Chalcogels are a new class of aerogel materials made of polymeric networks of metals and chalcogenide atoms with high internal surface area. Their open random frameworks are constructed by chalcogenido anionic building units linked with transition as well as main group metal ions. Gels are obtained using slow metathesis reactions and are transformed to aerogels after supercritical drying with liquid carbon dioxide. These low density sponge like materials can absorb conjugated organic molecules, heavy metals ions and can preferentially adsorb CO2 over H2, which illustrates their potential as gas separation media. These materials have narrow energy-gaps in the range of 0.2-3.4 eV depending on the building units and promise unique opportunities in optoelectronic, sensing, photosynthetic and photocatalytic applications. The chalcogel synthesis can also be adapted to a variety of biomimetic clusters as well as main group backbone, giving us an ideal platform for the design of artificial biomimetic photocatalysts for solar fuels. Chalcogels can be made containing transition metal clusters similar to those found in nature, such as [Fe4S4] and [MoFexSy]. Characterization of the [Fe4S4]-bearing chalcogels shows that their redox properties are preserved when compared to free clusters in solution, but more resistant to oxidation and/or hydrolysis when in chalcogel form. Furthermore, we can also incorporate light-harvesting dye molecules into the chalcogels in variable proximity to the [Fe4S4] clusters via a simple ion-exchange procedure, allowing for the possibility of photocatalysis of solar fuels in a stable, biomimetic system. The chalcogels containing the cluster Mo2Fe6S8(SPh)3 are capable of photocatalytic N2 fixation. The initial binding of N2 with chalcogels under illumination was observed with in situ diffuse-reflectance Fourier transform infrared spectroscopy (DRIFTS). 15N2 isotope experiments confirm that the generated NH3 derives from N2. Density Functional Theory (DFT) electronic structure calculations suggest that the N2 binding is thermodynamically favorable only with the highly reduced active clusters.

Nitrogen fixation at room temperature, pressure in water using light

253rd National Meeting (2017)

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