Solubilization of seven hydrophobic pesticides in quaternary ammonium based eco-friendly ionic liquid aqueous systems

Abstract

In this work, quaternary ammonium based ionic liquids (ILs) are proven to be good candidates to act as green solvents/solubilizers for pesticide formulations. The surface activity of six ionic liquids ([M₃C_nN]X; M = CH₃; n = 10, 12, 14; X = Cl, Br) was tested, along with the corresponding critical aggregation concentration (CAC), lowest surface tension (γ_CAC), maximum surface excess concentration (Γ_max), minimum area per molecule (A_min) and higher adsorption efficiency (pC₂₀), which were measured using several methods, including surface tension measurements, electrical conductivity measurements, steady-state fluorescence measurements and ¹H NMR. The thermodynamic parameters of micellization, the viscosities and the activation energies of the six ILs in 30% aqueous solutions, over the temperature range of 288–308 K, were determined and calculated. The results indicated that the solubilities of representative pesticides (metolachlor, acetochlor, clethodim, thiamethoxam, prochloraz, acetamiprid and fosthiazate) in different concentrations of these ILs were significantly higher than in pure water, especially for prochloraz (e.g., 137.2 g L⁻¹ in 30% C10Br, 4035 times higher than in pure water). The microenvironment existing between the pesticide and micelle was investigated using ¹H NMR techniques, revealing that micelle localization of pesticide molecules and a change in micelle conformation occurred in the dissolving process.