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 °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.

Studies of the electronic structure of titanium centers in titanium silicalite (TS-1) catalytic materials were carried out using electronic absorption and emission spectroscopy. A long-lived phosphorescent excited state with an emission maximum at 490 nm in the near UV was unambiguously assigned to the titanium. Resolved in the emission envelope was vibronic structure in 965 cm-1 mode, which corresponds to the Si−O−Ti stretching mode in TS-1. The lowest energy excited state is significantly lower in energy than was previously suggested by diffuse reflectance absorption spectroscopy. Emission excitation spectra indicate that, contrary to previous assertions, there are electronic transitions throughout the spectral region from ∼23000 to 48000 cm-1. These observations bring into question long-standing structural arguments for the coordination of titanium in the silicalite lattice that have been made using electronic spectroscopy.

Previous work has established the possibility of using known coordinating agents supported on silica gel in the removal of heavy metals such as lead, copper, cadmium, and nickel from aqueous media. Functionalized silica gel has been used in the removal of heavy metals with notable success. Silica gel is currently being used as a support for various monofunctional aliphatic amines as coordinating ligands. The current study reports the results of an investigation involving the use of saturated, straight chain primary amines as coordinating ligands in the removal of copper(II), cadmium(II), lead(II), nickel(II), and silver(I) ions from aqueous solutions of known concentration. Primary amines used in this investigation were n-butylamine, n-hexylamine, n-octylamine, n-decylamine, and n-hexadecylamine.

Transition metal bis(acetylacetonate) complexes of Co(II), Ni(II), Cu(II), and Zn(II) have been found to be active catalysts for the sol-gel process. The catalytic activity of these complexes decreases in going from Co(II) to Zn(II) and is highest for the acetylacetonate ligand system. 29Si NMR studies show that the complexes act primarily as condensation catalysts and are, in that regard, similar to Brønsted bases such as hydroxide. Mechanistically, however, they appear to differ significantly from hydroxide in how they induce condensation. This is revealed in the catalyst concentration dependence, which is 1/2 order for the metal complexes and 1st order in hydroxide. Differences are also apparent in the thermochemical parameters that indicate that the metal complexes act to increase the entropy of the transition state leading to condensation. The catalytic activity is proportional to the degree of ligand dissociation of the metal complex, and experiments suggest that the active catalytic species is specifically the first dissociation product, MII(acac)+.

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