Zn-Al Layered Double Hydroxides Research Articles

Coupling Molecular-Scale Spectroscopy with Stable Isotope Analyses to Investigate the Effect of Si on the Mechanisms of Zn-Al LDH Formation on Al Oxide.

While silicate has been known to affect metal sorption on mineral surfaces, the mechanisms remain poorly understood. We investigated the effects of silicate on Zn sorption onto Al oxide at pH 7.5 and elucidated the mechanisms using a combination of X-ray absorption fine structure (XAFS) spectroscopy, Zn stable isotope analysis, and scanning transmission electron microscopy (STEM). XAFS analysis revealed that Zn-Al layered double hydroxide (LDH) precipitates were formed in the absence of silicate or at low Si concentrations (≤0.4 mM), whereas the formation of Zn-Al LDH was inhibited at high silicate concentrations (≥0.64 mM) due to surface-induced Si oligomerization. Significant Zn isotope fractionation (Δ66Znsorbed-aqueous = 0.63 ± 0.03‰) was determined at silicate concentrations ≥0.64 mM, larger than that induced by sorption of Zn on Al oxide (0.47 ± 0.03‰) but closer to that caused by Zn bonding to the surface of Si oxides (0.60-0.94‰), suggesting a presence of Zn-Si bonding environment. STEM showed that the sorbed silicates had a close spatial coupling with γ-Al2O3, indicating that >Si-Zn inner-sphere complexes (">" denotes surface) likely bond to the γ-Al2O3 surface to form >Al-Si-Zn ternary inner-sphere complexes. This study not only demonstrates that dissolved silicate in the natural environment plays an important role in the fate and bioavailability of Zn but also highlights the potential of coupled spectroscopic and isotopic methods in probing complex environmental processes.

XANES characterizations of amorphous mixed metal oxides derived from Zn/Al layered double hydroxides through thermal treatment

The amorphous phase obtained by thermal treatment of Zn/Al-layered double hydroxide (Zn/Al-LDH) was characterized by X-ray absorption near-edge Spectroscopy (XANES) and Ultraviolet–Visible Diffuse Reflection (UV–vis DR). The highly crystalline Zn/Al-LDH was synthesized through homogeneous precipitation with urea as precursor, and then calcined up to 900 ​°C. X-ray Diffraction (XRD) and Thermogravimetry-Differential Thermal Analysis (TG-DTA) results showed that the crystalline Zn/Al-LDH was changed to amorphous phase through dehydroxylation by 300 ​°C. The amorphous phase decomposed to wurtzite-ZnO and spinel (Zn/Al2O4) above 600 ​°C. The amorphous phase was characterized with Zn L-edge, O K-edge and Al K-edge spectra. Those spectra determined the formation of amorphous Zinc/Aluminium mixed metal oxide (ZAO) with characteristic electron. The ZAO showed absorption of UV light which is higher energy band gap than pure zinc oxide. The analysis indicated changes in coordination due to the formation of a metal oxide phase by dehydration of the hydroxide layer of Zn/Al-LDH, and the formation of ZAO. This research is believed to be the first to apply Zn L-edge, along with O K-edge XANES spectra to analyses and clarify the thermal behavior of Zn/Al-LDH and is demonstrated to be a powerful tool for probing the structure of a variety of mixed metal oxides and catalysts based on Zn based LDH materials.

Sodium lignosulfonate-loaded ZnAl-layered double hydroxide decorated graphene oxide nanolayers; toward fabrication of sustainable nanocomposite for smart corrosion prevention

In this study, the NO3− intercalated ZnAl-based layered double hydroxide (LDH) nanostructures decorated graphene oxide (GO) nanosheets were synthesized, loaded with sodium lignosulfonate (SLS), and finally modified with aminopropyltriethoxysilane (APS) to reach a high-performance corrosion inhibitor nanocarriers. The morphology and chemistry of the LDH-rGO nanostructures were evaluated by the FE-SEM, EDX, FT-IR, XPS, XRD, Raman, and TGA techniques. Characterization results of SLS@LDH-rGO nanostructures proved the uniform decoration of GO nanosheets with LDH nanolayers and the loading of the SLS inhibitor. The active/barrier corrosion mitigation ability (CMA) of the synthesized nanostructures was studied by EIS and potentiodynamic polarization (PP) tests in both solution (NaCl) and coating (epoxy) phases. Results showed the increment of the total resistance and decrement of the current density of MSSs immersed in the SLS@LDH-rGO extract by 358 and 79%, respectively, compared to the blank solution after 48 h. EIS results proved the bi-functional active-inhibitive/barrier CMA for the SLS@APS-LDH-rGO filled epoxy coatings. The total impedance of the intact SLS@APS-LDH-rGO filled epoxy coating was enhanced by about 9700% after 8 weeks compared to that of the blank coating.

