Synthesis and electrochemical properties of sulfur-nitrogen-doped multi-walled carbon nanotubes

Multi-walled carbon nanotubes doped with sulfur and nitrogen (S-N-MWCNTs) were grown onto silicon/silicon oxide wafer by means of chemical vapor deposition upon decomposition of dimethyl sulfoxide (DMSO) and acetonitrile (ACN) in presence of catalyst. The S-N-MWCNTs were characterized by scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The findings demonstrate that S-N-MWCNTs exhibit bamboo-shaped nanostructure, quite similar to pure nitrogen-doped carbon nanotubes. The S-N-MWCNTs were investigated with respect to their electrochemical response to ferrocyanide/ferricyanide, [Fe(CN)(6)](4-/3-) in potassium chloride aqueous solutions by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The recorded CVs demonstrate strong dependence of electrochemical response, electron transfer kinetics, and sensitivity of S-N-MWCNTs on concentration of decomposed DMSO precursor. Namely, upon increasing concentration of decayed DMSO up to 2% wt. the current density, the electron transfer kinetics, and the sensitivity of S-N-MWCNTs toward [Fe(CN)(6)](4-/3-) tend to enhance. The extracted EIS results approve that when DMSO reaches the optimum concentration of 2% wt. the barrier for electron transfer decreases significantly leading, consequently, to faster electron transfer kinetics. The S-N-MWCNTs exhibit considerable stability and excellent reproducibility, and thus it can be considered suitable analytical tool for detection of redox systems at micromolar level.