Abstract Hollow carbon nanofibers (HCNFs) were formed on the bio-char surface during microwave pyrolysis of pine nut shell in the temperatures range of 400–700 °C without the use of any additional catalyst, except activated carbon added as a microwave absorber. Scanning electron microscopy (SEM) analysis showed that HCNFs were only formed on microwave pyrolysis chars and not fixed-bed chars, suggesting that microwave irradiation had a major influence on their formation. High resolution transmission electron microscope (HRTEM) results showed that the synthesized HCNFs at 500 °C and 600 °C had a diameter of about 400 nm and length of 1400–5000 nm. HCNFs had multi-walled structure with a d-spacing of about 0.35 nm. Unlike fixed-bed bio-chars, the X-ray diffraction (XRD) analysis of the microwave bio-chars showed typical graphite peak at around 2θ = 26.3° with the strongest peak observed in 600 °C bio-char. Raman spectroscopy analysis revealed that the highest degree of carbon order of HCNFs was achieved at 600 °C, which agreed well with XRD analysis results. Detailed analysis of the volatiles evolved during microwave pyrolysis suggested that hydrocarbons in bio-oil such as benzene and alkenes and CO, CO 2 , methane, and ethane in bio-gas acted as the carbon source during formation of HCNFs.

中文翻译：

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松仁壳微波热解生物炭直接合成中空碳纳米纤维

摘要 中空碳纳米纤维 (HCNFs) 在松仁壳微波热解过程中在 400-700 °C 的温度范围内形成，除了添加活性炭作为微波吸收剂外，不使用任何额外的催化剂。扫描电子显微镜 (SEM) 分析表明，HCNFs 仅在微波热解焦炭上形成，而不是在固定床焦炭上形成，这表明微波辐射对其形成有重大影响。高分辨率透射电子显微镜 (HRTEM) 结果表明，在 500 °C 和 600 °C 下合成的 HCNFs 的直径约为 400 nm，长度为 1400-5000 nm。HCNF 具有多壁结构，d 间距约为 0.35 nm。与固定床生物炭不同，微波生物炭的 X 射线衍射 (XRD) 分析显示在 2θ = 26.3° 附近具有典型的石墨峰，在 600 °C 生物炭中观察到最强的峰。拉曼光谱分析表明，HCNFs 的最高碳有序度在 600 °C 时达到，这与 XRD 分析结果非常吻合。对微波热解过程中挥发物的详细分析表明，生物油中的碳氢化合物如苯和烯烃以及沼气中的 CO、CO 2 、甲烷和乙烷在 HCNF 形成过程中充当碳源。