• Korean Journal of Materials Research
• /
• v.28 no.1
• /
• pp.32-37
• /
• 2018

We report on the efficient detection of NO gas by an all-oxide semiconductor p-n heterojunction diode structure comprised of n-type zinc oxide (ZnO) nanorods embedded in p-type copper oxide (CuO) thin film. The CuO thin film/ZnO nanorod heterostructure was fabricated by directly sputtering CuO thin film onto a vertically aligned ZnO nanorod array synthesized via a hydrothemal method. The transport behavior and NO gas sensing properties of the fabricated CuO thin film/ZnO nanorod heterostructure were charcterized and revealed that the oxide semiconductor heterojunction exhibited a definite rectifying diode-like behavior at various temperatures ranging from room temperature to $250^{\circ}C$. The NO gas sensing experiment indicated that the CuO thin film/ZnO nanorod heterostructure had a good sensing performance for the efficient detection of NO gas in the range of 2-14 ppm under the conditions of an applied bias of 2 V and a comparatively low operating temperature of $150^{\circ}C$. The NO gas sensing process in the CuO/ZnO p-n heterostructure is discussed in terms of the electronic band structure.

• Applied Chemistry for Engineering
• /
• v.28 no.5
• /
• pp.521-528
• /
• 2017

To find a recycling method for waste liquid crystal display (LCD) panel glasses, we investigated the synthesis process of zeolite with an ion exchange ability by hydrothermal reaction using waste LCD panel glass as a raw material. It was shown that the waste LCD panel glass can be used as a raw material for the production of zeolites having the ion exchange ability. Following conditions for the synthesis of the zeolite with an ion exchange ability were required : the molar ratio of Si to Al components of the waste LCD glass needs to be 2.0 to 2.8, and the temperature of $100^{\circ}C$ and reaction time of 12 hours are needed for the hydrothermal reaction. Based on the required conditions previously mentioned, the A type zeolite was synthesized when the molar ratio of the Si to Al component was 2.0, and the P type zeolite was produced when the molar ratio was 2.8. The type A zeolite synthesized by using the waste LCD panel glass showed a good ion exchange ability and heavy metal adsorption ability. Also, an excellent ion exchange capacity was observed as the crystal phase grows stably in a cubic phase.

• Korean Chemical Engineering Research
• /
• v.51 no.2
• /
• pp.195-202
• /
• 2013

$TiO_2$ powders were prepared from titanium (IV) sulfate ($Ti(SO_4)_2$) solution using ammonia solution at low reaction temperature ($80{\sim}100^{\circ}C$) and atmospheric pressure by hydrothermal precipitation method without calcination. The effect of reaction conditions, such as reaction temperature, initial concentration of titanium (IV) sulfate ($Ti(SO_4)_2$) solution, pH of mixture solution and the physical properties of the prepared $TiO_2$, such as crystallite structure, crystallite size were investigated. The photocatalytic activity of prepared $TiO_2$ was tested by the photolysis of brilliant blue FCF (BB-FCF) under the UV and the analysis of UV-VIS diffuse reflectance spectroscopy (DRS). The physical properties of prepared $TiO_2$ were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectrometer (PL), particle size distribution measurements. The crystallite size and crystallinity of prepared $TiO_2$ increased with increasing titanium (IV) sulfate ($Ti(SO_4)_2$) concentration, but photocatalytic activity decreased. The crystallite size decreased with increasing pH of mixture solution, but photocatalytic activity increased. The crystallinity and photocatalytic activity increased with increasing reaction temperature. The results showed that anatase type $TiO_2$ could be prepared by hydrothermal precipitation method using titanium (IV) sulfate ($Ti(SO_4)_2$) solution and ammonia solution at low reaction temperature and atmospheric pressure without calcination.

• Journal of the Mineralogical Society of Korea
• /
• v.15 no.3
• /
• pp.231-240
• /
• 2002

