• Journal of Electrochemical Science and Technology
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• v.11 no.1
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• pp.68-83
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• 2020

A fast and simple method for synthesis of Cu_xO-ZnO/PPy/RGO nanocomposite by electrochemical manner have been reported in this paper. For testing the utility of this nanocomposite we modified a GCE with the nanocomposite to yield a sensor for simultaneous determination of four analytes namely ascorbic acid (AA), dopamine (DA), uric acid (UA), and folic acid (FA). Cyclic voltammetry (CV) and Differential pulse voltammetry (DPV) selected for the study. The modified electrode cause to enhance electron transfer rate so overcome to overlapping their peaks and consequently having the ability to the simultaneous determination of AA, DA, UA, and FA. To synthesis confirmation of the nanocomposite, Field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS) were applied. The linearity ranges were 0.07-485 μM, 0.05-430 μM, 0.02-250 μM and 0.022-180 μM for AA, DA, UA, and FA respectively and the detection limits were 22 nM, 10 nM, 5 nM and 6 nM for AA, DA, UA, and FA respectively Also, the obtained electrode can be used for the determination of the AA, DA, UA, and FA in human blood, and human urine real samples.

• Nano
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• v.13 no.11
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• pp.1850135.1-1850135.8
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• 2018

A one-step high-temperature solvothermal approach to the synthesis of monolayer or bilayer $MoS_2$ anchored onto reduced graphene oxide (RGO) sheet (denoted as $MoS_2/RGO$) is described. It was found that single-layered or double-layered $MoS_2$ were synthesized directly without an extra exfoliation step and well dispersed on the surface of crumpled RGO sheets with random orientation. The prepared $MoS_2/RGO$ composites delivered a high reversible capacity of $900mAhg^{-1}$ after 200 cycles at a current density of $200mAg^{-1}$ as well as good rate capability as anode active material for lithium ion batteries. This one-step high-temperature hydrothermal strategy provides a simple, cost-effective and eco-friendly way to the fabrication of exfoliated $MoS_2$ layers deposited onto RGO sheets.

• Membrane Journal
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• v.30 no.1
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• pp.38-45
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• 2020

Although Lithium metal battery (LMB) has a very large theoretical capacity, it has a critical problem such as formation of dendrite which causes short circuit and short cycle life of the LMB. In this study, PDMS/GO composite with evenly dispersed graphene oxide (GO) nanosheets in poly (dimethylsiloxane) (PDMS) was synthesized and coated into a thin film, resulting in the effect that can physically suppress the formation of dendrite. However, PDMS has low ion conductivity, so that we attained improved ion conductivity of PDMS/GO thin film by etching technic using 5wt% hydrofluoric acid (HF), to facilitate the movement of lithium (Li) ions by forming the channel of Li ions. The morphology of the PDMS/GO thin film was observed to confirm using SEM. When the PDMS/GO thin film was utilized to lithium metal battery system, the columbic efficiency was maintained at 87.4% on average until the 100^th cycles. In addition, voltage profiles indicated reduced overpotential in comparison to the electrode without thin film.

• Clean Technology
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• v.22 no.4
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• pp.258-268
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• 2016

In this work, carboxymethylcellulose-based composite superabsorbent hydrogels were prepared by electron beam radiation. The composition of carboxymethylcellulose (CMC) varied from 4 wt%, 5 wt%, and 6 wt% to 7 wt% based on the amount of distilled water in the syntheses of hydrogels. Graphite oxide, reduced graphene oxide, activated carbon, and bentonite were used as additives for the synthesis of composite superabsorbent. The effect of CMC composition and the type of additives on the gel properties of the prepared hydrogels was investigated. In order to verify the functional groups in the prepared materials, Fourier transform infrared spectroscopy was used. In addition, mechanical strength, gel fraction, swelling kinetics, and equilibrium swelling ratios were measured for the prepared hydrogels. Swelling experiments were carried out in distilled water, urea solution, and physiological saline water. Prepared hydrogels were reused for 5 times, and gel fraction and swelling ratio were measured at every 24 hours. Among the prepared hydrogels, $C_{5%}GO$ and $C_{5%}rGO$ exhibited excellent mechanical property and relatively high swelling ratios for urea solution and physiological saline water with promising applicability as slow-release fertilizers.

