Inorganic membranes

Inorganic membranes consist of oxides, or metals, and can be present in multi-layer supporting structures, or as self-supporting structures. Dense membrane materials are ideally selective for O2 or H2 molecules. Micro-porous membranes (0.5–2 nm) can be highly selective for CO2, H2O and hydrocarbon. Meso-porous membranes (2–50 nm) are used as supporting structures, or in water purification. Macro-porous layers (>50 nm) are used as supporting structures and particulate filtration applications. Compared to polymeric membranes, inorganic membranes can be more selective and permeable, and can withstand more extreme conditions. To make them fully competitive their cost price must be reduced by improvements in processing, introduction of rapid fabrication methods, and possibly incorporation in hybrid, polymeric structures.

Graphical abstractTypical supported fully ceramic structure (left), and hybrid structure (right). Combinations or structures with more or less layers are also possible. The meso-porous and macro-porous structures can form a ‘bridge’ between large pores at one side and much smaller pores at the other side. Meso-porous layers can serve as a ‘scaffold’ for selective material or as a ‘diffusor’ to diminish spreading resistance at the support pores. Macro-porous support can also provide liquid suction pressure in the deposition of porous layers from dispersions (‘slip’ casting).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Inorganic membranes will be essential in energy conversion and water purification. Their properties must be adjusted to process conditions. ► The performance of inorganic membranes will be improved through better characterization, analysis and fabrication. ► The cost price of inorganic membranes will be much decreased by faster processing of thinner structures, and use of polymer-inorganic hybrids.