Growth Of Layered Double Hydroxides 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.

A Novel Coating System Based on Layered Double Hydroxide/HQS Hierarchical Structure for Reliable Protection of Mg Alloy: Electrochemical and Computational Perspectives.

Growing research activity on layered double hydroxide (LDH)-based materials for novel applications has been increasing; however, promoting LDH layer growth and examining its morphologies without resorting to extreme pressure conditions remains a challenge. In the present study, we enhance LDH growth and morphology examination without extreme pressure conditions. By synthesizing Mg-Al LDH directly on plasma electrolytic oxidation (PEO)-treated Mg alloy surfaces and pores at ambient pressure, the direct synthesis was achieved feasibly without autoclave requirements, employing a suitable chelating agent. Additionally, enhancing corrosion resistance involved incorporating electron donor-acceptor compounds into a protective layer, with 8-Hydroxyquinoline-5-sulfonic acid (HQS) that helps in augmenting Mg alloy corrosion resistance through the combination of LDH ion-exchange ability and the organic layer. DFT simulations were used to explain the mutual interactions in the LDH system and provide a theoretical knowledge of the interfacial process at the molecular level.

Status and Challenges in Biomedical Applications of LDHs

This work briefly discusses the applications of Layered Double Hydroxides (LDHs) to medicine and presents a study regarding the growth of LDHs on the biodegradable AZ31 alloy foreseen to manufacture a rib-fixator. Mg is one of the most investigated metallic materials for biomedical applications owing to its high biocompatibility and osteointegration, as well as a value of the elastic modulus close to that of human bone. Since Mg is essential for metabolism, when it degrades forming Mg2+ ions, it promotes healing and growth of bone tissue. Experiments have been carried out to grow LDHs on the alloy surface in view to retard corrosion in human body and intercalate drugs to be released in-situ, with anti-inflammatory, analgesic, and antimicrobial action.

Rapid preparation of Ni/Fe-LDH@ stainless steel mesh with interfacial emulsion breaking effect for efficient oil-in-water emulsion separation

Oil-water separation materials are particularly important for today's polluted water, especially the easy preparation of separation materials and the efficient separation of emulsions. The excellent properties of layered double hydroxide (LDH) have led to its successful application in the field of oil-water separation, but most of the existing studies have used high-temperature and long-time hydrothermal methods for the growth of LDH. Here, we present a stainless-steel mesh material for the preparation of LDH by electrochemical methods, which can be prepared in a few minutes, greatly improving the production efficiency. Adjusting the electrodeposition time of LDH can well regulate the aperture of the stainless-steel mesh to realize the sieving of emulsion droplets, in addition, the positive charge of LDH is helpful to promote the rupture of emulsion droplets and improve the emulsion separation efficiency. The separation efficiency of this rapidly prepared separation material for oil-in-water emulsions was stabilized at more than 99.3%. In addition, the preparation with low energy consumption is more in line with the concept of green development and more conducive to practical applications.

Study on growth behavior and properties of LDH nanosheet arrays enhanced Ni-based coatings on Mg-Li alloy

For the application of lightweight alloys, the corrosion and wear problems of magnesium-lithium (Mg-Li) alloys have always been important problems that cannot be ignored. The coupling protection of multiple technologies has gradually become a new trend. In this study, layered double hydroxides (LDH) nanosheet arrays were in-situ grown on Ni-P coating by the electroless plating technology combined with hydrothermal synthesis technology. The optimum deposition conditions (temperature-time-pH) were selected by orthogonal test. The surface morphology, structure, corrosion resistance and wear resistance of LDH/Ni composite coatings under different conditions were systematically studied by SEM, XRD, FT-IR, DSC, electrochemical and tribological tests. The growth mechanism of LDH suitable for Ni-P coating surface was proposed by analyzing the growth process of LDH nanosheet arrays. The results showed that the condition of 125 °C-12 h-13 was conducive to the growth of LDH nanosheet arrays. Compared with the Ni-P coating and the composite coating under other conditions, the LDH125°C-12h-13/Ni composite coating has the lowest self-etching current density (7.50 × 10−7 A·cm−2) and the average friction coefficient (0.35). The defect sealing effect and Cl− barrier property of LDH effectively improved the corrosion resistance of the coating. The frictional properties were improved by lubrication and heat absorption properties of LDH. In addition, it was found that the growth of LDH on the Ni-P coating surface followed the mechanism of “deposition nucleation-diffusion growth”.

