• Bulletin of the Korean Chemical Society
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• v.28 no.11
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• pp.2029-2033
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• 2007

Hydrotalcite, layered double hydroxides (LDH), with hexagonal morphology has been rapidly synthesized by microwave reaction within 1 hour by urea hydrolysis from homogeneous solution. Different synthesis parameters, Mg/Al molar ratio, microwave reaction temperature and microwave power were systematically investigated. Pure hydrotalcite phase was obtained for Mg/Al ratios of 2:1 and 3:1, and higher reaction temperature gave higher crystallinity. The hydrotalcite synthesized at 600W power shows the highest crystallinity and more homogeneous crystal size distribution. The hydrotalcite samples were characterized by powder X-ray diffraction (XRD), simultaneous thermogravimetric/differential thermal analysis (TG/DTA), Fourier Transform Infrared (FT-IR) and Scanning electron micrograph (SEM).

• Journal of the Mineralogical Society of Korea
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• v.22 no.4
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• pp.307-312
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• 2009

Motukoreaite and quintinite-3T, Mg-Al layered double hydroxides, were found in the Sinyangri Formation of Jeju Island. They fill the pores of basaltic volcaniclastic sediments in globular and botryoidal aggregates of fine platy particles. Globular aggregates of quintinite-3T were crusted with the parallel overgrowth of motukoreaite plates. X-ray diffraction data and chemical composition are consistent with those reported in literature, while the Mg/Al ratio of motukoreaite is higher. Structural formula of motukoreaite and quintinite-3T derived from electron microprobe analysis are $Na_{1.6}Ca_{0.1}Mg_{40.7}Al_{20.7}Si_{0.9}(CO_3)_{13.6}(SO_4)_{7.4}(OH)_{108}56H_2O$, and $Mg_{3.7}Al_{1.9}Si_{0.2}(OH)_{12}(CO_3)_{0.8}(SO_4)_{0.2}3H_2O$, respectively. Motukoreaite and quintinite-3T were formed by reaction between seawater and basaltic glass, and contributed to the cementation and lithification of the volcaniclastic sediments.

• Economic and Environmental Geology
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• v.57 no.5
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• pp.577-592
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• 2024

This study presents the synthesis and characterization of MgAl-layered double hydroxide (LDH)/rice husk hydrochar (RHH) nanocomposites (MgAl-LDH/RHHs) via an in situ one-pot hydrothermal route at 150 ℃, utilizing Mg:Al molar ratio of 2:1 for arsenic remediation. The formation of MgAl-LDH/RHHs and their physicochemical properties were evaluated under varying hydrothermal aging times systematically. Prolonging the aging period to 12 hrs significantly enhanced the crystallinity and crystal size of the LDHs, resulting in a 3D hierarchical structure with the highest specific surface area (27.98 m²/g) formed on the hydrochar surface. The hexagonal crystal structure (d₀₀₃ = 0.8246 nm) was characterized by a rhombohedral unit cell with lattice parameters a = 0.3049 nm and c = 2.4738 nm, and a high positive charge density of 4.284 e/nm². These properties were found to be favorable for the sorption of arsenic oxyanions. Batch adsorption experiments were conducted to assess the potential of MgAl-LDH/RHHs-12h for the remediation of arsenic-contaminated soils. The original soil sample (CY) was mechanically sieved into fine-grained (CYF, < 75 ㎛) and coarse-grained (CYC, 75 ㎛-2 mm) fractions. When these soil samples were reacted with deionized water, arsenate was identified as the dissolved arsenic species, with concentrations of 2.85 mg/L for CY, 4.02 mg/L for CYF, and 2.55 mg/L for CYC, respectively. Kinetic sorption experiments, conducted at pH 5.0 and 8.0 in the presence and absence of 0.1 M NaCl as a background electrolyte, revealed that arsenic sorption onto MgAl-LDH/RHHs-12h was inhibited at pH 8 in the presence of NaCl. These findings suggest that effective arsenic sorption requires low pH conditions with minimal background electrolytes in soils.

• Membrane Journal
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• v.23 no.2
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• pp.151-158
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• 2013

The effect of layered double hydroxides (LDH) on the gas separation properties of ethylene vinyl acetate copolymer was investigated. Mg-Al LDH/EVA nanocomposite membranes were prepared from solution intercalation using organically modified LDH (DS-LDH). Dodecyl sulfate (DS)-LDH was obtained by the intercalation of DS anion in the interlayer. The nanocomposite structure has been elucidated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). XRD pattern clearly shows that the DS-LDH layers are disorderly well dispersed in the EVA matrix. The maximum tensile strength and elongation of the LDH/EVA nanocomposite membrane were found with the LDH content 3 wt%. The thermal properties of nanocompostie membrane were enhanced by the incorporation of LDH in EVA matrix. Gas permeation of LDH/EVA nanocomposite membranes with LDH contents of 1, 3, 5 wt% was studied for $O_2$ and $CO_2$ single gases. The presence of 3 wt% LDH decreased $O_2$ permeability by up to 53% compared to the EVA membrane. In spite of barrier property of nanocomposite membrane, however, the gas permeability for $CO_2$ was increased due to its strong affinity with the residual OH groups on the LDH.