An efficient method for the carboxylation of few-wall carbon nanotubes with little damage to their sidewalls

•We report an efficient method for acid functionalization of carbon nanotubes.•The method produces uniform and stable suspensions of carbon nanotubes in water.•The surfaces of the tubes are not damaged by the treatment.

We report a novel method that is able to efficiently functionalize carbon nanotubes (few-walled: from 1 to 6 layers and multiwalled) with a high yield of carboxyl groups, based on treatments with H2O2 in the presence of UV light. The amount of carboxylic groups was quantified by X-ray photoelectron spectroscopy and back-titration, showing both measurements reasonable agreement. According to the zeta potential values and to the amount of suspended nanotubes, we demonstrate that the method is able to produce uniform and stable suspensions of carbon nanotubes in water. With the aid of scanning and transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy, we show that the surfaces of the tubes are not damaged by the treatment and that the functionalized tubes have an enhanced reactivity toward oxygen. This route is efficient and could now be used to fabricate polymer composites using few-walled and multiwalled carbon nanotubes.