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 °C 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.

Tungsten disulfide (WS2) nanosheets have attracted considerable attention because of their unique optical and electrical properties. Several methods for fabrication of WS2 nanosheets have been developed. However, methods for mass production of high-quality WS2 nanosheets remain challenging. In this study, WS2 nanosheets were fabricated using mechano-chemical ball milling based on the synergetic effects of chemical intercalation and mechanical exfoliation. The ball-milling time was set as a variable for the optimized fabricating process of WS2 nanosheets. Under the optimized conditions, the WS2 nanosheets had lateral sizes of 500–600 nm with either a monolayer or bilayer. They also exhibited high crystallinity in the 2H semiconducting phase. Thus, the proposed method can be applied to the exfoliation of other transition metal dichalcogenides using suitable chemical intercalants. It can also be used with highperformance WS2-based photodiodes and transistors used in practical semiconductor applications.

ZnO nanosheets have been used for many devices and antibacterial materials with wide bandgap and high crystallinity. Among the many methods for synthesizing ZnO nanostructures, we report the synthesis of ZnO/Zn(OH)2 nanosheets using the ionic layer epitaxy method, which is a newly-developed bottom-up technique that allows the shape and thickness of ZnO/Zn(OH)2 nanosheets to be controlled by temperature and time of synthesis. Results were analyzed by scanning electron microscopy and atomic force microscopy. The physical and chemical information and structural characteristics of ZnO/ Zn(OH)2 nanosheets were compared by X-ray photoelectron spectroscopy and X-ray diffraction patterns after various posttreatment processes. The crystallinity of the ZnO/Zn(OH)2 nanosheets was confirmed using scanning transmission electron microscopy. This study presents details of the control of the size and thickness of synthesized ZnO/Zn(OH)2 nanosheets with atomic layers.

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 μm and widths of ~50~300 nm are synthesized on fluorine-doped tin oxide substrates at 180 oC 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 oC 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.

In this work, economical, facile and eco-friendly technology for gas separation was utilized, especially for propane and propylene. This materials are commonly used in petrochemical process as principle and base sources. In present state, adsorption or cryogenic distillation method are used for their separation, however, intensive energy cost and complex process are needed. In particular, we fabricated polymeric composite membrane with high scalability, propylene and propane gases are effectively separated. Whats more, Ag ion is pivotal materials with pi complexation effect. MgO nanosheet was incorporated for enhancing and activating Ag ion in polymer composite membrane. Lastly, Ag-friend polymer matrix was used for getting higher perm-selecetivity.

RuO2 is a common active component of Dimensionally Stable Anodes (DSAs) for chlorine evolution that can be used in wastewater treatment systems. The recent improvement of chlorine evolution using nanostructures of RuO2 electrodes to increase the treatment efficiency and reduce the energy consumption of this process has received much attention. In this study, RuO2 nanorod and nanosheet electrodes were simply fabricated using the sol-gel method with organic surfactants as the templates. The obtained RuO2 nanorod and nanosheet electrodes exhibit enhanced electrocatalytic activities for chlorine evolution possibly due to the active surface areas, especially the outer active surface areas, which are attributed to the increase in mass transfers compared with a conventional nanograin electrode. The electrocatalytic activities for chlorine evolution were increased up to 20 % in the case of the nanorod electrode and 35% in the case of the nanosheet electrode compared with the nanograin electrode. The RuO2 nanorod 80 nm in length and 20-30 nm in width and the RuO2 nanosheet 40-60 nm in length and 40 nm in width are formed on the surface of Ti substrates. These results support that the templated RuO2 nanorod and nanosheet electrodes are promising anode materials for chlorine evolution in future applications.

태양광 발전시스템은 태양복사에너지를 반도체의 광전효과를 이용하여 전기에너지로 직접 전환시키는 에너지변환 시스템이다. 태양전지의 내구성과 에너지변환율에 영향을 미치는 핵심소재로는 다층형 필름구조를 갖는 백시트를 들 수 있다. 대표적인 상용 백시트는 고내구성 poly(vinyl fluoride) (PVF) 필름이 중심축에 위치하고 가격저감을 위해 도입된 poly(ethylene terephthalate) (PET) 필름이 그 양쪽에 접합된 삼층구조로 구성된다. 하지만, PVF 필름의 높은 가격은 저렴한 고내구성 백시트 를 요구하는 시장상황을 반영하기 어렵게 한다. 이를 위한 해결책으로는 PVF 필름을 결정성 PET 필름으로 대체한 탄화수소계 백시트가 될 수 있다. 하지만, PET 필름의 본질적인 가수분해에 대한 취약성으로 인해, 추가적인 수분에 대한 배리어성 부여 는 필수적이다. 이를 위해 본 연구에서는 소수성 실리카 나노입자 분산기술을 활용한 수분차단성 폴리우레탄 접착제를 개발 코자 하였다. 개발된 접착제는 내부에 위치한 PET 필름으로의 수분침투를 약화시켜, 가수분해속도를 지연시킬 것이라 기대 되었다. 본 개념의 효용성을 확인하기 위해, 표준화된 온습도조건에 노출된 이후의 일반접착제와 수분차단성 접착제가 도입 된 백시트의 기계적 강도 및 시간당 태양전지성능 변화가 비교평가되었다.

