Formation of nanoporous Cu-Ag by dealloying Mg-Cu-Y-Ag amorphous alloys and its electrocatalyst oxidation property

Hyun, J.I.,Kong, K.H.,Kim, W.C.,Kim, W.T.,Kim, D.H. Elsevier 2019 Intermetallics Vol.110 No.-

<P><B>Abstract</B></P> <P>The supersaturated Cu-Ag bimetallic nanoporous structure has been fabricated by dealloying of Mg<SUB>65</SUB>Cu<SUB>25-x</SUB>Y<SUB>10</SUB>Ag<SUB>x</SUB> (x = 0, 2, 4, 8) amorphous alloys and its electrocatalytic property for sodium borohydride (NaBH<SUB>4</SUB>) oxidation has been evaluated. In order to increase solid solubility of Ag into Cu, the dealloying process is proceeded in higher concentration sulfuric acid aqueous solution for shorter immersion time. When Mg<SUB>65</SUB>Cu<SUB>25-x</SUB>Y<SUB>10</SUB>Ag<SUB>x</SUB> amorphous alloys are dealloyed in 1.0 M solution for 30 s, the Cu-Ag bimetallic nanoporous structure in the form of solid solution is successfully obtained due to extended solid solubility in nm scale grain structure. Electrochemical oxidation of NaBH<SUB>4</SUB> at Cu-(Ag) electrodes is studied in a mixture solution of 2.0 M NaOH and 0.1 M NaBH<SUB>4</SUB>. The electrocatalytic property of nanoporous Cu-Ag bimetallic electrodes is higher than that of Cu monometallic electrode. The electrode dealloyed from Mg<SUB>65</SUB>Cu<SUB>21</SUB>Y<SUB>10</SUB>Ag<SUB>4</SUB> amorphous alloy exhibits the highest electrocatalytic property.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mg-Cu-Y amorphous alloys without and with minor Ag addition are dealloyed. </LI> <LI> Dealloying of Mg-Cu-Y-(Ag) results in nanoporous Cu-(Ag). </LI> <LI> Solid solution type bimetallic ligament forms with extended solid solubility. </LI> <LI> Solutionizing of Ag into Cu improves electrocatalytic property. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of Dealloying Condition on the Formation of Nanoporous Structure in Melt-Spun Al₆₀Ge₃₀Mn₁₀ Alloy

Kim, Kang Cheol,Kim, Won Tae,Kim, Do Hyang Korean Society of Microscopy 2016 Applied microscopy Vol.46 No.3

Effect of dealloying condition on the formation of nanoporous structure in melt-spun $Al_{60}Ge_{30}Mn_{10}$ alloy has been investigated in the present study. In as-melt-spun $Al_{60}Ge_{30}Mn_{10}$ alloy spinodal decomposition occurs in the undercooled liquid during cooling, leading to amorphous phase separation. By immersing the as-melt-spun $Al_{60}Ge_{30}Mn_{10}$ alloy in 5 wt% HCl solution, Al-rich amorphous region is leached out, resulting in an interconnected nano-porous $GeO_x$ with an amorphous structure. The dealloying temperature strongly affects the whole dealloying process. At higher dealloying temperature, dissolution kinetics and surface diffusion/agglomeration rate become higher, resulting in the accelerated dealloying kinetics, i.e., larger dealloying depth and coarser pore-ligament structure.

Controllable Switching Filaments Prepared via Tunable and Well-Defined Single Truncated Conical Nanopore Structures for Fast and Scalable SiO_<i>x</i> Memory

Kwon, Soonbang,Jang, Seonghoon,Choi, Jae-Wan,Choi, Sanghyeon,Jang, Sukjae,Kim, Tae-Wook,Wang, Gunuk American Chemical Society 2017 NANO LETTERS Vol.17 No.12

<P>The controllability of switching conductive filaments is one of the central issues in the development of reliable metal-oxide resistive memory because the random dynamic nature and formation of the filaments pose an obstacle to desirable switching performance. Here, we introduce a simple and novel approach to control and form a single silicon nanocrystal (Si-NC) filament for use in SiOx memory devices. The filament is formed with a confined vertical nanoscale gap by using a well-defined single vertical truncated conical nanopore (StcNP) structure. The physical dimensions of the Si-NC filaments such as number, size, and length, which have a significant influence on the switching properties, can be simply engineered by the breakdown of an Au wire through different StcNP structures. In particular, we demonstrate that the designed SiOx memory junction with a StcNP of pore depth of similar to 75 nrn and a bottom diameter of similar to 10 nm exhibited a switching speed of up to 6 ns for both set and reset process, significantly faster than reported SiOx memory devices. The device also exhibited a high ON-OFF ratio, multistate storage ability, acceptable endurance, and retention stability. The influence of the physical dimensions of the StcNP on the switching features is discussed based on the simulated temperature profiles of the Au wire and the nanogap size generated inside the StcNP structure during electrornigration.</P>

