scholarly journals Stabilization of 4H hexagonal phase in gold nanoribbons

2015 ◽  
Vol 6 (1) ◽  
Author(s):  
Zhanxi Fan ◽  
Michel Bosman ◽  
Xiao Huang ◽  
Ding Huang ◽  
Yi Yu ◽  
...  
Keyword(s):  
Metastable Phase ◽  
Hexagonal Phase ◽  
High Yield ◽  
Ambient Conditions ◽  
Solution Synthesis ◽  
Hexagonal Polytype ◽  
Gold Silver ◽  
The Face ◽  
Cubic Structure ◽  
Silver Palladium

Abstract Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

A Metastable Crystalline Phase Coexisted with the Decagonal Quasicrystals in Rapidly Solidified Al-Ir Al-Pd and Al-Pt Alloys

1990 ◽  
Vol 48 (1) ◽  
pp. 572-573
Author(s):  
Wang Rong ◽  
Ma Lina ◽  
K.H. Kuo
Keyword(s):  
Metastable Phase ◽  
Hexagonal Phase ◽  
Icosahedral Quasicrystal ◽  
Decagonal Quasicrystal ◽  
Decagonal Phase ◽  
Decagonal Quasicrystals ◽  
Pt Alloy ◽  
Pt Alloys ◽  
Diffraction Patterns ◽  
Rapidly Solidified

Up to now, decagonal quasicrystals have been found in the alloys of whole Al-Pt group metals [1,2]. The present paper is concerned with the TEM study of a hitherto unreported hexagonal phase in rapidly solidified Al-Ir, Al-Pd and Al-Pt alloys.The ribbons of Al5Ir, Al5Pd and Al5Pt were obtained by spun-quenching. Specimens cut from the ribbons were ion thinned and examined in a JEM 100CX electron microscope. In both rapidly solidified Al5Ir and Al5Pd alloys, the decagonal quasicrystal, with rosette or dendritic morphologies can be easily identified by its electron diffraction patterns(EDPs). The EDPs of the decagonal phase for the two alloys are quite similar. However, the existance of decagonal quasicrystal in the Al-Pt alloy has not been verified by our TEM study. It is probably for the reason that the cooling rate is not great enough for the Al5Pt alloy to form the decagonal phase. During the TEM study, a metastable hexagonal phase has been observed in the Al5Ir, Al5Pd and Al5Pt alloys. The lattic parameters calculated from the X-ray powder data of this phase are a=1.229 and c=2.647nm(Al-Pd) and a=1.231 and c=2.623nm(Al-Ir). The composition of this phase was determined by EDS analysis as Al4(Ir, Pd or Pt). It coexists with the decagonal phase in the alloys and transformed to other stable crystalline phases on heating to high temperature. A comparison between the EDPs of the hexagonal and the decagonal phase are shown in Fig.l. Fig. 1(a) is the EDPs of the decagonal phase in various orientions and the EDPs of the hexagonal phase are shown in Fig.1(b), in a similar arrangement as Fig.1(a). It can be clearly seen that the EDPs of the hexagonal phase, especially the distribution of strong spots, are quite similar to their partners of the decagonal quasicrystal in Fig.1(a). All the angles, shown in Fig.l, between two corresponding EDPs are very close to each other. All of these seem strongly to point out that a close structural relationshipexists between these two phases:[110]//d10 [001]//d2(D) //d2 (P)The structure of α-AlFeSi is well known [3] and the 54-atom Mackay icosahedron with double icosahedral shells in the α-AlFeSi structure [4] have been used to model the icosahedral quasicrystal structure. Fig.2(a) and (b) show, respectively, the [110] and [001] projections of the crystal structure of α- AlFeSi, and decagon-pentagons can easily be identified in the former and hexagons in the latter. In addition, the optical transforms of these projections show clearly decagons and hexagons of strong spots, quite similar to those in [110] and [001] EDPs in Fig.1(b). This not only proves the Al(Ir, Pt, Pd) metastable phase being icostructural with the α-AlFeSi phase but also explains the orientation relationship mentioned above.

