• Journal of Korean Society of Environmental Engineers
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• v.33 no.11
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• pp.804-811
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• 2011

The aim of this study is to evaluate the applicability of adsorption models for understanding adsorption properties of adsorbents. For this study, the adsorption charateristics of $NO_3^-$ by commercial anion exchange resin, PA-308, were investigated in bach process. The adsorption kinetic data for $NO_3^-$ by anion exchange resin showed two stage process comprising a fast initial adsorption process and a slower second adsorption process. Both the pseudo-first-order kinetic model and the pseudo-second-order kinetic model could not be used to predict the adsorption kinetics of $NO_3^-$ onto anion exchange resin for the entire sorption period. Only the fast initial portion ($t{\leq}20min$) of adsorption kinetics was found to follow pseudo-first-order kinetic model and controlled mainly by external diffusion that is very fast and high, whereas, the slower second portion (t > 20 min) of adsorption kinetics seems to be controlled by a second-order chemical reaction and by intraparticle diffusion.

• Carbon letters
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• v.7 no.2
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• pp.114-118
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• 2006

Isotropic pitch-based carbon fiber has been activated by steam diluted in nitrogen in order to characterize the microporosity. Especially, 40 wt% burn-off ACFs were prepared from different conditions to compare the pore structure and size. The ACFs were thinly sliced to investigate the inside pores by TEM and image analyzer. As expected, the adsorption characteristics of these ACFs were quite different from one another because of different pore structure and size. Most pores are not slit-shaped but rather round. Small round micropores become broad and irregular as increasing the activation time and temperature.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.4
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• pp.376-384
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• 2023

Nitrogen-doped graphene was synthesized by a hydrothermal method using graphene oxide (GO) as the raw material, urea as the reducing agent and nitrogen as the dopant. The morphology, structure, composition and electrochemical properties of the samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analysis, electrical conductivity and electrochemical tests. The results show that urea can effectively reduce GO and achieve nitrogen doping under the hydrothermal conditions. By adjusting the mass ratio of raw materials to dopants, the graphene with different nitrogen doping contents can be obtained; the nitrogen content range is from 5.28~6.08% (atomic fraction percentage).When the ratio of dopant to urea is 1:30, the nitrogen doping content reaches a maximum of 6.08%.The supercapacitor performance test shows that the nitrogen content prepared by the ratio of 6.08% is the best at 0.1 A·g^-1. The specific capacitance is 95.2 F·g^-1.

• Journal of Korean Society of Water and Wastewater
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• v.11 no.4
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• pp.99-109
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• 1997

To estimate the nutrients delivery characteristics of Chogang stream to Keum River, sediment and soil characteristics were analyzed in the stream and in the stream bank. Along the stream, soil samples from river sediment were collected and tested monthly for phosphorus and nitrogen concentrations. Nitrogen concentration in the sediment is much lower than that of soil in the river bank especially in summer presumably due to the high desorption characteristics of nitrogen by the increasing rainfall energy during summer. Instead, the concentrations of phosphorus were similar for the sediment and the soil in the river bank due to the strong adsorption characteristics of phosphorus. Batch tests were performed to evaluate the desorption potential of the sediments. Universal Soil Loss Equation (USLE) was applied to quantify soil erosion in each watershed due to rainfall. It was estimated that approximately 25% of total phosphorus by mass basis could be released from the sediment if the water was disturbed vigorously. The mass load of nitrogen and phosphorus into the Chogang Stream from the watershed were evaluated from the USLE and release ratio of phosphorus.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.5
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• pp.103-113
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• 1996

The properties of the deposited film depend on the deposition condition and these, in turn depend critically on the morphology and crystal orientation of the films. Therefore, it is important to clarify the nucleation occurrence and growth stage of the morphology and orientation of the film affected by deposition parameters, e.g. the gas pressure and bias voltage etc. In this work, magnesium thin flims were prepared on cold-rolled steel substrates by a thermo-eletron activation ion plating technique. The influence of nitrogen gas pressure and substrate bias voltage on their crystal orientation and morphology of the coated films were investigated by scanning electron microscopy (SEM) and X-ray diffraction, respectively. The diffraction peaks of magnesium film became less sharp and broadened with the increase of nitrogen gas pressure. With an increase in nitrogen gas pressure, flim morphology changed from colum nar to granular structure, and surface crystal grain-size decreased. The morphology of films depended not only on gas pressure but also on bias voltage, i.e., the effect of increasing bias voltage was similar to that of decreasing gas pressure. The effect of crystal orientation and morphology of magnesium films on corrosion behaviors was estimated by measuring anodic polarization curves in deaerated 3%NaCl solution. Magnesium, in general, has not a good corrosion resistance in all environments. However, these magnesium films prepared by changing nitrogen gas pressure showed good corrosion resistance. Among the films, magnesium films which exhibited granular structure had the highest corrosion resistance. The above phenomena can be explained by applying the effects of adsorption, occlusion and ion sputter of nitrogen gas.

