Capturing nanoplastics through a collagen fibrous membrane with hierarchical functional surfaces

Nanoplastics (NPs) pose a significant threat to ecosystems and human health due to their diminutive size and high potential for bioaccumulation. Most existing membranes for NPs separation, however, are composed of non-biodegradable, petroleum-based polymers that are difficult to recycle. This study introduces the development of an eco-friendly collagen fibrous membrane (CFM) with a hierarchical structure designed for NPs capture, achieved through crosslinking CFM with a polyphenol-Al^3 + coordination system (P/Al³⁺-CFM). The polyphenol-Al³⁺ crosslinking significantly enhances collagen fiber dispersion, imparting the membrane with increased porosity, hydrophilicity, mechanical strength, and thermal stability. P/Al³⁺-CFM exhibited high removal efficiency (> 98%) and flux (> 4400 L·m^-2·h^-1·bar^-1) for NPs with varying surface charges (PS-COOH and PS-NH₂), along with excellent resistance to interference from complex water matrices and satisfactory reusability. Furthermore, modulating the crosslinking degree tailors the pore structure, characterized by an increased proportion of pores smaller than 3 μm and a shift in the dominant pore size from approximately 10 μm to 6 μm, which enhances the removal of smaller NPs (e.g., 20 nm) but reduces permeation flux. Mechanistic investigations revealed that NPs capture is driven by a synergistic effect of the hierarchical functional surfaces, involving intra-particle diffusion and multi-site chemisorption, rather than mere size exclusion. This work offers a novel approach for developing high-performance, sustainable bio-based filtration materials.