• Membrane Journal
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• v.31 no.1
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• pp.16-34
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• 2021

Water supplies are decreasing in comparison to increasing clean water demands. Using nanofiltration is one of the most effective and economical methods to meet the need for clean water. Common methods for desalination are reverse osmosis and nanofiltration. However, pristine membranes lack the essential features which are, stability, economic efficiency, antibacterial and antifouling performances. To enhance the properties of the pristine membranes, graphene oxide (GO) is a promising and widely researched material for thin film composites (TFC) membrane due to their characteristics that help improve the hydrophilicity and anti-fouling properties. Modification of the membrane can be done on different layers. The thin film composite membranes are composed of three different layers, the top filtering active thin polyamide (PA) layer, supporting porous layer, and supporting fabric. Forward osmosis (FO) process is yet another energy efficient desalination process, but its efficiency is affected due to biofouling. Incorporation of GO enhance antibacterial properties leading to reduction of biofilm formation on the membrane surface. Pressure retarded osmosis (PRO) is an excellent process to generate clean energy from sea water and the biofouling of membrane is reduced by introduction of GO into the active layer of the TFC membrane. Different modifications on the membranes are being researched, each modification with its own advantages and disadvantages. In this review, modifications of nanofiltration membranes and their composites, characterization, and performances are discussed.

• Membrane Journal
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• v.32 no.6
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• pp.486-495
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• 2022

This study presents the improved recovery efficiency of rare metal ions through the modified separation membrane wettability and hydrogen ion permeation in the anion exchange membrane (AEM) under the recovery process of combined electrodialysis and solvent extraction. Specifically, the wettability of the separator was enhanced by hydrophilic modification on one separator surface through polydopamine (PDA) and lipophilic modification on the other surface through SiO₂ or graphene oxide (GO). In addition, the modified surface of AEM with polyethyleneimine (PEI), PDA, poly(vinylidene fluoride) (PVDF), etc. reduces the water uptake and modify the pore structure for proton ions generation. The suppressed transport resulted in the reduced hydrogen ion permeation. In the characterization, the surface morphology, chemical properties and composition of membrane or AEM were analyzed with Scanning Electron Microscopy (SEM) and Fourier Transform-Infrared Spectroscopy (FT-IR). Based on the analyses, improved extraction and stripping and hydrogen ion transport inhibition were demonstrated for the copper ion recovery system.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.613-613
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• 2013

그래핀은 저차원계 구조에서 기인하는 뛰어난 전기적, 물리적, 기계적 성질을 지니고 있어 실리콘 기반 기술을 대체할 전계 효과 트랜지스터 이외에도 투명전극, 초고용량 커패시터, 전계방출 디스플레이 등 다양한 응용분야에 적용 가능하다. 최근에는 이러한 응용 연구분야에서 그래핀과 탄소나노튜브 각각의 단점을 최소화하고 장점을 극대화하기 위한 그래핀-탄소나노튜브 혼성 나노구조에 대한 연구들이 진행되고 있는 추세이다. 이전 연구들에서 환원된 그래핀 산화물(Reduced Graphene Oxide, RGO)을 이용한 그래핀-탄소나노튜브 혼성 나노구조가 제작되었는데, 이는 RGO의 제작과정에서 복잡한 공정과 긴 합성과정이 요구될 뿐 아니라, 복합 물질에서 탄소나노튜브의 밀도 제어가 어렵다는 단점을 지닌다. 또한 현재까지 제작된 그래핀-탄소나노튜브 혼성 나노구조의 경우, 열 화학기상증착법으로 합성된 다층(few-layers)의 그래핀과 탄소나노튜브 혼성 나노구조를 제작하였다 [1-6]. 본 연구에서는 우수한 전기적 특성을 가진 단층(monolayer)의 그래핀을 열 화학기상증착법으로 합성한 후, 그래핀 위에 단일벽 탄소나노튜브를 성장시킴으로써 그래핀-탄소나노튜브 혼성 나노구조를 제작하였다. 합성된 그래핀-탄소나노튜브의 구조적 특징은 주사 전자 현미경과 라만 분광기 측정을 통해 확인하였고, 촉매의 표면 형상 및 화학적 상태는 원자힘 현미경과 X선 광전자 분광법을 통해 확인하였다. 또한 그래핀 기반의 전계 효과 트랜지스터의 경우, 상온에서 그래핀은 우수한 전하 이동도를 가지며 웨이퍼 스케일에서 제작하기 쉬우나 밴드 갭이 없으므로 높은 Ion/Ioff를 가지는 그래핀 기반의 트랜지스터를 만드는 것이 과제이다. 반면 탄소나노튜브는 큰 에너지 갭을 가지고 있으므로 높은 Ion/Ioff를 구현하는 소자 제작이 가능하다. 그리하여 제작된 그래핀-탄소나노튜브 혼성 나노구조의 소자 제작을 통해 전기적 특성을 조사하였다.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.362-368
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• 2022

