Synthesis and characterization of Cd-Cr and Zn-Cd-Cr layered double hydroxides intercalated with dodecyl sulfate

Cd-Cr and Zn-Cd-Cr layered double hydroxides (CdCr-LDH and ZnCdCr-LDH) containing alkyl sulfate as the interlamellar anion have been prepared through a coprecipitation technique. The resulting compounds were characterized using X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Magnetic property measurements indicate that antiferromagnetic interactions occur between the chromium ions in the two compounds at low temperatures. The introduction of zinc influences the ligand field of Cr^III and the Cr^III-Cr^III interactions in the LDH compound. It is found that both CdCr-LDH and ZnCdCr-LDH can be delaminated by dispersion in formamide, leading to translucent and stable colloidal solutions.     

Electric and dielectric behavior of copper-chromium layered double hydroxide intercalated with dodecyl sulfate anions using impedance spectroscopy

The Cu₂Cr-DS-LDH hybrid was successfully prepared by the anion exchange method at room temperature. The structure, the chemical composition and the physico-chemical properties of the sample were determined using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and inductively coupled plasma (ICP). In this work, the electrical and dielectric properties investigated are determined using impedance spectroscopy (IS) in a frequency range of 1 Hz to 1 MHz. Indeed, the Nyquist diagram modelized by an electrical equivalent circuit showed three contributions attributed respectively to the polarization of grains, grains boundaries and interface electrode-sample. This modelization allowed us to determine the intrinsic electrical parameters of the hybrid (resistance, pseudo-capacitance and relaxation time). The presence of the non-Debye relaxation phenomena was confirmed by the frequency analysis of impedance. Moreover, the evolution of the alternating current conductivity (σ_ac) studied obeys the double power law of Jonscher. The ionic conduction of this material was generated through a jump movement by translation of the charge carriers. As for the dielectric behavior of the material, the evolution of dielectric constant as a function of frequency shows relatively high values in a frequency range between 10 Hz and 1 KHz. The low values of the loss tangent obtained in this frequency zone can valorize this LDH hybrid.     

Solid-state chelation of metal ions by ethylenediaminetetraacetate intercalated in a layered double hydroxide

The solid-state chelation of transition metal ions (Co(2+), Ni(2+), and Cu(2+)) from aqueous solutions into the lithium aluminum layered double hydroxide ([LiAl(2)(OH)(6)]Cl x 0.5H(2)O or LDH) which has been pre-intercalated with EDTA (ethylenediaminetetraacetate) ligand has been investigated. The intercalated metal cations form [M(edta)](2)(-) complexes between the LDH layers as indicated by elemental analysis, powder X-ray diffraction, and IR and UV-vis spectroscopies. If metal chloride or nitrate salts are used in the reaction with the LDH then co-intercalation of either the Cl(-) or NO(3)(-) anions is observed. In the case of metal acetate salts the cations intercalate without the accompanying anion. This can be explained by the different intercalation selectivity of the anions in relation to the LDH. In the latter case the introduction of the positive charge into LDH structure was compensated for by the release from the solid of the equivalent quantity of lithium and hydrogen cations. Time-resolved in-situ X-ray diffraction measurements have revealed that the chelation/intercalation reactions proceed very quickly. The rate of the reaction found for nickel acetate depends on concentration as approximately k[Ni(Ac)(2)](3).     

Synthesis and characterization of 5-fluorocytosine intercalated Zn-Al layered double hydroxide

In this paper, the intercalation of 5-fluorocytosine (5-FC) into a layered inorganic host, Zn-Al layered double hydroxide (LDH), has been carried out using coprecipitation method to obtain 5-FC/LDH nanohybrids. The intercalated amount (A_In) of 5-FC into the LDH is remarkably dependent on the molar ratio (R_F/M) of 5-FC to metal ions and the pH of coprecipitation system. The morphology of 5-FC molecules in 5-FC/LDH nanohybrids is dependent on the A_In. It is interestingly found that the morphology of the nanohybrid particles may be changed with the increase of R_F/M from hexagonal plate particles to threadlike particles. The in vitro drug release from the nanohybrids is remarkably lower than that from the corresponding physical mixture and pristine 5-FC at either pH 4.8 or pH 7.5. In addition, the release rate of 5-FC from the nanohybrid at pH 7.5 is remarkably lower than that at pH 4.8, this is due to a possible difference in the release mechanism. The obtained results show these drug-inorganic nanohybrids can be used as a potential drug delivery system.     

