Layered Double Hydroxide Coatings Research Articles

Structural features and dynamic behaviour of the interlayer space of layered double hydroxide coatings

Layered double hydroxide (LDH) offer great potentialities to design functional coatings with customizable properties by exploiting their anion exchange properties. We investigated the anion exchange properties and expansion capacity of the interlayer space relating to the starting film morphology. ZnAl LDH coatings of different thicknesses and morphologies were first obtained by an in situ method using Al-based substrates. When the anion to intercalate is relatively bigger than the starting nitrates, the intercalation may be constrained by the initial LDH particle size and density composing the film. After optimising the morphology, the intercalation of three functional anions with potential antimicrobial properties was successfully achieved with an expansion of the interlayer space up to 150 % while holding the coating integrity. The release of the guest anion was studied by immersion in physiological saline solution. Finally, the possibility to regenerate the coating was demonstrated supporting the potential of these hybrid coatings for applications.

Development of anti-corrosive coating on AZ31 Mg alloy modified by MOF/LDH/PEO hybrids

The self-assembly of hybrid inorganic-organic materials on stationary platforms plays a critical role in improving their structural stability and wide usability. In this work, a novel two-step hydrothermal approach is proposed for synthesizing stable and advanced hybrid coatings on metal-oxide platforms through the surface modification of layered double hydroxide (LDH) films using novel metal-organic frameworks (MOFs). Initially, Mg-Al LDH nanocontainers, grown on a magnesium oxide layer produced through plasma electrolytic oxidation (PEO) of AZ31 Mg alloy substrate, were intercalated with cobalt via an oxidation route, providing the metallic coordination center for the MOF formation. In the subsequent step, a pioneering technique is introduced, utilizing tryptophan as the organic linker for the first time at a pH of 10. The self-assembly of cobalt- tryptophan complex, driven by the strong bonding between electrophilic sites of monomers and nucleophilic sites, facilitated the formation of a MOF network having a cloud-like structure on the surface of MgAl LDH's film. The resulting MOF-LDH encapsulation containers demonstrate exceptional electrochemical stability when exposed to a 3.5 wt.% NaCl solution, surpassing the performance of PEO and pure LDH coatings. This enhanced stability is attributed to the development of a dense top layer and a stable composition within the self-assembled MOF, effectively sealing flaws and preventing the infiltration of corrosive ions into the underlying metallic substrate. The formation mechanism of MOFs on LDH galleries is investigated using density functional theory calculations.

Effect of the Sr-Fe layered double hydroxide coating based on the microenvironment response on implant osseointegration in osteoporotic rats.

Osteoporosis is a disease that manifests itself as an abnormality of bone metabolism and is characterized by low bone mass and destruction of the bone microstructure. Since bone resorption occurs more rapidly than new bone formation, osteoporosis leads to reduced orthopedic implant stability. From a microenvironmental point of view, the rationale for this outcome is that osteoclasts are overactive in the bone tissue of patients with osteoporosis, and the large amount of H+ they produce leads to local chronic acidosis, which promotes bone mineral loss. Therefore, we designed a weakly alkaline layered double hydroxide (LDH) coating to modulate the pathologically acidic microenvironment and the osteogenic-osteoclastic coupling by releasing Sr2+. We prepared Sr-Fe LDH coatings on pure titanium implants using a hydrothermal method in this study and characterized the material using SEM, AFM, XRD, XPS, EDS, ICP, pH acidimeter, etc. We found that the coatings had good nanomorphology and were able to efficiently neutralize H+ as well as steadily release Sr2+ for up to 21 days. In vitro, the coating not only significantly promoted the adhesion, proliferation, and differentiation of osteoblasts, but also inhibited the differentiation of osteoclasts at the same time. In addition, in animal experiments, the coating significantly improved the mechanical stability of the implant in osteoporotic rats, increasing Sr-Fe LDH@Ti maximal push-out force by 72.2% compared to Ti. At the same time, the coating was effective in reversing the osteoporotic state, resulting in a 58.5% increase in BV/TV (%), and a 12.4% increase in Tb. N (1 mm-1), a 31.6% increase in Tb. Th (μm), and a 30.9% increase in BA (%). Our results suggest that this Sr-Fe LDH nanocoating material with acid-neutralizing, as well as long-term Sr2+-releasing capabilities, is a novel and effective orthopedic implant coating material under osteoporotic conditions.

