Cobalt ferrite nanoparticle intercalated carbon nanotubes for a nanomagnetic ultrasensitive sensor of Cr-VI in water

Nanocomposites of cobalt ferrite (CFO) magnetic nanoparticle intercalated carbon nanotubes (CNTs) are evaluated as a nanomagnetic ultrasensitive sensor for an environmental toxin, hexavalent chromium (Cr-VI). Specifically, the structural and magnetic changes that accompany the infiltration of the CFO/CNT composite by Cr-VI are presented. The extended x-ray absorption fine structure shows that the atomic spacing within the CFO structure changes in the presence of Cr, suggesting that the Cr is incorporated into the nanoparticles. Vibrating sample magnetometry (VSM) reveals that the CFO/CNT composite infiltrated with Cr-VI has a 71% enhancement in saturation magnetization compared with the uninfiltrated CFO/CNTs, while small-angle neutron scattering (SANS) suggests that this magnetic enhancement is not associated with the nanoparticle length-scales, but may arise from longer-ranged clusters. Both VSM and SANS clearly demonstrate that the Cr-doped CFO/CNTs are hysteretic with a net magnetization at remanence that is about 1/3 of saturation, while this hysteresis is absent in the undoped CFO/CNTs. These magnetic differences in either remanence or saturation are promising for the magnetic detection of Cr-VI using CFO/CNT sensors.