Weighted Homo-Lumo Energy Separations for the Polyene References of Fullerenes with Up to 100 Carbon Atoms

Abstract

The T value represents the HOMO-LUMO energy separation of a ?-electronic system weighted with the number of conjugated atoms. We found that this value is kept almost constant for the polyene references defined graph-theoretically for isolated-pentagon isomers of fullerenes with up to 100 carbon atoms. on this numerical basis, the T value can safely be considered as a realistic index of kinetic stability or chemical inertness for all fullerenes without abutting pentagons.     

Influence of Carbon Forms and Doped Elements in the Electrodes for the Production of Fullerenes

Production of fullereries using electrodes made of four kinds of pure carbon bearing materials and artificial graphite doped with seven kinds of elements such as B, Y, La, Gd, Ce, Pr and Nd have been examined. The yields of fullerenes were in a range between 12-20% of the soot produced for all pure carbon electrodes, even though the vaporization rate of amorphous carbon electrodes was about ten times higher than that of the natural graphite electrodes. However, for the doped graphite electrodes, the yield of fullerenes was less than 5%. From the above results it is concluded that fullerenes can be effectively produced with the pure carbon electrodes made of any form of carbon bearing materials used in this study and there is little material dependence on the yield of fullerences. Furthermore, the experiments using the artificaial graphite electrodes doped with metal elements suggests that the purity of the carbon electrodes affects the yeld of fullerenes greatly.     

A New Approach to Calculating the Potential Energy of Interaction between Two Atoms

A Fourier component of the potential energy of interaction between two atoms has been presented as a polynomial of the biquadratic atomic form factor. A numerical calculation has been performed in the screened Coulomb potential approximation. It is demonstrated that the account for the Pauli principle leads to the occurrence of a potential barrier and an additional region of attraction of two atoms. This model is shown to agree qualitatively with the results of the density-functional-theory calculation.     

Theory for the Growth of Fullerenes

Abstract

In view of recent experiments we extend our previous growth model for fullerene formation. It becomes clear how a high efficiency of C₆₀ formation is achieved. We estimate the size dependence of intermediate structures along the most efficient growth route and furthermore the stability of Si_2o, Ge_2o vs. the unstable C_20-     

Theory for the Growth of Fullerenes

In view of recent experiments we extend our previous growth model for fullerene formation. It becomes clear how a high efficiency of C₆₀ formation is achieved. We estimate the size dependence of intermediate structures along the most efficient growth route and furthermore the stability of Si_2o, Ge_2o vs. the unstable C_20-     

Effect of Graphene Oxide and Carbon Nanotubes on the Reaction of Tritium Atoms with Dalargin

Radiochemistry - Effect of carbon substrates materials (graphene oxide, reduced graphene oxide, single-walled carbon nanotubes) on the result of tritium introduction into dalargin peptide was...     

Environment Effects on the Electronic Properties of Carbon Fullerenes: A Local Approach

The electronic structure of some relevant carbon fullerenes are determined by using a sp-electron tight-binding Hamiltonian including Coulomb interactions in the Hartree-Fock approximation. Surfaces with positive, non-positive and mixed curvatures are considered in order to study the effect of the local environment on the relevant electronic properties. Nanotubes having different diameters and helicities are analyzed and the results are compared with previous calculations. In each case, the equilibrium bond-length R is optimized by maximizing the cohesive energy E_coh(N). The perspectives and extensions of this study are also discussed.     

