Dual-mechanism enhanced energy efficiency of nanofiber composite membrane for photothermal membrane distillation

A novel nanofiber composite membrane with dual-mechanism enhanced energy efficiency for efficient photothermal membrane distillation was constructed, by in-situ growth of copper-based metal-organic framework (Cu-CAT) on the surface of polyamide 6 nanofiber membrane (Cu-CAT@PA6 NM) as hydrophilic photothermal layer, polystyrene nanofiber membrane doped with phase change capsule as heat storage and insulation layer, polyvinylidene fluoride tree-like nanofiber membrane as hydrophobic support layer. The spiny structure of Cu-CAT has high photothermal efficiency, and the surface temperature of the Cu-CAT@PA6 NM reaches 68 °C. The fluffy middle layer can store heat energy generated by the photothermal layer, and reduce the heat diffusion to the permeation side. This configuration collaboratively heightens the transmembrane temperature difference, improves the energy efficiency, and thus improves the permeation flux. Furthermore, the support layer confers the essential resistance to wettability and long-term stability for PMD. Under 1 kw·m⁻² illumination, feed/permeation side temperature of 25 °C/20 °C, the photothermal phase change nanofiber composite membrane achieved a remarkable permeation flux of 1.60 kg m⁻² h⁻¹, coupled with a salt rejection rate of 99.99 %, and the energy utilization efficiency of 81.50 %. More importantly, after 7 days of continuous testing, the permeation flux remained consistently high at 1.15 kg m⁻² h⁻¹, with salt rejection maintaining above 99.99 %, demonstrating the membrane's durability.