• Membrane Journal
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• v.31 no.6
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• pp.417-425
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• 2021

As the demand for high-capacity batteries increases, there has been growing researches on the lithium metal anode with a capacity (3,860 mAh/g) of higher than that of conventional one and a low electrochemical potential (-3.040 V). In this study, using the anatase phased TiO₂ nanoparticles synthesized by hydrothermal synthesis, a PVdF-HFP/TiO₂ organic/inorganic composite material was designed and used as an interfacial protective layer for a Li metal anode. As-formed organic/inorganic-lithium composite thin film was confirmed through the crystalline structure and morphological analyses. In addition, the electrochemical test (cycle stability and voltage profile) confirmed that the protective layer of PVdF-HFP/TiO₂ composite (10 wt% TiO₂ and 1.1 ㎛ film thickness) contributed to the enhanced electrochemical performance of the lithium metal anode (Colombic efficiency retention: 90% for 77 cycles). Based on comparative test with the untreated lithium electrode, it was confirmed that our protective layer plays an important role to stabilize/improve the EC performance of the lithium metal negative electrode.

• Journal of the Mineralogical Society of Korea
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• v.10 no.2
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• pp.126-138
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• 1997

Serpentinite of the Yesan-Gongju-Cheongyang area has been formed by serpentinization of ultramafic rocks. The ultramafic rock might be composed mainly of oilvine with minor pyroxene and amphibole. Olivine has a considerably restricted chemical compositional ranging from Fo90 to Fo93. Fresh serpentinite containing large amount of oilvine is usually massive in occurrence and dark green to black in color. Serpentine minerals occur not only as major mineral of serpentinite, but also as remnants in the talc ore which was formed from serpentinite. XRD study indicates that antigorie is the most abundant serpentine mineral of the serpentinite. Serpentinite consisting of antigorite usually shows non-pseudomorphic texture, whereas that consisting of lizardite shows pseudomorphic texture. Antigorite is found along the margins or fractures of olivine grains resulting in the formation of network of magnetite which was formed at the time of serpentinization. Lizardite, subordinate constituent mineral of serpentinite, frequently shows pseudomorphic mesh-texture after olivine. The chemical differences between antigorite and lizardite/chrysotile are small, so both minerals are not easily discernible with the electron microprobe. Antigorite occuers as elongate blades, flakes, or plates forming interpenetrating texture to obliterate previous textures. SEM study also shows that most serpentine minerals occur in platy or tabular form rather than in asbestiform. Fractures formed after main serpentinization are observed within the pseudomorphic central olivine grain. Careful observation of the serpentine pseudomorphs gives a great deal of data on the pre-serpentinization nature of the serpentine pseudomorphs gives a great deal of data on the pre-serpentinization nature of the ultramafic rocks. It is inferred that the serpentinization took place after the emplacement of ultramafic body into the relatively wet environment ceased and the cooling intrusive body crossed into the stability field of serpentine. It is inferred that the final pervasive serpentinization took place over a long time, by hydrothermal water supplied through the fracture system produced during emplacement of ultramafic rock.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.463-472
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• 1997

A mesoporous molecular sieve, MCM-41, was synthesized and the effent of various initial pH of reaction mixtures on the synthesis and physical properties of MCM-41 was investigated. Adjustment of initial pH for reaction mixtures was made before starting hydrothermal reaction rather than during the reaction. Highly crystalline MCM-41 which shows pore diameters of $30{\AA}$ to $40{\AA}$ and specific surface areas greater than $1000m^2/g$ has been successfully prepared through a single adjustment of initial pH. Results also suggest that the initial pH adjustment has a significant effect on the formation of MCM-41 with a long-range ordered hexagonal array and an excellent thermal stability. Finally, it is speculated that the adjustment of initial pH might accelerate the dissolution of stable polymeric sodium silicate to highly reactive monomeric sodium silicate resulting in well-ordered MCM-41.

• Korean Chemical Engineering Research
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• v.56 no.3
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• pp.404-409
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• 2018

The integration of organic and inorganic building blocks into hierarchical porous architectures makes potentially desirable catalytic material in many catalytic applications due to their combination of dissimilar components and well-constructed reactant transport path. In this study, we prepared the hierarchical porous $Co_3O_4@graphene$ 3D gel by hydrothermal method to achieve high catalytic performance in PET glycolysis reaction. Obtained $Co_3O_4@graphene$ 3D gel consisted of interconnected networks of $Co_3O_4$ and graphene sheets, providing large number of accessible active sites for efficient catalytic reaction. These structural merits from synergistic effect of $Co_3O_4$ and graphene gave a high performance in the PET degradation reaction giving high conversion yield of BHET, fast degradation rate of PET, and remarkable stability.

• Applied Chemistry for Engineering
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• v.24 no.4
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• pp.391-395
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• 2013

In this study, zinc oxide (ZnO) nano powder, well known as an UV absorbing material, was synthesized with three synthetic conditions by the hydrothermal method. After ZnO nano powder was surface-modified with various silane coupling agents to improve dispersion property, a dispersion sol was prepared with dispersant for 72 h by the ball-milling of surface-modified ZnO nano powder. The dispersion sol, prepared by modifying the surface of the ZnO nano powder with an average size of about 30 nm using 3-chloropropyl trimethoxy silane, showed an excellent dispersion stability with a high UV-shielding and visible trnasparency.

