Synthesis and characterization of Naproxen intercalated Zn–Al layered double hydroxides

In this paper, naproxen was intercalated into Zn–Al layered double hydroxides (LDHs) by ion exchange method to obtain naproxen/LDHs nanohybrids. The effects of the contact time, the composition, and the structural charge density (σ _S,T ) and the specific surface area of LDHs, and pH value on the uptake of naproxen on LDHs, and the release of naproxen from the naproxen/LDHs nanohybrids were investigated. The adsorption isotherm curves of naproxen on the LDHs obey the Langmuir equation, and apparent monolayer capacity (A _m) in units of mmol m⁻² increases with the increase of the σ _S,T value of the LDHs samples. The release rate of naproxen from the naproxen/LDHs nanohybrids decreases with the increase of the σ _S,T value of the LDHs samples and is much lower than that of naproxen troche, indicating that the naproxen/LDHs nanohybrid is an efficient drug-controlled release system. In the pH range of 6~11.5, the uptake amount (A _eq) of naproxen on the LDHs decreases with the increase of pH value. The A _m values of LDHs(Cl⁻) are much higher than that of , which may contribute to that LDHs(Cl⁻), which has a stronger anion exchange ability than . The naproxen molecules are possibly adsorbed on each surface of the basal layer of LDHs. In other words, a bilayer is formed in the gallery of LDHs.     

In situ dielectric measurements of Zn–Al layered double hydroxide with anionic nitrate ions

Zn–Al–NO₃–layered double hydroxide (Zn–Al–NO₃–LDH) was prepared by the co-precipitation method with a ratio of Zn/Al = 4 and at a constant pH of 7. Powder XRD patterns showed the characteristic peaks of layered structure of the LDH sample. Thermogravimetric analysis (TGA) and infrared spectra of the sample were investigated. Because of the existence of water molecules and anionic NO₃⁻ in the interlayer of the LDH, the in situ dielectric spectroscopy of the LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law. Novel measurements of activation energy of LDH have been obtained at five different frequencies. The energy value increased from 0.05 eV at 1 MHz to 0.37 eV at 134 Hz. The conductivity spectra of sample were studied as a function in temperature of the in situ measurements. The ionic conductivity (dc) of LDH increased as the in situ temperature increased.     

Preparation of Co–Al and Ni–Al layered double hydroxide thin films by a sol–gel process with hot water treatment

Using hot water treatment of sol–gel derived precursor gel films, Co–Al and Ni–Al layered double hydroxide (LDH) thin films were prepared. The precursor gel films of Al₂O₃–CoO or Al₂O₃–NiO were prepared from cobalt or nickel nitrates and aluminum tri-sec-butoxide using the sol–gel method. Then, the precursor gel films were immersed in a NaOH aqueous solution of 100 °C. Nanocrystallites of Co–Al and Ni–Al LDH were precipitated with the hot water treatment with NaOH solution. The largest amounts of nanocrystals were obtained with a solution of pH = 10 for Co–Al LDH, and with that of pH = 9 for Ni–Al LDH. X-ray diffraction measurements confirmed that this process formed CO₃ ²⁻ intercalated LDHs. Both Co–Al and Ni–Al LDH thin films were confirmed to work as electrodes for electrochemical devices by cyclic voltammogram measurements.     

Electrochemical performance of Co–Al layered double hydroxide nanosheets mixed with multiwall carbon nanotubes

Regular hexagonal Co–Al layered double hydroxides (Co–Al LDH) were synthesized by urea-induced homogeneous precipitation. This material proved to be nanosheets by scanning electron microscopy and X-ray diffraction measurements. The electrochemical capacitive behavior of the nanosheets in 1 M KOH solution were evaluated by constant current charge/discharge and cyclic voltammetric measurements, showing a large specific capacitance of 192 F·g⁻¹ even at the high current density of 2 A·g⁻¹. When multiwall carbon nanotubes (MWNTs) were mixed with the Co–Al LDH, it was found that the specific capacitance and long-life performance of all composite electrodes at high current density are superior to pure LDH electrode. When the added MWNTs content is 10 wt%, the specific capacitance increases to 342.4 F·g⁻¹ and remains at a value of 304 F·g⁻¹ until the 400th cycle at 2 A·g⁻¹, showing that this is a promising electrode material for supercapacitors working at heavy load. According to the electrochemical impedance spectra, MWNTs greatly increase the electronic conductivity between MWNTs and the surface of Co–Al LDH, which consequently facilitates the access of ions in the electrolyte and electrons to the electrode/electrolyte interface.     

