Synergistic micro-nano composite and micron hierarchical structures enable hybrid wetting-state regulation for enhanced photothermal membrane distillation

The reversed heat transfer direction in photothermal membrane distillation overturns the design principles of conventional membrane distillation, necessitating a fundamental re-examination of how membrane microstructure dictates performance. Urushiol has intrinsic hydrophobicity and robust adhesion. Its catechol groups enable both self-assembly into micron-scale particle layers and subsequent conversion to sub-micron/nano features upon metal coordination, thus offering a chemically simple yet topographically versatile route to tailor hierarchical roughness for photothermal membrane distillation. Based on this, we developed a series of hydrophobic photothermal membranes with precisely tailored micro-nano structures via a single-variable strategy based on an urushiol-Fe 3+ coordination network. The inherent micron-scale pores of the substrate and the nano-scale topography governed by the terminal modification component synergistically facilitated the evolution of interfacial wetting states from the Cassie-Baxter to the hybrid wetting state. We identified a critical design trade-off: Structures with high micro-nano complexity exhibited enhanced photon capture, achieving solar absorption rates above 94.2 % in the 300–800 nm spectral range, whereas those with low micron-scale hierarchy demonstrated optimized thermal conduction performance. The synergistic integration of these two effects enabled a maximum distillation flux of 2.703 ± 0.022 kg·m −2 ·h −1 and a photothermal conversion efficiency of 91.22 ± 0.73 % under 2 sun illumination. This work establishes a generalizable structure-wetting-performance relationship model, providing a foundational design principle for engineering photothermal membranes with tailored functionalities.