A lotus-leaf-inspired bionic structured gel membrane made from straw, solvent-free preparation, and surface modification for oil-in-water emulsion separation

Addressing the persistent bottlenecks of low efficiency, high costs, and complex fabrication in large-scale oil-in-water emulsion separation, especially for submicron emulsions where environmental compatibility and performance further degrade, this work introduces a cost-effective, biomass-derived separation layer, a straw-based gel membrane (SBGM), that emphasizes green design and functional integration. Fabricated via simple straw pretreatment and surface modification under solvent-free conditions, the SBGM is produced through an entirely green and straightforward route: one-step regeneration of straw cellulose to form gel spheres and a supporting matrix, followed by surface coating with a blended PVA/TiO 2 functional layer. Featuring a lotus-leaf-inspired bionic structure and abundant hydrophilic groups, the membrane exhibits superhydrophilicity (WCA = 0°) and underwater superoleophobicity (UOCA = 162°), together with exceptional durability and stability against acids, alkalis, and extracellular polymers in wastewater. Critically, it delivers over 99 % separation efficiency across diverse submicron oil-in-water emulsions and maintains stable performance over repeated cycles, with a flux recovery rate of approximately 90 % and a fouling deposition ratio of approximately 30 %. Moreover, the photosensitive properties of TiO 2 confer superior hydrophilicity and self-cleaning capability, enabling the SBGM to sustain over 99 % separation efficiency even when treating real kitchen wastewater. Collectively, these advances markedly enhance the SBGM's practical potential for submicron oil-in-water emulsion separation.