Fabrication of Highly Hydrophobic Inorganic–Organic Silica Membranes for Application in Organic Solvent Nanofiltration (OSN)

Abstract

Tetraethoxysilane (TEOS) membranes are widely used in gas separation but show limited liquid/nanofiltration performance due to their hydrophilic silanol (Si–OH) groups. To overcome this, trimethoxy(3,3,3-trifluoropropyl)silane (TMTFS) was incorporated into the TEOS network and calcined at 250, 550, and 700 °C under N₂. Nanopermporometry using hexane and water confirmed a hydrophobic nanoporous structure at 550 °C, attributed to partially decomposed organic units from TMTFS. Higher calcination (≥700 °C) caused densification due to further decomposition, reducing performance. The hybrid membranes achieved an optimal water contact angle of 114° between 500 and 600 °C. Notably, the TEOS–TMTFS membrane calcined at 550 °C exhibited a hexane permeability of 7.6 × 10^–12 m³ m^–2 s^–1 Pa^–1, which remained stable after water exposure. These findings demonstrate successful modification of the TEOS network, enhancing hydrophobicity while minimizing densification effects.