Semiconducting Aerogels from Chalcogenido Clusters with Broad Applications (27012)
Northwestern chemists have created a novel family of chalogenide based hydrogels which readily afford a wide range of new aerogels. The materials exhibit high surface area, broad porosity range and narrow band gap properties with significant environmental, catalytic, electronic and sensor application potential.
ADVANTAGES: New chalogenide aerogel compositions providing a wide range of surface area, porosity, and electronic properties significantly different from known oxide based silica, alumina, titania, type materials.
SUMMARY: Aerogels resulting from sol gel chemistry of oxide based materials (e.g. SiO2, Al2O3, TiO2, etc) is well developed, but rare for non-oxide systems. New chemistry employing chalocogenides has been created to prepare novel materials (“chalcogels”) which upon supercritical drying form aerogel structures with high internal surface area and broad pore size distribution.
Chemistry capable of providing chalcogels in a wide range of compositions including the following has been established.
M 4[M’ 4Q 10] n , M 4[M’ 2Q 6] n , M 4[M’Q 4] n M 3[M’Q 4] n , M 3[M’Q 3] n M 2[M’Q 4] M’ = Ge, Sn; M’ = P, As, Sb M’ = Mo, W;
Q = S, Se, Te M= divalent ; trivalent , lanthanide; tetravalent metal ions.
A series of chalcogels, where M = Pt2+, was synthesized affording a continuous, extended Pt/M’/Q framework of covalently bonded atoms with solvent molecules encapsulated during polymerisation (Table). Supercritical drying affords highly porous aerogels (Figure). Transmission electron microscopy (TEM) images reveal empty mesopores with no long range order. These chalcogels appear to be morphologically similar to the silica aerogels where particles are connected in continuous amorphous networks. Mesoporosity was confirmed by nitrogen physisorption measurements. The materials possess extraordinary surface areas comparable or exceeding that of silica aerogels (100 – 1600 m2/g).
The chalcogels exhibit a remarkably high capacity to remove heavy metals from contaminated water. Chalcogel-2 for example, rendered a 150 ppm Hg2+ solution to 0.05 ppm after overnight stirring at room temperature. Chalcogels work directly as potential heavy metal adsorbents; in contrast mesoporous silicates are generally functionalised with surface modified thiolate ligands before use in environmental remediation. The chalcogels also efficiently absorb organic aromatic molecules from solution, thus chalcogel-1 effectively removed a porphyrin from a 5.67 µmolL-1 ethanol solution within 24 hours. The Pt chalcogels exhibit good thermal stability retaining amorphous structure over a wide range of temperatures. The materials absorb light in the visible and infrared regions having sharp energy gaps (Table). The optical properties of the porous semiconducting aerogels can be tuned by changing the Q and M’ components and chalogenide content. These unique materials offer promise in wide range of environmental, catalytic, optoelectronic and sensing applications.
Mercouri Kanatzidis, Santanu Bag
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