Removal of chromate from aqueous solution by reduction with nanoscale Fe–Al layered double hydroxide

Nanoscale layered double hydroxides of Fe^II and Al^III (Fe–Al LDH) have been applied for removal of chromate (Cr^VI) from aqueous solution. Given the reaction stoichiometry, Cr^VI was completely reduced to Cr^III and coprecipitated with Fe^III and Al^III oxyhydroxides. The extent of Cr^VI removal decreased with increasing initial pH and decreasing molar ratio of Cr^VI/structural Fe^II in the LDH. The chromate reduction rate at different initial concentrations of Cr^VI was well described by the pseudo-second-order model with reaction rate constant ranging from 197.4 to 13.53 (mmol min)^?1. Initial pH and substitution of various amounts of Fe^III in the LDH structure had little effect on the reaction rate. Backtransformation of Cr^III to Cr^VI by birnessite Mn oxide (δ-MnO₂) after 40 days of reaction was less than 1% of the initial Cr (as Cr^III solid), indicating high stability of the final reaction products and high efficiency of nanoscale Fe–Al LDHs for removal of chromate from aqueous solution.     

Mechanochemical synthesis of dodecyl sulfate anion (DS−) intercalated Cu-Al layered double hydroxide

Dodecyl sulfate anion (DS⁻) was successfully intercalated into the gallery space of Cu-Al layered double hydroxides (LDH) by a non-heating mechanochemical route, in which basic cupric carbonate (Cu₂(OH)₂CO₃) and aluminum hydroxide (Al(OH)₃) were first dry ground and then agitated in SDS solution under ambient environment. The organics modified Cu-Al LDH showed good adsorption ability toward 2,4-dichlorophenoxyacetic acid (2, 4-D). The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), CHS elemental analysis and Scanning electron microscopy (SEM). The LDH precursor prepared by ball-milling could directly react with SDS molecules forming a pure phase of DS⁻ pillared Cu-Al LDH, which was not observed with the LDH product through the ion-exchange of DS⁻ at room temperature. The process introduced here may be applied to manufacture other types of organic modified composites for pollutants removal and other applications.     

Thermal decomposition of SO4 2?-intercalated Mg–Al layered double hydroxide

The thermal properties of SO₄ ^2?-intercalated Mg?CAl layered double hydroxide (SO₄·Mg?CAl LDH) were investigated using simultaneous thermogravimetry?Cmass spectrometry (TG?CMS), and the elimination behavior of sulfur oxides from this double hydroxide was examined. The TG?CMS results showed that SO₄·Mg?CAl LDH decomposed in five stages. The first stage involved evaporation of surface-adsorbed water and interlayer water in SO₄·Mg?CAl LDH. In the second, third, and fourth stages, dehydroxylation of the brucite-like octahedral layers in SO₄·Mg?CAl LDH occurred. The fifth stage corresponded to the elimination of SO₄ ^2? intercalated in the interlayer of Mg?CAl LDH, producing SO₂ and SO₃. The thermal decomposition of SO₄·Mg?CAl LDH resulted in the formation of SO₂ and SO₃ at 900?C1000?°C, which then reacted with H₂O to form H₂SO₃ and H₂SO₄. The elimination of sulfur oxides increased with the decomposition time and temperature. Almost all of the intercalated SO₄ ^2? was desulfurized from SO₄·Mg?CAl LDH at 1000?°C; however, Mg?CAl oxide was not formed due to the production of MgO and MgAl₂O₄.     

Potential of Mg–Zn–Al layered double hydroxide (LDH)/montmorillonite nanocomposite in remediation of wastewater containing manganese ions

Research on Chemical Intermediates - A Mg–Zn–Al (LDH)/MMT nanocomposite was prepared by physical interaction between Mg–Zn–Al layered double hydroxide (LDH) and...     

