A magnetic organic-inorganic composite: Synthesis and characterization of magnetic 5-aminosalicylic acid intercalated layered double hydroxides

A core-shell structured magnetic layered organic-inorganic material involving 5-aminosalicylic acid (5-ASA) intercalated Zn-Al layered double hydroxides (LDHs) and magnesium ferrite (MgFe₂O₄) is assembled by a coprecipitation method. The powder X-ray diffraction results show the coexistence of the clear but weak diffractions of MgFe₂O₄ and ordered relatively stronger reflections of 5-ASA intercalated LDHs. The TEM image of magnetic 5-ASA intercalated LDHs reveals that the LDHs layer covers the MgFe₂O₄ particles or their aggregates with particle size of 50-80 nm. The vibration sample magnetization (VSM) measurements exhibit the increase in saturation magnetization of magnetic 5-ASA intercalated LDHs samples with increasing amount of magnetic core. The XPS analyses account for a majority of Zn, Al and O atoms on the surface of magnetic particles. It is suggested that the magnetic core MgFe₂O₄ was coated with LDHs layer probably through Zn-O-Mg and Al-O-Mg linkages, and a core-shell structured model is tentatively proposed.     

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.     

Synthesis and characterization of layered double hydroxides (LDH) intercalated with non-steroidal anti-inflammatory drugs (NSAID)

Layered double hydroxides (LDHs) with the hydrotalcite type structure and a Mg:Al ratio of two have been prepared, with salicylate or naproxen in the interlayer. Two synthetic routes have been used: reconstruction from a mildly calcined hydrotalcite-CO₃ precursor, and a coprecipitation method with chlorides of the metals. The solids have been characterized using several physicochemical techniques, i.e., powder X-ray diffraction, FTIR and ¹³C CP/MAS NMR spectroscopies and thermal analysis (thermogravimetric and differential thermal analyses). The gallery height determined is in all cases larger than the size of the drug, 11.5 Å for salicylate and 15.8 and 16.6 Å for naproxen, depending on the specific synthesis route followed. Experimental data suggest the anion molecules form a tilted bilayer, with the carboxylate groups pointing towards the brucite-like layers. The solids are stable up to 230 °C and their evolution from 350 °C upwards is very similar to that observed for a carbonate-containing hydrotalcite, forming mostly amorphous solids with a large specific surface area.     

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.     

Carboxylate-intercalated layered double hydroxides aged under microwave-hydrothermal treatment

Carboxylate-intercalated (terephthalate, TA and oxalate, ox) layered double hydroxides (LDHs) are aged under a microwave-hydrothermal treatment. The influence of the nature of the interlayer anion during the ageing process is studied. Characterization results show that the microwave-hydrothermal method can be extended to synthesize LDHs with anions different than carbonate, like TA. LDH-TA compounds are stable under microwave irradiation for increasing periods of time and the solids show an improved order both in the layers and in the interlayer region as evidenced by powder X-ray diffraction (PXRD), ²⁷Al MAS NMR and FT-IR spectroscopy. Furthermore, cleaning of the surface through removal of some organic species adsorbed on the surface of the particles also occurs during the microwave-hydrothermal treatment. Conversely, although the expected increase in crystallinity is observed in LDH-ox samples, the side-reaction between Al³⁺ and ox is also enhanced under microwave irradiation, and a partial destruction of the structure takes place with an increase in the M²⁺/M³⁺ ratio and consequent modification of the cell parameters.     

Mechano-hydrothermal preparation of Li-Al-OH layered double hydroxides

A mechano-hydrothermal (MHT) method was used to synthesize Li-Al-OH layered double hydroxides (LDHs) from LiOH·H₂O, Al(OH)₃ and H₂O as starting materials. A two-step synthesis was conducted, that is, Al(OH)₃ was milled for 1 h, followed by hydrothermal treatment with LiOH·H₂O solution. Effects of the LiOH/Al(OH)₃ molar ratio (R_Li/Al) and hydrothermal temperature (T_ht) on the crystallinity, morphology, and composition of the product were examined. The resulting LDHs were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared, and elemental analyses. The results showed that pre-milling plays a key role in the LDH formation during subsequent hydrothermal treatment. The Li/Al molar ratio of the obtained LDHs keeps constant at 0.5, independent from theR_Li/Al (0.5–5.0) in the starting materials. An increase in the T_ht (20–80 °C) can enhance the crystallinity and morphology regularity of the products. The so-obtained Li-Al-OH LDHs exhibit high crystallinity and well-dispersity, which may have wider applications than the aggregate ones obtained using conventional mechanochemical and Li⁺-imbibition methods.     

