The synergistic effects of incorporating bi-sulfonated covalent-organic frameworks nanosheets and surface modification on the durability of thin-film nanocomposite nanofiltration membranes

Improving the membrane durability without sacrificing perm-selectivity is an essential challenge in membrane technology. To address this challenge, a combination of incorporating bi-sulfonated covalent-organic frameworks nanosheets (TpPa-(SO3H)2 CONs) and surface modification was used to modify thin-film composite (TFC) nanofiltration membranes. The nanofiltration experiments and molecular dynamics (MD) simulations revealed that nanosheets dispersed in n-hexane could significantly modulate the piperazine diffusion. At the optimal nanosheet addition amount of 0.004 g/100 ml n-hexane, the pure water permeance (PWP) and Na2SO4 rejection of the thin-film nanocomposite (TFN) membranes increased to 9.35 L·m−2·h−1·bar−1 and 99.26 %. Meanwhile the corresponding values of the pristine TFC membranes were only 5.45 L·m−2·h−1·bar−1 and 96.99 %, respectively. Membrane surface modification was performed on the optimal TFN surface. When the surface was modified with Tp at a concentration of 0.004 g/100 ml n-hexane for 9 s, the PWP further increased to 11.42 L·m−2·h−1·bar−1, which was almost 2.10 folds higher than the original TFC membranes. In contrast, the Na2SO4 rejection slightly increased to 99.36 %. Moreover, the static immersion experiments results indicated that the surface modification enhanced the membrane durability. This study proved that the association of these two methods provides a simple and effective strategy to design nanofiltration membranes with excellent separation performance and durability simultaneously.