Structural Engineering of Polyacrylonitrile Ultrafiltration Membranes via Diamine Crosslinking and Hydrolysis for Enhanced Membrane Chemical and pH Stability in Seawater Pretreatment Applications

With an emerging trend of using ultrafiltration (UF) membranes for advanced seawater pretreatment, the current study aims to enhance the chemical and pH stability of polyacrylonitrile (PAN)-based UF membranes for seawater pretreatment applications. This was achieved using a simple and facile approach of crosslinking the PAN membranes with diamines of varying lengths of carbon chains. Diamines include hydrazine (Hz), ethylene diamine (EDA), and diamino propane (DAP), which were used to crosslink nitrile (-C≡N) groups on the PAN chains giving rise to imine linkages. In addition, a hydrolyzed (Hy) PAN membrane and a control neat PAN membrane were also prepared. Developed membranes showed excellent pretreatment potential for open seawater intake. Among the different membranes, the EDA-PAN membrane was superior, especially in terms of lower fouling tendency compared to other membranes. The EDA-PAN membrane showed rejections of > 95% and > 99% in the case of algal biomass and oil–water emulsion, respectively. EDA-PAN membrane showed resistance to membrane fouling with R_F values of 3.00 × 10¹⁰ and 1.24 × 10¹¹ m⁻¹ for humic acid and bovine serum albumin, respectively. More importantly, crosslinked membranes such as EDA-PAN showed increased stability toward corrosive polar solvents like N-methyl pyrrolidone (NMP), and acid–base exposures compared to the control membrane.