Facile preparation of antiadhesive and biocidal reverse osmosis membranes using a single coating for efficient water purification

Surface modification of reverse osmosis membranes by the deposition of antifouling coatings is a popular strategy for the control of membrane biofouling. This study reports the preparation of simultaneously antiadhesive and biocidal membrane surfaces by dip-coating of a single silane, N1-(3-trimethoxysilylpropyl) diethylenetriamine. The operational parameters for surface modification such as acid concentration and immersion time were optimized to obtain the best results. To improve the bacterial killing capabilities, the silane films were quaternized using ethyl iodide. Subsequent characterization of the coated membranes with Fourier Transform Infra Red (FTIR) spectroscopy confirmed the presence of the silane on the membrane surface. Surface elemental analysis of the modified surfaces using X-ray Photoelectron Spectroscopy (XPS) confirmed the quaternization of the Nitrogen atoms. Advanced microscopy techniques (Scanning Electron & Atomic force) revealed a smoothening of the coated surface after quaternization. Contact angle measurements showed a significant increase in surface hydrophilicity after silane deposition (from similar to 85 degrees to58 degrees)and a slightly further increase upon quaternization (similar to 58-53 degrees). Bacterial adhesion and antimicrobial studies with a B. subtilis species showed much significantly lower no. of bacterial cells on the coated and quaternized surface with a killing rate of more than 80%. Cross-flow filtration tests using a custom-built laboratory setup showed that the presence of coating did not compromise on the permeation characteristics; infact, quaternization resulted in a significant improvement (similar to 50%) in the permeate water flux. The coated membranes were quite effective in retarding biofilm formation and subsequent permeate flux decline in long-term fouling experiments with bacteria-containing water.