Unique CO2 adsorption of pine needle biochar-based activated carbons by induction of functionality transition

Chaehun Lim,Seo Gyeong Jeong,Seongmin Ha,Naeun Ha,Seongjae Myeong,Young Seak Lee 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.124 No.-

CO2 capture has become the world’s most urgent agenda nowadays. In this work, we induced functionalitytransition of heteroatom-rich pine needle biochar based activated carbon for CO2 adsorption bymodulating activation conditions. The surface functionalities and porosity of the activated carbon derivedfrom pine needles were investigated intensively according to the activation conditions. The transition ofsurface functional groups and development of porosity were observed as activation progressed. CO2adsorption performances were determined under various conditions, and the adsorption capacities,adsorption selectivities, and cyclabilities were evaluated. From these results, different CO2 adsorptionmechanisms based on the surface functionality and porosity were clearly defined. The pyridinic,pyrrolic(N- based), and Ca(OH)2(Ca-based) CO2 sorbing functional groups derived from mild activationenabled chemical sorption with great adsorption selectivity. The high porosity derived from the severeactivation conditions resulted in physical adsorption with excellent cyclability at 298 K but the chemicalsorption property was weakened by the shift of surface groups to graphitic-N and CaCO3 rich groups. Themodulation of functional groups and porosity enabled utilizing pine needles for effective CO2 removalunder various conditions.

Mesophase pitch production aided by the thermal decomposition of polyvinylidene fluoride

Lim Chaehun,Ko Yoonyoung,Kwak Cheol Hwan,김석진,이영석 한국탄소학회 2022 Carbon Letters Vol.32 No.5

The facile production of high-purity mesophase pitch has been a long-standing desire in various carbon industries. Recently, polymer additives for mesophase production have attracted much attention because of their convenience and efficiency. We propose polyvinylidene fluoride (PVDF) as a strong candidate as an effective additive for mesophase production. The mesophase content and structural, chemical, and thermal properties of pitches obtained with different amounts of added PVDF are discussed. The influence of PVDF decomposition on mesophase formation is also discussed. We believe that this work provides an effective option for mesophase pitch production.

Enhanced CO2 adsorption of activated carbon with simultaneous surface etching and functionalization by nitrogen plasma treatment

Chaehun Lim,Cheol Hwan Kwak,Seo Gyeong Jeong,Daesup Kim,Young‑Seak Lee 한국탄소학회 2023 Carbon Letters Vol.33 No.1

Removing CO2 gas to address the global climate crisis is one of the most urgent agendas. To improve the CO2 adsorption ability of activated carbon, nitrogen plasma surface treatment was conducted. The effect of nitrogen plasma treatment on the surface chemistry and pore geometry of activated carbon was extensively analyzed. The porosity and surface groups of the activated carbon varied with the plasma treatment time. By plasma treatment for a few minutes, the microporosity and surface functionality could be simultaneously controlled. The changed microporosity and nitrogen groups affected the CO2 adsorption capacity and CO2 adsorption selectivity over N2. This simultaneous surface etching and functionalization effect could be achieved with a short operating time and low energy consumption.

정전기 방전에 의해 제조된 흑연박리 그래핀 첨가 폴리이미드 막의 열전도 향상

임채훈 ( Chaehun Lim ),김경훈 ( Kyung Hoon Kim ),안동해 ( Donghae An ),이영석 ( Young-seak Lee ) 한국공업화학회 2021 공업화학 Vol.32 No.2

