Layered Double Hydroxide Gallery Research Articles

Electrodeposited graphene/layered double hydroxides micro/nanocontainers for both passive and active corrosion protection

The poor dispersibility of layered double hydroxides (LDHs) is considered to be the main drawback limiting their application in anti-corrosive coatings. In this work, the problem is solved by combining LDHs with graphene (Gr). A facile electrochemically assisted deposition technique (EAT) is developed to prepare Gr/LDH micro/nano-containers. The high-barrier Gr and LDHs synergistically build a ‘labyrinth effect’ to lengthen the diffusion path of corrosive mediums. Moreover, corrosion inhibitors can be released from the interlayer galleries of LDHs and impede corrosion of metal substrate by substituting the aggressive ions. Therefore, the polyvinyl butyral (PVB) coatings doped with Gr/LDH micro/nano-containers pre-loaded with inhibitors 2-Mercaptobenzothiazole (MBT) have both passive and active corrosion protection properties and provide excellent protection to copper substrate.

Enhancing Metallocene Catalyst Activity: Utilizing Layered Double Hydroxide for Ethylene–Propylene Copolymerization

AbstractThis study reports the heterogenization of metallocene catalysts on sodium dodecyl sulfate (DDS)‐modified layered double hydroxides (LDHs) for efficient ethylene–propylene (EP) slurry‐phase copolymerization. The LDH support offers considerable compositional tunability. NiFe LDHs with different anions () and metallic compositions are applied as support for the metallocene catalysts; these significantly influence the catalytic properties of the heterogenized catalyst system. The supported‐catalyst intercalating DDS− anion in the galleries of NiFe and ZnAl LDHs demonstrates a high catalytic activity. They produce EP copolymers with high molecular weights (Mw) and wide polydispersity, compared with the homogeneous Zr catalyst. Further, the supported catalyst complex containing anion produces EP with a tenfold high Mw and demonstrate subdued catalytic activity. The higher basicity of the support is associated with the enhanced activity and the wider polydispersity of the EP pertaining to the different interactions of the catalyst molecule with the support. Overall, Ni‐containing LDH favors a higher activity, whereas Fe‐containing LDH favors a higher Mw. Therefore, NiFe‐based LDH results in both higher activity and molecular weight. 13C and 27Al magnetic angle spinning solid‐state nuclear magnetic resonance confirm the formation of the supported catalyst complex.

Computational high-throughput screening of layered double hydroxides as cathodes for chloride ion batteries

The chloride-ion battery (CIB) based on the anion transfer plays an essential role in developing new battery technologies. As a rare anion intercalated layered material, layered double hydroxide (LDHs) has attracted considerable attention as promising cathodes for CIBs. However, driven by the great compositional diversity, developing a general methodology to effective design and assess the usability of unexploited LDHs for CIBs is still a challenging issue. Herein, a computational high-throughput screening is performed among MII3MIII/IV LDHs (MII = Ni and Co; MIII/IV = Ni, Co, Fe, V, Cr and Ti). When designated as the only guest in LDHs gallery, Cl atoms tend to absorb above the O atoms without MIII/IV around and adsorption energy increases with the order of Ti > Cr > V > Fe > Co > undoped hydroxides. During the chlorination reaction, a special ClHOMIII/IV electron transfer chain is proposed for the first time. Furthermore, Cl storage performance for 11 cathodes were evacuated by the theoretical voltage in a full CIB system. The results indicates Ti-containing LDHs is the most encouraging cathodes, which is verified by the experimental measurement. This work provides a clear guidance and a theoretical insight into the anion insertion electrochemistry for LDHs materials.

Intercalation of laminar Cu-Al LDHs with molecular TCPP(M) (M = Zn, Co, Ni, and Fe) towards high-performance CO2 hydrogenation catalysts.

