High resolution electron microscopy study of biologically derived ruthenium and palladium/ruthenium nanoparticles

This paper describes the preparation and morphological and fine structural characteristics of biologically derived ruthenium and bimetallic palladium/ruthenium nanoparticles. Cells of E. coli strain MC400 were used for production of bio-supported Ru and Pd/Ru bimetallic nanoparticles (bio-Ru NPs and bio-Pd/Ru NPs). High-resolution scanning transmission electron microscopy with a high-angle annular dark field detector and energy dispersive X-ray spectrometry attachment and elemental mapping was used to investigate the bio-supported synthesis of Ru and Ru/Pd NPs. Ru3+ ions were reduced by E. coli cells to the metallic state via bio-mineralisation process using hydrogen as a reducing agent. It was observed that Ru NPs were associated with the periplasmic region of E. coli, whereas Pd NPs were abundant in the periplasm and cytoplasm of the cells. Bimetallic Pd/Ru nanoparticles were observed only on the perimeter of the cells. Bio-Pd/RuE.coli preparations contain simultaneously Pd NPs, Ru NPs and Pd/Ru NPs which makes them a unique candidate for a heterogeneous catalyst. Possible configurations of the bimetallic NPs are discussed.