Simultaneous electrochemical sensing of sulphite and nitrite on acid-functionalized multi-walled carbon nanotubes modified electrodes

Abstract

Detection of anions like sulphite and nitrite, which are environmental pollutants, by utilizing conducting substrates like multiwall carbon nanotubes with metal oxides and others are highly desired to monitor pollution. Herein, we report construction of COOH-functionalized, multiwall carbon nanotubes (HOOC-MWCNT) modified GCE for simultaneous estimation of sulphite and nitrite under neutral condition. The physiochemical characterizations of HOOC-MWCNT were carried out by using advanced characterization techniques to probe the thermal stability, morphology and functional groups present in the HOOC-MWCNT. From morphological studies, it was confirmed that HOOC-MWCNT has discrete tube like morphology with more active surface area which enhanced the sensor response of sulphite and nitrite anions. The modified GCE was used to detect sulphite and nitrite by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The peak separation between sulphite and nitrite are comparatively higher to probe the sensing of anions in nanomolar concentrations, it was found to be around 420 mV by CV technique. This potential difference is highly attractive to determine the sulphite and nitrite simultaneously. The sensitivity for the simultaneous determination of SO32− and NO2− were 25.29 μA cm-2 mM-1 and 209.9 μA cm-2 mM-1 and it had low limit of detection (LOD) of 215 nM and 565 nM, respectively, for SO32− and NO2−. To demonstrate the practical applicability, the proposed sensor was utilized for the determination of sulphite and nitrite anions in low concentration levels in different water real samples by the well-known recovery method.