Layered Double Hydroxide Films Research Articles

Insights into in-situ synthesis of PEO-LDH composite film on AM50 Mg alloy: The effect of final voltage

MgAl layered double hydroxide (LDH) layer was in-situ grown on PEO coatings formed at different voltages. Influence of thickness, phase composition and stability of the initial PEO coating on LDH formation was investigated. A PEO layer consisting of thin and unstable amorphous phase can be recrystallized into LDH, while a dense coating slows down LDH growth. Balancing the dissolution of the PEO structure with formation of LDH nanocontainers can dramatically enhance the corrosion resistance of the resultant coating. The superior corrosion properties can be attributed to the intact parent PEO layer, the uniform coverage of the LDH film and its ion-exchange effect.

In-situ Zn-Al layered double hydroxide conversion coatings prepared on galvanized steels by a two-step electrochemical method

Zn-Al layered double hydroxide (LDH) pretreatment layer was prepared by a novel two-step electrochemical method on galvanized steel surface from a precursor solution containing Al3+-only. In the first step, anodic currents are applied to Zn deposit to produce Zn2+ in solution near the substrate surface. Cathodic currents are then applied to ensure the cathodic deposition of LDH film. The obtained LDH coatings not only provide excellent adhesion to the metal surface, but also enhance the adhesion between metal substrate and the top epoxy coatings. The “LDH/epoxy” painting system can protect galvanized steel from rusting for at least 150 days.

Optimization of Mg-Al Layered Double Hydroxide Film Preparation and Corrosion Resistance Study on AZ91D Mg Alloy by Multivariate Polynomial Regression Fitting.

Layered double hydroxide (LDH) films have received extensive attention for their unique physical barrier function and ion exchange properties, which make them promising candidates for corrosion protection of magnesium alloys. In this paper, we used the multiple polynomial regression fitting method to establish a regression equation for the electrochemical corrosion resistance with the reaction temperature (T), pH, and reaction time (t) of the Mg-Al LDH film on the AZ91D magnesium alloy. The goodness of fit, confidence, and residual analyses confirmed the high accuracy of the model equation. According to the calculation using the fmincon function, the best corrosion resistance of the prepared samples could be achieved when the parameters are T = 135 °C, pH = 12.0, and t = 15 h. Then, the experimental results showed that the corrosion current density (Icorr) of the obtained LDH film under the above conditions could be 1.07 × 10-7 A/cm2, approximately 3 orders of magnitude lower than the magnesium alloy substrate, after immersion in a 3.5 wt % NaCl solution for 180 h, the surface structure of the LDH film did not change significantly, and the Icorr was still 2 orders of magnitude higher than that of the magnesium alloy substrate. Hence, a synergistic effect equation for the reaction temperature, pH, and reaction time on the corrosion resistance of the LDH film on a magnesium alloy surface prepared by the hydrothermal method was obtained. Moreover, using this equation, we obtained an LDH film with good corrosion resistance and durability, providing theoretical guidance for optimizing the process of preparing the LDH film by the hydrothermal method in practical applications.

Growth mechanism and corrosion resistance of layered double hydroxide film on magnesium alloy without external addition of magnesium and aluminum salts

This study first reports in-situ growth of layered double hydroxide (LDH) coatings on magnesium alloy surface without external adding magnesium (Mg2+) and aluminum (Al3+) salts with the aid of a chelating agent at ambient pressure and relatively low temperature (≤ 95 °C). The morphology, composition, and structure of the deposits on the magnesium alloy surface were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), etc. Combined with open-circuit potential (OCP)-time curves, the mechanism of growth and formation process of the LDH film was proposed. The process was divided into four stages, i.e., dissolution of the Mg substrate, formation of Mg(OH)2, nucleation of LDH by transformation of Mg(OH)2 phase, and growth of LDH phase. The corrosion resistance of the LDH coating before and after treatment with vanadate and tungstate was evaluated through electrochemical impedance spectroscopy (EIS), Tafel curves, and immersion measurements. Compared to bare magnesium alloy and pristine and vanadate-treated LDH, the LDH coating modified with tungstate exhibited the most effective corrosion protection for magnesium alloy AZ31, without obvious signs of corrosion after exposure to a 3.5 wt% NaCl solution for seven days.

