The most significant results have come from a vigorous collaboration developed between Vienna and Novosibirsk. It involves the development of new, highly active catalysts for HS-oxidation (hydrogen sulfide and mercaptans), using sol-gel methods to incorporate substituted cobalt phthalocyanines into a porous titania matrix (1,2). The phthalocyanine needs to carry sulphonate or chlorosulphonate substituents which react with titanium alkoxides under controlled conditions. Further reaction with titanium alkoxides, under hydrolytic conditions, gives the supported catalysts, which have been characterised by electron microscopy and electron diffraction. The morphology, monomer vs dimer structure, and the catalytic activity all depend on the nature of the substituent on the original phthalocyanine and on the titanium alkoxide used. The catalysts are very stable in the liquid reaction media tested, and exhibit higher activity than the unsupported, homogeneous catalyst.
Other teams have been concerned with sol-gel processes to prepare silica-based porous materials incorporating organic functional groups with potential for extracting metal ions from solution. A wide variety of mono- and poly-dentate groups can be incorporated: amines, aminoacids, thioureas, Schiff-bases, etc. Some of these show high potential for the separation/extraction of metals such as cobalt(II) and nickel(II), others are being evaluated for specific binding of heavy metals.
Computer modelling of the sol-gel hydrolysis mechanism has been made (3).
Most of these later results await publication, but the field has been reviewed (4).