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Project Progress

Efforts during the last year have focused primarily on the determination of the structure of iron-sulfide nanoparticles synthesized in our laboratory using protein-cage assisted protocols. Our experimental technique of choice has been Pair Distribution Function (PDF) analysis – a method in which high-energy X-ray scattering is collected and Fourier transformed to obtain the real-space atomic correlations or PDF. In this approach, the function G(r) gives the probability of finding an atom at a distance r from an average atom within the structure; peaks in G(r) correspond to atom-atom distances in a crystalline lattice. This data can then be tested against various models of material structure. Experiments conducted at the Advanced Photon Source at Argonne National Laboratories have indicated that the protein-templated FeS particles form a distorted mackinawite structure with an extremely small crystalline domain size (< 1nm). Significant amounts of Fe oxide are still present (depending on preparation conditions), and the FeS probably forms a layer around an oxide core. Samples were prepared under a variety of pH conditions and at different Fe/cage loading ratios; these parameters appear to have had fairly little effect on the structure as determined by PDF.

Work has also been done on measuring hydrogen evolution from the FeS nanoparticles using gas chromatography. The assumption was that if the disordered FeS layer contains defects that are similar in structure to a hydrogenase active site, some H₂ evolution should be observed. Reaction conditions used methyl viologen as an electron carrier and dithionite as a sacrificial electron donor. H₂ evolution experiments were performed both on the FeS nanoparticles described above and on particles that had been doped with 7% Ni. In both cases, no hydrogen evolution was observed.