Layered Double Hydroxide Precursor Research Articles

Significantly Enhanced Separation using ZIF‐8 Membranes by Partial Conversion of Calcined Layered Double Hydroxide Precursors

Significantly enhanced H2 /CH4 (ca. 80) selectivity was realized by effective suppression of the framework flexibility of a prepared ZIF-8 membrane. Initially a ZnO buffer layer consisting of 20 nm-sized ZnO-nanoparticle aggregates was fabricated by controlled calcination of a ZnAl-NO3 layered double hydroxide membrane. Owing to its high chemical reactivity, the ZnO buffer layer was partially converted into a well-intergrown ZIF-8 membrane with a certain penetration depth upon solvothermal treatment with ligands. Our method may represent a new concept for the design of advanced MOF membranes with high selectivity.

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.

Supported Nickel Based Catalysts, Ni/Mg(Al)O, for Natural Gas Conversion, Prepared via Delamination and Restacking of MgAl- and NiAl-Nanosheets

Three different well-defined Ni/Mg(Al)O catalysts for natural gas conversion are prepared and exposed to the dry reforming of propane reaction at 600 °C. The catalysts have in common that they are based on layered double hydroxides (LDH) as precursor material. Two of the catalysts, Cat-A and Cat-B, are prepared via a novel delamination–restacking route of single layer nanosheets whereas the reference catalyst, Cat-C, is obtained using earlier established bulk procedures. All three catalysts show stable performance at the selected catalytic testing conditions, and the intrinsic activity appears to be mainly correlated with the mean Ni particle diameter. The novel catalysts, based on the nanostructured LDH precursors, have similar performance as the high performing reference catalyst, indicating that the delamination–restacking process do not alter the catalytic properties of the final nanostructured material. The new preparation route is concluded to be suited for controlling design of well-defined metal-on-support model catalysts for single parameter studies.

Mg–Al mixed metal oxide film derived from layered double hydroxide precursor film: Fabrication and antibacterial properties

Mg–Al layered double hydroxide (LDH) precursor films are fabricated in situ by urea hydrolysis using pure Al as both the substrate and Al source. X-ray diffraction patterns and scanning electron microscopy images show that Mg–Al LDH films are fabricated in situ. After calcination at 500 °C for 4 h, Mg–Al mixed metal oxide (MMO) films that inherited the microstructure of LDH precursor films are obtained. The surface concentration of nano-MgO dispersed in the MMO matrix and the microstructure of the films may be tailored by varying the crystallization time of LDH precursor films. The superhydrophilic property of MMO films arising from their microstructure can reduce the adsorption and adhesion of bacteria and retard biofilm formation. Moreover, nano-MgO dispersed in the MMO matrix has high bactericidal activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Vibrio fischeri. Mg–Al MMO films obtained in the present work have excellent antibacterial activities that are due to synergistic effects and thus have potentially applications in antibacterial coatings.

Tribological performance of Mg/Al/Ce layered double hydroxides nanoparticles and intercalated products as lubricant additives

Mg/Al/Ce ternary layered double hydroxides (LDHs) were synthesized via coprecipitation and intercalated by succinic acid and lauric acid through ion exchange method respectively. The LDHs products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FT-IR). Tribological properties of LDHs as lubricant additives were evaluated by four-ball friction and air compressor test. The results indicated that Mg/Al/Ce LDHs were prepared successfully with Ce/Al molar ratio of 0.05 and crystallization temperature of 140°C. The interlayer spacing of LDHs precursor was expanded by succinic acid and lauric acid to 8.838 and 17.519Å respectively. All the three LDHs products can reduce friction and wear of engine lubricating oil in the tests. LDHs intercalated with lauric acid showed best tribological performance among them which was attributed to sliding each other between laminates, good dispersibility in oil medium and a protective tribofilm formed on the worn surface.

