Enhanced Filtration Characteristics and Reduced Bacterial Attachment for Reverse Osmosis Membranes Modified by a Facile Method

In this study, we report the facile surface modification of reverse osmosis (RO) membranes for improved filtration as well as bacterial resistance properties. Thin films of two silanes, 3-aminopropyltriethoxysilane (3-APS) and 6-amino-hexylaminotriethoxysilane (6-AHAS), were dip-coated on commercial RO membranes, and their nitrogen atoms subsequently quaternized. Analyses of the modified membranes via scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy confirmed the “peak and valley” morphology of the original membrane, silane deposition, and N quaternization, respectively. The original membrane showed a water contact angle of ∼90−100° that was significantly decreased after silane coating: 63° for 3-APS and ∼52° for 6-AHAS. Filtration experiments with a high-salinity feed revealed significant improvements in the permeate flux (∼25−40%) and salt rejection (∼10−15%) after the surface modification. Bacterial adhesion studies with two different species, Bacillus subtilis and Pseudomonas aeruginosa, showed significantly reduced cell attachment on the modified membranes. In addition, the coated and quaternized membranes significantly restricted the biological activity and colony formation of both strains with a bacteriostasis rate of ∼75%. The enhanced filtration and antifouling capabilities of the modified membranes were attributed to the presence of polar functionalities (R₄N⁺).