Disclosing the pivotal role of Poly(vinylidene fluoride) omniphobic membrane surface morphology in performance of photothermal vacuum membrane distillation

Nowadays, water and energy crises are important worldwide challenges. Many efforts have been devoted to develop efficient photothermal membranes for water desalination based on membrane distillation (MD) using renewable solar energy. In the way of investigating the parameters influencing MD, photothermal membranes with different surface morphologies were prepared based on electrospinning and casting techniques by changing the relevant parameters. For this purpose, solutions containing carbon black nanoparticles were used. The longterm photothermal vacuum MD (PVMD) performance of the membranes was guaranteed by omniphobic modification of surface using low-pressure plasma polymerization of perfluorooctyl acrylate monomers. It was well demonstrated that membrane surface morphology (roughness and porosity) and its photothermal activity are linearly correlated with coefficients of determination (R2) more than 0.9. In other words, membrane with efficient PVMD performance is expected provided that the membrane surface morphology is sufficiently rough and porous to enhance light absorption and trapping and simultaneously create the lowest and highest resistance against transfer of water molecules and wetting, respectively. The membrane with designed surface morphology (average roughness of 306.7 nm and porosity of 32.6%) exhibited the most enhanced photothermal activity with evaporation efficiency as high as 93.5 %. Reducing average surface roughness and porosity to 101.1 nm and 5 %, respectively, led to a membrane with inferior PVMD performance and low evaporation efficiency as 60.7 %. The membrane with optimal performance exhibited a permeate flux of 2.85 kg/m2 & sdot;h. This membrane also provided long-term performance against wetting by the feed solution containing 0.6 mM sodium dodecyl sulfate for 540 min.