Periodic mesoporous organosilicas(PMOs):a new class of materials is coming of age

摘要

In the last 15 years enormous progress has been achieved in the field of porous solids,two of which are of particular importance.First,the development of the metal-organic framework(MOF)structures by Yaghi and co-workers[1].This new class of materials was extensively reviewed very recently[2].Second,the discovery of the long-range ordered mesoporous M41S silica phases by the Mobil research company in 1992,a major breakthrough within the efforts to extend the pore sizes of the long-established microporous zeolites[3,4].This was achieved by using supramolecular aggregates of long-chain ionic surfactants like tetraalkylammonium halides as structure-directing agents(SDA)in the presence of a silica source(precursor).With regard to potential applications such as catalysis,adsorption,chromatography,and chemical sensing considerable effort was spent on modifying the mesoporous silica frameworks of the M41S phases with organic functional groups.In general this can be realized by employing two pathways[5-7].The first is the grafting approach,where the organic functionalities are bound on the silica surface by a post-synthesis treatment and the second is the co-condensation method(so-called'one-pot'synthesis)of tetraalkoxysilanes and terminal organotrialkoxysilanes in the presence of SDAs.While it was possible to modify the frameworks with a wide variety of organic groups,it should be noted that both pathways have their limitations and inherent drawbacks.