Search

The adsorption, formation, and interaction energies between carbon dioxide (CO2) and carbon oxide functional groups on porous carbon surface were analyzed through XPS, textural analysis, CO2 gas adsorption, and theoretical study. Carbon molecular sieves (CMSs) as porous carbon were modified by several concentrations of hydrogen peroxide (H2O2) solution under atmospheric conditions in an attempt to introduce carbon oxide groups and increase their CO2 adsorption capacity. Created oxide groups on carbon surface of CMSs were determined by XPS analysis and the CO2 adsorption capacities were investigated through the CO2 adsorption isotherms at 273 and 298 K at low pressure (max. 800 mmHg). The CO2 uptake capacity on CMSs modified by H2O2 was increased compared to an unmodified CMS and increased with increasing carboxylic (-COOH) group concentration on the carbon surface of CMSs. For a theoretical approach, binding energies between CO2 and various functional groups on the surface of CMSs have been investigated using several electronic structure calculations. As the result of the computational study by the MP2 method, a carboxylic group has the highest binding energy for CO2 (-COOH····CO2) of 4.45 kcal/mol, compared to quinone (dbndO) of 3.9, phenol (-OH) of 3.2 and lactone (-O-C=O) of 3.57 kcal/mol. This work demonstrates that introducing -COOH groups on CMS by H2O2 are a suitable modification for CO2 adsorption.

The pitch-based high crystallinity cokes are investigated by evaluating its potential as electrode materials for electric double layer capacitors (EDLCs). After activation process, the high crystallinity cokes-based activated carbon (hc-AC) demonstrates great potential for use as an electrode material for EDLCs. The specific capacitance of hc-AC with the carbon to KOH ratio of 1:3 is 276 F g−1, even with a low specific surface area of 983 m2 g−1. These results are comparable to that of the most commonly used material for EDLCs, MSP 20 (256 F g−1), which has a high specific surface area of 1807 m2 g−1.

The effect of functionalized carbon surface on gas separation is investigated in modified carbon molecular sieves (CMSs) with H 2 O 2 for CO 2 /CH 4 mixed gas. The textural properties of the surface changed slightly, with a greater micropore volume and surface area enhancement. The amount of adsorbed CO 2 increased from 2.57 for the raw sample to 2.68 mmol/g for the modified CMSs. The breakthrough times for CO 2 were after 7.5 min for modified CMSs and 5 min for R-CMS. These effects were due to the interaction between CO 2 and oxide groups on the surfaces of CMSs resulting from the H 2 O 2 treatment.

Novel hollow shaped nanofibers with (Ti, Sn)O 2 solid-solutions have been synthesized for photocatalysts by the impregnation method using tin chloride (SnCl 2 ) and titanium tetraisopropoxide (TTIP), and further characterized by SEM, EDS, TGA, and XRD. The results showed that uniformly distributed hollow shaped nanofibers with (Ti, Sn)O 2 solid-solutions was successfully formed in the case of the optimum weight ratio of the Ti precursor. These hollow shaped nanofibers exhibited the higher photocatalytic reactivity by the conversion of methylene blue in aqueous solution under UV irradiation than not only prepared SnO 2 but also TiO 2 hollow shaped nanofibers. The highest degradation ratio was about 85% at 70 min using hollow shaped nanofibers with (Ti, Sn)O 2 solid-solutions photocatalysts, which exhibited more than 3.5 times that of TiO 2 . It has been found that enhanced MB degradation efficiency is not only due to the charge separation of electron–hole pairs but also increasing the photocatalytic reactive site.

The sensitivity of a biosensor electrode was increased by introducing hydrophilic N-groups onto the surface of a polyacrylonitrile (PAN) based activated carbon fiber. The electrospun carbon fiber was activated using KOH to improve the adsorption of glucose oxidase (GOx) enzymes through pore production and the introduction of oxygen functional groups. The activated carbon fibers (ACFs) were then reacted with urea to increase their hydrophilicity by doping their nitrogen groups. The sensor sensitivity and the Michaelis-Menten constant, Km, were altered by varying the percentages of functional groups on the electrode surfaces. Whereas the value of Km was affected by the kind of functional groups, the sensitivity of the biosensor electrode was chiefly affected by the amount of functional groups introduced urea modification because the enzyme was better immobilized onto urea-modified activated carbon fibers. Quantitatively, the sensitivity was two- to three-fold higher for the biosensors based on urea-treated ACFs than those based on untreated ones. This increased sensitivity is attributed to the nitrogen and oxygen functional groups on the urea-modified ACFs.

