• Journal of the Mineralogical Society of Korea
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• v.21 no.3
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• pp.321-329
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• 2008

Amorphous silica nanoparticles are among the most fundamental $SiO_2$ compounds, having implications in diverse geological processes and technological applications. Here, we explore structural details of amorphous silica nanoparticles with varying particle sizes (7 and 14 nm) using $^{29}Si$ and $^{1}H$ MAS NMR spectroscopy together with quantum chemical calculations to have better prospect for their size-dependent atomic structures. $^{29}Si$ MAS NMR spectra at 9.4 T resolve $Q^2,\;Q^3$ and $Q^4$ species at -93 ppm, -101 ppm, -110 ppm, respectively. The fractions of $Q^2,\;Q^3,\;O^4$ species are $7{\pm}1%,\;27{\pm}2%$, and $66{\pm}2%$ for 7 nm amorphous silica nanoparticles and $6{\pm}1%,\;21{\pm}2%$, and $73{\pm}2%$ for 14 nm amorphous silica nanoparticles. Whereas it has been suggested that $Q^2$ and $Q^3$ species exist on particles surfaces, the difference in $Q^{2}\;+\;Q^{3}$ fraction in both 7 and 14 nm particles is not significant, suggesting that $Q^2$ and $Q^3$ species could exist inside particles. $^{1}H$ MAS NMR spectra at 11.7 T shows diverse hydrogen environments, including physisorbed water, hydrogen bonded silanol, and non-hydrogen bonded silanol with varying hydrogen bond strength. The hydrogen contents in the 7nm silica nanoparticles (including water and hydroxyl groups) are about 3 times of that of 14 nm particles. The larger chemical shills for proton environments in the former suggest stronger hydrogen bond strength. The fractions of non-hydrogen bonded silanols in the 14 nm amorphous silica nanoparticles are larger than those in 7 nm amorphous silica nanoparticles. This observation suggests closer proximity among hydrogen atoms in the nanoparticles with smaller diameter. The current results with high-resolution solid-state NMR reveal previously unknown structural details in amorphous silica nanoparticles with particle size.

• Applied Chemistry for Engineering
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• v.10 no.4
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• pp.557-562
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• 1999

The reaction properties of Pd. Pd-Ce and Pd-La catalysts supported on ${\gamma}-Al_2O_3$ were investigated in the oxidation reaction of methane($CH_4$) exhausted from the compressed natural gas vehicle in a U-tube flow reactor with gas hourly space velocity of $72,000h^{-1}$. The catalysts were characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), BET surface area and hydrogen chemisorption. Pd catalyst prepared by $Pd(NO_3)_2$ as a palladium precursor and calcined at $600^{\circ}C$ showed the highest activity for a methane oxidation. Catalytic activity of calcined $Pd/{\gamma}-Al_2O_3$ in which most of palladium was converted into palladium oxide species was higher than that of reduced $Pd/{\gamma}-Al_2O_3$ in which most of palladium existed in palladium metal by XRD. As increasing the number of reaction cycles in the wide range of redox, the catalytic activity of $Pd/{\gamma}-Al_2O_3$ was decreased and the highly active window became narrower. Lanthanum oxide promoted Pd catalyst, $Pd/La/{\gamma}-Al_2O_3$ showed enhanced thermal stability compared with $Pd/{\gamma}-Al_2O_3$ even after aging at $1000^{\circ}C$, which was ascribed to the role of La as a promoter to suppress the sintering of palladium metal and ${\gamma}-Al_2O_3$ support. Almost all of methane was removed by the reaction with NO at the redox ratio of 1.2 in case of oxygen excluded steam, but that activity was significantly decreased in the steam containing oxygen.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.604-608
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• 2015