Processing porous architectures based on LDH: Synthesis and novel applications

The processing of porous architectures based on Layered Double Hydroxides (LDH) is reviewed. Especially, a focus was put on porosity in nm and μm ranges that can be prepared via various post-treatments and templating techniques for the enhancement of the original properties. A challenge toward the desired porosity is control of structural ordering as well as crystal growth of LDH. The present review paper is mainly dedicated to summarizing the synthetic approaches to access the porous LDH that have found a wide range of applications such as adsorption/environment purification, catalysis, energy storage & production and bio-applications.

Growth Mechanism and Corrosion Resistance of a Co-Al Layered Double Hydroxide Film Grown In Situ on a Steel Substrate

The growth mechanism of layered double hydroxide (LDH) films grown in situ on steel via hydrothermal treatment is still unclear. In this study, the mechanism of Co-Al-CO3-LDH film grown in situ on a steel substrate was investigated in detail. During the hydrothermal reaction, the in situ growth process of Co-Al LDH on steel involved three steps: (1) hydrolysis of Al3+ and etching of the steel surface, (2) hydrolysis of urea and promotion of LDH nuclei, and (3) crystallization of LDH. More importantly, the generation of Al(OH)3 determined the integrity of the LDH film grown on the steel surface, and a suitable heating rate was also the key factor that affected the growth of the ordered and regular LDH nanoflakes. Therefore, this work provides a comprehensive understanding of the in situ LDH growth mechanism on steel and may facilitate optimal LDH film preparation.

Enhanced Emulsifying Ability of Deoxycholate through Dynamic Interaction with Layered Double Hydroxide.

The emulsifying ability of the naturally occurring surfactant deoxycholic acid (DCA) was improved by dynamic interaction with nanometric layered particles, layered double hydroxide (LDH). As DCA molecules are rigid due to the facial configuration of hydrophobic-hydrophilic groups, they tend to form molecular aggregation in an acidic condition or imbalanced water-lipid ratios. In this study, the homogeneous hybrids of DCA and LDH were obtained by the in situ growth of LDH at a DCA molecule. The DCA-LDH hybrid successfully prevented the molecular aggregation of DCA at an acidic pH and imbalanced water-to-oil ratio. The dynamic light scattering showed that the hydrodynamic radius of micelle in the emulsion made with DCA-LDH maintained its small size (<500 nm), while upon pH change and dilution with water, that made with DCA only uncontrollably increased up to ~3000 nm. The polydispersity index value of the DCA-LDH emulsion remained constant (<0.3) after the pH change and dilution with water, indicating the high stability of the formulation. Furthermore, time-dependent turbidity monitoring revealed that the DCA-only formulation suffered from serious coalescence and creaming compared with the DCA-LDH formulation. It is suggested that the dynamic interaction between LDH layers and DCA prevented molecular aggregation under unfavorable conditions for the oil-in-water emulsion.

Double‐anticorrosion ability of in‐situ superhydrophobic MgAl‐LDH coating with excellent stability of the corrosion resistance on magnesium alloy AZ31

AbstractWe reported the realization of superhydrophobic layered double hydroxide (LDH) coating with the double‐anticorrosion mechanism on magnesium alloys. This coating was prepared via in‐situ growth of LDHs on the etched AZ31 alloy and the modification was caused by 1H, 1H, 2H, 2H‐perfluorooctyltrimethoxysilane. The water contact angle on the coating was as large as 161°, possessing the two‐scale rough structure consisting of microislands and LDH crystal nanosheets. The excellent corrosion resistance properties of the superhydrophobic LDH coating can be attributed to the double‐anticorrosion mechanism associated with LDH coating and superhydrophobic structure. In addition to the active protection of LDH coating, the passive protection of superhydrophobic coating can suppress the occurrence of ion‐exchange reactions, leading to excellent corrosion resistance stability.

