• Journal of Soil and Groundwater Environment
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• v.20 no.6
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• pp.117-126
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• 2015

Reductive degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by nanoscale zero-valent iron (nZVI) was investigated to evaluate the feasibility of using it for in-situ groundwater remediation. Batch experiments were conducted to quantify the kinetics and efficiency of RDX removal by nZVI, and to determine the effects of pH, dissolved oxygen (DO), and ionic strength on this process. Experimental results showed that the reduction of RDX by nZVI followed pseudo-first order kinetics with the observed rate constant (k_obs) in the range of 0.0056-0.0192 min⁻¹. Column tests were conducted to quantify the removal of RDX by nZVI under real groundwater conditions and evaluate the potential efficacy of nZVI for this purpose in real conditions. In column experiment, RDX removal capacity of nZVI was determined to be 82,500 mg/kg nZVI. pH, oxidation-reduction potential (ORP), and DO concentration varied significantly during the column experiments; the occurrence of these changes suggests that monitoring these quantities may be useful in evaluation of the reactivity of nZVI, because the most critical mechanisms for RDX removal are based on the chemical reduction reactions. These results revealed that nZVI can significantly degrade RDX and that use of nZVI could be an effective method for in-situ remediation of RDX-contaminated groundwater.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

• Applied Biological Chemistry
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• v.46 no.1
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• pp.1-6
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• 2003

Abstract: In order to improve the system for biological nitrogen oxidizing process in sewage and wastewater, a bacterium having high abilities to oxidize of nitrogen was isolated from wastewater and polluted soils. The strain was identified to Bacillus sp. CH-N, based on the physiological and biochemical properties. Characteristics and oxidizing ability of both ammonia and nitrite were examined for the strain, Bacillus sp. CH-N. The strain showed the oxidizing rate about 80% to 90% on the sewage and wastewater after 48 h culture. The nitrogen oxidizing rate was increased in proportion to the initial concentration of glucose. The microorganism, Bacillus sp. CH-N cell immobilized on ceramic carrier were evaluated for the oxidation of ammonia in culture media.

• Journal of Environmental Science International
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• v.20 no.7
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• pp.907-917
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• 2011

This study investigated the application of experimental design methodology to optimization of conditions of air-plasma and oxygen-plasma oxidation of N, N-Dimethyl-4-nitrosoaniline (RNO). The reactions of RNO degradation were described as a function of the parameters of voltage ($X_1$), gas flow rate ($X_2$) and initial RNO concentration ($X_3$) and modeled by the use of the central composite design. In pre-test, RNO degradation of the oxygen-plasma was higher than that of the air-plasma though low voltage and gas flow rate. The application of response surface methodology (RSM) yielded the following regression equation, which is an empirical relationship between the RNO removal efficiency and test variables in a coded unit: RNO removal efficiency (%) = $86.06\;+\;5.00X_1\;+\;14.19X_2\;-\;8.08X_3\;+\;3.63X_1X_2\;-\;7.66X_2^2$ (air-plasma); RNO removal efficiency (%) = $88.06\;+\;4.18X_1\;+\;2.25X_2\;-\;4.91X_3\;+\;2.35X_1X_3\;+\;2.66X_1^2\;+\;1.72X_3^2$ (oxygen-plasma). In analysis of the main effect, air flow rate and initial RNO concentration were most important factor on RNO degradation in air-plasma and oxygen-plasma, respectively. Optimized conditions under specified range were obtained for the highest desirability at voltage 152.37 V, 135.49 V voltage and 5.79 L/min, 2.82 L/min gas flow rate and 25.65 mg/L, 34.94 mg/L initial RNO concentration for air-plasma and oxygen-plasma, respectively.

