Fabrication and characterization of superhydrophobic poly (vinylidene fluoride) membrane for direct contact membrane distillation

Superhydrophobic membranes with nanostructure for membrane distillation are fabricated via spraying a mixture of polydimethylsiloxane (PDMS) and hydrophobic SiO2 nanoparticles on poly (vinylidene fluoride) (PVDF) flat sheet membranes. By changing the content of the particles in the spraying dispersion from 0 wt.% to 1.5 wt.%, the water contact angle (WCA) and the liquid entry pressure (LEPw) of the membrane vary from 107° and 210 kPa to 156° and 275 kPa, respectively. The direct contact membrane distillation (DCMD) tests with pure water show that the flux of the modified membrane is lower than that of the original membrane. However, the DCMD tests with 3.5 wt.% sodium chloride (NaCl) solution show that the permeate conductivity of the modified membrane changes little whereas it increases sharply for the original membrane. Furthermore, the 180 h DCMD tests with 25 wt.% NaCl solution show that the permeate flux of the modified membrane decreases slightly with the NaCl rejection rate above 99.99%, while the flux of the original membrane has a significant decrease with a lower rejection. The scanning electron microscopy (SEM) images of the post-tested membranes indicate that the modified membrane has an excellent anti-fouling property compared with the original one.