Single-step synthesis of graphene nanosheets-carbon nanotubes hybrid structure by chemical vapor deposition of methane using Fe-Mo-MgO catalysts

A set of Fe-Mo-Mg catalysts with varying Mo/Mg weight ratios (40/10, 30/20, 20/30, and 10/40) were prepared and evaluated for the synthesis of graphene nanosheets/carbon nanotubes (GNS/CNT) hybrid materials via methane chemical vapor deposition. The results showed that changing the Mo/Mg ratio had a significant impact on the yield and the nature of the deposited carbon. The XRD and TPR results revealed that the iron molybdate and magnesioferrite species were the main components of Fe-Mo-Mg catalysts. TEM images showed that GNS-CNT hybrid materials were successfully grown on the surface of all Fe-Mo-Mg systems, except for the catalyst with the Mo/Mg ratio of 10:40, which produced CNT only. Raman spectroscopy results revealed that all carbon products were of high quality, with ID/IG ratios ranging from 0.14 − 0.41. It was also noticed that increasing the MgO content in the catalyst composition increases the amount of CNT compared to GNS. The total carbon yield increased from 170% to 284% for Fe-40Mo-10Mg and Fe-10Mo-40Mg, respectively. The gradual incorporation of Mg into the Fe-Mo catalyst significantly increased catalytic growth activity due to the presence of numerous mixed oxide species with diverse structures, such as MgFeOx, MgMoOx, and FeMoOx.