In the present work, the improvement of nitrate removal ability was investigated to resolve a eutrophication problem by using Ulmus davidiana (U. davidiana) bark generated from Gangwon province. When the initial pH of aqueous solution was adjusted to 3.5 in batch experiments, the removal efficiencies for 10 and 20 mg/L nitrate increased up to 43 and 37%, respectively. In addition, when U. davidiana bark of 1.0 g/100 mL was used for 8 h, the removal efficiency for 20 mg/L nitrate was 68%. Moreover, when reforming reaction of U. davidiana bark was performed under oxyfluorination conditions, the optimal ratio of partial pressure between fluorine and oxygen was 1 : 9 for an enhanced nitrate adsorption amount. When reformed U. davidiana bark was used for 8 h operation under the optimal oxyfluorination condition, removal efficiencies for 10, 20 and 40 mg/L nitrate were found to be 96, 95 and 59%, respectively. Collectively, these results suggest that our water treatment technology can be effectively utilized to treat high concentrations of nitrate in water bodies.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.53-63
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• 1992

M/BM -series catalysts, $MoO_3$ supported on ${\alpha}-Bi_2Mo_3O_{12}$ were also prepared by impregnation method. BM/M-series catalysts, ${\alpha}-Bi_2Mo_3O_{12}$ supported on $MoO_3$ were also prepared by coprecipitation. Structure and catalytic properties of the two phase catalysts were studied by means of using nitrogen adsorption, X-ray diffraction, and scanning electron microscopy. The reaction test for the selective oxidation of propylene to acrolein over Bi-molybdate catalysts was studied using a fixed-bed reactor system. In M/BM-series catalysts, $MoO_3$ was dispersed on ${\alpha}-Bi_2Mo_3O_{12}$, and the crystal structure of ${\alpha}-Bi_2Mo_3O_{12}$ remains unchanged by the presence of excess $MoO_3$. However the surface morphology and bulk structure of BM/M-series catalysts were altered probably because the precipitated $Bi(OH)_3$ reacted with $MoO_3$ during the calcination to form ${\alpha}-Bi_2Mo_3O_{12}$ phase. The results of propylene oxidation on both series catalysts showed that the reaction took place over the surface of ${\alpha}-Bi_2Mo_3O_{12}$ particle and the role of excess $MoO_3$ was to supply oxygen to ${\alpha}-Bi_2Mo_3O_{12}$. These increasing effects on activity were also observed in the mechanical mixtures of ${\alpha}-Bi_2Mo_3O_{12}$ and $MoO_3$.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1100-1106
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• 2008

In this study, we presented rapid and simple fabrication method of functionalized surface on various substrates as a universal platform for the selective immobilization of cells. The functionalized surface was achieved by using deposition of polyelectrolyte such as poly(allyamine hydrochloride) (PAH), poly(diallyldimethyl ammonium chloride) (PDAC), poly(4-ammonium styrene sulfonic acid) (PSS), poly(acrylic acid) (PAA) and fabrication of poly(ethylene glycol) (PEG) microstructure through micro-molding in capillaries (MIMIC) technique on each glass, poly(methyl methacrylate) (PMMA), polystyrene (PS) and poly(dimethyl siloxane) (PDMS) substrate. The polyelectrolyte multilayer provides adhesion force via strong electrostatic attraction between cell and surface. On the other hand, PEG microstructures also lead to prevent non-specific binding of cells because of physical and biological barrier. The characteristic of each modified surface was examined by using static contact angle measurement. The modified surface onto several substrates provides appropriate environment for cellular adhesion, which is essential technology for cell patterning with high yield and viability in the micropatterning technology. The proposed method is reproducible, convenient and rapid. In addition, the fabrication process is environmentally friendly process due to the no use of harsh solvent. It can be applied to the fabrication of biological sensor, biomolecules patterning, microelectronics devices, screening system, and study of cell-surface interaction.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.592-592
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• 2016

