Sustainable sodium alginate-polyamide composite membranes for pervaporation desalination

Pervaporation desalination is a promising technology for treating hypersaline water, yet its broader application is constrained by the low water flux of conventional membranes. Herein, novel sodium alginate-polyamide (SA-PA) composite membranes were fabricated on hydrolyzed polyacrylonitrile (hPAN) ultrafiltration membranes via interfacial polymerization (IP) using a sequential deposition and one-step co-deposition method for pervaporation desalination. Comprehensive characterization revealed that the SA layer enhances hydrophilicity while the PA network ensures structural integrity. The sequentially fabricated s-SA-PA 1.0/hPAN membrane, with a well-defined layer structure, achieved a flux of 34.21 kg m −2  h −1 with 99.99% rejection (3.5 wt% NaCl, 70 °C), owing to its distinct hydrophilic SA layer and dense PA-selective layer. In the one-step co-deposition method, SA binds preferentially with piperazine (PIP) and tiles the water-hexane interface, thereby reducing the diffusion rate of PIP and restricting its diffusion pathways towards the hexane phase, resulting in a nanoscale structure with a thin, selective layer (~75–130 nm). This modulation of IP kinetics resulted in the one-step co-deposited c-SA-PA 2.0/hPAN membrane, which exhibited a superior flux (59.32 kg m −2  h −1 ) with a maintained rejection of 99.9%. Systematic evaluation of operational parameters and long-term testing confirmed the stability of these SA-PA composite membranes, demonstrating a sustainable strategy for high-performance desalination through bio-based polymers and scalable fabrication. This work establishes that precisely engineered nanoscale architectures in polymer composites can simultaneously enhance multiple membrane performance metrics, providing new design principles for advanced desalination materials.