• Journal of Environmental Health Sciences
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• v.39 no.5
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• pp.391-407
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• 2013

Micropollutants emerge in surface water through untreated discharge from sewage and wastewater treatment plants (STPs and WWTPs). Most micropollutants resist the conventional systems in place at water treatment plants (WTPs) and survive the production of tap water. In particular, pharmaceuticals and endocrine disruptors (ECDs) are micropollutants frequently detected in drinking water. In this review, we summarized the distribution of micropollutants at WTPs and also scrutinized the effectiveness and mechanisms for their removal at each stage of drinking water production. Micropollutants demonstrated clear concentrations in the final effluents of WTPs. Although chronic exposure to micropollutants in drinking water has unclear adverse effects on humans, peer reviews have argued that continuous accumulation in water environments and inappropriate removal at WTPs has the potential to eventually affect human health. Among the available removal mechanisms for micropollutants at WTPs, coagulation alone is unlikely to eliminate the pollutants, but ionized compounds can be adsorbed to natural particles (e.g. clay and colloidal particles) and metal salts in coagulants. Hydrophobicities of micropollutants are a critical factor in adsorption removal using activated carbon. Disinfection can reduce contaminants through oxidation by disinfectants (e.g. ozone, chlorine and ultraviolet light), but unidentified toxic byproducts may result from such treatments. Overall, the persistence of micropollutants in a treatment system is based on the physico-chemical properties of chemicals and the operating conditions of the processes involved. Therefore, monitoring of WTPs and effective elimination process studies for pharmaceuticals and ECDs are required to control micropollutant contamination of drinking water.

• Journal of Environmental Science International
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• v.17 no.11
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• pp.1195-1201
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• 2008

Enhancing with non-metallic elemental nitrogen(N) is one of several methods that have been proposed to modify the electronic properties of bulk titanium dioxide($TiO_2$), in order to make $TiO_2$ effective under visible-light irradiation. Accordingly, current study evaluated the feasibility of applying visible-light-induced $TiO_2$ enhanced with N element to cleanse aromatic compounds, focusing on xylene isomers at indoor air quality(IAQ) levels. The N-enhanced $TiO_2$ was prepared by applying two popular processes, and they were coated by applying two well-known methods. For three o-, m-, and p-xylene, the two coating methods exhibited different photocatalytic oxidation(PCO) efficiencies. Similarly, the two N-doping processes showed different PCO efficiencies. For all three stream flow rates(SFRs), the degradation efficiencies were similar between o-xylene and m,p-xylene. The degradation efficiencies of all target compounds increased as the SFR decreased. The degradation efficiencies determined via a PCO system with N-enhanced visible-light induced $TiO_2$ was somewhat lower than that with ultraviolet(UV)-light induced unmodified $TiO_2$, which was reported by previous studies. Nevertheless, it is noteworthy that PCO efficiencies increased up to 94% for o-xylene and 97% for the m,p-xylene under lower SFR(0.5 L $min^{-1}$). Consequently, it is suggested that with appropriate SFR conditions, the visible-light-assisted photocatalytic systems could also become important tools for improving IAQ.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.9
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• pp.681-684
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• 2010

The $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ multilayered structure for the transparent electrodes in plasma display panel was designed by essential macleod program (EMP) and the multilayered film was deposited on a glass substrate by direct-current (DC)/radio-frequency (RF) magnetron sputtering system. During film deposition process, the Ag layer in $TiO_2$/Ag/$TiO_2$ structure became oxidized and the filter characteristic was degraded easily. In this study, ZnS layer was adopted as a diffusion blocking layer between $TiO_2$ and Ag to prevent the oxidation of Ag layer efficiently in $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ structure. Based on the AES depth profiling analysis, the Ag layer was effectively protected by the ZnS layer as compared with the $TiO_2$/Ag/$TiO_2$ multilayered films without ZnS as an antioxidant layer. The 3 times stacked $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ films have low sheet resistance of $1.22{\Omega}/{\square}$ and luminous transmittance was as high as 62% in the visible ranges.