Corrosion Protection Behavior of Aluminate Ion-Loaded Layered Double Hydroxide Coating on AZ31 Magnesium Alloy

Effect of aluminate ion loading on the corrosion behavior of layered double hydroxide (LDH) coating of Mg-3Al-1Zn (AZ31) alloy was investigated. The corrosion inhibition performance of NaAlO2 for AZ31 was examined by immersion and polarization tests. Then, aluminate ion-loaded LDH (LDHAlO2) was synthesized from hydrotalcite (LDHCO3) and co-deposited with magnesium and aluminum double hydroxide on AZ31 by electrophoretic co-deposition. Polarization, electrochemical impedance (EI) and wet-dry cyclic corrosion tests were conducted on the LDHAlO2- and LDHCO3-coated specimens. Adding 10–50 mmol l−1 NaAlO2 to 0.1 mol l−1 NaCl solution induced a clear passive region on the polarization curves of AZ31 and shifted the breakdown potential over −1.0 V (Ag/AgCl), indicating the corrosion inhibition property of NaAlO2. In the polarization and EI tests, the aluminate ion loading did not noticeably enhance the corrosion protection ability of the LDH coating as shown by higher quasi-passive current density and lower R p than without loading. However, in the wet-dry corrosion tests, the LDHAlO2-coated AZ31 demonstrated less weight gain and fewer clusters of shallow micro-pits, while the LDHCO3-coated AZ31 showed numerous deeper pits on the entire surface. It was revealed that loading aluminate ions to the LDH coatings is promising for enhancing their corrosion protection ability in atmospheric environments.

Comparative Study on Corrosion Resistance of Binary and Ternary Layered Double Hydroxide Films on Magnesium Lithium Alloy

Layered double hydroxide (LDH) (Mg-Al and Mg-Al-Co) films were prepared on the surface of LA103Z magnesium-lithium alloy by hydrothermal synthesis method. Corrosion resistance of binary and ternary LDH coatings was studied by comparison. Structures of the two films were characterized using XRD, FTIR, SEM and EDS, and the corrosion resistance of the films was evaluated by polarization curve, EIS, and hydrogen evolution rate during immersion in 3.5 wt% NaCl solution. Results showed that Mg-Al LDH film was tightly bonded to the substrate and had a large number of nanosheets growing perpendicular to the substrate, while Mg-Al-Co LDH film was thinner with a smaller size and fewer nanosheets. Electrochemical test results showed that the polarization resistance of Mg-Al and Mg-Al-Co LDH films was two orders of magnitude higher than that of the substrate. Hydrogen precipitation experiments showed that corrosion resistance of both the films was improved compared to the substrate, and the films played a protective role for the substrate, among which the corrosion resistance of the Mg-Al LDH layer was better than that of the Mg-Al-Co LDH layer.

In-situ preparation of superhydrophobic Zn-Al layered double hydroxide coatings for corrosion protection of aluminum alloy

• The superhydrophobic Zn-Al LDHs coatings were fabricated on the aluminium alloy; • The superhydrophobic coatings significantly enhance metal corrosion resistance; • The anti-corrosion performance of coatings was dramatically affected by dopants. The superhydrophobic Zn-Al layered double hydroxides (LDHs) coatings were successfully in-situ fabricated on surface of 3003 aluminum alloy using hydrothermal and impregnation methods. The anti-corrosion performance of the superhydrophobic Zn-Al LDHs coatings was investigated using electrochemical tests as well as some surface characterizations. Results indicate that the superhydrophobic Zn-Al LDHs coatings can dramatically enhance the corrosion resistance of aluminum alloy. The different dopants can dramatically impact the anti-corrosion performance. It was attributed to the blocking effect and the capture capability of Cl - by the LDH films. Relevant mechanisms for corrosion protection of the superhydrophobic Zn-Al LDHs coatings have been proposed.

