• Nano
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• v.13 no.10
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• pp.1850118.1-1850118.17
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• 2018

Nanoparticles of the semiconductor catalyst $Cd_xZn_{1-x}S$ were embedded into the metal organic framework MIL-101(Cr) to obtain $Cd_xZn_{1-x}S@MIL-101$(Cr) nanocomposites. These materials not only possess high surface areas and mesopores but also show good utilization of light energy. The ultraviolet-visible diffuse reflectance patterns of $Cd_xZn_{1-x}S@MIL-101$(Cr) nanocomposites showed that $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) possessed good visible light response ability among the synthesized nanocomposites. The photocatalytic performance of the $Cd_xZn_{1-x}S@MIL-101$(Cr) nanocomposites were tested via degradation and mineralization of methylene blue in neutral water solution under light irradiation using a 300W xenon lamp. As a result, using $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) as a catalyst, 99.2% of methylene blue was mineralized within 30 min. Due to the synergistic effect of adsorption by the MIL-101(Cr) component and photocatalytic degradation provided by the $Cd_{0.8}Zn_{0.2}S$ component, the $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) catalyst displayed superior photocatalytic performance relative to $Cd_{0.8}Zn_{0.2}S$ and MIL-101(Cr). Furthermore, $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) possessed excellent stability during photodegradation and exhibited good reusability. The remarkable photocatalytic performance of $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) is likely due to the effective transfer of electrons and holes at the heterojunction interfaces.

• Korean Journal of Chemical Engineering
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• v.35 no.11
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• pp.2283-2289
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• 2018

$TiO_2$ microspheres were successfully synthesised by simple solution phase method by using various amount of titanium butoxide as precursor. The prepared $TiO_2$ were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance absorption spectra (UV-DRS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XRD analysis revealed that the as-synthesized $TiO_2$ microsphere poses an anatase phase. The photocatalytic degradation experiments were carried out with three different dyes, such as methylene blue, brilliant black, reactive red-120 for four hours under UV light irradiation. The results show that $TiO_2$ morphology had great influence on photocatalytic degradation of organic dyes. The experimental results of dye mineralization indicated the concentration was reduced by a high portion of up to 99% within 4 hours. On the basis of various characterization of the photocatalysts, the reactions involved to explain the photocatalytic activity enhancement due to the concentration of titanium butoxide and morphology include a better separation of photogenerated charge carriers and improved oxygen reduction inducing a higher extent of degradation of aromatics.

• Current Applied Physics
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• v.18 no.11
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• pp.1422-1425
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• 2018

$NaTa_{1-x}Fe_xO_3$ ($0{\leq}x{\leq}0.40$) nanocubes were synthesized by a relatively low temperature hydrothermal method, using $Ta_2O_5$, $FeCl_3$ and NaOH as the precursors. The UV-vis diffuse reflectance spectra showed that $NaTa_{1-x}Fe_xO_3$ had significant visible-light-absorbing capability, and the absorption edge of $NaTaO_3$ shifted to longer wavelength with the increase of Fe dopants. Moreover, $NaTa_{1-x}Fe_xO_3$ exhibited room-temperature ferromagnetism when $Fe^{3+}$ occupied $Ta^{5+}$ sites in $NaTaO_3$ crystal lattice. The ferromagnetism is mainly attributed to the superexchange interactions between doped $Fe^{3+}$, rather than the contribution of oxygen vacancies caused by Fe doping. Therefore, Fe doping can simultaneously regulate the optical and magnetic properties of $NaTaO_3$ semiconductor, which will enable its potential applications in multifunctional optical-electronics and opticalspintronics devices.

• Analytical Science and Technology
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• v.18 no.2
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• pp.139-146
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• 2005

Removal of NO contained in automobile exhaust gas was accomplished by the non-selective catalyst reduction method. The catalysts were prepared through loading of a specific amount of Ag into ${\gamma}-Al_2O_3$. The conversion of $NO_x$ was studied by varying the temperatures, $O_2$ concentrations and $SO_2$ concentrations for the prepared catalysts. The influence of the structure of catalyst to $NO_x$ conversion was followed through the analysis of the physical properties of the prepared catalysts. Experiments were conducted on each of the catalysts by varying the reaction conditions to find an optimum condition. The catalyst $Ag/{\gamma}-Al_2O_3$ shows a highest $NO_x$ conversion when the Ag content was 2 wt% and a reaction temperature of about $450^{\circ}C$. and after conducting the experiments, samples of before and after experiments analyzed using XRD, XPS, TPR, and UV-Vis DRS experiments. The result indicated that when Ag oxide content could not be maintained well at high temperatures $NO_x$ conversion decreased.

