Decorating carbon nanotubes with co-precipitated magnetite nanocrystals

•Activation of MWNT outer surface has been done using different acidic treatments.•Decoration of MWNTs with Fe3O4 NPs was performed using coprecipitation in situ.•Nitric acid functionalization provides the highest (~ 100%) attachment of MNPs.•Sulfuric acid functionalization best preserves the MWNTs with only 8% weight loss.•Functionalization with acids mixture is highly destructive with 46% MWNT weight loss.

The superior properties of carbon nanotubes (CNTs) are best manifest in bulk materials when the CNTs are organized in tandem and embedded in a continuous matrix. Decorating the CNTs with magnetic nanoparticles (MNPs) facilitates their expedient organization with a magnetic field. One of the most convenient methods for their decoration is to first treat the CNTs with nitric or sulfuric acid, or a mixture of the two, and then co-precipitate MNPs in situ. Here, six variations of this protocol are compared to identify their influence on the decoration of multi-walled CNTs (MWNTs). Acid-treated MWNTs are scrutinized using XPS, and the decorated MWNTs are examined using X-ray diffraction, transmission electron microscopy, Fourier transformer infrared spectroscopy and vibrating sample magnetometry. The results show that (1) treatment with nitric acid provides the highest (~ 100%) attachment of MNPs to the MWNT walls, (2) sulfuric acid best preserves the MWNTs with only ~ 8% weight loss, and (3) after acid-treatment, the MWNTs must be washed and filtered prior to co-precipitation to prevent the consumption of up to 70% of the iron through side reactions that yield non-magnetic phases.

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