Hydrophobic ceramic hybrid membranes for membrane distillation

Abstract Membrane distillation is gaining attention as a water recovery method for industrial wastewater. PFAS-coated membranes exhibit high water vapor permeance (>10−6 mol·m−2·s−1·Pa−1), but their toxicity and environmental persistence have raised concerns. This study aims to improve the acid resistance of PFAS-free ceramic membranes. Porous tubular α-alumina (1TC, Iwao Jiki, pore size: 0.9 μm) was modified with three PFAS-free silicon alkoxysilanes—Trimethoxypropylsilane (C3), Hexyltrimethoxysilane (C6), and Decyltrimethoxysilane (C10)—and three PFAS-based alkoxysilanes Trifluoropropyltrimethoxysilane (C3), Nonafluorohexyltrimethoxysilane (C6), and Perfluorodecyltriethoxysilane (C10). Post-treatment was performed with Hexamethyldisiloxane (HMDS) or Dimethylmethoxysilane (DMDMOS). Membrane performance was evaluated via nitrogen and water vapor permeation tests at room temperature. Acid resistance was assessed by immersion in 10 wt% sulfuric acid at 90 °C. PFAS-coated membranes exhibited higher acid resistance, likely due to their strong hydrophobicity and chemical stability. However, their nitrogen permeance increased from 7.0 × 10−6 to 7.5 × 10−6 mol·m−2·s−1·Pa−1 after post-treatment, suggesting limited effectiveness of the secondary modification. In contrast, PFAS-free membranes post-treated with HMDS maintained stable performance for over 300 hours, surpassing PFAS membranes, which lasted 230 hours. The bulky nature of PFAS groups may have inhibited effective interaction with the post-treatment agents.