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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