• Journal of Photoscience
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• v.6 no.3
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• pp.91-96
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• 1999

Zeolites and microporouos materials continue to attract attention as novel hosts for photochemical reactions. Zeolities are attractive because of their ability to selectivity exchange and incorporate species within the void spaces and interconnecting channels, providing a spatial arrangement of molecules. Our research has primarily focused on intrazeolitic electron transfer from excited Ru(bpy)32+ in supercages of zeolite Y to a series of bipyridinium ions. In the Ru(bpy)32+ viologen-zeolite Y samples, the slowing of the back electron transfer from the bipyridinium radical cation to Ru(bpy)32+ allows for charge propagation via self exchange between diquat molecules. This provides an opportunity for permanent charge separation. When the migrating charge on the diquat radical within the zeolite reaches the surface, it can be transferred to a neutral viologen (PVS) in solution, resulting in permanent charge separation. The advantage of long-lived charge separation can be exploited for useful chemistry if suitable catablysts can be assembled on the zeolities. We have studied Ru(bpy)2 as water oxdiation catalysts. We have demonstrated that synthesis of RuO2 fibers on a zeolite via thermal decomposition of Ru3(CO)12 leads to the most active water decomposition catalyst reported to date. Because of the extensive interest of photochemical water reduction to H2, much is known about catalytic systems usin gone electron catalyst, and even more importantly, that no reaction of viologen occurred with H2 over this catalyst. The present challenge is to incorporate all these elements of the system into an architecture and we are examining zeolite membranes for this purpose.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.2
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• pp.206-219
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• 2008

The purpose of this study is to evaluate concentrations of carbonyl compounds during summer season in Seoul metropolitan area. The air samples were collected at 7 sites in this area from June 2001 to June 2003. The carbonyl compounds were analyzed by DNPH/HPLC method. The analytical method applied in this study showed good repeatability, linearity, and sensitivity. The most abundant carbonyl was formaldehyde (average 4.48 ppb), and followed by acetone, acetaldehyde, methyl ethyl ketone, butyraldehyde, propionaldehyde and benzaldehyde, respectively. Concentrations of carbonyl compounds in June were higher than those in August. There was not only higher solar radiation but also higher ozone concentration in June than in August. As a result o photochemical reactions, carbonyl compounds from both primary and secondary sources are likely to contribute to the formation of ozone. The contributions to photochemical ozone creation of two carbonyl compounds such as formaldehyde and acetaldehyde were estimated to be about 70%. Ratios of formaldehyde to acetaldehyde in this study ranged from 1.13 to 4.26, which are generally equivalent levels to those of other urban areas in domestic and foreign countries.

• Journal of the Korean Chemical Society
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• v.47 no.3
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• pp.213-219
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• 2003

The photochemical transformation of carbon monoxide in aqueous solution has been investigated at $25{\pm}0.1^{\circ}C$using ZnO as a photocatalyst. After irradiation of 253.7 nm UV light in the solution, carboxylation and carbonylation processes were carried out, and the formation of formic acid, oxalic acid, glyoxylic acid, formaldehyde and glyoxal was observed. The formation of the products depended on the pH values in the solution. The yield of formaldehyde and glyoxal increased in acidic solution whereas it decreased in basic solution. When the pH values in the solution increased above 11.5, the yield of formic acid increased rapidly. The initial quantum yields of the products were determined and the probable mechanisms for the reactions were presented on the basis of the products analysis.

• Analytical Science and Technology
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• v.16 no.6
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• pp.466-474
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• 2003

This paper describes the concentrations of total dissolved iron (tFe) and $Fe^{2+}$ in rainwater and snow, the relationship of Fe species with other metals and ions in bulk rainwater, and the $Fe^{2+}$ generation mechanism in aqueous samples in rainwater of time series collection. Volume weight mean concentrations of tFe and $Fe^{2+}$ were 3.22 and $1.25{\mu}gL^{-1}$ in bulk rainwater, and 50.1 and $43.5{\mu}gL^{-1}$ in snow, respectively. $Fe^{2+}$ was significant fraction to the tFe, accounted for 3.25-93.4% of the tFe in rainwater and 87% in snow. We also investigated temporal variations of tFe, $Fe^{2+}$, other metals and ions in rainwater of time series collection during rain event. Although the concentration range of tFe was different from those of other species, a decreasing trend of tFe from the beginning of the rain event was similar with other species. However, though $Fe^{2+}$ did not show such a decreasing trend, $Fe^{2+}$/tFe was in good correlation with solar radiation. From the results of multiple linear regression analysis and thermodynamic calculations (Mineql+), $Fe^{2+}$ in our samples may be generated from photochemical reduction of $Fe^{3+}$ species (such as $Fe(OH)^{2+}$,$Fe(OH)^{2+}$ and Fe-oxalate) at daytime.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.240-246
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• 2023

This study was performed to convert NO_x in atmosphere by photochemical reaction utilizing the eco-friendly solar energy. The mortar specimen coated with photocatalyst was fabricated and the photochemical conversion efficiency of NO_x was analyzed. The photocatalyst coated concrete was fabricated by first adding TiO₂ photocatalyst on the bottom of mold first and next adding cement mortar and, then, curing the concrete mortar. The grease was sprayed on the bottom of mold in advance so that the concrete can be demolded easily after curing. The conversion efficiencies of NO_x by photochemical reactions were investigated systematically by changing the process variable conditions of amount of TiO₂ coating, UV-A light intensity, total gas flow rate, relative humidity and initial NO_x concentration. It was confirmed that the photocatalyst coated concrete fabricated in this study could convert NO_x successfully for various process conditions in atmosphere. In future, we believe this research result can be utilized as basic data to design the infrastructure of building, tunnel and road for controlling efficiently the air pollutants such as NO_x, SO_x, and VOCs.

