Facile preparation of superwetting surfaces by dip-coating of silane for efficient separation of different types of oils from water

Abstract

The application of membranes for environmental applications is becoming increasingly popular with researchers and scientists. This work reports the surface modification of membranes by a facile technique and its subsequent use for efficient separation of different types of oils from water. Stainless steel membranes were dip-coated with different concentrations of a low surface energy silane, perfluorooctyltrichlorosilane. The bonding between the silane film and substrate were confirmed by the use of spectroscopic techniques such as X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Scanning electron microscopic images showed the coatings to be continuous and uniform, an observation that was corroborated by the presence of almost spherical water droplets on different regions of the coated membrane. Contact angle measurements with representative oils and water revealed the superoleophilic (CA ∼0°) and superhydrophobic (CA ∼150.5°) character of the modified membrane after seven immersion cycles in the silane. The coated membrane was able to separate different types of oils from water with a high efficiency (>95 %) that was maintained after repeated passage. The separation mechanism was explained by a theoretical model that takes into account interfacial tension and pressure-driven forces. The usefulness of the coated membrane for large-scale applications was demonstrated by the high values of oil fluxes and the large intrusion pressures determined experimentally.