표면 요철구조를 적용한 나노 다공성 Ag 금속박막의 SERS 응답 특성 개선

김형주 ( Hyeong Ju Kim ),김봉환 ( Bonghwan Kim ),이동인 ( Dongin Lee ),이봉희 ( Bong-hee Lee ),조찬섭 ( Chanseob Cho ) 한국센서학회 2020 센서학회지 Vol.29 No.4

In this study, we developed a method of improving the surface-enhanced Raman spectroscopy (SERS) response characteristics by depositing a nanoporous Ag metal thin film through cluster source sputtering after forming a pyramidal texture structure on the Si substrate surface. A reactive ion etching (RIE) system with a metal mesh inside the system was used to form a pyramidal texture structure on the Si surface without following a complicated photolithography process, unlike in case of the conventional RIE system. The size of the texture structure increased with the RIE process time. However, after a process time of 60 min, the size of the structure did not increase but tended to saturate. When the RF power increased from 200 to 250 W, the size of the pyramidal texture structure increased from 0.45 to 0.8 μm. The SERS response characteristics were measured by depositing approximately 1.5 μm of nanoporous Ag metal thin film through cluster sputtering on the formed texture structure by varying the RIE process conditions. The Raman signal strength of the nanoporous Ag metal thin film deposited on the Si substrate with the texture structure was higher than that deposited on the general silicon substrate by up to 19%. The Raman response characteristics were influenced by the pyramid size and the number of pyramids per unit area but appeared to be influenced more by the number of pyramids per unit area. Therefore, further studies are required in this regard.

Pore Structure Characterization of Poly(vinylidene chloride)-Derived Nanoporous Carbons

Hwan Jung Jung,Yong-Jung Kim,Dae Ho Lee,Jong Hun Han,Kap Seung Yang,Cheol-Min Yang 한국탄소학회 2012 Carbon Letters Vol.13 No.4

Poly(vinylidene chloride) (PVDC)-derived nanoporous carbons were prepared by various activation methods: heat-treatment under an inert atmosphere, steam activation, and potassium hydroxide (KOH) activation at 873, 1073, and 1273 K. The pore structures of PVDC-derived nanoporous carbons were characterized by the N2 adsorption technique at 77 K. Heat treatment in an inert atmosphere increased the specific surface area and micropore volume with elevating temperature, while the average micropore width near 0.65 nm was not significantly changed, reflecting the characteristic pore structure of ultramicroporous carbon. Steam activation for PVDC at 873 and 1073 K also yielded ultramicroporosity. On the other hand, the steam activated sample at 1273 K had a wider average micropore width of 1.48 nm, correlating with a supermicropore. The KOH activation increased the micropore volume with elevating temperature, which is accompanied by enlargement of the average micropore width from 0.67 to 1.12 nm. The average pore widths of KOH-activated samples were strongly governed by the activation temperature. We expect that these approaches can be utilized to simply control the porosity of PVDC-derived nanoporous carbons.

Synthesis of Nanoporous Structured SnO_2 and its Photocatalytic Ability for Bisphenol A Destruction

Jieun Kim,Jun Sung Lee,강미숙 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.5

Nanoporous structured tin dioxide (SnO_2) is characterized and its application in the photocatalytic destruction of endocrine, Bisphenol A, is examined. Transmission electron microscopy (TEM) reveals irregularly shaped nanopores of size 2.0-4.5 nm. This corresponds to the result of an average nanopore distribution of 4.5 nm, as determined by Barret-Joyner-Halenda (BJH) plot from the isotherm curve. The photoluminescence (PL) curve,corresponding to the recombination between electron and hole, largely decreases in the TiO_2/nanoporous SnO_2composite. Finally, a synergy effect between TiO_2 and porous SnO_2 is exhibited in photocatalysis: the photocatalytic destruction of Bisphenol A is improved by combining the nanoporous structured SnO2 with TiO2, and 75% decomposition of 10.0 ppm of Bisphenol A is achieved after 24 h.

