• 한국세라믹학회지
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• 제51권6호
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• pp.570-574
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• 2014

Magnetic-graphene nanosheets have been synthesized via a simple effective chemical precipitation method followed by heat treatment. The composite nanosheets are super paramagnetic at room temperature and can be separated by an external magnetic field. The prepared magnetic-graphene nanosheets were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and BET surface area analysis. The results demonstrated the successful attachment of iron oxide nanoparticles to graphene nanosheets. It was found that the attached nanoparticles were mainly $Fe_3O_4$. The magnetic-graphene nanosheets showed near complete methyl orange removal within 10 mintues and would be practically usable for methyl orange separation from water.

• 한국재료학회지
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• 제33권5호
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• pp.222-228
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• 2023

Transition metal oxides formed by a single or heterogeneous combination of transition metal ions and oxygen ions have various types of crystal structures, which can be classified as layered structures and non-layered structures. With non-layered structures, it is difficult to realize a two-dimensional structure using conventional synthesis methods. In this study, we report the synthesis of cobalt oxide into wafer-scale nanosheets using a surfactant-assisted method. A monolayer of ionized surfactant at the water-air interface acts as a flexible template for direct cobalt oxide crystallization below. The nanosheets synthesized on the water surface can be easily transferred to an arbitrary substrate. In addition, the synthesizing morphological and crystal structures of the nanosheets were analyzed according to the reaction temperatures. The electrochemical properties of the synthesized nanosheets were also measured at each temperature. The nanosheets synthesized at 70 ℃ exhibited higher catalytic properties for the oxygen evolution reaction than those synthesized at other temperatures. This work suggests the possibility of changing material performance by adjusting synthesis temperature when synthesizing 2D nanomaterials using a wide range of functional oxides, resulting in improved physical properties.

• Tribology and Lubricants
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• 제35권6호
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• pp.343-349
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• 2019

According to a report in 2011, hexagonal boron nitride demonstrated good solubility in pure water, even without surfactants or organic functionalization. Hexagonal boron nitride nanosheets are an effective lubricant additive, and their solubility in pure water has motivated lubrication engineers to utilize aqueous solutions containing these nanosheets as water-based lubricants. In this study, we measure the width and height of the hexagonal boron nitride nanosheets dispersed in pure water by using the Zetasizer and atomic force microscopy. Without surfactants or functionalization, aqueous solutions containing 0.10, 0.07, 0.05, and 0.01 wt% of hexagonal boron nitride nanosheets are synthesized via sonication-assisted hydrolysis. The Zetasizer provides only a one-dimensional size of approximately 410 nm, regardless of the concentration of the solution. Thus, it does not allow the estimation of the shape of the nanosheet. To acquire the three-dimensional size of the nanosheets, atomic force microscopy is employed. The aqueous solutions containing 0.10, 0.07, 0.05, and 0.01 wt% of the hexagonal boron nitride nanosheets show average values of 740, 450, 700, and 610 nm in width, and 37, 26, 33, and 32 nm in thickness, respectively. No significant trend is observed between the concentration of the solution and size of the nanosheets. Therefore, when preparing a water-based lubricant, it may be appropriate to adjust conditions such as ultrasonication time rather than the concentration.

• 한국결정성장학회지
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• 제27권6호
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• pp.289-294
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• 2017

원자층 두께의 2차원 나노쉬트(2 dimensional nanosheets)를 이용하여 제작한 필름은 나노쉬트 크기에 따라 다양한 물성을 나타낸다. 이는 필름의 물성이 쉬트와 쉬트 사이 계면물성에 의존하기 때문이다. 따라서 큰 나노쉬트의 합성은 필름의 계면물성 의존도를 줄일 수 있다는 점에서 매우 중요하다. 본 연구에서 단결정 성장된 출발물질과 화학적 박리법을 이용하여 마이크로미터 이상의 크기를 갖는 원자층 두께의 $TiO_x$ 나노쉬트를 제조하는데 성공하였다. 또한 제조 공정 중 유기물을 이용한 박리 단계 시 기계적 원심 교반속도가 나노쉬트 크기와 농도에 밀접히 연관되어 있음을 알 수 있었다.

• Composites Research
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• 제28권5호
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• pp.270-276
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• 2015

Polyvinylidene fluoride (PVDF)-based nanocomposites are fabricated by incorporation of boron nitride (BN) nanosheets with anisotropic orientation for a potential high thermal conducting ferroelectric materials. The PVDF is dissolved in dimethylformamide (DMF) and homogeneously mixed with exfoliated BN nanosheets, which is then cast into a polyimide film under application of high magnetic fields (0.45~10 T), where the direction of the filler alignment was controlled. The BN nanosheets are exfoliated by a mixed way of solvothermal method and ultrasonication prior to incorporation into the PVDF-based polymer suspension. X-ray diffraction, scanning electron microscope and thermal diffusivity are measured for the characterization of the polymer nanocomposites. Analysis shows that BN nanosheets are exfoliated into the fewer layers, whose basal planes are oriented either perpendicular or parallel to the composite surfaces without necessitating the surface modification induced by high magnetic fields. Moreover, the nanocomposites show a dramatic thermal diffusivity enhancement of 1056% by BN nanosheets with perpendicular orientation in comparison with the pristine PVDF at 10 vol % of BN, which relies on the degree of filler orientation. The mechanism for the magnetic field-induced orientation of BN and enhancement of thermal property of PVDF-based composites by the BN assembly are elucidated.

