Preparation processes and characterizations of alumina-coated alumina support layers and alumina-coated natural material-based support layers for microfiltration

Recently, porous ceramic membranes have become a subject of significant interest due to their outstanding thermal and chemical stability. To reduce the high manufacturing costs of these porous ceramic membranes, recent research has focused on the utilization of inexpensive natural materials. However, there have not been any well-established direct comparisons of the membrane properties between typical alumina-based membranes and novel natural material-based membranes. Therefore, we compared alumina-coated alumina support layers (with average pore sizes ranging from 0.10 µm ~0.18 µm), alumina-coated diatomite-kaolin composite support layers (with an average pore size of 0.12 µm), and alumina-coated pyrophyllite-diatomite composite support layers (with an average pore size of 0.11 µm) via the dip-coating method and subsequent heat treatment ranging from 1200 °C–1400 °C for 1 h. The pure water permeability of the alumina-coated diatomite-kaolin composite support layer and the alumina-coated pyrophyllite-diatomite composite support layer was found to be approximately 2.0×102 L m−2 h−1 bar−1, which is similar to that of an alumina-coated alumina support layer. Therefore, we suggest that the average pore size of an alumina-coated natural material-based support layer can be effectively controlled while exhibiting acceptable water permeability.