Submicron-ultrathin PE/PDVB composite membrane for efficient oil/water separation

The increasing release of oily wastewater from both household and industrial activities has led to a significant environmental challenge. Among the various methods for treating oil-water mixtures, membranes with specialized wettability characteristics have emerged as one of the most effective and cost-efficient approaches. In this field, reducing the thickness of membranes is a key strategy to lessen resistance to mass transfer. This paper describes the creation of a super-hydrophobic, submicron-thin (945 nm) and even transparent (79.99% relative transparency at 600 nm wavelength) composite membrane for oil/water separation. This was achieved by depositing polydivinylbenzene (PDVB) onto ∼170 nm ultrathin freestanding polyethylene (PE) membranes to form hierarchical rough textures. Based on the super-hydrophobicity and high roughness, PE/PDVB composite membrane is enabled to separate oil from water in both mixtures and emulsions of immiscible oil/water. Moreover, PE/PDVB demonstrated a separation efficiency exceeding 99.91% for various water-in-oil emulsions. Impressively, this efficiency could be sustained above 99.87% even after 30 cycles of separation involving surfactant-stabilized isooctane/water emulsions. This performance robustness persisted against various chemical environments such as acidic, alkaline, and saline conditions over prolonged periods. To our knowledge, PE/PDVB is currently the thinnest oil/water purification membrane available, combining both an active layer and support. This work also highlights the practicality of using an ultra-thin support layer for efficient oil/water separation. This work may be at use for membrane scientists who are developing ultra-thin membrane materials and processes for future applications.