Double phase inversion of emulsions containing layered double hydroxide particles induced by adsorption of sodium dodecyl sulfate

A liquid paraffin-water emulsion was investigated using layered double hydroxide (LDH) particles and sodium dodecyl sulfate (SDS) as emulsifiers. Both emulsifiers are well-known to stabilize oil-in-water (o/w) emulsions. Surprisingly, a double phase inversion of the emulsion containing LDH particles is induced by the adsorption of SDS. At a constant LDH concentration, the emulsion is o/w type when SDS concentrations are low. At intermediate SDS concentrations, the first emulsion inversion from o/w to w/o occurs, which is attributed to the enhanced hydrophobicity of LDH particles caused by the desorption of the second layer of surfactant, leaving a densely packed SDS monolayer on the LDH exterior surfaces. The second inversion from water-in-oil (w/o) to o/w occurs at higher SDS concentrations, which may be due to the competitive adsorption at the oil/water interfaces between the LDH particles modified by the SDS bilayers and the free SDS molecules in the bulk solution, but the free SDS molecules dominate and determine the emulsion type. Laser-induced fluorescent confocal micrographs clearly confirm the adsorption of LDH particles on the surfaces of the initial o/w and intermediate w/o emulsion droplets, whereas no LDH particles were adsorbed on the final o/w emulsion droplet surfaces. Also, transmission electron microscopy (TEM) observations indicate that the shape of the final o/w emulsions is similar to that of the monomeric SDS-stabilized emulsion but different from that of the initial o/w emulsions. The adsorption behavior of SDS on LDH particles in water was investigated to offer an explanation for the emulsion double phase inversion. The zeta potential results show that the particles will flocculate first and then redisperse following surfactant addition. Also, X-ray diffraction (XRD) measurements indicate that SDS adsorption on the LDH interior surfaces will be complete at intermediate concentrations.     

Synthesis of layered zinc hydroxide intercalated with dodecyl sulfate organic–inorganic hybrid nanocomposite as a fiber coating for the headspace solid‐phase microextraction of aromatic hydrocarbons from water

We describe the synthesis of a layered zinc hydroxide‐dodecyl sulfate organic–inorganic hybrid nanocomposite as a new solid‐phase microextraction fiber. The fiber coating can be prepared easily in a short time and the reaction is at room temperature; it is mechanically stable and exhibits relatively high thermal stability. The synthesized layered zinc hydroxide‐dodecyl sulfate nanocomposite was successfully prepared and immobilized on a stainless steel wire and evaluated for the extraction of aromatic compounds from aqueous sample solutions in combination with gas chromatography and mass spectrometry. The method yields good results for some validation parameters. Under optimum conditions (extraction time: 15 min, extraction temperature: 50°C, desorption time: 1 min, desorption temperature: 250°C, salt concentration: 0.5 g/mL), the limit of detection and dynamic linear range were 0.69–3.2 ng/L and 10–500 ng/L, respectively. The method was applied to the analyses of benzene, toluene, ethylbenzene, and o‐, p‐, and m‐xylenes in two real water samples collected from the Aji river and Mehran river, Tabriz, Iran. Under optimum conditions, the repeatability and reproducibility for one fiber (n = 3), expressed as the relative standard deviation, was 3.2–7.3% and 4.2–11.2% respectively. The fibers are thermally stable and yield better recoveries than conventional methods of analysis.     

