A novel CNTs/QCS/BiOBr composite membrane with electron–ion transfer channel for Br- recovery in ESIX process

Based on the superior selectivity of bismuth oxybromide (BiOBr) for Br - , the excellent electrical conductivity of carbon nanotubes (CNTs), and the ion exchange capacity of quaternized chitosan (QCS), a three-dimensional network composite membrane electrode CNTs/QCS/BiOBr was constructed, in which BiOBr served as the storage space for Br - , CNTs provided the electron transfer pathway, and QCS cross-linked by glutaraldehyde (GA) was used for ion transfer. The CNTs/QCS/BiOBr composite membrane exhibits superior conductivity after the introduction of the polymer electrolyte, which is seven orders of magnitude higher than that of conventional ion-exchange membranes. Furthermore, the addition of the electroactive material BiOBr improved the adsorption capacity for Br - by a factor of 2.7 in electrochemically switched ion exchange (ESIX) system. Meanwhile, the CNTs/QCS/BiOBr composite membrane displays excellent Br - selectivity in mixed solutions of Br - , Cl - , SO 4 2- and NO 3 – . Therein, the covalent bond cross-linking within the CNTs/QCS/BiOBr composite membrane endows it great electrochemical stability. The synergistic adsorption mechanism of the CNTs/QCS/BiOBr composite membrane provides a new direction for achieving more efficient ion separation.