Jingjing Wang

Layered double hydroxide (LDH) has been widely used in the field of corrosion protection. LDH nanofillers can act as multifunctional additives in coatings based on the physical barrier effect and anion exchange effect. However, the preparation of the typical co-precipitation method needs to be simplified to realize large-scale industrialization. In this work, a wide range of synthesis parameters, including solution-mixing mode, reaction atmosphere, reaction pH control, titration rate and post-treatment on the obtained LDH, were systematically studied, and it was found that the one-step solution-mixing synthesis procedure and the adoption of N₂ atmosphere were able to alleviate the carbonate contamination to some degree. However, the one-step solution-mixing synthesis procedure has a negative influence on the formation of LDH, probably due to insufficient reaction, while the hydrothermal post-treatment is able to promote the continual growth of the LDH platelet and, thus, lead to an increase in crystallinity and particle size. Green inhibitor aspartates were used to modify LDH, and the electrochemical test results indicated that the adoption of N₂ atmosphere was able to clearly increase the corrosion protection ability of LDH, with an R_p value of 3.86 kΩ·cm² after immersion for 96 h in 0.1 mol/L NaCl, probably due to the intercalation of a relatively large amount of inhibitor anions since less carbonates were intercalated, followed by the LDH synthesized via co-precipitation without N₂ protection, pH control and hydrothermal post-treatment with an R_p value of 3.00 kΩ·cm². The LDH sample without inhibitor intercalation presented a corresponding R_p value of 2.45 kΩ·cm². Notably, the one-step solution-mixing method and a fast titration rate in co-precipitation would have a negative influence on the corrosion protection of LDH, probably due to insufficient reaction. This work could shed light on the simplification of LDH preparation, and it is able to provide a solid foundation and technical support for the wide promotion and application of LDH in anti-corrosion and other fields in the near future.

In order to enhance the corrosion resistance of aluminum alloys, mussel adhesive protein (MAP) was intercalated into layered double hydroxide (LDH) grown onto an Al substrate. The results from X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and energy dispersive spectroscopy (EDS) measurements all confirmed that part of the positively charged MAP can be successfully intercalated into the LDH based on the strong second reactivity. MAP is able to form complexes with the metal cations and hydroxides, leading to less positive charges on the hydroxide layers of the LDH. The intercalation results in the removal of the previously intercalated anions from the interlayer space of the LDH, which maintains the charge balance and lamellar structure. The MAP intercalated LDH film can provide effective corrosion protection to the Al substrate.

In this work, nitrite and molybdate-modified CaAl layered double hydroxide(CaAl-LDH) was first synthesized, and the corrosion protection mechanism of CaAl-LDH intercalated with nitrites in epoxy coatings was investigated. Scanning electronic microscopy (SEM) and the energy dispersive spectroscopy (EDS) was used to characterize the morphology and element composition of the synthesized powder. Fourier transform infrared spectroscopy (FTIR) was used to characterize the information of chemical composition, and X-ray diffraction (XRD) was used to analyze the structure. The SEM and XRD results indicated that the LDH structure was destroyed in the molybdate modification process, and CaMoO₄ precipitates were formed. Therefore, molybdates cannot be used to be loaded in CaAl-LDH interlayer space for synthesis of an active corrosion inhibition container. The nitrite release curve and the chloride concentration decreasing curve were measured to study the anion-exchange reaction by UV-Vis spectroscopy and a home-made Ag/AgCl probe, respectively. The corrosion protection effect of the CaAl-LDH loaded with nitrites towards the carbon steel was evaluated in 0.02 M NaCl solution by electrochemical impedance spectroscopy (EIS). Then the powder was added in the epoxy coating with 2% addition (weight vs. epoxy resin). The coating morphology and roughness were evaluated by SEM and laser microscopy, and the corrosion protection effect was investigated by EIS in an immersion period of 21 d. The fitted coating resistance of the sample with 2% LDH intercalated with nitrites was one order of magnitude higher than that with 2% LDH, and the latter one was two orders of magnitude higher than the blank sample. Local electrochemical impedance spectra (LEIS) was used to characterize the corrosion development process in micro-corrosion sites. The corrosion product of the scratched area after salt spray exposure was analyzed by EDS and Raman spectroscopy. The corrosion protection mechanism of the CaAl-LDH loaded with nitrites was proposed based on the above experimental results.