• 센서학회지
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• 제27권1호
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• pp.1-5
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• 2018

Two-dimensional (2D) niobate-based nanosheets have attracted attention as high-k dielectric materials. We synthesized strontiumsubstituted calcium niobate ($Ca_{0.8}Sr_{1.2}Nb_3O_{10}$) nanosheets by a two-step cation exchange process from $KCa_{0.8}Sr_{1.2}Nb_3O_{10}$ ceramic. The $K^+$ ions were exchanged with $H^+$ ions, and then H+ ions were exchanged with tetrabutylammonium ($TBA^+$) cations. The $Ca_{0.8}Sr_{1.2}Nb_3O_{10}$ nanosheets were then exfoliated, decreasing the electrostatic interaction between each niobate layer. Furthermore, $Ca_2Nb_3O_{10}$ nanosheets were synthesized in same process for comparison. Each exfoliated nanosheet shows a single-crystal phase and has a lateral size of over 100 nm. The nanosheets were deposited on a $Pt/Ti/SiO_2/Si$ substrate by the electrophoretic deposition (EPD) method at 40 V, followed by ultraviolet irradiation of the films in order to remove the remaining $TBA^+$ ions. The $Ca_{0.8}Sr_{1.2}Nb_3O_{10}$ thin film exhibited twice the dielectric permittivity (~60) and lower dielectric loss than $Ca_2Nb_3O_{10}$ thin films.

• Advances in nano research
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• 제10권5호
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• pp.481-491
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• 2021

Graphene Nanosheets play an important role in nanosensors due to their proper surface to volume ratio. Therefore, the main purpose of this paper is to consider the nonlinear vibration behavior of graphene nanosheets (GSs) under the influence of electromagnetic fields and electrical current create forces. Considering more realistic assumptions, new equations have been proposed to study the nonlinear vibration behavior of the GSs carrying electrical current and placed in magnetic field. For this purpose, considering the influences of the magnetic tractions created by electrical and eddy currents, new relationships for electromagnetic interaction forces with these nanosheets have been proposed. Nonlinear coupled equations are discretized by Galerkin method, and then solved via Runge-Kutta method. The effect of different parameters such as size effect, electrical current magnitude and magnetic field intensity on the vibration characteristics of GSs is investigated. The results show that the magnetic field increases the linear natural frequency, and decreases the nonlinear natural frequency of the GSs. Excessive increase of the magnetic field causes instability in the GSs.

• 한국재료학회지
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• 제31권2호
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• pp.92-96
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• 2021

We report the growth and enhanced photoelectrochemcial (PEC) water-splitting reactivity of few-layer MoS2 nanosheets on TiO2 nanowires. TiO2 nanowires with lengths of ~1.5 ~ 2.0 ㎛ and widths of ~50~300 nm are synthesized on fluorine-doped tin oxide substrates at 180 ℃ using hydrothermal methods with Ti(C4H9O)4. Few-layer MoS2 nanosheets with heights of ~250 ~ 300 nm are vertically grown on TiO2 nanowires at a moderate growth temperature of 300 ℃ using metalorganic chemical vapor deposition. The MoS2 nanosheets on TiO2 nanowires exhibit typical Raman and ultraviolet-visible light absorption spectra corresponding to few-layer thick MoS2. The PEC performance of the MoS2 nanosheet/TiO2 nanowire heterostructure is superior to that of bare TiO2 nanowires. MoS2/TiO2 heterostructure shows three times higher photocurrent than that of bare TiO2 nanowires at 0.6 V. The enhanced PEC photocurrent is attributed to improved light absorption of MoS2 nanosheets and efficient charge separation through the heterojunction. The photoelectrode of the MoS2/TiO2 heterostructure is stably sustained during on-off switching PEC cycle.

• 한국재료학회지
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• 제32권5호
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• pp.237-242
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• 2022

Designing and producing a low-cost, high-current-density electrode with good electrocatalytic activity for the oxygen evolution reaction (OER) is still a major challenge for the industrial hydrogen energy economy. In this study, nanostructured Fe-doped CuCo(OH)₂ was discovered to be a precedent electrocatalyst for OER with low overpotential, low Tafel slope, good durability, and high electrochemically active surface sites at reduced mass loadings. Fe-doped CuCo(OH)₂ nanosheets are made using a hydrothermal synthesis process. These nanosheets are clumped together to form a highly open hierarchical structure. When used as an electrocatalyst, the Fe-doped CuCo(OH)₂ nanosheets required an overpotential of 260 mV to reach a current density of 50 mA cm^-2. Also, it showed a small Tafel slope of 72.9 mV dec^-1, and superior stability while catalyzing the generation of O₂ continuously for 20 hours. The Fe-doped CuCo(OH)₂ was found to have a large number of active sites which provide hierarchical and stable transfer routes for both electrolyte ions and electrons, resulting in exceptional OER performance.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.257-266
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• 2018

Here, a controlled green synthesis route involving hydrothermal pre-carbonization cum pyrolysis is reported that converts cucumber into graphene-like carbon nanosheets for supercapacitor application. Transmission electron microscopy analysis reveals the formation of ultra-thin carbon nanosheets with distributed pores. This cucumber derived carbon exhibits high specific capacitance of $143F\;g^{-1}$ in aqueous electrolyte. The two-electrode symmetric cell exhibits a specific capacitance of $58F\;g^{-1}$ at high current density, and high capacitance retention of 97% after 1000 cycles. This simple low-cost process involving widely available cucumber as biomass precursor is a promising, commercially viable approach for developing high-performance supercapacitors.