Study of fabrication and CNT growth mechanisms of hybrid CFF/CNT composites

Over the past few decades, carbon hybrid composites have attracted the attention of many researchers for their applications in catalytic processes and pollutant removal. Carbon fiber felt/carbon nanotube (CFF/CNT) hybrid composites are promising candidates for such applications due to their high specific surface area, chemical stability, and high adsorption capacity as a result of the CNTs present in their composition. In this study, CFF/CNT hybrid composites were fabricated by methane decomposition on nickel surface in a CVI process at 700 degrees C over different times. The produced catalyst was characterized in terms of its shape, size, and distribution of the catalytic nickel particles formed on the surface of the CFF. Then, the desired composites had been fabricated; SEM, FESEM, and TEM were employed to investigate the morphology and the growth mechanism of the CNT; FTIR-ATR and Raman were used to determine its chemical structure; XRD technique was exploited to identify the phase structure; and BET was employed to measure the specific surface area while their mechanical properties were also characterized. FESEM images of the composite specimens confirmed the presence of CNTs 38-56 nm in diameter on the surface of the fibers. It was also observed that, with increasing process duration, the nanotubes did not lose their nanometric structure and they grew slightly larger in diameter due to the formation of new walls. Their lengths also increased by up to several micrometers. This increase in length and the intertwining of the synthesized CNTs resulted in the formation of a complex 3D CNT network around the CFF fibers. The BET test results also indicated an increase in specific surface area from 36.29 m(2)/g to 53.80 m(2)/g due to the increase in CVI process time from 2 to 10 h. Meanwhile, flexural strength exhibited a significant increase from 0.58 MPa (for CFF) to 1.36 MPa after 10 h of CVI. Finally, TEM images revealed CNT nucleation and growth in a bamboo-and octopus-like growth mechanism.