Sensor based on β - NiOx hybrid film/multi-walled carbon nanotubes composite electrode for groundwater salinization inspection

Abstract

The enrichment of groundwater with different nutrients (Na + , Ca 2+ , Mg 2+ , Cl − , CO3 2− , among others) triggers the salinization of the aquifer and makes it inappropriate for many purposes. In this work, we developed a highly sensitive and selective electrochemical sensor, based on Ni-inorganic films electrosynthetized in situ onto multiwalled carbon nanotubes composite paste electrode (MWCNE), which allows the early detection of salinization. The working sensor (β-NiOx/MWCNE) was derivatized from nickel hexacyanoferrate modified electrode in strong alkaline medium (pH = 12), producing a hybrid film composed by β-Ni(OH)2and β-NiO(OH). The electrochemical properties, morphology and chemical composition of the formed β-NiOx thin films were evaluated by voltammetry, scanning electron microscopy and X-ray spectroscopy. The developed β-NiOx/MWCNE sensor was highly sensitive to the presence of Na + cation by ion-exchange, and the increase of Na + concentration in the range 4.46 × 10 −7 to 4.93 × 10 −6 mol L −1 inhibited linearly the reversible electrochemical signal of the device, allowing to determine trace concentrations of this ion (LOD = 9.86 × 10 −8 mol L −1) with high correlation coefficient of the data (r = 0.999) and suitable precision/reproducibility of the measurements (RSD < 9%). Using Na + as salinization marker and β-NiOx/MWCNE as electroanalytical device, we found evidences of groundwater salinization in Grossos, a Brazil coast city, whose inhabitants have hypertension above the national average. The attained results were comparable to those obtained by the standard methods for Na + analysis (percentage error ranging from 0.5 to 1.6%), confirming the accuracy of the proposed electroanalytical platform.

New Generation of Electrochemical Sensors Based on Multi-Walled Carbon Nanotubes

“…The wide active area and low R tc observed for MWCNT, and related (nano)composites, have been providing important advances on the single and simultaneous electroanalytical quantification of metallic cations (Cd 2+ [56], Pb 2+ [56], Mn 2+ [57], and Na + [58]) and anions (SO [57], drinking water [56], and groundwater [58,59]). Trace concentrations of persistent organic pollutants (sunset yellow [61], tartrazine [62], and luteolin [62] dyes), as far as gases (chlorine [63], carbon dioxide [64], and methanol vapor [65]) and industrial by-products (glycerol [66], bisphenol A [67], hydrazine [68], and hydrogen peroxide [69]) are now being monitored with MWCNT-based sensors in a quick, reproducible, reliable, and cost-effective way when compared to the traditional analytical protocols, including those based on electrochemical devices from previous generations.…”