본 연구에서는 바나듐 레독스 흐름전지의 효율을 향상시키고자 탄소펠트에 열산화 반응과 암모니아수 처리를 이용하여 질소가 도핑된 탄소펠트 전극을 제조하였다. 또한 제조된 탄소펠트 전극의 전기화학적 특성평가를 위하여 CV 실험 및 충/방전 실험을 실시하였다. 암모니아수 처리온도가 증가함에 따라 탄소펠트 표면의 질소 관능기가 증가함을 XPS를 통하여 확인하였으며, CV 측정 결과 암모니아수 처리된 탄소펠트는 열산화된 탄소펠트에 비하여 산화/환원의 반응성이 우수함을 확인하였다. 충/방전 실험결과 300 ℃에서 암모니아수 처리한 탄소펠트 전극은 열산화된 탄소펠트 전극보다 에너지효율, 전압효율, 전류효율이 각각 약 6.93, 1.0, 4.5%씩 향상됨을 알 수 있었다. 이는 질소 관능기가 탄소펠트 전극과 전해질 사이의 전기화학적 성능 향상에 도움을 주었기 때문으로 사료된다. In this study, nitrogen doped carbon felt (CFt) is prepared using thermal oxidation and liquid phase ammonia treatment to improve the efficiency for vanadium redox flow batteries (VRFB). The electrochemical properties of prepared CFt electrodes are investigated using cyclic voltammetry (CV) and charge/discharge test. The XPS result shows that the increase of liquid phase ammonia treatment temperature leads to the increased nitrogen functional group on the CFt surface. Redox reaction char-acteristics using CV reveal that the liquid phase ammonia treated CFt electrodes are more reversible than the thermally oxi-dized CFt. When CFt is treated by the liquid phase ammonia at 300 ℃, VRFB cell energy efficiency, voltage efficiency, and current efficiency are increased about 6.93%, 1.0%, and 4.5%, respectively, compared to those of the thermally oxidized CFt. These results are because nitrogen functional groups on CFt help to improve the electrochemical properties of redox reaction between electrode and electrolyte interface.

Feasibility of utilizing unburned carbon residue in coal ash as a potential precursor for the production of activated carbon wasassessed to seek for solution to recycle unburned carbon residue. The unburned carbon concentrate generated from the 4 stagesof cleaner flotation has a grade of 87% carbon. The crystalline impurities in the concentrate included quartz and mullite.Unburned carbon had a low specific surface area of 10m 2 /g, which might be related to a high degree of coalification of domesticanthracite coal. Carbon particles were mostly porous and have a turbostratic structure. When 1g of carbon was activated with6g of KOH powder, the highest specific surface area value of 670m 2 /g was achieved. Low wettability of unburned carbon par-ticles, which was resulted from high temperature combustion in a boiler, might cause poor pore formation when they were acti-vated by KOH solution. The activated carbon produced in this study developed micropores, with an equivalent quality of * Received : November 5, 2013 · Revised : December 12, 2013 · Accepted : December 24, 2013Corresponding Author : Sujeong Lee (E-mail : crystal2@kigam.re.kr)Mineral Resources Research Division, Korea Institute of Geoscience & Mineral Resources, 124 Gwahang-no, Yuseong-gu, Daejeon,305-350 KoreaTel : +82-42-868-3125 / Fax : +82-42-868-3418ⓒThe Korean Institute of Resources Recycling. All rights reserved. This is an open-access article distributed under the termsof the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permitsunrestricted non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited.

Multi-walled carbon nanotube (MWCNT)/epoxy composites are prepared by a vacuum as- sisted resin transfer molding (VARTM) method. The mechanical properties, fracture sur- face morphologies, and thermal stabilities of these nanocomposites are evaluated for epoxy resins with various amounts of MWCNTs. Composites consisting of different amounts of MWCNTs displayed an increase of the work of adhesion between the MWCNTs and the matrix, which improved both the tensile and impact strengths of the composites. The tensile and impact strengths of the MWCNT/epoxy composite improved by 59 and 562% with 0.3 phr of MWCNTs, respectively, compared to the epoxy composite without MWCNTs. Thermal stability of the 0.3 phr MWCNT/epoxy composite increased compared to other ep- oxy composites with MWCNTs. The enhancement of the mechanical and thermal properties of the MWCNT/epoxy nanocomposites is attributed to improved dispersibility and strong interfacial interaction between the MWCNTs and the epoxy in the composites prepared by VARTM.

In this study, we prepared pelletized porous carbon adsorbent (PCA) according to the different pyrolysis temperature using activated carbon and polyvinyl alcohol (PVA) as a binder for the removal of toluene, which is one of the representative volatile organic compounds (VOCs). We investigated physical characteristics of PCA using FE-SEM, BET, TGA and evaluated their adsorption capacity for toluene using GC. It was confirmed that the formability of pellets composed of the activated carbon, PVA and solvent of mass mixing ratio was 1 : 0.2 : 0.8 was the most outstanding. Toluene adsorption capacity was evaluated by measuring the maximum time when more than 99% of toluene adsorbed on the pellet. The specific surface area of the adsorbent pyrolyzed at was measured as 4.7 times in compared to that of the unpyrolyzed pellet. Micropore volume and toluene adsorption capacity of PCA increased fivefold to be 0.30 cc/g and thirteenfold to be 26 hours compared to that of the unpyrolyzed pellet, respectively. These results were attributed to the change of pore size and specific surface area due to the PVA content and the different pyrolysis temperature.