The application of polymer composite electrolyte in all-solid-state lithium-sulfur battery (ASSLSBs) can guarantee high energy density and improve the interface contact between electrolyte and electrode, which has a broader application prospect. However, the inherent insulation of the sulfur-cathode leads to a low electron/ion transfer rate. Carbon materials with high electronic conductivity and electrolyte materials with high ionic conductivity are usually selected to improve the electron/ion conduction of the composite cathode. In this work, PEO-LiTFSI-LLZO composite polymer electrolyte (CPE) with high ionic conductivity was prepared. The ionic conductivity was 1.16×10^-4 and 7.26×10^-4 S cm^-1 at 20 and 60℃, respectively. Meanwhile, the composite sulfur cathode was prepared with Sulfur, reduced graphene oxide and composite polymer electrolyte slurry (S-rGO-CPEs). In addition to improving the ion conductivity in the cathode, CPEs also replaces the role of binder. The influence of different contents of CPEs in the cathode material on the performance of the constructed battery was investigated. The results show that the electrochemical performance of the all-solid-state lithium-sulfur battery is the best when the content of the composite electrolyte in the cathode is 40%. Under the condition of 0.2C and 45℃, the charging and discharging capacity of the first cycle is 923 mAh g^-1, and the retention capacity is 653 mAh g^-1 after 50 cycles.

• Journal of Adhesion and Interface
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• v.13 no.3
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• pp.137-144
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• 2012

Chemical functionalization of carbon nanomaterials (CNMs) is generally carried out for increasing interfacial adhesion between filler and polymer matrix for CNM-polymer nanocomposites. The chemically functionalized CNTs can produce strong interfacial bonds with many polymers, allowing CNT based nanocomposites to possess high mechanical and functional properties. Hence, increased surface adhesion can be measured indirectly by observing increased mechanical properties. However, there is a more direct way to observe interfacial bonds between polymer and CNM by measuring piezoresistivity behavior so that we can imagine the behavior of CNM particles in polymer matrix under deflection. Fuctionalization of MWCNT and rGO was carried out by oxidization reaction of MWCNT and rGO with $H_2SO_4/HNO_3$ solution. Electrical resistivities of MWCNT-PMMA and rGO-PMMA composites were decreased after functionalization because of the destructive fuctionalization process. Meanwhile, piezoresistivities of functionalized CNM-PMMA composites showed more sensitive behavior under the same deflection as compared to pristine CNM-PMMA composites. Therefore, mobility of CNM in polymer matrix was found to be improved with chemical functionalization.

• Journal of the Korean Electrochemical Society
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• v.15 no.3
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• pp.181-189
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• 2012

We developed a new high-yield synthesis method of free-standing germanium nanocrystals (Ge NCs) by means of the gas-phase photolysis of tetramethyl germanium in a closed reactor using an Nd-YAG pulsed laser. Size control (5-100 nm) can be simply achieved using a quenching gas. The $Ge_{1-x}Si_x$ NCs were synthesized by the photolysis of a tetramethyl silicon gas mixture and their composition was controlled by the partial pressure of precursors. The as-grown NCs are sheathed with thin (1-2 nm) carbon layers, and well dispersed to form a stable colloidal solution. Both Ge NC and Ge-RGO hybrids exhibit excellent cycling performance and high capacity of the lithium ion battery (800 and 1100 mAh/g after 50 cycles, respectively) as promising anode materials for the development of high-performance lithium batteries. This novel synthesis method of Ge NCs is expected to contribute to expand their applications in high-performance energy conversion systems.