Rapid fabrication of textured membrane with super-wettability using simple spray-coating of Pd-doped WO₃ nanoparticles for efficient oil-water separation

In this work, a membrane based, water passing, and gravity driven oil-water separation system using a separating membrane, with superhydrophilic-underwater superoleophobic surface wettability is presented. The surface with this unique wettability was realized by spray coating, locally synthesized palladium-doped tungsten oxide nanoparticles on the stainless steel mesh membranes. When oil water mixture comes in contact with the coated surface, the oil-water-solid system enters into Cassie wettability state, due to the micro-nano-hierarchical surface roughness. In the Cassie state, the water partially comes in contact with the air filled pits repels the oil in the oil water mixture, and this leads the surface to become under water superoleophobic. When the coated membrane of the uniquely engineered wettability is used in the oil water separating system, the water in the oil water mixture instantly passed through the membrane, while retaining the oil content on the top, which led to the oil water separation efficiency as high as 99.99 %. In addition to the improved separation efficiency, the fouling up of the membrane is almost completely eliminated, as the oil practically does not come in contact with the membrane surface, and this ensures the durability of the membrane for multiple uses. The reclaimed water could be contaminated with oil borne bacteria, which needs to be removed, and as palladium doped WO₃ is a proven visible light active photo-catalyst, the coating of this particular material can pave a way to develop a multi-functional system, that can simultaneously carry out oil-water separation, and demineralization of organic pollutants from the filtered water, with visible light irradiation. The morphological and structural characterizations of the surface along with the wettability studies were carried out to elucidate the high separation efficiency of the coated membrane.