One-step chemical vapor deposition synthesis of magnetic CNT-hercynite (FeAl2O4) hybrids with good aqueous colloidal stability

A multiwall carbon nanotube (MWCNT)/hercynite (FeAl2O4) hybrid nanomaterial was synthesized by one-step chemical vapor deposition (CVD) using acetylene as precursor and FeOx-AlOOH xerogel as catalyst. The hybrid material was composing by hercynite nanoparticles (diameter 10-50 nm) intimately attached to the walls of the MWCNTs. The diameter of the MWCNTs was related to particle size of the catalyst. The hybrid nanomaterial exhibited a characteristic magnetic behavior that can be considered as a combination of superparamagnetism and ferromagnetism, with a saturation magnetization of 5.7 emu/g at an applied field of 18 kOe and a coercivity of 520 Oe. The hybrid displayed a relatively low pHZPC (approx. 3.2) and formed very stable aqueous suspensions at pH 5.5. Controlled oxidation of the hybrid generated oxidized functional groups, as -OH and -COOH, and promoted the transformation of hercynite to hematite. Due to the high dispersibility of the hybrid in water, it presents an interesting potential as nanofiller for hydrophilic polymers.