Layered Double Hydroxide Gallery Research Articles

Mechanism of interaction of hydrocalumites (Ca/Al-LDH) with methyl orange and acidic scarlet GR

The development of new materials for water purification is of universal importance. Among these types of materials are layered double hydroxides (LDHs). Non-ionic materials pose a significant problem as pollutants. The interaction of methyl orange (MO) and acidic scarlet GR (GR) adsorption on hydrocalumite (Ca/Al-LDH-Cl) was studied by X-ray diffraction (XRD), infrared spectroscopy (MIR), scanning electron microscope (SEM), and near-infrared spectroscopy (NIR). The XRD results revealed that the basal spacing of Ca/Al-LDH-MO was expanded to 2.45 nm, and the MO molecules were intercalated with a interpenetrating bilayer model in the gallery of LDH, with 49° tilting angle. Yet, Ca/Al-LDH-GR was kept the same d-value as Ca/Al-LDH-Cl. The NIR spectrum for Ca/Al-LDH-MO showed a prominent band around 5994 cm −1, assigned to the combination result of the N H stretching vibrations, which was considered as a mark to assess MO − ion intercalation into Ca/Al-LDH-Cl interlayers. From SEM images, the particle morphology of Ca/Al-LDH-MO mainly changed to irregular platelets, with a “honey-comb” like structure. Yet, the Ca/Al-LDH-GR maintained regular hexagon platelets, which was similar to that of Ca/Al-LDH-Cl. All results indicated that MO − ion was intercalated into Ca/Al-LDH-Cl interlayers, and acidic scarlet GR was only adsorbed upon Ca/Al-LDH-Cl surfaces.

Controllable Photoluminescence Properties of an Anion-Dye-Intercalated Layered Double Hydroxide by Adjusting the Confined Environment

This article reports a novel method to tune the photoluminance properties of ammonium 1-anilinonaphthalene-8-sulfonate (ANS) in a 2D matrix of layered double hydroxide (LDH) by changing the interlayer microenvironment. ANS and a series of surfactants with different alkyl chain lengths (pentanesulphonate (PES), hexanesulphonate (HES), heptanesulphonate (HPS), decanesulphonate (DES), and dodecylsulphonate (DDS)) were respectively cointercalated into the galleries of ZnAl-LDH by the anion exchange method. Thin films of ANS/surfactant-LDHs obtained by the solvent evaporation method possess good c orientation as revealed by XRD and SEM. It was found that the ANS/HPS-LDH film showed the maximum fluorescence efficiency and the longest intensity-average lifetime among these ANS/surfactant-LDH composites owing to the "size-matching" rule between the organic dye and surfactant. Moreover, the fluorescence properties can be tuned by changing the relative molar ratio of ANS/HPS, and the film containing 20% ANS (molar percentage, expressed as ANS(20%)/HPS-LDH) exhibits the maximum fluorescence efficiency, the longest average lifetime, and significantly enhanced photo and thermal stability. In addition, the composite films show fluorescence anisotropy, attributed to the preferential orientation of ANS in the LDH gallery. Therefore, this work demonstrates a feasible approach to tuning the photoluminescence properties of a dye confined in an inorganic 2D matrix via changing the interlayer microenvironment, which may be considered to be a good candidate for solid photoluminescence materials, nonlinear optics, and polarized luminescence materials.

Tunable Photoluminescence Properties of Fluorescein in a Layered Double Hydroxide Matrix by Changing the Interlayer Microenvironment

This paper reports a novel method to tune the fluorescence properties of fluorescein (FLU) in a 2D matrix of layered double hydroxide (LDH) by changing the interlayer microenvironment. FLU and surfactants with different alkyl chain lengths were cointercalated in the galleries of a Zn2Al LDH by the anion exchange method. Thin films of FLU-CnH2n+1SO3/LDH (n = 5, 6, 7, 10, and 12, respectively; n stands for the number of carbon in the alkyl chain), which possess a well c-orientation revealed by XRD and SEM, were obtained by the solvent evaporation method on Si substrates. It was found that the orientation of FLU and its anisotropy, fluorescence wavelength, fluorescence quantum yield, and lifetime correlate with the microenvironment of the LDH gallery, which can be tuned by simply changing the alkyl chain length of the surfactant. The optimal fluorescence quantum yield, anisotropy, the longest fluorescence lifetime and the strongest photostability of the FLU-CnH2n+1SO3/LDH film can be obtained with n = 7, due...

