Advanced Materials Research Vols. 71-73

Abstract: Due to the photoelectric, semi-conducting and X-ray-sensing properties, selenium is an element of great economic potential. Since nanomaterials display special properties compared to bulk particles, the production of selenium nanostructures (wires, rods or spherical particles) has attracted much attention. In this study, alternative approaches to classical synthesis were investigated, producing selenium nanospheres biologically during treatment of contaminated water.

Abstract: This study was aimed at the development of a new heterogeneous Pd catalyst based on biologically mineralised palladium (Bio-Pd). Desulfovibrio desulfuricans was used to reduce Pd(II) to nanocrystalline Pd embedded in the bacterial surface. In this way the biomass provides support and prevents coalescence of the palladium nanoparticles. Palladised biomass exhibits catalytic activity, which was demonstrated in a range of applications including reduction, oxidation and hydrogenation reactions. Preparation of Bio-Pd under various conditions leads to the formation of a supported palladium catalyst with potentially different catalytic properties according to the preparation method.

Abstract: Bio-manufacturing of nano-scale palladium was achieved using bacterial cells. Highly active Pd-catalyst (Bio-Pd) produced by an E. coli mutant gave power output in a fuel cell. Up to ~115% of the maximum power generation was achieved by electrodes of Bio-Pd catalysts from Escherichia coli, compared to that from a commercial-Pd electrode (~0.099 W). A bio-precious-metals (Bio-PM) catalyst made directly from an industrial reprocessing solution by the E. coli was also made into fuel cell electrodes and ~0.06W of maximum power generation was observed.

Abstract: Chitosan (an aminopolysaccharide), cross-linked with glutaraldehyde, is very efficient for Pd(II) and Pt(IV) recovery from acidic solutions (pH 2). Due to poorly porous properties, it is necessary to condition the biopolymer as hydrogels. The uncontrolled drying of hydrogels depreciates the diffusion properties of original materials. A different method (to the acidic dissolving/alkaline neutralization procedure) has been used: after chitosan dissolving in acetic acid solution, the viscous solution was dropped into an ionotropic gelling solution (polyphosphate and glutaraldehyde to form stable gel beads with improved porosity. The restriction of diffusion properties due to drying step was less drastic with the modified procedure: a few hours were sufficient for reaching equilibrium while more than two days were required for standard material

Abstract: Nanoparticles of palladium were obtained with the help of hydrogen-oxidising, metal- reducing bacteria and used for the production of electricity in a proton exchange membrane (PEM) fuel cell. Earlier works have shown that palladised cells of Escherichia coli and Desulfovibrio desulfuricans (Bio-PdE.coli and Bio-PdD.desulfuricans, respectively) appeared similar by electron microscopy and were comparably active in a chemical test reaction. When tested in a PEM fuel cell they produced 0.018 and 0.108 W, respectively. Electron paramagnetic resonance analysis of Bio-PdE.coli mixed with activated carbon showed paramagnetic activity. However, Bio-PdD.desulfuricans under the same conditions quenched the intrinsic EPR signal. This quenching is indicative of the magnetic properties of the particles. The magnetic behaviour of Pd nanoparticles was theoretically predicted for particles between 10 and 20 nm in diameter and can be experimentally confirmed by EPR measurements.

Abstract: This study describes biofilm formation as a non line-of-sight coating method on support materials such as polyurethane foam, porous glass, polypropylene (PP) and titanium alloy, using a Serratia sp., which can manufacture extracellular nanoscale scaffolded hydroxyapatite (HA) crystals via enzymatic cleavage of glycerol 2-phosphate (G2P) in the presence of CaCl2. Various microscopies and non-invasive magnetic resonance imaging were used to visualize the biofilm coating on the support surface. A novel micromanipulation technique was used to estimate the adhesive strength of native and HA-mineralized biofilms. The biofilm with HA was up to forty times stronger than that without HA. A coating of nano-HA (> 80 m) onto a biofilm-Ti disc was achieved.

Abstract: Iron-grown Acidithiobacillus ferrooxidans MON-1 cells are highly resistant to organomercurial compounds as well as mercuric chloride (HgCl2). Existence of a novel Hg2+-reducing enzyme system, in which mercury resistant aa3-type cytochrome c oxidase catalyzes the reduction of Hg2+ with reduced mammalian cytochrome c or Fe2+ as an electron donor to give Hg0, has been shown in iron-grown MON-1 cells. There has been no reports on the mechanism of Hg2+ reduction by sulfur-grown A. ferrooxidans cells. The level of mercury resistance in sulfur-grown A. ferrooxidans MON-1 cells was compared with that of iron-grown MON-1 cells. Strain MON-1 was able to grow in 1% elemental sulfur medium (pH 2.5) containing 10 μM of Hg2+ or 0.2 μM phenylmercury acetate (PMA), suggesting that the levels of mercury resistance to inorganic and organic mercurial compounds are nearly the same in iron- and sulfur-grown MON-1 cells. Activity levels of Hg0 volatilization from HgCl2, PMA, and methylmercury chloride (MMC) were also nearly the same in iron- and sulfur-grown cells and these activities were markedly activated by 100 mM of Fe2+, but strongly inhibited by 1 mM of sodium cyanide, indicating that sulfur-grown MON-1 cells has the activity of ferrous iron-dependent mercury reducing enzyme system containing aa3-type cytochrome oxidase. aa3-type cytochrome c oxidase purified partially from sulfur-grown MON-1 cells showed both the iron oxidase and mercury reductase activities in the presence, but not in the absence, of rusticyanin and c-type cytochromes (Cyc1 and Cyc2) partially purified from iron-grown MON-1 cells.