Development of highly stable conductive multiwalled carbon nanotube ink using covalent and non-covalent functionalization for electrochemical sensors

The purpose of this work was the fabrication of a conductive carbon nanotube (CNT) ink. The proposed CNT ink remained remarkably stable over several months. The method includes combining the covalent and non-covalent functionalization, resulting in ink that exhibits excellent storage stability. The covalent functionalization was performed in the acid medium using H2SO4 and HNO3, while the non-covalent functionalization used sodium dodecyl sulfate (SDS) and ultrasonication. The materials were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), electro­chemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). FTIR and SEM confirmed that at the non-covalent functionalization, SDS was successfully adsorbed on the f-CNT surface, while at the covalent functionalization, the functional groups (-COOH, C=O and -OH) were inserted into the CNT surface. Voltammetry and EIS indicated that SDS in the presence of functional groups facilitates electron transfer by improved electrical conductivity. The final product was a well-dispersed CNT ink with an average ohmic resistance of 18.62 kΩ. This indicates that CNT ink can be used in the fabrication of electrochemical sensors.