Construction of a Hydrophilic α-Al₂O₃ Tight Ultrafiltration Membrane with a Narrow Pore Size via Fe-Lattice Doping

Ceramic tight ultrafiltration (UF) membranes exhibit excellent chemical and thermal stability. However, increased pore size and limited separation accuracy caused by high temperature sintering remain challenges in their preparation and application. In this study, a facile lattice-doping strategy using Fe-doped sol-gel precursors was developed to fabricate α-Al₂O₃ tight UF membranes. Fe incorporation effectively promoted the γ → α phase transformation at a reduced temperature (950 °C), suppressed grain growth, and produced smaller and more uniformly distributed pores with an average size of 5.5 nm. Increasing Fe content further enhanced surface hydrophilicity, corrosion resistance in biotic systems, and pure-water permeability (130 L·m^-2·h^-1·bar^-1). Nevertheless, excessive Fe loading (>10%) resulted in phase separation and pore size heterogeneity. The optimized 10% Fe-doped α-Al₂O₃ membrane exhibited outstanding separation performance, achieving a BSA rejection of 99.9% and a permeance of 80 L·m^-2·h^-1·bar^-1, nearly double the value of the undoped membrane. It also showed a significantly improved normalized flux and a flux recovery ratio exceeding 80%, demonstrating excellent antifouling capability. Similar antifouling and high removal were also observed in humic acid separation. These compelling features highlight its potential for efficient water purification applications.