Polyvinylidene Fluoride-Based Nanowire-Imprinted Membranes with High Flux for Efficient and Selective Separation of Artemisinin/Artemether

A traditional phase transformation method is commonly used to prepare molecular imprinting membranes for selective separation. However, traditional molecularly imprinted polymers are mostly micron-sized particles, and the imprinting sites in their membrane are easily embedded, leading to a reduced adsorption capacity and decreased selectivity. In this study, an ultra-long nanowire with a diameter of about 15 nm was synthesized for the separation of artemisinin (ART), and its adsorption capacity was as high as 198.29 mg g^-1 after imprinting polymerization. Molecular imprinting membranes were prepared, using polyvinylidene fluoride (PVDF), polyethersulfone (PES), and polysulfone (PSF) as the membrane matrix, for comparison. The average membrane pore size of PVDF-MIM was about 480 nm, and PVDF-MIM had the highest adsorption capacity (69 mg g^-1) for ART. The optimal flow rate for PVDF-MIM's dynamic adsorption of ART was 7 mL min^-1. Under this optimal flow rate, selectivity experiments were carried out to obtain the separation factor of PVDF-MIM (α = 8.37), which was much higher than the corresponding values of PES-MIM and PSF-MIM. In addition, the hydrophobicity and low flux of PES-MIM and PSF-MIM lead to higher non-specific adsorption. The hydrophobicity of PVDF-MIM is lower than that of PES-MIM and PSF-MIM, which greatly reduces the non-specific adsorption of the membrane, thus increasing the selectivity of the membranes. Therefore, the effective density of the imprinting sites in the pores and the membrane structure are the main factors determining the efficient separation of molecularly imprinted membranes.