Synthesis and characterization of a magnetite (Fe3O4) nanofiltration membrane

Abstract

Meso-porous magnetite membranes have been synthesized by dip-coating iron oxide dispersion on ∼2 mm thick α-Al2O3 supports, followed by nitrogen-environment thermal processing. Both gas and water permeabilities of magnetite membranes were investigated. At room temperature, the nitrogen permeance was 3×10−8, which increased to 3×10−7 at 400°C, but decreased to 9×10−8 at 500°C (still higher than room temperature). The argon permeance at corresponding temperature was slightly lower than nitrogen permeance. 0.001mol/L NaCl was used as feed solution for dead-end filtration test. Experimental result indicated the mechanical permeance of magnetite membrane was 5.5×10−16 m, and the maximum salt rejection was 44% at transmembrane pressure of 0.35 MPa. From the perspective of thermal stability, a magnetite membrane was immersed in 60°C deionized (DI) water for a week, and there was no change in thickness according to ellipsometry analysis. Meanwhile, it was found that the membrane was chemically stable in base solution, which is expected for Fe3O4. However, the membrane thickness increased in nitric acid solution at pH 5.0, which was tentatively ascribed to oxidation of Fe3O4 to Fe2O3.