Enhanced oxygen reduction reaction of Pt deposited Fe/N-doped bimodal porous carbon nanostructure catalysts

Park, Jin-Young,Kwak, Da-Hee,Ma, Kyeng-Bae,Han, Sang-Beom,Chai, Geun Seok,Kim, Sang-Kyung,Peck, Dong-Hyun,Kim, Chang-Soo,Kucernak, Anthony,Park, Kyung-Won Elsevier 2018 Journal of catalysis Vol.359 No.-

<P><B>Abstract</B></P> <P>For commercialization of proton exchange membrane fuel cells (PEMFCs), the loading amount of Pt-based cathode catalysts for oxygen reduction reaction (ORR) needs be significantly reduced. In this study, we propose Pt catalysts supported by an iron/nitrogen-doped porous carbon (FeNC) nanostructure having a catalytic activity for ORR in order to significantly reduce the utilization of Pt. The FeNC nanostructure was prepared using a template method with 50 and 500 nm SiO<SUB>2</SUB> beads and phthalocyanine as a dopant and carbon source. The nanosized Pt catalysts with different loading weights (5, 10, 20, 30 wt%) were uniformly deposited on the FeNC with a bimodal porous crystalline doped carbon nanostructure using an electron beam radiation method. In particular, the cathode catalyst having 5 wt% Pt on FeNC (Pt5/FeNC) exhibited enhanced ORR mass activities of 2.19 and 2.58 A mg<SUB>Pt</SUB> <SUP>−1</SUP> at 0.9 V measured by electrochemical half cells in acidic and alkaline media, respectively, compared to a commercial Pt(20 wt%)/C (Pt20/C). Furthermore, Pt5/FeNC showed a higher mass activity of 18.76 A mg<SUB>Pt</SUB> <SUP>−1</SUP> at 0.6 V as a unit cell performance than that of the commercial catalyst. The improved ORR activity of Pt/FeNC might be synergistically attributed to the homogeneous dispersion of Pt nanoparticles on the bimodal porous doped carbon nanostructure, the interaction (electronic effect) between the metallic catalyst and the doped support, and the dual catalytic effect of both Pt and the doped carbon nanostructure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Doped mesoporous carbon nanostructure (FeNC) were synthesized using template method. </LI> <LI> Pt nanoparticles were deposited on the FeNC via an electron beam irradiation method. </LI> <LI> Pt/FeNC showed highly improved ORR activity in acid & alkaline media. </LI> <LI> The improved activity was due to synergistic effect between Pt nanoparticle and FeNC. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of Pre-reducing Sb-Doped SnO2 Electrodes in Viologen-Anchored TiO2 Nanostructure-Based Electrochromic Devices

조성목,아칠성,김태엽,송주희,류호준,천상훈,김주연,김용해,황치선 한국전자통신연구원 2016 ETRI Journal Vol.38 No.3

In this paper, we investigate the effects of pre-reducing Sb-doped SnO2 (ATO) electrodes in viologen-anchored TiO2 (VTO) nanostructure–based electrochromic devices. We find that by pre-reducing an ATO electrode, the operating voltage of a VTO nanostructure–based electrochromic device can be lowered; consequently, such a device can be operated more stably with less hysteresis. Further, we find that a pre-reduction of the ATO electrode does not affect the coloration efficiency of such a device. The aforementioned effects of a pre-reduction are attributed to the fact that a pre-reduced ATO electrode is more compatible with a VTO nanostructure–based electrochromic device than a non-pre-reduced ATO electrode, because of the initial oxidized state of the other electrode of the device, that is, a VTO nanostructure–based electrode. The oxidation state of a pre-reduced ATO electrode plays a very important role in the operation of a VTO nanostructure–based electrochromic device because it strongly influences charge movement during electrochromic switching.

