Vanadia-silica sol-gel derived glass: Factors affecting homogeneity and morphology

The chemical and processing conditions under which multicomponent vanadia-silica sol-gel derived glass is synthesized have been investigated to determine the factors leading to homogeneity in the final material. In conjunction, studies were also conducted to assess changes in the morphological properties (porosity) of the silica xerogel due to the presence of vanadium. It was found that both the water content of the initial sol and the humidity under which aging of the gel was carried out dramatically affected the homogeneity of the final material. High initial water content or high humidity aging conditions resulted in the formation of green gels containing partially reduced vanadia, which, upon drying at 500 degrees C, yielded opaque orange xerogels. Vanadia-silica gels made with low water and aged at low humidity remained transparent after drying. The amount of vanadium that could be incorporated while still maintaining homogeneity was increased significantly if low water and low humidity conditions were used in the process. The presence of the vanadium, even in low concentrations, dramatically affected the pore structure of the resultant xerogel. Materials with vanadium concentrations as low as 0.01 mol % were found to be significantly more microporous than pure silica control samples. Imaging by atomic force microscopy revealed that the increased microporosity was due to filling of the mesopore regions in the materials containing vanadium.