A green route for the preparation of layered double hydroxides from basic magnesium carbonate

Layered double hydroxides(LDHs)have received extensive attention in many fields such as catalysis,environmental management and medical applications.Typically,expensive soluble metal salts are commonly used as the starting materials for the synthesis of LDHs.Here,we report a novel synthesis route for Mg/Al-LDH by using inexpensive basic magnesium carbonate as the starting material.X-ray diffraction(XRD)and solid-state nuclear magnetic resonance(ssNMR)data show that LDHs with rich defects are formed rapidly at room temperature and good crystallinity can be obtained after further hydrothermal treatment.These results provide a simple,rapid and green preparation method for LDHs.

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

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.

Corrosion inhibition of layered double hydroxides for metal-based systems

Layered double hydroxide(LDH),a kind of 2D layered materials,has been recognized as the promising anticorrosion materials for metal and its alloy.The microstructure,physical/chemical properties,usage in corrosion inhibition and inhibition performance of LDH have been studied separately in open literature.However,there is a lack of a complete review to summarize the status of LDH technology and the potential R&D opportunities in the field of corrosion inhibition.In addition,the challenges for LDH in corrosion inhibition of metal-based system have not been summarized systematically.Herein,we review recent advances in the rational design of LDH for corrosion inhibition of metal-based system(i.e.Mg alloy,Al alloy,steel and concrete)and high-throughput anticorrosion materials development.By evaluating the physical/chemical properties,usage in metal-based system and the corrosion inhibition mechanism of LDH,we highlight several important factors of LDH for anticorrosion performance and common features of LDH in applying different metal alloys.Finally,we provide our perspective and recommendation in this field,including high-throughput techiniques for combinatorial compositional design and rapid synthesis of anticorrosion alloys,with the goal of accelerating the development and application of LDH in corrosion inhibition of metal-based system.

Combining the 8-hydroxyquinoline intercalated layered double hydroxide film and sol-gel coating for active corrosion protection of the magnesium alloy

8-hydroxyquinoline(8-HQ)intercalated layered double hydroxides(LDH)film as underlayer and sol-gel layer was combined for active corrosion protection of the AM60B magnesium alloy.The LDH,LDH/sol-gel,and LDH@HQ/sol-gel coatings were analyzed using the scanning electron microscopy(SEM),field emission scanning electron microscopy(FESEM),energy dispersive X-ray spectroscopy(EDS),X-ray diffraction(XRD),atomic force microscopy(AFM),and electrochemical impedance spectroscopy(EIS)methods.The SEM images showed that the surface was entirely coated by the LDH film composed of vertically-grown nanosheets.The same morphology was observed for the LDH/sol-gel and LDH@HQ/sol-gel coatings.Also,almost the same topography was observed for both composite coatings except that the LDH@HQ/sol-gel coating had relatively higher surface roughness.Although the LDH film had the same impedance behavior as the alloy sample in 3.5wt%NaCl solution,its corrosion resistance was much higher,which could be due to its barrier properties as well as to the trap-ping of the chloride ions.Similar to the LDH film,the corrosion resistance of the LDH/sol-gel composite diminished with increasing the ex-posure time.However,its values were much higher than that of the LDH film,which was mainly related to the sealing of the solution path-ways.The LDH@HQ/sol-gel composite showed much better anti-corrosion properties than the LDH/sol-gel coating due to the adsorption of the 8-HQ on the damaged areas through the complexation.

