Sustainable Design of Bio-Composite Membranes for Dual Contaminant Separation and Environmental Remediation

The growing contamination of water bodies by micro- and nanoplastics (MNPs) and oil pollutants poses a critical challenge to environmental sustainability, public health, and the efficiency of present-day wastewater treatment technologies. Because conventional separation techniques generally target only a single class of pollutants and often rely on petroleum-based materials or toxic fabrication routes, there is a pressing need for sustainable, multifunctional purification systems. This study addresses that gap by developing an environmentally benign cellulose acetate (CA)-based composite membrane capable of simultaneously removing both MNPs and oil contaminants from water. A biodegradable CA membrane was fabricated using a modified non-solvent induced phase separation (NIPS) technique. To enhance adsorption capabilities and broaden pollutant selectivity, the CA matrix was functionalized with tannic acid (TA), chitosan (CH), and activated charcoal (AC) in a single-step synthesis. These natural and carbonaceous additives create hierarchical porosity, reduce hydrophobicity, and introduce multiple interaction sites, allowing the membrane to operate by synergistic mechanisms rather than single-mode filtration. Comprehensive morphological and chemical characterizations—FESEM, EDX, MATLAB image analysis, and FTIR—verified uniform dispersion of TA, CH, and AC throughout the CA matrix. Structural analysis showed an average pore radius of ~33 nm, enabling both size-based and adsorption-based capture. Chemical spectroscopy confirmed strong interfacial bonding, including hydrogen bonding, π–π stacking, hydrophilic interactions, and electrostatic coupling between CA and the incorporated additives. The separation performance of the CA–TA–CH–AC membrane was evaluated under flow-through conditions for both microplastic (30 µm) and nanoplastic (200 nm) polystyrene particles. Removal efficiencies exceeded 90% at higher membrane bed heights, driven by extended contact time and increased interaction pathways. FESEM imaging provided direct visual evidence of captured plastics embedded within membrane pores and adhered across the surface, confirming robust adhesion and mechanical stability during continuous filtration. The synergy of TA (π–π and hydrogen bonding), CH (electrostatic attraction and hydrophilicity), and AC (surface adsorption and van der Waals forces) is reflected in the high capture efficiency across particle sizes. In addition to plastic remediation, the composite membrane also demonstrated >90% demulsification efficiency for olive-oil-in-water emulsions. The dominant mechanisms include hydration-layer-mediated oil rejection through hydrophilic TA and CH domains, and droplet adsorption on the high-surface-area AC microstructure. These results confirm that both oil and polymeric contaminants can be passively removed in a single step without requiring surfactants or external energy inputs. Building upon these outcomes, the work proposes a layered membrane filtration device incorporating gradient functionality—pristine CA, CA–TA, CA–CH, and CA–AC—to sequentially achieve size exclusion, hydrophobic/π–π binding, electrostatic capture, and final adsorption polishing. This modular approach enables targeted contaminant removal, ease of regeneration, and long-term durability, establishing a scalable pathway toward advances in broad-spectrum water purification. In conclusion, this research presents a green, scalable, and multifunctional CA-based membrane platform capable of simultaneous MNP and oil contaminant separation using synergistic physicochemical interactions. The developed system aligns with principles of sustainable materials engineering and offers potential for expansion toward the removal of dyes, heavy metals, pharmaceuticals, and other emerging pollutants.