Pore-Filled Ion-Exchange Membranes with Optimal Cross-Linking Degrees for Efficient Membrane Capacitive Deionization

Abstract

In this work, we investigated the optimal design parameters of pore-filled ion-exchange membranes (PFIEMs) for the successful to a membrane capacitive deionization (MCDI) process. The PFIEMs were fabricated by employing a cheap and thin polyethylene-based porous substrate and filling ionomers based on the cross-linked polystyrene. In particular, the cross-linking degrees of the PFIEMs were controlled by adjusting the cross-linker (i.e., divinylbenzene) contents in the monomer mixture. The PFIEMs exhibited much lower electrical resistance compared to those of commercial membranes because of the largely reduced film thickness and the high ion-exchange capacities. The results also revealed that the cross-linking degree significantly affected the membrane characteristics by influencing the free volume and the density of fixed charge groups. In addition, the membrane permselectivity dominated by the cross-linking degree was shown to be the most significant parameter in determining the salt removal efficiency (η) of MCDI. Consequently, the PFIEMs with the optimal cross-linking conditions were able to the achieve excellent desalting efficiency (η = 88.5%) of the MCDI, which was superior to that of expensive commercial membranes (η = 78.7%).