Structure and release properties of pyrethroid/sulfobutyl ether β-cyclodextrin intercalated into layered double hydroxide and layered hydroxide salt.

The aim of this study was to realize the intercalation of the pyrethroid pesticides beta-cypermethrin (BCT) and lambda-cyhalothrin (LCT) into ZnAl-layered double hydroxides (LDH) and NiZn-layered hydroxide salt (LHS). BCT (LCT)/SBECD-LDH and BCT (LCT)/SBECD-LHS hybrids were obtained with the aid of sulfobutyl ether β-cyclodextrin (SBECD) through one step method. The hybrids were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetry and differential thermal analysis (TGA/DTA). The hybrids based on LHS had larger basal spacing than those on LDH. The LDH-hybrids prepared in N-methylpyrrolidone (NMP) had larger basal spacing than those in ethanol. These results were discussed in terms of the matrix structure and solvent properties. The supramolecular structure of the hybrid was reasonably proposed. Furthermore, the release properties of BCT (LCT) from the hybrids were investigated and discussed in two media. The release rate in pH = 5.0 was slower than that in pH = 6.8. The accumulated release amount of pesticide in pH = 5.0 was lower than that in pH = 6.8. LHS-hybrids synthesized in ethanol exhibit a sustainable release property. These depend on the inclusion complexes’ arrangement and release medium. The release kinetic processes could be described by pseudo-second order and parabolic diffusion models. The release behavior can be controlled by adjusting the synthesis conditions and the releasing media. This provides the guidance for the application of SBECD and LDH (LHS) in pesticide formulation.

Orange Zn–Al–O–N Powder Active for Photocatalytic Water Reduction and Oxidation Synthesized from a Zn–Al Layered Double Hydroxide Using Urea as the Nitriding Agent

Orange Zn–Al–O–N Powder Active for Photocatalytic Water Reduction and Oxidation Synthesized from a Zn–Al Layered Double Hydroxide Using Urea as the Nitriding Agent

Thickness-dependent piezo-photo-responsive behavior of ZnAl-layered double hydroxide for wastewater remediation

Understanding of the structural–performance correlations allow for the rational design of piezo-photocatalytic materials with profound benefits for catalytic activity. In this study, the ZnAl layered double hydroxides (ZnAl-LDHs) with different thickness are applied in the piezo-photocatalytic process for carbamazepine (CBZ) pollutants degradation. The piezo-photocatalytic efficiency of ultra-thin ZnAl-LDHs sheets (ZnAl-U) reaches 95.8 % with the reaction rate constant of 0.148 min-1 for CBZ degradation, being 1.61 and 3.02 times of the thin ZnAl-LDH (ZnAl-T) and bulks ZnAl-LDHs (ZnAl-B), respectively. This result is attributed to that ZnAl-U is more sensitive towards light irradiation and external stress than ZnAl-T and ZnAl-B, thus producing higher current and more reactive oxygen species (O2•−, HO• and 1O2) for piezo-photocatalytic degradation of CBZ. At the same time, the piezo-photocatalytic rate constant of ZnAl-U is 3.36 times of the sum of the individual piezocatalysis and photocatalysis, which is due to that the piezoelectric field boosts the separation of photo-induced electron-hole pairs and modulates the alignment of band energy, resulting in a synergetic enhanced piezo-photocatalytic reaction. This work discloses the significance of structure on the ZnAl-LDHs piezo-photocatalytic performance, and highlights the role of piezoelectric field on the improvement of photocatalytic process.

