Fabrication of bioinspired dual-scale needle-like micro/nanostructures for efficient oil–water separation

Inspired by the morphology of cactus spines and their water collection ability, this study presents dual-scale needle-like micro/nanostructures (DNMNs) for efficient oil–water separation. Currently, oil-water separation faces significant challenges: traditional technologies suffer from issues such as low efficiency, high energy consumption, and the tendency to generate secondary pollution; moreover, most bio-inspired functional surfaces are still confined to the replication of single-scale structures, failing to achieve multi-level synergistic regulation of microstructures and wettability, which consequently restricts their separation performance and adaptability to complex oil-water systems. The DNMNs are fabricated via a two-step process comprising laser etching followed by high-temperature oxidation. The effects of laser etching and oxidation parameters on the DNMN morphology are systematically investigated. The results show that the laser power controls the geometric dimensions of the microneedle arrays by adjusting the energy distribution. Optimized oxidation conditions (500°C, 2 h) promote the formation of uniform and high-density nanoneedles. The obtained DNMNs exhibit outstanding superhydrophobicity and superoleophilicity after fluorination modification, with a water contact angle of 158.4° and an oil contact angle of approximately 0°. Theoretical analysis reveals that the directional transport of oil droplets is synergistically driven by surface wettability gradients and Laplace pressure differences induced by the dual-scale needle curvature. Oil–water separation experiments confirm that the DNMNs can rapidly adsorb both light and heavy oil droplets, achieving efficient and complete adsorption of both floating and submerged oil droplets on the water surface. Overall, the DNMNs realize efficient and universal separation of light/heavy oil–water systems, addressing the limitations of single-scale biomimetic materials in poor adaptability. This work not only enriches the design theory of bio-inspired oil–water separation surfaces but also provides a feasible technical path for the practical application of micro/nanostructured separation materials.