Trioctylammonium-based Ionic liquids for metal ions Extraction: Synthesis, characterization and application

•trioctylammonium-based ionic liquids (ILs) were synthesized for heavy metal extraction.•ILs were characterized using 1H NMR, 13C NMR, and FT-IR spectroscopy.•density, viscosity, and electrical conductivity for the liquid ILs were investigated.•Vogel–Fulcher–Tammann model and the Arrhenius model were applied in respect to temperature.•Extraction of metal ions from aqueous solution and recyclability of ILs were studied. Hydrophobic trioctylammonium-based ionic liquids (ILs) were synthesized for heavy metal extraction from aqueous solutions. The ILs were characterized using 1H NMR, 13C NMR, and FT-IR spectroscopy, confirming the synthesis of the ILs. The thermal stability of the ILs was investigated using thermogravimetric analysis, and the synthesized ILs had decomposition temperatures between 205 and 222 °C. The temperature dependences of density, viscosity, and electrical conductivity for the liquid ILs were investigated in the temperature range of 293.15–333.15 K and modelled using a linear model, the Vogel–Fulcher–Tammann model, and the Arrhenius model, respectively. The efficacy of [HTOA][phthalate] and [HTOA][adipate] as extraction solvents in liquid–liquid extraction of Cd(II), Cu(II), and Zn(II) from aqueous solutions was then determined by investigating the effect of extraction time on the extraction process, with four extraction times being used: 5, 15, 30, and 60 min. [HTOA][adipate] performed better than [HTOA][phthalate], having extraction efficiencies of 85, 67 and 69% for Cd(II), Cu(II), and Zn(II), respectively, after 60 min. In comparison, [HTOA][phthalate] had extraction efficiencies of 85, 53, and 37% for Cd(II), Cu(II), and Zn(II), respectively, after 60 min. The recyclability of the [HTOA][adipate] was investigated by using 0.1 M EDTA solution as the regenerating agent. The EDTA solution was effective in extracting Cd(II) and Cu(II), with back-extraction efficiencies of 89 and 82%, respectively. Its extraction of Zn(II) was less effective with a back-extraction efficiency of 41% being achieved.