Rapid and eco-friendly technique for surface modification of TFC RO membrane for improved filtration performance

Abstract

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O2) gas were respectively introduced to the membrane's polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O2-modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O2 plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O2-modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O2-modified membrane could be noticed when its water contact angle was reduced from 88.39° (unmodified) to 79.46° in just 15-s plasma treatment. Furthermore, this O2-modified membrane achieved an outstanding NaCl and Na2SO4 rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O2-modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O2 plasma treatment to improve RO membrane performance.