• Analytical Science and Technology
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• v.11 no.4
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• pp.266-270
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• 1998

The Ag-treated activated carbon was prepared by the impregnation of Ag on the home made activated carbon. We investigated the nitrogen adsorption property, surface structure, and antibacterial activity of the carbon. The BET surface areas of Ag impregnated activated carbon are distributed to $740-1112.2m^2/g$ region. The results of nitrogen adsorption property show that BET surface areas move gradually to lower value with increasing $AgNO_3$ mole concentration. From the SEM results, we observed window blocking effect for micropores of external surface of adsorbent by Ag impregnation. Escherichia coli which is a kind of colon bacillus was used as bacteria for antibacterial test. From these results, we also observed that activity increase gradually to larger range with increasing $AgNO_3$ mole ratio.

• Clean Technology
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• v.23 no.1
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• pp.1-14
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• 2017

At high nitrate concentrations, water must be treated to meet regulated concentrations because it results in threat to human health and eutrophication of natural water. However, it is almost impossible to remove nitrate by conventional water treatment methods such as coagulation, filtration and precipitation, due to its high water solubility. Therefore, other technologies including adsorption, ion exchange, reverse osmosis, denitrification, and electrodialysis are required to effectively remove nitrate. Each of these technologies has their own strengths and drawbacks and their feasibility is weighted against factors such as cost, water quality improvement, residuals handling, and pre-treatment requirements. An adsorption technique is the most popular and common process because of its cost effectiveness, ease of operation, and simplicity of design. Surface modifications of adsorbents have been enhanced their adsorption of nitrate. The nitrate-selective membrane process of electrodialysis reversal and reverse osmosis have proven over time and at many locations to be highly effective in removing nitrate contaminating problems in aqueous solutions. Both electrodiaysis and reverse osmosis methods generate highly concentrated wastes and need careful consideration with respect to disposal.

• Journal of the Korean Chemical Society
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• v.21 no.5
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• pp.353-361
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• 1977

In this paper we propose a new theory of multilayer physical adsorption based on the view that a second or higher layer molecule will be adsorbed above the center of a square or triangular array of molecules, rather than on top of molecules themselves, in the next lower layer and the corresponding adsorption isotherm is derived. The derived isotherm contains three adjustable parameters; $v_m$ (monolayer capacity), q/$q_1$ (ratio of the molecular partition function for the second or higher layer vs. that for the first layer) and n (a parameter characterizing the piling pattern of adsorbed molecules). When applied to adsorption of argon on "Carbolac" carbon and nitrogen on Linde silica, excellent agreements between observed and calculated values are obtained up to p/$p_0$ = 0.8. In both cases n = 3 gives the best fit and this probably indicates that adsorbed molecules are piled up in a closest packing pattern.

• Korean Journal of Materials Research
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• v.29 no.5
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• pp.336-341
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• 2019

The gas adsorption isotherm requires accurate measurement for the analysis of porous materials and is used as an index of surface area, pore distribution, and adsorption amount of gas. Basically, adsorption isotherms of porous materials are measured conventionally at 77K and 87K using liquid nitrogen and liquid argon. The cold volume calibration in this conventional method is done simply by splitting a sample cell into two zones (cold and warm volumes) by controlling the level sensor in a Dewar filled with liquid nitrogen or argon. As a result, BET measurement for textural properties is mainly limited to liquefied gases (i.e. $N_2$ or Ar) at atmospheric pressure. In order to independently investigate other gases (e.g. hydrogen isotopes) at cryogenic temperature, a novel temperature control system in the sample cell is required, and consequently cold volume calibration at various temperatures becomes more important. In this study, a cryocooler system is installed in a commercially available BET device to control the sample cell temperature, and the automated cold volume calibration method of temperature variation is introduced. This developed calibration method presents a reliable and reproducible method of cryogenic measurement for hydrogen isotope separation in porous materials, and also provides large flexibility for evaluating various other gases at various temperature.

• Journal of the Korean Vacuum Society
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• v.2 no.4
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• pp.491-500
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• 1993

The adsorption of nitrogen (77K) and carbon dioxide(273K) was performed on a series of activated carbon fiber. Theadsorption iotherm of nitrogen was typical type 1 and that of carbon dioxide was convex. As the specific surface area increases, there are linear increases in BET constant C mean pore diameter, the width of pore size distribution, wide micropore volume, total micropore volume, total pore volume and external surface area, however, narrow micropore volume was nealy constant . The total micorpore volume fraction in total pore volume is above 97%.