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Layered double hydroxides (LDHs) can serve as corrosion inhibitor reservoirs. In the present work, hydrotalcite-like LDHs were synthesized and employed as host matrixes for the release of phosphate. The morphological and structural properties of the as-prepared LDH-PO4 were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The PO43- adsorption uptake was successfully confirmed by the XRD results. The corrosion resistance of the coating with LDH-PO4 was investigated by electrochemical impedance spectroscopy (EIS), which was approximately 1 order of magnitude higher than that of the blank coating after immersion for 168 h. Results of the scanning Kelvin probe technique revealed that the potential of LDH-PO4 coating was higher and smoother than that of the blank coating after exposure to 0.5 M NaCl solution. This effect is attributed to the release of PO43− that forms a phosphate protective film in the scratched region. [ABSTRACT FROM AUTHOR]

A controlled release method of antifouling agent was demonstrated via the model coating which was fabricated by sodium paeonolsilate (PAS) intercalated into Zn 2 Al Layered Double hydroxides (LDH) and then dispersed in the mixture of acrylic resin and colophony with weight ratio of 2:1. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of Zn 2 Al-LDH. Some larger particles of Zn 2 Al-PAS-LDH composite in the coating were observed owing to its aggregation, which was revealed by Laser scanning confocal microscope (LSCM). The release tests of the Zn 2 Al-PAS-LDH coating in 3.5% NaCl solution showed that no burst release phenomenon occurred at the beginning stage and a slower release rate of PAS (0.54 ppm/d) was obtained compared with the pristine PAS coating (1.06 ppm/d), exhibiting its preferable controlled release behavior. The adhesion experiment using Ulva zoospores indicated that Zn 2 Al-PAS-LDH composite obviously increases the utilization rate of PAS owing to its controlling release property. Therefore, the present work provided a useful strategy to decrease the waste of antifouling agent and prolong the lifetime of antifouling coatings. [ABSTRACT FROM AUTHOR]

Abstract: A novel optical chemosensor was fabricated based on 1-amino-8-naphthol-3,6-disulfonic acid sodium (H-acid) intercalated layered double hydroxide (LDH) film via the electrophoretic deposition (EPD) method. The film of H-acid/LDH with the thickness of 1μm possesses a well c-orientation of the LDH microcrystals confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fluorescence detection for Hg(II) in aqueous solution was performed by using the H-acid/LDH film sensor at pH 7.0, with a linear response range in 1.0×10−7 to 1.0×10−5 molL−1 and a detection limit of 6.3×10−8 molL−1. Furthermore, it exhibits excellent selectivity for Hg(II) over a large number of competitive cations including alkali, alkaline earth, heavy metal and transitional metals. The specific fluorescence response of the optical sensor is attributed to the coordination between Hg(II) and sulfonic group in the H-acid immobilized in the LDH matrix, which was verified by NMR spectroscopy and UV–vis spectra. In addition, density functional theory (DFT) calculation further confirms that the coordination occurs between one Hg2+ and two O atoms in the sulfonic group, which is responsible for the significant fluorescence quenching of the H-acid/LDH film. The results indicate that the H-acid/LDH composite film can be potentially used as a chemosensor for the detection of Hg2+ in the environmental and biomedical field. [Copyright &y& Elsevier]

Abstract: The inorganic–organic composites have been prepared by intercalation of ammonium 1-anilinonaphthalene-8-sulfonate (ANS) into ZnAl and MgAl layered double hydroxide (LDH) with the molar ratio (M2+/M3+) of 2:1 and 3:1, respectively. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of ANS into the galleries of LDH. Fluorescence polarization method was applied to investigate the preferential orientation of the interlayer ANS molecule, and the results show that ANS anions are accommodated between the sheets of Zn2Al-LDH, Zn3Al-LDH, Mg2Al-LDH and Mg3Al-LDH with an orientation angle Ψ (defined as the angle between the transition moment of ANS molecule with respect to the normal to the LDH layer) of 58°, 57°, 55° and 52°, respectively. TG–DTA results reveal that the thermal stability of ANS was markedly enhanced upon intercalation. Fluorescence spectra demonstrate that the Zn3Al-ANS-LDH sample exhibits the optimal luminous intensity among the four ANS-LDH composites. It was also found that the luminescence behavior of ANS can be modulated via changing the two parameters: the type and ratio of cation species in LDH matrix due to host–guest interactions. Therefore, the ANS-LDH composites can be used as good candidates for solid photoluminescence materials. [Copyright &y& Elsevier]

