• 방사선산업학회지
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• 제6권3호
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• pp.205-209
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• 2012

The decomposition of 50 pesticides present in an aqueous solution using ${\gamma}-irradiation$ from a $^{60}Co$ gamma-ray source was investigated using laboratory-scale experiment. The rates of decomposition were determined using a gas chromatography-electron capture detector (GC-ECD), high-performance liquid chromatography-photo diode array detector (HPLC-PDA), and HPLC-fluorescence detector (FLD). When the initial concentration of pesticides was 10 ppm, and the radiation dose was 2, 5, 10, 20, and 30 kGy, respectively, 14 pesticide samples showed high removal rates (>50%) at absorbed doses of more than 10 kGy. With the exception of procymidone, they were all completely removed at a 30 kGy irradiation dose. These results provide fundamental data on the reactivity between gamma-irradiation and pesticides in an aqueous solution. Further, an evaluation of the toxicity of radiolytic intermediate products is required.

• Journal of Ecology and Environment
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• 제33권3호
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• pp.261-270
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• 2010

Increasing atmospheric $CO_2$ affects the soil carbon cycle by influencing microbial activity and the carbon pool. In this study, the effects of elevated $CO_2$ on extracellular enzyme activities (EEA; ${\beta}$-glucosidase, N-acetylglucosaminidase, aminopeptidase) in salt marsh sediment vegetated with Suaeda japonica were assessed under ambient atmospheric $CO_2$ concentration (380 ppm) or elevated $CO_2$ concentration (760 ppm) conditions. Additionally, the community structure of sulfate-reducing bacteria (SRB) was analyzed via terminal restriction fragments length polymorphism (T-RFLP). Sediment with S. japonica samples were collected from the Hwangsando intertidal flat in May 2005, and placed in small pots (diameter 6 cm, height 10 cm). The pots were incubated for 60 days in a growth chamber under two different $CO_2$ concentration conditions. Sediment samples for all measurements were subdivided into two parts: surface (0-2 cm) and rhizome (4-6 cm) soils. No significant differences were detected in EEA with different $CO_2$ treatments in the surface and rhizome soils. However, the ratio of ${\beta}$-glucosidase activity to N-acetylglucosaminidase activity in rhizome soil was significantly lower (P < 0.01) at 760 ppm $CO_2$ than at 380 ppm $CO_2$, thereby suggesting that the contribution of fungi to the decomposition of soil organic matter might in some cases prove larger than that of bacteria. Community structures of SRB were separated according to different $CO_2$ treatments, suggesting that elevated $CO_2$ may affect the carbon and sulfur cycle in salt marshes.

• 한국세라믹학회지
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• 제24권5호
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• pp.453-460
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• 1987

β'-sialon(Z=2.7) specimens with <30%wt. graphite as a reducing agent were decomposed at 1350°up to 1,450℃ under the atmosphere of 90% N2-10%H2. The decomposition of β'-sialon was calculated from the change in Z-value, and the formation of new minerals was identified from X-ray diffraction patterns. The decomposition reactions of sialon were considered to yield a stable sialon close to β-silicon nitride and some aluminum compounds according to the following equations; β'-sialon(s)＋C(s)＋N2(g)→β2-sialon(metastable)＋β3-sialon(stalbe phase) β2-sialon(s)＋C(s)＋N2(g)→β3-sialon(s)＋AlN(s)＋α-Al2O3(s)＋15R(s)＋SiO(g)＋Al2O(g)＋CO(g) Z-value; β2( 3.5)>β'( 2.7)>β3( 0.5) The decomposition rate of sialon was controlled by two mechanisms ; One was characterized by the interface area of contact, corresponding to an apparent activation energy of 50.5Kcal/mol in the initial stage, and the other by the diffusion, corresponding to that of 104.3Kcal/mol in the final stage of the decomposition.