Preparation of hydrophilic MgAl type layered double hydroxide films with elevated Mg/Al molar ratio on aluminum substrates via a facile approach

A straightforward method is necessary for synthesizing hydrophilic films on aluminum fins and heat sinks intended for water vaporization-based cooling applications. Herein, a facile synthesis approach is presented for generating hydrophilic films of MgAl type layered double hydroxides (LDH) at temperatures of 20 and 50 °C, with a synthesis duration of less than 120 min. The synthesized films were comprehensively characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and field emission scanning electron microscopy. The film hydrophilicity was assessed through contact angle (CA) measurements with water. XRD analysis revealed a higher intensity of LDH film peaks at 50 °C than at 20 °C. Additionally, the Mg/Al and Cl/Al ratios within the films increased with increasing concentrations of MgCl2. Notably, chloride anions constituted approximately 70–80% of the anions in the LDH films, with the remaining 20–30% expected to be CO32−. The surface morphology of the films displayed net-like and porous flower-like structures, which varied based on the synthesis conditions. The hydrophilicity of the LDH films was found to be more strongly influenced by the Mg/Al molar ratio than by the surface morphology. Particularly, the CA test indicated a hydrophilicity threshold at a Mg/Al molar ratio of approximately 2.0, with a CA of 0° when the molar ratio exceeded 2. The resultant hydrophilic film on aluminum is potentially applicable to vaporization-type coolers.

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.

Novel interface engineering of LDH-based materials on Mg alloy for efficient photocatalytic systems considering the geometrical linearity of condensed phosphates

This study presents a facile and rapid method for synthesizing novel Layered Double Hydroxide (LDH) nanoflakes, exploring their application as a photocatalyst, and investigating the influence of condensed phosphates’ geometric linearity on their photocatalytic properties. Herein, the MgO film, obtained by plasma electrolysis of AZ31 Mg alloys, was modified by growing an LDH film, which was further functionalized using cyclic sodium hexametaphosphate (CP) and linear sodium tripolyphosphate (LP). CP acted as an enhancer for flake spacing within the LDH structure, while LP changed flake dispersion and orientation. Consequently, CP@LDH demonstrated exceptional efficiency in heterogeneous photocatalysis, effectively degrading organic dyes like Methylene blue (MB), Congo red (CR), and Methyl orange (MO). The unique cyclic structure of CP likely enhances surface reactions and improves the catalyst's interaction with dye molecules. Furthermore, the condensed phosphate structure contributes to a higher surface area and reactivity in CP@LDH, leading to its superior photocatalytic performance compared to LP@LDH. Specifically, LP@LDH demonstrated notable degradation efficiencies of 93.02%, 92.89%, and 88.81% for MB, MO, and CR respectively, over a 40 min duration. The highest degradation efficiencies were observed in the case of the CP@LDH sample, reporting 99.99% for MB, 98.88% for CR, and 99.70% for MO. This underscores the potential of CP@LDH as a highly effective photocatalyst for organic dye degradation, offering promising prospects for environmental remediation and water detoxification applications.

Tumor microenvironment-responsive arsenic-loaded layered double hydroxides film with synergistic anticancer and bactericidal activity

Tumor microenvironment-responsive arsenic-loaded layered double hydroxides film with synergistic anticancer and bactericidal activity

Influence of Mg substrate on the formation mechanism and corrosion resistance of LDH films

Layered double hydroxides (LDH) layer has been synthesized on various Mg substrates (pure Mg, MgLi and AZ91 alloy) under atmospheric pressure. Presence of alloying elements resulted in formation of a new composition and accelerated film growth rate. Li promoted homogeneous growth of LDH film, while the cathodic intermetallics in AZ91 Mg resulted in heterogeneous growth and formation of a porous LDH film, leading to deteriorated corrosion resistance. The dense MgLi LDH layer demonstrated high impedance value (4030 Ω·cm2) after 240 h electrochemical impedance spectroscopy (EIS) test, which was much higher than that of the substrate (146 Ω·cm2).