Study of aerobic oxidation of phenyl PtII complexes (dpms)PtIIPh(L) (dpms = di(2-pyridyl)methanesulfonate; L = water, methanol, or aniline)

2009 ◽  
Vol 87 (1) ◽  
pp. 110-120 ◽  
Author(s):  
Julia R Khusnutdinova ◽  
Peter Y Zavalij ◽  
Andrei N Vedernikov
Keyword(s):  
Aqueous Solution ◽  
Aerobic Oxidation ◽  
Reductive Elimination ◽  
High Yield ◽  
Ambient Conditions ◽  
Activation Barriers ◽  
Methanol Solutions ◽  
Anionic Species ◽  
Mechanism Of Oxidation ◽  
Solution Mechanism

Oxidation of phenyl PtII complexes K[(dpms)PtIIPh2], 1, (dpms)PtIIPh(MeOH), 2, (dpms)PtIIPh(OH2), 3, and methyl PtII complex (dpms)PtIIMe(NH2Ph), 6, with O2 in aqueous or methanol solutions under ambient conditions leads to corresponding (dpms)PtIVR(X)OH complexes (R = X = Ph, 7; R = Ph, X = OH, 8; R = Ph, X = OMe, 9; R = Me, X = NHPh; 11; dpms = di(2-pyridyl)methanesulfonate). Complexes 7–9 could be isolated in high yield. Complex 11 as well as its phenyl analogue (dpms)PtIVPh(NHPh)OH, 10 can be prepared in high yield by oxidation of corresponding (dpms)PtIIR(NH2Ph) with H2O2 in methanol. Phenyl PtII complexes (dpms)PtIIPh(HX) derived from HX = aniline and DMSO, 4 and 5, respectively, are inert toward O2. The rate of oxidation of 1–5 with O2 decreases in the order 1 > 3 ~ 2 » 4, and 5 is unreactive. Methyl analogues are significantly more reactive compared with their phenyl counterparts. Proposed mechanism of oxidation with O2 includes formation of anionic species (dpms)PtIIR(X)– responsible for reaction with dioxygen. Attempts at C–O and C–N reductive elimination from phenyl PtIV complexes 7–10 do not lead to phenyl derivatives PhX at 80–100 °C, consistent with the results of the DFT estimates of corresponding activation barriers, ΔG0 exceeding 28 kcal/mol.Key words: platinum phenyl complexes, oxidation, dioxygen, aqueous solution, mechanism.

Preparation of CuO Nanopowder in Aqueous Solution by Applying Ultrasonic and its CO Gas Sensitivity

2007 ◽  
Vol 544-545 ◽  
pp. 901-904 ◽  
Author(s):  
Ji Bum Yang ◽  
Tae Gyung Ko ◽  
Sang Jin Jung ◽  
Jae Hee Oh
Keyword(s):  
Aqueous Solution ◽  
Gas Sensing ◽  
Spherical Shape ◽  
Particle Morphology ◽  
High Yield ◽  
Ambient Conditions ◽  
Gas Sensitivity ◽  
Molar Ratios ◽  
Naoh Solution ◽  
Co Gas

We report on a process in which CuO nanopowder was produced in a high yield by adopting ultrasonic in aqueous solution. In our experiment, CuCl2 solution was reacted with NaOH solution and NaNO2, at ambient conditions applying ultrasonic for 5 min. Precipitation was performed by varying the molar ratios of NaOH/CuCl2 and NaNO2/CuCl2. CuO nanoparticles of ~ 5 nm and spherical shape were obtained at the NaOH/CuCl2 of 2.0 and the NaNO2/CuCl2 of 0.097. Without ultrasonication, an amorphous phase was formed at these conditions. This indicates that sonochemical reaction facilitates direct formation of the nanosized CuO particles. In addition, the particle morphology varied from sphere through ellipsoid to needle forms depending on pH. In thick films prepared with the CuO powder for gas sensing, the maximum CO gas sensitivity reached 93 % at the temperature of 250 °C and depended linearly on CO concentration in log scale over the range of 10 ~ 104 ppm.

scholarly journals Epimerization-free C-term Activation of Peptide Fragments by Ball-Milling

2020 ◽  
Author(s):  
Yves Yeboue ◽  
Marion Jean ◽  
Gilles Subra ◽  
Jean Martinez ◽  
Frédéric Lamaty ◽  
...  
Keyword(s):  
Amino Acids ◽  
Ball Milling ◽  
High Yield ◽  
Coupling Agents ◽  
Peptide Fragment ◽  
Peptide Fragments ◽  
Solution Synthesis ◽  
High Yields ◽  
Synthesis Approach ◽  
Yield And Purity

Ball-milling enabled to perform [2+1], [2+2], and [2+3] peptide couplings with high yields and, if any, very low epimerization. Very good results were obtained with peptide fragments containing highly epimerization-prone and/or highly hindered amino acids at C-term such as phenylglycine, cysteine and valine. Ball-milling was clearly identified as the key element to obtain both high yield and purity along with low epimerization. Indeed, the ball-milling conditions proved to be superior to the classical solution synthesis approach on a various array of widely used coupling agents. These results open avenues for the development of highly efficient, convergent and flexible peptide synthesis strategies based on peptide fragment couplings mediated by ball-milling.

scholarly journals Epimerization-free C-term Activation of Peptide Fragments by Ball-Milling