Spinel type CoFe oxide porous nanosheets as magnetic adsorbents with fast removal ability and facile separation

Adsorption is often time consuming due to slow diffusion kinetic. Sizing he adsorbent down might help to accelerate adsorption. For CoFe spinel oxide, a magnetically separable adsorbent, the preparation of nanosheets faces many challenges including phase separation, grain growth and difficulty in preparing two-dimensional materials. In this work, we prepared porous CoFe oxide nanosheet with chemical formula of Co2.698Fe0.302O4 through topochemical transformation of a CoFe precursor, which has a layered double hydroxide (LDH) analogue structure and a large interlayer spacing. The LDH precursor was synthesized from a cheap deep eutectic solvent (DES) system. The calcined Co2.698Fe0.302O4 has small grain size (10–20nm), nanosheet morphology, and porous structure, which contribute to a large specific surface area of 79.5m2g−1. The Co2.698Fe0.302O4 nanosheets show fast removal ability and good adsorption capacity for both organic waste (305mgg−1 in 5min for Congo red) and toxic heavy metal ion (5.27mgg−1 in 30min for Cr (VI)). Furthermore, the Co2.698Fe0.302O4 can be separated magnetically. Considering the precursor can be prepared through a fast, simple, surfactant-free and high-yield synthetic strategy, this work should have practical significance in fabricating adsorbents.

Sulfur-doped mesoporous carbon from surfactant-intercalated layered double hydroxide precursor as high-performance anode nanomaterials for both Li-ion and Na-ion batteries

We describe a preparation of sulfur-doped mesoporous amorphous carbon (SMAC) from a commercially available alkyl surfactant sulfonate anion-intercalated NiAl-layered double hydroxide precursor via thermal decomposition and subsequent acid leaching. The resultant amorphous carbon is endowed with the integrated advantage of featuring high reversible capacity and long cycling stability: intrinsic doping of sulfur, large specific area, and broad mesopore size distribution. Electrochemical evaluation shows that the SMAC electrode exhibits highly enhanced electrochemical performances, compared with the electrode of non-doped mesoporous and amorphous carbon prepared by using a different surfactant (sodium laurate). A high reversible capacity of 958mAhg−1 is achieved for the SMAC electrode after 110 cycles at 200mAg−1, and especially a superlong cycle life with a reversible capacity of 579mAhg−1 after 970 cycles at 500mAg−1. Moreover, the SMAC electrode can facilitate the reversible insertion/extraction of Na ion, owing to the proper specific area and mesopore size distribution, as well as the improved electronic conductivity resulted from doping of sulfur.

Enhanced adsorption of Congo red dye by functionalized carbon nanotube/mixed metal oxides nanocomposites derived from layered double hydroxide precursor

Functionalized carbon nanotube/mixed metal oxides (CNT/MMO) nanocomposites composed of CNT and Mg(Al)O nanoparticles have been synthesized by pyrolysis of a terephthalic intercalated layered double hydroxide (LDH) precursor. The chemical composition and morphology of this nanocomposites were investigated by XRD, SEM, and TEM measurements. FTIR characterization shows that the surface of the prepared CNT is functionalized with abundant oxygen-containing groups without further modification. As a novel adsorbent, the as-prepared functionalized CNT/Mg(Al)O nanocomposites exhibit very high performance in the removal of Congo red (CR) dye from aqueous solutions. The initial pH of dye solution and dosage of adsorbent have an important influence on the adsorption property of the CNT/Mg(Al)O nanocomposites. The adsorption isotherm obeys the Langmuir model, with the maximum adsorption capacity greatly enhanced to 1250mg/g, exhibiting potential applications in wastewater treatment. A adsorption mechanism that involves (i) strong interactions between the functional groups on the surface of CNT and CR molecules and (ii) electrostatic interactions between positively charged reconstructed LDH layer and negatively charged CR molecules, was proposed.