In Situ Growth of Mg-Fe Layered Double Hydroxides (LDH) Film on Titanium Dental Implant Substrates for pH Regulation in Oral Environments

Layered double hydroxides (LDHs) consist of two-dimensional, positively charged lamellar structures with the ability to host various anions in the interlayer spaces, which grants them unique properties and tunable characteristics. LDHs, a class of versatile inorganic compounds, have recently emerged as promising candidates for enhancing osseointegration. A suitable alkaline microenvironment is thought to be beneficial for stimulating osteoblasts’ differentiation (responsible for bone matrix formation) while suppressing osteoclast generation (responsible for bone matrix disintegration). LDHs are prone to adjusting their alkalinity and thus offering us the chance to study how pH affects cellular behavior. LDHs can indeed modulate the local pH, inflammatory responses, and oxidative stress levels, factors that profoundly influence the behavior of osteogenic cells and their interactions with the implant surface. Herein, we deposited Mg–Fe LDH films on titanium substrates for dental implants. The modified Ti substrates was more alkaline in comparison to the bare ones, with a pH higher than 8 after hydrolysis in an aqueous environment.

Development of ultrathin nanoflakes of Ni–Co LDH films by hydrothermal route for energy storage application

For energy storage systems, high capacitance, long cycling life, superior energy density, and ultrafast charge-discharge rates are important characteristics to meet the energy demands of various modern areas. Recently, the combination of Nickel (Ni) and Cobalt (Co) binary hydroxides has been recognized as a class of new materials due to their excellent electrochemical activity, high capacitance, excellent redox reversibility, spatial structure, and good electrical conductivity. Herein, Ni–Co layered double hydroxides (LDH) nanocomposites were prepared from different Ni–Co precursors under optimized preparation conditions by hydrothermal technique for supercapacitor application. As-obtained Ni–Co LDH exhibits an exceptionally high specific capacitance of 700.42 F/g was achieved at a current density of 1 A/g. Moreover, the Ni–Co LDH electrode showed a superior specific energy density of 19.69 Wh/kg and a specific power density of 2.8 Wh/kg. These excellent electrochemical results illustrate the potential of utilizing Ni–Co LDH materials for supercapacitor application and provide innovative direction for the development of future high-performance energy storage systems.

Influence of pH on corrosion resistance of slippery liquid-infused porous surface on magnesium alloy

A slippery liquid-infused porous surface (SLIPS) was developed on the AZ31 Mg alloy to provide corrosion protection. A layered double hydroxide (LDH) was applied to providing accommodation for liquid lubricants. The electrolyte pH was adjusted to obtain the best LDH film for the development of a SLIPS. The surface morphology, surface wettability, and electrochemical behavior of the SLIPS formed at different pH values were investigated. The results indicated that the MgAl-LDH film synthesized at a pH of 10.5 had a maximum thickness of 3.51 μm to accommodate the most silicone oil, with a mass of 0.22 mg/mm2, which provided the best corrosion protection, with the lowest corrosion current density of 3.72×10−9 A/cm2. On the other hand, compared with the superhydrophobic surface, the SLIPS imparted better corrosion resistance for the AZ31 substrate in both electrochemical behavior and long-term immersion test. The improved corrosion resistance of the SLIPS can further accelerate the application of Mg alloys in practice.

Electrodeposition-hydrothermal synthesis of inhibitor anion-intercalated layered double hydroxide films for corrosion resistance on steel substrates

The in-situ growth of layered double hydroxide (LDH) film on steel substrates holds huge potential for corrosion protection in reinforced concrete. However, because steel will passivate in alkaline environments, almost only CO32−-LDH films can be grown in situ on carbon steel surfaces at present, limiting the ability of LDH to release inhibitory anions. In this study, we proposed a novel electrodeposition-hydrothermal method to grow Mg/Al-NO3−-LDH films in situ on Q235 steel substrates. Subsequently, CO32−, PO43−, and V2O74− anion-intercalated LDH films were successfully prepared through anion exchange to enhance their functional applications. All LDH films were dense, uniform, and exhibited good adhesion to the substrate, with a thickness of approximately 20 μm. The electrochemical results demonstrated a significant improvement in the corrosion resistance of the steel containing LDH films. Specifically, the LDH films with intercalated inhibitory PO43− and V2O74− anions exhibited corrosion protection efficiencies exceeding 97.37 % in 3.5 wt% NaCl solution and 99.99 % in simulated concrete pore solution with chlorides.