In situ growth process of Mg-Fe layered double hydroxide conversion film on MgCa alloy

In this study,an environment-friendly layered double hydroxide(LDH)film has been deposited on Mg Ca alloy by a two-step technique.To improve the chemical conversion technique and control the film properties,batch studies have been carried out to address various process parameters such as pH value,treatment temperature and immersion time.The chemical composition was determined by X-ray diffractometry and energy dispersive X-ray spectroscopy.The morphology was characterized by scanning electron microscopy.The corrosion resistance of the samples with various films was compared by polarization curves and immersion test.It is found that the transformation duration of Mg-Fe LDH is long.Too high pH value and temperature has harmful effect on the purity of the film composition.The corrosion resistance of the films formed at low value of pH or high temperature or short treatment time is deteriorative.The optimum process is as follows:the sample is first immersed in the solution containing Fe^(3+)/HCO_(3)^-/CO_(3)^(2-)with a pH value of 5 at a temperature of 55℃for 1 h to form a precursor film,and then this precursor film is immersed into the solution containing Fe^(3+)/HCO_(3)^-/CO_(3)^(2-)with a pH of 11 at 55℃for 24 h to obtain the Mg-Fe LDH conversion film.

A comparison of corrosion inhibition of magnesium aluminum and zinc aluminum vanadate intercalated layered double hydroxides on magnesium alloys

The magnesium aluminum and zinc aluminum layered double hydroxides intercalated with NO3^- （MgAl-NO3-LDH and ZnAl-NO3-LDH） were prepared by the coprecipitation method, and the magnesium aluminum and the zinc aluminum layered double hydroxides intercalated with VO; （MgAl-VOx-LDH and ZnAl-VOx-LDH） were prepared by the anion-exchange method. Morphologies, microstructures and chemical compositions of LDHs were investigated by SEM, EDS, XRD, FTIR, Raman and TG analyses. The immersion tests were carried to determine the corrosion inhibition properties of MgAl-VOx-LDH and ZnAl-VOx-LDH on AZ31 Mg alloys. The results showed that ZnAl-VOx-LDH possesses the best anion-exchange and inhibition abilities. The influence of treatment parameters on microstructures of LDHs were discussed. Additionally, an inhibition mechanism for ZnAl-VOx-LDH on the AZ31 magnesium alloy was proposed and discussed.

Next-generation aluminum adjuvants:Immunomodulatory layered double hydroxide NanoAlum reengineered from first-line drugs

Aluminum adjuvants(Alum),approved by the US Food and Drug Administration,have been extensively used in vaccines containing recombinant antigens,subunits of pathogens,or toxins for almost a century.While Alums typically elicit strong humoral immune responses,their ability to induce cellular and mucosal immunity is limited.As an alternative,layered double hydroxide(LDH),a widely used antacid,has emerged as a novel class of potent nano-aluminum adjuvants(NanoAlum),demonstrating advantageous physicochemical properties,biocompatibility and adjuvanticity in both humoral and cellular immune responses.In this review,we summarize and compare the advantages and disadvantages of Alum and NanoAlum in these properties and their performance as adjuvants.Moreover,we propose the key features for ideal adjuvants and demonstrate that LDH NanoAlum is a promising candidate by sum-marizing its current progress in immunotherapeutic cancer treatments.Finally,we conclude the review by offering our integrated perspectives about the remaining challenges and future directions for NanoAlum's application in preclinical/clinical settings.

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 Mg（OH）2/Mg-Al-layered double hydroxide coatings on magnesium alloy AZ31:influence of hydrolysis degree of silane

Mg(OH)2/Mg-Al-layered double hydroxide (LDH) coatings were modified with methyltrimethoxysilane (MTMS) on magnesium alloys. Effect of hydrolysis degree of silane solution on coating formation was investigated. Chemical compositions and surface morphologies of the coatings were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electronic microscopy (FESEM). Results indicated that the composite coatings consisted of polymethyltrimethoxysilane (PMTMS), LDH and Mg(OH)2. Electrochemical and hydrogen evolution measurements revealed that the composite coatings possessed good corrosion resistance, especially the ones prepared in a high hydrolysis degree of silane. The optimum corrosion resistance of the composite coati ng was LDH/PMTMS-3 coating, which had the lowest value of corrosion current density (5.537×10^-9 A·cm^-2) and a dense surface.Plausible mechanism for coating formation and corrosion process of MTMS-modified Mg(OH)2/Mg-Al-LDH coatings were discussed.

