Salinity gradient power reverse electrodialysis: Cation exchange membrane design based on polypyrrole-chitosan composites for enhanced monovalent selectivity

Design of Monovalent Ion Selective Membranes for Reducing the Impacts of Multivalent Ions in Reverse Electrodialysis

“…However, design strategies involving an insignificant change in membrane resistance could be envisaged to overcome this challenge. Tufa et al reported an improved OCV and power density with pyrrole-and chitosan-modified CEM membranes in the presence of multivalent ions (Figure 7b) [39]. This improvement was mainly attributed to the insignificant change in membrane resistance during modification, although most studies showed insignificant changes in power density when using monovalent selective IEMs [24,49].…”

“…The development of a new generation of monovalent ion-selective membranes represents one of the key strategies to overcoming the problem of uphill transport in the RED process [24,26,48,49]. monovalent ion-selective membranes allow the passage of monovalent ions, but block the transport of multivalent ions (Figure 7a) [24,26,39,48,49]. Several factors, such as the differences in hydrated ionic radii, the differences in migration rate within the membrane phase, and the affinity of the ions with the membrane, affect the permselectivity between ions of the same charge [3].…”

“…Several factors, such as the differences in hydrated ionic radii, the differences in migration rate within the membrane phase, and the affinity of the ions with the membrane, affect the permselectivity between ions of the same charge [3]. Size exclusion and electrostatic repulsion are the two mechanisms that govern the mono/multivalent ions selectivity in RED/ED [39,[48][49][50][51][52]. According to Coulomb's law, electrostatic repulsion between multivalent anions/cations and a negative/positive surface potential is greater than that between monovalent anions/cations and a negative/positive surface potential [48][49][50][51].…”

“…where t mon and t div are the transport numbers of the mono-and the divalent ions, respectively, and C mon and C div are the average concentrations of the mono-and the divalent ions in dilute solution, respectively. A higher transport number ratio implies better monovalent selectivity, and vice versa [24,39,48,49,51,53]. Only a few studies focusing on the use of monovalent selective IEMs for RED applications are available [24,26,39,48,49].…”

“…The QPSF-SF-0.09 exhibited higher monovalent ion selectivity of 24.55 at pH = 10 compared to the commercial Neosepta ACS monovalent AEMs [60]. Recently, Tufa et al prepared monovalent selective Fuji CEM T1 coated with pyrrole (i.e., 0.0025-1 M with a polymerization time of 1-8 h) and cross-linked with chitosan containing a weakly basic amino group at its end [39]. This modification led to membranes exhibiting a high degree of cross-linking with a thin cationic surface layer.…”