A confined space is broadly applied to enhance the dispersion and limit the aggregation of catalytically active sites, especially at high temperatures. In this work, we provided an efficient approach to immobilize transition metal ions (e.g., Zn2+, Co2+, Ni2+, and Fe2+) into the confined space of laminar Cu-Al layered double hydroxides (LDHs) using a range of molecular metalloporphyrins (viz., TCPP(M)) as shuttles. The deprotonated TCPP(M) not only provides nitrogen-based coordination sites to anchor a series of transition metal ions, but also intercalates and diffuses facilely into the interlayer gallery of LDHs by ion exchange. The obtained TCPP(M)@Cu-Al LDHs were then used as solid precursors for the fabrication of a series of heterogeneous catalysts for CO2 hydrogenation via high-temperature calcination. Two restriction forces contributed to the enhanced dispersion of the active species over the catalyst surface structures. Remarkably, the transition metals positioned within the confined space of LDHs significantly affected the catalytic performance of CO2 hydrogenation. Mainly CO, methanol, and methane were found as the C1 products, and their selectivities are highly dependent on the reaction intermediates, as suggested by the in situ DRIFTS study. Moreover, the designed catalysts fabricated via molecular TCPP(M) intercalation exhibited much better performance than the conventional catalysts derived from surface-supported CA-LDHs, due to their better metal dispersion and smaller particle size.

Preparation and Characterization of Lignosulfonate Intercalated Layered Double Hydroxides and Their Application in Improving Ultraviolet Aging Resistance for Bitumen

In order to develop economically anti-ultraviolet (UV) aging additives to bitumen and extend the comprehensive utilization of lignin materials, lignosulfonate (LS) was selected to intercalate into layered double hydroxides (LDHs), then the LS intercalated LDHs (LS-LDHs) were applied to improve UV aging resistance of bitumen. With the characterization of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, chemical analysis and scanning electron microscopy (SEM), LS was successfully intercalated into the galleries of LDHs. The ultraviolet and visible (UV-vis) absorbance curves showed LS-LDHs had excellent UV absorptive ability from 200 to 400 nm. Thermogravimetry and differential scanning calorimetry (TG-DSC) indicated LS-LDHs could have a good thermal stability during the processing of bitumen. Compared with the LDHs, the LS-LDHs exhibited better performance in UV aging resistance of bitumen.

Intercalation of $$\hbox {LDH NO}_{{3}}$$ LDH NO 3 with short-chain intercalants

Intercalation behaviour of layered-double hydroxide (LDH) with short-chain intercalants (\({-}(\hbox {CH}_{2})_{n}{-}, n<9\)) is significantly difficult and less reported than with long-chain intercalants. The present study reports an efficient way to intercalate LDH with short-chain intercalants (\(n=4\) and 8) and investigates the effect of layer charge on intercalation behaviour of LDHs. Short-chain anionic surfactants were successfully intercalated with synthetic LDHs \([\hbox {Zn}_{1-x}\hbox {Al}_{x}(\hbox {OH})_{2}\hbox {NO}_{{3}}{\cdot } n\hbox {H}_{2}\hbox {O},\,x=0.2{-}0.33]\) by an ion-exchange intercalation technique in a slightly acidic medium (\(\hbox {pH}=5.4\)). The adverse effect of a carbonate anion was avoided by performing the ion-exchange intercalation in slightly acidic medium (\(\hbox {pH}=5.4\)). It was found that basal spacing \((d_{003})\) and experimental organic loading of intercalated LDH (O-LDH) increase monotonically with increasing anion-exchange capacity of LDH and intercalant chain length. The evolution of intercalated LDH (O-LDH) structures with increasing intercalant chain length and layered charge has been deciphered by correlating basal spacing of O-LDHs (by X-ray powder diffraction), organic loading data (by thermogravimetric analysis) and molecular conformation of O-LDHs (by Fourier-transform infrared spectroscopy) within the LDH gallery. Successful intercalation of LDH with these short-chain intercalants in slightly acidic medium has not been reported previously.

