• Journal of Powder Materials
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• v.28 no.6
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• pp.470-477
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• 2021

Energy storage systems should address issues such as power fluctuations and rapid charge-discharge; to meet this requirement, CoFe₂O₄ (CFO) spinel nanoparticles with a suitable electrical conductivity and various redox states are synthesized and used as electrode materials for supercapacitors. In particular, CFO electrodes combined with carbon nanofibers (CNFs) can provide long-term cycling stability by fabricating binder-free three-dimensional electrodes. In this study, CFO-decorated CNFs are prepared by electrospinning and a low-cost hydrothermal method. The effects of heat treatment, such as the activation of CNFs (ACNFs) and calcination of CFO-decorated CNFs (C-CFO/ACNFs), are investigated. The C-CFO/ACNF electrode exhibits a high specific capacitance of 142.9 F/g at a scan rate of 5 mV/s and superior rate capability of 77.6% capacitance retention at a high scan rate of 500 mV/s. This electrode also achieves the lowest charge transfer resistance of 0.0063 Ω and excellent cycling stability (93.5% retention after 5,000 cycles) because of the improved ion conductivity by pathway formation and structural stability. The results of our work are expected to open a new route for manufacturing hybrid capacitor electrodes containing the C-CFO/ACNF electrode that can be easily prepared with a low-cost and simple process with enhanced electrochemical performance.

• Journal of Electrochemical Science and Technology
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• v.14 no.3
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• pp.252-261
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• 2023

Glucose detection is particularly important for clinical diagnosis and personal prevention and control. Herein, the smartphone-based amperometric glucose sensors were constructed using the NiS/CuS nanorods (NRs) as sensing electrodes. The NiS/CuS NRs were prepared through a facile hydrothermal process accompanied by the subsequent vulcanization treatment. The morphological and structural properties of NiS/CuS NRs were characterized with SEM, EDS, XRD, and XPS. Electrochemical measurements including cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy display that NiS/CuS NRs can act as highly efficient electrocatalyst for glucose detection. The NiS/CuS NRs electrodes present a wide detection range of 1-8000 µM for glucose sensing with the sensitivity of 956.38 µA·mM^-1·cm^-2. The detection limit was 0.35 µM (S/N=3). When employed in smartphone-based glucose sensing device, they also display a high sensitivity of 738.09 µA·mM^-1·cm^-2 and low detection limit of 1.67 µM. Moreover, the smartphone-based glucose sensing device also presents favorable feasibility in determination of glucose in serum samples with the recoveries ranging between 99.5 and 105.8%. The results may provide a promising viewpoint to design other new portable glucose sensors.

• Applied Chemistry for Engineering
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• v.34 no.2
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• pp.199-205
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• 2023

Arsenic is a highly toxic element, and its contamination is widespread around the world. The natural materials with high selectivity and efficiency toward pollutants are important in wastewater treatment technology. In this study, the mesoporous synthetic hectorite was synthesized by facile hydrothermal crystallization of gels comprising silica, magnesium hydroxide, and lithium fluoride. Additionally, the naturally available clay was modified using zirconium at room temperature. Both synthetic and modified natural clays were employed in the removal of arsenate from aquatic environments. The materials were fully characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform-infrared (FT-IR) analyses. The synthesized materials were used to remove arsenic (V) under varied physicochemical conditions. Both materials, i.e., Zr-bentonite and Zr-hectorite, showed high percentage removal of arsenic (V) at lower pH, and the efficiency decreased in an alkaline medium. The equilibrium-state sorption data agrees well with the Langmuir and Freundlich adsorption isotherms, and the maximum sorption capacity is found to be 4.608 and 2.207 mg/g for Zr-bentonite and Zr-hectorite, respectively. The kinetic data fits well with the pseudo-second order kinetic model. Furthermore, the effect of the background electrolytes study indicated that arsenic (V) is specifically sorbed at the surface of these two nanocomposites. This study demonstrated that zirconium intercalated synthetic hectorite as well as zirconium modified natural clays are effective and efficient materials for the selective removal of arsenic (V) from aqueous medium.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1B
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• pp.91-96
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• 2009

Layered double hydroxide is synthesized and used in the arsenate adsorption experiments. The shapes of two materials analyzed by TEM showed that unheated material is amorphous in shape, micro-sized while heat treated material showed more crystallized in shape and nano-sized. X-ray diffraction showed this result more obvious. $N_2$ adsorption-desorption results showed that the materials are mesoporous and the specific surface area of the heated material is more than two times larger than the unheated material. Adsorption of As(V) is expected to be more in the heated material than the unheated material. Kinetic test of arsenate adsorption showed very fast reaction. The reactivity of Fe with As(V) might be the main factor for this result. The reaction kinetic of the heated and the unheated materials were similar and even the adsorption isotherms showed similar results for both materials. Both materials are found to be useful in remediation of soil and groundwater polluted by waste mine tailings consist of high concentration of As(V).

