Design and fabrication of gradient wettability PAN nanofiber membrane for enhanced liquid transport and efficient air purification

Airborne particulate pollutants pose significant risks to public health and ecosystems, underscoring the urgent need for advanced air filtration materials. While nanofiber membranes have demonstrated exceptional performance, their effectiveness in high-humidity environments is often compromised by surface condensation droplets. In this study, we developed a gradient wettability polyacrylonitrile nanofiber membrane (PAN NFM), featuring a gradual transition from hydrophobicity on one side to hydrophilicity on the other across its thickness. This innovatively structure was achieved via electrospinning hydrophobic PAN NFM doped with F-TiO₂ NPs, followed by spatially selective UV irradiation to modulate pore surface chemistry and establish gradient wettability. A two-layer composite method was developed to quantitatively assess the gradient wettability structure, revealing its role in generating a continuous directional force for enhanced liquid transport. The fabricated gradient wettability PAN NFM exhibited an average pore size of 1.34 μm, a gas permeance of 907 m³·m⁻²·h⁻¹·kPa⁻¹. Under high-humidity conditions (RH = 80 %), it achieved exceptional filtration efficiency of 99.85 %, with a pressure drop of only 862 Pa, significantly lower than the 2873 Pa observed for the PAN NFM. This work establishes a paradigm for designing gradient wettability structured membranes, offering transformative potential in air purification, water treatment, and multifunctional separation technologies.