A primary goal of research in the Shimizu group is the preparation and characterization of novel porous solids. Textbook porous materials are aluminosilicates such as clays and zeolites. While the utility of these compounds cannot be disputed (detergents, catalysts), their structures and, therefore, their range of function, are limited by the fact they have only aluminum, silicon, and oxygen as constituent atoms. We employ a "metal-organic" approach to making porous solids. Essentially, Si and Al are replaced by a range of metals and the O2- anion is replaced by any number of organic ligands. The main advantage is much greater diversity with respect to structure and hence function of these solids. The main targets for these porous solids are their use as storage vessels, separators, and sensing agents for guests, particularly gaseous molecules such as H2, CH4, and CO2. A number of metal-organic frameworks (MOF's) have been reported which show ability to uptake and store H2, an important issue if hydrogen is to be viable for mobile fuel cell technology.
In the Shimizu group, we focus on the use of metal sulfonates and metal phosphonates as these groups have the ability to bridge multiple metal centers and form very stable aggregates structures. As far as required skills, ligands typically require a 1-5 step synthesis accompanied by all the standard means of small molecule characterization (NMR, IR, MS, EA). Metal complexes are characterized by powder and single crystal X-ray diffraction, SS NMR, DSC/TGA, and by surface area measurements. Graduate students perform all aspects of the research including their own X-ray crystallography.
Another project related to fuel cells is the synthesis of new H+ conducting membranes. This is related to the above in that, rather than using the sulfonate and phosphonate groups to actually bind metal centers, they are incorporated into polymer structures via metal ion templation. This serves to form new morphologies and aggregates of H+ conducting clusters. Again, the above techniques are required in addition to impedance spectroscopy.