A new, low-cost adsorbent: Preparation, characterization, and adsorption behavior of Pb(II) and Cu(II)

This work aimed to develop waste (i.e., sulfonated lignin) application in simulated wastewater treatment. Sulfonated lignin (LS), a byproduct of the paper industry, was intercalated into a parent host of layered double hydroxides (LDH) by swelling–restacking method. X-ray diffraction patterns of the composite confirmed that long-chain LS anions exited in the interlayer of Mg2Al–LDH in two forms: (1) a “flat” form with d003=0.88nm; and (2) a “vertical” form with d003=9.08nm. Results showed that the obtained Mg2Al–LS–LDH composite was highly selective and efficient for the removal of Pb2+ and Cu2+, especially Pb2+, compared with the NO3–LDH precursor. The coexisting cations decreased the removal efficiency of Pb2+ or Cu2+ on Mg2Al–LS–LDH composite, which could be ascribed to outer-sphere sorption style, and the effect order of cations is Li+>Ca2+>K+>Na+. The pseudo-second-order model appropriately described the sorption kinetics of Mg2Al–LS–LDH composite for Pb2+ and Cu2+. Sorption isotherms for Pb2+ and Cu2+ by the Mg2Al–LS–LDH composite were found to be more satisfactorily fitted by the Langmuir model than by the Freundlich one. With increased Pb2+ or Cu2+ concentration from 2ppm to 200ppm, the maximum absorption capacity of the composite toward Pb2+ was ∼123mg/g and that toward Cu2+ was ∼64mg/g. Therefore, a new, low-cost adsorbent was synthesized by utilizing the byproduct LS, which may be a potential remedy for Pb2+ or Cu2+ in contaminated water.

Flux-Assisted Fabrication of Vertically Aligned Layered Double Hydroxide Plates on in Situ Formed Alumina Particles

Layered double hydroxide (LDH) is an environmentally benign anion exchanger that can adsorb various toxic anions. In this work, we demonstrate the fabrication of plate-like Mg–Al-type LDH crystals on in situ formed alumina particles using a flux method at a relatively low temperature (∼350 °C). At or below 300 °C, the melted Al source crystallized to form AlOOH or γ-alumina particles in KNO3–NaNO3 flux. However, LDH crystals did not form due to the inferior crystallization properties of the Mg precursor. Increasing the holding temperature up to 350 °C and above facilitated crystallization of the dissolved Mg and Al species in flux to yield plate-like LDH crystals on the preformed alumina particles. Top-surface and cross-sectional FE-SEM and EPMA analyses revealed the vertical alignment of the crystalline LDH plates on the surface of the alumina particles. On the other hand, solid-state reactions did not yield these well-grown, plate-like LDH crystals. The TG-DTA profile of the LDH precursors with flux depicted the decomposition and crystallization events that the Al and Mg precursors undergo. On the basis of the results from these characterization studies, we propose a mechanism in which LDH crystals sequentially form on the surface of the alumina particles.

Gas phase hydrogenation of dimethyl-1,4-cyclohexane dicarboxylate over highly dispersed and stable supported copper-based catalysts

Highly dispersed and stable supported copper-based catalysts for gas-phase hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate (DMCD) to 1,4-cyclohexane dimethanol (CHDM) were synthesized from a single-source Cu–Zn–Al layered double hydroxide (LDH) precursor. The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), N2 sorption, H2-N2O titration and transmission electron microscopy (TEM) techniques. The results revealed that calcination temperature for LDH precursors significantly affected the composition, structure, chemical states, and catalytic performance of copper-based catalysts. In the gas-phase selective hydrogenation of DMCD, a high CHDM yield of 95.6% was achieved over copper-based catalyst obtained at calcination temperature of 600°C. Compared with the conventional Cu/ZnO/Al2O3 and Cr2O3 promoted copper-based catalysts, LDH-derived Cu-based catalysts exhibited higher catalytic performance, which was mainly attributed to the presence of highly dispersed and stable active metallic copper species, as well as a reasonable amount of Cu+ species facilitating the activation of ester groups of reactants.