Coupling few-layer MXene nanosheets with NiFe layered double hydroxide as 3D composites for the efficient removal of Cr(VI) and 1-naphthol

The application of few-layer MXene combined with layered double hydroxides (LDH) as adsorbent for the removal of pollutant is scarce. Herein, a series of novel flower-like MXene modified NiFe-LDH composites (MNFL) were fabricated via in situ growth of LDH on the MXene substrate. The results demonstrated that the added amount of MXene played a significant role in the physicochemical properties of MNFL. Among them, the formed MNFL-60 possessed wonderful dispersion, appreciable surface area (64.04 m2/g) and saturation magnetization (∼10 emu/g). The maximum removal capacities of MNFL-60 were highest, with the value of 372.9 mg/g for Cr(VI) and 201.8 mg/g for 1-naphthol at 288 K. Furthermore, the removal capacities of MNFL-60 for Cr(VI)/1-naphthol increased with the rise of temperature, indicating that the adsorption processes were more favorable under a higher temperature. The addition of LDH decreased the bio-toxicity of MXene, with mortality rates of more than 76 % for E. coli and 48 % for S. aureus at 100 mg/L MNFL-60 and 80 % for E. coli and 57 % for S. aureus at 200 mg/L MNFL-60. Based on the results of XPS, the removal of 1-naphthol was ascribed to the inter-reaction with N/O–containing groups, whereas the eliminate of Cr(VI) was attributed to the electrostatic attraction, complexation and partial reduction of Cr(VI) to Cr(III). Additionally, the outstanding reusability and easy recyclability could make MNFL-60 can be a promising material for remediating organic and inorganic pollutants from wastewaters.

Hydrothermal in situ synthesis of high-crystallinity layered double hydroxide on electrospun polyacrylonitrile non-woven membrane: Application as anion capture filter

Layered double hydroxide (LDH) crystals were grown in the presence of polyacrylonitrile (PAN) nanofibers to develop a three-dimensionally-structured hybrid filter with high anion adsorption performance. The tensile strength and chemical resistance of the PAN nanofibers manufactured by electrospinning were improved upon heat treatment at 250 °C for 60 min. The growth of LDH on PAN was conducted by hydrolysis using urea or hexamethylenetetramine (HMT), and optimum conditions for this “in situ synthesis” were investigated. As a result, LDH plate-like crystals with a lateral size of ~20 μm were obtained by hydrothermal treatment at 140 °C for 24 h using HMT. The crystals grew densely perpendicular to the surface of the PAN fibers. After converting the LDH grown on the fiber fabric to LDH contain Cl− in the interlayer, the resulting fabric was set in a filter holder and a phosphoric acid adsorption test was conducted. The results showed that the hybrid filter prepared by this in situ hydrothermal synthesis had good phosphate adsorption characteristics, and that small amounts of phosphate ions were adsorbed selectively from water containing competing sulfate ions.

Controllable Synthesis of Ultrathin Defect-Rich LDH Nanoarrays Coupled with MOF-Derived Co-NC Microarrays for Efficient Overall Water Splitting.

Water electrolysis has attracted immense research interest, nevertheless the lack of low-cost but efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reactionsgreatly hinders its commercial applications. Herein, the controllable synthesis of ultrathin defect-rich layered double hydroxide (LDH) nanoarrays assembled on metal-organic framework (MOF)-derived Co-NC microarrays for boosting overall water splitting is reported. The Co-NC microarrays can not only provide abundant nucleation sites to produce a large number of LDH nuclei for favoring the growth of ultrathin LDHs, but also help to inhibit their tendency to aggregate. Impressively, five types of ultrathin bimetallic LDH nanoarrays can be electrodeposited on the Co-NC microarrays, forming desirable nanoarray-on-macroarray architectures, which show high uniformity with thicknesses from 1.5 to 1.9nm. As expected, the electrocatalytic performance is significantly enhanced by exploiting the respective advantages of Co-NC microarrays and ultrathin LDH nanoarrays as well as the potential synergies between them. Especially, the optimal Co-NC@Ni2 Fe-LDH as both cathode and anode can afford the lowest cell voltage of 1.55V at 10mA cm-2 , making it one of the best earth-abundant bifunctional electrocatalysts for water electrolysis. This study provides new insights into the rational design of highly-active and low-cost electrocatalysts and facilitates their promising applications in the fields of energy storage and conversion.

