Configuration Of Carbon Atom Research Articles

Adsorption Property and Morphology Evolution of C Deposited on HCP Co Nanoparticles.

Despite extensive studies of deposited carbon in Fischer-Tropsch synthesis (FTS), an atomic-level comprehension of the effect of carbon on the morphology of cobalt-based FTS catalysts remains elusive. The adsorption configurations of carbon atoms on different crystal facets of hexagonal close-packed (hcp) Co nanoparticles were studied using density functional theory (DFT) calculations to explore the interaction mechanism between C and Co surfaces. The weaker adsorption strength of C atoms on Co(0001), Co(10-10), and Co(11-20) surfaces accounted for lower diffusion energy, leading to the facile formation of C dimers. Electronic property analysis shows that more electrons are transferred from Co surfaces to C atoms on corrugated facets than on flat facets. The deposition of carbon atoms on Co nanoparticles affects surface energy by forming strong Co-C bonds, which causes the system to reach a more energetically favorable morphology with an increased proportion of exposed Co(10-12) and Co(11-20) areas as the carbon content increases slightly. This transformation in morphology implies that C deposition plays a crucial role in determining the facet proportion and stability of exposed Co surfaces, contributing to the optimization of cobalt-based catalysts with improved performance.

Twist angle, strain, corrugation and moire unit cell in twisted bi-layer graphene

Knowledge of the internal configuration of carbon atoms inside a moire unit cell of twisted bi-layer graphene (TBG) would enhance the accuracy of many-body quantum mechanical calculations related to TBG. This work put forward a comprehensive theoretical study of moire pattern in TBG, supported with computational analysis; which seek a mechanism to determine the internal configuration of carbon atoms inside a moire unit cell of TBG. This study first time establishes that all twist angles are commensurate twist angles which produce perfectly periodic commensurate moire patterns of TBG. It is also first time established that strain appearing in moire patterns of TBG can occur purely due to intrinsic reasons. Taking some insight from available experimental data related to TBG systems and conventional bi-layer graphene systems, a mathematical model is also presented for corrugation in TBG. Finally we present an universal algorithm to determine the internal configuration of carbon atoms inside a moire unit cell of TBG, which is first of its kind.

Statistical Verification of Anomaly in Chiral Angle Distribution of Air-Suspended Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNT) have long attracted attention due to their distinct physical properties, depending on their chiral structures (chiralities). Clarifying their growth mechanism is important toward perfect chirality-controlled bulk synthesis. Although a correlation between the chirality distribution and the carbon atom configuration at an open tube edge has been predicted theoretically, lack of sufficient statistical data on metallic and semiconducting SWCNTs prohibited its verification. Here, we report statistical verification of the chirality distribution of 413 as-grown individual air-suspended SWCNTs with a length of over 20 μm using broadband Rayleigh spectroscopy. After excluding the impact of the difference in the number of possible SWCNT structures per chiral angle interval, the abundance profile with chiral angle exhibits an increasing trend with a distinct anomaly at a chiral angle of approximately 20°. These results are well explained considering the growth rate depending on armchair-shaped site configurations at the catalyst–nanotube interface.

Amorphous state of sp2 solid carbon

Two-mode valence electron configuration of carbon atoms lays the foundation of the unique two-mode amorphous state of the carbon solid. From the fundamentals of solid-state physics, sp3 and sp2 amorphous carbons are two different species characterized by conceptually different short-range orders, namely, groups of tetrahedrally bonded sp3 configured atoms and nanoscale size-restricted sp2 graphene domains framed with heteroatom necklaces. Molecular character of sp2 amorphics is provided with chemical reactions accompanying the solids amorphization in due course of the enforced fragmentation.

Efficient Bifunctional Catalytic Electrodes with Uniformly Distributed NiN2 Active Sites and Channels for Long-Lasting Rechargeable Zinc-Air Batteries.

