(601e) Janus Quaternarized-Hemicellulose-Modified PVDF Membrane for Desalination of Oily Seawater in Membrane Distillation

Membrane distillation (MD) is an emerging thermally driven separation technology to recover pure water from seawater to alleviate severe water shortage problems. It is particularly attractive for its moderate operation temperatures (50-90 ℃), which can utilize renewable or waste energy resources such as solar energy and geothermal energy, which contribute to reducing carbon emissions. However, conventional hydrophobic membranes are susceptible to membrane fouling and pore wetting when dealing with lightly polluted seawater (e.g., oil or other organic pollutants) due to hydrophobic-hydrophobic attractions. To address these challenges, asymmetric hydrophilic modification of hydrophobic membranes can effectively impede membrane failure by forming a hydration layer on the surface in the MD process. Hemicelluloses is a promising natural polymer candidate for hydrophilic modification in terms of the abundant hydrophilic hydroxyl groups, sustainability, and low cost. In this study, we used the hemicellulose that was extracted from the pretreatment wastewater of hardwood pulping process. Then, a Janus hydrophobic-hydrophilic dual-surface was constructed via a covalently anchoring hydrophilic layer with quaternarized hemicellulose, 2, 3-epoxypropyl trimethyl ammonium chloride (EPTMAC) modifying hemicellulose, through PVA and GA cross-linking on poly (vinylidene fluoride) (PVDF) membrane surface. The electrostatic interactions between negatively charged PVDF membranes and cationic hemicellulose can improve the grafting effects on the membrane surface and allow the formation of a stable hydration layer on the membrane surface. The quaternarized hemicellulose layer can provide double functions. First, the electrostatic interaction between quaternary ammonium salts and water molecules provides underwater oleophobicity and serves as an energetic barrier to prevent the adsorption of surfactants and oil droplets. Second, the positive charge on the membrane surface repels the mineral ions in seawater by electrostatic repulsion, improving the antifouling properties of the membrane and the penetration of pure water molecules. In comparison with the pristine PVDF membrane, the Janus membrane exhibited remarkably stable water vapor flux during long-term treatments of Tween® 80-stabilized oil-in-seawater emulsion in the bench-scale direct contact membrane distillation (DCMD) experiments. This study provides not only a high-value application of hemicellulose derived from the pulping process but also a sustainable fouling-resistant membrane for high-efficiency polluted salt water distillation.