Formation of Shell‐Shaped Carbon Nanoparticles Above a Critical Laser Power in Irradiated Acetylene

Abstract

In the last two decades, a series of novel nanostructured carbon materials have been synthesized in the laboratory, [1] including carbon nanotubes, [2] carbon onions, [3] and carbon nanocapsules. [4,5] Intensive studies of nanostructured carbon synthesis are motivated by potential applications such as intercalation materials for Li batteries, [6] gas-storage media, cold-electron field emitters, [7] etc. Consisting of bent graphene layers (GLs), these nanomaterials possess unique electric properties due to their finite characteristic size, making them attractive for such applications. Depending on the curvature of the graphene sheets, carbon nanomaterials can demonstrate metallic or semiconducting behavior. [8] As has been shown in our recent paper, [9] alternating metallic and semiconducting regions within carbon nanomaterials produces high levels of cold-electron field emission (FE) from nanostructured carbon materials. Therefore, there is a strong need to find an industrially attractive pathway to synthesize carbon nanoparticles with this structure. It is worth noting that although a variety of methods have been developed to produce carbon nanomaterials, these methods generate only a raw product requiring either further purification (e.g., after laser ablation or arc discharge) or the removal of catalysts (after chemical vapor deposition). Herein, we report a new synthesis pathway for generating onionlike shell-shaped carbon nanoparticles (SCNPs) which is a one-step process. Our SCNPs are highly crystalline and not mixed with other types of carbon, and therefore do not need further purification. Furthermore, our method does not use any catalysts. We show that a transparent acetylene flow can produce onion-like SCNPs (which have continuous bent GLs) in bulk quantities when it is exposed to external irradiation from a continuous-wave (CW) infrared CO 2 laser. The striking feature of this process is that it is launched only above a critical threshold of laser irradiance. Below the irradiance threshold, the flame generates carbon soot. It is this critical threshold phenomenon that distinguishes our work from any other work in the field of flame-formed carbon nanoparticles. At the same time, we demonstrate that the formation of hollow SCNPs in our experiment has nothing to do with soot restructuring due to the ordering of basic structural units (BSUs), which has been recently reported in a hydrocarbon flame under pulsed irradiation from a Nd:YAG (YAG: yttrium aluminum garnet) laser.[10] The generation of SCNPs is governed by the direct growth of graphene sheets from precipitating acetylene molecules. The demonstration of the possibility of this latter process should be a significant contribution to the field of flame-formed carbon nanoparticles. We also show that our SCNPs exhibit FE performance comparable to that of carbon nanotubes. Experiments have been carried out with the setup used successfully in our previous work.[11±15] The multi-nozzle-type burner allowed us to supply gases through different annular coaxia...

Synthesis of Ordered Mesoporous Carbon Materials with Semi-Graphitized Walls via Direct In-situ Silica-Confined Thermal Decomposition of CH4 and Their Hydrogen Storage Properties

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Laser induced transition from soot generation to shell shaped carbon nanoparticles in an acetylene flow: aerosol characterization

“…We reported a high resolution TEM image of shellshaped particles shown in Fig. 4(f) [1]. From the image (Fig.…”

“…Therefore, there is a strong need to find an industrially attractive pathway to synthesize nanocarbons having varying curvatures and, moreover, to investigate their properties in many aspects such as electrical and mechanical ones. Previously, we developed a method synthesizing shell shaped carbon nanoparticles (SCNPs) having curved graphene layers in a spherical form at large scale [1,9]. In the method, an assistant oxy-hydrogen diffusion flame was utilized for preheating acetylene which undergoes CW CO 2 laser irradiation.…”

On the Response of Nascent Soot Nanostructure and Oxidative Reactivity to Photoflash Exposure

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