• Journal of Photoscience
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• v.10 no.1
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• pp.9-20
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• 2003

Recent studies on the photoreactivity of l,4-unsaturated systems have changed some ideas that were firmly established in this area of research for many years. Thus, we have described the first examples of 2-aza-di-$\pi$-methane (2-ADPM) rearrangements promoted by triplet-sensitization and by single electron transfer (SET) using electron-acceptor sensitizers. These reactions afford N-vinylaziridine and cyclopropylimine photoproducts in the first examples of di-$\pi$-methane processes that yield three-membered ring heterocycles. l-Aza-1,4-dienes also undergo SET-promoted l-aza-di-$\pi$-methane (l-ADPM) rearrangements via radical-cation intermediates using electron acceptor sensitizers. In some cases, alternative cyclizations yielding different carbocycles and heterocycles have been observed. The l-ADPM and di-$\pi$-methane (DPM) reactions also occur via radical-anion intermediates on irradiation using electron donor sensitizers. On the other hand, the photoreactivity reported for $\beta$,${\gamma}$-unsaturated aldehydes for many years was decarbonylation to the corresponding alkenes. However, our studies demonstrate that these compounds undergo the oxa-di-$\pi$-methane (ODPM) rearrangement with high chemical and quantum efficiency. A comparison of the photochemical reactivity of $\beta$,${\gamma}$-unsaturated aldehydes and corresponding methyl ketones has shown that the ketones do not undergo the ODPM rearrangement while the corresponding aldehydes are reactive by this pathway. Monosubstituted $\beta$,${\gamma}$-unsaturated aldehydes at C-2 undergo the ODPM rearrangement yielding the corresponding cyclopropane carbaldehydes diastereoselectively. Finally, we have described the first examples of reactions, similar to the well know Norrish Type I process, which take place in the triplet excited state of $\beta$,${\gamma}$-unsaturated carbonyl compounds by excitation of the C-C double bond instead of the carbonyl group.

• Economic and Environmental Geology
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• v.32 no.1
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• pp.101-111
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• 1999

Sedimentary organic matter, exposed to continental surficial environment, reacts with oxygen supplied from the atmosphee and forms carbon-containing oxidation products. Knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time. Under the abiological conditions, the oxidation rate of coal organic matter by molecular oxygen is enhanced by the increase of oxygen concentration and temperature. At ambient temperature and pressure, aqueous coal oxidation results in the formation of dissolved $CO_2$ dissolved organic carbon and solid oxidation products which are all quantitatively significant reaction products. The effects of pH, ultraviolet light, and microbial activity on the weathering of sedimentary organic matter are poorly contrained. Based on the results of geochmical and environmental studies, it is believed that the photochemical reaction should play an important role in the decomposition and oxidation of sedimentary organic matter removed from the weathering profile. At higher pH conditions, the production rate of DOC can be accelerated due to base catalysis. These high molecular weight oranic matter can react with man-made pollutants such as heavy metal ions via adsorption/desorption or ion exchange reactions. The effect of microbial activity on the oxidative weathering of sedimentary organic matter is poorly understood and remains to be studied.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1108-1114
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• 2013

Photochemical reactions of fluoro- vs. nonfluoro-substituted polymethylenoxy chain linked phthalimide were carried out to explore how electronegative fluorine atoms inside the donor chain influence photocyclization reaction efficiencies and to briefly determine the alkali metal binding properties of the photoproducts. The results of this study show that the fluorine-substituted donor chain linked phthalimide undergoes inefficient photocyclization via single electron transfer (SET)-induced excited state pathways to generate 14-membered cyclic amidol compared to nonfluoro-analog due to low electron donor ability of the terminal oxygen donor site. These results show that photoinduced intramolecular SET processes arising from ${\alpha}$-silyl ether electron donors to phthalimides are largely dependent on the kinds of substituents inside donor chain. Finally, a preliminary study with the cyclic amidols generated in this effort showed that they have weak alkali metal cation binding properties regardless of absence/presence of fluoro-substituents.

• Journal of the Korean Chemical Society
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• v.23 no.2
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• pp.115-118
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• 1979

The photochemical reactions and spectral properties of 1,1-diphenyl-2-vinylcyclopropane were studied. Upon direct irradiation of the compound at 253.7nm, 1,1-diphenylethylene was formed as a major product along with a small amount of 4,4-diphenylcyclopentene. Sensitized photoreactions showed quite a different phenomena from those of conjugated dienes supporting the spectral results that the cyclopropane ring does not transmit the conjugation in the compound.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.76.2-76.2
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• 2015

I will present my research group's recent investigation on how the localized plasmon of a nanoparticle interacts with another plasmon, and with nearby molecules. First, I will demonstrate the use of scattering-type scanning near-field microscopy (s-SNOM) to directly visualize the capacitive / conductive coupling in dimeric nanoparticles and heterometallic nanorods. Second, I will talk about the use of gap-plasmons to locally induce photochemical reactions, and to follow chemical kinetics of individual organic molecules using the gap-plasmons. As a last topic, I will talk about the use of near-field coupling between a scanning probe and graphenes to visualize / identify the stacking domains (e. g., ABA versus ABC-type stacking in triple layer) hidden in multilayer graphenes.