A novel free-standing flexible molecularly imprinted membrane for selective separation of synephrine in methanol–water media

Flexibility was very important for molecularly imprinted membrane (MIM) to apply to practical use. A novel free-standing flexible MIM was prepared using methacrylic acid (MAA) and 2-hydroxyethyl acrylate (HEA) as co-functional monomer, and ionic liquid as porogen. HEA was able to effectively improve the flexibility of MIM. Ionic liquid, 1-butyl-3-methylimidazolium bromide, was able to accelerate the synthesis process and improve the selectivity and adsorption of the MIM. The properties of MIM were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), thermo gravimetric analysis (TGA), differential thermal analysis (DTA) and X-ray photoelectron spectroscopy (XPS). Two structurally similar compounds (octopamine and tyramine) were selected as competitors to examine the selective recognition of MIM to synephrine (SYN). The competitive adsorption and permeation selectivity experiments showed that the MIM could selectively recognize SYN, and was able to be used to selectively separate SYN from the standard mixtures or the extract of stir-baked Aurantii Fructus Immaturus in methanol/water (4:1, v/v) media.