Seong Ho Yang

Ni-dispersed fullerenes: Hydrogen storage and desorption properties

Our study shows that the H2 storage media using Ni-dispersed fullerenes could be viable alternatives to reversible hydrogen storage. It is demonstrated that a single Ni coated on the fullerene surface can store up to three H2 molecules. Consequently, at high Ni coverage, Ni-dispersed fullerenes are considered to be the novel hydrogen storage media capable of storing ~6.8 wt % H2, thus exceeding the Department of Energy target (6.5 wt %) for automobile applications. Moreover, the H2 desorption activation barrier of 11.8 kcal/mol H2 is ideal for many practical hydrogen storage applications.

Ionic‐Liquid‐Assisted Sonochemical Synthesis of Carbon‐Nanotube‐Based Nanohybrids: Control in the Structures and Interfacial Characteristics

A versatile, facile, and rapid synthetic method of advanced carbon nanotube (CNT)-based nanohybrid fabrication, or the so-called ionic-liquid-assisted sonochemical method (ILASM), which combines the supramolecular chemistry between ionic liquids (ILs) and CNTs with sonochemistry for the control in the size and amount of uniformly decorated nanoparticles (NPs) and interfacial engineering, is reported. The excellence in electrocatalysis of hybrid materials with well-designed nanostructures and favorable interfaces is demonstrated by applying them to electrochemical catalysis. The synthetic method discussed in this report has an important and immediate impact not only on the design and synthesis of functional hybrid nanomaterials by supramolecular chemistry and sonochemistry but also on applications of the same into electrochemical devices such as sensors, fuel cells, solar cells, actuators, batteries, and capacitors.

Influence of Additives Including Amine and Hydroxyl Groups on Aqueous Ammonia Absorbent for CO2 Capture

Aqueous ammonia absorbent (10 wt %) was modified with four kinds of additives (1 wt %) including amine and hydroxyl groups, i.e., 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-methyl-1,3-propandiol (AMPD), 2-amino-2-ethyl-1,3-propandiol (AEPD), and tri(hydroxymethyl) aminomethane (THAM), for CO(2) capture. The loss of ammonia by vaporization was reduced by additives, whereas the removal efficiency of CO(2) was slightly improved. These results were attributed to the interactions between ammonia and additives or absorbents and CO(2) via hydrogen bonding, as verified by FT-IR spectra and computational calculation. Molecular structures as well as binding energies were obtained from the geometries of (ammonia + additives) and (ammonia + additives + CO(2)) at the optimized state. These experimental and theoretical findings demonstrate that additives including amine and hydroxyl group are suitable for modifying aqueous ammonia absorbent for CO(2) removal.

Nitrogen-mediated fabrication of transition metal-carbon nanotube hybrid materials

The authors report the simple and easy method to fabricate transition-metal–carbon nanotube hybrid materials through nitrogen mediation. Ni nanoparticles were uniformly dispersed on carbon nanotubes without any pretreatment such as defect activation by strong acids or covalent functionalization processes. A theoretical study of the nitrogen-mediated mechanism using first-principles density functional theory calculations is also presented. The first-principles calculations reveal that pyridinelike nitrogen in carbon nanotubes significantly enhances the binding energy of Ni interacting with carbon nanotubes.

Ni adsorption on Stone-Wales defect sites in single-wall carbon nanotubes

Ni adsorption on Stone-Wales defect sites in (10,0) zigzag and (5,5) armchair single-wall carbon nanotubes was studied using the density functional theory. The stable adsorption sites and their binding energies on different Stone-Wales defect types were analyzed and compared to those on perfect side walls. It was determined that the sites formed via fusions of 7-7 and 6-7 rings are the most exothermic in the cases of (10,0) and (5,5) defective tubes. In addition C-C bonds associated with Stone-Wales defects are more reactive than the case for a perfect hexagon, thus enhancing the stability of the Ni adsorption. Moreover, the Ni adsorption was found to show a noticeable relationship to the orientation of the Stone-Wales defects with respect to the tube axis. The nature of the Ni adsorption on Stone-Wales defects that have the similar orientation is identical, in spite of the different chiralities.

