In this research, carbon nanotubes (CNTs) were synthesized on iron oxide/graphene oxide composites (Fe/GO) by chemical vapor deposition (CVD) with n-Hexane as the carbon source. The Fe/GO composites and the carbon nanotube/graphene (CNT/G) hybrid materials were characterized using FESEM, FTIR, XRD, and Raman. The effect of synthesizing temperature on the morphology and structure of products was investigated. With the synthesizing temperature varied from 700 to 800, 900 and 1000 °C, sizes of the iron oxide nanoparticles before a formation of CNTs increased from 14 to 72, 98, and 119 nm, respectively. The synthesis obtained CNTs with 20-50, 20-80, and 50-100 nm in diameter, and carbon spheres with 320-730 nm in diameter, corresponded to synthesizing temperature of 700, 800, 900, and 1000 °C, respectively. Moreover, FESEM image of CNTs synthesized over alpha iron in Fe/GO composite catalyst at 900 °C revealed the optimum temperature for CVD synthesis of CNTs. The crystallinity of CNTs from Raman spectra showed the high crystallinity than 700 and 800 °C. The degree of crystallinity (IG/ID ratio) of products synthesized at 700, 800, and 900 °C increased from 0.76, 1.45, and 1.77, respectively. In addition, the phase transformation of iron occurred completely within synthesizing temperature 1000 °C. The iron rich gamma phase in Fe/GO treated at 1000 °C was used to synthesize CNTs at 900 °C. The carbon-encapsulated iron nanoparticles was occurred over gamma iron after CVD of n-Hexane. Therefore, the formation of CNTs was required the alpha phase of iron