Oriented growth of LDH for constructing multifunctional cotton fabric with flame retardancy, smoke suppression, and filtering capability

A strategy to achieve flame retardancy, smoke suppression, and filtering capability simultaneously for the cotton fabrics was proposed. The cotton fabric sample was firstly treated with a polydopamine (PDA) solution through a dip-nip process, then the layered double hydroxides (LDH) were vertically introduced on the fabric surface before depositing Fe3+ chelated with phytic acid (PA). The obtained Cotton-PDA-LDH-Fe3+PA sample exhibited excellent flame retardancy and smoke suppression. The limiting oxygen index of the treated cotton sample reached 33.9%. For the Cotton-PDA-LDH-Fe3+PA sample, the total heat release was dropped to only 1.9 MJ/m2 from 8.7 MJ/m2 of the control cotton fabric sample, and the total smoke production was decreased from 138.9 m2/m2 to 68.1 m2/m2. The Cotton-PDA-LDH-Fe3+PA sample showed excellent ability of filtering particulate matter with a filtration efficiency of 91%. It is expected that this work provides a useful method to produce superior multi-functional cotton fabrics

Improvement of corrosion resistance of PEO coatings on Al alloy by formation of ZnAl layered double hydroxide

Thin plasma electrolytic oxidation (PEO) coating was produced on 2024 aluminum alloy as pre-treatment process, which was subsequently treated by hydrothermal method to grow layered double hydroxide (LDH) layer to seal the open pores and defects to enhance corrosion performance of the oxide layer. Vanadate and molybdate was exchanged and loaded into LDH layer to further improve the corrosion resistance of the composite coating. The porous PEO coating was sealed substantially after growth of LDH, although thickness of the composite layer was reduced due to dissolution during post-treatment process. Exchange of inhibitors can greatly enhance the corrosion performance of the coating. The impedance of vanadate containing coating was maintained in the level of 106 Ω·cm2 for 20 days during immersion in 3.5 wt% NaCl solution and showed superior corrosion protection for Al surface after performing neutral salt spray test for 60 days.

In situ growth of corrosion resistant Mg-Fe layered double hydroxide film on Q235 steel

HypothesisIn situ grown layered double hydroxide (LDH) is commonly used one of the anticorrosion ways for metal materials; Due to the dense growth of LDH on the metal surface, its special layered structure can effectively delay the corrosion rate of metal. MethodsIn this study, we use a hydrothermal method to successfully grow Mg-Fe LDH film on steel substrates based on self-supplied Fe3+ ions. The films were characterized by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectrometry. The potential corrosion resistance of the obtained Mg-Fe LDH film was confirmed using electrochemical impedance spectroscopy and polarization curves. FindingsAfter systematic adjustment and parameter optimization, it was found that Mg-Fe LDH film exhibited the best growth morphology and comprehensive performance with an initial pH value of 10, Mg2+/urea ratio of 1:4 and reaction time of 12 h. The SEM and electrochemical results further demonstrated that Mg-Fe LDH film play a good protection effect on carbon steel surface. This study provides an important reference for the processing of anticorrosion LDHs film.

Preparation of layered double hydroxide films using an electrodeposition and subsequent crystal growth method

AbstractThe surface coating of a gas reaction electrode with layered double hydroxides (LDHs) featuring various electrode catalyst activities was prepared via electrodeposition and the subsequent crystal growth of LDHs. LDH formation was confirmed by X-ray diffraction and Raman scattering measurements after subsequent crystal growth on respective electrodeposited precursor films in Ni-Fe and Zn-Al LDH systems. However, the crystal growth of LDHs in Ni-Mn and Cu-Mn systems was observed on the Mg-Al LDH-electrodeposited films. LDH films were also deposited on the surface of a carbon paper electrode with a rugged surface via electrodeposition and subsequent crystal growth. Using the prepared LDH-coated carbon paper electrodes, the electrode catalytic activity for the oxygen reduction reaction (ORR) was examined. For Ni-Mn, Ni-Al and Ni-Fe LDH-coated carbon paper electrodes, the threshold voltages of the ORR decreased. Hence, the LDHs electrodeposited on a gas reaction electrode have high electrochemical catalytic activity for the ORR.

Superhydrophobic and Self-Healing Mg-Al Layered Double Hydroxide/Silane Composite Coatings on the Mg Alloy Surface with a Long-Term Anti-corrosion Lifetime.

