Membrane distillation of saline with phenolic compound using superhydrophobic PVDF membrane incorporated with TiO 2 nanoparticles: Separation, fouling and self-cleaning evaluation

Superhydrophobic polyvinylidene fluoride (PVDF) membrane was used to study membrane distillation of saline with phenolic compound. Besides addition of TiO2 nanoparticles, superhydrophobic surface of PVDF membrane was created by silane grafting after phase inversion. Three types of silane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) triethoxysilane, (tridecafluro-1,1,2,2-tetrahydrooctyl) triethoxysilane and (3,3,3-trifluoropropyl) trimethoxysilane were used in this work. All the membranes achieved superhydrophobicity (water contact angle > 150°), but pore size and porosity were significantly reduced by increasing silane concentration. Lithium chloride (LiCl, 2 wt%) was used to improve superhydrophobic PVDF/TiO2 membranes. Membranes were further evaluated in terms of separation performance, fouling tendency and self-cleaning properties. In membrane distillation, all membranes retained 99.9% of the phenolic content in feed (100 g/L of gallic acid). However, superhydrophobic PVDF/TiO2 membranes modified using (tridecafluro-1,1,2,2-tetrahydrooctyl) triethoxysilane (1 mL silane: 50 mL ethanol) and 2 wt% of LiCl was the only membrane that maintained the permeate flux near to 6 kg.m− 2.h− 1 without much flux decline after 8 h of operation. It also retained 99.9% of sodium chloride (NaCl) and gallic acid simultaneously at a higher feed temperature of 70 °C. Although some of these modified membranes were fouled by gallic acid, they could be easily cleaned under UV radiation.