Freestanding bifunctional electrodes with outstanding oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties are of great significance for zinc-air batteries, attributed to the avoided use of organic binder and strong adhesion with substrates. Herein, a strategy is developed to fabricate freestanding bifunctional electrodes from the predeposited nickel nanoparticles (Ni-NCNT) on carbon fiber paper. The steric effect of monodispersed SiO2 nanospheres limits the configuration of carbon atoms forming 3D interconnected nanotubes with uniformly distributed NiN2 active sites. The bifunctional electrodes (Ni-NCNT) demonstrate ideal ORR and OER properties. The zinc-air batteries assembled with Ni-NCNT directly exhibit extremely outstanding long term stability (2250 cycles with 10 mA cm-2 charge/discharge current density) along with high power density of 120 mV cm-2 and specific capacity of 834.1 mA h g-1 . This work provides a new view to optimize the distribution of active sites and the electrode structure.

Backbone effects in the synthesis, coordination chemistry and catalytic properties of new chiral heterobidentate ligands with P,N and S,N donor sets

Novel alkane-diyl based heterobidentate P,N and S,N ligands with the general formula R1R2NCH(R3)(CH2)nCH(R4)Q (R1 = Me or iPr; R2 = H or Me; R3, R4 = H or Me; n = 0, 2; Q = PPh2 or SPh) have been prepared starting from cyclic sulfate esters or naturally occurring compounds with C1 symmetry. The length of the ligands’ backbone and the reaction conditions applied strongly affected the stereochemical outcome of the synthesis when using cyclic sulfates as starting materials. Palladium(II)-complexes of the new ligands were characterized by 1D and 2D NMR spectroscopy in solution and in several cases by X-ray crystallography in the solid phase. The structural versatility of the ligands enabled the straightforward comparison of the stereoselectivity of their coordination as a function of their tether length, backbone substitution pattern, donor sets and relative carbon atom configuration in their backbone. The catalytic features of the novel compounds were investigated in asymmetric allylic alkylation reactions where the tether length proved to be a crucial factor in determining enantioselectivity.

Effect of potassium on carbon adsorption on the Co(0001) surface.

The effect of potassium on carbon adsorption and deposition on the Co(0001) surface was studied on the basis of theoretical calculations. Thermodynamically, the surface Cn species is expected, and C2 dimer may be a critical elementary unit. With the increase of carbon coverage, a fraction of the carbon atoms may diffuse into the subsurface. But kinetically, the formation of Cn species is more favorable, and there is no driving force for carbon to migrate into the subsurface. As the surface carbon concentration increases, the adsorbed carbon atoms turn into carbon chains and then into graphene sheets parallel to the surface. Potassium promoter has little effect on the most stable adsorption configurations of carbon atoms but increases the adsorption energy of carbon species, which can be explained by the decreasing of the surface work function resulting from the electron effect of potassium promoter. The potassium promotes carbon deposition and carbonization of the cobalt surface to a certain extent. These results could support some useful information for the carbon deposition and cobalt carbide formation.

3D Printing On-Water Sports Boards with Bio-Inspired Core Designs.

Modeling and analyzing the sports equipment for injury prevention, reduction in cost, and performance enhancement have gained considerable attention in the sports engineering community. In this regard, the structure study of on-water sports board (surfboard, kiteboard, and skimboard) is vital due to its close relation with environmental and human health as well as performance and safety of the board. The aim of this paper is to advance the on-water sports board through various bio-inspired core structure designs such as honeycomb, spiderweb, pinecone, and carbon atom configuration fabricated by three-dimensional (3D) printing technology. Fused deposition modeling was employed to fabricate complex structures from polylactic acid (PLA) materials. A 3D-printed sample board with a uniform honeycomb structure was designed, 3D printed, and tested under three-point bending conditions. A geometrically linear analytical method was developed for the honeycomb core structure using the energy method and considering the equivalent section for honeycombs. A geometrically non-linear finite element method based on the ABAQUS software was also employed to simulate the boards with various core designs. Experiments were conducted to verify the analytical and numerical results. After validation, various patterns were simulated, and it was found that bio-inspired functionally graded honeycomb structure had the best bending performance. Due to the absence of similar designs and results in the literature, this paper is expected to advance the state of the art of on-water sports boards and provide designers with structures that could enhance the performance of sports equipment.