Thermal behavior of Mg–Al–CO3 layered double hydroxide characterized by emanation thermal analysis

Emanation thermal analysis (ETA) was used to characterize microstructure changes during heating of Mg–Al–CO₃ layered double hydroxide (LDH) in the temperature range of 293–1473 K. It was confirmed by ETA that the formation of an intermediate phase with grafted CO₃^2– anions in the hydroxide layers took place in the temperature range of 508–523 K and the formation of Mg–Al mixed oxide (MO) occurred in the range 623–773 K. The small peak of the emanation rate at 603 K indicated the degradation of the layered structure and the broad peak in the range of 1073–1273 K characterized the onset of the separation of the decomposition products of MO into MgO and Mg₂Al₄O₇. The ETA results revealed that dehydration of the product with grafted CO₃^2– anions occurred at lower temperatures than that of the initial Mg–Al–CO₃ LDH.     

Synthesis and controlled release properties of β-naphthoxyacetic acid intercalated Mg–Al layered double hydroxides nanohybrids

Controlled release formulations have been proven to have potential in overcoming the drawbacks of conventional plant growth regulators. Novel controlled-release formulation of β-naphthoxyacetic acid (BNOA) intercalated MgAl-layered double hydroxides (LDHs) was prepared by co-precipitation method. The effects of temperature, pH value, and release medium on BNOA release were studied and the releasing mechanisms were discussed. The results of release show that the increase of temperature induces the increase of BNOA release extent. The release rate and accumulated release amount of BNOA are found to be dependent to the anion in the aqueous solution in the order of CO₃²⁻ > SO₄²⁻ > Cl⁻. Moreover, the pH is the key controlling factor for the BNOA release processes, and with strong acid medium, the release character of BNOA is different from those at pH 7 and 12, which accompanies with fast collapse of LDHs nanolayered structure. The nanohybrid of BNOA intercalated LDHs possessed good controlled release properties and the BNOA release character from the nanohybrid fitted pseudo-second-order model in neutral medium.     

Thermodynamic equilibrium analyses of the uptake of aromatic compounds from an aqueous solution by magnesium–aluminum (Mg–Al) layered double hydroxide intercalated with 1-naphthol-3,8-disulfonate

Magnesium–aluminum layered double hydroxide (Mg–Al LDH) intercalated with 1-naphthol-3,8-disulfonate (1-N-3,8-DS²⁻) was prepared by coprecipitation. Thermodynamically, the prepared Mg–Al LDH showed greater preferential uptake of 1,3-dinitrobenzene (DNB) than of 1,2-dimethoxybenzene (DMB). This preferential uptake of aromatic compounds, which is adequately expressed by the Dubinin–Radushkevich adsorption isotherm, was attributed to the π–π stacking interactions between the benzene ring of the aromatic compounds and the naphthalene core of 1-N-3,8-DS²⁻ intercalated in the interlayer spaces of Mg–Al LDH. Negative values of ΔG for DNB and DMB indicate that the adsorption process is spontaneous at all temperatures. The value of ΔS for DNB was much lower than that for DMB. This implies that DNB was far more strongly adsorbed to 1-N-3,8-DS²⁻ than was DMB, resulting in a lower degree of freedom for and higher uptake of DNB than those in the case DMB. The absolute values of |ΔH| for DNB and DMB were less than 20 kJ mol⁻¹, indicating that the uptake of DNB or DMB by 1-N-3,8-DS·Mg–Al LDH can be considered a physical adsorption process caused by π–π stacking interactions.     

Layer-by-layer assembly of luminescent ultrathin films by layered double hydroxides and neutral Al–Phen–Hq

Highly transparent ultrathin films (UTFs) were fabricated via layer-by-layer assembly of 110-Phenanthroline monohydrate (Phen)–8-hydroxyquinoline (Hq)–Al³⁺(Phen–Hq–Al), polyvinyl alchol(PVA) and Mg–Al-layered double hydroxide (LDH)nanosheets. UV–visible absorption and fluorescence spectroscopy showed regular growth of UTFs increasing the numbers of assembly. The structure and morphology of Mg–Al-layered double hydroxide and UTFs were measured by Fourier transform infrared spectroscopy, XRD and SEM. We found that it can detect Fe³⁺ ion with relative selectivity and high sensitivity (K_sv?=?2.214?×?10⁴ M^?1) which indicates that UTFs can be a potential fluorescent probe for selectively of the Fe³⁺ ion.

