Eutectic mixtures (EMs) were used for functionalization of carbon nanotubes (CNTs). The process consists of two main steps: a pretreatment with an acidic KMnO4 solution followed by an ultrasound treatment of CNT with the EM as a new class of environmentally-friendly solvents. Various ammonium and phosphonium based-EMs were used in the process and changes were recorded with respect to the functional groups on the CNT surface. Raman spectroscopy and X-ray diffraction analysis confirmed successful covalent functionalization without substantial damage to the structure. Accurate characterization of CNT dispersions was also carried out using UV-Vis spectroscopy and zeta potential. Studying the dispersion behavior of CNTs in aqueous solutions showed that modified-CNTs presented different dispersibility due to the changes in hydrophilicity after functionalization. The suspension stability of all modified-CNTs improved considerably compared to pristine CNT. Textural and structural characterization suggested an increase in surface area after functionalization due to exfoliation, open-ended tubes, and elimination of catalyst particles. EM-functionalized-CNTs were found applicable in electrochemical sensing. The electrochemical performance for one of the functionalized-CNTs was studied on the surface of a glassy carbon (GC) electrode for the detection of nitrite. Improved catalytic activity and sensitivity were obtained compared to bare and pristine CNT-modified GC electrodes with a detection limit of 1.35 mu M. (C) 2016 Elsevier B.V. All rights reserved.