Electrochemical synthesis of layered manganese oxides intercalated with tetraalkylammonium ions

Thin films of birnessite-type layered manganese oxides with various interlayer spacings have been prepared on a platinum electrode by a one-step electrochemical procedure. The process involves a potentiostatic oxidation of aqueous Mn(2+) ions at around +1.0 V (Ag/AgCl) in the presence of tetraalkylammonium cations with different alkyl chain lengths. X-ray diffraction indicates that the films deposited with tetrabutylammonium (TBA), tetrapropylammonium (TPA), and tetraethylammonium (TEA) ions are composed of a single phase where unhydrated tetraalkylammonium ions are accommodated as a monolayer between manganese oxide layers. The interlayer spacing of the products increases in an order of TEA < TPA < TBA. The film deposited with tetramethylammonium (TMA) is a mixture of two phases relating to hydrated and unhydrated guest cations, the former being predominant probably as a result of less hydrophobic property of TMA compared to that of other tetraalkylammonium ions. The TBA(+)-intercalated Mn oxide film-coated electrode exhibits a good charge/discharge property in a KCl solution between 0 and +0.8 V. In this case, TBA(+) ions between the Mn oxide layers are rapidly replaced with K(+) in solution by ion exchange, accompanying a shrinkage of the interlayer. The incorporated K(+) ions as well as protons play an important role in the electrochemical conversion between Mn(4+) and Mn(3+) in the oxide layer. In the TBACl solution, the interlayer TBA(+) ions can be excluded electrochemically during the positive-going scan, concomitant with the oxidation of Mn(3+) sites. This causes an anodic current and the accompanying shrinkage of the interlayer. On the reverse scan, however, the compressed interlayer does not allow the incorporation of bulky TBA(+) ions from the electrolyte, with virtually no cathodic current observed. Such an obvious difference in electrochemical behavior between the two electrolytes can be recognized by considering that most of the Mn oxide surface is present inside the layered structure, not on the external surface. This indicates that the layered structure is formed over the entire film.     

Synthesis and characterization of sulfate and dodecylbenzenesulfonate intercalated zinc-iron layered double hydroxides by one-step coprecipitation route

Inorganic sulfate- and organic dodecylbenzenesulfonate (DBS)-intercalated zinc-iron layered double hydroxides (LDHs) materials were prepared by one-step coprecipitation method from a mixed salt solutions containing Zn(II), Fe(II) and Fe(III) salts. The as-prepared samples have been characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption, scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP), and Mössbauer spectroscopy (MS). The XRD analyses demonstrate the typical LDH-like layered structural characteristics of both products. The room temperature MS results reveal the characteristics of both the Fe(II) and Fe(III) species for SO₄²⁻-containing product, while only the Fe(III) characteristic for DBS-containing one. The combination characterization results and Rietveld analysis illustrate that the SO₄²⁻-containing product possesses the Green Rust two (GR2)-like crystal structure with an approximate chemical composition of [Zn_0.435·Fe^II_0.094·Fe^III_0.470·(OH)₂]·(SO₄²⁻)_0.235·1.0H₂O, while the DBS-containing one exhibits the common LDH compound-like structure. The contact angle measurement indicates the evident hydrophobic properties of DBS-containing nanocomposite, compared with SO₄²⁻-containing product, due to the modification of the internal and external surface of LDHs by the organic hydrophobic chain of DBS.     

Synthesis of Mg2Al-Cl layered double hydroxide nanosheets in a surfactant-free reverse microemulsion

The synthesis of Mg₂Al-Cl layered double hydroxide (LDH) nanosheets in a surfactant-free reverse microemulsion is described. The microemulsion was composed of toluene, isopropanol, and an aqueous solution as the dispersed phase. An aqueous LDH nanosheet dispersion was obtained by a double-microemulsion technique. LDH nanosheets were characterized by X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and thermogravimetric and elemental analyses. The LDH nanosheets consisted of a single brucite layer without any loading of organic molecules. To the best of our knowledge, this is the first report of a naked LDH monolayer aqueous dispersion being directly obtained. The LDH monolayers can be used as building blocks for LDH-based functional materials.     

