Exploiting sulfonated covalent organic frameworks to fabricate long-lasting stability and chlorine-resistant thin-film nanocomposite nanofiltration membrane

Incorporating hydrophilic and charged porous nanofillers to prepare high-performance thin film nanocomposite (TFN) nanofiltration (NF) membranes is an effective method to achieve efficient water treatment. In this study, we synthesize the sulfonated covalent organic framework nanosheets (S-CONs) with higher hydrophilicity and electronegativity by immobilizing sulfonic acid groups (-SO₃H) on TpPa-1 nanosheets. The S-CONs are incorporated in the PA layer by interfacial polymerization (IP) reaction. The results indicated that the S-CONs could modulate the hydrophilicity, thickness, and electronegativity of TFN-NF membranes. At the optimal addition of S-CONs (0.006 g), the pure water permeance increases to 8.84 L·m⁻²·h⁻¹·bar⁻¹, which is about 1.75 times than the TFC membrane, with a high Na₂SO₄ rejection reaching 98.97%. The improvement of the separation performance mainly results from the reduction of PA layer thickness (from ~178.00-198.00 to ~100.00-128.00 nm) and the increase of surface electronegativity (from -20.37 to -44.41 mV at pH = 7.00). More interestingly, the amide bond formed between the S-CONs and TMC improved the chlorine resistance of the membranes. This study reveals the potential of using functionalized 2D CONs as nanofillers to modify TFC membranes for efficient nanofiltration.

Wenqiao Meng, Qiang Xue, Jinyuan Zhu, Kaisong Zhang