Corrosion resistance of Zn-AI layered double hydroxide/ poly（lactic acid） composite coating on magnesium alloy AZ31

A Zn-AI layered double hydroxide （ZnAI-LDH） coating consisted of uniform hexagonal nano-plates was firstly synthesized by co-precipitation and hydrothermal treatment on the AZ31 alloy, and then a poly（lactic acid） （PLA） coating was sealed on the top layer of the ZnAI-LDH coating using vacuum freeze-drying. The characteristics of the ZnAI-LDH/PLA composite coatings were investigated by means of XRD, SEM, FTIR and EDS. The corrosion resistance of the coatings was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy （EIS）. The results showed that the ZnAI-LDH coating contained a compact inner layer and a porous outer layer, and the PLA coating with a strong adhesion to the porous outer layer can prolong the service life of the ZnAI-LDH coating. The excellent corrosion resistance of this composite coating can be attributable to its barrier function, ion-exchange and self-healing ability.

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.

Development of metal-organic framework(MOF) decorated graphene oxide/Mg Al-layered double hydroxide coating via microstructural optimization for anti-corrosion micro-arc oxidation coatings of magnesium alloy

An efcient and simple in-situ growth strategy has been discovered for the preparation of highly reproducible and continuous symbiotic ZIF-8-based anticorrosion coating by using graphene oxide(GO)/Mg AlNO3layered double hydroxides(G/LDHs) buffer layer as a new type of connecting carrier based on micro-arc oxide(MAO) coating of AZ31 magnesium alloy. The components of ZIF-8 were adsorbed and bounded to the surface of the G/LDHs buffer layer-modified substrates to promote the nucleation of ZIF-8,thus growing a phase-pure, uniform, and good symbiosis ZIF-8 membrane. ZIF-8 particles with different growth times compensate for the grain boundary defects of the G/LDHs coating precursor buffer layer to different degrees. The prepared ZIF-8-based coating has excellent stability and corrosion resistance. The results demonstrate that the G/LDHs buffer layer provides a new channel for the MOF-modified MAO substrate of AZ31 magnesium alloy. It also proves that it is feasible to build high-performance anticorrosive coatings with MOF materials.

Biocorrosion resistance and biocompatibility of Mg-AI layered double hydroxide/poly(L-lactic acid) hybrid coating on magnesium alloy AZ31

A Mg-AI layered double hydroxide(Mg-AI-LDH)coating was firstly synthesized via an in-situ steam coating growth method on the AZ31 Mg alloy,and then was modified with poly(L-lactic acid)(PLLA)via dipping and vacuum freeze-drying.The microstructure and composition of LDH/PLLA hybrid coating were analyzed by XRD,SEM,EDS and FT-IR.The biocorrosion behavior of hybrid coating was evaluated by potentiodynamic polarization,electrochemical impedance spectroscopy(EIS)and hydrogen evolution test in the Hank's solution.The results showed that LDH/PLLA coatings exhibited a much dense layer compared to the unmodified Mg-AI-LDH coating with unobvious boundary between PLLA and LDH coatings.The corrosion current density of the LDH/PLLA-10 hybrid coating decreased three orders of magnitude in comparison to its substrate.It was proven that the existence of the PLLA coating further prolonged the service life of the Mg-AI-LDH coating.What's more,the MTT assay and livel dead staining showed that the LDH/PLL A-10 coating had good biocompatibility for Mouse NIH3T3 fibroblasts.The formation mechanism and the anti-corrosion mechanism of hybrid coatings were proposed.