Influence of Helium Atoms Absorption on the Emission Properties of Carbon Nanotubes

We investigated the emission properties of charge sources based on carbon nanotubes prepared by arc discharge deposition of nanotubes onto a flat copper substrate (Borisenko et al. in Instrum Exp Tech 57(6):755, 2014; Low Temp Phys 41(7):567, 2015). The charge sources were submerged into superfluid helium at temperature \(T=1.3\) K. The collector fixed above the charge source at a distance of 0.3 mm was connected to an electrometer. The current of charges was measured by the electrometer when a high voltage was applied to the charge source. In the originally prepared source, the emission of charges (electrons) on the level of \(10^{-10}\hbox {A}\) is observed at a negative voltage above \(U=80\) V and increases with increasing voltage. If the source of charge was kept in liquid helium for 15 h, the current–voltage characteristic changed significantly. The current of charges on the same level of \(10^{-10}\) A was registered at a voltage of \(U=150\) V. Extraction of gases from the source placed in a vacuum chamber at room temperature for 48 h leads to the complete recovery of the emission properties. One can assume that the degradation of the emission properties of the sources is associated with the adsorption of helium atoms by carbon nanotubes at low temperatures. We did not observe any degradation of the emission properties of the charge sources in the case of positive charges injection into superfluid helium.     

Set Up and Characterization of a System for the Generation of Reference Magnetic Fields From 1 to 100 kHz

This paper describes the design process, the specific features, and the characterization procedures of the Istituto Nazionale di Ricerca Metrologica (I.N.RI.M.) set up for the generation of reference magnetic fields in the frequency range from 1 to 100 kHz. Numerical techniques, validated by comparison with experimental data, make it possible to choose the best solutions for obtaining magnetic flux densities up to 100 muT at 1 kHz and 25 muT at 100 kHz with relative uncertainty from a few parts in 10³ up to the percent     

Methods for the Recovery and Purification of Polyene Antifungals

Despite the development of newer antifungal drugs, the polyene antifungals continue to be the most potent broad-spectrum fungicides available for clinical use. The incidence and severity of fungal infections are on the rise, underscoring the need for new and more effective antifungal drugs. Thus, the search for new polyene antifungals is ongoing. The limited solubility, polymorphic character, and inherent chemical instability of these compounds make their economical recovery and purification from mass culture challenging problems in biotechnology. This article provides a comprehensive review of the methods that have been developed for the recovery and purification of amphotericin B and nystatin, the two most important polyenes currently in clinical use.     

Methods for the Recovery and Purification of Polyene Antifungals

Despite the development of newer antifungal drugs, the polyene antifungals continue to be the most potent broad-spectrum fungicides available for clinical use. The incidence and severity of fungal infections are on the rise, underscoring the need for new and more effective antifungal drugs. Thus, the search for new polyene antifungals is ongoing. The limited solubility, polymorphic character, and inherent chemical instability of these compounds make their economical recovery and purification from mass culture challenging problems in biotechnology. This article provides a comprehensive review of the methods that have been developed for the recovery and purification of amphotericin B and nystatin, the two most important polyenes currently in clinical use.     

Practical Design for Improving the Sensitivity to Search for Dark Matter Axions with Rydberg Atoms

A microwave single-photon detector was developed with highly-excited alkaline Rydberg-atoms in a cooled resonant cavity to search for dark matter axions. This detector belongs to a microwave single-photon counter, thus being free from the standard quantum limit (SQL). High sensitivity of the present detector system was demonstrated by measuring the thermal blackbody radiations in the cavity at temperatures as low as 70 mK where the sensitivity is below the SQL. The detection sensitivity of the present system is mainly limited by stray electric fields present in the detection region. Practical design of a new experimental scheme with a guiding electric field through the atomic-beam trajectory is here presented and discussed to avoid the effect of stray electric field and thus to improve the detection sensitivity.      

Oxalate-Assisted Synthesis of Hollow Carbon Nanocage With Fe Single Atoms for Electrochemical CO2 Reduction

Metal single-atom catalysts are promising in electrochemical CO₂ reduction reaction (CO₂RR). The pores and cavities of the supports can promote the exposure of active sites and mass transfer of reactants, hence improve their performance. Here, iron oxalate is added to ZIF-8 and subsequently form hollow carbon nanocages during calcination. The formation mechanism of the hollow structure is studied in depth by controlling variables during synthesis. Kirkendall effect is the main reason for the formation of hollow porous carbon nanocages. The hollow porous carbon nanocages with Fe single atoms exhibit better CO₂RR activity and CO selectivity. The diffusion of CO₂ facilitated by the mesoporous structure of carbon nanocage results in their superior activity and selectivity. This work has raised an effective strategy for the synthesis of hollow carbon nanomaterials, and provides a feasible pathway for the rational design of electrocatalysts for small molecule activation.     

