Desenvolvimento de sensor a base nanotubo de carbono e óxido de ferro para determinação de BTX em água subterrânea e solo de postos de combustíveis em São Luís/MA

Abstract

Environmental contamination by organic compounds represents serious problems for public health and the environment, especially for groundwater and soil contamination. One of the main problems is contamination by aromatic hydrocarbons. Among the monoaromatic hydrocarbons, known as BTX [benzene (B), toluene (T) and xylenes (X)], B stands out for being the most toxic among BTX, being considered highly carcinogenic, including their derivatives. Monitoring these contaminants in groundwater and soil of great importance. The present work

proposes an electrochemical sensor based on iron oxide nanoparticles supported on carboxyl- functionalized multi-wall carbon nanotubes (ECV/Fe2O3/MWCNT-COOH) for the

determination of B, T and X in soil and groundwater samples from gas stations. The physicochemical properties of Fe2O3/MWCNT-COOH were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Diffraction (XRD). Using the square wave voltammetry (SWV) technique the ECV/Fe2O3/MWCNT-COOH sensor was evaluated from the electroanalytical point of view for BTX analysis. After optimizing the experimental parameters, the following best conditions were found: electrolyte = H2SO4 0.1mol L-1

; pH = 1.0; frequency = 40 mV; amplitude = 20 mV; potential step = 2 mV. Under these optimized conditions, the proposed sensor presented an excellent electroanalytical performance for BTX oxidation and analysis, showing a linear behavior between anode peak currents and analyte concentrations, in the range of 5 to 35 μmol L -1 for benzene, and 20.00 to 53.00 μmolL-1

for toluene and xylenes. Through the standard deviations of the calibration curves the LD were calculated for the analytes (0.78 μmol L-1 for benzene, 5.33 μmol L-1 for toluene and 20.38 μmol L-1 for xylenes). The precision (relative standard deviation (RSD) of the method) was assessed by the repeatability of the analyte current (n = 6) in the solution. Good RSD values were found (0.81% for benzene, 3.99% for toluene and 2.82% for xylene). The application of the new method was carried out through the enrichment in real samples. Recovery (accuracy) showed excellent statistical results in samples of soil (B = 99.9%; T = 100%% and X = 99.8%) and groundwater (B = 100%; T = 99.7% e X = 99.8%). No significant interferences were observed for other species (catechol and benzoquinone) possibly present in the analysis of each of the analytes. The good results indicate that the proposed new electrochemical nanosensor is suitable for the determination of BTX in soil and groundwater samples.