자기 제조공정 중 고온에서 형성된 클레이 나노입자를 충진제로 하여 LDPE-클레이 나노컴포지트 시트를 제조하였으며, 이의 산소, 이산화탄소 및 수분에 대한 투과도를 서로 다른 세 온도(20, 30 및 40oC)에서 측정하였다. 사용한 클레이 입자의 주성분은 ICP-OES를 통하여 Ca(40.733%)임을 확인하였으며, 나노컴포지트 내 클레이 나노입자가 잘 분산되어있음을 TEM을 통해 확인하였고, FT-IR을 통하여 클레이 나노입자의 첨가가 LDPE의 작용기에 특별한 영향을 주지 않았다는 것을 확인하였다. 산소, 이산화탄소 및 수분투과도는 예상하였던 바와 같이 온도가 상승함에 따라 증가하는 경향을 보여주었다. 클레이 나노입자의 혼입으로 시트 내 기체분자의 확산 경로가 증가됨에 따라 모든 테스트 온도에서 나노컴포지트 시트는 대조구보다 유의적으로 향상된 기체차단효과를 나타내었는데, 산소와 이산화탄소에 대해서는 30 및 40oC에서 보다 20oC에서 상대적으로 강한 차단성을 나타내었으며, 수분에 대해서는 30oC에서 차단성이 상대적으로 높았고 20 및 40oC에서는 비슷한 차단효과를 나타내었다. 본 연구결과를 통하여 나노입자를 혼입 함으로서 LDPE 시트의 산소, 이산화탄소 및 수분에 대한 차단효과를 향상시킬 수 있음을 확인하였으며, 동시에 이러한 차단효과 향상의 정도는 온도에 따라 상당히 차이가 있음을 알 수 있었다. 차단효과의 온도 의존성에 대한 구체적인 이유는 아직 밝혀지지 않았지만, 온도에 따라 기체확산 및 고분자운동의 정도가 달라지므로 나노입자에 의한 기체확산 경로 증가의 효과 역시 변하게 되기 때문으로 사료된다. 따라서 나노컴포지트를 포장재로 사용할 경우, 반드시 목적온도에서 기체차단효과를 확인한 후 응용하여야 할 것으로 사료된다. 또한 시트나 필름의 내부 고분자 배열은 그 형성방법에 따라 달라지므로, 이것이 나노컴포지트의 기체차단효과에 미치는 영향 역시 신중히 고려되어야 한다. 이러한 현상에 대한 충분한 이해를 위해서는 나노입자 및 고분자의 배열구조와 기체차단효과의 상관관계에 대한 연구가 필요할 것으로 사료된다.

As a growth-template of ZnO nanorods (NR), a hexagonal β-Ni(OH)2 nanosheet (NS) was synthesized with the low temperature hydrothermal process and its microstructure was investigated using a high resolution scanning electron microscope and transmission electron microscope. Zinc nitrate hexahydrate was hydrolyzed by hexamethylenetetramine with the same mole ratio and various temperatures, growth times and total concentrations. The optimum hydrothermal processing condition for the best crystallinity of hexagonal β-Ni(OH)2 NS was determined to be with 3.5 mM at 95˚C for 2 h. The prepared Ni(OH)2 NSs were two dimensionally arrayed on a substrate using an air-water interface tapping method, and the quality of the array was evaluated using an X-ray diffractometer. Because of the similarity of the lattice parameter of the (0001) plane between ZnO (wurzite a = 0.325 nm, c = 0.521 nm) and hexagonal β-Ni(OH)2 (brucite a = 0.313 nm, c = 0.461 nm) on the synthesized hexagonal β-Ni(OH)2 NS, ZnO NRs were successfully grown without seeds. At 35 mM of divalent Zn ion, the entire hexagonal β-Ni(OH)2 NSs were covered with ZnO NRs, and this result implies the possibility that ZnO NR can be grown epitaxially on hexagonal β-Ni(OH)2 NS by a soluble process. After the thermal annealing process, β-Ni(OH)2 changed into NiO, which has the property of a p-type semiconductor, and then ZnO and NiO formed a p-n junction for a large area light emitting diode.

Electromagnetic wave energies are consumed in the form of thermal energy, which is mainly caused by magnetic loss, dielectric loss and conductive loss. In this study, CNT was added to the nanocrystalline soft magnetic materials inducing a high magnetic loss, in order to improve the dielectric loss of the EM wave absorption sheet. Generally, the aspect ratio and the dispersion state of CNT can be changed by the pre-ball milling process, which affects the absorbing properties. After the various ball-milling processes, 1wt% of CNTs were mixed with the nanocrystalline base powder, and then further processed to make EM absorption sheets. As a result, the addition of CNT to Fe-based nanocrystalline materials improved the absorption properties. However, the increase of ball-milling time for more than 1h was not desirable for the powder mixture, because the ballmilling caused the shortening of CNT length and the agglomeration of the CNT flakes.

The amorphous (at%) alloy strip was pulverized using a jet mill and an attrition mill to get flake-shaped powder. The flake powder was mixed with dielectric powder and its dispersant to increase the permittivity. The powders covered with dielectric powders and its dispersant were mixed with a binder and a solvent and then tape-cast to form sheets. The absorbing properties of the sheets were measured to investigate the roles of the dielectric powder and its dispersant. The results showed that the addition of powders and its dispersant improved the absorbing properties of the sheets noticeably. The powder sheet mixed with 5 wt% of powder and 1 wt% of dispersant showed the best electromagnetic wave absorption rate because of the increase of the permittivity and the electrical resistance

Electromagnetic wave absorbing materials have been developed to reduce electromagnetic interference (EMI) for electronic devices in recent years. In this study, Fe-Si-B-Nb-Cu base amorphous strip was pulverized using a jet mill and an attritor and heat-treated to get flake-shaped nanocrystalline powders, and then the powders were mixed, cast and dried with dielectric powders and binders. As a result, the addition of powders improved the absorbing properties of the sheets noticeably compared with those of the sheets without dielectric materials. The sheet mixed with 2 wt% powder showed the best electromagnetic wave absorption, which was caused by the increase of the permittivity and the electric resistance due to the dielectric materials finely dispersed on the Fe-based powder