Synthesis of Amorphous Carbon Nanostrcutures on Copper Nanoparticles at Low Temperature: A Surface Diffusion Process
Zusammenfassung der Projektergebnisse
This project was motived by the absence of a growth mechanism able to explain the lowtemperature CVD growth of CNs. To support the modeling work, a variety of catalytic CVD growth below 350°C based on Cu catalysts were studied comprehensively. Thanks to a systematic characterization of the growth products and by taking the interactions between copper nanocrystals and hydrocarbon gas species (like acetylene) into account, we were able to propose a growth model. This model considers a Vapor (adsorption) - Facet (diffusion) – Solid (precipitation) process and was therefore name ‘VFS mechanism’ to distinguish it from the classical VLS and VSS (vapor-solid-solid) ones. For this new mechanism, hydrocarbon molecules instead of carbon atoms play the key role of structural-units to build the corresponding nanostructures. The VFS mechanism is composed of a series of surface processes. In detail, it corresponds to a 3-step growth model: 1) hydrocarbon source gas coupling on a catalyst surface to form oligomers, 2) oligomers diffusion through the catalyst surface between facets of a different index, 3) further polymerization of oligomers and nanofiber construction. A dedicated analysis of the kinetics reveals, for the case of Cu catalyzed nanofiber growth, that the polymerization is the rate-determining-step. The polymerization as well as the whole growth can be accelerated by certain additional oxygen-containing-molecules in the reaction atmosphere, such as H2O, which is utilized in the present study. Additionally, H2O promoted the reconstruction of the Cu catalyst itself. Due to this surface reconstruction, during growth, the catalyst particles eventually transformed into a regular appearance featuring certain low index facets. A sustainable growth consists of a carbon feedstock generation, transportation and precipitation. It relies on the collaboration among different catalyst facets. In this context the geometrical features of the catalyst particle are crucial and therefore attracted our special attention. We tried a variety of methods to change the size and shape of the catalysts as well as the catalytic activity of the corresponding catalyst facets. These efforts included an elaborate catalyst preparation and a regulation of process parameters such as temperature, pressure, gas composition. Finally, they culminated in the ability to precisely control the morphology of the growth product. Accordingly, various novel CNs were synthesized, including symmetrical straight and helix nanofiber, thin nanofiber in tip growth as well as 3-, 6-, 8- branched nanostructures. The novel CNs synthesized within the framework of this project feature a distinct morphology and microstructure. Furthermore, the VFS mechanism proposed here allowed developing methods for insitu synthesis of dope CNs. Finally, our investigations illustrated the value of those nanostructures in a variety of applications such as glucose sensor, optical absorber, and energy storage.
Projektbezogene Publikationen (Auswahl)
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Hydrogen rich carbon nanofiber growth at low temperature via a trimerization-polymerization-surface diffusion process on Ni catalyst, International Conference on Diamond and Carbon Materials 2014 7-11 September 2014, Madrid, Spain
Yao Ma, Christian Weimer, Lei Zhang, Xin Jiang
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Vapor-Facet-Solid (VFS) mechanism: a new route for catalytic CVD growth of one-dimensional nanostructures at low temperature (Schriftenreihe der Arbeitsgruppe des Lehrstuhls für Oberflächen- und Werkstofftechnologie im Institut für Werkstofftechnik; 4) Siegen, 2014
Yao Ma
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Lowtemperature growth of carbon nanofiber using a vapor–facet–solid process. Materials Today Communications, 2, e55–e61(2015)
Yao Ma, Christian Weimer, Nianjun Yang, Thorsten Staedler, Xin Jiang
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Shape-Controlled Growth of Carbon Nanostructures: Yield and Mechanism. Chem. Eur. J., 21, 12370 – 12375 (2015)
Yao Ma, Xiao Sun, Nianjun Yang, Junhai Xia, Lei Zhang, Xin Jiang
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Thermal CVD Growth of Carbon Nanostructures: Shape Control, Yield and Growth Mechanism, E MRS 2015 Fall Meeting, Sept. 15-18, Warsaw, Poland
Yao Ma, Xiao Sun, Nianjun Yang, Junhai Xia, Lei Zhang, Xin Jiang
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Electrophoretic Deposition of Carbon Nanofibers/Co(OH)2 Nanocomposites: Application for Non-Enzymatic Glucose sensing. Electroanalysis, 28, 119-125 (2016)
Qian Wang, Yao Ma, Xin Jiang, et al.
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One-Dimensional Carbon Nanostructures: Low-Temperature Chemical Vapor Synthesis and Applications, S. 47-76 in: Carbon Nanoparticles and Nanostructures, edited by N. Yang, X. Jiang, D.-W. Pang. Springer 2016
Yao Ma, Nianjun Yang, Xin Jiang