Both a superhydrophobic structure and layered double hydroxide (LDH) coating were effective to improve the corrosion resistance of alloys. In this study, a superhydrophobic composite coating based on LDHs was constructed on Mg alloy by laser treatment, in situ growth of Mg-Al LDHs, and modification with octadecyl-trimethoxy-silane (OTS). The so-obtained composite coating was coded as L-LDHs-OTS, where L stands for laser treatment. Results showed that the L-LDHs-OTS composite coating presented the best anti-corrosion performance and the corrosion current density was reduced by about 5 orders of magnitude compared with that of the Mg alloy substrate. The excellent corrosion resistance was related to the superhydrophobicity of the composite coating, the compactness and ion-exchange capacity of the LDH layer, and the dense Si-O-Si network within the OTS layer. Moreover, the L-LDHs-OTS composite coating was still effective after 20 days of immersion tests, showing good long-term corrosion resistance due to the existence of hydrophobicity of the composite coating and the self-healing ability of LDHs.

In-situ layered double hydroxides on Mg−Ca alloy: Role of calcium in magnesium alloy

Mg−Al layered double hydroxides (LDHs), produced on cast Mg−xCa (x=0.5, 0.8, 2.0, wt.%) alloys by an in-situ growth method, showed good corrosion resistance compared to the bare magnesium substrate. The influence mechanism of the second phase (Mg2Ca) on LDHs production was investigated. Increasing Ca content increased the amount of Mg2Ca, decreasing the grain size and the corrosion rate of the alloys. The increased amount of the second phase particles and the grain refinement promoted the growth of LDHs, and thus led to the decreasing of corrosion rate of the Mg−xCa alloys with LDHs. A higher Mg2Ca amount resulted in forming fluffy LDHs. Due to the dual effects of the second phase (Mg2Ca) for LDHs growth and microgalvanic corrosion, LDHs/Mg−0.8Ca showed the lowest corrosion rate.

One-step spontaneous growth of NiFe layered double hydroxide at room temperature for seawater oxygen evolution

Electrochemical seawater splitting is a promising technique because it addresses two major challenges, clean energy production and seawater desalination, at the same time. Therefore, seeking out a facile and cost-effective way to synthesize highly active and stable seawater-splitting catalysts is of great interest to both the research community and industry. Here we developed an Fe2+-driven, one-step, and spontaneous fabrication method for a seawater-oxygen-evolution-active NiFe layered double hydroxide (LDH) at room temperature. The NiFe LDH was found to exhibit very high activity and stability toward the oxygen evolution reaction (OER) in an alkaline natural seawater electrolyte, delivering current densities of 100 and 500 mA/cm2 at low overpotentials of 247 and 296 mV, respectively, and with no significant degradation observed over long-term stability testing of 96 h under a large current density of 500 mA/cm2 in 1 M KOH seawater electrolyte. After coupling with a good hydrogen evolution reaction (HER) catalyst, NiMoN, the two-electrode electrolyzer was found to achieve current densities of 10, 100, and 500 mA/cm2 at voltages of 1.477, 1.533, and 1.665 V, respectively, in alkaline natural seawater with good durability over 100 h at 500 mA/cm2. The oxidation of Fe2+ is the driving force for the growth of NiFe LDH, and this mechanism is universal to the fabrication of other Fe-based hydroxides as efficient OER catalysts.

Development of Mesopore Structure of Mixed Metal Oxide through Albumin-Templated Coprecipitation and Reconstruction of Layered Double Hydroxide.

Mixed metal oxide (MMO) with relatively homogeneous mesopores was successfully obtained by calcination and reconstruction of albumin-templated layered double hydroxide (LDH). The aggregation degree of albumin-template was controlled by adjusting two different synthesis routes, coprecipitation and reconstruction. X-ray diffraction patterns and scanning electron microscopic images indicated that crystal growth of LDH was fairly limited during albumin-templated coprecipitation due to the aggregation. On the hand, crystal growth along the lateral direction was facilitated in albumin-templated reconstruction due to the homogeneous distribution of proteins moiety. Different state of albumin during LDH synthesis influenced the local disorder and porous structure of calcination product, MMO. The N2 adsorption-desorption isotherms demonstrated that calcination on reconstructed LDH produced MMO with large specific surface area and narrow distribution of mesopores compared with calcination of coprecipitated LDH.