Layered Double Hydroxide Thin Films Research Articles

ZPCC-Zn-Al-LDH surface bilayer; toward designing a durable self-healable nano-structured film with the utmost corrosion resistance

BackgroundDesigning thin films with utmost corrosion resistance stability and long-term metal protection from corrosive species attacks is the main idea of this work. Zinc phosphate conversion films are greatly exploited for improving the anticorrosion properties and surface preparation prior to organic coating application. Layered double hydroxide (LDH) thin films consist of a dense layer and a plate-shaped part, which perform the functions of the barrier and ion exchange, respectively. MethodsA bilayer conversion coating composed of a modified zinc phosphate layer and LDH crystals was fabricated on mild steel and then loaded with a glutamate corrosion inhibitor. These coatings were characterized by FE-SEM, XRD, FT-IR, and XPS methods. Significant findingsEIS results showed that log |Z|0.01 Hz reached its maximum value (6.14 Ω cm2) for the conversion coating sample loaded with inhibitor. Also, the active properties of the polyester organic coating with the introduced primer were ameliorated insofar as the total resistance of the scratched coating was obtained at around 115 KΩ cm2 after 48 h of exposure to the salty solution.

Ce-Doped-MgAl Superhydrophobic Layered Double Hydroxide for Enhanced Corrosion Resistance Properties

Double doped layered double hydroxide thin films were developed directly on the aluminum substrate in two steps: Initially cerium-based MgAl-layered double hydroxide (LDH) were synthesized directly on the anodic aluminum surface via the in situ growth method, and were then modified with the stearate anions through an ion-exchange mechanism to achieve compact multifunctional protective thin films. The structural and morphological characteristics of the developed LDH films were investigated, and the surface contact angle measurements (CA) and self-cleaning properties were analyzed. The obtained double doped LDH film displayed the superhydrophobic characteristic with a water contact angle of ~155°. Furthermore, the superhydrophobic behavior of LDH on exposure to UV radiation (λ = 310 nm) was examined to evaluate outdoor applications. Long-term Electrochemical Impedance Spectroscopy (EIS) analysis was performed to understand the corrosion resistance properties. The introduction of double doped LDHs demonstrates significantly higher corrosion resistance properties than only cerium-modified LDHs and has shown superior stability against 0.1 M NaCl solution.

Protective Cerium-Based Layered Double Hydroxides Thin Films Developed on Anodized AA6082

In this work, CeMgAl-LDHs protective thin films were developed directly on the anodized aluminum surface, and on the “hot water-sealed” anodized aluminum specimens. The synthesized coatings were investigated by SEM-EDS and XRD and through long-term electrochemical impedance spectroscopy (EIS) spectra. The growth of CeMgAl-LDHs into/onto the micropores/defects of anodized film was found to significantly improve the LDH barrier properties with delaying coating degradation compared to LDHs developed on the “hot water-sealed” surface. The unmodified LDHs “without cerium addition” were also developed to compare the influence of cerium on the structural and electrochemical properties of LDHs. It is also noteworthy that LDHs grown on the anodized surface provided dense and finer growth, while the addition of cerium ions was found to exhibit influential higher long-term corrosion resistance properties after the 1200 h immersion period.

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.

Pulsed laser deposition of functionalized Mg–Al layered double hydroxide thin films

In this paper, magnesium–aluminium layered double hydroxide (LDH) has been functionalized with sodium dodecyl sulfate (DS) and deposited as thin film by pulsed laser deposition (PLD). Mg, Al-LDH powders were prepared by co-precipitation and used as reference material. Intercalation of DS as an anionic surfactant into the LDHs host layers has been prepared in two ways: co-precipitation (P) and reconstruction (R). DS intercalation occurred in LDH powder via both preparation methods. The films deposited via PLD, in particular at 532 and 1064 nm, preserve the organic intercalated layered structure of the targets prepared from these powders. The results reveal the ability of proposed deposition technique to produce functional composite organo-modified LDHs thin films.