Carbon Formation Mechanism of C2H2 in Ni-Based Catalysts Revealed by in Situ Electron Microscopy and Molecular Dynamics Simulations.

Understanding the carbon formation mechanism is critical for designing catalysts in various applications. Here, we report the observation of the carbon formation mechanism on Ni-based catalysts by environmental transmission electron microscopy (ETEM) over a wide temperature range in combination with molecular dynamics simulations and density functional theory calculations. In situ TEM observation performed in a C2H2/H2 atmosphere provides real-time evidence that Ni3C is an intermediate phase that decomposes to graphitic carbon and metallic Ni, leading to carbon formation. Mechanisms of acetylene decomposition and evolution of carbon atom configuration are revealed by molecular dynamics simulations, which corroborate the experimental results. The modification of MgO on NiO can effectively decrease the formation of graphitic layers and thus enhance the catalytic performance of NiO. This finding may provide an insight into the origin of the carbon deposition and aid in developing effective approaches to mitigate it.

The Effect of Demineralization Stage of Agar’s Solid Waste on the Characterization of Activated Carbon

Agar’s solid waste contains quite high amount of crude fiber at 38.05%, so it can be used as activated carbon. Activated carbon is carbon whose configuration of carbon atoms is freed from bonding with other elements. The effectiveness of activated carbon as an adsorbent is seen from the ash content. High level of ash in a material can reduce the ability of activated carbon in the adsorption process, making it undesirable in the manufacture of activated charcoal. Demineralization using HCl solution can affect the decrease in ash content. This study used the experimental method of pre-post test and the analysis was carried out using the associated T-Test (paired T-Test). Pre-test was conducted using 0% HCl or without demineralization and Post-test was conducted using 5% HCl. Study results show that there is no effect on the characteristics of ash content, volatile substances, pure activated carbon, yield and there is effect on water content. It indicates that demineralization process using 5% HCl on the yet optimum material does not have tangible impact on the resulted ash content and characteristics of activated carbon.

Active sites for oxygen reduction reaction on nitrogen-doped carbon nanotubes derived from polyaniline

Understanding exact electronic configurations of carbon atoms bonded by nitrogen (N) functionalities at atomic-level may literally open a door to advance metal-free carbon materials as efficient catalysts for the oxygen reduction reaction (ORR). In this paper, a set of well-defined carbon nanotubes with controlled doping of various N species, such as pyrrolic, pyridinic and graphitic N, have been achieved by in-situ pyrolysis of polyaniline (PANI) nanotubes at different temperatures. Among these synthesized samples, the carbon nanotubes fabricated at 700 °C exhibit the highest electro-catalytic ORR activity, long-standing stability and good tolerance against methanol in alkaline medium. The improved activity is mainly attributed to the high nitrogen level of the active pyridinic and graphitic N. But, the pyridinic N possesses higher activity than the graphitic N because of their different sp2 electronic structures. Pyridinic N, after bonding with two carbon(C) atoms, has two distorting N−C orbitals and one dangling orbital occupied by a lone electron pairs which are exposed, as the N sits at the edge of the carbon planes. Such unique electronic configuration makes the nitrogen and surrounding carbon atoms, bonded in the CN bonds, can serve host of active sites or work as active sites for the ORR.

Nanoparticle mass detection by single and multilayer graphene sheets: Theory and simulations

The discovery of graphene opened up a new field of research and led to the development of various nanosensors and actuators that form new classes of nano electro mechanical systems (NEMSs) called graphene based nano resonators (GBNRs). Recently, GBNRs have been used in mass detection applications. In such applications and others, single-layer graphene sheets play a fundamental role. However, the synthesis of monolayer graphene is usually challenging and expensive. This makes the commercial use of multilayer graphene systems more attractive and necessary. Moreover, it is now more possible to control the number of layers in large-size graphene systems, and thus the theoretical design tools could help the engineers develop more efficient graphene-based sensors for everyday applications. This paper introduces a non-local elasticity theory for the general configurations of carbon atoms that could form carbon nanotubes (CNTs), nanosheets (graphene) and nanospheres (fullerenes) by means of the laminated plate theory. The problem is solved by the generalized differential quadrature element method (GDQEM). Then, a molecular dynamics approach is used in conjunction with the operational modal analysis (OMA) to perform a nano metric modal analysis. Several comparisons are presented to validate the introduced approaches; and finally, the effects of the number of layers and of nanoparticle mass and position on the frequency shift and sensitivity of the designed sensors are studied. It is demonstrated that the frequency shift decreases slightly and the sensitivity increases by increasing the number of graphene layers. It is also demonstrated that, depending on the positions of nanoparticles in a senor, various mode shapes of a graphene sheet could be excited; and consequently, the shift of the first natural frequency may not be appropriate for particles far from the middle of graphene sheet.

