Multiwalled Carbon Nanotubes Coated with Nitrogen–Sulfur Co-Doped Activated Carbon for Detecting Fenitrothion

A nonenzymatic electrochemical sensor is drop casted for sensitive and specific fenitrothion (FT) detection, where a glassy carbon electrode (GCE) is modified by depositing an ink containing nitrogen–sulfur co-doped activated carbon-coated multiwalled carbon nanotubes (NS-AC-MWCNTs). We provide a method for NS-AC-MWCNT synthesis as follows. First, polypyrrole is coated on multiwalled carbon nanotubes (PPy-MWCNT). Then, the PPy coating is carbonized and chemically activated to enhance the specific surface area. The activated carbon coating, co-doped with nitrogen–sulfur, improves its surface electrical conductivity and electrocatalytic response as an electrode. Electrochemical impedance spectroscopy (EIS) confirms enhanced charge transfer for the NS-AC-MWCNT/GCE in comparison with MWCNT/GCE and GCE. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) with fast Fourier transform (FFT) elucidate the morphology of the material, and X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy its chemical and structural characteristics. An NS-AC-MWCNT-containing ink is prepared and deposited on a GCE to fabricate a sensor to detect FT. The volume of NS-AC-MWCNT ink deposited, buffer solution pH, accumulation potential Vpp and time tpp, and square wave voltammetry (SWV) parameters are optimized. For 0.05–40 μM FT concentrations, the sensor provides a linear current response with a 4.91 nM limit of detection (LOD) with a signal-to-noise (S/N) ratio of 3. Chemical interferents have negligible influence on FT detection. The sensor detects FT in real lake and tap water samples.