2020 ◽  
Author(s):  
Yves Yeboue ◽  
Marion Jean ◽  
Gilles Subra ◽  
Jean Martinez ◽  
Frédéric Lamaty ◽  
...  
Keyword(s):  
Amino Acids ◽  
Ball Milling ◽  
High Yield ◽  
Coupling Agents ◽  
Peptide Fragment ◽  
Peptide Fragments ◽  
Solution Synthesis ◽  
High Yields ◽  
Synthesis Approach ◽  
Yield And Purity

Ball-milling enabled to perform [2+1], [2+2], and [2+3] peptide couplings with high yields and, if any, very low epimerization. Very good results were obtained with peptide fragments containing highly epimerization-prone and/or highly hindered amino acids at C-term such as phenylglycine, cysteine and valine. Ball-milling was clearly identified as the key element to obtain both high yield and purity along with low epimerization. Indeed, the ball-milling conditions proved to be superior to the classical solution synthesis approach on a various array of widely used coupling agents. These results open avenues for the development of highly efficient, convergent and flexible peptide synthesis strategies based on peptide fragment couplings mediated by ball-milling.

Introduction

1990 ◽  
Author(s):  
Steven Kim
Keyword(s):  
New York ◽  
Difficult Problem ◽  
Two Dimensions ◽  
Three Dimensions ◽  
High Yield ◽  
Acceptable Solution ◽  
Theory Of Intelligence ◽  
Creative Solutions ◽  
The World ◽  
The Face

The world around us abounds with problems requiring creative solutions. Some of these are naturally induced, as when an earthquake levels a city or an epidemic decimates a population. Others are products of our own creation, as in the “need” to curb pollution, to develop a theory of intelligence, or to compose works of art. Still others are a combination of both, as in the development of high-yield grains to feed an overpopulated planet, or the maintenance of health in the face of ravaging diseases. The word problem is used in a general sense to refer to any mental activity having some recognizable goal. The goal itself may not be apparent beforehand. Problems may be characterized by three dimensions relating to domain, difficulty, and size. These attributes are depicted in Figure 1.1. The domain refers to the realm of application. These realms may relate to the sciences, technology, arts, or social crafts. The dimension of difficulty pertains to the conceptual challenge involved in identifying an acceptable solution to the problem. A difficult problem, then, is one that admits no obvious solution, nor even a well-defined approach to seeking it. The size denotes the magnitude of work or resources required to develop a solution and implement it. This attribute differs from the notion of difficulty in that it applies to the stage that comes after a solution has been identified. In other words, difficulty refers to the prior burden in defining a problem or identifying a solution, while size describes the amount of work required to implement or realize the solution once it has jelled conceptually. For convenience in representation on a 2-dimensional page, the domain axis may be compressed into the plane of other attributes. The result is Figure 1.2, which presents sample problems to illustrate the two dimensions of difficulty and size. Cleaning up spilled milk is a trivial problem having numerous simple solutions. In contrast, refacing the subway trains in New York City with a fresh coat of paint is a formidable task that could require hundreds of workyears of effort.

Electrochemical reduction of N2 to ammonia on Co single atom embedded N-doped porous carbon under ambient conditions

2019 ◽  
Vol 7 (46) ◽  
pp. 26358-26363 ◽  
Author(s):  
Yanming Liu ◽  
Qi Xu ◽  
Xinfei Fan ◽  
Xie Quan ◽  
Yan Su ◽  
...  
Keyword(s):  
Electrochemical Reduction ◽  
Porous Carbon ◽  
Energy Efficient ◽  
Single Atom ◽  
High Yield ◽  
Ambient Conditions

Co single atom embedded N-doped porous carbon is energy efficient for electrochemical reduction of N2 to NH3 with a high yield.

First-Principles Study on the Structural, Electronic and Elastic Properties of Alloyed Austenite with Co and Ni

2012 ◽  
Vol 503-504 ◽  
pp. 684-687
Author(s):  
Z. Q. Lv ◽  
Z. P. Shi ◽  
Y. Li
Keyword(s):  
Crystal Structure ◽  
Elastic Properties ◽  
First Principles ◽  
Orthorhombic Structure ◽  
Ambient Conditions ◽  
First Principles Study ◽  
Crystal Type ◽  
Cubic Structure ◽  
Alloyed Austenite

The crystal structure of alloyed austenite distorted after Ni and Co replaced Fe. The crystal type of austenite changed from cubic structure to tetragon or orthorhombic structure due to the influence of Co and Ni. The ratio (B/G) for γ-Fe (C) is equal to 2.841, which is higher than that for other alloyed austenite with Co and Ni. The workability of alloyed austenite with Co and Ni are poorer than γ-Fe (C). The formation of alloyed austenite needs more energy than γ-Fe (C) at ambient conditions.

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