Performance e caracterização de um sensor eletroquímico utilizando MWCNT/Fe3O4 para a detecção do herbicida Diuron

Abstract

This work describes the development and characterization of a carbon paste electrochemical sensor modified with multi-walled carbon nanotubes functionalized with iron oxide nanoparticles (MWCNT/Fe₃O₄) for the voltammetric detection of the herbicide diuron (DRN) in water samples. Material functionalization was confirmed by thermogravimetric analysis (TGA/DSC) and Fourier-transform infrared spectroscopy (FTIR). Electrochemical characterization by cyclic voltammetry in a [Fe(CN)₆]³⁻/⁴⁻ solution demonstrated that the redox process at both electrodes is diffusion-controlled, in agreement with the Randles-Ševčík equation. The MWCNT/Fe₃O₄ electrode presented an Ipa/Ipc ratio of 0.99 and R² = 0.993, indicating a quasi-reversible behavior and higher regularity in electron transfer compared to MWCNT-OX (R² = 0.844; Ipa/Ipc = 0.78). Electrochemical impedance spectra (EIS) revealed a lower charge transfer resistance for the MWCNT/Fe₃O₄ electrode (Rct = 231 Ω) compared to MWCNT-OX (Rct = 343 Ω), confirming the kinetic superiority of the magnetic composite. The pH optimization study, conducted by DPV in 0.05 mol L⁻¹ Britton-Robinson buffer, indicated pH 3 as the optimum condition for DRN detection. The analytical curve showed two distinct linear ranges: from 0.05 to 1.0 µmol L⁻¹, with a LOD of 0.52 µmol L⁻¹ and LOQ of 1.74 µmol L⁻¹; and from 1.0 to 50 µmol L⁻¹, with a LOD of 5.85 µmol L⁻¹ and LOQ of 19.50 µmol L⁻¹. The selectivity study demonstrated that most evaluated interferents did not significantly compromise the analytical response of the sensor, except for thidiazuron (TDZ), which showed significant interference. Application in a real tap water sample evidenced a matrix effect with analytical signal suppression. The results obtained demonstrate that the MWCNT/Fe₃O₄ sensor constitutes a promising electroanalytical platform for diuron monitoring in aqueous environmental matrices.