Effect of -CN introduction on the extraction of Cu2+ from water in imidazolyl ionic liquid/DDTC system

The extraction efficiency of five imidazole-based hydrophobic ionic liquids (ILs) for copper ions (Cu2+) in aqueous solutions was investigated by flame atomic absorption spectroscopy (FAAS), employing sodium diethyldithiocarbamate (DDTC) as the chelating agent. The extraction was conducted under optimized conditions: temperature 27.5 ± 2.5 °C, pH 6, IL volume 225 μL, DDTC concentration 0.2 g·L−1, with an extraction duration of 3 min at 3000 rpm stirring speed, followed by 4 min centrifugation. The extraction efficiencies followed the order: [EMIM][NTf2] ≈ [BMIM][NTf2] ≈ [PCNMIM][NTf2] > [BMIM][PF6] > [MCNMIM][NTf2]. The key operational parameters—including temperature, pH, IL volume, DDTC concentration, and extraction time—were systematically optimized for the four [NTf2]−-based IL extraction systems. Under the optimized conditions, the influence of cyano-group functionalization on the extraction efficiency was comparatively evaluated for [EMIM][NTf2], [BMIM][NTf2], [MCNMIM][NTf2], and [PCNMIM][NTf2]. The extraction kinetics of these four ILs were modeled, revealing similar extraction mechanisms. Thermodynamic analysis indicated consistent trends across all systems: ΔH > 0, ΔG < 0, and ΔS < 0. The influence of coexisting ions (Ni2+, Fe³+, Ca2+, Mg2+, K+, Cl−, NO3−, CO32−) on Cu2+ extraction efficiency was investigated. Among these, Ag+, Ni2+, and Fe³+ exhibited notable interference with the extraction process. The stoichiometric ratio of the Cu2+-ligand complex was determined to be approximately 1:2.5. Reusability tests demonstrated that nitric acid facilitates efficient regeneration of [BMIM][NTf2] and [PCNMIM][NTf2], with extraction efficiency remaining at 96% after five consecutive cycles. Five kinds of hydrophobic ILs [EMIM][NTf2], [BMIM][NTf2], [BMIM][PF6], [MCNMIM][NTf2], [PCNMIM][NTf2] were used for the extraction of Cu(II) in water combined with DDTC. The ILs have shown excellent extraction efficiency compared with traditional extractant tri-chloromethane. The optimum condition of the metal extraction and re-extraction and anti-interference ability of the system have been studied. The extraction mechanism of Cu(II) and reutilization of ILs were also discussed in deeply. The addition of DDTC enabled the extraction of ILs from 3% to 99%.Maximum extraction rate of 99% for all five ILs under optimal conditions.[BMIM][NTf2] and [PCNMIM][NTf2] were still able to reach 96% extraction after five cycles. The addition of DDTC enabled the extraction of ILs from 3% to 99%. Maximum extraction rate of 99% for all five ILs under optimal conditions. [BMIM][NTf2] and [PCNMIM][NTf2] were still able to reach 96% extraction after five cycles.