Partial Sulphidation to Regulate Coordination Structure of Single Nickel Atoms on Graphitic Carbon Nitride for Efficient Solar H2 Evolution

To develop a non-precious highly efficient cocatalyst to replace Pt on graphitic carbon nitride (g-C₃N₄) for solar H₂ production is great significant, but still remains a huge challenge. The emerging single-atom catalyst presents a promising strategy for developing highly efficient non-precious cocatalyst owing to its unique adjustability of local coordination environment and electronic structure. Herein, this work presents a facile approach to achieve single Ni sites (Ni₁-N₂S) with unique local coordination structure featuring one Ni atom coordinated with two nitrogen atoms and one sulfur atom, confirmed by high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and density functional theory calculation. Thanks to the unique electron structure of Ni₁-N₂S sites, the 1095 µmol g⁻¹ h⁻¹ of high H₂ evolution rate with 4.1% of apparent quantum yield at 420 nm are achieved. This work paves a pathway for designing a highly efficient non-precious transition metal cocatalyst for photocatalytic H₂ evolution.     

新型金属结构材料中碳原子扩散行为的模拟研究

采用有限元法,模拟了用渗碳-脱碳化学热处理和外加涂层制备的新型金属结构材料中碳原子的扩散情况以及最终的碳浓度分布,分析了涂层尺寸对碳浓度分布的影响.结果表明,在涂层尺寸为0.4～0.5mm的条件下,渗碳过程中当外界碳势为1.48%(质量分数)、传质系数为1.34×10-7m/s时或脱碳过程中当外界碳势为0%(质量分数)、传质系数为1×10-7m/s时,材料比较容易获得外软内硬的力学性能.薄膜尺寸分别为0.4mm和0.5mm时,渗碳时间为900～1000s和1300～1400s,相应的脱碳时间为1800～1900s和2200～2300s时可获得最佳的扩散效果.     

Controlled Synthesis of Graphene on Copper Using the Method of Implantation of Carbon Recoil Atoms

Technical Physics Letters - A method of graphene synthesis on the surface of copper foil by cold implantation of carbon recoil atoms is considered. It is established that monolayer graphene films...     

Edge Coordination of Ni Single Atoms on Hard Carbon Promotes the Potassium Storage and Reversibility

Hard carbon is the most promising anode for potassium-ion batteries (PIBs) due to its low cost and abundance, but its limited storage capacity remains a major challenge. Herein, edge coordination of metal single atoms is proved to be an effective strategy for promoting potassium storage in hard carbon for the first time, taking B, N co-doped hard carbon nanotubes anchored by edge Ni-N₄-B atomic sites (Ni@BNHC) as an example. It is revealed that edge Ni-N₄-B can provide active sites for interlayer adsorption of K⁺ and that Ni atoms can facilitate the reversibility of K⁺ storage on N and B atoms. Furthermore, an unprecedentedly reversible K⁺ storage capacity of 694 mAh g⁻¹ at 0.05 A g⁻¹ is realized by introducing commercial carbon nanotubes. This work provides a new perspective for the application of single-atom engineering and the design of high-performance carbon anodes for PIBs.     

Automatic Production of Fullerenes by A JxB ARC Jet Discharge Preventing Carbon Vapor from Depositing on the Cathode

Deposition of carbon atoms on a cathode in a DC arc discharge to produce fullerenes is reduced by JxB force of a magnetic field in an arc flame. By this modification, more effective synthesis of fullerenes and easier control of discharge conditions are achieved.