The interfacial ionic transport of two-dimensional ZnAl-mixed metal oxides nanocomposite

Exploring environmentally friendly electrolyte materials with high ionic conductivity is regarded as a critical challenge for developing low temperature solid oxide fuel cells (LTSOFC). In this study, the two-dimensional ZnAl-mixed metal oxides (ZnAl-MMO) nanocomposite was derived from ZnAl-layered double hydroxide. The obtained ZnAl-MMO nanocomposite is provided with high concentration of oxygen vacancies at the surface, which achieved a high ionic conductivity of 0.26 S cm−1 and the maximum power density of 860 mW cm−2 at 550 °C. Significant improvement of open circuit voltage to 1.16 V is testified that the in-situ grown Zn6Al2O9 can effectively inhibit electron long-range transmission among ZnO. In addition, the unique proton transport at the interface of ZnAl-MMO heterostructure was proposed. This work presents an approach to develop environmental-friendly two-dimensional mixed metal oxides for the application of renewable energy conversion.

A novel corrosion inhibitive system comprising Zn-Al LDH and hybrid sol-gel silane nanocomposite coating for AA2024-T3

A novel layered double hydroxide (LDH)/silane bilayer system was introduced as an effective non-hazardous protective coating for AA2024-T3. Also, the loaded corrosion inhibitors' effect on the bilayer coating system's active anticorrosion properties was studied. For this purpose, diethyldithiocarbamate (DEDTC) molecules, as an eco-friendly corrosion inhibitor, were intercalated in the LDH conversion layer. Furthermore, Ce3+ cations were loaded in the sodium montmorillonite and then incorporated in the mixture of tetraethoxysilane and γ-amino propyltriethoxysilane. The grazing incidence X-ray diffraction, Fourier-transform infrared spectroscope, and scanning electron microscope (SEM) equipped with energy dispersive spectroscope were used to analyze the structural, surface functional groups, microstructure, and chemical composition of the coatings. Electrochemical impedance spectroscopy, potentiodynamic polarization, and electrochemical current noise technique were employed to investigate the layers' protection behavior. Based on the obtained results, the presence of corrosion inhibitors in the structure of the coatings resulted in a dramatic enhancement in the protection behavior of the substrate. The polarization results illustrated that the corrosion current density of the bilayer system was reduced from 170 to 6.7 nA/cm2 after employing the corrosion inhibitors into the coating structure. The electrochemical tests and SEM results illustrated the induction of the active anticorrosion properties for the bilayer system containing the DEDTC molecules and Ce3+ cations. The total noise energy for the scratched double-layer coating in the presence and absence of corrosion inhibitors was calculated to be 4.1 and 9.5 pA2, respectively, indicating efficient corrosion inhibition.

Enhanced sorption of perfluorooctanoic acid with organically functionalized layered double hydroxide

Sorption is recognized as an effective and economical approach for the practical treatment of water contaminated with per- and polyfluoroalkyl substances (PFAS). In this study, we reported the development, characterization, and evaluation of a family of new organically functionalized layered double hydroxide (LDH) adsorbents for PFAS removal with a primary focus on perfluorooctanoic acid (PFOA). The organic functional groups were introduced to the Zn-Al LDH by covalent bonding through a post-grafting process. The organically functionalized LDHs were very efficient for PFOA adsorption, likely due to the synergy of the positively charged structural layers of LDHs that provide strong electrostatic interactions and the modified organic functional groups that provide enhanced hydrophobic interactions to capture PFOA. Specifically, our adsorption kinetics and isotherm studies found that organically functionalized LDHs exhibited faster adsorption kinetics and greater adsorption capacities for PFOA than the unmodified LDH. Furthermore, organically functionalized LDHs showed substantially improved performance for PFOA removal under various water chemistry conditions in comparison to the unmodified LDH, and remained more effective following repeated adsorption-regeneration cycles. The best-performed organically functionalized LDH also exhibited high efficiency for the treatment of a mixture of PFAS with varied fluoroalkyl chain lengths and functionalities. Results of this work suggested that organically functionalized LDHs hold great promises for the treatment of PFAS-contaminated water.

Enhanced Photocatalytic Activity of Zn-Al Layered Double Hydroxides for Methyl Violet and Peat Water Photooxidation.

