An investigation on the effect of alumina on hydrothermal stability of nanostructured silica membrane prepared by sol-gel method

In the present study, the effect of alumina on the pore structure and hydrothermal stability of nanostructured silica was investigated. SiO2 and SiO2-15wt%Al2O3 membranes were prepared by dip coating on mesoporous γ-Al2O3 coated macroporous α-alumina support. The particle sizes of sol were increased by adding of alumina to silica sol. Through the addition of the alumina up to 15 wt% and heat treatment at 500 °C, the silica structure was remained amorphous and the thickness of the top layer was in the range of 200-500 nm because of an increase in the sol viscosity. FT-IR analysis showed the formation of Si-O-Al bonds after heat treatment in the SiO2-15wt%Al2O3 membrane. After placing the membranes under hydrothermal test, the pore volume and size were slowly decreased by means of alumina addition in that order. Furthermore,  the permeability of gas molecules (H2, He, CO2,…) from the silica membrane was abruptly decreased compared to the SiO2-15wt%Al2O3 membrane. Therefore, the membrane containing the added alumina had a more suitable hydrothermal stability due to the formation of more stable Si-O-Al bonds.