Stabilization of antioxidant gallate in layered double hydroxide by exfoliation and reassembling reaction

As for the stabilization of chemically sensitive bioactive molecule in this study, gallic acid (GA) with antioxidant property was intercalated into interlayer space of layered double hydroxide (LDH), which was realized by exfoliation and reassembling reaction. At first, the pristine nitrate-type Zn₂Al-LDH in solid state was synthesized via co-precipitation followed by the hydrothermal treatment at 80 °C for 6 h, and then exfoliated in formamide to form a colloidal solution of exfoliated LDH nanosheets, and finally reassembled in the presence of GA to prepare GA intercalated LDH (GA-LDH) desired, where the pH was adjusted to 8.0 in order to deprotonate GA to form gallate anion. According to the XRD analysis, GA-LDH showed well-developed (00l) diffraction peaks with a basal spacing of 1.15 nm, which was estimated to be larger than that of the pristine LDH (0.88 nm), indicating that gallate molecules were incorporated into LDH layers with perpendicular orientation. From the FT-IR spectra it was found that gallic acid was completely deprotonated into gallate, and stabilized in between LDH lattices via electrostatic interaction. The content of GA in GA-LDH was determined to be around 23 wt% by UV–vis spectroscopic study, which was also confirmed by HPLC analysis. According to the in-vitro release of GA out of GA-LDH in PBS solution (pH 7.4) at 4 °C, GA was sustainably released from GA-LDH nanohybrid up to 86% within 72 h. The antioxidant property of GA-LDH was almost the same with that of intact GA which was examined by DPPH. The photostability of GA-LDH under UV light irradiation was immensely enhanced compared to intact GA. It is, therefore, concluded that the present GA-LDH nanohybrid can be considered as an excellent antioxidant material with high chemical- and photo-stabilities, and controlled release property.     

Intercalation of dodecyl sulfate into layered double hydroxides

The intercalation of sodium dodecyl sulfate and exchange of dodecyl sulfate anion into layered double hydroxides has been examined by means of X-ray diffraction, infrared and thermogravimetric procedures. Three types of derivatives were obtained having mean interlayer spacings of 26 Å, 36 Å and 47 Å, respectively. These interlayer distances did not correlate with the amount of organic incorporated between the layers but, as shown by computer simulations, depended upon the orientation of the chains within the interlamellar space. In several reactions both intercalation of neutral sodium dodecyl sulfate as well as exchange of the dodecyl anion took place. Attempts to remove the alkyl sulfate chains with dilute acid resulted in dissolution of the more basic metals producing non-stoichiometric layered products.     

Selective adsorption of mercury ion by mercaptocarboxylic acid intercalated Mg-Al layered double hydroxide

Intercalations of mercaptocarboxylic acid and dithiodicarboxylic acid in Mg-Al layered double hydroxide and their adsorption properties for heavy metal ions were examined. During the intercalation of mercaptocarboxylic acids, mercapto group was oxidized, and the corresponding dithiodicarboxylic acids were intercalated in the interlayer space of Mg-Al layered double hydroxide. The intercalation compounds adsorbed mercury and silver ions effectively, whereas there was no adsorption of copper ion practically.     

Potassium polytitanates intercalated with nickel ions and their thermal transformations

The intercalation of nickel ions into the layered structure of ultradispersed amorphous potassium polytitanate powder on treatment with an aqueous solution of nickel sulfate was studied. The limiting nickel content that can be attained by intercalation is 12.8 wt %. The nickel ion intercalation results in a decrease in the average particle size of potassium polytitanate and in the structural ordering. Heat treatment of the resulting intercalate promotes the formation of a nanocomposite consisting of the solid solution K_1.35(Ni _x Ti_{8 − x} )O₁₆ with the hollandite structure, Ti₂O₃, and, depending on the treatment schedule, either NiO nanocrystals or Ni metal.     