국내에는 17,500여개의 농업용 저수지가 전국적으로 분포하고 있다. 국내 농업용 저수지는 대부분이 소규모이며, 연중 수량 변동이 심하고, 유역배율이 작아 태생적으로 수질오염에 취약한 구조로 되어 있다. 특히 농업용 저수지는 도시 근교나 농촌지역에 많이 위치하고 있어 유역 내 축산 농가나 미처리 생활하수에서 유래된 유기물 및 영양염류 유입에 의한 수질오염도가 높다. 저수지에 고농도로 유입되는 유기물, TN, TP를 처리하기 위하여 농어촌연구원과 수생태복원(주)에서는 공동으로 친환경 수처리시설인 생태융합형 접촉산화시스템을 개발하였다. 생태융합 접촉산화수로는 상부 식생과 수로 내의 섬유상 끈상 미생물 접촉재를 이용하여 오염수가 수로를 흐르면서 침전, 여과, 흡착, 산화, 흡수 등 물리학적, 화학적, 생물학적 원리를 이용하여 고농도의 유기물과 질소, 인을 제거하는 물리적, 생물학적 공정을 융복합 기술이다. 본 연구에서는 경기도 시흥시에 소재하고 있는 M 저수지에 현장 Test-bed를 구축하여 수질정화효율을 평가하였다. M 저수지는 유효저수지량이 약 23만톤에 해당하는 소규모 저수지로, 1941년도 준공된 아주 노후화된 저수지로 평균 수심이 2m 이하이고 연중 수질오염도가 높은 저수지이다. 매화저수지 수변에 설치된 생태융합형 접촉산화수로의 전체규모는 길이 8.6m, 폭 2m, 수심 2m에 해당하며, 끈상 미생물 메디아조 3개($2{\times}2{\times}6m^3$), 침전조 1개($2{\times}2{\times}2m^3$)로 구성되어 있다. 기타 부대 장치로는 끈상 메디아조에 산소공급을 위한 Air-mist(마이크로 버블 발생장치), 자동운전계기판, 유입펌프 등이 있다. 생태융합형 접촉산화수로의 처리 공정은 유입수${\rightarrow}$에어미스트${\rightarrow}$고속복합응집장치${\rightarrow}$융복합 산화조(3조)${\rightarrow}$침전조${\rightarrow}$방류로 구성되어 있다. 테스트 베드는 2015년 8월 말경에 구축 완료하였으며, 끈상 미생물 메디아조의 수질정화효율을 평가하기 위하여 9월부터 11월까지 총 7회 걸쳐 유입수와 유출수를 각각 조사하였다. 현장 측정항목인 수온, pH, EC, DO 등은 유입수 및 유출수간 큰 차이가 없었고, COD, SS, Chl-a, TP 등은 수처리시스템 초기 가동시에는 메디아에 미생물 부착율 저조로 유입수 및 유출수 수질농도에 큰 차이가 없었으나, 운영시간의 경과와 함께 메디아의 미생물 충진율이 높아짐에 따라 처리효율이 최대 SS 69.6%, Chl-a 89.3%, TP 89%까지 도달하는 것으로 나타났다. 생태융합 접촉산화수로는 부지 집약적인 컴팩트한 수처리 시설로서 현재 널리 이용되고 있는 인공습지를 대체할 수 있는 경제적인 시설로 판단된다.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.35-41
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• 2021

VWTi, which is used as a commercial catalyst in NH3-SCR, exhibits excellent denitrification performance at 300 to 400 ℃, but there is a problem that efficiency decreases at low temperatures below 300 ℃. Research on catalysts containing promoter to increase low-temperature denitrification efficiency is steadily progressing. However, research on the cause of the improvement in low-temperature denitrification efficiency of the catalyst and the catalyst properties is insufficient. In this study, it was confirmed that by adding Sb to VWTi, denitrification performance was improved by more than 10% in NH3-SCR reaction below 300 ℃. At this time, the space velocity and the size of the catalyst particles were controlled to exclude the influence of external/internal diffusion. In addition, the catalytic properties according to the presence or absence of Sb were investigated by performing BET, TEM/EDS, O2-TPD, H2-TPR and DRIFTs analysis. It was judged that the addition of Sb increased the adsorbed oxygen species on the surface of the catalyst, thereby enhancing the redox properties of the catalyst at low temperature and exhibiting excellent denitrification performance.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.609-614
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• 2013

This study investigated the spontaneous combustion behavior of solvent-treated low rank coals. Indonesian lignite (a KBB and SM coal) and sub-bituminous (a Roto coal) were mixed with non-polar 1-methyl naphthalene (1MN) either by mechanical agitation or ultrasonication. The property change associated with 1MN treatment was then analyzed using proximate analysis, calorific value analysis, Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy and moisture re-adsorption test. Susceptibility to spontaneous combustion was evaluated using crossingpoint temperature (CPT) measurement along with gas analysis by GC. A FT-IR profile showed that oxygen functional groups and C-H bonding became weaker when treated by 1 MN. XPS results also indicated a decrease of the oxygen groups (C-O-, C=O and COO-). Increased hydrophobicity was found in the 1MN treated coals during moisture readsorption test. A CPT of the treated coals was ${\sim}20^{\circ}C$ higher than that of the corresponding raw coals and the ultrasonication was more effective way to enhance the stability against spontaneous combustion than the agitation. In the gas analysis less CO and $CO_2$ were emitted from 1MN treated coals, also indicating inhibition of pyrophoric behavior. The surface functional groups participating in the oxidation reaction seemed to be removed by the ultrasonication more effectively than by the simple mechanical agitation.