본 연구에서는 폴리이미드(polyimide; PI) 막(film)의 열전도도를 향상시켜 그 응용성을 확대하고자, 정전기 방전법을 이용하여 흑연봉으로부터 그래핀을 제조하고 제조된 그래핀을 첨가하여 폴리아믹산(polyamic acid; PAA) 전구체로부터 200 μm두께의 폴리이미드 기반 열전도 막을 제조하였다. 정전기 방전 기법으로 생산된 그래핀은 라만, XPS, TEM등을 이용하여 물성을 평가하였다. 제조된 그래핀은 라만 스펙트럼 분석 결과 I_D/I_G 값이 0.138이며, XPS 분석 결과 C/O 비율이 24.91로 구조적, 표면화학적으로 우수한 물성을 나타내었다. 또한, 흑연 박리 그래핀의 첨가량에 따라 폴리이미드 막의 열전도도는 지수함수적으로 증가하였으며, 그래핀 함량을 40% 초과 시에는 폴리이미드 막을 제조할 수 없었다. 그래핀을 폴리아믹산 중량 대비40 wt% 첨가하여 제조된 폴리이미드 막의 열원반(hot disk) 열전도도는 51 W/mK를 나타내었으며, 순수한 폴리이미드 막의 열전도도(1.9 W/mK)보다 크게 향상되었다. 이 결과는 정전기 방전기법으로 제조된 박리 그래핀의 우수한 물성에 기인한 것으로 판단된다. A thermally conductive 200 μm thick polyimide-based film was made from a polyamic acid (PAA) precursor containing graphene prepared from graphite rod using an electrostatic discharge method in order to improve the thermal conductivity and expand the applicability of polyimide (PI) film. Properties of graphene produced by electrostatic discharge were measured by Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). As a result of Raman spectrum and XPS analyses of as-prepared graphene, the I_D/I_G ratio was 0.138 and C/O value was 24.91 which are excellent structural and surface chemical properties. Moreover, thermal conductivities of polyimide films increased exponentially according to graphene contents but when the graphene content exceeded 40%, the polyimide film could not maintain its shape. The thermal conductivity of carbonized PI film made from PAA containing 40 wt% of graphene was 51 W/mK which is greatly enhanced from the pristine carbonized PI film (1.9 W/mK). This result could be originated from superior properties of graphene prepared from the electrostatic discharge method.

Analysis of Shear Properties from Numerical Shear Test on Rock Joints with PFC2D

( Jeongdu Noh ),( Chaehun Lim ),( Namhyun Hwang ),( Hyeon-seo Kim ),( Seong-seung Kang ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

The most important factor to be considered in analyzing the stability of a rock slope is the geometry of the rock mass behind the slope face. The other important factor is the shear strength of the potential failure surface. The shear strength is controlled by various factors, such as frictional resistance, cohesion failure surface, rock mass density, joint continuity, and surface roughness, and so on. The surface roughness of them is affected on the mechanical properties of the joint. In particular, it plays an important role in the determination of the shear strength, and in the characterization of various mechanical and hydraulic properties of joint. In this study, numerical shear test were performed on the rock surface roughness with 10 typical rock roughness profiles in order to investigate the effect of asperity change on the shear strength of joint surface. The simulation of numerical shear test on a rock joint was applied with PFC2D (Particle Flow Code 2D). The model of numerical shear test was modelled to be 1000 mm width, and 250 mm height. Input data were density of 2200 kg/cm2, particle radius ratio of 1.5, particle mean radius of 0.15 mm, particle contact modulus of 0.18 GPa, particle stiffness ratio of 2.0, particle friction coefficient of 0.5, contact bond normal strength of 18.0 MPa, and contact bond shear strength of 18.0 MPa, respectively. Results of numerical shear test was presented cohesion of 1.77 Pa, and friction angle of 60.5°.

Carbon-coated SiOx anode materials via PVD and pyrolyzed fuel oil to achieve lithium-ion batteries with high cycling stability

김대섭,김경훈,Lim Chaehun,이영석 한국탄소학회 2022 Carbon Letters Vol.32 No.1

Silicon oxide (SiOx) has been considered one of the most promising anode materials for lithium-ion batteries due to having a higher capacity than the commercial graphite anodes. However, its practical application is hampered by very large volume variations. In this work, pyrolysis fuel oil is the carbon coating precursor, and physical vapor deposition (PVD) is performed on SiOx at 200 and 400 °C (SiOx@C 200 and SiOx@C 400), followed by carbonization at 950 °C. SiOx@C 200 has a carbon coating layer with a thickness of ~ 20 nm and an amorphous structure, while that of SiOx@C 400 is approximately 10 nm thick and has a more semigraphitic structure. The carbon-coated SiOx anodes display better charge–discharge performance than the pristine SiOx anode. In particular, SiOx@C 200 shows the highest reversible capacity compared with the other samples at high C-rates (2.0 and 5.0 C). Moreover, SiOx@C 200 exhibits excellent cycling stability with a capacity retention of 90.2% after 80 cycles at 1.0 C. This result is ascribed to the suppressed volume expansion by the PFO carbon coating on SiOx after PVD.

