Synthesis of ordered mesoporous silica membranes containing iron oxide nanocrystallites

This paper reports the first effort in synthesis of iron-containing ordered mesoporous silica membrane on porous α-alumina support by a dip-coating process. A pure silica sol and a series of iron-containing silica sol with Fe/Si molar ratio of 0.1, 0.2 and 0.3 were prepared using Pluronic P123 as template, tetraethylorthosilicate as silica source and hydrated iron nitrite as precursor under acid condition. The unsupported membranes were characterized by Fourier transform infra-red (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen isothermal adsorption measurement. Characterization revealed that iron species present as highly dispersed γ-Fe₂O₃ nanocrystals in hexagonal walls for higher iron-containing samples (Fe/Si = 0.2, 0.3). All unsupported membranes maintain ordered mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. Introduction of iron to silica matrix can decrease pore diameter and increase the wall thickness of mesopores. Scanning electron microscopy (SEM) studies show that the prepared supported membrane is defect-free and energy-dispersive spectroscopy (EDS) analysis further confirm the formation of continuous mesoporous layer on α-alumina porous support. The gas permeance results indicate the supported membranes exhibit Knudsen diffusion behavior confirming the good quality of the membrane.