The fabrication of carbon nanohorns (CNHs) from a methane precursor with argon in an inductively coupled plasma was recently demonstrated with a high production rate of ∼20 g/h by Casteignau et al. [Plasma Chem. Plasma Process. 42, 465 (2022)]. The presence of a promotor gas such as hydrogen was found to be important for the growth of CNHs, but the mechanisms at play remain unclear. Here, we study the impact of different promotor gases by replacing hydrogen with nitrogen and helium at different promotor:precursor (Pm:Pr) ratios, X:CH₄ = 0.3–0.7 (X = H₂ or N₂, Ar, and He), and global flow rates $F_X+F_{\mathrm{C}{\mathrm{H}}_4}=1.7$ and 3.4 slpm. The nature of the promotor gas is shown to directly influence the morphology and the relative occurrence of CNHs, graphitic nanocapsules (GNCs), and graphene nanoflakes. Using quantitative transmission electron microscopy, we show that CNHs are favored by an X:CH₄= 0.5, preferably with X = He or N₂. With a lower total flow rate (1.7 slpm) of N₂, even larger production rates and higher selectivity toward CNHs are achieved. Optical emission spectroscopy was used to probe the plasma and to demonstrate that the nature promotor gas strongly modulates the C₂ density and temperature profile of the plasma torch. It is shown that CNHs nucleation is favored by high C₂ density at temperatures exceeding 3500 K localized at the exit-end of the nozzle, creating a reaction zone with extended isotherms. H₂ favors CH₄ dissociation and creates a high C₂ density but cools the nucleation zone, which leads to structures with a strong graphitic character such as GNCs.

中文翻译：

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电感耦合等离子体生长环境对碳纳米角合成及形貌的影响

Casteignau等人最近证明，在电感耦合等离子体中用甲烷前体和氩气制造碳纳米角 (CNH) 的生产率高达 ~20 g/h 。[等离子化学。等离子工艺。42 , 465 (2022)]。人们发现氢气等促进剂气体的存在对 CNHs 的生长很重要，但其作用机制仍不清楚。在这里，我们通过在不同的促进剂：前体 (Pm:Pr) 比率 X:CH ₄  = 0.3–0.7（X = H ₂或 N ₂、Ar 和 He ）下用氮气和氦气代替氢来研究不同促进剂气体的影响), 和全局流量$F_X+F_{\mathrm{C}{\mathrm{H}}_{\mathrm{4个}}}=1.7$和 3.4 slpm。促进剂气体的性质显示直接影响 CNH、石墨纳米胶囊 (GNC) 和石墨烯纳米薄片的形态和相对出现。使用定量透射电子显微镜，我们表明 CNH 受 X:CH ₄ = 0.5，优选 X = He 或 N ₂的青睐。_{在较低的 N 2}总流速 (1.7 slpm) 的情况下，实现了甚至更高的生产率和更高的 CNH 选择性。发射光谱用于探测等离子体并证明自然促进剂气体强烈调节等离子体炬的C ₂密度和温度分布。结果表明，高C _{2有利于CNHs成核}温度超过 3500 K 时的密度集中在喷嘴的出口端，形成具有扩展等温线的反应区。H ₂有利于CH ₄解离并产生高C ₂密度但冷却成核区，这导致具有强石墨特性的结构，例如GNC。