Antifouling composites with self-adaptive controlled release based on an active compound intercalated into layered double hydroxides

This paper reports a novel method to prepare the antifouling composites with properties of self-adaptive controlled release (defined as control the release rate autonomously and adaptively according to the change of environmental conditions) by intercalation of sodium paeonolsilate (PAS) into MgAl and ZnAl layered double hydroxide (LDH) with the molar ratio (M2+/M3+) of 2:1 and 3:1, respectively. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of LDH. The controlled release behavior triggered by temperature for the PAS-LDH composites has been investigated, and the results show that the release rate of all PAS-LDH composites increases as the increase of temperature. However, the MgAl-PAS-LDH composites (Mg2Al-PAS-LDH and Mg3Al-PAS-LDH) exhibit the increased release rate of 0.21ppm/°C from 15 to 30°C in 3.5% NaCl solution, more than three times of the ZnAl-PAS-LDH composites (0.06ppm/°C), owing to the confined microenvironment influenced by metal types in LDH layers. In addition, a possible diffusion-controlled process with surface diffusion, bulk diffusion and heterogeneous flat surface diffusion has been revealed via fitting four kinetic equations. Moreover, to verify the practical application of the PAS-LDH composites, a model coating denoted as Mg2Al-PAS-LDH coating was fabricated. The release result displays that the release rate increases or decreases as temperature altered at 15 and 25°C alternately, indicating its self-adaptive controlled release behavior with temperature. Moreover, the superior resistance to the settlement of Ulva spores at 15 and 25°C was observed for the Mg2Al-PAS-LDH coating, as a result of the controllable release of antifoulant. Therefore, this work provides a facile and effective method for the fabrication of antifouling composites with self-adaptive controlled release behavior in response to temperature, which can be used to prolong the lifetime of antifouling coatings.

Active corrosion protection of Mg-Al-PO 4 3− LDH nanoparticle in silane primer coated with epoxy on mild steel

Abstract Mg-Al-PO 4 3− layered double hydroxide (LDH) nanoparticle was synthesized through an anion exchange method and characterized by XRD, IR spectroscopy and SEM. The phosphate and Mg 2+ release ability of Mg-Al-PO 4 3− LDH in the 3.5 wt. % NaCl solution was measured by inductively coupled plasma-optical emission spectrometer (ICP-OES). Results showed the release of Mg 2+ from the LDH scaffold along with phosphate anion from LDH gallery, illustrating importance of solubility rather than ion-exchange mechanism. Then, the corrosion inhibitive behavior of Mg-Al-PO 4 3− LDH in 3.5 wt. % NaCl solution was assessed by electrochemical measurements and FE-SEM in comparison with the Mg-Al-NO 3 − LDH. The results showed that Mg-Al-PO 4 3− LDH forms inhibitive film on the mild steel and significantly mitigate corrosion compared to Mg-Al-NO 3 − LDH. The LDHs were also employed in a silane primer top-coated by epoxy-polyamide on mild steel. The results of electrochemical measurements showed significant active corrosion protection ability of Mg-Al-PO 4 3− LDH in the coating with an artificial defect. Furthermore, the adhesion strength of the coating including Mg-Al-PO 4 3− LDH to mild steel after exposure to salt spray (5% NaCl solution) was improved.

Insight into the preparation of Fe3O4 nanoparticle pillared layered double hydroxides composite via thermal decomposition and reconstruction

As one of layered double hydroxides (LDH) based heterogeneous catalysts, transition metal oxide pillared LDH composite has attracted considerable research interests as its excellent catalytic efficiency and thermal stability. However, during the preparation especially by reconstruction techniques, abundant interlayer regions of LDH are contaminated by some unexpected anion such as LDH affinitive CO32−, which will result in inaccessible interlayer active site. In this paper, magnetic nanoparticle Fe3O4 pillared LDH composite was synthesized with exchangeable NO3− as the main interlayer anion by decomposition and reconstruction route. The anion exchange, decomposition and reconstruction processes were comprehensively investigated. XRD, TG-DTA-MS, SEM and other methods have been employed to characterize materials. The results show that anion exchange between ferric citrate anion and LDH follows Langmuir isotherm model and pseudo-second-order model. The decomposition and oxidation of anion exchange product (LDH-Fe(C6H4O7)−) can be complete at 550°C for 20min and crystal Fe3O4 with nanostructure is formed between 500 and 600°C. When calcined product (LDO-Fe3O4) is reconstructed by rehydration in 0.015M HNO3-30wt% NaNO3 mixture aqueous solution, CO32− contamination derived from CO2 in air can be averted and lamellar structure is successfully recovered with Fe3O4 and NO3− remaining in the interlayer gallery of LDH.

