Hyperphilic/hydrophobic hybridized surfaces for efficient fog harvesting

Abstract

The desert beetle, as one of the most classical mist-collecting bionic models, has a region of alternating hydrophilic and hydrophobic properties. The hydrophobic region enables rapid droplet transportation, but the macroscopic hydrophilic region is easily covered by a water film due to the pinning effect, resulting in the surface flooding phenomenon. Inspired by the desert beetle, this study selected ZrO₂ nanoparticles and micron-sized CuO/nanometer-sized Cu₂O particles, and used a simple spray coating and octadecanethiol selective modification to prepare a stable upgraded beetle-like superhydrophilic/hydrophobic hybrid surface. The surface reduces the macroscopic hydrophilic region to nanoscale hydrophilic sites, which effectively reduces the critical volume required for water droplet slippage to achieve nanoscale drag reduction, thus avoiding the occurrence of surface flooding due to water droplet retention. At the same time, the surface can be adjusted by varying the mass ratio of micro–nanoparticles to achieve different rough structures and chemical properties, resulting in different wetting properties. When the mass ratio of ZrO₂ to CuO/Cu₂O in the spray suspension is 4 : 1, the sample prepared has both superhydrophilicity and superhydrophobicity, with the highest fog collection efficiency of approximately 554.24 mg cm⁻² min⁻¹, twice that of the original sample. This surface provides more hydrophilic nucleation sites while enabling timely transport and transfer of droplets, reconciling the contradiction between nucleation and transport, and greatly improving the efficiency of fog harvesting.