• Economic and Environmental Geology
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• v.52 no.6
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• pp.509-517
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• 2019

The birnessite (7Å manganate, δ-MnO₂) which is a manganese oxide and comprises manganese nodules, is a major manganese mineral on the earth surface and a precursor in the synthesis of todorokite. In this study birnessite was synthesized by three different methods: Feng et al. (2004) and Luo et al. (1998) based on redox reaction and Ma et al. (1999) based on reduction reaction. 12 birnessite samples were synthesized by different combinations of Na⁺ and K⁺ cations based on the base (OH^-) and permanganate (MnO₄^-) reagents in the synthesis. The mineral compositions of synthesized birnessite were identified by XRD, and the two cation ratio in the mineral was measured by ICP. The products obtained after hydrothermal treatment of Mg-buserite, by the precursor of birnessite, was examined by XRD, and then phase transition to todorokite and their characteristics were compared. Our results show that the byproducts and the characteristics of phase transition by each synthetic method have different trends. Hausmannite (γ-Mn₃O₄) and feitknechtite (β-MnOOH) were formed by both methods in the redox reaction mechanism. By Feng et al. (2004)'s method, manganite (γ-MnOOH) phase only appeared when cation was predominantly Na⁺. Two birnessite samples synthesized by redox reaction mechanism showed phase transition to todorokite (10Å manganate, OMS-1) when both NaOH and KMnO₄ were used together. However, single-phase birnessite was formed by Ma et al. (1999)'s method, and phase transition was confirmed only for the sample when the cation was only composed of Na⁺.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.6
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• pp.659-665
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• 2008

This study is about zeolite synthesis from the sewage sludge incinerator fly ash of "S" sewage treatment center located in Seoul. For this purpose, the properties of raw fly ash as starting material, the hydrothermal conditions for zeolite synthesis and the environmental applicabilities of synthesized zeolites were examined. Fly ash from sewage sludge incinerator has large quantities of SiO$_2$ and Al$_2$O$_3$ and their contents are 42.8 wt.% and 21.2 wt.% respectively. So fly ash is considered to be possible starting material for zeolite synthesis. The results from leaching test of fly ash showed that the concentration of hazardous metals were very low as compared with the Korea leaching standard of the Waste Management Law. But the concentration from total recoverable test of fly ash were higher than the fertilizer standard of Fertilizer Management Law. Major zeolite products synthesized by hydrothermal reaction are analcime in teflon vessel and zeolite P1 in borosilicate flask. Optimum conditions for the synthesis of analcime were 1 N of NaOH concentration, 16 hour of reaction time and 135$^{\circ}C$ of reaction temperature. For the zeolite P1 formation, the proper conditions were demonstrated to be 5 N of NaOH concentration, 16 hour reaction time and 130$^{\circ}C$ of reaction temperature in this study. Hazardous metal contents in the analcime product are similar with those in raw fly ash. In case of the zeolite P1, the contents are reduced to nearly a half. Raw fly ash and the analcime product showed NH$_4{^+}$ ion exchange capacity of 0$\sim$1.0 mg of NH$_4{^+}$g$^{-1}$ and 3.0$\sim$7.4 mg of NH$_4{^+}$g$^{-1}$, respectively. However, the zeolite P1 product reached exchange capacity to 14.6$\sim$17.8 mg of NH$_4{^+}$g$^{-1}$. This values are in the range of those of natural clinoptilolite and phillipsite. From this point of view, zeolite synthesis from sewage treatment sludge incinerator fly ash is a good alternative for solid waste recycling.

• Korean Chemical Engineering Research
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• v.44 no.2
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• pp.179-186
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• 2006

Two types of $TiO_2$, nanotube and nanoparticle, were used for the mesoporous coatings by doctor blade technique followed by calcining at $450^{\circ}C$. The coatings were used as working materials for dye-sensitized solar cells (DSCs) later on and their photovoltaic characterization was carried out. The nanoparticle was synthesized from hydrogen titanate nanotube by hydrothermal treatment at $180^{\circ}C$ for 24 hr. The solar energy conversion efficiency (${\eta}$) of DSCs prepared by this nanoparticle reached 8.07％ with $V_{OC}$ (open-circuit potential) of 0.81 V, $I_{SC}$ (short-circuit current) of $18.29mV/cm^2$, and FF (fill factor) of 66.95％, respectively. For the preparation of nanotube, the concentration of NaOH solution varied from 3 M to 5 M. In the case of DSCs fabricated with nanotubes from 3 M NaOH solution, the ${\eta}$ reached 6.19％ with $V_{OC}$ of 0.77 V, $I_{SC}$ of $12.41mV/cm^2$, and FF of 64.49％, respectively. On the other hand, in the case of 5 M solution, the photovoltaic ${\eta}$ was decreased with 4.09％ due to a loss of photocarriers. In conclusion, it is demonstrated that the solar energy conversion efficiency of DSCs made from $TiO_2$ nanoparticle showed best results among those under investigation.