• Applied Chemistry for Engineering
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• v.27 no.1
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• pp.92-100
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• 2016

Low-temperature conversion of nitrogen oxides using plasma-assisted hydrocarbon selective catalytic reduction of (HC-SCR) was investigated. Plasma was created in the catalyst-packed bed so that it could directly interact with the catalyst. The effect of the reaction temperature, the shape of catalyst, the concentration of n-heptane as a reducing agent, the oxygen content, the water vapor content and the energy density on $NO_x$ removal was examined. $NO_x$ conversion efficiencies achieved with the plasma-catalytic hybrid process at a temperature of $250^{\circ}C$ and an specific energy input (SIE) of $42J\;L^{-1}$ were 83% and 69% for one-dimensional Ag catalyst ($Ag\;(nanowire)/{\gamma}-Al_2O_3$) and spherical Ag catalyst ($Ag\;(sphere)/{\gamma}-Al_2O_3$), respectively, whereas that obtained with the catalyst-alone was considerably lower (about 30%) even with $Ag\;(nanowire)/{\gamma}-Al_2O_3$ under the same condition. The enhanced catalytic activity towards $NO_x$ conversion in the presence of plasma can be explained by the formation of more reactive $NO_2$ species and partially oxidized hydrocarbon intermediates from the oxidation of NO and n-heptane under plasma discharge. Increasing the SIE tended to improve $NO_x$ conversion efficiency, and so did the increase in the n-heptane concentration; however, a further increase in the n-heptane concentration beyond $C_1/NO_x$ ratio of 5 did not improve the $NO_x$ conversion efficiency any more. The increase in the humidity affected negatively the $NO_x$ conversion efficiency, resulting in lowering the $NO_x$ conversion efficiency at the higher water vapor content, because water molecules competed with $NO_x$ species for the same active site. The $NO_x$ conversion efficiency increased with increasing the oxygen content from 3 to 15%, in particular at low SIE values, because the formation of $NO_2$ and partially oxidized hydrocarbon intermediates was facilitated.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.11
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• pp.1067-1074
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• 2008

In this study, the organic carbon normalized-sorption coefficients (Koc) for the binding affinity of phenanthrene (PHE) to 16 different soil humic and fulvic acids of various origins were determined by fluorescence quenching. The humic and fulvic acids used in this study were isolated from 6 different domestic soils including Mt. Hanla soil, IHSS standard soil and peat as well as Aldrich humic acid and characterized by elemental composition, ultraviolet absorption at 254 nm, composition of main structural fragments determined by CPMAS $^{13}$C NMR. The Koc values($\times$10$^4$, L/kg C) for each of HA and FA samples were in the range of 1.48$\sim$8.65 and higher in HA compared to that of FA(3.13$\sim$8.65 vs 1.48$\sim$2.48) in the experimental condition([PHE]/[HS] = 0.02$\sim$0.2(mg/L)/(mg-OC/L), pH 6). The correlation study between the structural descriptors of humic and fulvic acids and log Koc values of phenanthrene, show that the magnitude of Koc values positively correlated with the UV$_{254}$ absorptivity([ABS]$_{254}$) and two $^{13}$C NMR descriptors (C$_{Ar-H,C}$, $\sum$C$_{Ar}$/$\sum$C$_{Alk}$), while negatively correlated with the independent descriptors of the(N+O)/C atomic ratios and $^{13}$C NMR descriptors (I$_{C-O}$/I$_{C-H,C}$). These results confirmed that the binding affinity for the hydrophobic organic compound, phenanthrene are significantly influenced by the polarity and aromaticity of soil humc and fulvic acids.