A modified Hummers soft oxidative method for functionalization of CNTs: Preparation, characterization and potential application for selective determination of norepinephrine

Abstract

Functionalized carbon nanotubes, CNTs(COOH), of excess oxygen containing functional groups were prepared using a modified Hummers method. The method is based on oxidizing pristine carbon nanotubes (P-CNTs) by moderately concentrated sulfuric acid and potassium permanganate at low temperature to avoid possible CNTs fragmentation and to preserve the aspect dimensional ratio. The resulting compatible materials were characterized and confirmed by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and electrochemical method including cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Fabrication of a sensitive sensor was much reliable by directly casting of CNTs(COOH) onto the surface of a glassy carbon electrode, CNTs(COOH)-GCE, rather than the tradition electrochemically reduced deposition method, ER-CNTs(COOH)-GCE, which ultimately misplaces large number of surface oxides. The functionalized surface materials exhibited an exceptional electrochemical activity on norepinephrine (NOR) oxidation in the presence of high concentrations of electrochemical active interference species such as ascorbic acid (AA) and uric acid (UA). The proposed sensor was excellently passed the selectivity test and lowered the detection limit of NOR (DL3σ, NOR) into 0.035 μM (6 ppb). It was also applied successfully for detection of NOR in serum blood sample with tolerable recovery percentages.