One-step fabrication of photothermal membranes via spray-assisted nonsolvent induced phase inversion for solar-driven distillation desalination

To address the global freshwater crisis, the development of hydrophobic photothermal membranes for solar-driven membrane distillation has gained significant attention. In this work, a novel one-step spray-assisted nonsolvent induced phase separation (SANIPS) method was developed to fabricate poly(vinylidene fluoride)/multi-walled carbon nanotube (PVDF/MWCNT) photothermal membranes. The SANIPS process enables the formation of a bicontinuous porous structure, which simultaneously provides high hydrophobicity (water contact angle > 140°), large porosity, and enhanced light-trapping through multiple internal reflections. The optimized PVDF-0.2%CNT membrane exhibited efficient photothermal conversion, reaching a surface temperature of 55.70 °C under 1 sun irradiation, approximately 25 °C higher than its unmodified counterpart. In photothermal membrane distillation tests using a 3.5 wt% NaCl feed under 1 sun irradiation, this membrane achieved a high water flux of 1.37 kg·m⁻²·h⁻¹ and an overall photothermal conversion efficiency of 85.91% under optimized conditions while maintaining salt rejection above 99.99%. This work demonstrates that the SANIPS strategy offers a scalable and integrated approach to design high-performance photothermal membranes, presenting a promising route toward energy-efficient and sustainable solar-driven desalination.