Fig. 2: Ion selectivity and conductivity of microporous covalent triazine framework membranes.
From: High selectivity framework polymer membranes chemically tuned towards fast anion conduction
a Schematic showing the transport of anions across rigid micropores within positively charged covalent triazine framework (QCTF) membranes. Coulombic/steric exclusion and intimate ion‒pore wall interactions enable selective and fast anion transport. Red and blue spheres: fixed functional groups or charged triazine rings; green spheres: counterions or charge carrier ions; blue and gray spheres: positively charged ions with large or small hydrated diameters. The dashed lines indicate ion‒pore wall interactions, while the arrowed lines suggest rejection or transport of ions. b Current‒voltage (I‒V) curves of the M-QCTF, P–QCTF, QCTF, Selemion® DSV, Selemion® AMV and Sustainion® X37-50 membranes under a 10-fold concentration gradient in KCl solution. The intercept at 0 µA correlates to the transmembrane potential because of selective ion transport, from which the transference number t- can then be deduced. c The permeability coefficient of BTMAP-Vi and KCl across QCTF membranes and three commercial membranes, as determined from a two-compartment diffusional H-cell. d Cl- conductivity plotted as a function of hydration number for the M-QCTF, P-QCTF, QCTF, Selemion® DSV, Selemion® AMV and Sustainion® X37-50 membranes. The conductivity was measured via the four-probe EIS method. Each data point represents the Cl- conductivity at an individual temperature: from left to right (or from larger data points to smaller data points), 30‒80 °C, with a 10 °C increment. e A plot of activation energy versus hydration number (λ) at 30 °C for QCTF membranes, framework membranes, polymer of intrinsic microporosity (PIM) membranes and flexible polymer membranes. f Comparison on activation energy for QCTF membranes, representative commercial membranes and those reported previously. The detailed values can be found in Supplementary Table 1. Error bars are standard deviations derived from three parallel measurements based on separate membrane samples, while experimental errors of data from references were not shown. Source data are provided as a Source data file.