Effect of microwave-assisted hydrothermal process parameters on formation of different TiO₂ nanostructures

Cho, Sung Hun,Nguyen, Huy Hao,Gyawali, Gobinda,Son, Jie-Eun,Sekino, Tohru,Joshi, Bhupendra,Kim, Seung Ho,Jo, Yong Hyun,Kim, Tae Ho,Lee, Soo Wohn Elsevier 2016 CATALYSIS TODAY - Vol.266 No.-

<P><B>Abstract</B></P> <P>TiO<SUB>2</SUB> nanostructures by the hydrothermal process can be potential materials in the various fields of application due to their inherent ion-exchange capabilities and unique morphologies. However, to effectively utilize these nanostructures, their phase, and the formation mechanism with various synthesis parameters need to be fully understood for maximizing their potential. In this study, nanostructured TiO<SUB>2</SUB> are fabricated by using microwave method with various experimental parameters such as in different NaOH concentrations of 4, 6, 8, and 10M at different hydrothermal treatment temperatures of 100, 120, 140, 150°C, and for the different reaction time of 1, 2, 3, 4h. The phase and composition of different nanostructures were studied by using X-ray diffraction patterns (XRD) and X-ray photoelectron spectroscopy (XPS). Morphologies of nanostructures were observed by Transmission electron microscopy (TEM). The optical property of the nanostructures was confirmed through the absorption behavior using UV–vis spectrophotometer. Diffuse reflectance spectroscopy (DRS) was used to calculate the band gap energies. To confirm the basic properties of the TiO<SUB>2</SUB> nanostructures, the specific surface area was compared. The TiO<SUB>2</SUB> nanostructures fabricated by microwave hydrothermal process have been classified according to the different NaOH concentrations, reaction temperatures, and time. The photocatalytic dye decomposition test for different TiO<SUB>2</SUB> nanostructures was performed under the simulated solar light irradiation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> TiO<SUB>2</SUB> nanostructures were synthesized by microwave hydrothermal process. </LI> <LI> Effects of temperature, NaOH concentration and processing time were studied. </LI> <LI> A phase diagram was presented to understand the formation of TiO<SUB>2</SUB> nanostructures. </LI> <LI> Mechanism of the formation of TiO<SUB>2</SUB> nanostructures has been proposed. </LI> </UL> </P>

Study on the optimization of graphene sensors using Ag-nanostructures decoration

Hang, Nguyen Thuy,Zhang, Shaolin,Noh, Jin-Seo,Yang, Woochul Elsevier 2018 THIN SOLID FILMS - Vol.660 No.-

<P><B>Abstract</B></P> <P>In this work, we carried out a systematic study of the effects of morphology and coverage of decorated silver (Ag) nanostructures on the sensing performance of monolayer graphene. Ag nanowires (AgNWs) and Ag nanoparticles (AgNPs) were uniformly coated on the chemical vapor deposition-grown graphene. Raman spectra showed that both AgNPs and AgNWs served as n-type dopants to graphene. After decoration of the Ag nanostructures, the sensing performance of the graphene towards NO<SUB>2</SUB> gas at room temperature was significantly improved. For a graphene and AgNWs hybrid sensor, the sensitivity was approximately 2 time higher and the recovery time was ~10 times shorter than the pristine graphene. In addition, we found that the behavior of NO<SUB>2</SUB> adsorption depends on the shape of the decorated Ag nanostructures. The surface coverage ratio of the Ag nanostructures on graphene presented a contrary trend, in that lower coverage of AgNWs and higher coverage of AgNPs on graphene exhibited better sensing properties. The effect of each nanostructure on improving graphene sensing is discussed in terms of the surface energy of different facets of Ag nanostructures and the electronic properties of the hybrid structures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ag-nanostructures decorated on graphene serve as n-typed dopants to graphene. </LI> <LI> Sensitivity of graphene sensor to NO<SUB>2</SUB> is optimized by control of decorated Ag-nanostructures. </LI> <LI> Enhanced sensing performance of hybrid structure is due to modification of electric structures. </LI> </UL> </P>

Antibacterial and bioactive properties of stabilized silver on titanium with a nanostructured surface for dental applications

Kim, Sungwon,Park, Cheonil,Cheon, Kwang-Hee,Jung, Hyun-Do,Song, Juha,Kim, Hyoun-Ee,Jang, Tae-Sik Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.451 No.-