Optical pH Sensor with Rapid Response Based on a Fluorescein‐Intercalated Layered Double Hydroxide

AbstractThe preparation of a highly oriented photoluminescent film of fluorescein (FLU) and 1‐heptanesulfonic acid sodium (HES) co‐intercalated in a layered double hydroxide (LDH) matrix by electrophoretic deposition (EPD) is reported, and its application as an optical pH sensor is demonstrated. The FLU‐HES/LDH films with thickness ranging from nanometer to micrometer on indium tin oxide substrates exhibite good c‐orientation of LDH platelets (the ab‐plane of the LDH platelets parallel to the substrate), as confirmed by X‐ray diffraction and scanning electron microscopy. Polarized luminescence of the film is observed with anisotropy value r = 0.29, resulting from the highly oriented FLU in the LDH gallery. Furthermore, the optical pH sensor with film thickness of 300 nm exhibits a broad linear dynamic range for solution pH (5.02–8.54), good repeatability (relative standard deviation (RSD) less than 1.5% in 20 consecutive cycles) and reversibility (RSD less than 1.5% in 20 cycles), high photostability and storage stability (ca. 95.2% of its initial fluorescence intensity remains after one month) as well as fast response time (2 s). Therefore, this work creates new opportunities for the preparation and application of LDH‐based chromophores in the field of optical sensors.

Synthesis and release behavior of composites of camptothecin and layered double hydroxide

A simple method, reconstruction of calcinated layered double hydroxides (CLDH) in an organic (ethanol)–water mixed solvent medium containing drug, was developed to intercalate partially a non-ionic and poorly water-soluble drug (camptothecin) into the gallery of layered double hydroxides (LDHs) to form the drug–LDH composites. The purpose of choosing organic–water mixed solvent is to increase remarkably the solubility of camptothecin (CPT) in the reconstruction medium. A probable morphology of CPT molecules in the gallery of LDHs is that CPT molecules arrange as monolayer with the long axis parallel to the LDH layers. The in vitro drug release from the composites was remarkably lower than that from the corresponding physical mixture, which shows these drug–inorganic composites can be used as a potential drug delivery system.

Preparation of an anion dye intercalated into layered double hydroxides and its controllable luminescence properties

The inorganic–organic composites have been prepared by intercalation of ammonium 1-anilinonaphthalene-8-sulfonate (ANS) into ZnAl and MgAl layered double hydroxide (LDH) with the molar ratio (M 2+/M 3+) of 2:1 and 3:1, respectively. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of ANS into the galleries of LDH. Fluorescence polarization method was applied to investigate the preferential orientation of the interlayer ANS molecule, and the results show that ANS anions are accommodated between the sheets of Zn 2Al-LDH, Zn 3Al-LDH, Mg 2Al-LDH and Mg 3Al-LDH with an orientation angle Ψ (defined as the angle between the transition moment of ANS molecule with respect to the normal to the LDH layer) of 58°, 57°, 55° and 52°, respectively. TG–DTA results reveal that the thermal stability of ANS was markedly enhanced upon intercalation. Fluorescence spectra demonstrate that the Zn 3Al-ANS-LDH sample exhibits the optimal luminous intensity among the four ANS-LDH composites. It was also found that the luminescence behavior of ANS can be modulated via changing the two parameters: the type and ratio of cation species in LDH matrix due to host–guest interactions. Therefore, the ANS-LDH composites can be used as good candidates for solid photoluminescence materials.

Preparation of Glycy- l-Tyrosine intercalated layered double hydroxide film and its in vitro release behavior

This paper describes the preparation of films of peptide (Glycy- l-Tyrosine, denoted as GlyTyr) intercalated layered double hydroxide (LDH) and its release performances. GlyTyr has been intercalated into a magnesium–aluminum LDH, and the resulting film was fabricated by solvent evaporation method in order to exploit new formulation in drug carrier especially used in skin medicament. Based on the results of XRD, FT-IR, FT-IR-ATR, UV–vis, 13C NMR, ICP and elemental analysis, it was found that GlyTyr has been successfully intercalated into LDH gallery. TG/DTA, in situ FT-IR, in situ XRD and polarimetry indicate that the chemical stability of GlyTyr was enhanced significantly in the confined region of LDH galleries compared with its pristine form. SEM reveals that the film thickness is about 12.6 μm with c-orientation of LDH platelets ( ab plane parallel to the substrate). In vitro release tests of the GlyTyr-LDH film in pH 7.4 phosphate buffered saline (PBS) showed that no burst release phenomenon occurred at the beginning stage and a high release ratio of GlyTyr (91%) was obtained, exhibiting controlled release behavior. Furthermore, the parabolic diffusion model was used to simulate the release kinetics of GlyTyr from the LDH carrier, indicating that the external surface diffusion or the intraparticle diffusion via ion-exchange is the rate-determining step in the release process. Therefore, this work demonstrates that Mg/Al-LDH is an effective inorganic matrix for the peptide storage and controlled delivery at the required time.