A Facile Way to Control the Number of Walls in Carbon Nanotubes through the Synthesis of Exposed‐Core/Shell Catalyst Nanoparticles

There is currently great interest in the controlled synthesis of carbon nanotubes (CNTs) with unique structures. Much of this attraction lies in the fact that the functionality of CNTs can be significantly tailored by control of their composition, diameter, and number of walls. CNTs are known to act as either metals or semiconductors, depending on their diameters and chiralities, for example; therefore, precise control of their nanostructures is essential for various applications, such as field-emitter tips in displays, transistors, interconnection and memory elements in integrated circuits, scan tips for atomic force microscopy, and energy-storage media. One conventional method for growing vertically aligned CNTs involves the use of chemical vapor deposition (CVD). In this case, CNTs can be grown selectively on catalytic sites and their properties depend to a large extent on the nanostructure of the catalyst, particularly the particle size, interparticle distance, and composition. 12] It is therefore necessary to develop improved catalysts using highly innovative methods in order to obtain desired CNT functionalities. Traditional methods for designing and preparing catalyst particles to control the properties of CNTs include a metal film sputtering method, 14] an organic silica mesoporous template method, a nanoparticle method, and a selfassembled block copolymer template method. These methods, however, only focus on controlling the diameter or interparticle distance of CNTs by controlling the size or interparticle distance of the catalyst particles. While it has been reported that controlling the number of walls in CNTs is possible by adjusting the catalyst size, some limitations remain with respect to controlling the diameter and number of walls simultaneously. This suggests that CNT nanostructures with required diameters and interlayer walls cannot be adequately controlled with current methods, and that a new innovative technique for controlling the diameter and the number of CNT walls simultaneously is required. Herein we report a facile way of controlling the number of CNT walls and their diameters simultaneously by using exposed-core/shell (ECS) catalysts composed of catalytically active iron in the shell layer and inactive iron nitride in the exposed core area. As these ECS catalysts were prepared using an Fe-loaded diblock copolymer micelle to pattern the nanoparticles in a controllable manner, this approach provides a total solution for controlling the CNT alignment and pattern as well as its nanostructure simultaneously. The synthetic process is illustrated in Scheme 1. Thus, after synthesizing the diblock copolymer micelle solution, Fe precursors were loaded into the micelle core. This Fe-loaded micelle solution was then coated onto a Si/SiO2 substrate in a spin-coater to give a hexagonally arrayed pattern of micelles. Subsequent low-temperature plasma treatment resulted in the formation of metal particles upon reduction of the metal precursors in the micelle core and removal of the micelle polymers. The resulting Fe nanoparticles patterned on a substrate were placed in a nitrogen plasma to precipitate the iron nitride inside each particle at high temperature. After this precipitation step, a chemical etching process was followed to remove the outer part of the iron shell and expose the iron nitride core. The resulting ECS catalysts, which are composed of an exposed core area (catalytically inactive) and a shell layer (catalytically active), were found to be arranged on the substrate with a constant size and interparticle distance.

Spectroscopic and Computational Insight into the Intermolecular Interactions between Zwitter‐Type Ionic Liquids and Water Molecules

Geometric and conformational changes of zwitter-type ionic liquids (ZILs) due to hydrogen-bonding interactions with water molecules are investigated by density functional theory (DFT), two-dimensional IR correlation spectroscopy (2D IR COS), and pulsed-gradient spin-echo NMR (PGSE NMR). Simulation results indicate that molecular structures in the optimized states are strongly influenced by hydrogen bonding of water molecules with the sulfonate group or imidazolium and pyrrolidinium rings of 3-(1-methyl-3-imidazolio)propanesulfonate (1) and 3-(1-methyl-1-pyrrolidinio)propanesulfonate (2), respectively. Concentration-dependent 2D IR COS reveals kinetic conformational changes of the two ZIL-H(2)O systems attributable to intermolecular interactions, as well as the interactions of sulfonate groups and imidazolium or pyrrolidinium rings with water molecules. The dramatic changes in the (1)H self-diffusion coefficients elucidate the formation of proton-conduction pathways consisting of ZIL networks. In ZIL domains, protons are transferred by a Grotthuss-type mechanism through formation, breaking, and restructuring of bonds between ZILs and H(2)O, leading to an energetically favorable state. The simulation and experimental investigations delineated herein provide a perspective to understanding the interactions with water from an academic point of view as well as to designing ILs with desired properties from the viewpoint of applications.

Nitrogen Porosity in Nitrogen Bearing Austenitic Stainless Steel

The formation of nitrogen gas pores is affected by various factors such as solidification sequence, solubility of nitrogen, cooling rate, melt pressure, nitrogen content etc. Nitrogen porosity in Fe-16Cr-3Ni-9Mn austenitic stainless steel solidifying to primary d-ferrite that can cause nitrogen gas pores was examined. And also the effect of nitrogen content, cooling rate and melt pressure on nitrogen porosity was investigated.