Design of self-healing PEO-based protective layers containing in-situ grown LDH loaded with inhibitor on the MA8 magnesium alloy

The high corrosion rate of magnesium and its alloys in chloride-containing solution significantly reduces the potential of this material for diverse applications.Therefore,the formation of a smart protective coating was achieved in this work to prevent degradation of the MA8 magnesium alloy.A porous ceramic-like matrix was obtained on the material by plasma electrolytic oxidation(PEO).Further surface functionalization was performed using layered double hydroxides(LDH) served as nanocontainers for the corrosion inhibitor.Several methods of LDH intercalation with benzotriazole(BTA) were proposed.The composition and morphology of the formed coating were studied using SEM-EDX analysis,XRD,XPS,and Raman microspectroscopy.The corrosion behavior of the coated samples was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization.The corrosion rate was estimated using volumetry and gravimetry methods.The formed composite coating provides the Mg alloy with the lowest corrosion activity(|Z|_(f)=0.1 Hz)=8.48·10^(5) Ω·cm^(2),I_(c)=1.4·10^(-8)A/cm^(2),P_(H)=0.21 mm/year) and improves the protective properties of the PEO-coated sample(|Z|_(f)=0.1 Hz)=8.37·10^(3) Ω·cm^(2),I_(c)=4.1·10^(-7)A/cm^(2),P_(H)=0.31 mm/year).The realization of the self-healing effect of the inhibitor-containing LDH/PEO-coated system was studied using localized electrochemical methods(SVET and SIET) with two artificial defects on the surface.A mechanism involving three stages for the active corrosion protection of the alloy was proposed.These findings contribute to the follow-up work of developing modified LDH/PEO-based structures that promote the Mg alloy with high corrosion resistance,superior electrochemical performance for applications in various fields of industry and medicine.

Black Mn-containing layered double hydroxide coated magnesium alloy for osteosarcoma therapy, bacteria killing, and bone regeneration

Osteosarcoma (OS) tissue resection with distinctive bactericidal activity, followed by regeneration of bone de-fects, is a highly demanded clinical treatment. Biodegradable Mg-based implants with desirable osteopromotive and superior mechanical properties to polymers and ceramics are promising new platforms for treating bone-related diseases. Integration of biodegradation control, osteosarcoma destruction, anti-bacteria, and bone defect regeneration abilities on Mg-based implants by applying biosafe and facile strategy is a promising and challenging topic. Here, a black Mn-containing layered double hydroxide (LDH) nanosheet-modified Mg-based implants was developed. Benefiting from the distinctive capabilities of the constructed black LDH film, including near-infrared optical absorption and reactive oxygen species (ROS) generation in a tumor-specific microenvi-ronment, the tumor cells and tissue could be effectively eliminated. Concomitant bacteria could be killed by localized hyperthermia. Furthermore, the enhanced corrosion resistance and synergistic biofunctions of Mn and Mg ions of the constructed black LDH-modified Mg implants significantly facilitated cell adhesion, spreading and proliferation and osteogenic differentiation in vitro, and accelerated bone regeneration in vivo. This work offers a new platform and feasible strategy for OS therapeutics and bone defect regeneration, which broadens the biomedical application of Mg-based alloys.

Corrosion resistance of a silane/ceria modified Mg-Al-layered double hydroxide on AA5005 aluminum alloy

The present work aimed at assessing the electrochemical behavior and the corrosion inhibition performance of Mg-Al-layered double hydroxide(LDH)coatings modified with methyltrimethoxysilane(MTMS)and cerium nitrate on AA5005 aluminum alloy.The chemical compositions and surface morphologies of the coatings were investigated by XRD,FT-IR and FE-SEM,while their corrosion resistance was evaluated by electrochemical and immersion tests.An optimum corrosion resistance of the composite coatings was obtained by adding 10^−2 mol·L^−1 cerium nitrate.An excess addition of cerium nitrate resulted in a loose structure and poor corrosion resistance of the coating.The corrosion mechanism of the composite coatings was proposed and discussed.

Comparative study of oxidative stress induced by sand flower and schistose nanosized layered double hydroxides in N2a cells

Magnesium-aluminum layered double hydroxide （Mg/ALLDH） nanoparticles have strong potential application as drug delivery systems because of their low toxicity and suitable biocompatibility. However, few studies have described the morphological effects of these hydroxides on nerve cells. The present study compares the oxidative stress induced by different concentrations （i.e., 0, 50, 100, 200, 400, and 800 μg/mL） of sand flower and flake nano-Mg/ AI-LDHs in mouse neuroblastoma cells （N2a） when these cells were exposed for 24 and 48 h. Cell viability was detected by MTT assay, and production of reactive oxygen species （ROS）, glutathione （GSH）, and malondialdehyde （MDA） were monitored to evaluate oxidative damage. Results suggested that sand flower nano-LDHs, at the appropriate concentrations （less than 200 μg/mL）, especially those of about 100-200 nm in size, induce no harmful effects on N2a cells.

