Fig. 4: Simulations and characterizations on hydration shells of COF membranes.
From: Covalent organic framework membranes for efficient separation of monovalent cations
a Simulation on the structures of hydrated acid groups. b Schematic illustration of hydrated acid groups in COF membranes. c Principle of contact AFM measurements for the evaluation of confined water layer and the scheme of jump-to-contact region corresponding to the confined water layer. d Force-distance curve of variable COF nanosheets deposited on highly oriented pyrolytic graphite. The separation displacement was defined as piezo height minus cantilever deflection. e Length of jump-to-contact region of variable COF nanosheets. The Force-distance curve on 30 different points over 5 × 5 μm2 area were collected for each sample for statistical analysis. f Representative dielectric loss spectrum of TpPa–CO2H, TpPa–PO3H2, and TpPa–SO3H collected at 25 °C and 90% RH. The spectrum was fitted by the model of Havriliak–Negami relaxation model, and the fitting results are illustrated by the solid lines. g Relaxation time generated from the dielectric loss spectrum of COF membranes. All the error bars in this figure represent the standard deviation of the experiments. Source data are provided as a Source Data file.