• 한국재료학회지
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• 제22권5호
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• pp.253-258
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• 2012

Activated magnetite ($Fe_3O_{4-{\delta}}$) was applied to reducing $CO_2$ gas emissions to avoid greenhouse effects. Wet and dry methods were developed as a $CO_2$ removal process. One of the typical dry methods is $CO_2$ decomposition using activated magnetite ($Fe_3O_{4-{\delta}}$). Generally, $Fe_3O_{4-{\delta}}$ is manufactured by reduction of $Fe_3O_4$ by $H_2$ gas. This process has an explosion risk. Therefore, a non-explosive process to make $Fe_3O_{4-{\delta}}$ was studied using $FeC_2O_4{\cdot}2H_2O$ and $N_2$. $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$ were used as starting materials. So, ${\alpha}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method. During the calcination process, $FeC_2O_4{\cdot}2H_2O$ was decomposed to $Fe_3O_4$, CO, and $CO_2$. The specific surface area of the activated magnetite varied with the calcination temperature from 15.43 $m^2/g$ to 9.32 $m^2/g$. The densities of $FeC_2O_4{\cdot}2H_2O$ and $Fe_3O_4$ were 2.28 g/$cm^3$ and 5.2 g/$cm^3$, respectively. Also, the $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by CO. From the TGA results in air of the specimen that was calcined at $450^{\circ}C$ for three hours in $N_2$ atmosphere, the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was estimated. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was 0.3170 when the sample was heat treated at $400^{\circ}C$ for 3 hours and 0.6583 when the sample was heat treated at $450^{\circ}C$ for 3 hours. $Fe_3O_{4-{\delta}}$ was oxidized to $Fe_3O_4$ when $Fe_3O_{4-{\delta}}$ was reacted with $CO_2$ because $CO_2$ is decomposed to C and $O_2$.

• 한국재료학회지
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• 제20권8호
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• pp.429-433
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• 2010

In this study, activated carbon (AC) as a carbon source was modified with different concentrations of cobalt chloride ($CoCl_2$) to prepare a Co-AC composite, and it was used for the preparation of Co-AC/$TiO_2$ composites with titanium oxysulfate (TOS) as the titanium precursor. The physicochemical properties of the prepared Co-AC/$TiO_2$ composites were characterized by $N_2$ adsorption at 77 K, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. The photocatalytic treatments of organic dyes were examined under an irradiation of visible light with different irradiation times. $N_2$ adsorption data showed that the composites had decreased surface area compared with the pristine AC, which was $389\;m^2/g$. From the XRD results, the Co-AC/$TiO_2$ composites contained a mixturephase structuresof anatase and rutile, but a cobalt oxide phase was not detected in the XRD pattern. The EDX results of the Co-AC/$TiO_2$ composites confirmed the presence of various elements, namely, C, O, Ti, and Co. Subsequently, the decomposition of methylene orange (MO, $C_{14}H_{14}N_3NaO_3S$) and rhodamine B (Rh.B, $C_{28}H_{31}ClN_2O_3$) in an aqueous solution, respectively, showed the combined effects of an adsorption effect by AC and the photo degradation effect by $TiO_2$. Especially, the Co particles in the Co-AC/$TiO_2$ composites could enhance the photo degradation behaviors of $TiO_2$ under visible light.

• 한국환경과학회지
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• 제16권4호
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• pp.433-440
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• 2007

The photodegradation and by-products of the gaseous toluene with $TiO_2$ (P25) and short-wavelength UV ($UV_{254+185nm}$) radiation were studied. The toluene was decomposed and mineralized efficiently owed to the synergistic effect of photochemical oxidation in the gas phase and photocatalytic oxidation on the $TiO_2$ surface. The toluene by the $UV_{254+185nm}$ photoirradiated $TiO_2$ were mainly mineralized $CO_2$ and CO, but some water-soluble organic intermediates were also formed under severe reaction conditions. The ozone and secondary organic aerosol were produced as undesirable by-products. It was found that wet scrubber was useful as post-treatment to remove water-soluble organic intermediates. Excess ozone could be easily removed by means of a $MnO_2$ ozone-decomposition catalyst. It was also observed that the $MnO_2$ catalyst could decompose organic compounds by using oxygen reactive species formed in process of ozone decomposition.