Enhancement of corrosion resistance of AZ31B magnesium alloy by preparing MgAl-LDHs coatings modified with imidazolium based dicationic ionic liquids

Fabricating layered double hydroxides (LDHs) coatings intercalated with corrosion inhibitors is considered an effective strategy for improving the corrosion resistance of metal substrates. However, to our best knowledge, studies applying LDHs coatings modified with ionic liquids (ILs) as environmentally friendly corrosion inhibitors to corrosion protection of metals and alloys have not been reported. In this contribution, two kinds of MgAl-LDHs coatings modified with imidazolium based dicationic ILs, namely LDH-C6(m2im)2-I and IL@LDH-C6(m2im)2-I, were successfully prepared on AZ31B magnesium alloy. The LDH-C6(m2im)2-I coating intercalated with C6(m2im)2-I ionic liquid was synthesized by the co-precipitation method and hydrothermal treatment, followed by a facile immersion experiment in a dimethyl sulfoxide solution containing C6(m2im)2-PF6 ionic liquid to produce the IL@LDH-C6(m2im)2-I composite coating. The surface morphologies and anti-corrosion properties of the two MgAl-LDHs coatings immersed in 3.5 wt% NaCl solution were investigated. The present results reveal that the LDH-C6(m2im)2-I coating exhibits a uniform and dense petal-like nanoflowers structure, while the IL@LDH-C6(m2im)2-I composite coating contains a compact C6(m2im)2-PF6 IL film and a lamellar-structured LDH-C6(m2im)2-I, which provides a double corrosion protection to the Mg alloy. As a result, the corrosion current density of IL@LDH-C6(m2im)2-I is only thirty-eighth of that of LDH-C6(m2im)2-I and 4 orders of magnitude lower than that of bare AZ31B Mg alloy. More importantly, the surface of samples coated with IL@LDH-C6(m2im)2-I is still compact without being destroyed after 168 h of immersion, which can be ascribed to the synergistic effect of excellent self-healing and durable corrosion resistance. This work opens a new way of preparing MgAl-LDHs coatings modified with ionic liquids to remarkably enhance the anti-corrosion performance of Mg alloys.

Mg-Fe LDH sealed PEO coating on magnesium for biodegradation control, antibacteria and osteogenesis

l Mg-Fe LDH films were fabricated on PEO treated Mg by transforming FeOOH. l Mg-Fe LDH films could enhance the corrosion resistance of Mg. l Mg-Fe LDH films exhibit good photothermal antibacterial and osteogenesis activity. l Animal experiments showed Mg-Fe LDH films show good histocompatibility in vivo . Attempt of developing bio-safety and functional layered double hydroxides (LDHs) modified plasma electrolytic oxidation (PEO) coatings, has become a hotspot in the protection of magnesium (Mg) based biomedical implants. In the present work, Mg-Fe LDH films with different Fe contents were fabricated on PEO coating via a novel two-step method: firstly, the FeOOH films were prepared by immersing PEO sample in Fe 2+ -containing solution, and then Mg-Fe LDH films were formed by transforming the FeOOH films via a hydrothermal treatment in water. The highly-oriented LDH nano-sheets could enhance the anti-corrosion performance of PEO coating, which was proved by the results of electrochemical test, hydrogen evolution and corroded morphology. PEO/Mg-Fe LDH coatings showed a low hemolysis rate (less 5%) than PEO coating. In addition, PEO/Mg-Fe LDH coatings were more favorable for cell adhesion and proliferation than PEO coating. Moreover, PEO/Mg-Fe LDH coatings showed good photothermal conversion property, which demonstrated the excellent rapid antibacterial effect under NIR light. In vitro culture of rat bone marrow stem cell (rBMSC) suggested that cells cultured in the extract of PEO/Mg-Fe LDH coatings had a better osteogenic activity. In vivo subcutaneous implantation test revealed that PEO/Mg-Fe LDH coatings exhibited good anti-corrosion and histocompatibility.

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.

Corrosion Resistance of Electrochemically Synthesized Modified Zaccagnaite LDH-Type Films on Steel Substrates.