High-efficiency oil/water separation of hydrophobic stainless steel Mesh filter through carbon and fluorine surface treatment

Myeong Seongjae,Lim Chaehun,Kim Seokjin,이영석 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.6

With the rapid industrial development, the discharge of oily wastewater has increased and polluted the environment. The conventional oil/water separation method has problems, such as generating harmful by-products, high operating costs, and low efficiency. For this reason, research on the development of ideal oil/water separation materials is being actively conducted. In this work, a hydrophobic mesh filter with excellent separation efficiency and separation speed was prepared through the surface coating of stainless steel Mesh (SUS Mesh), which has a large aperture size. After carbon coating on the surface of the SUS Mesh using the physical vapor deposition method, hydrophobicity was improved by giving fluorine functional groups to the surface using fluorine plasma. The manufactured mesh filter separated the oil at a high flux (6,062 Lm−2h−1) in a horizontal condition without external force, and at a high speed of fewer than two minutes, with a separation efficiency is 99.88%. Very high separation efficiency was observed. In addition, the average efficiency of 99.77% was maintained even in continuous oil/water separation. The hydrophobic mesh filter fabricated by a simple process in this study can be evaluated as a promising oil/water separation material that can be actually applied to separate oil from oily wastewater.

플라즈마 불소화에 의해 제조된 불소 도핑 PVDF의 표면 및 부식방지 특성

김석진 ( Seokjin Kim ),임채훈 ( Chaehun Lim ),김대섭 ( Daesup Kim ),이영석 ( Young-seak Lee ) 한국공업화학회 2021 공업화학 Vol.32 No.6

Polyvinylidene fluoride (PVDF)는 우수한 가공성을 가지고 있어 코팅 재료로 유망하지만 다른 불소계 고분자에 비하여 소수성이 약하여 부식 방지 등 그 응용에 제한이 있다. 본 연구에서는 PVDF의 부식방지 특성을 향상시키고자 사불화탄소(CF₄) 가스를 이용하여 플라즈마 불소화를 수행하였고, 유량에 따른 불소 함량 및 소수성 변화를 고찰하고 부식방지 특성을 확인하였다. PVDF 막 표면의 불소 함량은 사불화탄소 유량이 증가함에 따라 46.70%로 증가하였으나 그 표면자유에너지는 불소함량의 증가와 일치하지 않았다. 한편, PVDF 표면의 표면 거칠기는 불소화 유량에 따라 최대 150% 증가하다가 다시 감소하는 경향을 보였다. 이는 플라즈마 불소화는 불소화 기능기 도입 및 표면식각으로 인하여 표면자유에너지에 영향을 주는 것으로 판단된다. 또한, PVDF 코팅된 철판의 부식 정도는 미처리 철판에 비하여 표면 산소 함량이 49.2%에서 19.0% 이하로 크게 개선되었으며, 특히, 불소화 처리된 PVDF의 산소함량은 13.6%으로 불소화 처리되지 않은 PVDF보다 28.4 % 정도 낮아져 우수한 부식방지 특성을 보이는 것으로 관찰되었다. Polyvinylidene fluoride (PVDF) is a promising coating material because of its outstanding processability. The PVDF coating, however, has limitations in anti-corrosion application due to its weak hydrophobicity compared to that of other fluoropolymers. In this study, plasma fluorination was performed using carbon tetrafluoride (CF₄) gas to improve anti-corrosion properties of PVDF. The fluorine content and hydrophobicity of PVDF were investigated in different CF₄ flow rates, followed by the determination of anti-corrosion properties. The fluorine content on the surface of the PVDF film increased by up to 46.70%, but the surface free energy was independent of CF₄ flow rate. Meanwhile, the surface roughness of the PDVF film tended to increase by up to 150% and then decrease with increasing CF₄ flow rate. It is considered that the plasma fluorination affects the surface free energy due to the introduction of fluorine functional groups and surface etching. In addition, the degree of corrosion of the PVDF-coated Fe plate was significantly reduced from 49.2% to 19.0% compared to that of the uncoated Fe plate. In particular, the degree of corrosion of the fluorinated PVDF-coated Fe plate was 13.6%, which was 28.4% lower than that of the PVDF-coated Fe plate, showing improved anti-corrosion protection.