Ultrahigh-rate-capability of a layered double hydroxide supercapacitor based on a self-generated electrolyte reservoir

A supercapacitor based on hierarchical OH−-containing CoAl layered double hydroxide (LDH) arrays exhibits excellent energy and power output, especially an ultrahigh-rate-capability, which is attributed to the self-generated electrolyte (OH−) reservoir in the LDH gallery.

Polyoxometalates Hosted in Layered Double Hydroxides: Highly Enhanced Catalytic Activity and Selectivity in Sulfoxidation of Sulfides

Layered double hydroxides (LDHs) are a class of layered materials with tunable interlayer galleries. In this paper, a series of Mg3Al–P2W17X (X = MnIII, FeIII, ZnII, CoII, CuII, NiII) have been prepared successfully by intercalating the polyoxometalate (POM) of [α2-P2W17O61(X·OH2)]n− ([P2W17X]n−, n = 7 or 8) into a Mg3Al–suberic precursor. Catalytic tests for H2O2-based sulfoxidation of various sulfides demonstrate that Mg3Al–P2W17Zn exhibits better catalytic efficiency and selectivity than pure POM or LDH precursors under mild conditions. The uniform and well-ordered dispersion of POM in the confined gallery of LDHs and the multiple interactions between POMs and LDHs contribute to the excellent catalytic performance. Moreover, Mg3Al–P2W17Zn is stable and can be easily separated from the reaction system. The recycled Mg3Al–P2W17Zn maintains both the intact structures of the POM anion and LDHs. The scaled-up experiment provides further support for its potential use for industrial applications.

Synthesis and characterization of layered double hydroxides intercalated by UV absorbents and their application in improving UV aging resistance of bitumen

Two different types of UV absorbents, 2-hydroxybenzoic acid and 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, were intercalated into layered double hydroxides (LDHs) to synthesize organic LDH by anion-exchange method, and then the synthesized organic LDHs were applied to modify bitumen aiming to improve UV aging resistance of bitumen. According to the characterization with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), the two UV absorbents were successfully intercalated into the galleries of LDH, leading to the expansion of interlayer distance of LDH. Thermogravimetry and differential scanning calorimetry (TG–DSC) and UV–vis absorbance analyses indicated that the thermal stability and UV absorptive ability of UV absorbents were enhanced significantly. Compared with LDH, organic LDH exhibited better improvement in UV aging resistance of bitumen by restraining the oxidation of bitumen and generation and stacking of asphaltenes cluster during UV exposure, which was due to the enhanced UV absorptive ability of organic LDH and compatibility between organic LDH and bitumen.

Preparation of Sodium Paeonolsilate Intercalated into Layered Double Hydroxides and its Release Properties

A controlled release composite has been prepared by intercalation of sodium paeonolsilate (PAS) into Mg/Al layered double hydroxide (LDH) with the molar ratio (M2+/M3+) of 2:1. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of LDH. The chemical composites of PAS-LDH were revealed by elemental analysis. Release tests of the PAS-LDH composite showed that no burst release phenomenon occurred at the beginning stage and a high release ratio of PAS (89.8%) was obtained, exhibiting controlled release behavior. Furthermore, the parabolic diffusion model was used to simulate the release kinetics of PAS from the LDH carrier, indicating that the intraparticle diffusion via ion-exchange is the rate-determining step in the release process. It is significance in this work for introducing the PAS-LDH composite to develop antifouling materials with long-term activity.

