Green synthesis of a hydrophobic deep eutectic solvent and application as electrode modifier for electrochemical detection of diuron

This study reports, for the first time, the optimisation of the synthesis of a hydrophobic deep eutectic solvent (HDES) composed of decanoic acid and tetrabutylammonium bromide, monitored using <i>in situ</i> infrared spectroscopy. The results show that the preparation can be completed in less than 5 minutes at 80 °C, allowing all molecular interactions between the precursors to occur during HDES formation. This remarkably short preparation time reduces energy consumption and, consequently, aligns with the principles of green chemistry and environmental sustainability. Furthermore, the applicability of the synthesised HDES in electrochemical sensor development was assessed by modifying a carbon paste electrode with HDES, multiwalled carbon nanotubes, and mineral oil for the sensitive detection of diuron, a widely used herbicide. Voltammetric analysis exhibited excellent reproducibility (RSD < 5%) and efficient recovery of diuron from tap water samples, 92 and 97%, indicating minimal matrix effects. Moreover, the sensor demonstrated a sensitivity of 0.16 μA L μmol^-1 over a concentration ranging from 1.0 to 47.2 μmol L^-1, along with a low limit of detection (LOD) of 0.20 μmol L^-1, highlighting its potential for environmental monitoring. This study highlights the promise of HDES as an environmentally friendly alternative for electrochemical sensor fabrication, advancing the field of sustainable analytical chemistry. In addition, it confirms the viability of employing simple and green materials in sensor design, thereby strengthening the alignment of this work with the core principles of green chemistry.