Electrochemical behaviors of iron-based layered double hydroxide thin-films

The ordered ultrathin films based on the fabrication of Mg/Fe-LDHs ([Mg6Fe2(OH)16CO3·(H2O)4.5]0.375) nanosheets and hexacyanoferrate(III) anions via the self-assembly procedure were prepared. The electrodes modified by the films demonstrated a couple of well-defined reversible redox peaks attributed to [Fe(CN)6]3−/4− and Fe2+/3+ couples. The effects of cycle number, scan rate and Mg/Fe molar ratio on the CV performance of the thin-film electrodes were observed in K3[Fe(CN)6] electrolyte. The [Fe(CN)6]3− pillared Mg/Fe-LDHs with Mg/Fe molar ratio of 3 (LDH-(CN)-3) demonstrated an excellent electrochemical behavior with a potential window between − 0.2 and 1.0 V, high specific capacitance and sensitivity, indicating that the high crystallinity, large specific surface area and plentiful [Fe(CN)6]3− anions in interlayer spaces were necessary. Especially, the interlayer [Fe(CN)6]3− anions significantly affected the electrochemical behavior of the electrode, where the electrode reaction was controlled by the diffusion of [Fe(CN)6]3−/4− and Fe2+/3+ couples. Under current density of 2.5 A g−1, the optimized LDH-(CN)-3 electrode exhibited high specific capacitance of 250.81 F g−1 with good cycling stability. This facile synthesis strategy and the good electrochemical properties indicated that the LDH-(CN)-3 was a potential economical alternative material for supercapacitor application.

Cycling stability of iron-based layered double hydroxide thin-films for battery-type electrode materials

The [Fe(CN)6]3− intercalated Mg/Fe-LDH (LDH-CN) thin film was prepared by the intercalation-reconstruction method. By using a three-electrode system, the electrochemical performance of the film was also investigated to evaluate the cycling stability for its potential as electrode materials. The LDH-CN thin film was characterized by XRD, FT-IR, SEM and TG-DSC, indicating that the microstructure and surface morphology of the films remained basically unchanged before and after CV scanning for 50 cycles. Redox cycling of the LDH-CN/GCE kept a strong stability at 100 mV s−1 for 50 cycles by virtue of the stability of the microstructure of the LDH-CN thin film. Such stability was likely imparted by the formation of a network of mixed-valent Fe2+/3+ oxo-bridges that underwent chemical reactions and electrochemical reactions as main capacitive charge storage ions. The LDH-CN electrode presented a maximum specific capacity of 147.2 mAh g−1 and excellent cycle life, while it still exhibited 133.9 mAh g−1 at the 1000th cycle at a current density of 3 A g−1. Such a thin-film electrode made up of the LDH-CN material may be a potential economical alternative battery-type electrode material and possess electrochemical capacitors possibilities.

Growth and characterization of ternary Ni, Mg–Al and Ni–Al layered double hydroxides thin films deposited by pulsed laser deposition

Layered double hydroxides (LDHs) are a class of layered materials consisting of positively charged brucite-like layers and exchangeable interlayer anions. Layered double hydroxides containing a transition metal which undergoes a reversible redox reaction in the useful potential range have been proposed as electrode coating materials due to their properties of charge transport and redox catalysts in basic solutions.Ni–Al,(Ni,Mg)–Al and, as reference, non-electronically conductive Mg–Al double hydroxides thin films were obtained via pulsed laser deposition technique. The thin films were deposited on different substrates (Si, glass) by using a Nd:YAG laser (1064nm) working at a repetition rate of 10Hz. X-ray diffraction, Atomic Force Microscopy, Energy Dispersive X-ray spectroscopy, Fourier Transform Infra-Red Spectroscopy, Secondary Ions Mass Spectrometry, Impedance Analyzer and ellipsometry were the techniques used for the as deposited thin films investigation. The optical properties of Ni based LDH thin films and the effect of the Ni amount on the structural, morphological and optical response are evidenced.The optical band gap values, covering a domain between 3.84eV and 4.38eV, respond to the Ni overall concentration: the higher Ni amount the lower the band gap value.

Selective Tumor Cell Inhibition Effect of Ni-Ti Layered Double Hydroxides Thin Films Driven by the Reversed pH Gradients of Tumor Cells.

Nitinol is widely fabricated as stents for the palliation treatment of many kinds of cancers. It is of great importance to develop nitinol stents with selective tumor cell inhibition effects. In this work, a series of pH sensitive films composed of Ni(OH)2 and Ni-Ti layered double hydroxide (Ni-Ti LDH) with different Ni/Ti ratios were prepared on the surface of nitinol via hydrothermal treatment. The films with specific Ni/Ti ratios would release a large amount of nickel ions under acidic environments but were relatively stable in neutral or weak alkaline medium. Cell viability tests showed that the films can effectively inhibit the growth of cancer cells but have little adverse effects to normal cells. Besides, extraordinarily high intracellular nickel content and reactive oxygen species (ROS) level were found in cancer cells, indicating the death of cancer cells may be induced by the excessive intake of nickel ions. Such selective cancer cell inhibition effect of the films is supposed to relate with the reversed pH gradients of tumor cells.

Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD

Layered double hydroxides (LDHs) thin films with Mg–Al were deposited using pulsed laser deposition (PLD) technique. We studied the ability of our films to detect copper ions in aqueous solutions. Copper is known to be a common pollutant in water, originating from urban and industrial waste. Clay minerals, including layered double hydroxides (LDHs), can reduce the toxicity of such wastes by adsorbing copper. We report on the uptake of copper ions from aqueous solution on LDH thin films obtained via PLD.The obtained thin films were characterized using X-ray Diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis. The results in this study indicate that LDHs thin films obtained by PLD have potential as an efficient adsorbent for removing copper from aqueous solution.

Synthesis and morphological modification of semiconducting Mg(Zn)Al(Ga)–LDH/ITO thin films

Layered double hydroxide (LDH) thin films with different chemical compositions (MgZnAl, MgZnGa, MgGaAl) and varying thicknesses were easily prepared by sol–gel method followed by dip-coating. Films were chemically uniform, transparent and well adhered to a conductive indium tin oxide (ITO) substrate. Structure, chemical composition and morphology of the thin films were characterized by XRD-GADDS, SEM-EDS and AFM. Additionally, the semiconducting properties of all the prepared films were studied through the Mott–Schottky relationship; such properties were closely related to the chemical compositions of the film. The films were characterized after electrochemical treatment and important modifications regarding surface morphology, particle and crystal sizes were observed. An in-depth study was conducted in order to investigate the effect of several different electrochemical treatments on the morphology, particle size distribution and crystal size of LDH thin films. Upon electrochemical treatment, the films' surface became smooth and the particles forming the films were transformed from flaky open LDH platelets to uniformly distributed close-packed LDH nanoparticles.

Retention of heavy metals on layered double hydroxides thin films deposited by pulsed laser deposition

Heavy metals are toxic and hazardous pollutants in the environment due to their nonbiodegradability and persistence, which can pose serious threats to living organisms. The ability of Mg–Al based layered double hydroxides (LDHs) thin films to retain heavy metals from aqueous solutions at different concentrations is a novel topic with prospects of attractive applications, such as detection of heavy metals. We report on the ability of a series of Mg–Al based layered double hydroxides thin films to detect Ni and Co cations in aqueous solutions.Uptake of heavy metals ions such as Ni2+, Co2+ from aqueous solutions was studied as function of contact time at a standard metal ion concentration.The LDHs thin films were deposited using pulsed laser deposition (PLD). The different adsorption mechanisms were studied in connection with different heavy metals used as probe cations. X-ray diffraction, atomic force microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Fourier transform infra-red spectroscopy were the techniques used for the investigation of as deposited and after heavy metals retention thin films.

Preparation of oriented zinc oxide thin films by firing Zn–Al layered double hydroxide thin films

The Zn–Al layered double hydroxide (LDH) particles were prepared by heating aqueous solutions of Zn(NO3)2 and Al(NO3)3 with ethylenediamine at 348K for 24h. The obtained particles, which had sheet morphology, were well dispersed in water. The sol of LDH nanoparticles was dried on an alkali-free glass substrate and LDH thin films were obtained easily. Firing the LDH films at temperatures higher than 573K produces a highly oriented zinc oxide film. The obtained films had orientation of zinc oxide (002) on the glass substrate. This orientation reflected that of the LDH films. The zinc oxide films showed more than 80% of the optical transmittance when the wavelength was 400nm.

Correlation among Structure, Microstructure, and Electrochemical Properties of NiAl–CO3Layered Double Hydroxide Thin Films

We studied a series of NiAl–CO3 layered double hydroxides (LDHs) of various degrees of crystallinity prepared by a glycine-assisted hydrothermal method. The structures and the microstructures were determined by Rietveld refinement with a spherical harmonic-implemented algorithm using high-resolution synchrotron powder X-ray diffraction (XRD) data. These XRD results combined with transmission electron microscopy (TEM) observations indicate that the broadening of 00l diffraction lines is mainly due to size effects, while both size and strain effects contribute to the anisotropic broadening of the other hkl reflections. The in-plane TEM dimensions of LDH platelets are found larger than the coherent lengths in the 110 direction, indicating a noncoherent coalescence of domains during crystal growth. The DIFFaX program was also used to model structural defects, i.e., CO32–/SO42– interstratification and intergrowth between rhombohedral 3R1 and hexagonal 2H1 polytypes. Furthermore, the distribution of the cations...

