Impregnation of polyethylene membranes with 1-butyl-3-methylimidazolium dicyanamide ionic liquid for enhanced removal of Cd²⁺, Ni²⁺, and Zn²⁺ from aqueous solutions

In this study, commercial hydrophobic polyethylene (PE) membranes were impregnated with 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) hydrophilic ionic liquid (IL) and tested for the rejection of metals ions. Three homogenous mixtures containing ethanol and IL with ethanol: IL volume ratio of 15:5 (M-IL1), 12:8 (M-IL2), and 10:10 (M-IL3) were prepared. The impregnation of the IL was ascertained using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Structural and surface characteristics of the membranes, including porosity, water contact angle, tensile strength, and surface charge, were studied. Results showed that the IL impregnation has led to remarkable changes in the surface properties of the PE membrane. For instance, the water contact angle and surface porosity of the membranes have decreased from 130.1 ± 1.5° to 94.5 ± 6.7°, and from 85% to 10% in the PE and M-IL3 membranes; respectively. The heavy metal ions Cd²⁺, Ni²⁺, and Zn²⁺ rejection percentage has increased from 35.73 ± 4.41, 39.40 ± 1.23, and 52.89 ± 3.08% in the pristine PE membrane to 52.87 ± 1.82, 51.47 ± 0.61, and 68.05 ± 1.27%; respectively in the M-IL3 membrane. This removal was reported at pure water flux of 22.12 ± 1.22 L m⁻² h⁻¹. The enhanced removal was attributed to the ability of the IL DCA- anion to form stable complexes with the heavy metal cations through ion exchange, the formation of hydroxides species, and electrostatic attraction forces. The new membranes have great potential for their application in the remediation of industrial wastewater containing heavy metal ions.