Studies on the Orientation and Polarized Photoluminescence of α-Naphthalene Acetate in the Layered Double Hydroxide Matrix

This paper reports a novel method to tune the fluorescence properties of α-naphthalene acetate (α-NAA) in a two-dimensional matrix of layered double hydroxide (LDH) by changing the orientation of the chromophore. The α-NAA and 1-heptanesulfonic acid sodium (HES) with different molar ratios were co-intercalated in the galleries of Zn2Al LDH by the anion exchange method. Thin films of α-NAA−HES/LDH (x%, x stands for the molar percentage of α-NAA), which have a well c-orientation confirmed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM), were obtained by the solvent evaporation method on Si substrates. On the basis of the results from XRD and fluorescence polarization, the orientation (Ψ angle) of the α-NAA molecule in the LDH matrix was calculated to be 59° (x = 12.1%), 61° (x = 15.1%), 64° (x = 20.0%), 65° (x = 23.3%), 68° (x = 30.0%), and 71° (x = 34.4%) with respect to the normal to the thin film, respectively. Furthermore, the fluorescence wavelength, emission intensity, and lifeti...

Study of assembly of arachidic acid/LDHs hybrid films containing photoactive dyes

Hybrid monolayers formed with an floating arachidic acid (AA) anions monolayer binding with a densely packed layered double hydroxides (LDHs) monolayer at an air/LDHs suspension interface has been studied by π– A isotherms and TEM images. An ordered multilayer film of AA/LDHs has been fabricated by Langmuir–Blodgett technique on various substrates. The photoactive dyes (methyl orange, MO, and Congo red, CR) can be incorporated into the galleries of LDHs in the AA/LDHs hybrid LB film by an ion intercalation method. The results of FTIR and UV–vis absorption spectra can approve the formation of AA/LDHs/dyes composite films. In addition, UV–vis absorption spectra and LAXRD analyses also provide evidence for the good vertical uniformity and stable layered periodic structure of AA/LDHs/dyes films. More interestingly, it was found that the dye molecules intercalated can be induced by a positively charged LDHs sheet to align in a special orientation and form different aggregates: MO molecules form sandwich H-type aggregates, while CR molecules form head-to-tail J-type aggregates. On the basis of these data, a possible model of the AA/LDHs/dyes composite films was proposed. Also, the dye molecules incorporated into AA/LDHs films exhibit excellent configuration stability under the irradiation of UV light because the LDHs matrix offers a more rigid and constrained environment for them.

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 $$ {\text{LDHs}}{\left( {{\text{CO}}^{{2 - }}_{3} } \right)} $$ , which may contribute to that LDHs(Cl−), which has a stronger anion exchange ability than $$ {\text{LDHs}}{\left( {{\text{CO}}^{{2 - }}_{3} } \right)} $$ . 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.

Epoxidation by Layered Double Hydroxide-Hosted Catalysts. Catalyst Synthesis and Use in the Epoxidation of R-(+)-Limonene and (-)-α-Pinene Using Molecular Oxygen

A novel chiral sulphonato–salen–manganese(III) complex has been intercalated into a Zn(II)–Al(III) layered double hydroxide (LDH) host to produce a stable heterogeneous epoxidation catalyst. Powder X-ray diffraction, IR and UV–Visible (solid) spectroscopy and TGA confirmed the successful intercalation of the Mn complex within the LDH gallery height. The intercalated sulphonato–salen–manganese(III) complex was found to be an effective heterogeneous catalyst for the stereoselective epoxidation of R-(+)-limonene and (−)-α-pinene at room temperature and using molecular oxygen at atmospheric pressure as oxidant. At close to 100% conversion, R-(+)-limonene was converted into the corresponding epoxide with 93% selectivity and 43% de (diastereomeric excess), whereas (−)-α-pinene was converted with 93% selectivity and 98% de. The catalyst could be recycled without loss of efficiency.