Features of the Zeeman Splitting and G-Factors of 2p5f Configuration Levels of Carbon Atom

The gyromagnetic ratios of levels (the g-factors) – are one of the most important characteristics of atoms. There are no corresponding experimental data in the literature for npn`l configurations of carbon atom. That is why the theoretical study of the fine and the Zeeman structures for the determination of the g-factors is ongoing. All the calculations are effected in one configuration approximation, with the energy operator matrix, in which the maximum possible number of interactions is taken into account, including the magnetic, spin-orbit (own and other) and spin-spin interactions. The fine structures were studied in three approximations (LS, LK, jK) for the establishment of the character of the coupling in 2p5f C I configuration. During the study of Zeeman splitting (except the g-factors) features of it were determined: the fields of crossings and anticrossings of magnetic components. In all steps of calculations the numerical digitalization of corresponding energy operator matrices were effected, e.g. the results presented in the paper were obtain in the intermediate coupling approximation.

Absolute Configuration of Beer′s Bitter Compounds

Absolute Configuration of Beer′s Bitter Compounds

Synthesis and Properties of ApA Analogues with Shortened Phosphonate Internucleotide Linkage

A complete series of the 2 ′–5 ′ and 3 ′–5 ′ regioisomeric types of r(ApA) and 2 ′-d(ApA) analogues with the α-hydroxy-phosphonate C3 ′-O-P-CH(OH)-C4 ″ internucleotide linkage, isopolar but non-isosteric with the phosphodiester one, were synthesized and their hybridization properties with polyU studied. Due to the chirality on the 5 ′-carbon atom of the modified internucleotide linkage bearing phosphorus and hydroxy moieties, each regioisomeric type of ApA dimer is split into epimeric pairs. To examine the role of the 5 ′-hydroxyl of the α-hydroxy-phosphonate moiety during hybridization, the appropriate r(ApA) analogues with 3 ′(2 ′)-O-P-CH2-C4 ″ linkage lacking the 5 ′-hydroxyl were synthesized. Nuclear magnetic resonance (NMR) spectroscopy study on the conformation of the modified sugar-phosphate backbone, along with the hybridization measurements, revealed remarkable differences in the stability of complexes with polyU, depending on the 5 ′-carbon atom configuration. Potential usefulness of the α-hydroxy-phosphonate linkage in modified oligoribonucleotides is discussed.

Molecular Dynamics Simulation on Tensile Deformation of Graphene with Nanomeshes

Nanomeshes, introduced into the graphene sheet, are a very effective method to open up the band gap and thus to improve the electronic properties. In this paper, the deformation behaviors of graphene sheet with nanomeshes were simulated by Molecular Dynamics methods. It was found that the fracture stress and the corresponding strain depend on the radius of nanomeshes, which was further confirmed by analyzing the potential energy as well as radial distribution function. One intrinsic mechanism, based on the spatial configurations of carbon atoms, was suggested to reveal the distinct deformation behaviors. This will be helpful to design the next carbon-based materials in micro-electronic devices.