In this work, nitrite intercalated CaAl-LDH was firstly prepared in this work. Scanning electronic microscopy (SEM) coupled with the energy dispersive spectrometer (EDS) was used to characterize the morphology and element composition of the synthesized powder. Fourier transform infrared spectroscopy (FTIR) was used to characterize the chemical composition and X-ray diffraction (XRD) was used to analyze the structure. The nitrite release curve and the chloride concentration change curve were obtained to study the anion-exchange reaction. The corrosion protection effect of the CaAl-LDH loaded with nitrites towards the carbon steel was evaluated in 0.02 M NaCl solution by electrochemical impedance spectroscopy (EIS). Then the powder was added in the epoxy coating with a percentage of 2% (vs. epoxy resin). The coating morphology and roughness was evaluated by SEM and laser microscopy, and the corrosion protection effect was investigated by EIS in an immersion period of 21 d. Local electrochemical impedance spectra (LEIS) was used to characterize the corrosion development process in micro-corrosion sites. The corrosion product of the scratched area after salt spray exposure was analyzed by EDS and Raman spectroscopy. The corrosion protection mechanism of the CaAl-LDH loaded with nitrites was proposed based on the above experimental results.

Antibiotics are considered a new type of organic pollutant. Antibiotic residues have become a global issue due to their harm to human health. As the use of antibiotics is increasing in human life, such as in medicine, crops, livestock, and even drinking water, the accurate analysis of antibiotics is very vital. In order to develop rapid and on-site approaches for the detection of antibiotics and the analysis of trace-level residual antibiotics, a high-sensitivity, simple, and portable solution is required. Meanwhile, the rapid nanotechnology development of a variety of nanomaterials has been achieved. In this review, nanomaterial-based techniques for antibiotic detection are discussed, and some reports that have employed combined nanomaterials with optical techniques or electrochemical techniques are highlighted.

The positive influence of chloride adsorption on the enhanced protection effect was always emphasized in the published literature. The concrete contribution of chloride adsorption and physical barrier effect of LDH in coatings still remains unclear at present. This work was aimed at exploring the significance of the chloride adsorption role of LDH in the corrosion protection of epoxy coatings. The synthesized LDH samples were characterized by scanning electronic microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to show the influence of different parameters on its morphology, structure and composition, respectively. The corrosion-electrochemical behavior was investigated using electrochemical impedance spectroscopy (EIS) and salt spray test. It was found that although CaAl-LDH presented a lower chloride adsorption ability in comparison with other samples; it showed effective corrosion protection due to the higher physical barrier effect of CaAl-LDH with typically hexagonal and plate-like morphology due to good compatibility with the epoxy coatings. The results indicated that the corrosion protection effect of the incorporated LDH was more closely related to its physical barrier role rather than the role of the chloride adsorption, which was misunderstood in the previous publications. This work clarified the contribution comparison of the chloride adsorption and physical barrier of LDH in epoxy coating corrosion protection for the first time.

In recent years, layered double hydroxide (LDH) has attracted extensive attention of researchers in the field of corrosion protection due to its unique structure and anion exchange characteristics. However, its chloride adsorption capacity remains to be further optimized to increase its corrosion protection ability. In this work, the influence of reactant concentration on the prepared MgAl-LDH intercalated with nitrates was investigated, and the morphology, composition, and structure were characterized by scanning electronic microscopy/energy dispersive spectrometer (SEM/EDS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), respectively. The results indicate that the reactant concentration did not have an obvious influence on the particle size and morphology of LDH, while the composition and crystalline structure were changed to some extent. The corresponding reasons were interpreted deeply. The chloride absorption behavior was investigated, and the powder after immersion in NaCl solutions with different concentrations was characterized by XRD to explain the difference in chloride adsorption amounts. The MgAl-LDH powder synthesized at higher concentrations presented excellent chloride adsorption ability with a Qm value of 155.88 mg/g, which was much better than that reported in the literature. This work demonstrated the superior chloride adsorption of the synthesized MgAl-LDH, and it is of great significance for providing a solid foundation and guidance for the industrial application of LDH in the field of corrosion protection in the future.