• Journal of Electrochemical Science and Technology
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• v.11 no.1
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• pp.50-59
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• 2020

Birnessite-type manganese dioxide (δ-MnO₂) with hierarchical micro-/mesoporosity was synthesized via sacrificial graphene template approach under mild hydrothermal conditions for the first time. Graphene template was obtained by a surfactant (cetyltrimethylammonium bromide, CTAB) assisted liquid phase exfoliation (LPE) in water. A thin PEDOT:PSS (poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate)) layer was applied to improve electrical conductivity and rate capability of MnO₂. The MnO₂ (535 F g^-1 at 1 A g^-1 and 45 F g^-1 at 10 A g^-1) and MnO₂/PEDOT:PSS nanocomposite (550 F g^-1 at 1 A g^-1 and 141 F g^-1 at 10 A g^-1) delivered electrochemical performances superior to their previously reported counterparts. An asymmetric supercapacitor, composed of MnO₂/PEDOT:PSS (positive) and Fe₃O₄/Carbon (negative) electrodes, provided a maximum specific energy of 18 Wh kg^-1 and a maximum specific power of 4.5 kW kg^-1 (ΔV= 2 V, 1M Na₂SO₄) with 85% capacitance retention after 1000 cycles. The graphene-templated MnO₂/PEDOT:PSS nanocomposite obtained by a simple and green approach promises for future energy storage applications with its remarkable capacitance, rate performance and cycling stability

• Membrane Journal
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• v.27 no.6
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• pp.469-476
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• 2017

Membrane separation is a technology of low energy consumption. Membranes made of zeolites are of great interest because their fixed and open pores in the size of small molecules inside crystalline structures allow separation processes under harsh conditions. While zeolite NaA (LTA-type) is industrially used for dewatering of organic solvents, its pore size and thermal and hydrothermal stability can be tuned by exchange of framework and extra-framework elements. SOD with pores of only 0.28 nm is of great interest for $H_2$- und $H_2O$-separation and also can be tuned by ion exchange. Zeolites open the opportunity to create membranes of adapted separation behavior for small molecules in conditions of surrounding technical processes.

• Korean Journal of Materials Research
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• v.31 no.6
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• pp.345-352
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• 2021

In this study, Ni nanoparticle supported by graphene oxide (GO) (Ni-GO) is successfully synthesized through hydrothermal synthesis and calcination, and Cr(VI) is extracted from aqueous solution. The morphology and structure of Ni-GO composites are characterized by scanning electron microscopy (SEM), trans mission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HRTEM) and XRD confirms the high dispersion of Ni nanoparticle after support by GO. Loading Ni on GO can obviously enhance the stability of Ni-GO composites. It can be calculated from TGA that the mass percentage of Ni is about 60.67 %. The effects of initial pH and reaction time on Cr(VI) removal ability of Ni-GO are investigated. The results indicate that the removal efficiency of Cr(VI) is greater than that of bared GO. Ni-GO shows fast removal capacity for Cr(VI) (<25 min) with high removal efficiency. Dynamic experiments show that the removal process conforms to the quasi-second order model of adsorption, which indicates that the rate control step of the removal process is chemical adsorption. The removal capacity increases with the increase of temperature, indicating that the reaction of Cr(VI) on Ni-GO composites is endothermic and spontaneous. Combined with tests and characterization, the mechanism of Cr(VI) removal by rapidly adsorption on the surface of Ni-GO and reduction by Ni nanoparticle is investigated. The above results show that Ni-GO can be used as a potential remediation agent for Cr(VI)-contaminated groundwater.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.593-600
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• 2021

Herein, a series of g-C₃N₄ modified Bi₂MoO₆ nanocomposites using Bi₂MoO₆ and melamine as original materials are fabricated via sintering process. For presynthesis of Bi₂MoO₆ an ultrasonic-assisted hydrothermal technique is researched. The structure and composition of the nanocomposites are characterized by Raman spectroscopy, X-ray diffraction (XRD), and high-resolution field emission scanning electron microscopy (SEM). The improved photoelectrochemical properties are studied by photocurrent density, EIS, and amperometric i-t curve analysis. It is found that the structure of Bi₂MoO₆ nanoparticles remains intact, with good dispersion status. The as-prepared g-C₃N₄/Bi₂MoO₆ nanocomposites (BMC 5-9) are selected and investigated by SEM analysis, which inhibits special morphology consisting of Bi₂MoO₆ nanoparticles and some g-C₃N₄ nanosheets. The introduction of small sized g-C₃N₄ nanosheets in sample BMC 9 is effective to improve the charge separation and transfer efficiency, resulting in enhancing of the photoelectric behavior of Bi₂MoO₆. The improved photoelectronic behavior of g-C₃N₄/Bi₂MoO₆ may be attributed to enhanced charge separation efficiency, photocurrent stability, and fast electron transport pathways for some energy applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.1
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• pp.10-15
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• 2023

The carbonaceous materials have attracted much attention for utilization of anode materials for lithium-ion batteries. Among them, hollow carbon spheres have great advantages (high specific capacity and good rate capability) to replace currently used graphite anode materials, due to their unique features such as high surface areas, high electrical conductivities, and outstanding chemical and thermal stability. Herein, we have synthesized various sizes of hollow carbon spheres by a facile hardtemplate method and investigated the anode properties for lithium-ion batteries. The obtained hollow carbon spheres have uniform diameters of 350 ~ 600 nm by varying the template condition, and they do not have any cracks after the optimization of the process. Increasing the diameter of hollow carbon spheres decreases their specific capacities, since the larger hollow carbon spheres have more useless spaces inside that could have a disadvantage for lithium storage. The hollow carbon spheres have outstanding rate and cyclic performance, which is originated from the high surface area and high electrical properties of the hollow carbon spheres. Therefore, hollow carbon spheres with smaller diameters are expected to have higher specific capacities, and the noble channel structures through various doping approaches can give the great possibility of high lithium storage properties.