     

Removal of textile dye mixtures by using modified Mg–Al–Cl layered double hydroxide (LDH)

The removal of Indigo Carmin (IC) and Congo Red (CR) dye mixtures using layered double hydroxide (LDH) (modified with sodium dodecyl sulfate (SDS)) has been studied. In the experimental context of this study, LDH was synthesized under a nitrogen atmosphere at room temperature using the coprecipitation method and characterized by Fourier transform infrared specroscopy (FTIR), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and scanning electron microscopy (SEM) analyses. Contact time, temperature, and initial dye concentration on the adsorption process have been investigated. Results show that the maximum removal of IC and CR was obtained as about 50% and 95%, respectively. The isothermal data were fitted to Langmuir, Freundlich, and Temkin adsorption isotherms. Elovich and other kinetic model equations were applied. Adsorption depended on the starting naphthalene concentration at investigated various temperatures (298, 308, and 318?K) significantly.     

Synergistic enhancement of vinyltriethoxysilane and layered Mg–Al double hydroxide on the tracking and erosion resistance of silicone rubber

It is of great significance and challenge to efficiently improve the tracking and erosion resistance of silicone rubber along with the growing requirements in the field of outdoor high voltage insulation. In this work, we herein proposed an effective way to address this issue by incorporating vinyltriethoxysilane (ViTES) and layered Mg–Al double hydroxide (LDH) into high temperature vulcanized silicone rubber (HTVSR). ViTES/LDH notably enhanced the tracking and erosion resistance of HTVSR. With addition of 3.33 phr ViTES and 5.00 phr LDH, the anti-tracking performance of HTVSR reached the 1A 4.5 level, and the eroded mass was merely 0.3%. The results of scanning electron microscopy and equilibrium swelling showed that ViTES substantially improved the interfacial interaction between HTVSR and LDH and the crosslinking density of HTVSR, and enhanced the dispersion of LDH sheets in the HTVSR matrix. The possible synergistic suppression mechanism of ViTES/LDH on the tracking and erosion of HTVSR was further studied and demonstrated by the plasma irradiation analysis, thermogravimetry and thermogravimetry-Fourier transform infrared spectrometry. It was indicated that under the high voltage arcing discharge, LDH facilitated the formation of a dense barrier layer consisting of bimetal mixed oxides on the HTVSR surface, exerting outstanding lamellar barrier effect. The further degradation and the generation as well as development of electrical tracking were efficiently suppressed. Our findings provided a new approach to fabricate silicone rubber with excellent tracking and erosion resistance.     

Mg–Al hydroxide intercalated ionic liquids for quasi-solid-state lithium batteries

Journal of Solid State Electrochemistry - Solid -state lithium batteries are considered safer energy storage, but their payload and energy density are limited due to the large interfacial impedance...     

Preparation of Mg–Al layered double hydroxides intercalated with alkyl sulfates and investigation of their capacity to take up N,N-dimethylaniline from aqueous solutions

This study examined the effect of the interlayer spacing of a Mg–Al layered double hydroxide (Mg–Al LDH) on the ability of the Mg–Al LDH to take up a nonionic organic material. Mg–Al LDHs, intercalated with 1-propanesulfonate (PS^?), 1-hexanesulfonate (HS^?), and 1-dodecanesulfonate (DS^?), were prepared by coprecipitation, yielding PS·Mg–Al LDH, HS·Mg–Al LDH, and DS·Mg–Al LDH, respectively. The increase in the alkyl chain lengths of the Mg–Al LDHs (PS^? < HS^? < DS^?) resulted in the perpendicular orientation of the organic acid anions in the interlayer of Mg–Al LDH, which in turn resulted in more organic acid anions being accommodated in the interlayer space. An organic acid anion with a large molecular length was more easily intercalated in the interlayer of Mg–Al LDH than one with a small molecular length. This was attributed to the hydrophobic interaction between the alkyl chains, affecting the intercalation of the organic acid anions. The uptake of N,N-dimethylaniline (DMA) by Mg–Al LDHs increased in the order PS·Mg–Al LDH < HS·Mg–Al LDH < DS·Mg–Al LDH. The uptake was attributed to the hydrophobic interactions between DMA and the intercalated PS^?, HS^?, and DS^?. Thus, Mg–Al LDH, which has a lot of large interlayer spacings when intercalated with organic acid anions, can take up a large number of DMA molecules from an aqueous solution.