Synthesis of Nanoporous Structured SnO₂ and its Photocatalytic Ability for Bisphenol A Destruction

Kim, Ji-Eun,Lee, Jun-Sung,Kang, Mi-Sook Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.5

Nanoporous structured tin dioxide ($SnO_2$) is characterized and its application in the photocatalytic destruction of endocrine, Bisphenol A, is examined. Transmission electron microscopy (TEM) reveals irregularly shaped nanopores of size 2.0-4.5 nm. This corresponds to the result of an average nanopore distribution of 4.5 nm, as determined by Barret-Joyner-Halenda (BJH) plot from the isotherm curve. The photoluminescence (PL) curve, corresponding to the recombination between electron and hole, largely decreases in the $TiO_2$/nanoporous $SnO_2$ composite. Finally, a synergy effect between $TiO_2$ and porous $SnO_2$ is exhibited in photocatalysis: the photocatalytic destruction of Bisphenol A is improved by combining the nanoporous structured $SnO_2$ with $TiO_2$, and 75% decomposition of 10.0 ppm of Bisphenol A is achieved after 24 h.

Structures of Anodic Aluminum Oxide from Anodization with Various Temperatures, Electrical Potentials, and Basal Plane Surfaces

김영애(Yeongae Kim),황운봉(Woonbong Hwang) Korean Society for Precision Engineering 2016 한국정밀공학회지 Vol.33 No.3

Since the development of anodic aluminum oxide (AAO), extensive studies have been conducted ranging from fundamental research to the applications of AAO. Most of the research on AAO structures have focused on well-aligned nanoporous structures fabricated under specific conditions. This study investigated fabricable AAO structures with anodization performed with various temperatures, electrical potentials, and basal plane surfaces. As a result, nanoporous and nanofibrous structures were fabricated. The nanopores were formed at a relatively lower temperature and potential, and the nanofibers were formed at a relatively higher temperature and potential regardless of the basal plane surface. The shape of the base surface was found to influence the structural arrangement in nanoporous morphologies. These interesting findings relating to new morphologies have the potential to broaden the possible applications of AAO materials.

FABRICATION OF NANOPOROUS CHITOSAN MEMBRANES

XIAOLIANG WANG,XIANG LI,ELEANOR STRIDE,MOHAN EDIRISINGHE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.1

Naturally derived biopolymers have been widely used for biomedical applications such as drug carriers, wound dressings, and tissue engineering scaffolds. Chitosan is a typical polysaccharide of great interest due to its biocompatibility and film-formability. Chitosan membranes with controllable porous structures also have significant potential in membrane chromatography. Thus, the processing of membranes with porous nanoscale structures is of great importance, but it is also challenging and this has limited the application of these membranes to date. In this study, with the aid of a carefully selected surfactant, polyethyleneglycol stearate-40, chitosan membranes with a well controlled nanoscale structure were successfully prepared. Additional control over the membrane structure was obtained by exposing the suspension to high intensity, low frequency ultrasound. It was found that the concentration of chitosan/surfactant ratio and the ultrasound exposure conditions affect the structural features of the membranes. The stability of nanopores in the membrane was improved by intensive ultrasonication. Furthermore, the stability of the blended suspensions and the intermolecular interactions between chitosan and the surfactant were investigated using scanning electron microscope and Fourier transform infrared spectroscopy (FTIR) analysis, respectively. Hydrogen bonds and possible reaction sites for molecular interactions in the two polymers were also confirmed by FTIR analysis.

Determination of diffusion coefficient and partition coefficient of photoinitiator 2-hydroxy-2-methylpropiophenone in nanoporous polydimethylsiloxane network and aqueous poly(ethylene glycol) diacrylate solution

신광인,유현지,김정욱 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.56 No.-

We determine diffusion and partition coefficients of 2-hydroxy-2-methylpropiophenone, a widely usedphoto-initiator, in nanoporous polydimethylsiloxane network and poly(ethylene glycol) diacrylatesolution as model precursor solution. We spectroscopically measure average concentration of 2-hydroxy-2-methylpropiophenone in each media, which is compared to the one estimated from one-dimensionaldiffusion models to obtain diffusion coefficient. Partition coefficient is obtained by measuring saturatedconcentration of 2-hydroxy-2-methylpropiophenone in each media. Our results enables predictingconcentration of 2-hydroxy-2-methylpropiophenone as it diffuses from precursor solution to crosslinkedPDMS, which typically occurs when hydrogel is formed inside microfluidic device via photo-polymerization to create nano-structured or micro-structured hydrogel including microfluidic valves.