• Biomolecules & Therapeutics
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• v.23 no.6
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• pp.557-563
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• 2015

Skin aging is the most readily observable process involved in human aging. Ultraviolet B (UVB) radiation causes photo-oxidation via generation of reactive oxygen species (ROS), thereby damaging the nucleus and cytoplasm of skin cells and ultimately leading to cell death. Recent studies have shown that high levels of solar UVB irradiation induce the synthesis of matrix metalloproteinases (MMPs) in skin fibroblasts, causing photo-aging and tumor progression. The MMP family is involved in the breakdown of extracellular matrix in normal physiological processes such as embryonic development, reproduction, and tissue remodeling, as well as in disease processes such as arthritis and metastasis. We investigated the effect of diphlorethohydroxycarmalol (DPHC) against damage induced by UVB radiation in human skin keratinocytes. In UVB-irradiated cells, DPHC significantly reduced expression of MMP mRNA and protein, as well as activation of MMPs. Furthermore, DPHC reduced phosphorylation of ERK and JNK, which act upstream of c-Fos and c-Jun, respectively; consequently, DPHC inhibited the expression of c-Fos and c-Jun, which are key components of activator protein-1 (AP-1, up-regulator of MMPs). Additionally, DPHC abolished the DNA-binding activity of AP-1, and thereby prevented AP-1-mediated transcriptional activation. These data demonstrate that by inactivating ERK and JNK, DPHC inhibits induction of MMPs triggered by UVB radiation.

• Journal of Korea Soil Environment Society
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• v.5 no.1
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• pp.97-108
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• 2000

A Gram-type negative bacteria that can utilize crude oil as the sole source of carbon and energy was isolated from an activated sludge of a local sewage treatment plant and identified tentatively as belonging to the genus Acinetobacter. The isolate could degrade n-alkanes and unidentified hydrocarbons in crude oil and utilize n-alkanes, hydrophobic substrates, as sole carbon and energy sources. n-Alkanes from tridecane (Cl3) to triacontane (C30) in crude oil were degraded simultaneously with no difference in degradation characteristics between the two close odd and even numbered alkanes in carbon numbers. The linear growth of the isolate and the degradation characteristics of Pr-alkanes suggested that the transport of substrates from the oil phase to the site where the substrates undergo the initial oxidation in microorganism might be the rate limiting in the biodegradation process of crude oil constituents. The remainder fraction of substrates after cultivation was considered to reflect the hydrocarbon inclusions in the cell mass, characteristics in Acinetobacter species, and to control the transport of substrates from crude oil phase. On the basis of the results, the isolate was considered to play an important role in the degradation study of hydrophobic environmental pollutants.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.130-131
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• 2013

Nanostructured oxides are widely used in heterogeneous catalysis where their catalytic properties are closely associated with the size and morphology at nanometer level. The effect of particle size has been well decumented in the past two decades, but the shape of the nanoparticles has rarely been concerned. Here we illustrate that the redox and acidic-basic properties of oxides are largely dependent on their shapes by taking $Co_3O_4$, $Fe_2O_3$, $CeO_2$ and $La_2O_3$ nanorods as typical examples. The catalytic activities of these rod-shaped oxides are mainly governed by the nature of the exposed crystal planes. For instance, the predominant presence of {110} planes which are rich in active $Co^{3+}$ on $Co_3O_4$ nanorods led to a much higher activity for CO oxidation than the nanoparticles that mainly exposed the {111} planes. The simultaneous exposure of iron and oxygen ions on the surface of $Fe_2O_3$ nanorods have significantly enhanced the adsorption and activation of NO and thereby promoted the efficiency of DeNOx process. Moreover, the exposed surface planes of these rod-shaped oxides mediated the reaction performance of the integrated metal-oxide catalysts. Au/$CeO_2$ catalysts exhibited outstanding stability under water-gas shift conditions owing to the strong bonding of gold particle on the $CeO_2$ nanorods where the formed gold-ceria interface was resistant towards sintering. Cu nanoparticles dispersed on $La_2O_3$ nanorods efficiently catalyzed transfer dehydrogenation of primary aliphatic alcohols based on the uniue role of the exposed {110} planes on the support. Morphology control at nanometer level allows preferential exposure of the catalytically active sites, providing a new stragegy for the design of highly efficient nanostructured catalysts.