Programmable oil/water separation performance of wood-based membranes via structural anisotropy and delignification

Wood-based membranes offer a promising, sustainable platform for oil/water separation due to their intrinsic porosity, renewability, and structural anisotropy. However, current approaches often require complex chemical modifications and lack a systematic understanding of how structural and processing parameters govern separation performance. This study introduced a simple yet robust strategy leveraging intrinsic structural anisotropy of natural wood to fabricate high-performance membranes without synthetic coating or surface functionalization. By altering the cutting direction, two distinct membrane architectures were obtained: cross-section membranes with longitudinal channels enabled the gravity-driven separation of light oil/water mixtures, while longitudinal membranes with interconnected transverse pores facilitated vacuum-assisted separation of oil-in-water emulsions. Quantitative analysis revealed that delignification time and thickness jointly governed wetting and transport behavior. Increasing delignification reduced the water contact angle from ∼115° to <40°, enabling tunable flux (∼90–1000 L m −2 ·h −1 ) and efficiency (75–99.9 %). For CW membranes, flux decreased and efficiency increased with thickness—thinner samples (0.5–1 mm) exhibited the highest flux (∼995 L m −2 ·h −1 ) but moderate efficiency (85–95 %), while thicker ones (∼3 mm) achieved up to 99.8 % efficiency at lower flux. For LW membranes, a similar trade-off was observed: thinner membranes (0.5–1 mm) offered higher flux (75–95.9 % efficiency), intermediate thickness (1–2 mm) balanced both (up to 99.1 %), and thicker membranes (∼3 mm) provided the highest efficiency (98.9–99.9 %) but reduced flux. Through systematic characterization, this study established a clear structure–property–performance relationship, revealing how processing parameters (cutting orientation, thickness, and lignin content) govern key structural features and, in turn, separation efficiency and flux. This work not only provides a sustainable route for fabricating high-performance membranes using natural materials but also delivers quantitative mechanistic insights and predictive design principles for liquid–liquid separation, with broad relevance for environmental remediation and resource recovery.