Effects of Compound Oxides on the Fire Performance of Polypropylene Composite

Compound oxides (NiFeO and CoFeO) were obtained by calcining layered double hydroxide (LDH) precursors prepared by microwave-hydrothermal method. The structure of LDHs and compound oxides was characterized by X-ray diffraction (XRD). The thermal behavior and flammability of polypropylene (PP) composites containing different types of compound oxides were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), and cone calorimeter. Fire performance characterization has demonstrated that both NiFeO and CoFeO can significantly increase the LOI of PP/IFR. NiFeO and CoFeO can improve the char quality of PP/intumescent flame retardant (IFR) composite and the thermal stability of formed char. The heat release rate (HRR) of a PP/IFR sample containing 2 wt % CoFeO could be decreased by 33%, compared with that of PP/IFR sample. The char residue of PP composites after cone test was characterized by laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). It is suggested that c...

Comparison of CuxZnAlO mixed oxide catalysts derived from multicationic and hybrid LDH precursors for methane total oxidation

CuxZnAlO mixed oxide catalysts for methane total oxidation have been obtained by thermal activation of layered double hydroxides (LDHs) precursors. LDHs have been prepared following two different routes: (i) conventional coprecipitation (pH=8 or 10) and (ii) hybridation achieved by intercalation of Cu-containing anionic complexes ([Cu-EDTA]2− and [Cu-citrate]−) into host ZnAl-LDH. The mixed oxide catalysts showed only ZnO phase at Cu<5 at.% and a mixture of ZnO and CuO phases at higher Cu content. CuO particles differently interacting with the oxide supports were revealed by TPR analysis. They were reduced at lower temperature but with a lower H2 consumption in the mixed oxides derived from the hybrids suggesting lower accessibility. The activity of the catalysts in the total oxidation of methane strongly depended on the method of preparation of the LDH precursors and on the Cu content. Cu10ZnAlO (10 at.% Cu) derived from a coprecipitated LDH showed the highest intrinsic activity and a good stability suggesting an optimum dispersion of the copper-containing active species. Among the catalysts derived from the hybrid precursors, the higher activity of the Cu(EDTA)-ZnAl ones may be due to their higher Cu content. The lower intrinsic activities and higher activation energies of this series of catalysts compared to the coprecipitated ones may be due to the lower accessibility to the CuO active sites.

Preparation of Monodisperse Ferrite Nanocrystals with Tunable Morphology and Magnetic Properties

The synthesis of monodisperse magnetic ferrite nanomaterials plays an important role in several scientific and technological areas. In this work, dibasic spinel MFe2O4 (M=Mg, Ni, Co, Fe, Mn) and polybasic spinel ferrite MCoFeO4 (M=Mg, Ni, Mn, MgNi) nanocrystals were prepared by the calcination of layered double hydroxide (LDH) precursors at 900 °C, which was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate that the as-obtained spinel ferrites present a single-crystalline nature with uniform particle size and good dispersibility. The composition, morphology, and particle size can be effectively tuned by changing the metal ratio, basicity, reaction time, and temperature of the LDH precursors. In addition, these spinel ferrites show high magnetic saturation values in the range 21.7-84.3 emu g(-1), which maintain a higher level than the previously reported magnetic nanoparticles. Therefore, this work provides a facile approach for the design and fabrication of spinel ferrites with controllable nanostructure and improved magnetism, which could potentially be used in magnetic and biological fields, such as recording media, sensors, drug delivery, and intracellular imaging.

Layered double hydroxide (LDH) derived catalysts for simultaneous catalytic removal of soot and NOx

Nitrogen oxides (NO(x)) and soot which come from vehicle engine exhausts cause serious environmental pollution and human health problems. Recently, the catalytic purification technology, particularly the simultaneous catalytic removal of soot and NO(x), has received more and more attention. For this technology, the key is to develop highly efficient and robust catalysts. Due to the unique chemical and structural properties of layered double hydroxides (LDHs), LDH-derived catalysts have shown great potential, and much effort has been devoted to this type of catalyst. In this manuscript, we reviewed the latest progress in the LDH derived catalysts by classifying the LDH precursors according to the number of metals into binary, ternary, and quaternary, and discussed their advantages and disadvantages in detail. We hope that this review paper could provide a clearer picture of this topic and theoretical support for its better development.