탄소섬유강화플라스틱 유래 폐 탄소섬유로 제조된 불화탄소 기반 리튬일차전지의 전기화학적 특성

하나은 ( Naeun Ha ),임채훈 ( Chaehun Lim ),하성민 ( Seongmin Ha ),명성재 ( Seongjae Myeong ),이영석 ( Young-seak Lee ) 한국공업화학회 2023 공업화학 Vol.34 No.5

본 연구에서는 탄소섬유강화플라스틱(CFRP)을 열분해하여 얻은 폐 탄소섬유를 이용하여 기상 불소화를 통해 불화탄소를 제조하고 리튬일차전지의 환원극 소재로 재활용하고자 하였다. 먼저 열분해로 얻은 폐 탄소섬유의 물리화학적 특성을 파악하였으며, 이 폐 탄소섬유에 기상 불소화 효과를 평가하기 위하여 불화탄소의 구조적, 화학적 특성을 분석하였다. XRD 분석에 의해 폐 탄소섬유의 육각망탄소 적층구조(002피크)는 기상 불소화의 온도가 증가함에 따라 점차 불화탄소 구조(001피크)로 전환되었음을 확인하였다. 이 불화탄소를 이용하여 제조된 리튬일차전지의 방전용량은 최대 862 mAh/g이었다. 이는 다른 탄소 재료로 제조한 불화탄소 기반 리튬이온차전지의 방전용량과 비교하였을 때 우수한 성능을 보였다. 이러한 결과는 폐 CFRP 기반 폐탄소섬유를 이용한 불화탄소는 리튬일차전지의 환원극 소재로 활용할 수 있을 것으로 여겨진다. In this study, waste carbon fiber obtained by pyrolysis of carbon fiber reinforced plastic (CFRP) was used to produce carbon fluoride through vapor phase fluorination and recycled as a reducing electrode material for lithium primary batteries. First, the physicochemical properties of the waste carbon fiber obtained by pyrolysis were determined, and the structural and chemical properties of carbon fluoride were analyzed to evaluate the effect of vapor phase fluorination on the waste carbon fiber. XRD analysis confirmed that the hexagonal network carbon laminated structure (002 peak) of the waste carbon fiber was gradually converted into a carbon fluoride structure (CF_X, 001 peak) as the temperature of gas phase fluorination increased. The discharge capacity of the lithium primary battery produced using this carbon fluoride was up to 862 mAh/g. This was compared to the discharge capacity of carbon fluoride-based Li-ion batteries made of other carbon materials. These results suggest that carbon fluoride made from waste CFRP-based carbon fibers can be used as a reducing electrode material for Li-ion batteries.

기상 불소화법을 이용한 WO3-xFx 광촉매의 합성 및 광분해 특성

이혜련 ( Hyeryeon Lee ),임채훈 ( Chaehun Lim ),이란은 ( Raneun Lee ),이영석 ( Young-seak Lee ) 한국공업화학회 2021 공업화학 Vol.32 No.6

In this research, fluorine doping was performed to enhance the photocatalytic activities of WO₃ which were measured using methylene blue dye. WO_3-xF_x photocatalyts were prepared by a vaper phase fluorination during a sintering for preparing WO₃ photocatalysts from a WCl₆ precursor. The bandgap energy of WO₃ photocatalysts decreased from 2.95 eV to 2.54 eV, and the oxygen vacancies site increased by about 55% after fluorine doping. In addition, the initial degradation efficiency of methylene blue showed that the fluorine doped sample showed a 6-fold increase in photocatalytic activities from 10% to 60% compared to that of the untreated sample. It is believed that fluorine is doped to reduce the band gap of photocatalysts, enabling the catalytic activity with low energy, and that oxygen vacancies-generated surface defects increase the visible light absorption region of WO₃ photocatalysts, thereby increasing photocatalytic activity. In this study, it was confirmed that fluorine-doped WO_3-xF_x photocatalysts with an excellent photocatalytic activity can be manufactured easily using a one-step vaper phase fluorination that does not require a post-treatment process.