Effects of organo-clay and sodium dodecyl sulfonate intercalated layered double hydroxide on thermal and flame behaviour of intumescent flame retarded polypropylene

The thermal and flame performances of intumescent flame retarded polypropylene (PP/IFR) composites with organically modified clay or sodium dodecyl sulfonate intercalated layered double hydroxide (SDS-LDH) were studied. The organo-clay particles were partially exfoliated in the PP matrix, while intercalation and aggregation was obtained for SDS-LDH. Incorporation of SDS-LDH improved the thermal stability and flame retardancy of the intumescent flame retarded PP composite in the early stage of heating and combustion; while the effects of organo-clay came into play in the middle-later stage. Differences in degradation pathway of clay and LDH were responsible for the above phenomenon which bore important implication for the barrier mechanism. The introduction of organo-clay into PP/IFR not only increased the char residue, but also formed compact and folded morphology of char residue which provided more effective protect for underlying materials against heat and oxygen relative to LDH, thus improved the flame retardancy of intumescent flame retarded PP samples more efficiently.     

不同金属离子层状双氢氧化物制备及表征

本文采用恒定pH值共沉淀法制备六种层板金属离子不同的层状双氢氧化物(LDH).通过傅立叶变换红外光谱仪(FT-IR)、X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对LDH进行了表征,并利用热重分析(TG)研究了LDH的热分解行为.研究表明,不同金属离子对LDH的层间距、晶粒尺寸等参数有一定影响,团聚程度也有较大的差异.     

Synthesis and characterisation of lamellar ZnS nanosheets containing intercalated diamines

A solvothermal method has been used to prepare hybrid inorganic–organic composites with a lamellar structure in which layers of wurtzite ZnS are separated by intercalated diamine molecules. A hybrid composite prepared with diethylenetriamine has been isolated and characterised and its structure and properties compared with those of the composite prepared using ethylenediamine. Comparative structural and morphological studies of the two lamellar hybrid composites are described on the basis of powder XRD, electron and scanning probe microscopies and thermal analysis of the materials.     

Scalable exfoliation for few-layered hexagonal boron nitride nanosheets (BNNSs) by microwave-assisted expansion and liquid nitrogen intercalation

The low cost and facile scalable exfoliation route for two-dimensional hexagonal boron nitride (h-BN) was still indispensable for potential applications. In this work, we presented a convenient and scalable exfoliation for few-layer BNNSs. Taking advantage of the advantages of swift heating of microwave and ultra low temperature vaporization of liquid nitrogen, bulk h-BN was high-efficiently exfoliated into few-layer BNNSs. The as-exfoliated BNNSs had a 2−6 nm thickness and approximately 7.91% yield, exhibiting scalable, facile and environment-friendly features. Furthermore, the as-exfoliated BNNSs were applied as additive in oil for reducing friction of oil. The COF of the BNNSs-based grease reduced by 20.10% compared to grease, and the antiwear performance decreased by 55.8% and 45.1% relative to grease and h-BN-based grease.     

Fabrication of nickel hydroxide electrodes with open-ended hexagonal nanotube arrays for high capacitance supercapacitors

A nickel hydroxide electrode with open-ended hexagonal nanotube arrays, prepared by hydrolysis of nickel chloride in the presence of hexagonal ZnO nanorods, shows a very high capacitance of 1328 F g(-1) at a discharge current density of 1 A g(-1) due to the significantly improved ion transport.     

Charge storage characteristics of layer-by-layer assembled nickel hydroxide and graphene oxide nanosheets

Journal of Solid State Electrochemistry - In this study, layer-by-layer assembled thin films composed of nickel hydroxide and graphene oxide nanosheets were produced via simple dip coating process....