Monodisperse embedded nanoparticles derived from an atomic metal-dispersed precursor of layered double hydroxide for architectured carbon nanotube formation

Monodisperse metal nanoparticles (NPs) with high activity and selectivity are among the most important catalytic materials. However, the intrinsic process to obtain well-dispersed metal NPs with tunable high density (ranging from 1013 to 1016 m−2) and thermal stability is not yet well understood. Herein, the preparation of metal NPs with tunable areal density from layered double hydroxide (LDH) precursors in which the metal cations were pre-dispersed at an atomic scale was explored. Large quantities of mesopores induced by the Kirkendall effect were formed on the as-calcined layered double oxide (LDO) flakes. The O atoms bonded with Fe3+ cations were easy to be extracted at a temperature higher than 750 °C, which greatly increased the mobility of Fe. Consequently, coalescence of the reduced Fe atoms into large NPs enhanced the Kirkendall effect, leading to the formation of monodisperse embedded Fe NPs on the porous LDO flakes. The flake morphology of LDHs was well preserved, and the areal density of Fe NPs on the LDO flakes can be well controlled through adjusting the Fe content in the LDH precursor. With higher Fe loading, larger Fe NPs with higher areal density were available. When the areal density was increased from 0.039 to 0.55, and to 2.1 × 1015 m−2, the Fe NPs embedded on the LDO flakes exhibited good catalytic performance for the growth of entangled carbon nanotubes (CNTs), aligned CNTs, and double helical CNTs, respectively. This work provides not only new insights into the chemical evolution of monodisperse NPs from an atomic metal-dispersed precursor, but also a general route to obtain tunable NPs as heterogeneous catalysts for chemical and material production.

Glycerol valorization by etherification to polyglycerols by using metal oxides derived from MgFe hydrotalcites

This work investigates the use of MgFe mixed oxides, derived from layered double hydroxides (LDH) with Mg/Fe molar ratio ranging from 1 to 4, as base catalysts for the etherification of glycerol. LDH precursors and catalysts were characterized by XRD, XPS, CO2-TPD, NH3-TPD, N2 adsorption and DTA–TG analysis. The MgFe mixed oxides exhibit excellent textural properties, with specific surface areas close to 200m2g−1 and average pore diameters in the mesoporous range. This family of catalysts has shown to be active in the formation of polyglycerols from glycerol without solvent, at 220°C, in a batch reactor. The highest conversion (41%) is found for the MgFeO4 catalyst prepared with a Mg/Fe molar ratio of 4, whereas full selectivity to diglycerols is only reached for the MgFeO1 catalyst. Only diglycerols (DGs) and triglycerols (TGs) have been detected after 24h of reaction.

A novel Ni–Mg–Al-LDHs/γ-Al2O3 Catalyst Prepared by in-situ synthesis method for CO2 reforming of CH4

A novel Ni–Mg–Al catalyst derived from layered double hydroxides (LDHs) which was prepared on γ-Al2O3 by in-situ synthesis method. The catalyst was evaluated by CO2 reforming of CH4 and a better catalytic performance was obtained compared with a reference catalyst of Ni/MgO/γ-Al2O3 prepared by impregnation. The novel catalyst was also characterized by XRD, N2-adsorption-stripping, TEM, TG and AAS (atomic absorption spectrum). The results showed that the excellent performance of the catalyst benefited from its larger specific surface area and smaller active-crystal grain which is due to the molecular-order dispersion of active components over the LDHs precursor.

