Layer-by-layer modified cigarette filter membranes with tannic acid-ferric chloride complexes for antifouling oil-water emulsion separation

The persistent contamination of water bodies by oil-in-water emulsions originating from industrial, agricultural, and automotive activities presents a complex challenge for conventional treatment systems. Herein, a sustainable membrane engineering strategy is proposed by repurposing post-consumer cigarette filter waste into cellulose acetate-based ultrafiltration membranes, subsequently modified via vacuum-assisted layer-by-layer (LbL) surface assembly using tannic acid and ferric chloride. Four membrane variants were investigated: pristine (M0), and membranes coated with one (M-L1), two (M-L2), and three (M-L3) successive TA-Fe 3+ layers. Surface modification progressively enhanced membrane hydrophilicity, improved antifouling behavior as reflected by higher flux recovery ratios, and maintained excellent oil rejection (∼97%). However, increasing the number of coating layers introduced additional hydraulic resistance and affected operational stability. Among the modified membranes, M-L2 exhibited the most favorable balance between antifouling performance and permeability, whereas excessive coating (M-L3) resulted in mechanical instability during cyclic operation. The performance trends are discussed based on structure–performance correlations rather than direct mechanistic verification. This study highlights the importance of optimizing coating layer number when integrating waste-derived polymer substrates with bio-inspired metal–phenolic surface modification, offering practical guidance for developing antifouling membranes for oily wastewater treatment within a circular economy framework.