Crosslinking improved ion transport in polymer inclusion membrane‐electrodialysis process and the underlying mechanism

Abstract

Electric field intensification has been demonstrated as an effective strategy for facilitating ion transfer and separation in polymer inclusion membrane (PIM) involved processes. However, it is still a challenge to develop compatible PIMs with high performance and to reveal the underlying mechanisms. Herein, crosslinked PIMs with different base polymers have been employed in PIM‐electrodialysis processes. Cross‐linked cellulose triacetate (CTA) based PIMs exhibited significant improvement in Cr(VI) transport, which permeability coefficient was 5.9 times larger than the non‐cross‐linked counterpart. The characterizations of cross‐linked PIMs showed higher hydrophilicity and lower membrane area resistance. Furthermore, cross‐linked polymeric network inside CTA based PIMs structure increased their crystallinity, thus supporting the fixed‐site jumping mechanism, thereby enabling ions to be transported directly in a manner of continuous pathway at low current density. This study shed light on further improvement of efficient ion transport and gave insights into the mechanism understanding in PIM‐ED systems.

Recent Advances in the Selective Transport and Recovery of Metal Ions using Polymer Inclusion Membranes

“…The carrier and base polymer in PIMs are held together by strong secondary bonds, such as van der Waals forces and hydrogen bonds, which is the main reason for the outstanding stability of PIMs compared to SLMs. [ 12 ] Due to their bulky nature, the carriers have restricted mobility within the PIMs. Appropriate carriers can be selected to achieve selective separation and recovery of specific metal ions in various application scenarios.…”

“…Among them, Aliquat 336 has been the most extensively used carrier for PIM preparation in recent years. [ 12 ] The interest in Aliquat 336 application is because Aliquat 336, as an ionic liquid, exhibits many particular properties, such as high selectivity for specific ions, high thermal and electrochemical stability, negligible vapor pressure and nonflammability, and excellent ionic conductivity. [ 52 ] Furthermore, the plasticizing properties of Aliquat 336 simplified the preparation process without the application of plasticizer.…”

“…According to the current research, there are two main transport mechanisms of target metal ions in PIM, namely, “carrier diffusion” and “fixed‐site jumping” mechanisms (Figure 8b). [ 12,21,23,119 ] The mechanism of carrier diffusion is the process by which the metal‐carrier complex migrates and diffuses within the membrane. In the fixed‐site jumping mechanism, the target metal ion is transported along a continuous chain composed of carriers through the formation and dissociation of the metal‐carrier complexes.…”

“…Interestingly, the transport of metal ions within the PIMs in the presence of an electric field also relies on both mechanisms. [ 12,23,63 ] Unlike the PIM process without an applied electric field, the transport of metal ions under an applied electric field is mainly dominated by the fixed‐site jumping mechanism. [ 23 ] This phenomenon occurs because the transport of metal ions by PIM via a carrier diffusion mechanism occurs in a neutral carrier‐metal ion‐pair form.…”

“…PIM is a new type of membrane in which the liquid phase, comprising plasticizer and carrier, is firmly fixed between the entangled polymer chains through robust secondary bonds such as hydrogen bonds and van der Waals forces. [ 12 ] The carrier functions as a selective ion‐exchanger or complexing agent, binding with the desired metal species and facilitating its transport across the PIM. The base polymer imparts mechanical strength to the PIM, while the plasticizer confers elasticity and flexibility.…”