Simultaneous synthesis of carbon nanobelts and carbon/Fe–Cu hybrids for microwave absorption

By acetylene decomposition at 450 °C over the Fe–Cu nanoparticles (Fe:Cu molar ratio = 29:1, 5:1) derived from a combined sol–gel/reduction method, carbon nanobelts (CNBs) and carbon/Fe–Cu hybrid nanoparticles (CNPs) were synthesized simultaneously with high yield. The two carbon species could be easily separated according to color and were collected at different locations of the ceramic plates where the catalysts were placed. Over Fe–Cu nanoparticles of high Cu content (Fe:Cu = 2:1), the product was carbon nanofibers. A series of comparison experiments was designed to study the optimal conditions for the formation of CNBs, and the results indicate that CNBs and CNPs can be selectively synthesized at 450 °C by adjusting the Cu content of the catalyst. Moreover, the complex permittivity and permeability of the mixture that contains CNPs or CNBs (30 wt.%) (paraffin wax as binder matrix) were measured in the 2–18 GHz frequency range. Despite the low mass percentage of CNBs, microwave absorption is good. Below −10 dB, there are two, three, and four distinct reflection loss peaks when the thicknesses of CNB composites are within the 5.5–7.5 mm, 9.5–11.5 mm, and 11.5–13.5 mm ranges, respectively.