Zn-Al Layered Double Hydroxides (Zn-Al LDHs) and its calcined form were successfully prepared and utilized for the removal of methyl violet (MV) and treatment of peat water by photocatalytic oxidation. The research was aimed to evaluate the effect of calcination to Zn-Al LDHs for the effect on the physicochemical character and the capability as a photocatalyst. The characterization of the samples was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller specific surface area (BET), and X-ray photoelectron spectroscopy (XPS). The results showed that the increased BET specific surface area along with the enhanced porous structure was achieved by the calcination procedure, which is associated with the enhanced interlayer space of d003 identified by XRD analysis. Thermal conversion showed an influence to the increased band gap energy from 3.10 eV in the uncalcined Zn-Al LDHs into 3.16 eV for the calcined material. These character changes contributed to the enhanced photocatalytic activity of the Zn-AL LDHs by calcination, which was proposed and verified by experiments. It was observed that photocatalytic activity of the material for MV gave about a 45.57% removal of MV and a 68% removal for the natural organic material of the peat water.

Enhanced reduction of nitrobenzene derivatives using reusable Ni nanoparticles supported on multi-layered poly(1,2-phenylenediamine)-coated layered double hydroxides

Recently, nanomaterials with layered double hydroxide (LDH) cores have been the subject of intense research regarding their promising applications in organic synthesis. In this study, nitrobenzene reduction is investigated by designing and synthesizing a novel LDH-based heterogeneous catalyst containing a nickel-1,2-phenylenediamine complex. The Cu–Zn–Al LDH was functionalized with copolymer bearing a glycidyl methacrylate (GMA) linkage that makes it suitable for grafting with 1,2-phenylenediamine. Overall, the synthesized LDH@MPS-GMA-PDA-Ni was found to be a highly efficient heterogeneous nanocatalyst that can catalyze nitroarene reduction with high yields under mild conditions.

Quantitative Analysis of the Structure of Organic Acids and Their Degradation Rates during Ozonation Catalyzed with ZnAl Layered Double Hydroxide

ABSTRACT The structure of organic compounds is critical to their degradation rates in various advanced oxidation processes. In this research, 16 organic acids (such as oxalic acid, D-malic acid, oxamic acid, etc.) were used as model contaminants to investigate the mineralization efficiencies of catalytic ozonation with ZnAl layered double hydroxide (ZnAl-LDH). All tests organic acids could be effectively degraded during catalytic ozonation, and good reusability was observed since the unique structure of ZnAl-LDH was kept after the reaction. The effect of temperature on the oxidation of different organic compounds varied based on their molecular structures. In most cases, a proper temperature increase could promote the degradation of organic compounds by catalytic ozonation. The TOC removal kinetic constants had a good linear relationship with the temperature, which proved that the catalytic ozonation of organic matters conformed to the Arrhenius equation, in which the activation energy of various organic acids were between −9.0 and 51.0 kJ·mol−1, and the pre-exponential factors were between 0.003 and 2.45 × 106 min−1. By using linear regression model, it was found that the activation energies of organic acids had a greater correlation with quantum chemical parameters, such as Fukui(0)max, Fukui(+)max, EB3LYP, ELUMO, EHOMO and Bond orders(C-C)max. High correlation of Fukui(0)max and Fukui(+)max indicated the attacking of both free radicals and ozone molecule, respectively. Organic acids with lower energy and C-C bond orders were proved to be simple and readily degradable, and thus much easier to be mineralized during catalytic ozonation.

Enhanced bioelectrochemical performance of microbial fuel cell with titanium dioxide-attached dual metal organic frameworks grown on zinc aluminum - layered double hydroxide as cathode catalyst

In this study, a three-step distributed feeding method was used to prepare TiO2-attached dual CoZn-metal organic frameworks growing on ZnAl-layered double hydroxide (TiO2@ZIF-67/ZIF-8@ZnAl-LDH) as cathode catalyst of microbial fuel cell (MFC). The composite material was a composite core–shell structure constructed by multi-layer coating with sheet-like ZnAl-LDH as the base, dual MOFs as the magnetic core and TiO2 as the rough surface. The composite material had crystal planes (009), (110), (101) interface. The rough surface, core–shell core and polyhedral structure of TiO2@ZIF-67/ZIF-8@ZnAl-LDH were observed. The complete distribution of Ti, Zn, Al, and Co in the material was observed and offered active sites. The contents of Ti (15.97 %), Al (5.53 %), Na (5.04 %), N (3.52%), Zn (1.47 %) were found out. TiO2@ZIF-67/ZIF-8@ZnAl-LDH was excellent in electrochemical activity and the maximum power density was 409.6 mW/m2, the stable continuous output voltage was 538.4 mV for 8 d.

