SYNTHESIS AND CHARACTERIZATION OF UNSUPPORTED FERRIC-OXIDE CERAMIC MEMBRANES

Unsupported ferric oxide ceramic membranes have been synthesized by the sol-gel method using two different formulations. These materials have been characterized by N2 sorption, electron microscopy and FTIR spectroscopy. In one formulation, mesoporous membranes with a mean pore radius of 5 nm were fabricated from asymmetric goethite (alpha-FeOOH) by control of the particle surface charge during drying. This material also developed slit-shaped intraparticle micropores during thermal dehydration to hematite (alpha-Fe2O3), resulting in a considerable increase in active surface area without affecting membrane microstructure or mesoporosity. These membranes may be suitable as an intermediate support layer in a multilayer catalytic ceramic membrane configuration. In a second formulation, highly uniform microporous unsupported membranes with a pore radius less than 1.7 nm were prepared from the hydrolytic iron oxide polymer [Fe(O,OH,H2O)6]n. It was found that the initial hydrolysis reaction conditions determine the microstructure of the formed membranes. The effects of hydrolysis conditions and post-hydrolysis treatment on polymer formation and membrane microstructure is discussed.