To improve the electrochemical performance of an activated carbon (AC)-based electric double-layer capacitor (EDLC), the AC surface, which is used as an electrode, was modified using different concentrations of phosphoric acid. The effects of the treatment on the surface and electrochemical properties of the AC electrodes were investigated. The specific capacitance increased from 256 F/g for an untreated sample to 452 F/g for a sample treated with a 2 M solution at a scan rate of 5 mV/s. This increase can be attributed to an increase in the mesopore volume caused by the etching effect of the reaction between the carbon surfaces and phosphoric acid. In addition, oxygen functional groups, which were introduced by the treatment, improved the electrochemical properties of the resulting AC-based electrode. Therefore, simultaneous etching and oxygen introduction with phosphoric acid can easily bind oxygen functional groups (particularly C O) onto the surface of an AC electrode. This method is effective at preparing AC for use in an EDLC with improved electrochemical properties.

In this study, the breakthrough curve behaviors of aminated carbon molecular sieves (CMSs) were investigated for a CO2/CH4 mixed gas, and the selective separation of CO2 was demonstrated. Nitrogen functional groups were effectively introduced onto the surfaces of the a-CMSs, and they attached themselves to the pores of the CMSs as the ammonium hydroxide concentration was increased. Nitrogen functional groups on the surfaces of the aminated CMSs, such as NH2 and CN, played an important role in guiding CO2 into the micropores via the attractive forces felt by the electrons in the CO2 molecules.

Nanoporous non-woven carbon fibers for a gas sensor were prepared from a pitch/polyacrylonitrile (PAN) mixed solution through an electrospinning process and their gas-sensing properties were investigated. In order to create nanoscale pores, magnesium oxide (MgO) powders were added as a pore-forming agent during the mixing of these carbon precursors. The prepared nanoporous carbon fibers derived from the MgO pore-forming agent were characterized by scanning electron microscopy (SEM), N2-adsorption isotherms, and a gassensing analysis. The SEM images showed that the MgO powders affected the viscosity of the pitch/PAN solution, which led to the production of beaded fibers. The specific surface area of carbon fibers increased from 2.0 to 763.2 m 2 /g when using this method. The template method therefore improved the porous structure, which allows for more efficient gas adsorp tion. The sensing ability and the response time for the NO gas adsorption were improved by the increased surface area and micropore fraction. In conclusion, the carbon fibers with high micropore fractions created through the use of MgO as a pore-forming agent exhibited improved NO gas sensitivity.

The surface of carbon molecular sieves (CMSs) was fluorinated to investigate the separation behavior of CH4/CO2. The fluorination of CMSs was carried out at various F2 partial pressures to determine the effect of the F2 content. Fluorine functional groups were effectively introduced on the surface of the CMSs, and the volume of pores in the CMSs was increased due to fluorination, especially those with a diameter less than 8 A. As the fluorine partial pressure was increase, an increase in the CO2 adsorption capacity of CMSs was observed due to Lewis acid–base interactions between the functional groups of CMSs and CO2. Based on the selective CO2 adsorption results, the CO2 breakthrough with fluorinated CMS occurred at later stages of CH4/CO2 gas separation process compared to Raw-CMS. Therefore the presence of fluorine on the surfaces of CMSs affects the pore volumes of CMSs. According to the adsorption isotherms, the CO2 adsorption efficiency of CMSs was improved from 1.61 to 2.04 mmol/g at 298 K.

The surface of phenol-based activated carbon (AC) was seriatim amino-fluorinated with solution of ammonium hydroxide and hydrofluoric acid in varying ratio to fabricate electrode materials for use in an electric double-layer capacitor (EDLC). The specific capacitance of the amino-fluorinated AC-based EDLC was measured in a 1 M H 2 SO 4 electrolyte, in which it was observed that the specific capacitances increased from 215 to 389 F g −1 and 119 and 250 F g −1 with the current densities of 0.1 and 1.0 A g −1 , respectively, in comparison with those of an untreated AC-based EDLC when the amino-fluorination was optimized via seriatim mixed solution of 7.43 mol L −1 ammonium hydroxide and 2.06 mol L −1 hydrofluoric acid. This enhancement of capacitance was attributed to the synergistic effects of an increased electrochemical activity due to the formation of surface N- and F-functional groups and increased, specific surface area, and mesopore volumes, all of which resulted from the amino-fluorination of the electrode material.