<P><B>Abstract</B></P> <P>Titanium (Ti) is used in dental applications owing to their excellent mechanical properties, corrosion resistance, and biocompatibility. However, postoperative bacterial infection may cause serious complications and remains one of the most difficult challenges hindering the development of long term Ti dental implants. Therefore, the desire for high quality dental care has led to significant interest in designing implant surfaces that offer stable antibacterial activity with excellent cellular response. In this study, we propose a simple and efficient approach for fabricating an antibacterial stabilized Ag nanostructure on a Ti surface, which is based on a two-step process involving target-ion induced plasma sputtering (TIPS) and Ag sputtering. The TIPS process generates a nanostructured Ti surface that provides a nanotemplate on which the Ag nanostructure may be deposited through Ag sputtering. The Ag nanoclusters adhere tightly to the TIPS-treated Ti (TIPS-Ti) nanostructured surface with no noticeable defects, and the amount of stabilized Ag deposited may be controlled by simply adjusting the Ag-sputtering time. The silver ion is released continuously from the Ag-TIPS-Ti surface for 7 d. The Ag nanostructured TIPS-Ti (Ag-TIPS-Ti) surface not only offers outstanding antibacterial activity toward <I>Escherichia coli</I> and <I>Staphylococcus aureus</I> over 12 h of culturing but also exhibits no severe cytotoxicity for fibroblast cells for up to 10 days. In particular, Ag stabilization by 10 s Ag-sputtering on TIPS-Ti provides the best balance between antibacterial activity and cellular performances, and the resulting fibroblast cell-attachment morphology and proliferation level are similar to those for a polished Ti surface. Therefore, the controllable antibacterial activity and fibroblast tissue affinity of the Ag-TIPS-Ti present a promising avenue for producing reliable, long term dental implants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanostructured Ag on Ti was fabricated via target-ion induced plasma sputtering (TIPS) followed by Ag sputtering. </LI> <LI> TIPS process generated a mechanically stable template for fabricating Ag nanostructures. </LI> <LI> Amount of stabilized Ag was easily controlled by adjusting the Ag-sputtering time. </LI> <LI> Ag nanostructured TIPS-Ti (Ag-TIPS-Ti) surface killed bacteria upon contact. </LI> <LI> TIPS-Ag sputtering process provided balanced antibacterial and cellular properties. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A top-down chemical approach to tuning the morphology and plasmon resonance of spiky nanostars for enriched SERS-based chemical sensing

Joseph, Dickson,Huh, Yun Suk,Han, Young-Kyu Elsevier Sequoia 2019 Sensors and actuators. B Chemical Vol.288 No.-

<P><B>Abstract</B></P> <P>Gold-silver (AuAg) alloys, an important noble bimetallic system, have received significant attention due to their chemical stability and unique properties for use in catalysis, surface-enhanced Raman scattering (SERS) and biomedical applications. We report a chemical approach to reconstruct the morphology of AuAg spiky nanostars using additional metal ions, into nanostructures that exhibits enriched SERS-based chemical sensing. To achieve this, we developed a two-step reduction process involving the simultaneous reduction of gold and silver followed by a successive reduction process. First, AuAg nanostars were synthesized by reducing Au and Ag using a one-pot method. Secondly, Au and Ag ions were separately deposited on the as-prepared AuAg nanostars and reduced. Successive reduction of Ag onto the AuAg nanostar resulted in a layered core-shell nanostructure with minimal mixing of the two metals. The deposition of Au ions onto the AuAg nanostars yielded maximally mixed alloyed nanostructures. There was no significant change in the morphology of the spiky nanostars with the use of high or low Ag feed concentrations or low Au concentrations. However, a new star-like nanostructure was formed as a result of the successive reduction of Au ions at a high feed concentration. The properties evaluated by SERS studies reveals that the as-prepared maximally mixed random alloy outperforms the minimally mixed layered core-shell nanostructures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A green, one-pot, seedless route towards synthesis of spiky branched nanostars. </LI> <LI> Successive reduction of Ag or Au onto spiky branched nanostars. </LI> <LI> AuAg@Ag alloy@metal core@shell layered nanostructures. </LI> <LI> AuAg@Au maximally mixed random alloy nanostructures. </LI> <LI> Maximally mixed random AuAg alloy nanostructures as efficient SERS substrates. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Novel bimetallic layered core-shell and maximally mixed random alloy nanostructures has been prepared with varying Au and Ag elemental distribution and their chemical sensing SERS properties characterised.</P> <P>[DISPLAY OMISSION]</P>

Mass production of DNA nanostructure via rolling circle amplification

고오성,한상우,이종범 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

DNA have attracted attention as the building materials for self-assembled nanostructure. Watson-Cricks base pairing based DNA nano system enables programming of DNA into the various forms of the nanostructure. Over the past decades, DNA have been studied to create from DNA simple structure to DNA supramolecules. Despite these attractions, there is a disadvantage in terms of the high cost for DNA synthesis. Rolling Circle Amplification is a powerful tool that elongate long single-stranded DNA from circular DNA template, containing millions of repeated units. Herein, we report a strategy that produce DNA hydrogel by RCA containing Y and X shaped DNA nanostructures and their separation from the DNA hydrogel with two kinds of restriction enzyme. Because elongated ssDNA contains a restriction site, DNA hydrogel can be digested into Y and X-shaped structures which are rationally designed. Thus, we expect this study offer amplification tool of various complex DNA and RNA nanostructures.