Molecular-level insights into the corrosion protection mechanism of Mg/Al CO32−-LDH films on steel in aqueous chloride environments

Despite their thickness of only a few microns, layered double hydroxide (LDH) films offer excellent corrosion protection for steel. However, the lack of molecular-level comprehension of this protective mechanism has hindered the optimal design of LDH films. Herein, we developed a molecular model of Mg/Al-CO32−-LDH and investigated the nanoscale characteristics of water and ions in proximity to the LDH surface. Results underscore a robust attachment of water and ions to the LDH surface, accompanied by the attenuation of diffusion as they approach. The diffusion of interfacial water is predominantly influenced by H-bond interactions stemming from hydroxyl groups on the LDH surface. Additionally, the impediment of Cl− diffusion can be attributed to both anionic competition adsorption and the chemical bonding interactions of LDH.

Preparation and corrosion behavior of Mg(Li)-M layered double hydroxides films on the surface of magnesium-lithium alloy

Different Mg(Li)-M (M: Al, Fe, Cr) layered double hydroxides (LDHs) films were successfully prepared on Mg-Li alloy with in-situ growth method. Further, the corrosion inhibitor was screened and the tartaric acid-loaded LDHs (Mg(Li)-M LDHs-TA) films were prepared. The morphologies, compositions, structures and corrosion resistance of the LDHs films changed before and after tartaric acid loading. The Mg(Li)-Cr LDHs-TA film exhibits the most excellent corrosion resistance with a current density icorr 1.5 × 10–9 A cm–2. Moreover, corrosion mechanisms of the Mg(Li)-M LDHs and Mg(Li)-M LDHs-TA films were discussed in combination with Scanning Vibrating Electrode Technique.

Benzotriazole modified Zn-Al layered double hydroxide conversion coating on galvanized steel for improved corrosion resistance

BackgroundIn-situ grown layered double hydroxide (LDH) conversion coatings could be modified with corrosion inhibitors to improve corrosion resistance of the films. In this paper, a Zn-Al layered double hydroxide conversion coating on galvanized steel was modified with benzotriazole, as an organic corrosion inhibitor, for the first time. MethodsTo achieve the modification, the as-synthesized Zn-Al layered double hydroxide was firstly immersed in a methanol solution containing ammonium nitrate, followed by dipping in benzotriazole solution. Microstructural and elemental analysis as well as electrochemical experiments were performed to study the changes in the modified coatings. Significant FindingsResults verified partly intercalation of benzotriazole (BTA) in the layered double hydroxide (LDH) structure. The electrochemical impedance spectroscopy (EIS) assessment indicated that modification with benzotriazole increased the impedance of the as-prepared films by 4 times. Ultraviolet–visible spectroscopy showed the BTA release in the sodium chloride solutions containing BTA loaded LDH plates. In order to analyze the active protection feature of the modified conversion coatings, a polymeric topcoat, based on epoxy-polyamide, was applied. The EIS results showed a 3.6-time increase in the impedance values of the samples with benzotriazole loaded conversion coating compared to those with as-synthesized LDH films. The data, gathered from scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping, verified inhibitor release in the artificial scribe zones of the modified specimen.

Fabrication of branch-like Aph@LDH-MgO material through organic-inorganic hybrid conjugation for excellent anti-corrosion performance

