Investigation of the stability of metal oxide powders and ceramic membranes grafted by perfluoroalkylsilanes

• Metal oxide powders and membranes are successfully grafted with PFAS molecules.
• Modified hydrophobic powders are thermally stable up to 250 °C.
• Hydrophobic nanolayers are stable in organic solvents (e.g. hexane and chloroform).
• PFAS nanolayers are partially removed in alkaline media (pH ≥ 12).

Tubular and planar ceramic titania membranes as well as metal oxide powders (Al2O3, TiO2 and ZrO2) were modified by various perfluoroalkylsilanes molecules. During the modification process, the hydrophobic layer on the membrane or powder surface was created. Grafting efficiency was determined by liquid entry pressure (LEPw), contact angle or FT-MIR analysis. Subsequently grafted samples were exposed to air (2 years) or water (1 year), to evaluate the stability of hydrophobic layer with time. The chemical and thermal stability of modified powders and membranes was also estimated. Moreover, the tubular membranes of various porosity were tested in pervaporation (PV) and air-gap membrane distillation (AGMD) process after 2 years exposure to the air since grafting.The modified powders were thermally stable up to temperature of 250 °C. However, the grafted metal oxide powders were not stable in alkaline solutions at pH ≥ 12.Furthermore, the metal oxide powders and the planar membranes were also stable in organic solvents like hexane or chloroform. Moreover, a significant decrease of contact angle from 132° to 62° was observed after 1 year of contact with water for planar membrane grafted by C10 molecules.An important impact on the transport properties of pure water in PV and AGMD after 2 years contact with air was also observed. In PV, the water flux decreased from 1200 g h−1 m−2 to 430 g h−1 m−2 for Ti-5nm-C8 membrane. AGMD the water fluxes decreased by 21% and 27% for Ti-300kD-C6 and Ti-300kD-C12 membranes, respectively.

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