging (UV aging for short)) of bitumen modified with various mass ratios of the LDHs were investigated. The TFOT and UV aging process were used to simulate short-term field thermal-oxidative aging and long-term field light UV aging of bitumen, respectively. The influences of LDHs on the fatigue properties of LDHs were evaluated by dynamic shear rheometer (DSR) and indirect tensile fatigue test. Results indicated that the introduction of LDHs could change the fatigue properties of bitumen under a stress control mode. The mixture with modified bitumen showed better fatigue resistance than the mixture with base bitumen. The results illustrated that the LDHs would be alternative modifiers used in the bitumen to improve the lifetime of asphalt pavements.

Theoretical Processing in Understanding the Structures and Properties of Layered Double Hydroxides

We review the techniques,applications,characteristics,and insights gained from the use of theoretical calculations that were applied to the study of layer double hydroxides (LDHs) materials by using a series of typical case studies. The advantages and shortcomings of different theoretical calculation methods (quantum mechanics,molecular mechanics,geometric model,and electrostatic potential energy model) for the study of the properties of LDHs minerals are compared. Based on quantum mechanics calculations,we obtained information about template effects on the construction of layered double hydroxides,super molecular interactions in LDHs containing simple anions,electronic properties,and reaction pathways etc. Compared with quantum mechanics,molecular mechanics is quicker in obtaining information about the interlayer structure,arrangement,orientation,hydration,and the swelling trajectory as well as elastic constants etc of LDHs intercalated with various anions. The geometric model and electrostatic potential energy model offer a more intuitive and visual mathematical model of LDHs minerals. The calculations were done on the verge of full size LDHs,which may allow the prediction of the crystal structure. Along with the development of theoretical methods and computer techniques,computational simulation method has become an effective adjust to experimental techniques for obtaining the microscopic structures,electronic and dynamic properties of LDHs minerals.

層状複水酸化物(LDH)－ポリマーナノコンポジットの調製と機械的性質

層状複水酸化物(LDH)－ポリマーナノコンポジットの調製と機械的性質

Nitrate Ion-sieve Properties of Layered Double Hydroxides

Abstract Layered double hydroxides (LDHs) with different kinds of metals in the brucite layer were prepared and their anion exchange properties were studied batchwise. A nitrate ion-sieve property was observed for LDHs depending on the basal spacing of the brucite layer. The distribution coefficient of nitrate ion was a maximum on the Ni–Fe type LDHs having a basal spacing of 0.81 nm.

Use of the Ion-Exchange Properties of Layered Double Hydroxides for Water Purification

The sorption of chromate and dichromate ions by a [Zn-Al-Cl] layered double hydroxide was investigated. The anionic clay, prepared by coprecipitation at pH 8, was found to be pure upon characterization by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetry and to have low BET surface area and small pore volume. The interaction of the clay with both chromate and dichromate ions has been studied by UV-VIS spectroscopy. The treatment of water containing 15-300 ppm of CrO42- or Cr2O72- was successful. The sorption capacities of the clay for CrO42- and Cr2O72- are close to 1 and 0.6 mmol/g, respectively.

Catalytic Properties of Layered Double Hydroxides and Their Calcined Derivatives

Studies on the effect of the structural and compositional properties of layered double hydroxides (LDHs) and their decomposition products on the ethanolysis of propylene oxide to form glycol ethers are reported. The reaction, supported by results of indicator titrations, is used as a tool for elucidating the identity of the active sites in these materials. For LDHs, the catalytic behavior relates to their structural properties and the active sites can therefore be rationalized. In the case of their calcined derivatives, however, there is no apparent correlation due to the diversity of the active sites.