Study on bonding mechanism of carbon fiber/carbon matrix interface in C/C by fundamental model
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Chemisorption of singlet (1)Delta(g) O2 on single-walled carbon nanotubes is reexamined by first principles calculations, and the reaction barrier is substantially lower than previously reported when the spin on O2 is correctly treated. The process is initiated by the cycloaddition of a singlet O2 on top of a C-C bond and ended with an epoxy structure with each of the two oxygen atoms occupying a bridge position. The overall process is exothermic, with an activation barrier as low as 0.61 eV for the (8, 0) tube. Our results raise the possibility that carbon nanotubes with small diameters could be degraded after exposure to air and sunlight, similar to the degradation of natural rubber and synthetic plastics.
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To improve the structural properties of engineering ceramics, carbon nanotubes have been used as a reinforcement phase to produce stronger ceramic matrix composites. This paper investigates the possible chemical bond formation between a carbon nanotube and alumina with the aid of quantum mechanics analysis. The cases with and without functionalizing the nanotubes were examined. The nanotubes were modeled by nanotube segments with hydrogen atoms added to the dangling bonds of the perimeter carbons. The cleaved ceramic (0001) surface was represented by an alumina molecule with the oxygen atoms on either end terminated with hydrogen. Methoxy radicals were used to functionalize the CNTs. The study predicts that covalent bonding between Al atoms on a cleaved single crystal alumina surface and C atoms on a nanotube are energetically favorable.
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The use of covalently bonded molecular layers provides a way to combine the outstanding stability and electrochemical properties of carbon-based structures with the unique properties of molecular structures for applications such as electrocatalysis and solar conversion. The functionalization of vertically aligned carbon nanofibers (VACNFs) with 1-alkenes, using ultraviolet light, was investigated as a potential way to impart a variety of different functional groups onto the nanofiber sidewalls. We report how variations in the nanofiber growth rate impact both the amount of exposed edge-plane sites and the resulting electrochemical activity toward Ru(NH3)63+/2+ and Fe(CN)63−/4− redox couples. Measurements of the distribution of surface oxides show that surface oxides are unaffected by the grafting of alkenes to the nanofibers. Carbon nanofiber reactivity was also compared to multiwalled and single-walled carbon nanotubes. Our results demonstrate that edge-plane sites are preferred sites for photochemical grafting, but that the grafting of molecular layers only slightly reduces the overall electrochemical activity of the nanofibers toward the Ru(NH3)63+/2+ couple. These results provide new insights into the relationships between the chemical reactivity and electrochemical properties of nanostructured carbon materials and highlight the crucial role that exposed edge-plane sites play in the electrochemical properties of carbon nanotubes and nanofibers.
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Understanding the role of fillers in the thermal transport of composite materials is of great importance to engineering better materials. The filler induces material interfaces within the composite, which influence the thermal transport between the matrix and themselves. The filler can also alter the molecular arrangement of the matrix in its vicinity, which may also impact the thermal transport ability. In this paper, molecular dynamics simulations are performed to study the thermal transport across the matrix-filler interfaces in hexagonal boron nitride (h-BN)-organic molecule composites. Four different organic molecules are studied as the matrixes. They include hexane (C6H14), hexanamine (C6H13NH2), hexanol (C6H13OH), and hexanoic acid (C5H11COOH), which feature the same molecular backbone but increasingly different polar functional groups. The nominal local thermal conductivities of the hexane matrix with varying distances to the interface are calculated to demonstrate the influence of the filler on the thermal transport properties of the matrix. It is found that a more polar matrix exhibits a higher density in the near-interface region and a higher nominal local thermal conductivity, suggesting that the interfacial interaction can impact the local heat transfer ability of the matrix. In addition, the more polar matrix also leads to a larger interfacial thermal conductance with h-BN (hexane: 90.47 ± 14.49 MW/m2 K, hexanamine: 113.38 ± 17.72 MW/m2 K, hexanol: 136.16 ± 25.12 MW/m2 K, and hexanoic acid: 155.17 ± 24.89 MW/m2 K) because of the higher matrix density near the interface and thus more atoms exchanging energy with the filler. The results of this study may provide useful information for designing composite materials for heat transfer applications.
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The development of new, appealing metal-free photocatalysts is of great significance for photocatalytic hydrogen evolution. Herein, an electrostatic self-assembly method to form a unique core–shell architecture of a colloid of carbon spheres with graphitic carbon nitride (g-C3N4) has been developed by a one-step chemical solution route. The chemical protonation of g-C3N4 solids with strong oxidizing acids (such as HNO3) is an efficient pathway toward the sol procedure of stable carbon nitride colloids, which can cover the surface of carbon spheres via electrostatic adsorption. On account of the unique polymeric matrix of g-C3N4 and reversible hydrogen bonding, the carbon@g-C3N4 derived from the sol solution showed high mechanical stability with broadened light absorption and enhanced conductivity for charge transport. Thus, the carbon@g-C3N4 core–shell structure exhibited remarkably enhanced photoelectrochemical performance. This polymer system is envisaged to hybridize with desirable functionalities (such as carbon nanorods) to form unique architectures for various applications.
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An analysis of the molecular dynamics (МD) of the interaction between a carbon nanotube (CNT) and a carbon disulfide active solvent (CS2) has been carried out. The aim of the present work is to estimate the dynamical and structural behavior of the CNTCS2 system at different relative atomic concentrations and under temperature changes. The structural radial distribution functions and the dynamical configurations have been built for a CNT interacting with a CS2 solvent. A nontrivial observation for the CNTCS2 system is that the solvent carbon disulfide atoms make up a patterned (layered) formation around the carbon nanotube.
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A new innovative electrode material (Fe-P800) consisting of a metal complex anchored on carbon via the utilization of iron-porphyrin conjugated microporous polymer (Fe-CMP) was prepared after pyrolyzing at 800 °C. The usage of the polymer with iron-porphyrin repeating units maximized the possible formation of Fe-Nx coordination within the bulk of the sample while the thermal treatment rendered the carbon framework to form a distinct arrangement between metal, nitrogen and carbon with a high surface area of 450 m2 g-1. The formation of the M-N-C bond, confirmed through XPS analysis, established a direct interaction between metal and carbon material. Thus, an indisputable synergistic effect was observed leading to a high capacitance of 182 F g-1 at a current density of 1 A g-1 despite its low metal loading of ∼1%. It also exhibited a highly robust cycling stability of ∼100% capacitance retention even after 5000 cycles (10 A g-1). In this study, a new mechanism was proposed wherein the metal (iron) center features an electron access point via its highly reversible redox reactivity, providing a shuttle effect for charge transfer to the conductive graphitic carbon matrix.
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