1,721,252 research outputs found
Corrigendum to “Temperature-dependent selective nucleation of single-walled carbon nanotubes from stabilized catalyst nanoparticles” [Chem. Eng. J. 431 (2022) 133487] (Chemical Engineering Journal (2022) 431(P4), (S1385894721050610), (10.1016/j.cej.2021.133487))
No full textThe authors regret the equal contribution notation was neglected. We are sorry for not finding out this mistake during proof reading. The first three authors, Qianru Wu, Lu Qiu and Lili Zhang contributed equally to the work. The authors would like to apologise for any inconvenience caused. © 2022
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The utilization of metal nanoparticles supported on oxides substrate as a catalyst for rational single-walled
carbon nanotube (SWCNT) growth is hindered by particle coarsening at high synthesis temperature, despite
many empirical advances in supported catalyst design. In this study, a newly developed MgO-supported cobalt
(Co-MgO) catalyst affords the formation of well-stabilized Co nanoparticles upon reduction, which is attributed
to the electronic metal-support interaction and electrostatic stabilization at the Co-MgO interface. The highly
stabilized Co nanoparticles led to the predominant growth of (6, 5) SWCNTs at 700 ◦C by CO disproportionation
and the major SWCNT species was found to be (7, 5) SWCNTs at a reaction temperature of 800 ◦C. The
temperature-dependent selective growth of the two SWCNT species was found, by density functional theory
calculation, to be strongly correlated with the change of the relative thermodynamic stability of the SWCNT
nuclei in the chirality assigning process at different temperatures.11Nsciescopu
Contact-Induced Phase Separation of Alloy Catalyst to Promote Carbon Nanotube Growth
Full text linkIn this Letter, using density functional theory based molecular dynamics simulations, we report that contact to a carbon nanotube (CNT) induces phase separation in an alloy catalyst, which promotes CNT growth. During growth of a CNT, the growth front tends to preferentially bond to the more active metal atom in the alloy catalyst, thus triggering a phase separation of the alloy catalyst particle. The accumulation of the active metal stabilizes the open end of the CNT, attracts carbon precursors to rapidly diffuse to the growth front, and avoids catalyst poisoning by preventing the encapsulation of the catalyst. This study resolves a long-term mystery surrounding the higher efficiency of alloy catalysts in CNT growth as compared to a pure metal catalyst and thereby paves the way to a more rational catalyst design for controlled CNT growth
Understanding Single-Walled Carbon Nanotube Growth for Chirality Controllable Synthesis
No full textChirality defines the structural and electronic properties of a single-walled carbon nanotube (SWCNT), and therefore, synthesizing SWCNT samples with single chirality is essential for future high-end applications, such as replacing silicon in next-generation electronics. Since its discovery in 1991, to realize the selective growth of SWCNTs with a unique structure has been a key focus of SWCNT research. Chirality is currently understood to be assigned at birth and might be changed during the growth process. Understanding the mechanism of chirality assignment during nucleation and chirality-dependent growth kinetics is essential for realizing the final goal of SWCNT synthesis, i.e., the large-scale synthesis of SWCNTs with a specific chiral index. From 2003, we have systematically explored chirality assignment during SWCNT nucleation, how the chirality of a SWCNT affects its growth, and how the chirality changes during growth. Together with our experimental collaborators, we have realized the chirality-specific growth of SWCNTs via a few designed experimental routes. In this account, we will review all these studies and present our perspectives on this very important research topic.
We will first introduce the screw dislocation theory of SWCNT growth to elucidate how the chirality affects the growth rate of a SWCNT and the abundance of each SWCNT in the final product. Second, a modified screw dislocation theory, which describes the SWCNT???s growth kinetics on a solid catalyst and its impact on chirality control during synthesis is presented. Third, the random chiral angle assignment during SWCNT nucleation on liquid catalysts is discussed as well as why chirality control in SWCNT growth is so challenging. Together with previous experimental reports, we further demonstrate that solid catalysts have a great advantage in realizing chirality-selective SWCNT growth. Based on our current understanding, we propose three strategies to realize chirality-selective SWCNT growth, (i) controlling the symmetry of solid catalyst particles, (ii) varying the growth conditions, and (iii) controlling the feedstock and etching agent during growth. We expect this account will give the reader a comprehensive understanding of the mechanism behind SWCNT growth and motivate further studies on selective growth to achieve the best performance of SWCNT-based devices in the future
Is the Carbon Nanotube-Catalyst Interface Clean during Growth?
