Thermally stable polysulfone nanofiltration/reverse osmosis membranes via amino grafting

Abstract

Membrane technology is a promising, efficient, and eco-friendly solution for the difficult and hazardous task of treating high-temperature wastewater for recycling. However, most polymer composite membranes perform poorly at high temperatures owing to the thermally induced relaxation of polymer chains that disrupts the membrane's pore structure and charge distribution. To improve the temperature resistance of polymer membranes, researchers have predominantly focused on modifying either the support layer or the selective layer. While enhancing polymer chain confinement is a core strategy to alleviate thermal relaxation, this mechanism remains poorly quantified, creating a key knowledge gap in membrane thermal stability. To address this research gap, this study systematically investigated the effect of the grafted amino group concentration on the temperature resistance of polysulfone (PSF) membranes. Contrary to expectations of a monotonic relationship, membrane thermal stability did not increase linearly with increasing amino group concentration; instead, an optimal grafting dosage was identified. Under the optimal conditions, the modified membrane exhibited enhanced hydrophilicity. More importantly, it demonstrated excellent thermal stability and superior anti-fouling capability in both nanofiltration (NF) and reverse osmosis (RO) processes. The membrane's high-temperature resistance was confirmed by a stable Na₂SO₄ rejection rate above 97% during a 72-hour NF operation at 90 °C and above 98% for NaCl during a 24-hour RO operation at 80 °C and 60 bar. This study thus proposes a promising strategy for fabricating high-temperature-resistant NF and RO membranes.