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Carbon onions have shown potential applications in many fields due to their low density, tunable conductivity, excellent thermal and chemical stability. In this study, we report an efficient method for synthesis of gram-scale hollow carbon onions (HCNOs). A chemical vapor deposition (CVD) process was carried out at 700 °C with magnesium oxide supported cobalt as catalyst. Abundant HCNOs were obtained by leaching the CVD product in hydrochloric acid when the precursor weight ratio of cobalt and magnesium oxide is 5%. Scanning electron microscopy and transmission electron microscopy images indicate the sample is composed of hollow polyhedral particles with diameter of 10–50 nm. The thermogravimetric analysis indicates the purity of HCNOs is about 99%. X-ray diffraction and Raman spectra demonstrates a moderate graphitization of HCNOs in which graphite carbon and defective carbon both present. The graphite carbon can provide good conduction that is beneficial to introduce the microwave, while the defects can provide abundant polarization center to stimulate the formation of multiple dielectric resonances. The calculated reflection loss curve of HCNOs with a thin thickness of 2 mm exhibit wide absorption bandwidth at high frequency (13.5–16.9 GHz), indicating an excellent microwave absorption performance at high frequency.

Low-cost catalysts are of great significance for the batch synthesis of carbon nanotubes. In this study, the low-cost red soil was directly used as a natural catalyst to catalyze the growth of multi-walled carbon nanotubes (MWCNTs). The results of SEM, TEM, Raman, TG and carbon yields of the products consistently showed that 400 °C calcined red soil lead to high quality MWCNTs growth, the Raman IG/ID of the product is 1.66, which indicates that the product has exceeded the graphitization of many industrially synthesized MWCNTs. The high catalyzation efficiency may be attributed to the fact of composition characteristics that red soil lacks alkali metals and alkaline earth metals but is rich in iron and aluminum oxide, making the composition of red soil similar to the catalyst composition used in the synthesis of carbon nanotubes by common chemical vapor deposition method. Meanwhile the impurity content is less than other natural catalytic materials. The porous structure formed after proper calcination has also played a positive role to the catalytic growth of MWCNTs, which improved catalyst utilization by facilitating the gas phase diffusion. We explored a technique for synthesis of high-quality MWCNTs at low cost using soil as a catalyst.

Based on the domestic and foreign oil field used heating furance, the pipes and instruments are worn and jammed by the sand in the heavy oil. The incrustation are formed on pipes’ inner surface which can cause cross-sectional area to be reduced, the thermal resistance rate and fuel costs to be increased. Even the probability of pipeline leak, maintenance or human resource spending increased too. This research presents a new device which is a kind of heating furnace used in the oil field. Most of the sand in the heavy oil can be removed before it flows into the heating furnace. With the sand reduced, the pipeline jam, incrustation and wear are all reduced, and the safety and reliability of the heating furnace is improved, too. Besides the objective of energy conserving and environmental protection is achieved, service life is prolonged, and the cost and material is reduced.