• Korean Chemical Engineering Research
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• v.51 no.2
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• pp.195-202
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• 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 Korean Chemical Society
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• v.51 no.3
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• pp.265-269
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• 2007

A comparative study on crystal structures and UV-visible diffuse reflectance spectra for Nb-containing oxyfluorides was performed to probe the relationship between energy band gap and local structure. The oxyfluorides, RbSrNb2O6F, RbCaNb2O6F and RbNb2O5F are commonly composed of the corner-sharing NbO5F octahedra as structural building units. The average Nb-O(F)-Nb bond angles, which can be a measure of the structural distortion, are 158.6° for RbSrNb2O6F, 149.6° for RbCaNb2O6F and 139.5° for RbNb2O5F. As the bond angle decreases, the band gap increases: 3.48eV for RbSrNb2O6F, 3.75eV for RbCaNb2O6F and 4.03 eV for RbNb2O5F. This experimental result implies that the band gap can be controlled with a range of 0.6 eV through a variation of local structure for the Nb-containing oxyfluorides.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.107-120
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• 2011

Several MODIS AQUA products have been compared with shipboard data to assess the possibility of using remote sensing to estimate particulate organic carbon (POC) concentration in the surface waters of the East Sea. A total of 30 POC profiles obtained in spring and summer seasons of the years of 2006~2010 were compared with remote sensing reflectance at various wavelengths and diffuse attenuation coefficient at 490 nm observed by MODIS AQUA. The algorithm thus established was $POC=266.85^*[R_{rs}(488)/R_{rs}(555)]^{-1.447}$ ($R^2=0.924$) with root mean square error of 20.9 mg $m^{-3}$. Remotely sensed POC contents derived using our algorithm appeared also not to be affected by the presence of non-POC component in suspended particulate matter. Therefore this algorithm could be applied to obtain POC concentration over the East Sea using MODIS Aqua observation.

• Applied Chemistry for Engineering
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• v.16 no.3
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• pp.328-336
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• 2005

In order to remove the NO contained in exhaust gas by the non-selective catalyst reduction method, the catalysts were prepared by varing the loading amount of Ag and V into ${\gamma}-Al_2O_3$. The conversion of $NO_x$ using the prepared catalysts was studied by varying the temperatures, $O_2$ concentrations and $SO_2$ concentrations using. The influence of the catalyst structure on $NO_x$ conversion was studied through the analysis of the physical properties of the prepared catalysts. In the case of $AgV/{\gamma}-Al_2O_3$ catalyst, the $NO_x$ conversion was lower than that of $Ag/{\gamma}-Al_2O_3$ at higher temperatures but higher than that of $Ag/{\gamma}-Al_2O_3$ at lower temperatures. Even though $SO_2$ was contained in the reaction gas, the $NO_x$ conversion did not decrease. Based on the analysis including XRD, XPS, TPR, and UV-Vis DRS before and after the experiments, the experimental results were examined. The results indicated that, $NO_x$ conversion decreased at higher temperatures since Ag oxide could not be maintained well due to the addition of V, whereas it increased at temperatures lower than $300^{\circ}C$ due to the catalytic action of V.

• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.2
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• pp.48-55
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• 2011

Solar radiation components reflected by the sea surface ($R_{ss}\uparrow$) are additional energy sources comprising the solar radiation regime. Previous studies, based on observational approaches, indicated that $R_{ss}\uparrow$ is an available climatological resource. However, an estimation process for $R_{ss}\uparrow$ has not been established. In this case study over Jeju Island in South Korea, we applied a new estimation process to solar radiation modeling and discussed the spatial distribution of $R_{ss}\uparrow$ and its seasonal variation. Our results showed that the illuminated area and the intensity of $R_{ss}\uparrow$ became greatest at the winter solstice and least at the summer solstice. We estimated the illuminated area of $R_{ss}\uparrow$ as it expanded over the southern slope of Jeju Island. At the winter solstice, on a daily basis, the area and intensity of illumination by $R_{ss}\uparrow$ were $182.3km^2$ and $0.41\;MJ\;m^{-2}\;day\;{-1}$, respectively. Comparing the daily accumulative and instantaneous values of $R_{ss}\uparrow$ intensity, the difference was about 20 times greater in daily cases than in instantaneous cases. On the other hand, for instantaneous values, the $R_{ss}\uparrow$ intensity accounted for up to 33% of the three components, i.e., direct, diffuse and reflected radiation in winter solstice. In addition, it was estimated that the sea surface reflectance depended on the wind speed. Therefore, in a practical use of this revised model, wind conditions should be considered as a critical factor in estimating $R_{ss}\uparrow$.

• Clean Technology
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• v.26 no.1
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• pp.7-12
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• 2020

Ti-SBA-15 catalysts doped with lanthanide ions (Ln/Ti-SBA-15) were successfully synthesized using conventional hydrothermal method. In addition, they were characterized by XRD, FT-IR, DRS, BET, and PL. The activity of these materials on the photocatalytic decomposition of methylene blue under ultraviolet light irradiation was also examined. Ti-SBA-15 catalysts doped with various lanthanide ions maintained their mesoporous structure. The pore size and pore volume of Ln/Ti-SBA-15 materials decreased but their surface area increased upon the doping of lanthanide ion. Ln/Ti-SBA-15 materials exhibited the type IV nitrogen isotherm with desorption hysteresis loop type H2, which was characteristic of mesoporous materials. The size of hysteresis increased in the doping of lanthanide ions on Ti-SBA-15 material. There was no absorption in the visible region (> 400 nm) regardless of the doping of lanthanide ions to TiO₂ particles, while the broad bands at 220 nm appeared at the Ln/Ti-SBA-15 samples, indicating the framework incorporation of titanium into SBA-15. 1 mol% Pr/ Ti-SBA-15 catalysts showed the highest photocatalytic activity on the decomposition of methylene blue but the Ti-SBA-15 catalysts doped with Eu, Er, and Nd ions showed lower activity compared to pure Ti-SBA-15 catalyst. The PL peaks appeared at about 410 nm at all catalysts while the excitonic PL signal was proportional to the photocatalytic activity for the decomposition of methylene blue.