The Role of an In-Situ Grown Zn-Al Layered Double Hydroxide Conversion Coating in the Protective Properties of Epoxy Coating on Galvanized Steel

A Zn–Al layered double hydroxide (LDH) conversion coating was investigated as a surface treatment for galvanized steel. Zn–Al LDH crystals were grown in situ on the galvanized steel surface in room temperature at different periods. Grazing Incidence Xray Diffraction verified the formation of Zn–Al LDH flakes on the surface. Scanning Electron Microscopy showed that Zn–Al LDH flakes were evenly distributed as a continuous coating on the surface of galvanized steel. Roughness and surface free energy of the coatings were evaluated by Atomic Force Microscopy and contact angle measurements. Corrosion propensity of the LDH coatings was analyzed utilizing Electrochemical Impedance Spectroscopy (EIS) and polarization. A 6 times increase in impedance at 0.01 Hz and 10 times decrease in corrosion current density was achieved for galvanized steel by LDH conversion coating in best practice. To assess the role of the LDH conversion coatings on adhesion strength and corrosion resistance of overlying organic coatings, epoxy coating was applied on LDH conversion coated surfaces and tested by pull-off, salt spray and EIS. Results signified 23 times increase in impedance at 0.01 Hz and 80% decrease in adhesion loss for organically coated galvanized steel after LDH treatment at optimal condition.

Enhanced corrosion resistance and cytocompatibility of zinc by Zn-Al layered double hydroxide films

Zinc (Zn) is promising candidate to construct biodegradable medical devices. However, the poor corrosion resistance limits its clinical application. Herein, Zn-Al layered double hydroxide (LDH) films were constructed. Results showed that Zn-Al LDHs films could effectively enhance the anti-corrosion ability and biocompatibility of the Zn substrate, which provided new insights in the surface modification of Zn.

Improved SERS detection of anionic pollutant with Ag Nanoparticles-decorated ZnAl layered double hydroxide nanosheets array

Enrichment is a valuable strategy to further improve the detection limit. In this work, ZnAl-layered double hydroxide (ZnAl-LDH) nanosheets array in situ synthesized on Al foil was used as the enrichment frame for surface-enhanced Raman spectroscopy (SERS) substrate to further improve the detection limit of anionic pollutant. High density of Ag nanoparticles (Ag-NPs) with an average diameter of 29 nm sputtered onto the surface of the ZnAl-LDH could create localized electromagnetic field enhancement for SERS detection. The as-prepared Ag-NPs@ZnAl-LDH composite substrates showed improved sensitivity to anionic pollutants methyl orange and erythrosin B, demonstrating the promising potentials to improve the detection limit of anion analytes based on SERS spectroscopy.

Studying the Active Corrosion Inhibition Effect of the Ce3+/2-Mercaptobenzothiazole Loaded NaY Zeolite/Zn-Al LDH Based Containers in a Silane Coating

In the present study, the corrosion protective ability of the sol-gel based composite coatings containing two-different types of the cationic/anionic based inhibitors loaded containers. For this purpose, the NaY zeolite and Zn-Al Layered double hydroxides (LDHs) containers were loaded with Ce3+ cations and 2- mercaptobenzothiazole (MBT) separately. The morphology and composition of the constructed micro/nanocontainers were studied using analytical methods, confirming the successful loading of the inhibitors. In this study, the Ce3+/MBT inhibitors were successfully introduced into the LDH/NaY-based zeolite containers.Results evidenced that the combination of the two inhibitors has a constructive effect on the active protection of the AA2024-T3 sheets. SEM micrographs of the unfilled LDH and stupefaction with MBT show that the prepared LDHs have sheet-like morphology. The addition of single-inhibitor filled containers to the sol-gel hybrid coating, and water-based epoxy coating provided active protection for the AA2024-T3 coated substrate. However, the combination of the filled containers with the inhibitor in the above-mentioned coatings resulted in the improvement of the active protection of the substrate, which confirms the synergy between the particles. The NaY containers loaded with the Ce3+ resulted in a significant increase of the |Z|0.01 Hz of the gel-sol hybrid coatings, which indicates the formation of a stable oxide layer with higher resistance. Whereas the |Z|0.01 Hz of the hybrid sol-gel coatings loaded with LDH-MBT were in the same range as the NaY-Ce loaded coatings, containing NaY-Ce and LDH-MBT, showed the highest |Z|0.01 Hz values that indicate the synergy between the inorganic (Ce3+) and organic (MBT) inhibitors in sol-gel hybrid coatings.

