Highly stable SiO2-ZrO2 hollow fiber membrane via phase-transformation derived α-Al2O3 interlayer for nanofiltration under extreme conditions

Compared to organic nanofiltration (NF) membranes, ceramic NF membranes exhibit higher stability under harsh conditions such as extreme pH and elevated temperatures. γ-Al 2 O 3 is commonly employed as an interlayer in multilayer ceramic NF membranes, but it is restricted to relatively mild conditions. In this study, on a macroporous alumina hollow fiber support, a boehmite sol coating is transformed from γ-Al 2 O 3 to α-Al 2 O 3 at a reduced phase-transformation temperature under the induction of TiO 2 , forming a uniform ultrafiltration interlayer for the fabrication of SiO 2 -ZrO 2 separation layer in a single step. By dual regulating the TiO 2 doping content in boehmite sol and sintering temperatures, the resulting SiO 2 -ZrO 2 /α-Al 2 O 3 NF membrane with a pore size of 1.4 nm demonstrates extended stability across a wide pH range of 1–13 under elevated temperatures. During the long-term dynamic textile wastewater treatment test, it maintains stable permeance and selectivity for over 24 h at pH 2/12 under 60 °C, significantly outperforming γ-Al 2 O 3 -supported SiO 2 -ZrO 2 membranes. Meanwhile, it displays a permeance of up to 18 LMH/bar and superior dye desalination performance (CR: 99.23%, NaCl <12%). This optimization strategy not only enhances the stability of SiO 2 -ZrO 2 NF membranes with the aid of an α-Al 2 O 3 interlayer but also provides a simplified route for their fabrication.