A facile approach toward preparation of sulfonated multi-walled carbon nanotubes and their dispersibility in various solvents

• The multiwalled carbon nanotubes were treated with acetyl sulfate.
• FT-IR, TGA, Raman, XPS, SEM, EDS, UV–vis, and DLS were used for characterization.
• The s-MWCNTs can be well dispersed in water, ethanol, DMF, DMSO, and dichloromethane.
• The method is a simple and mild approach for MWCNTs modified with sulfonic groups.

The multi-walled carbon nanotubes modified with sulfonic acid groups were prepared using acetyl sulfate as a complexing sulfonation agent. Acetyl sulfate was formed by the reaction between acetic anhydride and concentrated sulfuric acid. The multi-walled carbon nanotubes were covalently modified with sulfonic acid groups by the reaction between acetyl sulfate and multi-walled carbon nanotubes under a mild circumstance. The product was characterized with FT-IR spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive spectrometer. The results indicate that sulfonic acid groups are successfully introduced on the surface of multi-walled carbon nanotubes and their structure are well retained. Moreover, the dispersibility of functionalized multi-walled carbon nanotubes was investigated with UV–vis absorption spectra, dynamic light scattering analysis, and digital photograph. The results show that multi-walled carbon nanotubes modified with sulfonic acid groups can be well dispersed in water, ethanol and dimethylformamide to form the homogeneous dispersions for over 6 months.

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