Reconstruction and intercalating anion exchange of ZnAl-layered double hydroxide

Layered double hydroxides (LDHs) have recently attracted considerable attention as a promising multi-functional material due to their controllable properties depending on the type and composition ratio of metal cations and interlayer anions. Despite active research on controlling the composition to improve the properties of LDHs, anion intercalation techniques capable of obtaining the desired morphologies of LDHs have rarely been investigated. Herein, we report the anion exchange of ZnAl-LDHs grown on a silicon substrate using a post-treatment-based reconstruction process. Structural and chemical investigations verified that the calcined ZnAl-LDH was reconstructed by a NaCl solution during the anion exchange process. The anion exchange rate and the reconstructed fraction of the ZnAl-LDH increased as the NaCl concentration increased from 0.15 M to 0.60 M, though they decreased when the NaCl concentration exceeded 0.90 M. Therefore, the anion composition and morphology of the ZnAl-LDHs could be modulated by controlling the NaCl concentration during the reconstruction process. These results provide important information about the probability of controlling the structure and composition of LDHs intercalated with desired anions for a wide variety of device applications, such as memory, sensor, and energy storage.

Fabrication of ZnAl-LDH mixed metal-oxide composites for photocatalytic degradation of 4-chlorophenol.

In this work, two different types of ZnAl-layered double hydroxide (LDH) mixed metal-oxide composites (CeO2 and SnO2) were synthesized and applied for the photodegradation of 4-chlorophenol (4-CP) in wastewater. The fabricated CeO2/ZnAl-LDH and SnO2/ZnAl-LDH were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and theoretical density functional theory (DFT) calculations, suggesting that the band gaps of the synthesized hybrid composites were much lower than those of traditional ZnAl-LDH. In addition, the photocatalytic activity for 4-CP degradation and reaction kinetics were investigated to evaluate the catalytic behavior of the prepared composites. The results indicated that the photocatalytic process in this case followed a pseudo-first-order kinetic model, and SnO2/ZnAl-LDH illustrated the optimum performance for 4-CP degradation with an efficiency of 95.2% due to its stability and recyclability. Additionally, the reaction mechanism of 4-CP photodegradation was studied over SnO2/ZnAl-LDH; it presented that 4-CP could be oxidized by hydroxyl radicals, holes, and superoxide radicals, where hydroxyl radicals were identified as the dominant active species during the degradation process. Finally, decomposition intermediates were measured to deduce the reaction pathway of 4-CP, and three tentative pathways were proposed and discussed.

Composite nanocontainers synthesized by in-situ growth of metal organic frameworks on layered double hydroxides having both passive and active protecting capabilities

A novel composite nanocontainer is prepared by in-situ growth of zeolitic imidazolate framework-8 (ZIF-8), a typical metal organic framework, on ZnAl layered double hydroxides (LDH). The polyvinyl butyral (PVB) coatings embedded with LDH/ZIF-8 nanocontainers pre-loaded with 1H-benzotriazole exhibit both active and passive protection on copper substrates. The active protecting property is ensured by the trap of corrosive chloride of LDHs and the on-demand release of the pre-loaded corrosion inhibitors from ZIF-8. The passive protecting property is provided by the barrier capability of brucite-like layers of ZnAl LDH nanosheets. In addition, the excellent compatibility with PVB resin and the highly porous structure of the in-situ grown ZIF-8 on LDH substrate can also explain the excellent corrosion performance of the composite coatings.