Influence of the alignment degree of CVD-grown carbon nanotubes on their functionalization and adsorption capacity

• Functionalized CNTs were prepared from aligned and bundle-like CVD-grown CNTs.
• Less severe treatments led to increased COH/CO groups in aligned CNTs.
• Most severe treatments led to the highest COOH groups in aligned CNTs.
• In the benzene adsorption in water, aligned CNTs showed faster kinetics.
• Most severely treated aligned CNTs showed the best adsorption capacity.

Oxygen functionalized multiwalled carbon nanotubes (CNTs) were prepared from aligned and bundle-like CVD-grown CNTs by chemical treatment with different reagents of increased oxidation degree. As the severity in the oxidation degree increases elimination of the amorphous carbon is observed. However, contrary to what was previously reported, aligned CNTs treated in less severe oxidation conditions they exhibit an increased number of oxygen containing functional groups (COH/CO groups). Meanwhile, when treated in the more severe oxidation conditions, they have the highest number of COOH groups due to the appearance of defects and shortening of the tubes. In the benzene adsorption in water, aligned CNTs display faster kinetics in all cases. The best adsorption capacity is achieved with aligned CNTs treated in very severe conditions possibly due to their enhanced solubility in water, which favors electrostatic interactions and π–π interactions between the benzene rings and the CNT walls.