Wood-Mimetic hierarchical porous sponges from Chitosan and tannin for efficient microplastic remediation and Closed-loop upcycling

The non-degradable microplastics (MPs) have emerged as a concerning and global issue, demanding effective and sustainable removal strategies. Existing bio-based adsorbents show great potential in MPs remediation, yet their practical application is impeded by the intrinsic trade-off between hydraulic permeability and active site accessibility. Herein, inspired by the tracheids and pits of softwood, a natural derived composite sponges were prepared via tannin-induced phase separation coupled with temperature controlled directional freezing. Mechanistically, condensed tannin acts as a supramolecular modulator by forming strong hydrogen-bonding and polyphenol-amine interactions with chitosan chains, locally disrupting polymer homogeneity and triggering phase separation that evolves into pit-like secondary pores on the aligned channel walls during directional freezing. This architecture resolves the conflict between flow speed and adsorption efficiency by combining vertical channels for reducing flow resistance with secondary wall pores for effective trapping. The optimal sponge removed over 96% of polystyrene (PS, 1 μm) MPs within 6 h. High removal efficiencies were also achieved for PS across a broad size range (100 nm–100 μm) and various MP types, including poly(vinyl chloride) (PVC, 10 μm), polyethylene (PE, 1 μm), and polyethylene terephthalate (PET, 1 μm). Beyond remediation, we demonstrate a circular strategy by carbonizing the spent sponge after recyclable adsorption to decompose the residual MPs and develop porous 3D photothermal evaporators. The resulting device delivers a high solar-to-vapor efficiency of 86.9% for clean water production. By coupling hierarchical porous structure with tannin-mediated affinity, this study demonstrates a a wood-mimetic, regenerable sponge for efficient MP capture, which can be upcycled into photothermal carbon to reduce secondary waste.