Layered double hydroxides (LDH) frameworks have shown significant enhancement in stability and reusability, and their tailorable architecture brings new insight into the development of the next generation of hybrid materials, which attracted considerable attention in many fields over the years. One of the factors contributing to the widespread applicability of layered double hydroxides is their adaptable composition, which can accommodate a wide spectrum of potential anionic guests. This exceptional property makes the LDH system simple to adjust for various applications. However, most LDH systems are synthesized in situ in an autoclave at high temperatures and pressures that severely restrict the industrial use of such coating systems. In this study, LDH was directly synthesized on a magnesium alloy that had undergone plasma electrolytic oxidation (PEO) treatment in the presence of ethylenediaminetetraacetic acid, thereby avoiding the use of hydrothermal autoclave conditions. This LDH system was compared with a hybrid architecture consisting of organic-inorganic self-assembly. An organic layer was fabricated on top of the LDH film using 4-Aminophenol (Aph) compound, resulting in a smart hierarchical structure that can provide a robust Aph@LDH film with excellent anti-corrosion performance. At the molecular level, the conjugation characteristics and adsorption mechanism of Aph molecule were studied using two levels of theory as follows. First, Localized orbit locator (LOL)-π isosurface, electrostatic potential (ESP) distribution, and average local ionization energy (ALIE) on the molecular surface were used to highlight localization region, reveal the favorable electrophilic and nucleophilic attacks, and clearly explore the type of interactions that occurred around interesting regions. Second, first-principles based on density functional theory (DFT) was applied to study the hybrid mechanism of Aph on LDH system and elucidate their mutual interactions. The experimental and computational analyses suggest that the high π-electron density and delocalization characteristics of the functional groups and benzene ring in the Aph molecule played a leading role in the synergistic effects arising from the combination of organic and inorganic coatings. This work provides a promising approach to design advanced hybrid materials with exceptional electrochemical performance.

Improvement of Anticorrosion Properties of LA103Z Mg-Li Alloy Based on Fabricated Mg-Al Layered Double Hydroxide Films

Improvement of Anticorrosion Properties of LA103Z Mg-Li Alloy Based on Fabricated Mg-Al Layered Double Hydroxide Films

Two‐Dimensional LDH Film Templating for Controlled Preparation and Performance Enhancement of Polyamide Nanofiltration Membranes

AbstractTailored design of high‐performance nanofiltration membranes that can be used in a variety of applications such as water desalination, resource recovery, and sewage treatment is desirable. Herein, we describe the use of layered double hydroxides (LDH) intermediate layer to control the interfacial polymerization between trimesoyl chloride (TMC) and piperazine (PIP) for the preparation of polyamide (PA) membrane. The dense surface of LDH layer and its unique mass transfer behavior influence the diffusion of PIP, and the supporting role of the LDH layer allows the formation of ultrathin PA membranes. By only changing the concentration of PIP, a series of membranes with controllable thickness from 10 to 50 nm and tunable crosslinking‐degree can be prepared. The membrane prepared with a higher concentration of PIP shows excellent performance for divalent salt retention with water permeance of 28 Lm−2 h−1 bar−1, high rejection of 95.1 % for MgCl2 and 97.1 % for Na2SO4. While the membrane obtained with a lower concentration of PIP can sieve dye molecules of different sizes with a flux of up to 70 Lm−2 h−1 bar−1. This work demonstrates a novel strategy for the controllable preparation of high‐performance nanofiltration membranes and provides new insights into how the intermediate layer affects the IP reaction and the final separation performance.

Two-dimensional LDH films templating for controlled preparation and performance enhancement of polyamide nanofiltration membranes.

Tailored design of high-performance nanofiltration membranes that can be used in a variety of applications such as water desalination, resource recovery, and sewage treatment is desirable. Herein, we describe the use of layered double hydroxides (LDH) intermediate layer to control the interfacial polymerization between trimesoyl chloride (TMC) and piperazine (PIP) for the preparation of polyamide (PA) membrane. The dense surface of LDH layer and its unique mass transfer behavior influence the diffusion of PIP, and the supporting role of the LDH layer allows the formation of ultrathin PA membranes. By only changing the concentration of PIP, a series of membranes with controllable thickness from 10 to 50 nm and tunable crosslinking-degree can be prepared. The membrane prepared with a higher concentration of PIP shows excellent performance for divalent salt retention with water permeance of 28 Lm-2h-1bar-1, high rejection of 95.1% for MgCl2 and 97.1% for Na2SO4. While the membrane obtained with a lower concentration of PIP can sieve dye molecules of different sizes with a flux of 70 Lm-2h-1bar-1. This work demonstrates a novel strategy for the controllable preparation of high-performancemembranes and provides new insights into how the intermediate layer affects the IP reaction and the final separation performance.