No full textRevealing a "true" picture of the carbon nanotube (CNT) growth front at the catalyst surface is critical to understanding the mechanism of CNT growth. If the CNT-catalyst interface is clean or messy, which will greatly affect the mechanism of controlled CNT growth, has never been properly solved either experimentally or theoretically. Here, this issue by ab initial calculation-based kinetic analysis and classical molecular dynamic (MD) simulations is revisited. It is found that the appearance of carbon chains at the CNT-catalyst interfaces or the "messy" interfaces in MD simulations is a consequence of the very short simulation time, and a "clean" CNT-catalyst interface will emerge if the simulation time is close to that in real experiments. This study reveals that, during real CNT experimental growth, a "clean" CNT-catalyst interface with zigzag, armchair, and/or kink sites dominates the growth kinetics, and therefore, the controllable CNT growth by tuning the CNT-catalyst interface is feasible
Selective growth of two-dimensional phosphorene on catalyst surface
No full textAlthough the study of black phosphorene (BP) and its isomers has attracted enormous attention, the method of synthesizing high-quality samples in a large area is still pending. Here we explore the potential of using the chemical vapor deposition method to synthesize large-area two-dimensional (2D) phosphorene films on metal surfaces. Our ab initio calculations show that BP can be synthesized by using tin (Sn) as a catalyst, while one of its isomers, blue phosphorene (BLP), is very possible to be synthesized by using most other metals, such as Ag and Au. Besides, our study also suggests that the large binding energy between the 2D phosphorene and the active metal substrate may prohibit the exfoliation of the 2D phosphorene for real applications and, therefore, tin, silver and gold are predicted to be the most suitable catalysts for the synthesis of BP and BLP
Dynamic State and Active Structure of Ni???Co Catalyst in Carbon Nanofiber Growth Revealed by in Situ Transmission Electron Microscopy
No full textAlloy catalysts often show superior effectiveness in the growth of carbon nanotubes/nanofibers (CNTs/CNFs) as compared to monometallic catalysts. However, due to the lack of an understanding of the active state and active structure, the origin of the superior performance of alloy catalysts is unknown. In this work, we report an in situ transmission electron microscopy (TEM) study of the CNF growth enabled by one of the most active known alloy catalysts, i.e., Ni???Co, providing insights into the active state and the interaction between Ni and Co in the working catalyst. We reveal that the functioning catalyst is highly dynamic, undergoing constant reshaping and periodic elongation/contraction. Atomic-scale imaging combined with in situ electron energy-loss spectroscopy further identifies the active structure as a Ni???Co metallic alloy (face-centered cubic, FCC). Aided by the molecular dynamics simulation and density functional theory calculations, we rationalize the dynamic behavior of the catalyst and the growth mechanism of CNFs and provide insight into the origin of the superior performance of the Ni???Co alloy catalyst
Highly stable phosphorene isomers based on a buckled honeycomb lattice
No full textDue to their high stabilities and tuneable electronic structures, two dimensional isomers of black phosphorene (BP) have drawn great attention recently. By carefully considering the bonding characteristics of phosphorus atoms, we propose a buckled honeycomb lattice strategy to search for possible highly stable phosphorene isomers. As an example, phosphorene isomers with a unit cell size no larger than 8 atoms are fully explored and 14 isomers, including the well-known ??-, ??-, ??-, ??-, and ??-phosphorene, are discovered and named from P-I to P-XIV in the order of their relative stabilities. Among these isomers, P-II and P-III are two newly found isomers with superior stability comparable to BP, whose formation energies are just 0.01 and 0.03 eV per atom higher than that of BP (??-phosphorene), respectively, and both are more stable than the well-known blue phosphorene (??-phosphorene). These new phosphorene isomers exhibit a wide range of medium energy band gaps from 0.30 to 2.66 eV, various HOMO/LUMO energy levels and, therefore, can be used for various optoelectronic and device applications
Tunable growth of one-dimensional graphitic materials: graphene nanoribbons, carbon nanotubes, and nanoribbon/nanotube junctions
No full textGraphene nanoribbons (GNRs) and carbon nanotubes (CNTs), two representative one-dimensional (1D) graphitic materials, have attracted tremendous research interests due to their promising applications for future high-performance nanoelectronics. Although various methods have been developed for fabrication of GNRs or CNTs, a unified method allowing controllable synthesis of both of them, as well as their heterojunctions, which could largely benefit their nano-electronic applications, is still lacking. Here, we report on a generic growth of 1D carbon using nanoparticles catalyzed chemical vapor deposition (CVD) on atomically flat hexagonal boron nitride (h-BN) substrates. Relative ratio of the yielded GNRs and CNTs is able to be arbitrarily tuned by varying the growth temperature or feeding gas pressures. The tunability of the generic growth is quantitatively explained by a competing nucleation theory: nucleation into either GNRs or CNTs by the catalysts is determined by the free energy of their formation, which is controlled by the growth conditions. Under the guidance of the theory, we further realized growth of GNR/CNT intramolecular junctions through changing H2 partial pressure during a single growth process. Our study provides not only a universal and controllable method for growing 1D carbon nanostructures, but also a deep understanding of their growth mechanism, which would largely benefit future carbon-based electronics and optoelectronics. © 2023, The Author(s).11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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