A facile and novel approach towards carboxylic acid functionalization of multiwalled carbon nanotubes and efficient water dispersion

•A new protocol for carboxylic acid functionalization of MWCNTs.•The MWCNTs were treated with NaNO2/HCl, HNO3/H2O2.•Treated MWCNTs were characterized with FTIR, TGA, SEM and TEM.•The dispersibilities of treated MWCNTs in various solvents were evaluated.•The method was a mild approach for MWCNTs modified with carboxyl groups.

A convenient, cheap and mild covalent functionalization route for multiwalled carbon nanotubes (MWCNTs) have been developed for the first time. The MWCNTs were treated with wet chemical oxidants (NaNO2/HCl, HNO3/H2O2) in order to modify MWCNTs with carboxyl groups. Surface functionality groups and morphology of MWCNTs were analyzed by FTIR, TGA, SEM and TEM. The results consistently confirmed the formation of carboxyl functionalities on MWCNTs, while the structure of MWCNTs has remained relatively intact. Functionalized MWCNTs showed good dispersion in aqueous media than untreated MWCNTs. Results show that NaNO2/HCl treatment is best suited for the chemical functionalization, giving optimum surface carboxyl groups and minimum length shortening of MWCNTs.