Zeolite, ordered mesoporous, and hierarchical ceramic membranes

The article describes recent advances in the preparation of ceramic membranes exhibiting an ordered microporosity or mesoporosity. The case of zeolite membranes is first examined. Various synthesis strategies are presented and discussed like the infiltration of macroporous substrates or the multi-step deposition of thin layers, the use of microwave activation and the removal of the structure-directing agents by ozonation. The mesoporous membranes resulting from the templating effect of lyotropic liquid crystal mesophases are then discussed. The main problem is to get layers with interconnected mesoporosity. The separative properties are usually related to the microporosity of the inorganic walls. It is however possible to take benefit of the generated mesoporosity and of possible additional macroporosity for preparing membranes with hierarchical porosity. Such membranes exhibit a higher permeability due to an increase in the total porosity of the membrane.