Thermal, solution and reductive decomposition of Cu-Al layered double hydroxides into oxide products

Cu-Al layered double hydroxides (LDHs) with [Cu]/[Al] ratio 2 adopt a structure with monoclinic symmetry while that with the ratio 0.25 adopt a structure with orthorhombic symmetry. The poor thermodynamic stability of the Cu-Al LDHs is due in part to the low enthalpies of formation of Cu(OH)₂ and CuCO₃ and in part to the higher solubility of the LDH. Consequently, the Cu-Al LDH can be decomposed thermally (150 °C), hydrothermally (150 °C) and reductively (ascorbic acid, ambient temperature) to yield a variety of oxide products. Thermal decomposition at low (400 °C) temperature yields an X-ray amorphous residue, which reconstructs back to the LDH on soaking in water or standing in the ambient. Solution decomposition under hydrothermal conditions yields tenorite at 150 °C itself. Reductive decomposition yields a composite of Cu₂O and Al(OH)₃, which on alkali-leaching of the latter, leads to the formation of fine particles of Cu₂O (<1 μm).     

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.     

Intercalation of an oxalatooxoniobate complex into layered double hydroxide and layered zinc hydroxide nitrate

A Zn/Al layered double hydroxide with molar ratio of 3 was prepared by coprecipitation in alkaline pH and used as a matrix to intercalate the ionic complex diaquadioxalatooxoniobate(V) (DDON), derived from NH₄[NbO(C₂O₄)₂(H₂O)₂]2H₂O. In a similar way, the layered zinc hydroxide nitrate, Zn₅(OH)₈(NO₃)₂2H₂O, was synthesized, preexpanded with azelate ions (⁻OOC(CH₂)₇COO⁻), and then intercalated with the niobium complex. For both layered matrices, the results from X-ray powder diffractometry, Fourier transform infrared spectroscopy, and thermal analysis (TG/s-DTA) indicate the presence of the oxalate ion. In addition, results from X-ray photoelectron and Raman spectroscopy indicate the presence of the niobium center bonded to oxygen atoms. Finally, diffuse reflectance UV–vis spectroscopy suggests that the niobium centers are coordinated to oxalate ions. This is the first report of the intercalation of niobium into a layered matrix.     

Synthesis and UV absorption properties of 5-sulfosalicylate-intercalated Zn-Al layered double hydroxides

5-sulfosalicylic acid (SSA) anions have been intercalated into layered double hydroxides (LDHs) by an anion-exchange reaction using ZnAl-NO₃-LDHs as a precursor. The samples were characterized by XRD, FT-IR, TG-DTA/MS and UV-visible spectroscopy. The results show that the NO₃⁻ anions in the precursor have been completely replaced by SSA anions to give ZnAl-SSA-LDHs having a high degree of crystallinity. Detailed studies reveal the existence of a supramolecular structure in ZnAl-SSA-LDHs involving electrostatic attraction between opposite charges, hydrogen bonding and other weak chemical bonding interactions between host layers and SSA anions. The thermal stability of ZnAl-SSA-LDHs is considerably enhanced compared with that of a mixture of ZnAl-NO₃-LDHs and SSA. After addition of 2.0 wt% ZnAl-SSA-LDHs to polypropylene (PP), the resistance of the polymer to UV degradation is significantly improved.     

4-Benzoylbenzoate intercalated in layered double hydroxides: a new catalyst for photo-oxidation of sulfides in solution and in the gas phase

A new mixed organic-inorganic photosensitizer, based on 4-benzoylbenzoate intercalated into a layered double hydroxide has been prepared, characterized and successfully tested for the photo-oxidation of dialkylsulfides, both in acetonitrile and in the gas phase.     

Synthesis and intracrystalline oxidation of nitrite-intercalated layered double hydroxides

Nitrite-intercalated LDHs could be prepared by a two-stage process that involves coprecipitation in the presence of nitrite ions followed by stirring the product with excess of nitrite ions. The nitrite ion lies flat in these LDHs with its c₂-axis lying approximately perpendicular to the crystallographic c-axis. The interlayer nitrite ions in these LDHs could be quantitatively oxidized to nitrate ions using H₂O₂ solution. In the LDHs thus obtained the nitrate ion lies flat with its c₃-axis parallel to the crystallographic c-axis (D_3h symmetry) in the interlayer region resulting in lower basal spacing.     

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.     

Synthesis and characterization of layered double hydroxides with a high aspect ratio

A new route for synthesis of Mg/Al layered double hydroxide (Mg₆Al₂(OH)₁₆(CO₃)·4H₂O) has been introduced, which can be considered as a modified calcination-rehydration method. Under the hydrothermal conditions, LDHs with a high aspect ratio were synthesized and characterized by inductively coupled plasma-atom emission spectrometer (ICP-AES), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermal measurement (TG-DTG) and scanning electron microscopy (SEM). XRD patterns display the crystalline enhanced with the increase of hydrothermal temperature and aging time. TG-DTG curves show the more stable LDHs were synthesized at higher temperature. SEM images indicate the lateral size of the synthesized LDHs locates at ca. 1-6 μm and the thickness at ca. 35-60 nm. And the particle size depends strongly on the treatment temperature and aging time. A buffer solution consisted of HCO₃⁻ and CO₃²⁻ keeps the pH of reaction system in a certain range and offers a low supersaturated reaction circumstance. This is of high importance for the formation of LDHs with a high aspect ratio.     

