Plasticization-induced oriented micro-channels within polymer inclusion membranes for facilitating Cu(II) transport

Abstract

Although polymer inclusion membranes (PIMs) have been potentially used for facilitating the ion transport, the internal structure evolution of the PIMs is still controversial. This work focused on the effect of the composition and structure of PIMs on the transport of Cu(II), which were composed of poly(vinyl chloride) (PVC) as skeleton, 2-nitrophenyloctyl ether (NPOE) as the plasticizer, and commercial LIX84I as the carrier. The results suggested that the transport flux of Cu(II) is significantly dependent on the membranous composition. While correlating the membranous composition, the microstructural information of the PVC-based PIMs was explored and evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and electrochemical impedance spectroscopy (EIS), respectively. XRD patterns and SAXS spectral features indicated that the significant structure transition occurred while increasing the NPOE content. Micro-channels of around 9 nm average diameter were clearly disclosed by SAXS for the PIM containing 40 wt% PVC, 30 wt% NOPE and 30 wt% LIX84I. And the well-organized pathway within in the PIMs was essential for efficient Cu(II) transport. The membrane's electrical parameters including dielectric constant and conductivity were also found to be depended on the membranous composition and structure. Besides, the selective transport of Cu(II) towards Ni(II) and Co(II) with PIM were further examined.