Toward sustainable membrane distillation: Green solvent-driven SANIPS to fabricate superhydrophobic membranes from...

The development of superhydrophobic membranes is crucial for advancing membrane distillation (MD) under sustainable manufacturing. This work demonstrates for the first time that dimethyl sulfoxide (DMSO), a green solvent, can be effectively integrated into the eco-friendly spray assisted nonsolvent induced phase separation (SANIPS) method to fabricate superhydrophobic polyvinylidene fluoride (PVDF) membranes. Compared to conventional toxic N-methyl-2-pyrrolidone (NMP) systems, DMSO-based membranes achieve superhydrophobicity more efficiently, reaching a water contact angle of 151.6° within 30 s of air spray. A switching of air spray to water spray further enhances the hydrophobicity to 160° and reduces the sliding angle to 14.5° Mechanistic analyses confirm that the faster water uptake, earlier cross over the cloud point, and accelerated phase separation in DMSO systems are the reasons for rapid formation of hierarchical surface structures and superior superhydrophobicity of the resulting membranes. In DCMD tests using a NaCl feed of 10 wt%, the water-sprayed membrane (DMSO-w30) delivers a flux of 20 kg m^-2 h^-1 with a salt rejection exceeding 99.99 %, outperforming both the air-sprayed (DMSO-a30) and the pristine DMSONIPS membranes, which exhibit fluxes of 13.7 and 13.5 kg m^-2 h^-1, respectively. Moreover, it maintains stable performance over a continuous operation of 108 hr with a salty feed containing a Rose Bengal dye of 100 ppm. These results demonstrate the potential of combining DMSO with the SANIPS approach to design fouling resistant and high-performance MD membranes for high purity water production, sustainable and environmentally friendly water reuse applications.