Enhanced growth of carbon nanotube bundles in a magnetically assisted fluidized bed chemical vapor deposition

The efficient fabrication of carbon nanotube (CNT) bundles is the prerequisite for their bulk applications. However, the poor fluidization behavior of metal nanoparticle catalysts hinders the effective growth of high quality CNT bundles. Herein magnetically assisted fluidized bed (MFB) chemical vapor deposition was proposed for bulk growth of long CNT arrays. By introducing a uniform magnetic field into the fluidized bed reactor, the fluidization behavior of the ultrafine catalyst particles derived from FeMgAl layered double hydroxides (LDHs) was significantly improved with reduced bed pressure drop and increased bed expansion. Possibly, the magnetic LDH-catalyst flakes were arranged orderly in a magnetic field, which facilitated the steady and durative growth of CNT bundles. Compared with the CNT products grown in a routine fluidized bed reactor, the as-produced CNTs in the MFB reactor were with a much higher yield of 9.1 g_CNT/g_catal, improved graphitic degree, increased length up to ∼100 μm, together with smaller diameters and narrower diameter distribution as well. A gradient-magnetically assisted fluidized bed reactor was also explored for facile fabrication of very long CNT bundles over 100 μm.