Modified zaccagnaite layered double hydroxide (LDH) type films were synthesized on steel substrates by pulsed electrochemical deposition from aqueous solutions. The resulting films were characterized by X-ray diffraction, scanning electron microscopy/X-ray dispersive spectroscopy, and Fourier transform infrared spectroscopy. Structural characterization indicated a pure layered double hydroxide phase; however, elemental analysis revealed that the surface of the films contained Zn:Al ratios outside the typical ranges of layered double hydroxides. Layer thickness for the deposited films ranged from approximately 0.4 to 3.0 μm. The corrosion resistance of the film was determined using potentiodynamic polarization experiments in 3.5 wt.% NaCl solution. The corrosion current density for the coatings was reduced by 82% and the corrosion potential was shifted 126 mV more positive when 5 layers of modified LDH coatings were deposited onto the steel substrates. A mechanism was proposed for the corroding reactions at the coating.

Hydrothermal synthesis of Zn-Mg-based layered double hydroxide coatings for the corrosion protection of copper in chloride and hydroxide media

Hydrothermal synthesis of Zn-Mg-based layered double hydroxide coatings for the corrosion protection of copper in chloride and hydroxide media

Enhanced protective nanoparticle-modified MgAl-LDHs coatings on titanium alloy

MgAl LDHs (layered double hydroxides) coatings were deposited on the surface of titanium alloy Ti10V2Fe3Al, accompanied by modification with ZrO2 and MoS2 nanoparticles through electrophoretic deposition. FE-SEM, XRD and EDS measurements were used to investigate the microstructure and composition of the composite coatings. Corrosion resistance was measured by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. The LDHs/MoS2 composite coating exhibited the best corrosion resistance. Ball on disc tests was implemented to obtain morphology, the friction coefficient and wear loss of the worn surfaces. The LDHs/ZrO2 composite coating exhibited the best wear resistance. A mechanism for enhancing the wear-resistance of the different nanoparticles-modified MgAl-LDHs coatings was proposed.

Sol-Gel Synthesis and Characterization of Coatings of Mg-Al Layered Double Hydroxides.

In this study, new synthetic approaches for the preparation of thin films of Mg-Al layered double hydroxides (LDHs) have been developed. The LDHs were fabricated by reconstruction of mixed-metal oxides (MMOs) in deionized water. The MMOs were obtained by calcination of the precursor gels. Thin films of sol–gel-derived Mg-Al LDHs were deposited on silicon and stainless-steel substrates using the dip-coating technique by a single dipping process, and the deposited film was dried before the new layer was added. Each layer in the preparation of the Mg-Al LDH multilayers was separately annealed at 70 °C or 300 °C in air. Fabricated Mg-Al LDH coatings were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM). It was discovered that the diffraction lines of Mg3Al LDH thin films are sharper and more intensive in the sample obtained on the silicon substrate, confirming a higher crystallinity of synthesized Mg3Al LDH. However, in both cases the single-phase crystalline Mg-Al LDHs have formed. To enhance the sol–gel processing, the viscosity of the precursor gel was increased by adding polyvinyl alcohol (PVA) solution. The LDH coatings could be used to protect different substrates from corrosion, as catalyst supports, and as drug-delivery systems in medicine.

Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg−Al layered double hydroxide coating

Abstract To further enhance the corrosion resistance of the porous micro-arc oxidation (MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg−Al layered double hydroxide (LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.

Potential Applications of Layered Double Hydroxides in Membrane-Based Separation and Anti-Corrosion

Layered double hydroxides (LDHs) are representative of inorganic layered compounds consisting of positively charged brucite-like sheets and charge compensating anions located in interlayer galleries. The high length-to-width ratio, uniform gallery height, flexible chemical compositions, active surface functionality and unique calcination properties of LDHs have inspired us to explore their potentials in gas separation. In the presentation we demonstrated that LDHs not only enabled to effectively separate hydrogen-containing gas mixtures relying on the uniform interlayer galleries, but also could serve as efficient perch, active heterogeneous nucleation center and qualified single metal source of MOF crystals for the preparation of high performance MOF membranes. In addition, potential applications of LDHs in anti-corrosion were further explored. Relying on the dense in-plane structure of LDHs, preferentially c-oriented NiAl-CO3 LDH coatings were prepared showing excellent anti-corrosion performance. In addition, well-intergrown MOF coatings exhibiting excellent anti-corrosion performance could be in situ grown on Al substrates further by simple solvothermal treatment of ZnAl-CO3 LDH buffer layers. To sum up, full utilization of both microstructural and physicochemical properties of LDHs had greatly expanded their potential applications in membrane-based separation and anti-corrosion.