• 한국환경과학회지
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• 제10권5호
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• pp.315-321
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• 2001

This study was conducted to estimate the decomposition capacity for organic matter by microbe of tidal flat sediments (Hajae, Dongjin and Mankyung). The decomposition rate constants (K') have been determined by Thomas slope method and compared with the values of each tidal flats. The decomposition rates of organic matter by microbe were initially very slow, but at the end of 12 hours, very sharply increased. The values of decomposition rate constant for Dongjin, Mankyung and Hajae tidal flat sediment were 1.364$day^{-1}$/, 1.080d$day^{-1}$ and 0.735$day^{-1}$, respectively. The decomposition rate constant of Dongjin tidal flat sediment which affected by livestock wastewater was higher than others. The decomposition quantity (mg/g/day) of organic matter by microbe of tidal flat sediments was 0.4mg/g/day for Dongjin, 0.36mg/g/day for Mankyung and 0.36mg/g/day for Hajae. The average of decomposition quantity was 0.37mg/g/day. To calculate purification capacity (kg/ha) of organic matter by microbe, we applied to two assumption ; 1) biological action by microbe is occur within 0.1cm under surface 2) specific gravity of sediment are 2.5g/$\textrm{cm}^2$. The purification capacity of organic matter by microbe of tidal flat sediment was calculated to 9.25kg/ha. The relationships between decomposition rate constant (K') and ignition loss (I. L), chemical oxygen demand by sediment (CO $D_{sed}$), total carbon(TC), silt and clay as index of organic matter were a high positive($R^2$=0.97~1.00).

• 한국대기환경학회지
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• 제16권4호
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• pp.373-380
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• 2000

A new type of photocatalyst plasma air purification filter for decomposition of some VOCs has been developed. The photocatalyst plasma air purification filter employs the pulsed discharge plasma as an energy source of TiO2. photocatalyst instead of UV light. In closed room(2m3) test removal efficiency of some VOCs was 80∼100% in 15∼24 hours. In the initial step of phptocatalyst plasma reaction. Acetone and Nitromethane etc were detected. But they were completely oxidized to CO2 and H2O.

• 한국대기환경학회지
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• 제22권1호
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• pp.43-51
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• 2006

Nonthermal plasma-driven catalysis (PDC) was investigated for the decomposition of benzene and toluene as model compounds of volatile organic compounds (VOCs) at atmospheric pressure and low temperature. Two types of catalysts Ag/$TiO_{2}$ and Pt/$\gamma-Al_{2}O_{3}$ were tested in this study. The amount of catalysts packed in the PDC reactor did not influence on the decomposition efficiency of benzene. The type of catalysts also had no influence on the decomposition efficiency of toluene and carbon balance. The Ag/$TiO_{2}$ catalyst showed constant $CO_{2}$ selectivity of about $73\%$ regardless of the specific input energy. However, the selectivity of $CO_{2}$ was greatly enhanced with the Pt/$\gamma-Al_{2}O_{3}$ catalysts, and reached $97\%$ at 205 J/L. Two test runs with 20 fold difference in the gas flow clearly indicated that lab-scale data can be successfully applied for the scaling-up of PDC system.

• 한국응용과학기술학회지
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• 제26권2호
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• pp.205-212
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• 2009

Solution copolymerization of Styrene(St.) with 2-Hydroxypropylacrylate(2-HPA) was carried out with Benzoylperoxide(BPO) as an initiator in toluene at $80^{\circ}C$ in a batch reactor. Reaction volume and reaction time were 0.3 liters, 8 hours respectively. The time to reach steady state was about the six time. The monomer reactivity ratios, $r_1$(St.) and $r_2$(2-HPA) were determined by both the Kelen-Tudos method and the Fineman-Ross method ; $r_1$(St.)=0.376(0.330), $r_2$(2-HPA)=0.408(0.778). The activation energy of thermal decomposition was in the range of $33{\sim}55kcal/mol$.