The intercalation of bicyclic and tricyclic carboxylates into layered double hydroxides

Twenty-four nanocomposites built from layered double hydroxides and bicyclic and tricyclic carboxylates have been synthesised for the first time. Eight carboxylates were successfully intercalated into [LiAl₂(OH)₆]Cl·yH₂O, [Ca₂Al(OH)₆]NO₃·yH₂O, and [Mg₂Al(OH)₆]NO₃·yH₂O, and the products fully characterised. Guest species incorporated include 1-adamantane carboxylate (1-AC) and 5-norbornene-2-endo-3-exo-dicarboxylate. In some cases, carbonate anions were co-intercalated with the organic guest, and in others poorly crystalline aluminium hydroxides formed as by-products. Sharper resonances were observed in the ¹³C solid-state NMR spectra of the 1-AC intercalates than in the spectrum of pure 1-AC, suggesting increased order in the arrangement of the cyclic cages in the intercalates. Where possible, time-resolved in situ X-ray diffraction was employed to study the nanoscopic steps involved in the intercalation reactions. These investigations showed that the reactions are one-step processes, proceeding directly to the fully exchanged intercalate with no intermediate phases. The intercalation processes were found to be nucleation controlled.     

Synthesis and properties of Mg2Al layered double hydroxides containing 5-fluorouracil

A pharmaceutically active compound, 5-fluorouracil (5-FU) has been firstly intercalated into layered double hydroxide with the restructure method. Powder X-ray diffraction and spectroscopic analysis indicate that 5-FU molecule is stabilized in the host interlayer by electrostatic interaction and intermolecular interaction, and that the orientation of 5-FU is different when changing the pattern of aging treatment or the swelling agent. The release studies show that a rapid release of the drug during the first 40 min is followed by a more sustained one, and that the total amount of drug released from hybrid material into the aqueous solution is almost 87% and 74% at pH 4 and 7, respectively. The studies mentioned above suggest that layered double hydroxide might be used as the basis of a tunable drug delivery carrier.     

Synthesis and UV absorption properties of 5, 5′-thiodisalicylic acid intercalated Zn−Al layered double hydroxides

5, 5′-Thiodisalicylic acid (TDSA) has been intercalated into a ZnAl-NO₃ layered double hydroxide (LDH) by an ion-exchange reaction. After intercalation of TDSA, the basal spacing in the LDH increased from 0.89 to 1.53 nm, suggesting that the TDSA anions were arranged in the interlayer galleries of ZnAl-TDSA-LDH as a tilted monolayer arrangement of dianions. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TGA-DTA), and UV-Visible spectroscopy (UV-Vis). The results show that the NO₃⁻ anions in the precursor have been completely replaced by TDSA anions to give ZnAl-TDSA-LDH having crystalline-layered structure. Detailed studies reveal the presence of a complex system of supramolecular interactions between LDH layers and TDSA anions. TGA-DTA curves suggest that the thermostability of TDSA was markedly enhanced by intercalation in the LDH host. Photostability tests show that the film of ZnAl-TDSA-LDH/PP possessed higher stability to UV radiation than either the film of TDSA/PP or pristine PP.     

Separation of nucleoside monophosphates using preferential anion exchange intercalation in layered double hydroxides

We report the first example of selective intercalation of nucleoside monophosphates in a layered host material. The intercalated nucleoside monophosphates can then be quantitatively recovered from the inorganic host and so this opens up the possibility of using simple layered inorganic hosts as rapid, cost effective and recyclable materials for the purification and separation of complex biomolecules.     

Synergistic effect of carbon nanotubes and layered double hydroxides on the mechanical reinforcement of nylon-6 nanocomposites

Synergistic effect in network formation of nylon-6 （PA6） nanocomposites containing one dimensional （ID） multi-walled carbon nanotubes （CNTs） and two dimensional （2D） layered double hydroxide （LDH） platelets on improving the mechanical properties has been studied. Mechanical tests show that, with incorporation of 1 wt% LDHs and 0.5 wt% CNTs, the tensile modulus, the yield strength as well as the hardness of the ternary composite are greatly improved by about 230%, 128% and 110% respectively, as compared with neat PA6. This is mainly attributed to the unique, strong interactions between the CNTs and the LDHs as well as the jammed network-like structure thus formed between the nanofillers, as confirmed by the morphological observations. As compared with the binary nanocomposites, a much enhanced solid-like behavior in the terminal region of the rheological curves can clearly be observed for the ternary system, which also indicates the formation of a percolating filler network.     

Synthesis pretreatment and characterization of a magnetic layered double hydroxides fluorescent probe

Using magnetic layered double hydroxide （MLDH） as carrier of fluorescein （FLU）, a fluorescent composite of MLDH-FLU was prepared via intercalation reaction of ion change. The crystal properties of MLDH-FLU were investigated through XRD, IR, TEM and TG-DSC characterization. It is shown that the crystal type of MLDH-FLU composite matched well with R-hexagonal crystal system of MLDH, with crystal cell parameters of a, c and channel height h equal to 0.3199, 2.411 and 0.3267 nm respectively. The superabundant pigment adsorbed outside the composite should be cleared before interference with cells, but excessive wash would decrease stability and cause crystal phase transformation of MLDH.