Facile fabrication of superhydrophobic/superoleophilic microporous membranes by spray-coating ytterbium oxide particles for efficient oil-water separation

For oil-water separation, micron-sized stainless steel membranes were fabricated by spray-coating using dispersions of ytterbium oxide (Yb2O3). The operational parameters such as particles concentration and annealing temperature were optimized to achieve the best separation efficiency. Scanning electron microscopy (SEM) images of (Yb2O3) particles revealed that annealing at 200 °C results in sharp-edged grains that are uniformly distributed on the surface. These findings were further corroborated by X-ray diffraction (XRD) and selected area electron diffraction (SAED) analyses that confirmed the highest degree of crystallinity for the particles annealed at 200 °C. The analyses with Fourier Transform Infra-Red (FTIR) spectroscopy showed that annealing does not alter the bonding chemistry of the particles. SEM of the surface-modified membrane showed that the particles completely cover the target surface and are distributed uniformly. Wettability studies with water and oil clearly demonstrated that the membranes coated with Yb2O3 particles acted to be simultaneously superhydrophobic (contact angle of ~ 150°) and superoleophilic (near-zero contact angle). By measuring water contact angle of coated membranes annealed at different temperatures, a relationship between crystallinity and hydrophobicity was also established. These findings were reflected in oil-water separation studies performed under gravity where the modified membrane allowed all of the oil to pass through but completely blocked the water having a separation efficiency close to 100%. This efficiency was maintained after repeated cycles of oil-water passage confirming the stability of the coating.