In vitro controlled release of vitamin C from Ca/Al layered double hydroxide drug delivery system

A new drug delivery system for vitamin C (VC), Ca/Al layered double hydroxide (LDH), is demonstrated in this work. VC anions were intercalated successfully in the Ca/Al LDH gallery by a coprecipitation method. The interlayer space of 9.8Å suggests that VC anions are vertical to the LDH layers in the form of interdigitated bilayer. The loading of VC in LDH is 36.4wt.%. The thermal stability of VC is significantly enhanced after intercalation. In vitro VC release results show that the release time of VC in a phosphate buffer at pH7.4 was significantly extended, and the maximal percentage of VC released is 80% of the total. The Avrami–Erofe'ev equation most satisfactorily explains the release kinetics of VC, which is that the release of VC is mainly dominated by the ion-exchange reaction.

Facile synthesis of camptothecin intercalated layered double hydroxide nanohybrids via a coassembly route

A method has been developed for the synthesis of intercalated layered double hydroxide (LDH) nanohybrids of the charge-neutral and poorly water-soluble anticancer drug camptothecin (CPT) using a coassembly route. For this route, CPT molecules were initially incorporated into the micelles of a biocompatible surfactant, such as sodium cholate (SCh) or sodium deoxycholate (SDC). The resulting negatively charged CPT-loaded micelles and the positively charged LDH nanosheets were then coassembled together into the CPT intercalated LDH nanohybrids. The resulting nanohybrids were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and elemental analyses. The results revealed that the loading of CPT in the nanohybrids could reach as high as 13%, indicating that this route could be used to achieve the effective intercalation of charge-neutral and poorly water-soluble drugs into the LDH gallery. The in vitro release of CPT from the nanohybrids was examined, and the results showed that the release was a diffusion-controlled process and that the diffusion process through the LDH particles was the rate-limiting step. The parabolic diffusion equation effectively described the kinetic process associated with the release of CPT from the nanohybrids.

Immobilization of triazabicyclodecene in surfactant modified Mg/Al layered double hydroxides

In recent years, layered double hydroxides (LDHs) have received much interest as host materials for the construction of organic–inorganic supramolecular structures by an anion exchange method. This study demonstrates the preparation of a series of solid base catalysts through attachment of triazabicyclodecene (TBD) to Mg/Al-LDH surfaces with different Mg/Al molar ratios (Mg/Al = 3, 4 and 5). A new three-stage approach was taken to obtain TBD-LDH materials: (i) an anionic surfactant, sodium dodecyl sulfate (SDS) was intercalated in parent LDH replacing nitrates from interlayer via anion exchange to widen the gallery of LDH, (ii) a silane coupling agent (3-glycidyloxypropyl) trimethoxysilane (3GPS) was used to attach TBD with the terminal glycidyl groups, and (iii) interlayer molecules from SDS-LDH gallery were replaced by the 3GPS moieties containing TBD. The surfactant modified Mg/Al LDH materials showed an increase in interlayer distance (maximum 44.8 Å) as compared to unmodified Mg/Al LDH (8.8 Å). Infrared and Raman spectroscopy results were in agreement with the proposed organic functionalized structure. Therefore, based on these observations, a schematic representation of the TBD functionalized LDH surface is also presented. The temperature programmed desorption (TPD) study on the different products showed approximately 3–5 times higher basic properties than those of pristine LDHs. Thermal decomposition was changed significantly after organic modification of LDHs. All TBD-LDHs are found to be effective catalysts for the transesterification of canola oil with dimethyl carbonate (DMC) for biofuel production under mild conditions (atmospheric pressure and 70 °C).

