Sustainable fabrication of superhydrophilic polypropylene nonwovens via tannic acid/silk fibroin coating and confined in-situ zinc oxide synthesis for robust oil/water separation.

To address the pressing issue of oily wastewater pollution, superhydrophilic membranes with favorable oleophobic properties have garnered considerable attention for their potential in oil/water separation. This study proposed a green strategy to fabricate superhydrophilic/underwater superoleophobic membranes from waste polypropylene nonwovens (PP) for efficient oil/water separation. The design leverages hydrogen-bond-driven co-assembly of silk fibroin (SF) and tannic acid (TA), whereby TA's catechol/o-benzenetriol groups form robust hydrogen bonds with SF's carbonyl residues, ensuring robust adhesion of the coating even in aqueous environments. Innovatively, Zn2+ ions, initially dissolved with SF, were confined within the TA/SF matrix via in-situ synthesis, building hierarchical micro/nano rough structures. This dual-functional coating, combining TA/SF hydrophilic networks and ZnO-induced surface topography, endowed the membrane with exceptional superhydrophilicity (water contact angle ∼0°), underwater superoleophobicity (underwater oil contact angle ∼160°), and ultralow oil adhesion, which enhance the superhydrophilicity and underwater superoleophobicity of the membranes. The modified membranes exhibited high separation efficiency (>99.5 %) for oil/water mixtures and oil-in-water emulsions under gravity-driven, with outstanding separation efficiency (>99.4 %) over cycles. Moreover, the modified membranes demonstrated notable resistance to harsh conditions (wide pH range, high salinity, and extreme temperatures), attributable to the synergistic effects of hydrogen-bond crosslinking and ZnO-anchored durability. This work not only advances the mechanistic understanding of hydrogen-bond-assisted interfacial research, but also offers a sustainable approach for reusing plastic waste into high-performance separation materials.