Preparation of Co–Al and Ni–Al layered double hydroxide thin films by a sol–gel process with hot water treatment

Using hot water treatment of sol–gel derived precursor gel films, Co–Al and Ni–Al layered double hydroxide (LDH) thin films were prepared. The precursor gel films of Al2O3–CoO or Al2O3–NiO were prepared from cobalt or nickel nitrates and aluminum tri-sec-butoxide using the sol–gel method. Then, the precursor gel films were immersed in a NaOH aqueous solution of 100 °C. Nanocrystallites of Co–Al and Ni–Al LDH were precipitated with the hot water treatment with NaOH solution. The largest amounts of nanocrystals were obtained with a solution of pH = 10 for Co–Al LDH, and with that of pH = 9 for Ni–Al LDH. X-ray diffraction measurements confirmed that this process formed CO32− intercalated LDHs. Both Co–Al and Ni–Al LDH thin films were confirmed to work as electrodes for electrochemical devices by cyclic voltammogram measurements.

Facile fabrication of stable superhydrophobic films on aluminum substrates

Compact and uniform layered double hydroxides thin films were fabricated on aluminum substrates using a simple solution-immersion process; upon chemical modification with perfluorosilane, the wettability of the aluminum surface changed from hydrophilic to superhydrophobic. The products were characterized by scanning electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. It is confirmed that the synergic effect of the surface morphology and the surface free energy contribute to this unique surface water repellence. In addition, the superhydrophobic films possess long-term storage stability and good adhesion strength to aluminum substrates, which enhance their potential practical applications.

Oriented printable layered double hydroxide thin films via facile filtration

Highly oriented layered double hydroxide (LDH) thin films are obtained from colloidal dispersion of exfoliated LDH nanosheets in formamide by vacuum filtration. Through filtration, positively charged LDH nanosheets are stacked in interlocking arrangements, which endow LDH thin films with excellent mechanical properties. Consequently, the fresh prepared LDH thin films are printed on different substrates, forming transparent, strong and flexible LDH layers. Utilizing coassembly of positively charged LDH nanosheets with polymeric anions, negatively charged LDH nanohybrids can be obtained. By adding various types of anions into a colloidal dispersion of LDHs and subsequent filtration, LDH thin films with tunable composition and nanostructure can be prepared easily. However, the addition of carbonate or small molecular anionic surfactants leads to aggregation of LDH nanosheets. This facile filtration method will facilitate the fabrication of functional LDH thin films.

Molecular Orientation and Fluorescence Studies on Naphthalene Acetate Intercalated Zn2Al Layered Double Hydroxide

This paper describes a systematic study on molecular orientation and fluorescence properties for the Zn2Al layered double hydroxide (LDH) intercalated with α-naphthalene acetate (α-NAA) and β-naphthalene acetate (β-NAA), respectively. α-NAA and β-NAA intercalated Zn2Al LDH (denoted as α-NAA LDH and β-NAA LDH) were prepared by the ion-exchange method and their thin films on Si substrates were obtained by the solvent evaporation method. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) of α-NAA LDH and β-NAA LDH confirm the intercalation of guests between sheets of LDH. The XRD and scanning electron microscope (SEM) images of α-NAA LDH and β-NAA LDH thin films show that they are well c-oriented assembly with platelet-like morphology. UV−vis absorption and fluorescence spectra (emission, lifetime, and time resolution) indicate that the intercalated NAA is accommodated in its monomer form and depolarization factors exhibit no influence on its fluorescence emission process,...

Microstructure-controlled synthesis of oriented layered double hydroxide thin films: Effect of varying the preparation conditions and a kinetic and mechanistic study of film formation

The microstructure-controlled synthesis of oriented layered double hydroxide (LDH) thin films on polystyrene substrates has been investigated in detail and the effect of varying the preparation conditions, such as the extent of sulfonation of the substrate, the total concentration of metal ions in the precursor solution, the temperature, and the reaction time are described. The kinetic features of the formation of the LDH films have also been derived; it was found that the best fit corresponds to a second-order exponential nucleation law. As a result, a possible mechanism for the formation of LDH films on the polystyrene substrate has been proposed, involving transportation of metal cations to the surface of the substrate, adsorption, and enrichment of the cations on the substrate, followed by nucleation and oriented growth of LDH films at the phase boundary.

Direct Formation of Zn-Al Layered Double Hydroxide Thin Films Intercalated with Various Organic Anions through the Sol-Gel Method with Hot Water Treatment

Zn-Al layered double hydroxide (LDH) thin films intercalated with various organic anions were prepared by immersion of sol-gel derived amorphous Al2O3-ZnO thin films in hot water containing organic salts like sodium dodecyl sulfate (SDS), sodium p-toluenesulfonate, and benzenecarboxylates. In all the systems, extended interlayer spacing of the Zn-Al LDH was observed after immersion in distilled water with the organic salts in comparison to the LDH with carbonate anions, indicating that we have succeeded in direct formation of Zn-Al LDH films with various organic anions on the substrates. It is suggested that divalent anions such as terephthalate ion have higher selectivity than monovalent anions.