TiO2 encapsulated cross-linked polystyrene-polyacrylic acid membranes for waste oil-water separation

Special wetting polystyrene (PS) based superhydrophobic material has been investigated as a potential cost-effective and efficient oil-water separation membrane to remediate the oil spills. However, superhydrophobic properties of polystyrene based materials are susceptible to harsh physical or chemical conditions and their superhydrophobic properties can be diminished easily. To address the stability of polystyrene based superhydrophobic membranes, polystyrene was cross-linked with the acrylic acid (AA) either by ex-situ or in-situ polymerization on the TiO2 nanoparticles. Membranes fabricated either by ex-situ or in-situ polymerization of styrene-acrylic acid on the TiO2 nanoparticles exhibited enhanced oleophilic properties having the oil contact angles of ~ 0°. The water contact angles of different membranes varied in the range 141 ~155° demonstrating the variation of hydrophobic properties of different membranes fabricated by controlling the styrene-acrylic acid co-polymer coating method. Membranes fabricated with co-polymerized PS-polyacrylic acid(PAA)/TiO2 NPs can be used to separate for both highly viscous and light oils having exceptional oil-water separation efficiencies of ~99%. The in-situ co-polymerized PS-PAA/TiO2(NP) membranes separate high and low density oils from water with a separation efficiency of over ~99% with a flux of ~50,000–60,000 L m−2 h−1 under gravity driven process and a flux of ~7500–9000 L m−2 h−1 under antigravity driven process due to excellent oil-wetting properties. It was demonstrated that the oil–water separation efficiency, reusability, durability and hydrophobicity of the styrene-acrylic acid co-polymer coated TiO2 membranes can be enhanced by using appropriate membrane fabrication methods.