Osteogenesis, angiogenesis and immune response of Mg-Al layered double hydroxide coating on pure Mg

Layered double hydroxides(LDHs)are widely studied to enhance corrosion resistance and biocompatibility of Mg alloys,which are promising bone implants.However,the influence of LDH coating on the osteointegration of Mg implants lacks of a systematic study.In this work,Mg-Al LDH coating was prepared on pure Mg via hydrothermal treatment.The as-prepared Mg-Al LDH coated Mg exhibited better in vitro and in vivo corrosion resistance than bare Mg and Mg(OH)2 coated Mg.In vitro culture of mouse osteoblast cell line(MC3T3-E1)suggested that Mg-Al LDH coated Mg was more favorable for its osteogenic differentiation.In vitro culture of HUVECs revealed that cells cultured in the extract of Mg-Al LDH coated Mg showed superior angiogenic behaviors.More importantly,the immune response of Mg-Al LDH coated Mg was studied by in vitro culturing murine-derived macrophage cell line(RAW264.7).The results verified that Mg-Al LDH coated Mg could induce macrophage polarize to M2 phenotype(anti-inflammatory).Furthermore,the secreted factor in the macrophageconditioned culture medium of Mg-Al LDH group was more suitable for the bone differentiation of rat bone marrow stem cells(rBMSCs)and the angiogenic behavior of human umbilical vein endothelial cells(HUVECs).Finally,the result of femoral implantation suggested that Mg-Al LDH coated Mg exhibited better osteointegration than bare Mg and Mg(OH)2 coated Mg.With favorable in vitro and in vivo performances,Mg-Al LDH is promising as protective coating on Mg for orthopedic applications.

Green corrosion inhibitors intercalated Mg:Al layered double hydroxide coatings to protect Mg alloy

Mg alloy was protected with Mg:Al layered double hydroxide(LDH)coating intercalated with three green corrosion inhibitors(sodium benzoate,3-aminopropyltriethoxysilane and 8-hydroxyquinoline).The in-situ hydrothermal approach was adopted to intercalate corrosion inhibitors into Mg:Al LDH coating.The intercalated Mg:Al LDH coating was successfully acquired,and the crystalline structure of Mg:Al LDH coating was verified with X-ray diffraction(XRD).The organic functional groups of corrosion inhibitors were identified with the help of Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS).The compact and uniform morphology was confirmed by scanning electron microscopy(SEM).The electrochemical measurement revealed better corrosion resistance of corrosion inhibitorintercalated Mg:Al LDH coatings as compared to that of pristine Mg alloy.The corrosion protection mechanism of corrosion inhibitors was described and unearthed the corrosion inhibitor with the best performance.

Corrosion of in-situ grown Mg Al-LDH coating on aluminum alloy

Mg Al-layered double hydroxides（LDH） coatings were fabricated by the in-situ hydrothermal treatment method on the AA5005 aluminum alloy.The characteristics of the coatings were investigated by XRD,FT-IR,SEM and EDS.The effect of the p H value of the solution on the formation of the LDH coatings was studied.The optimum p H value of the solution was 10.0.The corrosion resistance of the LDH coatings was studied using potentiodynamic polarization tests and electrochemical impedance spectrum（EIS）.The results demonstrate that the LDH coatings,characterized by platelets vertically to the substrate surface possess excellent corrosion resistance.The influence of the hydrothermal crystallization time on the corrosion resistance was evaluated.Prolonging the crystallization time can increase the corrosion resistance of the obtained LDH coatings.The anticorrosion mechanism of the LDH coatings was discussed.