• A multistage controlled release material of antifouling agent was developed. • The utilization rate of antifouling agent has effectively increased by about 50%. • The coating has a good adhesion inhibition effect on typical fouling organisms. Improving the utilization rate of environmentally friendly antifouling agents is highly important for reducing the economic costs of ship operations and protecting the marine environment. In this work, a new method for preparing a multistage controlled release material of an environmentally friendly antifouling agent, which first incorporates 2-(p-chlorophenyl)-3-cyano-4-bromo-5-trifluoromethyl pyrrole (Econea) into carboxyl-modified β -cyclodextrin (Econea@CMCD) followed by intercalation into Mg 2 Al layered double hydroxides (Mg 2 Al-Econea@CMCD-LDH), was reported. Powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirmed the incorporation of Econea@CMCD into the galleries of Mg 2 Al-LDH. Release tests conducted in 3.5 % NaCl solution demonstrated an initial burst release, followed by a slower release rate of Econea (12.3 µg/cm2·d) compared to that of the pristine Econea coating, indicating favorable controlled release behavior. Adhesion experiments using diatoms and mussels showed that Mg 2 Al-Econea@CMCD-LDH effectively inhibited the adhesion of typical fouling organisms. Hence, this study presents a practical approach for constructing a controlled release system that involves intercalating neutral and insoluble antifouling agents into LDH interlayers, effectively reducing the waste of antifouling agents and extending the service life of antifouling coatings. [ABSTRACT FROM AUTHOR]

Abstract: A novel fluorescent film based on 8-aminonaphthalene-1,3,6-trisulfonate/layered double hydroxide composite (ANTS/LDH) has been synthesized by the electrophoretic deposition (EPD) method, and its application as an optical sensor for Mg2+ is demonstrated. The ANTS/LDH film with a thickness of 2μm exhibits a good c-orientation of LDH platelets, which is confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ANTS/LDH film shows a good fluorescent response for Mg2+ ion. Meanwhile, a linear correlation between the fluorescence intensity of the ANTS/LDH film and the concentration of Mg2+ is obtained (I =0.496+0.0708log c (Mg2+), R 2 =0.996), with a detection limit of 2.37×10−7 M. The results indicate that ANTS/LDH film has a high fluorescence selectivity for Mg2+ ions, with no significant response to other metal ions, including Ca2+, Na+, K+, Fe3+, Co2+, Ni2+, or Cu2+. Furthermore, the ANTS/LDH thin film shows a good reusable ability for Mg2+ by alternately changing the solution of Mg2+ (5.0×10−3 M) and EDTA (8.0×10−2 M), and the relative standard deviation of 8 cycles is calculated as 1.7% (EDTA) and 0.14% (Mg2+). The specific fluorescence response of the film sensor is attributed to the complexation between ANTS and Mg2+, which is verified by 13C solid state NMR spectroscopy. In addition, density functional theory (DFT) calculation confirms that a strong interaction occurs between Mg2+ and ANTS molecule, which is responsible for the significant fluorescence quenching of the ANTS/LDH film. The results indicate that the ANTS/LDH thin film in this work can be used as a chemsensor for the quantitative detection of Mg2+. [Copyright &y& Elsevier]

This paper reports a novel method to prepare the antifouling composites with properties of self-adaptive controlled release (defined as control the release rate autonomously and adaptively according to the change of environmental conditions) by intercalation of sodium paeonolsilate (PAS) into MgAl and ZnAl layered double hydroxide (LDH) with the molar ratio (M 2+ /M 3+ ) of 2:1 and 3:1, respectively. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of LDH. The controlled release behavior triggered by temperature for the PAS-LDH composites has been investigated, and the results show that the release rate of all PAS-LDH composites increases as the increase of temperature. However, the MgAl-PAS-LDH composites (Mg 2 Al-PAS-LDH and Mg 3 Al-PAS-LDH) exhibit the increased release rate of 0.21 ppm/°C from 15 to 30 °C in 3.5% NaCl solution, more than three times of the ZnAl-PAS-LDH composites (0.06 ppm/°C), owing to the confined microenvironment influenced by metal types in LDH layers. In addition, a possible diffusion-controlled process with surface diffusion, bulk diffusion and heterogeneous flat surface diffusion has been revealed via fitting four kinetic equations. Moreover, to verify the practical application of the PAS-LDH composites, a model coating denoted as Mg 2 Al-PAS-LDH coating was fabricated. The release result displays that the release rate increases or decreases as temperature altered at 15 and 25 °C alternately, indicating its self-adaptive controlled release behavior with temperature. Moreover, the superior resistance to the settlement of Ulva spores at 15 and 25 °C was observed for the Mg 2 Al-PAS-LDH coating, as a result of the controllable release of antifoulant. Therefore, this work provides a facile and effective method for the fabrication of antifouling composites with self-adaptive controlled release behavior in response to temperature, which can be used to prolong the lifetime of antifouling coatings. [ABSTRACT FROM AUTHOR]