Controllable bulk growth of few-layer graphene/single-walled carbon nanotube hybrids containing Fe@C nanoparticles in a fluidized bed reactor

A family of layered double hydroxides (LDHs) with varied Fe contents were employed as catalyst precursors for the controllable bulk growth of few-layer graphene/single-walled carbon nanotube (G/SWCNT) hybrids in a fluidized-bed reactor through chemical vapor deposition of methane at 950°C. All the G/SWCNT hybrids exhibited the morphology of SWCNTs interlinked with graphene layers. The purity, thermal stability, graphitization degree, specific surface area, and total pore volume of the G/SWCNT hybrids decreased with the increasing Fe contents in the LDH precursors. A high yield of 0.97gG/SWCNTs/gcat can be achieved by tuning the Fe content in the FeMgAl LDHs after a 15-min growth. After the removal of the as-calcined FeMgAl layered double oxide flakes, a high carbon purity of ca. 98.3% for G/SWCNT hybrids was achieved when the mole ratio of Fe–Al is 0.05:1. The size and density of Fe nanoparticles decorated in the as-obtained G/SWCNT hybrids depend largely on Fe content in the FeMgAl LDH precursors. Furthermore, the mass ratio of graphene materials to SWCNTs in the as-prepared G/SWCNT hybrids can be well controlled in a range of 0.4–15.1.

An egg-shell type Ni/Al2O3 catalyst derived from layered double hydroxides precursor for selective hydrogenation of pyrolysis gasoline

Egg-shell type catalysts, in which a thin layer of catalytically active component is distributed on the outer surface of the support particle, have been theoretically and experimentally proved to be useful in processes where the reaction has a very high rate and the intraparticle diffusion becomes the limiting step. Herein we report the preparation of an egg-shell Al2O3-supported nickel (Ni/Al2O3) catalyst derived from layered double hydroxides (LDHs) precursor, and its catalytic performance for selective hydrogenation of pyrolysis gasoline (PyGas), an important by-product of ethylene industry from thermal decomposition of heavier oil fractions, which was carried out in the liquid phase. Firstly, a Ni2+Al3+-containing LDHs (NiAl-LDHs) precursor was in situ grown on the surface of γ-Al2O3 spheres by using a diluted ammonia solution as precipitator. Then, egg-shell Al2O3-supported nickel oxide (NiO/Al2O3) sample with NiO crystallites highly dispersed on the external edge of the Al2O3 support was obtained after calcination at 450°C. The experimental study of selective hydrogenation of styrene (PyGas model 1) for revealing the intrinsic hydrogenation kinetics was carried out in a batch reactor at 60°C using the egg-shell Ni/Al2O3 catalyst (denoted LP-Ni/Al2O3; LP is expressed as layered precursor) fabricated by subsequent ex situ presufidation and final H2 reduction at 500°C of the NiO/Al2O3 sample. In addition, an Ni/Al2O3 catalyst with uniform distribution of Ni in the catalyst was prepared by a conventional wet impregnation method (denoted IM-Ni/Al2O3; IM is expressed as impregnation method) with the consistent Ni loading amounts and given into the consideration for comparison. The estimated effectiveness factor (η) of the LP-Ni/Al2O3 catalyst was higher than that of the IM-Ni/Al2O3 one, demonstrating the catalyst with egg-shell structure has a lower intraparticule mass transfer resistance. The catalytic hydrogenation activities of both Ni-based catalysts were further evaluated by selective hydrogenation of diolefins (PyGas model 2), along with selective hydrogenation of PyGas model 1, in a micro-flow reactor. The egg-shell Ni/Al2O3 catalyst derived from LDHs precursor exhibited a superior catalytic hydrogenation performance, which mainly be due to Ni metal being deposited on the Al2O3 support in a much thinner outer layer, as well as a smaller average size of nickel particles with stronger interaction between the nickel species and support. Several characterization techniques including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), low temperature N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction of hydrogen (TPR)/temperature programmed desorption of hydrogen (H2-TPD) were adopted to investigate the physical–chemical properties of the two supported Ni catalysts in detail.