A novel bilayer system comprising LDH conversion layer and sol-gel coating for active corrosion protection of AA2024

In this work active corrosion protection of AA2024 by a bilayer system consisting of a LDH (layered double hydroxides) conversion layer coated by a sol-gel film was studied. Impedance and Scanning vibrating electrode technique (SVET) studies demonstrated an efficient active corrosion protection and self-healing abilities of the systems containing LDH layer loaded with vanadate corrosion inhibitor. Microstructural and chemical analysis of the surface after corrosion testing showed accumulation of chlorine signal in LDH coatings. The scavenging of chlorides and release of vanadate inhibitor from LDH can explain high efficiency of corrosion inhibition of AA2024 by the novel protective system.

Layered double hydroxide coatings on magnesium alloys: A review

Layered double hydroxides (LDHs) as a class of anionic clays have extensive applications due to their unique structures. Nowadays, the emphasis is laid on the development of LDH coatings for corrosion resistance and medical applications. Thus, this review highlights synthetic methods of LDH coatings and LDH-based composite coatings on magnesium alloys. Special attention is focused on self-healing, biocompatible and self-cleaning LDH-based composite coatings on magnesium alloys.

Corrosion Resistance of the Superhydrophobic Mg(OH)2/Mg-Al Layered Double Hydroxide Coatings on Magnesium Alloys

Coatings of the Mg(OH)2/Mg-Al layered double hydroxide (LDH) composite were formed by a combined co-precipitation method and hydrothermal process on the AZ31 alloy substrate in alkaline condition. Subsequently, a superhydrophobic surface was successfully constructed to modify the composite coatings on the AZ31 alloy substrate using stearic acid. The characteristics of the composite coatings were investigated by means of X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electronic microscope (SEM) and contact angle (CA). The corrosion resistance of the coatings was assessed by potentiodynamic polarization, the electrochemical impedance spectrum (EIS), the test of hydrogen evolution and the immersion test. The results showed that the superhydrophobic coatings considerably improved the corrosion resistant performance of the LDH coatings on the AZ31 alloy substrate.

Synthesis of layered double hydroxide coatings with an oriented structure and controllable thickness on aluminium substrates

Layered double hydroxides (LDHs) are applied in environmental purification and biomedicine because of their anion intercalation and exchange properties. This study investigates the formation of LDH layers on aluminium substrates, through the reaction of substrates in solution containing magnesium ions at 30–90 °C. The resulting LDH layer was constructed from many plate-shaped crystals. The LDH crystal size increased with increasing reaction temperature. The LDH layer was preferentially oriented perpendicular to the substrate, thus the LDH crystal orientation was out-of-plane. The oriented structure was formed by crystal-growth-controlled geometrical selection. The LDH layer growth rate also increased with increasing reaction temperature. A high reaction temperature (90 °C) resulted in rapid formation of an approximately 10 μm-thick LDH layer. Milder temperatures (30 and 60 °C) resulted in a moderate LDH layer growth rate, which allowed the LDH layer thickness to be precisely controlled. The LDH layer removed toxic fluoride anions from aqueous solution without damaging the layer. These findings promote the development of oriented LDH coatings with precisely controlled microstructures and thickness.

Corrosion Resistance of Superhydrophobic Mg–Al Layered Double Hydroxide Coatings on Aluminum Alloys

A superhydrophobic surface was successfully constructed to modify the layered double hydroxide (LDH) coatings on aluminum alloy using stearic acid. The characteristics of the coatings were investigated using SEM, XRD, FT-IR and XPS. The corrosion resistance of the prepared coatings was studied using potentiodynamic polarization and electrochemical impedance spectrum. The results revealed that the superhydrophobic surface considerably improved the corrosion-resistant performance of the LDH coatings on the aluminum alloy substrate. The formation mechanism of the superhydrophobic surface was proposed.