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

Abstract

A nonenzymatic\nelectrochemical sensor is drop casted for sensitive\nand specific fenitrothion (FT) detection, where a glassy carbon electrode\n(GCE) is modified by depositing an ink containing nitrogen–sulfur\nco-doped activated carbon-coated multiwalled carbon nanotubes (NS-AC-MWCNTs).\nWe provide a method for NS-AC-MWCNT synthesis as follows. First, polypyrrole\nis coated on multiwalled carbon nanotubes (PPy-MWCNT). Then, the PPy\ncoating is carbonized and chemically activated to enhance the specific\nsurface area. The activated carbon coating, co-doped with nitrogen–sulfur,\nimproves its surface electrical conductivity and electrocatalytic\nresponse as an electrode. Electrochemical impedance spectroscopy (EIS)\nconfirms enhanced charge transfer for the NS-AC-MWCNT/GCE in comparison\nwith MWCNT/GCE and GCE. Scanning electron microscopy (SEM) and high-resolution\ntransmission electron microscopy (HRTEM) with fast Fourier transform\n(FFT) elucidate the morphology of the material, and X-ray photoelectron\nspectroscopy (XPS) and Raman spectroscopy its chemical and structural\ncharacteristics. An NS-AC-MWCNT-containing ink is prepared and deposited\non a GCE to fabricate a sensor to detect FT. The volume of NS-AC-MWCNT\nink deposited, buffer solution pH, accumulation potential <i>V</i>_pp and time <i>t</i>_pp,\nand square wave voltammetry (SWV) parameters are optimized. For 0.05–40\nμM FT concentrations, the sensor provides a linear current response\nwith a 4.91 nM limit of detection (LOD) with a signal-to-noise (S/N)\nratio of 3. Chemical interferents have negligible influence on FT\ndetection. The sensor detects FT in real lake and tap water samples.