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.2
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• pp.192-197
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• 2017

Objective: The study was conducted to evaluate the stability of commercial coated lipase (CT-LIP) in vitro. Methods: The capsules were tested under different conditions with a range of temperature, pH, dry heat treatment and steaming treatment, simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) in this work, respectively. Free lipase (uncoated lipase, UC-LIP) was the control group. Lipase relative activities measured in various treatments were used as a reference frame to characterize the stability. Results: The lipase activities were decreased with increasing temperatures (p<0.05), and there was a markedly decline (p<0.01) in lipase comparative activities of UC-LIP at $80^{\circ}C$ compared with CT-LIP group. Higher relative activities of lipase were observed in CT-LIP group compared with the free one under acidic ambient (pH 3 to 7) and an alkaline medium (pH 8 to 12). Residual lipase activities of CT-LIP group were increased (p<0.05) by 5.67% and 35.60% in dry heat and hydrothermal treatments, respectively. The lipase relative activity profile of CT-LIP was raised at first and dropped subsequently (p<0.05) compared with constantly reduced tendency of UC-LIP exposed to both SGF and SIF. Conclusion: The results suggest that the CT-LIP possesses relatively higher stability in comparison with the UC-LIP in vitro. The CT-LIP could retain the potential property to provide sustained release of lipase and thus improved its bioavailability in the gastrointestinal tract.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.3
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• pp.31-35
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• 2014

$TiO_2$-nanoparticle-dispersed silicone was applied to a LED package and the light efficiency of the LED package was evaluated in this study. The addition of $TiO_2$ nanoparticles in silicone increased refractive index, which improved the light efficiency of the LED package. The $TiO_2$ nanoparticles were fabricated by hydrothermal synthesis and were dispsersed by a vinyl silane coating treatment. After the silane treatment, the $TiO_2$ nanoparticles dispersed with diameters of 10~40 nm but rod-shape $TiO_2$ nanoparticles with lengths of 100 nm were also observed. The refractive index increased with the $TiO_2$ concentration in silicone, while the transmittance decreased with the $TiO_2$ concentration. The light efficient of the LED package with $TiO_2$+silicone encapsulant was higher than that of the LED package with no $TiO_2$ in silicone encapsulant.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.556-571
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• 2004

Statement of problem: Surface texture of the implant is one of the important factors of the implant success, especially in the immediate implant loading. Many methods of the surface treatment of implant have developed and introduced. Purpose : This study was to evaluate the effects of the Ca-P coating implant crystallized the hydroxyapatite on the surface by the removal torque test and the histomorphometric analysis in vivo. Material and methods: 135 screw type implants, 4.0mm in length and 3.75mm in diameter were used in this study. Implants were divided into 3 groups and treated in the different mothods. Group I was not treated, Group II was treated in the SLA method, and Group III was treated in the Ca-P coating with the anodizing method and the hydroxyapatite was crystallized on the surface with the hydrothermal treatment. Firstly, the surface roughness of each group was measured, 45 rabbits were used in this experiment. Two implants were inserted on right tibial metaphysis and one implant was inserted on left side with the alternating order. After the healing periods of 3, 5, and 12 weeks, the rabbits were sacrificed to evaluate the osseointergration by the removal torque test and the histomorphometric analysis. Results : 1. In the analysis for the surface roughness, Group II showed the highest roughness. And Group III showed higher secondly. There was a significant difference one another statistically 2. In the removal torque test, Group III and II were significantly higher than Group I. There was no statistical difference between Group III and Group II. 3. For all Groups, the removal torque values at 12th week were significantly higher than at 3rd and 5th week. 4. In histomorphometric analysis, the bone implant contact rates of Group III and II were higher than that of Group I at 3rd and 5th week. There was a significant difference at 5th week. 5. In histomorphometric analysis, the bone implant contact rate of Group III and II increased from 3rd week to 5th week, but decreased at 12th week. In Group I, the contact rate at 12th week was significantly higher than at 3rd week and 5th week.