Synthesis and characterization of 10-hydroxycamptothecin – sebacate – layered double hydroxide nanocomposites

10-Hydroxycamptothecin (HCPT) as a hydrophobic anticancer drug brings many challenges in the clinical applications due to its poor water solubility and the presence of a chemically unstable lactone ring. In this work, the nanocomposites of HCPT intercalated layered double hydroxide (LDH) were prepared by a secondary intercalation method, and the encapsulated HCPT could keep the biologically active lactone form. A Zn–Al–NO3 LDH was pillared with sebacate anions by a co-precipitation method in an aqueous medium, and then HCPT was intercalated into the LDH's gallery via hydrophobic interaction in an ethanol medium. The parallel alkyl chains of perpendicularly arranged sebacate anions in the LDH gallery provide a hydrophobic space for the drug intercalation. The in vitro release kinetics of HCPT from the nanocomposites could be fitted with the pseudo-second-order kinetic model, and the diffusion of HCPT through the LDH particles played an important role in controlling the drug release. The nanocomposites can be considered as a potential drug delivery system.

Synthesis and Applications of Layered Double Hydroxides Based Pigments

Layered double hydroxides (LDHs) have attracted a great deal of attention owing to their structural anisotropy, anion-exchange capability and compositional flexibility and have been widely investigated as catalysts, adsorbents, anion-exchangers, polymer additives, optical materials, and so on. The intercalation of chromophores into the interlayer galleries of LDHs has drawn considerable interest since it can result in a kind of functional pigments showing different photophysical and photochemical properties from the pristine chromophores due to the host-guest and guest-guest interactions. This paper reviews recent patents progress made for the synthesis and applications of LDHs based pigments. The potentional applications and the future development are also discussed.

Intercalation of Fe(III) complexes into layered double hydroxides: Synthesis and structural preservation

In this study, intercalation of Fe(III) complexes [Fe(Ox)3]3− and [Fe(Cit)2]3− in Mg2Al layered double hydroxides (LDHs) had been carried out by different routes: direct self-assembly, reconstruction and anion exchange. The result of XRD indicated that these two kinds of Fe(III) complexes intercalated LDHs (LDHs/Fe-complexes) could be successfully synthesized by anion exchange obtaining two well crystallized LDHs both with a large basal spacing. The chemical environment of iron ion in the intercalated Fe complexes was determined by FTIR, XPS and XAFS, the results of which concertedly proved that the intercalated Fe complexes were well preserved in the interlayer of LDHs. The arrangement of the Fe(III) complexes anions in the galleries of LDHs was studied by one-dimensional electron density projection. The results showed that the [Fe(Ox)3]3− anions were probably accommodated in the gallery of LDHs as an interdigitated bilayer arrangement, and the [Fe(Cit)2]3− were perpendicularly arranged against the LDHs sheets. Through the research, it is proved that the obtained LDHs/Fe-complexes markedly enhanced the UV–vis absorption ability of Fe complexes.

Preparation of intercalated Mg‐Al layered double hydroxides and its application in PVC thermal stability

AbstractThe Mg‐Al oxide precursor prepared by the calcination of Mg‐Al‐carbonated layered double hydroxide (LDH) at 500 K for 4 h is used as the host material, 2‐hydroxy‐4‐methoxybenzophenone‐5‐sulfonic acid (BP) is used as the guest material, BP‐intercalated LDH (LDH‐BP) is prepared by ion‐exchange method. The structure of LDH‐BP is characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), and thermogravimetry and differential thermal analysis (TG‐DTA). The thermal stability of PVC/BP, PVC/LDH, PVC/LDH‐BP composites, as well as pure PVC is investigated by conventional Congo Red test and dynamic thermal stability analysis in both the open and closed processing environments. According to XRD and FTIR, BP anions have been intercalated into interlayer galleries of LDH. TG‐DTA results show that the layer‐anionic interaction results in the improvement of the thermal stability of BP. Congo Red tests indicate that the addition of BP catalyzes the thermal degradation of PVC. A little amount of LDH (such as 1 phr) makes PVC more stable, but excessive addition accelerates the thermal degradation of PVC. The addition of LDH‐BP markedly improves the static thermal stability of PVC. The results of dynamic thermal stability tests in both the open and closed processing environments are consistent with that of Congo Red tests. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011