Microbial metal reduction influences the biogeochemical cycles of carbon and metals as well as plays an important role in the bioremediation of metals, radionuclides, and organic contaminants. The use of bacteria to facilitate the production of magnetite nanoparticles and the formation of carbonate minerals may provide new biotechnological processes for material synthesis and carbon sequestration. Metal-reducing bacteria were isolated from a variety of extreme environments, such as deep terrestrial subsurface, deep marine sediments, water near Hydrothemal vents, and alkaline ponds. Metal-reducing bacteria isolated from diverse extreme environments were able to reduce Fe(III), Mn(IV), Cr(VI), Co(III), and U(VI) using short chain fatty acids and/or hydrogen as the electron donors. These bacteria exhibited diverse mineral precipitation capabilities including the formation of magnetite ($Fe_3$$O_4$), siderite ($FeCO_3$), calcite ($CaCO_3$), rhodochrosite ($MnCO_3$), vivianite [$Fe_3$($PO_4$)$_2$ .$8H_2$O], and uraninite ($UO_2$). Geochemical and environmental factors such as atmospheres, chemical milieu, and species of bacteria affected the extent of Fe(III)-reduction as well as the mineralogy and morphology of the crystalline iron mineral phases. Thermophilic bacteria use amorphous Fe(III)-oxyhydroxide plus metals (Co, Cr, Ni) as an electron acceptor and organic carbon as an electron donor to synthesize metal-substituted magnetite. Metal reducing bacteria were capable of $CO_2$conversion Into sparingly soluble carbonate minerals, such as siderite and calcite using amorphous Fe(III)-oxyhydroxide or metal-rich fly ash. These results indicate that microbial Fe(III)-reduction may not only play important roles in iron and carbon biogeochemistry in natural environments, but also be potentially useful f3r the synthesis of submicron-sized ferromagnetic materials.

• Economic and Environmental Geology
• /
• v.21 no.1
• /
• pp.45-56
• /
• 1988

Many hydrothermal skarn-type iron ore deposits inchiding Mulgeum, Yangseong, Maeri and Kimhae mines are distributed in the south-eastern Gyeongnam Province, Korea. The deposits are magnetite veins which occurred in propylitized andesitic rock near the contact with late Cretaceous Masanite. Symmetrical zoned skarns are commonly developed around the magnetite veins. The order of the skarn zones from the vein is garnet-quartz skarn, epidote skarn, and epidote-orthoclase skarn. The garnets include isotropic or anisotropic andradite($Ad_{100{\sim}70}$), and the epidotes are composed of pistacite($Ps_{21-31}$). Fe contents of the epidotes generally increase toward the magnetite veins. Epidotes and garnets often show compositional variations from grain to grain, that is, their Fe and Al contents vary inversely. This suggests that the variations depend mainly upon $fo_2$ during the skarnization. Oxygen and carbon isotope analyses of minerals from andesitic rock, micrographic granite, major skarn zones and post-mineralization zones were conducted to provide the information on the formation temperature, the origin and the evolution of the hydrothermal solution forming the iron ore deposits. Becoming more distant from the ore vein, temperatures of skarn zones represent the decreasing tendency, but most ${\delta}O^{18}$ and ${\delta}O^{18}_{H_2O}$ values of skarn minerals represent no variation trend, and also the values are relatively low. Judging from all the isotopic data from the ore deposits, the major source of hydrothemal solution altering the skarn zones and precipitating the ore bodies was magmatic water derived from the more deeply seated micrographic granite. This high temperature hydrothermal solution rising through the fissures of propylitized andesitic rock was mixed with some meteoric water, and the extensive isotopic exchange occurred with the propylitized andesitic rock. During this process, the temperature and ${\delta}O^{18}_{H_2O}$ value of hydrothermal solution were lowered gradually. At the stage of iron ore precipitation, because after all the alteration was already finished, the oxygen isotopic exchange with the wall rock was nearly not taken. The relatively high ${\delta}O^{18}$ and ${\delta}O^{18}_{H_2O}$, and relatively low ${\delta}C^{13}$ values of calcites of post mineralization stage, are the results of leaching of the high ${\delta}O^{18}$ chert xenolith in the andesitic rock and low ${\delta}C^{13}$ andesitic rock.

• Journal of the Mineralogical Society of Korea
• /
• v.18 no.2
• /
• pp.109-115
• /
• 2005

Beidellite, a member of the smectite group, was synthesized hydrothermally from dickite. Physical and chemical properties of the synthetic Na-beidellite were characterized by the analytical methods of XRD, IR, TG, DTA, EDS, XRF and ICP. The result of Greene-Kelly test indicates that the synthesized smectite is Na-beidellite. IR spectrum of synthesized beidellite exhibited Al-O-H bending vibration at $818\;cm^{-1}\;and\;770\;cm^{-1}$ which was observed particularly in pure beidellite. TGA analysis revealed that the synthesized Na-beidellite comprises $16\;wt\%$ of water. DTA curve showed an endothermic peak at $117^{\circ}C$ due to dehydration reaction and peaks at $482^{\circ}C$ and $685^{\circ}C$ due to dehydroxylation reaction. The clay mineral was transformed to mullite and cristobalite at the temperature of $1028^{\circ}C$. The CEC value, Methylene Blue test and swelling capacity was determined to be $116\~118\;cmol/kg,\;84\~91\%,\;29\~32\;mL/2g$, respectively. The chemical composition of the synthesized phase was identified as $Na_{0.5}Al_{2.5}Si_{3.5}O_{10}(OH)_2$ from EDS and XRF analyses.

