Sustainable synthesis of thin film composite covalent organic framework membranes using dual bio-derived solvents

This study investigates the fabrication of composite membranes using polyethersulfone (PES) as the support material and a thin film composite (TFC) covalent organic framework (COF) membrane as the active layer. The polymeric supports were synthesized using two different solvents: a conventional solvent, N-methyl-2-pyrrolidone (NMP), and a green, bio-based solvent, Cyrene (Cyr). For the COF active layer, a bio-derived solvent, p-cymene, was used for TFC membrane fabrication. Through systematic optimization of fabrication parameters, such as precursor concentration, reaction time, and heating duration, the study identified optimal conditions for both the conventional and green solvent systems. The results revealed that the TpPa/PES-Cyr composite membrane, fabricated with the environmentally friendly Cyr solvent, exhibited significantly better dye rejection compared to the conventional TpPa/PES-NMP membrane, though with lower water permeance. The TpPa/PES-NMP composite membrane exhibited an optimal pure water permeance (PWP) of 264.8 ± 13.2 L·m −2 ·h −1 ·bar −1 , with dye rejection rates of 97.7 ± 4.9 % for alcian blue (AB, 1298.86 g/mol) and 99.6 ± 0.6 % for congo red (CR, 696.66 g/mol). The TpPa/PES-Cyr composite membrane achieved a lower PWP of 45.0 ± 2.3 L·m −2 ·h −1 ·bar −1 , but with improved dye rejection for most dyes. This suggests a trade-off between permeability and selectivity, which is a key consideration in membrane performance. A life cycle assessment (LCA) further demonstrated the environmental benefits of using green solvents, highlighting that the use of Cyr and p-cymene significantly reduces both global warming potential (GWP) and abiotic depletion (fossil fuels) compared to traditional solvents. This underscores the potential of bio-based solvents in reducing the carbon footprint and resource consumption of membrane production, aligning with the growing demand for more sustainable and eco-friendly technologies in water treatment and other filtration processes.