Theoretical and spectroscopic investigations on the structure and bonding in B–C–N thin films

In this study, we have synthesized boron, carbon, and nitrogen containing films using RF sputter deposition. We investigated the effects of deposition parameters on the chemical environment of boron, carbon, and nitrogen atoms inside the films. Techniques used for this purpose were grazing incidence reflectance-Fourier-transform infrared spectroscopy (GIR-FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). GIR-FTIR experiments on the B–C–N films deposited indicated presence of multiple features in the 600 to 1700cm−1 range for the infrared (IR) spectra. Analysis of the IR spectra, XPS and the corresponding EELS data from the films has been done in a collective manner. The results from this study suggested even under nitrogen rich synthesis conditions carbon atoms in the B–C–N films prefer to be surrounded by other carbon atoms rather than boron and/or nitrogen. Furthermore, we have observed a similar behavior in the chemistry of B–C–N films deposited with increasing substrate bias conditions. In order to better understand these results, we have compared and evaluated the relative stability of various nearest-neighbor and structural configurations of carbon atoms in a single BN sheet using DFT calculations. These calculations also indicated that structures and configurations that increase the relative amount of C–C bonding with respect to B–C and/or C–N were energetically favorable than otherwise. As a conclusion, carbon tends to phase-segregate in to carbon clusters rather than displaying a homogeneous distribution for the films deposited in this study under the deposition conditions studied.

Sugar-based phosphite and phosphoroamidite ligands for the Cu-catalyzed asymmetric 1,4-addition to enones

A modular sugar-based phosphoroamidite L1– L5a– g and phosphite L6– L9a– g ligand library was tested in the asymmetric Cu-catalyzed 1,4-conjugate addition reactions of β-substituted (cyclic and linear) and β,β′-disubstituted (cyclic) enones. The selectivity depended strongly on the configuration of carbon atom C-3, the size of the sugar backbone ring, the flexibility of the ligand backbone, the substituents and configurations in the biaryl phosphoroamidite moieties a– g, the type of functional group attached to the ligand backbone and the substrate structure. Therefore, by carefully selecting the ligand parameters, enantioselectivities of up to 60% for cyclic substrates and 72% for linear ones were achieved.

Influence of Glycosidic Linkage Neighbors on Disaccharide Conformation in Vacuum

Correct description of the free energy of conformation change of disaccharides is important in understanding a variety of biochemical processes and, ultimately, in the manufacture of better food and paper products. In this study, we determine the relative free energy of a series of 12 disaccharides in vacuum using replica exchange molecular dynamics (repMD) simulations. The chosen sugars and the novel application of this method allow the exploration of the role of glycosidic linkage neighbors in conformer stabilization. In line with expectations, we find that hydrogen bonding (and therefore energetically preferred conformations) are determined both by the nature of the glycosidic linkage (i.e., 1 --> 2, 1 --> 3, or 1 --> 4), the C1 epimer of the of the nonreducing monosaccharide, and by the configuration of carbon atoms once removed from the glycosidic linkage. Contrary to suggestions by prior authors for repMD more generally, we also demonstrate that repMD provides enhanced sampling, relative to conventional MD simulations of equivalent length, for disaccharides in vacuum at 300 K. (Zuckerman, D. M.; Lyman, E. J. Chem. Theory Comput. 2006, 2, 1200-1202.)

Chemical Functionalization of Carbon Nanotubes by Carboxyl Groups on Stone-Wales Defects: A Density Functional Theory Study

Chemical functionalization of carbon nanotubes with Stone-Wales (SW) defects by carboxyl (COOH) groups is investigated by density functional calculations. Due to the localized donor states induced by the SW defect, the binding of the COOH group with the defective carbon nanotube is stronger than that with the perfect one. A quasi-tetrahedral bonding configuration of carbon atoms, indicating sp3 hybrid bonding, is formed in the adsorption site. The charge distribution analysis shows that, in comparison with benzoic acid, the localized or delocalized pi states on the nanotube would affect the polarities of chemical bonds of the COOH group without losing the acidity. Furthermore, it is found that the double-adsorption system (two COOH groups are respectively adsorbed on two individual carbon atoms of the SW defect) is more energetically favorable than the monoadsorption one. The adsorption of COOH groups leads to a significant change of the electronic states around the Fermi level, which is advantageous for the electrical conductivity. The functionalization by introducing functional groups on the topological defects provides a pathway for applications of carbon nanotubes in chemical sensors and nanobioelectronics.