• Journal of the Mineralogical Society of Korea
• /
• v.20 no.1 s.51
• /
• pp.1-6
• /
• 2007

Hectorite was synthesized by a two-step hydrothermal process from $Mg(OH)_{2}$, water glass (${\sim}30\;wt%\;SiO_{2}$) and Li-compound at $90{\pm}5^{\circ}C$. The product shows excellent dispersion and swelling properties. The mixture of the starting materials was heated in a glass vessel for the first reaction with continuous stirring and the pH of the solution was adjusted to $6{\sim}8$, resulting in the formation of a precursor of hectorite. The excess salt components were washed out from the resulting slurry and then was matured in the glass vessel for the 2nd reaction. Li compound was added during the reaction. After a 10 h retention, the gel of hectorite was formed. The XRD pattern of the synthesized one was coincided with that of natural hectorite and SEM study revealed uniform grains 50 m in diameter. The d001 basal spacing of the product moved from 12 to $17.4\;{\AA}$ after glycolation treatment. The measured value of CEC and the swelling capacity was 90 cmol/kg and $60{\sim}70\;mL/2\;g$, respectively.

• Journal of the Korean Electrochemical Society
• /
• v.16 no.3
• /
• pp.151-156
• /
• 2013

As the cathode material for li-ion battery, $LiNi_{0.5}Mn_{0.3}Co_{0.2}O_2$ were synthesized by supercritical hydrothermal method and calcined $850^{\circ}C$ and $900^{\circ}C$ for 10hrs in air. The effect of temperature in the heat treatment on the powder and its performance were studied of xray diffraction pattern, SEM-image, physical properties and electrochemical behaviors. As a result, calcined at $900^{\circ}C$ material particle size more increase than calcined at $850^{\circ}C$ material, especially shows excellent electrochemical performance with initial reversible specific capacity of 163.84 mAh/g (0.1C/2.0-4.3V), 186.87 mAh/g (0.1C/2.0-4.5V) and good capacity retention of 91.49% (0.2C/2.0-4.3V) and 90.36% (0.2C/2.0-4.5V) after 50th charge/discharge cycle.

• Journal of the Korean Applied Science and Technology
• /
• v.36 no.3
• /
• pp.685-699
• /
• 2019

Antioxidant, antibacterial, and skin penetration tests were conducted to investigate the skin absorption of Pyrus serotina var leaf extracts using polymer micelles and their applicability to cosmetic ingredients. Total polyphenol content was found to be $118.83{\pm}9.39mg/g$ in Pyrus serotina var leaf ethanol extract and $106.89{\pm}4.45mg/g$ in Pyrus serotina var leaf hydrothermal extract. The DPPH radical scavenging activity was found to be the highest radical scavenging activity of $74.39{\pm}7.48%$ of the Pyrus serotina var leaf ethanol extract at the concentration of 500 mg/L. The SOD-like activity was $91.62{\pm}0.43%$, the highest value at the concentration of 1,000 mg/L in the hydrothermal extract. After the experiment, antioxidation, wrinkle improvement and whitening activity were confirmed, and the Pyrus serotina var leaf extract was highly likely to be realized as antioxidant and antibacterial material. In the skin penetration experiment with the Pyrus serotina var leaf ethanol extract, the permeation amount of total accumulated tannic acid was found to be Formulation 2 ($55.45{\mu}g/cm^2$), Formulation 1 ($46.43{\mu}g/cm^2$), Formulation 0 ($34.36{\mu}g/cm^2$). In the liposome's skin penetration experiment containing pear leaf hydrothemal extract, the total amount of accumulated tannic acid permeation was found to be Formulation 5 ($75.01{\mu}g/cm^2$), Formulation 4 ($64.01{\mu}g/cm^2$) and Formulation 3 ($36.60{\mu}g/cm^2$). Through this study, we confirmed the possibility of antioxidant and wrinkle effects of Pyrus serotina var leaf extract. In addition, as a result of skin penetration through the production of polymer micelles and liposome containing Pyrus serotina var leaf extract, It will be more usable in cosmetic industry.