2단계 수열합성을 이용한 ZnO 계층 나노구조 기반 UV 센서 제작

우현수 ( Hyeonsu Woo ),김건휘 ( Geon Hwee Kim ),김수현 ( Suhyeon Kim ),안태창 ( Taechang An ),임근배 ( Geunbae Lim ) 한국센서학회 2020 센서학회지 Vol.29 No.3

Ultraviolet (UV) sensors are widely applied in industrial and military fields such as environmental monitoring, medicine and astronomy. Zinc oxide (ZnO) is considered as one of the promising materials for UV sensors because of its ease of fabrication, wide bandgap (3.37 eV) and high chemical stability. In this study, we used the hydrothermal growth of ZnO to form two types of ZnO nanostructures (Nanoflower and nanorod) and applied them to a UV sensor. To improve the performance of the UV sensor, the hydrothermal growth was used in a two-step process for fabricating ZnO hierarchical nanostructures. The fabricated ZnO hierarchical nanostructure improved the performance of the UV sensor by increasing the ratio of volume to surface area and the number of nanojunctions compared to onestep hydrothermal grown ZnO nanostructure. The UV sensor based on the ZnO hierarchical nanostructure had a maximum photocurrent of 44 μA, which is approximately 3 times higher than that of a single nanostructure. The UV sensor fabrication method presented in this study is simple and based on the hydrothermal solution process, which is advantageous for large-area production and mass production; this provides scope for extensive research in the field of UV sensors.

Highly porous and capacitive copper oxide nanowire/graphene hybrid carbon nanostructure for high-performance supercapacitor electrodes

Luan, Van Hoang,Han, Jong Hun,Kang, Hyun Wook,Lee, Wonoh Elsevier Science Ltd 2019 Composites Part B, Engineering Vol.178 No.-

<P><B>Abstract</B></P> <P>Three-dimensionally porous carbon nanostructures have been widely used in energy storage applications owing to their large specific surface areas and excellent electrical properties. In addition, copper oxide has been considered as an effective pseudocapacitive material to significantly increase the energy density. In this paper, we introduce the synergetic combination of one-dimensional copper oxide nanowires and two-dimensional graphene sheets to fabricate a highly porous and electrically conductive three-dimensional hybrid nanostructure for high-performance supercapacitor electrodes with increased capacitances. The copper oxide nanowires were synthesized by reduction of copper nitrate and sequential oxidation at a high temperature. The copper oxide nanowire/graphene hybrid three-dimensional nanostructure was obtained by a self-assembly technique through a simple hydrothermal treatment. The hybrid nanostructure had an acceptable surface area and increased thermal stability. The porous hybrid nanostructure utilized as a supercapacitor electrode provided 1.6 times higher electrochemical capacitance than that of a graphene-only nanostructure-based electrode as well as superior capacitance stability with a retention of 91.2% retention after 5,000 charge−discharge cycles. Owing to the increased capacitance, the manufactured electrode exhibited high a specific energy density of 50.6 Wh kg<SUP>−1</SUP> at a power density of 200 W kg<SUP>−1</SUP>, which demonstrates its potential for use in electrochemical energy storage devices.</P>

Transparent and superhydrophobic surface using dual scale nanostructure

이유진,하영근 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

In this study, we demonstrate a simple spin-coating method for the preparation of transparent superhydrophobic surface using dual scale nanostructure.. Various ratios of different size aluminum NPs were chosen to fabricate dual scale nanostructure and to study the effect of the surface roughness, affecting superhydrophobicity and optical transparency. The dual scale nanostructure films were then modified to have the hydrophobicity by dipping in octadecylphosphonic acid (ODPA). The resulting coated surface displayed a static water contact angle of 158° showing excellent superhydrophobicity. Moreover, the spin-coated superhydrophobic films were also highly transparent with greater than 90% transmittance in the visible region.